ncg

bachelorthesis in physics
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commit 258e29d485faf66c87ca5d12b75124d7621b86b0
parent 9c62b5a750a93f4f219109435edd51149c7f239b
Author: miksa234 <milutin@popovic.xyz>
Date:   Wed, 21 Jul 2021 15:04:10 +0200

checkpoint

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Msrc/thesis/back/title.tex | 7++++---
Dsrc/thesis/chapters/1 | 754-------------------------------------------------------------------------------
Msrc/thesis/chapters/electroncg.tex | 975+++++++++++++++++++++++++++++++++++++++----------------------------------------
3 files changed, 491 insertions(+), 1245 deletions(-)

diff --git a/src/thesis/back/title.tex b/src/thesis/back/title.tex @@ -5,7 +5,7 @@ \hspace{8.8cm} \includegraphics[width=8cm]{pics/uni_logo} \end{figure} -\vspace*{2cm} +\vspace*{1cm} \fontsize{22}{0} \fontfamily{lmss}\selectfont \textbf{Bachelor's Thesis}\\ @@ -15,7 +15,8 @@ \vspace*{0.4cm} -\fontsize{18}{0} \selectfont \textbf{Noncommutative Geomtetry and Physics}\\ +\fontsize{18}{0} \selectfont \textbf{From Noncommutative Geometry to +Electrodynamics}\\ \vspace*{1.5cm} @@ -26,7 +27,7 @@ \vspace*{2cm} - {\fontsize{12}{0} \selectfont in partial fulfilment of the requirements for the degree of}\\ + {\fontsize{12}{0} \selectfont in partial fulfillment of the requirements for the degree of}\\ \vspace*{0.4cm} { \fontsize{14}{0} \selectfont Bachelor of Science (BSc)}\\ diff --git a/src/thesis/chapters/1 b/src/thesis/chapters/1 @@ -1,754 +0,0 @@ -\subsection{Noncommutative Geometry of Electrodynamics} -\subsubsection{The Two-Point Space} -One of the basics forms of a noncommutative space is the the two point space $X -:= \{x, y\}$, it can be represented by the following spectral triple -\begin{align} - F_x := (C(X) = \mathbb{C}^2, H_F, D_F; J_F, \gamma _f). -\end{align} -There are three properties of $F_x$ that stand out, first of all the action of -$C(X)$ on $H_F$ is faithful for $dim(H_F) \geq 2$. Thus we can make a simple -choice for the Hilbertspace, $H_F = \mathbb{C}^2$. Furthermore $\gamma_F$ is -the $\mathbb{Z}_2$ grading, which allows us to decompose $H_F$ into -\begin{align} - H_F = H_F^+ \otimes H_F^- = \mathbb{C} \otimes \mathbb{C}, -\end{align} -where -\begin{align} - H_F^\pm = \{\psi \in H_F |\; \gamma_F\psi = \pm \psi\}, -\end{align} -are two eigenspaces. And lastly the Dirac operator $D_F$ lets us -interchange between $H_F^\pm$, -\begin{align} - D_F = - \begin{pmatrix}0 & t \\ \bar{t} & 0\end{pmatrix}, \;\;\;\;\; - \text{with} \;\; t\in\mathbb{C}. -\end{align} - - The Two-Point space $F_x$ can only have a real structure if the Dirac - operator vanishes, i.e. $D_F = 0$, in that case we have KO-dimension of 0, - 2 or 6. - - To elaborate on this, we know that there are two diagram representations of - $F_x$ at $\underbrace{\mathbb{C} \oplus \mathbb{C}}_{C(X)}$ on - $\underbrace{\mathbb{C} \oplus\mathbb{C}}_{H_F}$, which are: - \begin{figure}[h!] \centering - \begin{tikzpicture}[ - dot/.style = {draw, circle, inner sep=0.06cm}, - no/.style = {}, - ] - \node[no](a) at (0,0) [label=left:$\textbf{1}^\circ$] {}; - \node[no](b) at (0, -1) [label=left:$\textbf{1}^\circ$] {}; - \node[no](c) at (1, 0.5) [label=above:$\textbf{1}$] {}; - \node[no](d) at (2, 0.5) [label=above:$\textbf{1}$] {}; - \node[dot](d0) at (2,0) [] {}; - \node[dot](d0) at (1,-1) [] {}; - - \node[no](a1) at (6,0) [label=left:$\textbf{1}^\circ$] {}; - \node[no](b2) at (6, -1) [label=left:$\textbf{1}^\circ$] {}; - \node[no](c2) at (7, 0.5) [label=above:$\textbf{1}$] {}; - \node[no](d2) at (8, 0.5) [label=above:$\textbf{1}$] {}; - \node[dot](d0) at (7,0) [] {}; - \node[dot](d0) at (8,-1) [] {}; - \end{tikzpicture} - \end{figure}\newline -If the Two-Point space $F_x$ would be a real spectral triple then $D_F$ can -only go vertically or horizontally. This would mean that $D_F$ vanishes. - -The diagram on the left has KO-dimension 2 and 6, the diagram on the -right has KO-dimension 0 and 4. Yet KO-dimension 4 is not ruled out because -$dim(H_F^\pm) = 1$ (see Lemma 3.8 Book), which ultimately means $J_F^2 = -1$ is -not allowed. -\subsubsection{The product Space} -By Extending the Two-Point space with a four dimensional Riemannian spin -manifold, we get an almost commutative manifold $M\times F_x$, given by -\begin{align} - M\times F_x = (C^\infty(M), \mathbb{C}^2), L^2(S)\otimes \mathbb{C}^2, - D_M\otimes 1 ; J_M\otimes J_F, \gamma_M \otimes \gamma_F), -\end{align} -where -\begin{align} - C^\infty(M, \mathbb{C}^2) \simeq C^\infty(M) \oplus C^\infty(M). -\end{align} -According to Gelfand duality the algebra $C^\infty(M, \mathbb{C}^2)$ of the -spectral triple corresponds to the space -\begin{align} - N:= M\otimes X \simeq M\sqcup X -\end{align} -Keep in mind that we still need to find an appropriate real structure on the -Riemannian spin manifold, $J_M$. -\newline -The total Hilbertspace can be decomposed into $H = L^2(S) \oplus L^2(S)$, such -that for -\newline -$\underbrace{a,b\in C^\infty(M)}_{(a, b) \in C^\infty(N)}$ -and $\underbrace{\psi, \phi \in L^2(S)}_{(\psi, \phi) \in H}$ we have -\begin{align} - (a, b)(\psi, \phi) = (a\psi, b\phi) -\end{align} -Along with the decomposition of the total Hilbertspace we can consider a -distance formula on $M\times F_x$ with -\begin{align}\label{eq:commutator inequality} - d_{D_F}(x,y) = \sup\left\{ |a(x) - a(y)|:a\in A_F, ||[D_F, a]|| \leq - 1 \right\}. -\end{align} -To calculate the distance between two points on the Two-Point space $X= \{x, -y\}$, between $x$ and $y$, we consider an $a \in \mathbb{C}^2 = C(X)$, which is -specified by two complex numbers $a(x)$ and $a(y)$. Then we simplify the -commutator inequality in \ref{eq:commutator inequality} -\begin{align} - &||[D_F , a]|| = ||(a(y) - a(x))\begin{pmatrix}0 &t\\\bar{t} &0 - \end{pmatrix}|| \leq 1,\\ - &\Rightarrow |a(y) - a(x)|\leq \frac{1}{|t|}, -\end{align} -and the supremum gives us the distance -\begin{align} - d_{D_F} (x,y) = \frac{1}{|t|}. -\end{align} -Note that if there exists $J_M$ (real structure) $\Rightarrow t=0$ then -$d_{D_F}(x,y) \rightarrow \infty$! -\newline - -Now let $p \in M$, then take two points on $N=M\times X$, $(p, x)$ and -$(p,y)$ and $a \in C^\infty(N)$ is determined by $a_x(p):=a(p, x)$ and -$a_y(p):=a(p, y)$. The distance between these two points is then -\begin{align} - d_{D_F\otimes 1}(n_1, n_2) = \sup \left\{ |a(n_1) - a(n_2)|: a\in - A, ||[D\otimes 1, a]||\right\} -\end{align} -\textbf{Remark}: If $n_1 = (p,x)$ and $n_2 = (q, x)$ for $p,q \in M$ then -\begin{align} - d_{D_M \otimes 1} (n_1, n_2) = |a_x(p) - a_x(q)| \;\;\; a_x\in - C^\infty(M) \;\; \text{with} \;\; ||[D\otimes 1, a_x]|| \leq 1 -\end{align} -The distance turns to the geodestic distance formula -\begin{align} - d_{D_M\otimes1}(n_1, n_2) = d_g(p, q) -\end{align} - -However if $n_1 = (p, x)$ and $n_2 = (q, y)$ then the two conditions are -$||[D_M, a_x]|| \leq 1$ and $||[D_M, a_y|| \leq 1$. They have no -restriction which results in the distance being infinite! And $N = -M\times X$ is given by two disjoint copies of M which are separated by -infinite distance - -\textbf{Note}: distance is only finite if $[D_F, a] \neq 1$. The -commutator -generates a scalar field say $\phi$ and the finiteness of the distance is -related to the existence of scalar fields. -\subsubsection{$U(1)$ Gauge Group} -Here we determine the Gauge theory corresponding to the almost -commutative -Manifold $M\times F_x$. - -\textbf{Gauge Group of a Spectral Triple}: -\begin{align} - \mathfrak{B}(A, H; J) := \{ U = uJuJ^{-1} | u\in U(A)\} -\end{align} -\begin{definition} - A *-automorphism of a *-algebra $A$ is a linear invertible - map - \begin{align} - &\alpha:A \rightarrow A\;\;\; \text{with}\\ - \nonumber\\ - &\alpha(ab) = \alpha(a)\alpha(b)\\ - &\alpha(a)^* = \alpha(a^*) - \end{align} - The \textbf{Group of automorphisms of the *-Algebra $A$} is - $(A)$.\newline - The automorphism $\alpha$ is called \textbf{inner} if - \begin{align} - \alpha(a) = u a u^* \;\;\; \text{for} \;\; U(A) - \end{align} - where $U(A)$ is - \begin{align} - U(A) = \{ u\in A|\;\; uu^* = u^*u=1\} \;\;\; - \text{(unitary)} - \end{align} -\end{definition} -The Gauge group is given by the quotient $U(A)/U(A_J)$. -We want a nontrivial Gauge group so we need to choose $U(A_J) \neq -U(A)$ which is the same as $U((A_F)_{J_F}) \neq -U(A_F)$. -We consider $F_x$ to be -\begin{align} - F_x := \left(\mathbb{C}^2,\mathbb{C}^2, D_F =\begin{pmatrix} - 0&0\\0&0\end{pmatrix}; J_f =\begin{pmatrix} - 0&C\\C&0\end{pmatrix}, - \gamma_F = \begin{pmatrix}1&0\\0&-1\end{pmatrix}\right). -\end{align} -Here $C$ is the complex conjugation, and $F_X$ is a real even finite - spectral triple (space) with $KO-dim=6$ - -\begin{proposition} - The Gauge group $\mathfrak{B}(F)$ of the two point space is given by - $U(1)$. -\end{proposition} -\begin{proof} - Note that $U(A_F) = U(1) \times U(1)$. We need to show that - $U(\mathcal{A}_F) - \cap U(A_F)_{J_F}) \simeq U(1)$, such that $\mathfrak{B}(F) - \simeq U(1)$.\newline - - So for $a \in \mathbb{C}^2$ to be in $(A_F)_{J_F}$ it has - to satisfy $J_F a^* J_F = a$. - \begin{align} - J_F a^* J^{-1} = - \begin{pmatrix}0&C\\C&0\end{pmatrix} - \begin{pmatrix}\bar{a}_1&0\\0&\bar{a}_2\end{pmatrix} - \begin{pmatrix}0&C\\C&0\end{pmatrix} - = - \begin{pmatrix}a_2&0\\0&a_1\end{pmatrix} - \end{align} - Which is only the case if $a_1 = a_2$. So we have - $(A_F)_{J_F} \simeq \mathbb{C}$, whose unitary elements - from $U(1)$ are contained in the diagonal subgroup of - $U(\mathcal{A}_F)$. -\end{proof} - -Now we need to find the exact from of the field $B_\mu$ to calculate the -spectral action of a spectral triple. Since $(A_F)_{J_F} \simeq -\mathbb{C}$ we find that $\mathfrak{h}(F) = \mathfrak{u}((A_F)_{J_F}) -\simeq i\mathbb{R}$. Where $\mathfrak{h}(F)$ is the Lie Algebra on $F$ -and $\mathfrak{u}((A_F)_{J_F})$ is the Lie algebra of the unitary group -$(A_F)_{J_F}$.\newline - -An arbitrary hermitian field $A_\mu = -ia\partial _\mu b$ is given by -two -$U(1)$ Gauge fields $X_\mu^1, X_\mu^2 \in C^\infty(M, \mathbb{R})$. -However $A_\mu$ appears in combination $A_\mu - J_F A_\mu J_F^{-1}$: -\begin{align} - B_\mu = A_\mu - J_F A_\mu J_F^{-1} = - \begin{pmatrix}X_\mu^1&0\\0&X_\mu^2 \end{pmatrix} - - - \begin{pmatrix}X_\mu^2&0\\0&X_\mu^1 \end{pmatrix} - =: - \begin{pmatrix}Y_\mu&0\\0&-Y_\mu \end{pmatrix}= - Y_\mu \otimes \gamma _F -\end{align} -where $Y_\mu$ the $U(1)$ Gauge field is defined as -\begin{align} - Y_\mu := X_\mu^1 - X_\mu^2 \in C^\infty(M, \mathbb{R}) = C^\infty(M, - i\ u(1)). -\end{align} - -\begin{proposition} - The inner fluctuations of the almost-commutative manifold $M\times - F_x$ described above are parametrized by a $U(1)$-gauge field $Y_\mu$ - as - \begin{align} - D \mapsto D' = D + \gamma ^\mu Y_\mu \otimes \gamma_F - \end{align} - The action of the gauge group $\mathfrak{B}(M\times F_X) \simeq - C^\infty (M, U(1))$ on $D'$ is implemented by - \begin{align} - Y_\mu \mapsto Y_\mu - i\ u\partial_\mu u^*; \;\;\;\;\; (u\in - \mathfrak{B}(M\times F_X)). - \end{align} -\end{proposition} - -\subsection{Electrodynamics} -Now we use the almost commutative Manifold and the abelian gauge group -$U(1)$ to describe Electrodynamics. We arrive at a unified description of -gravity and electrodynamics although in the classical level. -\newline - -The almost commutative Manifold $M\times F_X$ describes a local gauge group -$U(1)$. The inner fluctuations of the Dirac operator describe $Y_\mu$ the -gauge field of $U(1)$. There arise two Problems: -\newline -(1): With $F_X$, $D_F$ must vanish, however this implies that the electrons -are massless (this we do not want) -\newline - -(2): The Euclidean action for a free Dirac field is -\begin{align} - S = - \int i \bar{\psi}(\gamma ^\mu\partial _\mu - m) \psi d^4x, -\end{align} -$\psi,\ \bar{\psi}$ must be considered as independent variables, which means -$S_F$ need two independent Dirac Spinors. We write $\{e, \bar{e}\}$ for the -ONB of $H_F$, where $\{e\}$ is the ONB of $H_F^+$ and $\{\bar{e}\}$ the ONB -of $H_F^-$ with the real structure this gives us the following relations -\begin{align} - J_F e &= \bar{e} \;\;\;\;\;\; J_F \bar{e} = e \\ - \gamma_F e &= e \;\;\;\;\;\; \gamma_F \bar{e} = \bar{e}. -\end{align} -The total Hilbertspace is $H = L^2(S) \otimes H_F$, with $\gamma _F$ we can -decompose $L^2(S) = L^2(S)^+ \oplus L^2(S)^-$, so with $\gamma = \gamma _M -\otimes \gamma _F$ we can obtain the positive eigenspace $H^+$ -\begin{align} - H^+ = L^2(S)^+ \otimes H_F^+ \oplus L^(S)^- \otimes H_F^-. -\end{align} -For a $\xi \i H^+$ we can write -\begin{align} - \xi = \psi _L \otimes e + \psi _R \otimes \bar{e} -\end{align} -where $\psi _L \in L^2(S)^+$ and $\psi _R \in L^2(S)^-$ are the two Wheyl -spinors. We denote that $\xi$ is only determined by one Dirac spinor $\psi := -\psi_L + \psi _R$, \textbf{but we require two independent spinors}. This is -too much restriction for $F_X$. -\subsubsection{The Finite Space} -Here we solve the two problems by enlarging(doubling) the Hilbertspace. This -is done by introducing multiplicities in Krajewski Diagrams which will also -allow us to choose a nonzero Dirac operator which will connect the two -vertices (next chapter). -\newline - -We start of with the same algebra $C^\infty(M, \mathbb{C}^2)$, corresponding -to space $N= M\times X \simeq M\sqcup M$. -\newline - -The Hilbertspace will describe four particles, -\begin{itemize} - \item left handed electrons - \item right handed positrons -\end{itemize} -Thus we have $\{ \underbrace{e_R, e_L}_{\text{left-handed}}, -\underbrace{\bar{e}_R, \bar{e}_L}_{\text{right-handed}}\}$ the ONB for $H_F -\mathbb{C}^4$. -\newline -Then with $J_F$ we interchange particles with antiparticles we have the -following properties -\begin{align} - &J_F e_R = \bar{e}_R \;\;\;\;\; &J_F e_L = \bar{e_L} \\ - &\gamma _F e_R = -e_R \;\;\;\;\; &\gamma_F e_L = e_L \\ - \text{and}& \nonumber \\ - &J_F^2 = 1 \;\;\;\;\; & J_F \gamma_F = - \gamma_F J_F -\end{align} -This corresponds to KO-dim$= 6$. Then $\gamma_F$ allows us to can decompose -$H$ -\begin{align} - H_F = \underbrace{H_F^+}_{\text{ONB } \{e_L, \bar{e}_L\}} - \oplus \underbrace{H_F^-}_{\text{ONB } \{e_R, \bar{e}_R\}}. -\end{align} -Alternatively we can decompose $H$ into the eigenspace of particles and their -antiparticles (electrons and positrons) which we will use going further. -\begin{align} - H_F = \underbrace{H_{e}}_{\text{ONB } \{e_L, e_R\}} \oplus - \underbrace{H_{\bar{e}}}_{\text{ONB } \{\bar{e}_L, \bar{e}_R\}} -\end{align} -Now the action of $a \in A = \mathbb{C}^2$ on $H$ with respect to the ONB -$\{e_L, e_R, \bar{e}_L, \bar{e}_R\}$ is represented by -\begin{align} - a = - \begin{pmatrix}a_1 & a_2 \end{pmatrix} \mapsto - \begin{pmatrix} - a_1 &0 &0 &0\\ - 0&a_1 &0 &0\\ - 0 &0 &a_2 &0\\ - 0 &0 &0 &a_2\\ - \end{pmatrix} -\end{align} -Do note that this action commutes wit the grading and that -$[a, b^\circ] = 0$ with $b:= J_F b^*J_F$ because both the left and the right -action is given by diagonal matrices. -\begin{proposition} - The data - \begin{align} - \left( \mathbb{C}^2, \mathbb{C}^2, D_F=0; J_F = - \begin{pmatrix} - 0 & C \\ C &0 - \end{pmatrix}, - \gamma _F = - \begin{pmatrix} - 1 & 0 \\ 0 &-1 - \end{pmatrix} - \right) - \end{align} - defines a real even spectral triple of KO-dimension 6. -\end{proposition} -This spectral triple can be represented in the following Krajewski diagram, -with two nodes of multiplicity two - \begin{figure}[h!] \centering - \begin{tikzpicture}[ - dot/.style = {draw, circle, inner sep=0.06cm}, - bigdot/.style = {draw, circle, inner sep=0.09cm}, - no/.style = {}, - ] - \node[no](a) at (0,0) [label=left:$\textbf{1}^\circ$] {}; - \node[no](b) at (0, -1) [label=left:$\textbf{1}^\circ$] {}; - \node[no](c) at (0.5, 0.5) [label=above:$\textbf{1}$] {}; - \node[no](d) at (1.5, 0.5) [label=above:$\textbf{1}$] {}; - \node[dot](d0) at (1.5,0) [] {}; - \node[dot](d0) at (0.5,-1) [] {}; - \node[bigdot](d0) at (1.5,0) [] {}; - \node[bigdot](d0) at (0.5,-1) [] {}; - \end{tikzpicture} - \end{figure} -\subsubsection{A noncommutative Finite Dirac Operator} -Add a non-zero Dirac Operator to $F_{ED}$. From the Krajewski Diagram, we see -that edges only exist between the multiple vertices. So we construct a Dirac -operator mapping between the two vertices. -\begin{align}\label{dirac} - D_F = - \begin{pmatrix} - 0 & d & 0 & 0 \\ - \bar{d} & 0 & 0 & 0 \\ - 0 & 0 & 0 & \bar{d} \\ - 0 & 0 & d & 0 - \end{pmatrix} -\end{align} -We can now consider the finite space $F_{ED}$. -\begin{align} - F_{ED} := (\mathbb{C}^2, \mathbb{C}^4, D_F; J_F, \gamma_F) -\end{align} -where $J_F$ and $\gamma_F$ like before, $D_F$ like above. -\subsubsection{The almost-commutative Manifold} -The almost commutative manifold $M\times F_{ED}$ has KO-dim$=2$, it is the -following spectral triple -\begin{align} - M\times F_{ED} := \left(C^\infty(M,\mathbb{C}^2),\ L^2(S)\otimes - \mathbb{C}^4,\ - D_M\otimes 1 +\gamma _M \otimes D_F;\; J_M\otimes J_F,\ \gamma_M\otimes - \gamma _F\right) -\end{align} - -The algebra decomposition is like before -\begin{align} - C^\infty(M, \mathbb{C}^2) = C^\infty (M) \oplus C^\infty (M) -\end{align} - -The Hilbertspace decomposition is -\begin{align} - H = (L^2(S) \otimes H_e ) \oplus (L^2(S) \otimes H_{\bar{e}}). -\end{align} -Here we have the one component of the algebra acting on $L^2(S) \otimes H_e$, -and the other one acting on $L^2(S) \otimes H_{\bar{e}}$ -\newline - -The derivation of the gauge theory is the same for $F_{ED}$ as for $F_X$, we -have $\mathfrak{B}(F) \simeq U(1)$ and for $B_\mu = A_\mu - J_F A_\mu -J_F^{-1}$ -\begin{align} \label{field} - B_\mu = - \begin{pmatrix} - Y_\mu & 0 & 0 & 0 \\ - 0 & Y_\mu& 0 & 0 \\ - 0 & 0 & Y_\mu& 0 \\ - 0 & 0 & 0 & Y_\mu - \end{pmatrix} \;\;\;\;\;\ \text{for} \;\;\ Y_\mu (x) \in \mathbb{R}. -\end{align} -We have one single $U(1)$ gauge field $Y_\mu$, carrying the action of the -gauge group -\begin{align} - \text{$\mathfrak{B}$}(M\times F_{ED}) \simeq C^\infty(M, U(1)) -\end{align} - -Our space $N = M\times X \simeq M\sqcup M$ consists of two compies of $M$. -If $D_F = 0$ we have infinite distance between the two copies. Now we have $D_F$ -nonzero but $[D_F, a] = 0$ $\forall a \in A$ which still yields infinite -distance. -\begin{question} - What does this imply (physically, mathematically)? Why can we continue - even thought we have infinite distance between the same manifold? What do - we get if we fix this? -\end{question} -\subsubsection{The Spectral Action} -Here we calculate the Lagrangian of the almost commutative Manifold $M\times -F_{ED}$, which corresponds to the Lagrangian of Electrodynamics on a curved -background Manifold (+ gravitational Lagrangian). It consists of the spectral -action $S_b$ (bosonic) and of the fermionic action $S_f$. - -The simples spectral action of a spectral triple $(A, H, D)$ is given by the -trace of some function of $D$, we also allow inner fluctuations of the Dirac -operator $D_\omega = D + \omega + \varepsilon' J\omega J^{-1}$ where $\omega = -\omega ^* \in \Omega_D^1(A)$. -\begin{definition} - Let $f:\mathbb{R} \rightarrow \mathbb{R}$ be a suitable function - \textbf{positive and even}. The spectral action is then - \begin{align} - S_b [\omega] := \text{Tr}f(\frac{D_\omega}{\Lambda}) - \end{align} - where $\Lambda$ is a real cutoff parameter. The minimal condition on $f$ - is that $f(\frac{D_\omega}{\Lambda})$ is a traclass operator, which mean - that it should be compact operator with well defined finite trace - independent of the basis. The subscript $b$ of $S_b$ refers to bosonic, - because in physical applications $\omega$ will describe bosonic fields. - - Furthermore there is a topological spectral action, defined with the - grading $\gamma$ - \begin{align} - S_{\text{top}}[\omega] := \text{Tr}(\gamma\ - f(\frac{D_\omega}{\Lambda})). - \end{align} -\end{definition} -\begin{definition} - The fermionic action is defined by - \begin{align} - S_f[\omega, \psi] = (J\tilde{\psi}, D_\omega \tilde{\psi}) - \end{align} - with $\tilde{\psi} \in H_{cl}^+ := \{\tilde{\psi}: \psi \in H^+\}$. - $H_{cl}^+$ is the set of Grassmann variables in $H$ in the +1-eigenspace - of the grading $\gamma$. -\end{definition} -The grasmann variables are a set of Basis vectors of a vector space, they -form a unital algebra over a vector field say $V$ where the generators are anti commuting, that is for -$\theta _i, \theta _j$ some Grassmann variables we have -\begin{align} - &\theta _i \theta _j = -\theta _j \theta _i \\ - &\theta _i x = x\theta _j \;\;\;\; x\in V \\ - &(\theta_i)^2 = 0 \;\;\; (\theta _i \theta _i = -\theta _i \theta _i) -\end{align} -\begin{proposition} - The spectral action of the almost commutative manifold $M$ with $\dim(M) - =4$ with a fluctuated Dirac operator is. - \begin{align} - \text{Tr}(f\frac{D_\omega}{\Lambda}) \sim \int_M \mathcal{L}(g_{\mu\nu}, - B_\mu, \Phi) \sqrt{g}\ d^4x + O(\Lambda^{-1}) - \end{align} - with - \begin{align} - \mathcal{L}(g_{\mu\nu}, B_\mu, \Phi) = - N\mathcal{L}_M(g_{\mu\nu}) - \mathcal{L}_B(B_\mu)+ - \mathcal{L}_\phi(g_{\mu\nu}, B_\mu, \Phi) - \end{align} - where $N=4$ and $\mathcal{L}_M$ is the Lagrangian of the spectral triple - $(C^\infty(M) , L^2(S), D_M)$ - \begin{align}\label{lagr} - \mathcal{L}_M(g_{\mu\nu}) := \frac{f_4 \Lambda ^4}{2\pi^2} - - \frac{f_2 \Lambda^2}{24\pi ^2}s - \frac{f(0)}{320\pi^2} C_{\mu\nu - \varrho \sigma}C^{\mu\nu \varrho \sigma}. - \end{align} - Here $C^{\mu\nu \varrho \sigma}$ is defined in terms of the Riemannian - curvature tensor $R_{\mu\nu \varrho \sigma}$ and the Ricci tensor - $R_{\nu\sigma} = g^{\mu\varrho} R_{\mu\nu \varrho\sigma}$. - - - Furthermore $\mathcal{L}_B$ describes the kinetic term of the gauge field - \begin{align} - \mathcal{L}_B(B_\mu) := \frac{f(0)}{24\pi^2} - \text{Tr}(F_{\mu\nu}F^{\mu\nu}). - \end{align} - Last $\mathcal{L}_\phi$ is the scalar-field Lagrangian with a boundary - term. - \begin{align} - \mathcal{L}_\phi(g_{\mu\nu}, B_\mu, \Phi) := - &-\frac{2f_2\Lambda^2}{4\pi^2}\text{Tr}(\Phi^2) + \frac{f(0)}{8\pi^2} - \text{Tr}(\Phi^4) + \frac{f(0)}{24\pi^2} \Delta(\text{Tr}(\Phi^2))\\ - &+ \frac{f(0)}{48\pi^2}s\text{Tr}(\Phi^2) - \frac{f(0)}{8\pi^2}\text{Tr}((D_\mu \Phi)(D^\mu \Phi)). - \end{align} -\end{proposition} -\begin{proof} - the dimension of our manifold $m$ is $\dim(m) = \text{tr}(id) =4 $. let us - take a $x \in m$, we have an asymtotic expansion of - $\text{tr}(f(\frac{d_\omega}{\lambda}))$ as $\lambda \rightarrow \infty$ - \begin{align} - \text{tr}(f(\frac{d_\omega}{\lambda})) \simeq& \ 2f_4 \lambda ^4 - a_0(d_\omega ^2)+ 2f_2\lambda^2 a_2(d_\omega^2) \\&+ f(0) a_4(d_\omega^4) - +o(\lambda^{-1}). - \end{align} - note that the heat kernel coefficients are zero for uneven $k$, - furthermore they are dependent on the fluctuated dirac operator - $d_\omega$. we can rewrite the heat kernel coefficients in terms of $d_m$, - for the first two we note that $n:= \text{tr}\mathbbm{1_{h_f}})$ - \begin{align} - a_0(d_\omega^2) &= na_0(d_m^2)\\ - a_2(d_\omega^2 &= na_2(d_m^2) - \frac{1}{4\pi^2}\int_m - \text{tr}(\phi^2)\sqrt{g}d^4x - \end{align} - for $a_4$ we need to extend in terms of coefficients of $f$, look week9.pdf - for the standard version, - \begin{align} - &\frac{1}{360}\text{tr}(60sf)= -\frac{1}{6}s(ns + 4 - \text{tr}(\phi^2))\\ - \nonumber\\ - &f^2 = \frac{1}{16}s^2\otimes 1 + 1\otimes \phi^4 - \frac{1}{4} - \gamma^\mu\gamma^\nu \gamma^\varrho\gamma^\sigma f_{\mu\nu}f^{\mu\nu}+\\ - &\;\;\;\;\;\;\;+\gamma^\mu\gamma^\nu\otimes(d_\mu\phi)(d_\nu - \phi)+\frac{1}{2}s\otimes \phi^2 + \ \text{traceless terms}\\ - \nonumber\\ - &\frac{1}{360}\text{tr}(180f^2) = \frac{1}{8}s^2n + 2\text{tr}(\phi^4) - + \text{tr}(f_{\mu\nu}f^{\mu\nu}) +\\ - &\;\;\;\;\;\;\;+2\text{tr}((d_\mu\phi)(d^\mu\phi)) - + s\text{tr}(\phi^2)\\ - \nonumber\\ - &\frac{1}{360}\text{tr}(-60\delta f)= - \frac{1}{6}\delta(ns+4\text{tr}(\phi^2)). - \end{align} - now for the cross terms of $\omega_{\mu\nu}^e\omega^{e\mu\nu}$ the trace - vanishes because of the anti-symmetric properties of the riemannian - curvature tensor - \begin{align} - \omega_{\mu\nu}^e\omega^{e\mu\nu} = \omega_{\mu\nu}^s\omega^{s\mu\nu} - \otimes 1 - 1\otimes f_{\mu\nu}f^{\mu\nu} + 2i\omega_{\mu\nu}^s - \otimes f^{\mu\nu} - \end{align} - the trace of the cross term vanishes because - \begin{align} - \text{tr}(\omega^{s}_{\mu\nu} = \frac{1}{4} - r_{\mu\nu\varrho\sigma}\text{tr}(\gamma^\mu\gamma^\nu) = \frac{1}{4} - r_{\mu\nu\varrho\sigma}g^{\mu\nu} =0 - \end{align} - and the trace of the whole term is - \begin{align} - \frac{1}{360}\text{tr}(30\omega^e_{\mu\nu}\omega^{e\mu\nu}) = - \frac{n}{24}r_{\mu\nu\varrho\sigma}r^{\mu\nu\varrho\sigma} - -\frac{1}{3}\text{tr}(f_{\mu\nu}f^{\mu\nu}). - \end{align} - plugging the results into $a_4$ and simplifying we can write - \begin{align} - a_4(x, d_\omega^4) &= na_4(x, d_m^2) + \frac{1}{4\pi^2}\bigg(\frac{1}{12} s - \text{tr}(\phi^2) + \frac{1}{2}\text{tr}(\phi^4) \\ - &+ \frac{1}{4} - \text{tr}((d_\mu\phi)(d^\mu \phi)) + \frac{1}{6} - \delta\text{tr}(\phi^2) + \frac{1}{6} - \text{tr}(f_{\mu\nu}f^{\mu\nu})\bigg) - \end{align} - the only thing left is to plug in the heat kernel coefficients into the - heat kernel expansion above. -\end{proof} - -Here on we go and calculate the spectral action of $M\times F_{ED}$ -\begin{proposition} - The Spectral action of $M\times F_{ED}$ is - \begin{align} - \text{Tr}(f\frac{D_\omega}{\Lambda}) \sim \int_M \mathcal{L}(g_{\mu\nu}, - Y_\mu) \sqrt{g}\ d^4x + O(\Lambda^{-1}) - \end{align} - where the Lagrangian is - \begin{align} - \mathcal{L}(g_{\mu\nu}, Y_\mu) = - 4\mathcal{L}_M(g_{\mu\nu})+ - \mathcal{L}_Y(Y_\mu)+ - \mathcal{L}_\phi(g_{\mu\nu}, d) - \end{align} - here the $d$ in $\mathcal{L}_\phi$ is from $D_F$ in equation - \ref{dirac}. The Lagrangian $\mathcal{L}_M$ is like in equation - \ref{lagr}. The Lagrangian $\mathcal{L}_Y$ is the kinetic term of the - $U(1)$ gauge field $Y_\mu$ - \begin{align} - \mathcal{L}_Y(Y_\mu):= \frac{f(0)}{6\pi^2} - Y_{\mu\nu}Y^{\mu\nu}\;\;\;\;\;\;\;\;\text{with}\;\;\; Y_{\mu\nu} = - \partial_\mu Y_\nu - - \partial_\nu Y_\mu. - \end{align} - Then there is $\mathcal{L}_\phi$, which has two constant terms - (disregarding the boundary term) that add up to the Cosmological Constant - and a term that for the Einstein-Hilbert action - \begin{align} - \mathcal{L}_\phi(g_{\mu\nu}, d) := \frac{2f_2 \Lambda ^2}{\pi^2} - |d|^2 + \frac{f(0)}{2\pi^2} |d|^4 + \frac{f(0)}{12\pi ^2} s |d|^2. - \end{align} -\end{proposition} -\begin{proof} - The Trace of $\mathbb{C}^4$ (the Hilbertspace) gives $N=4$. With $B_\mu$ - like in equation \ref{field} we have $\text{Tr}(F_{\mu\nu} - F^{\mu\nu})=4Y_{\mu\nu}Y^{\mu\nu}$. This provides $\mathcal{L}_Y$. - Furthermore we have $\Phi^2 = D_F^2 = |d|^2$ and $\mathcal{L}_\phi$ only - give numerical contributions to the cosmological constant and the - Einstein-Hilbert action. - - The proof is relying itself on just plugging the terms into the previous - proposition, for which I didn't write the proof for. -\end{proof} - - -\subsection{fermionic action} -a quick reminder with what we are dealing with, the fermionic action is defined -in the following way. -\begin{definition} - the fermionic action is defined by - \begin{align} - s_f[\omega, \psi] = (j\tilde{\psi}, d_\omega \tilde{\psi}) - \end{align} - with $\tilde{\psi} \in h_{cl}^+ := \{\tilde{\psi}: \psi \in h^+\}$. - $h_{cl}^+$ is the set of grassmann variables in $h$ in the +1-eigenspace - of the grading $\gamma$. -\end{definition} - -the almostcommutative manifold we are dealing with is the following -\begin{align} - &m\times f_{ed} := \left(c^\infty(m,\mathbb{c}^2),\ l^2(s)\otimes - \mathbb{c}^4,\ - d_m\otimes 1 +\gamma _m \otimes d_f;\; j_m\otimes j_f,\ \gamma_m\otimes - \gamma _f\right).\\ - \nonumber\\ - &\text{where:} \nonumber \\ - &c^\infty(m,\mathbb{c}^2) = c^\infty(m) \otimes c^\infty(m) - &\mathcal{h} = \mathcal{h}^+ \otimes \mathcal{h}^-\\ - &\mathcal{h} = l^2(s)^+ \otimes h_f^+ \oplus l^2(s)^- \otimes h_f^-. -\end{align} -where $h_f$ is separated into the particle-anitparticle states with onb $\{e_r, -e_l, \bar{e}_r, \bar{e}_l\}$. the onb of $h_f^+$ is $\{e_l, \bar{e}_r\}$ and -for $h_f^-$ we have $\{e_r, \bar{e}_l\}$. furthermore we can decompose a spinor -$\psi \in l^2(s)$ for each of the eigenspaces $h_f^\pm$, $\psi = \psi_r -\psi_l$. thus we can write for an arbitrary $\psi \in \mathcal{h}^+$ -\begin{align} - \psi = \chi_r \otimes e_r + \chi_l \otimes e_l + \psi_l \otimes \bar{e}_r - \psi_r \otimes \bar{e}_l -\end{align} -for $\chi_l, \psi_l \in l^2(s)^+$ and $\chi_r, \psi_r \in l^2(s)^-$. -\begin{proposition} - we can define the action of the fermionic art of $m\times f_{ed}$ in the - following way - \begin{align} - s_f = -i\big(j_m\tilde{\chi}, \gamma(\nabla^s_\mu - i\gamma_\mu) - \tilde{\psi}\big) + \big(s_m\tilde{\chi}_l, \bar{d}\tilde{\psi}_l\big) - - \big(j_m\tilde{\chi}_r, d \tilde{\psi}_r\big) - \end{align} -\end{proposition} -\begin{proof} - we take the fluctuated dirac operator - \begin{align} - d_\omega = d_m \otimes i + \gamma^\mu \otimes b_\mu + \gamma_m \otimes - d_f - \end{align} -\end{proof} -the fermionic action is $s_f = (j\tilde{\xi}, d_\omega\tilde{\xi})$ for a $\xi -\in \mathcal{h}^+$, we can begin to calculate (note that we add the constant -$\frac{1}{2}$ to the action) -\begin{align} - \frac{1}{2}(j\tilde{\xi}, d_\omega\tilde{\xi}) =&\\ - &+\frac{1}{2}(j\tilde{\xi}, (d_m \otimes i)\tilde{\xi})\label{eq:1}\\ - &+\frac{1}{2}(j\tilde{\xi}, (\gamma^\mu \otimes b_\mu) - \tilde{\xi})\label{eq:2}\\ - &+\frac{1}{2}(j\tilde{\xi}, (\gamma_m\otimes - d_f)\tilde{\xi})\label{eq:3}. -\end{align} -for equation \ref{eq:1} we calculate -\begin{align} - \frac{1}{2}(j\tilde{\xi}, (d_m\otimes 1)\tilde{\xi}) &= - \frac{1}{2}(j_m\tilde{\chi}_r,d_m\tilde{\psi}_l)+ - \frac{1}{2}(j_m\tilde{\chi}_l,d_m\tilde{\psi}_r)+ - \\&+\frac{1}{2}(j_m\tilde{\psi}_l,d_m\tilde{\psi}_r)+ - \frac{1}{2}(j_m\tilde{\chi}_r,d_m\tilde{\chi}_l)\\ - &= (j_m\tilde{\chi},d_m\tilde{\chi}). -\end{align} -for equation \ref{eq:2} we have -\begin{align} - \frac{1}{2}(j\tilde{\xi}, (\gamma^\mu \otimes b_\mu)\tilde{\xi})&= - -\frac{1}{2}(j_m\tilde{\chi}_r, \gamma^\mu y_\mu\tilde{\psi}_r) - -\frac{1}{2}(j_m\tilde{\chi}_l, \gamma^\mu y_\mu\tilde{\psi}_r)+\\ - &+\frac{1}{2}(j_m\tilde{\psi}_l, \gamma^\mu y_\mu\tilde{\chi}_r)+ - \frac{1}{2}(j_m\tilde{\psi}_r, \gamma^\mu y_\mu\tilde{\chi}_l)=\\ - &= -(j_m\tilde{\chi}, \gamma^\mu y_\mu\tilde{\psi}). -\end{align} -for equation \ref{eq:3} we have -\begin{align} - \frac{1}{2}(j\tilde{\xi}, (\gamma_m\otimes d_f)\tilde{\xi})&= - +\frac{1}{2}(j_m\tilde{\chi}_r, d\gamma_m\tilde{\chi}_r) - +\frac{1}{2}(j_m\tilde{\chi}_l, \bar{d}\gamma_m\tilde{\chi}_l)+\\ - &+\frac{1}{2}(j_m\tilde{\chi}_l, \bar{d}\gamma_m\tilde{\chi}_l) - +\frac{1}{2}(j_m\tilde{\chi}_r, d\gamma_m\tilde{\chi}_r)=\\ - &= i(j_m\tilde{\chi}, m\tilde{\psi}) -\end{align} -note that we obtain a complex mass parameter $d$, so we write $d:=im$ for $m\in \mathbb{r}$, -which stands for the real mass and we obtain a nice result - -\begin{theorem} - the full lagrangian of $m\times f_{ed}$ is the sum of purely gravitational - lagrangian - \begin{align} - \mathcal{l}_{grav}(g_{\mu\nu})=4\mathcal{l}_m(g_{\mu\nu}) - \mathcal{l}_\phi (g_{\mu\nu}) - \end{align} - and the lagrangian of electrodynamics - \begin{align} - \mathcal{l}_{ed} = -i\bigg\langle - j_m\tilde{\chi},\big(\gamma^\mu(\nabla^s_\mu - iy_\mu) -m\big)\tilde{\psi}) - \bigg\rangle - +\frac{f(0)}{6\pi^2} y_{\mu\nu}y^{\mu\nu}. - \end{align} - -\end{theorem} diff --git a/src/thesis/chapters/electroncg.tex b/src/thesis/chapters/electroncg.tex @@ -1,12 +1,12 @@ \subsection{Noncommutative Geometry of Electrodynamics} \subsubsection{The Two-Point Space} -One of the basics forms of a noncommutative space is the the two point space $X -:= \{x, y\}$, it can be represented by the following spectral triple +One of the basics forms of noncommutative space is the Two-Point space $X +:= \{x, y\}$. The Two-Point space can be represented by the following spectral triple \begin{align} - F_x := (C(X) = \mathbb{C}^2, H_F, D_F; J_F, \gamma _f). + F_X := (C(X) = \mathbb{C}^2, H_F, D_F; J_F, \gamma _f). \end{align} -There are three properties of $F_x$ that stand out, first of all the action of -$C(X)$ on $H_F$ is faithful for $dim(H_F) \geq 2$. Thus we can make a simple +Three properties of $F_X$ stand out. First of all the action of +$C(X)$ on $H_F$ is faithful for $dim(H_F) \geq 2$, thus we can make a simple choice for the Hilbertspace, $H_F = \mathbb{C}^2$. Furthermore $\gamma_F$ is the $\mathbb{Z}_2$ grading, which allows us to decompose $H_F$ into \begin{align} @@ -24,12 +24,10 @@ interchange between $H_F^\pm$, \text{with} \;\; t\in\mathbb{C}. \end{align} - The Two-Point space $F_x$ can only have a real structure if the Dirac - operator vanishes, i.e. $D_F = 0$, in that case we have KO-dimension of 0, - 2 or 6. - - To elaborate on this, we know that there are two diagram representations of - $F_x$ at $\underbrace{\mathbb{C} \oplus \mathbb{C}}_{C(X)}$ on + The Two-Point space $F_X$ can only have a real structure if the Dirac + operator vanishes, i.e. $D_F = 0$. In that case we have KO-dimension of 0, + 2 or 6. To elaborate on this, we know that there are two diagram representations of + $F_X$ at $\underbrace{\mathbb{C} \oplus \mathbb{C}}_{C(X)}$ on $\underbrace{\mathbb{C} \oplus\mathbb{C}}_{H_F}$, which are: \begin{figure}[h!] \centering \begin{tikzpicture}[ @@ -51,19 +49,18 @@ interchange between $H_F^\pm$, \node[dot](d0) at (8,-1) [] {}; \end{tikzpicture} \end{figure}\newline -If the Two-Point space $F_x$ would be a real spectral triple then $D_F$ can +If the Two-Point space $F_X$ would be a real spectral triple then $D_F$ can only go vertically or horizontally. This would mean that $D_F$ vanishes. - -The diagram on the left has KO-dimension 2 and 6, the diagram on the -right has KO-dimension 0 and 4. Yet KO-dimension 4 is not ruled out because +As for the KO-dimension The diagram on the left has KO-dimension 2 and 6, the diagram on the +right 0 and 4. Yet KO-dimension 4 is ruled out because $dim(H_F^\pm) = 1$ (see Lemma 3.8 Book), which ultimately means $J_F^2 = -1$ is not allowed. -\subsubsection{The product Space} +\subsubsection{The Product Space} By Extending the Two-Point space with a four dimensional Riemannian spin -manifold, we get an almost commutative manifold $M\times F_x$, given by +manifold, we get an almost commutative manifold $M\times F_X$, given by \begin{align} - M\times F_x = (C^\infty(M), \mathbb{C}^2), L^2(S)\otimes \mathbb{C}^2, - D_M\otimes 1 ; J_M\otimes J_F, \gamma_M \otimes \gamma_F), + M\times F_X = \big(C^\infty(M, \mathbb{C}^2), L^2(S)\otimes \mathbb{C}^2, + D_M\otimes 1 ; J_M\otimes J_F, \gamma_M \otimes \gamma_F\big), \end{align} where \begin{align} @@ -72,21 +69,17 @@ where According to Gelfand duality the algebra $C^\infty(M, \mathbb{C}^2)$ of the spectral triple corresponds to the space \begin{align} - N:= M\otimes X \simeq M\sqcup X + N:= M\otimes X \simeq M\sqcup X. \end{align} Keep in mind that we still need to find an appropriate real structure on the -Riemannian spin manifold, $J_M$. -\newline -The total Hilbertspace can be decomposed into $H = L^2(S) \oplus L^2(S)$, such -that for -\newline +Riemannian spin manifold, $J_M$. Furthermore total Hilbertspace can be decomposed into $H = L^2(S) \oplus L^2(S)$, such that for $\underbrace{a,b\in C^\infty(M)}_{(a, b) \in C^\infty(N)}$ and $\underbrace{\psi, \phi \in L^2(S)}_{(\psi, \phi) \in H}$ we have \begin{align} (a, b)(\psi, \phi) = (a\psi, b\phi) \end{align} Along with the decomposition of the total Hilbertspace we can consider a -distance formula on $M\times F_x$ with +distance formula on $M\times F_X$ with \begin{align}\label{eq:commutator inequality} d_{D_F}(x,y) = \sup\left\{ |a(x) - a(y)|:a\in A_F, ||[D_F, a]|| \leq 1 \right\}. @@ -98,7 +91,7 @@ commutator inequality in \ref{eq:commutator inequality} \begin{align} &||[D_F , a]|| = ||(a(y) - a(x))\begin{pmatrix}0 &t\\\bar{t} &0 \end{pmatrix}|| \leq 1,\\ - &\Rightarrow |a(y) - a(x)|\leq \frac{1}{|t|}, + &\Leftrightarrow |a(y) - a(x)|\leq \frac{1}{|t|}, \end{align} and the supremum gives us the distance \begin{align} @@ -106,45 +99,57 @@ and the supremum gives us the distance \end{align} An interesting observation here is that, if the Riemannian spin manifold can be represented by a real spectral triple then a real structure $J_M$ exists, -then it follows that $t=0$ and the distance becomes infinite. This is a purely -mathematical observation and has no physical meaning. +then it follows that $t=0$ and the distance becomes infinite. This is a +purely mathematical observation and has no physical meaning. -Now let $p \in M$, then take two points on $N=M\times X$, $(p, x)$ and -$(p,y)$ and $a \in C^\infty(N)$ is determined by $a_x(p):=a(p, x)$ and -$a_y(p):=a(p, y)$. The distance between these two points is then +We can also construct a distance formula on $N$ (in reference to a point $p +\in M$) between two points on $N=M\times X$, $(p, x)$ and $(p,y)$. Then an $a +\in C^\infty(N)$ is determined by $a_x(p):=a(p, x)$ and $a_y(p):=a(p, y)$. +The distance between these two points is \begin{align} d_{D_F\otimes 1}(n_1, n_2) = \sup \left\{ |a(n_1) - a(n_2)|: a\in - A, ||[D\otimes 1, a]||\right\} + A, ||[D\otimes 1, a]||\right\}. \end{align} -\textbf{Remark}: If $n_1 = (p,x)$ and $n_2 = (q, x)$ for $p,q \in M$ then +On the other hand if we consider $n_1 = (p,x)$ and $n_2 = (q, x)$ +for $p,q \in M$ then \begin{align} - d_{D_M \otimes 1} (n_1, n_2) = |a_x(p) - a_x(q)| \;\;\; a_x\in + d_{D_M \otimes 1} (n_1, n_2) = |a_x(p) - a_x(q)| \;\;\;\text{for}\;\; + a_x\in C^\infty(M) \;\; \text{with} \;\; ||[D\otimes 1, a_x]|| \leq 1 \end{align} -The distance turns to the geodestic distance formula +The distance formula turns to out to be the geodesic distance formula \begin{align} - d_{D_M\otimes1}(n_1, n_2) = d_g(p, q) + d_{D_M\otimes1}(n_1, n_2) = d_g(p, q), \end{align} - +which is to be expected since we are only looking at the manifold. However if $n_1 = (p, x)$ and $n_2 = (q, y)$ then the two conditions are -$||[D_M, a_x]|| \leq 1$ and $||[D_M, a_y|| \leq 1$. They have no -restriction which results in the distance being infinite! And $N = -M\times X$ is given by two disjoint copies of M which are separated by -infinite distance +\begin{align} + &||[D_M, a_x]|| \leq 1, \;\;\; \text{and}\\ + &||[D_M, a_y|| \leq 1. +\end{align} +These conditions have no restriction which results in the distance being +infinite! And $N = M\times X$ is given by two disjoint copies of M which are +separated by infinite distance -\textbf{Note}: distance is only finite if $[D_F, a] \neq 1$. The -commutator -generates a scalar field say $\phi$ and the finiteness of the distance is +The distance is only finite if $[D_F, a] < 1$. In this case the commutator +generates a scalar field and the finiteness of the distance is related to the existence of scalar fields. -\subsubsection{$U(1)$ Gauge Group} -Here we determine the Gauge theory corresponding to the almost -commutative -Manifold $M\times F_x$. -\textbf{Gauge Group of a Spectral Triple}: +\subsubsection{$U(1)$ Gauge Group} +To get a insight into the physical properties of the almost commutative +manifold $M\times F_X$, that is to calculate the spectral action, we need to +determine the corresponding Gauge theory. +For this we set of with simple definitions and important propositions to +help us break down and search for the gauge group of the Two-Point $F_X$ +space which we then extend to $M\times F_X$. We will only be diving +superficially into this chapter, for further reading we refer to +\cite{ncgwalter}. +\begin{definition} +Gauge Group of a real spectral triple is given by \begin{align} \mathfrak{B}(A, H; J) := \{ U = uJuJ^{-1} | u\in U(A)\} \end{align} +\end{definition} \begin{definition} A *-automorphism of a *-algebra $A$ is a linear invertible map @@ -154,7 +159,7 @@ Manifold $M\times F_x$. &\alpha(ab) = \alpha(a)\alpha(b)\\ &\alpha(a)^* = \alpha(a^*) \end{align} - The \textbf{Group of automorphisms of the *-Algebra $A$} is + The \textbf{Group of automorphisms of the *-Algebra $A$} is denoted by $(A)$.\newline The automorphism $\alpha$ is called \textbf{inner} if \begin{align} @@ -166,65 +171,53 @@ Manifold $M\times F_x$. \text{(unitary)} \end{align} \end{definition} -The Gauge group is given by the quotient $U(A)/U(A_J)$. -We want a nontrivial Gauge group so we need to choose $U(A_J) \neq -U(A)$ which is the same as $U((A_F)_{J_F}) \neq -U(A_F)$. -We consider $F_x$ to be +The Gauge group of $F_X$ is given by the quotient $U(A)/U(A_J)$. +We want a nontrivial Gauge group so we need to choose a $U(A_J) \neq +U(A)$ and $U((A_F)_{J_F}) \neq U(A_F)$. +We consider our Two-Point space $F_X$ to be equipped with a real structure, +which means the operator vanishes, and the spectral triple representation is \begin{align} - F_x := \left(\mathbb{C}^2,\mathbb{C}^2, D_F =\begin{pmatrix} + F_X := \left(\mathbb{C}^2,\mathbb{C}^2, D_F =\begin{pmatrix} 0&0\\0&0\end{pmatrix}; J_f =\begin{pmatrix} 0&C\\C&0\end{pmatrix}, \gamma_F = \begin{pmatrix}1&0\\0&-1\end{pmatrix}\right). \end{align} Here $C$ is the complex conjugation, and $F_X$ is a real even finite - spectral triple (space) with $KO-dim=6$ +spectral triple (space) of KO-dimension 6. \begin{proposition} - The Gauge group $\mathfrak{B}(F)$ of the two point space is given by - $U(1)$. +The Gauge group of the Two-Point space $\mathfrak{B}(F_X)$ is $U(1)$. \end{proposition} \begin{proof} - Note that $U(A_F) = U(1) \times U(1)$. We need to show that - $U(\mathcal{A}_F) - \cap U(A_F)_{J_F}) \simeq U(1)$, such that $\mathfrak{B}(F) - \simeq U(1)$.\newline - - So for $a \in \mathbb{C}^2$ to be in $(A_F)_{J_F}$ it has - to satisfy $J_F a^* J_F = a$. + Note that $U(A_F) = U(1) \times U(1)$. We need to show that $U(A_F) \cap + U(A_F)_{J_F}) \simeq U(1)$, such that $\mathfrak{B}(F) \simeq U(1)$. So + for an element $a \in \mathbb{C}^2$ to be in $(A_F)_{J_F}$, it has to + satisfy $J_F a^* J_F = a$, \begin{align} J_F a^* J^{-1} = \begin{pmatrix}0&C\\C&0\end{pmatrix} \begin{pmatrix}\bar{a}_1&0\\0&\bar{a}_2\end{pmatrix} \begin{pmatrix}0&C\\C&0\end{pmatrix} = - \begin{pmatrix}a_2&0\\0&a_1\end{pmatrix} + \begin{pmatrix}a_2&0\\0&a_1\end{pmatrix}. \end{align} - Which is only the case if $a_1 = a_2$. So we have + This can only be the case if $a_1 = a_2$. So we have $(A_F)_{J_F} \simeq \mathbb{C}$, whose unitary elements from $U(1)$ are contained in the diagonal subgroup of - $U(\mathcal{A}_F)$. + $U(A_F)$. \end{proof} -Now we need to find the exact from of the field $B_\mu$ to calculate the -spectral action of a spectral triple. Since $(A_F)_{J_F} \simeq -\mathbb{C}$ we find that $\mathfrak{h}(F) = \mathfrak{u}((A_F)_{J_F}) -\simeq i\mathbb{R}$. Where $\mathfrak{h}(F)$ is the Lie Algebra on $F$ -and $\mathfrak{u}((A_F)_{J_F})$ is the Lie algebra of the unitary group -$(A_F)_{J_F}$.\newline - An arbitrary hermitian field $A_\mu = -ia\partial _\mu b$ is given by -two -$U(1)$ Gauge fields $X_\mu^1, X_\mu^2 \in C^\infty(M, \mathbb{R})$. +two $U(1)$ Gauge fields $X_\mu^1, X_\mu^2 \in C^\infty(M, \mathbb{R})$. However $A_\mu$ appears in combination $A_\mu - J_F A_\mu J_F^{-1}$: \begin{align} - B_\mu = A_\mu - J_F A_\mu J_F^{-1} = + A_\mu - J_F A_\mu J_F^{-1} = \begin{pmatrix}X_\mu^1&0\\0&X_\mu^2 \end{pmatrix} - \begin{pmatrix}X_\mu^2&0\\0&X_\mu^1 \end{pmatrix} =: - \begin{pmatrix}Y_\mu&0\\0&-Y_\mu \end{pmatrix}= - Y_\mu \otimes \gamma _F + \begin{pmatrix}Y_\mu&0\\0&-Y_\mu \end{pmatrix} + = Y_\mu \otimes \gamma _F, \end{align} where $Y_\mu$ the $U(1)$ Gauge field is defined as \begin{align} @@ -234,8 +227,7 @@ where $Y_\mu$ the $U(1)$ Gauge field is defined as \begin{proposition} The inner fluctuations of the almost-commutative manifold $M\times - F_x$ described above are parametrized by a $U(1)$-gauge field $Y_\mu$ - as + F_X$ are parameterized by a $U(1)$-gauge field $Y_\mu$ as \begin{align} D \mapsto D' = D + \gamma ^\mu Y_\mu \otimes \gamma_F \end{align} @@ -247,91 +239,99 @@ where $Y_\mu$ the $U(1)$ Gauge field is defined as \end{align} \end{proposition} + \subsection{Electrodynamics} -Now we use the almost commutative Manifold and the abelian gauge group -$U(1)$ to describe Electrodynamics. We arrive at a unified description of -gravity and electrodynamics although in the classical level. -\newline +In this chapter we describe Electrodynamics with the almost commutative +manifold $M\times F_X$ and the abelian gauge group $U(1)$. +We arrive at a unified description of gravity and electrodynamics although in the classical level. The almost commutative Manifold $M\times F_X$ describes a local gauge group -$U(1)$. The inner fluctuations of the Dirac operator describe $Y_\mu$ the -gauge field of $U(1)$. There arise two Problems: -\newline -(1): With $F_X$, $D_F$ must vanish, however this implies that the electrons -are massless (this we do not want) -\newline +$U(1)$. The inner fluctuations of the Dirac operator relate to $Y_\mu$ the +gauge field of $U(1)$. According to the setup we ultimately arrive at two +serious problems. + +First of all in the Two-Point space $F_X$, the operator $D_F$ must vanish for +us to have a real structure. However this implies that the electrons +are massless, which would be absurd. -(2): The Euclidean action for a free Dirac field is +The second problem arises when looking at the Euclidean action for a free +Dirac field \begin{align} S = - \int i \bar{\psi}(\gamma ^\mu\partial _\mu - m) \psi d^4x, \end{align} -$\psi,\ \bar{\psi}$ must be considered as independent variables, which means -$S_F$ need two independent Dirac Spinors. We write $\{e, \bar{e}\}$ for the -ONB of $H_F$, where $\{e\}$ is the ONB of $H_F^+$ and $\{\bar{e}\}$ the ONB -of $H_F^-$ with the real structure this gives us the following relations +where $\psi,\ \bar{\psi}$ must be considered as independent variables, which +means that the fermionic action $S_f$ needs two independent Dirac spinors. +Let us try and construct two independent Dirac spinors with our data. To do +this we take a look at the decomposition of the basis and of the total +Hilbertspace $H = L^2(S) \otimes H_F$. For the orthonormal basis of $H_F$ we +can write $\{e, \bar{e}\}$ , where $\{e\}$ is the orthonormal basis of +$H_F^+$ and $\{\bar{e}\}$ the orthonormal basis of $H_F^-$. Accompanied with +the real structure we arrive at the following relations \begin{align} - J_F e &= \bar{e} \;\;\;\;\;\; J_F \bar{e} = e \\ + J_F e &= \bar{e} \;\;\;\;\;\; J_F \bar{e} = e, \\ \gamma_F e &= e \;\;\;\;\;\; \gamma_F \bar{e} = \bar{e}. \end{align} -The total Hilbertspace is $H = L^2(S) \otimes H_F$, with $\gamma _F$ we can -decompose $L^2(S) = L^2(S)^+ \oplus L^2(S)^-$, so with $\gamma = \gamma _M -\otimes \gamma _F$ we can obtain the positive eigenspace $H^+$ +Along with the decomposition of $L^2(S) = L^2(S)^+ \oplus L^2(S)^-$ and $\gamma = \gamma _M +\otimes \gamma _F$ we can obtain the positive eigenspace \begin{align} H^+ = L^2(S)^+ \otimes H_F^+ \oplus L^(S)^- \otimes H_F^-. \end{align} -For a $\xi \i H^+$ we can write +So, for a $\xi \in H^+$ we can write \begin{align} \xi = \psi _L \otimes e + \psi _R \otimes \bar{e} \end{align} -where $\psi _L \in L^2(S)^+$ and $\psi _R \in L^2(S)^-$ are the two Wheyl +where $\psi_L \in L^2(S)^+$ and $\psi _R \in L^2(S)^-$ are the two Wheyl spinors. We denote that $\xi$ is only determined by one Dirac spinor $\psi := -\psi_L + \psi _R$, \textbf{but we require two independent spinors}. This is -too much restriction for $F_X$. +\psi_L + \psi _R$, \textbf{but we require two independent spinors}. Our +conclusion is that the definition of the fermionic action gives too much +restrictions to the Two-Point space $F_X$. \subsubsection{The Finite Space} -Here we solve the two problems by enlarging(doubling) the Hilbertspace. This -is done by introducing multiplicities in Krajewski Diagrams which will also -allow us to choose a nonzero Dirac operator which will connect the two -vertices (next chapter). -\newline +To solve the two problems we simply enlarge (double) the Hilbertspace. This +is visualized by introducing multiplicities in Krajewski Diagrams which will also +allow us to choose a nonzero Dirac operator that will connect the two +vertices and preserve real structure making our particles massive and +bringing anti-particles into the mix. We start of with the same algebra $C^\infty(M, \mathbb{C}^2)$, corresponding -to space $N= M\times X \simeq M\sqcup M$. -\newline - -The Hilbertspace will describe four particles, -\begin{itemize} - \item left handed electrons - \item right handed positrons -\end{itemize} -Thus we have $\{ \underbrace{e_R, e_L}_{\text{left-handed}}, -\underbrace{\bar{e}_R, \bar{e}_L}_{\text{right-handed}}\}$ the ONB for $H_F -\mathbb{C}^4$. -\newline -Then with $J_F$ we interchange particles with antiparticles we have the -following properties +to space $N= M\times X$. The Hilbertspace describes four particles, meaning +it has four orthonormal basis elements. It describes \textbf{left handed +electrons} and \textbf{right handed positrons}. Pointing this out, we have +$\{ \underbrace{e_R, e_L}_{\text{left-handed}}, \underbrace{\bar{e}_R, +\bar{e}_L}_{\text{right-handed}}\}$ the orthonormal basis for $H_F = +\mathbb{C}^4$. Accompanied with the real structure $J_F$, which allows us to +interchange particles with antiparticles by the following equations +\begin{align} + &J_F e_R = \bar{e}_R, \\ + &J_F e_L = \bar{e_L}, \\ + \nonumber \\ + &\gamma _F e_R = -e_R,\\ + &\gamma_F e_L = e_L \\ +\end{align} +where $J_F$ and $gamma_F$ have to following properties \begin{align} - &J_F e_R = \bar{e}_R \;\;\;\;\; &J_F e_L = \bar{e_L} \\ - &\gamma _F e_R = -e_R \;\;\;\;\; &\gamma_F e_L = e_L \\ - \text{and}& \nonumber \\ - &J_F^2 = 1 \;\;\;\;\; & J_F \gamma_F = - \gamma_F J_F + &J_F^2 = 1,\\ + & J_F \gamma_F = - \gamma_F J_F. \end{align} -This corresponds to KO-dim$= 6$. Then $\gamma_F$ allows us to can decompose -$H$ +By means of $\gamma_F$ we have two options to decompose the total +Hilbertspace $H$, firstly into \begin{align} H_F = \underbrace{H_F^+}_{\text{ONB } \{e_L, \bar{e}_L\}} - \oplus \underbrace{H_F^-}_{\text{ONB } \{e_R, \bar{e}_R\}}. + \oplus \underbrace{H_F^-}_{\text{ONB } \{e_R, \bar{e}_R\}}, \end{align} -Alternatively we can decompose $H$ into the eigenspace of particles and their -antiparticles (electrons and positrons) which we will use going further. +or alternatively into the eigenspace of particles and their +antiparticles (electrons and positrons) which is preferred in literature and +which we will use going further \begin{align} H_F = \underbrace{H_{e}}_{\text{ONB } \{e_L, e_R\}} \oplus - \underbrace{H_{\bar{e}}}_{\text{ONB } \{\bar{e}_L, \bar{e}_R\}} + \underbrace{H_{\bar{e}}}_{\text{ONB } \{\bar{e}_L, \bar{e}_R\}}. \end{align} -Now the action of $a \in A = \mathbb{C}^2$ on $H$ with respect to the ONB +Here ONB means orthonormal basis. + +The action of $a \in A = \mathbb{C}^2$ on $H$ with respect to the ONB $\{e_L, e_R, \bar{e}_L, \bar{e}_R\}$ is represented by -\begin{align} +\begin{align}\label{eq:leftrightrepr} a = - \begin{pmatrix}a_1 & a_2 \end{pmatrix} \mapsto + (a_1 , a_2 ) \mapsto \begin{pmatrix} a_1 &0 &0 &0\\ 0&a_1 &0 &0\\ @@ -340,11 +340,11 @@ $\{e_L, e_R, \bar{e}_L, \bar{e}_R\}$ is represented by \end{pmatrix} \end{align} Do note that this action commutes wit the grading and that -$[a, b^\circ] = 0$ with $b:= J_F b^*J_F$ because both the left and the right -action is given by diagonal matrices. -\begin{proposition} - The data - \begin{align} +$[a, b^\circ] = 0$ with $b:= J_F b^*J_F$ because both the left and the right +action is given by diagonal matrices by equation \ref{eq:leftrightrepr}. Note +that we are still left with $D_F = 0$ and the following spectral +triple +\begin{align}\label{eq:fedfail} \left( \mathbb{C}^2, \mathbb{C}^2, D_F=0; J_F = \begin{pmatrix} 0 & C \\ C &0 @@ -353,13 +353,11 @@ action is given by diagonal matrices. \begin{pmatrix} 1 & 0 \\ 0 &-1 \end{pmatrix} - \right) + \right). \end{align} - defines a real even spectral triple of KO-dimension 6. -\end{proposition} -This spectral triple can be represented in the following Krajewski diagram, +It can be represented in the following Krajewski diagram, with two nodes of multiplicity two - \begin{figure}[h!] \centering + \begin{figure}[H] \centering \begin{tikzpicture}[ dot/.style = {draw, circle, inner sep=0.06cm}, bigdot/.style = {draw, circle, inner sep=0.09cm}, @@ -376,10 +374,11 @@ with two nodes of multiplicity two \end{tikzpicture} \end{figure} \subsubsection{A noncommutative Finite Dirac Operator} -Add a non-zero Dirac Operator to $F_{ED}$. From the Krajewski Diagram, we see -that edges only exist between the multiple vertices. So we construct a Dirac -operator mapping between the two vertices. -\begin{align}\label{dirac} +To extend our spectral triple with a non-zero Operator, we need to take a +closer look at the Krajewski diagram above. Notice that edges only exist +between multiple vertices, meaning we can construct a Dirac operator mapping +between the two vertices. The operator can be represented by the following matrix +\begin{align}\label{eq:feddirac} D_F = \begin{pmatrix} 0 & d & 0 & 0 \\ @@ -388,37 +387,38 @@ operator mapping between the two vertices. 0 & 0 & d & 0 \end{pmatrix} \end{align} -We can now consider the finite space $F_{ED}$. +We can now define the finite space $F_{ED}$. \begin{align} F_{ED} := (\mathbb{C}^2, \mathbb{C}^4, D_F; J_F, \gamma_F) \end{align} -where $J_F$ and $\gamma_F$ like before, $D_F$ like above. +where $J_F$ and $\gamma_F$ are like in equation \ref{eq:fedfail} and $D_F$ +from equation \ref{eq:feddirac}. + \subsubsection{The almost-commutative Manifold} -The almost commutative manifold $M\times F_{ED}$ has KO-dim$=2$, it is the -following spectral triple +The almost commutative manifold $M\times F_{ED}$ has KO-dimension 2, and is +represented by the following spectral triple \begin{align} - M\times F_{ED} := \left(C^\infty(M,\mathbb{C}^2),\ L^2(S)\otimes + M\times F_{ED} := \big(C^\infty(M,\mathbb{C}^2),\ L^2(S)\otimes \mathbb{C}^4,\ D_M\otimes 1 +\gamma _M \otimes D_F;\; J_M\otimes J_F,\ \gamma_M\otimes - \gamma _F\right) + \gamma _F\big) \end{align} - -The algebra decomposition is like before +The algebra didn't change, thus we can decompose it like before \begin{align} C^\infty(M, \mathbb{C}^2) = C^\infty (M) \oplus C^\infty (M) \end{align} - -The Hilbertspace decomposition is +As for the Hilbertspace, we can decomposition it in the following way \begin{align} H = (L^2(S) \otimes H_e ) \oplus (L^2(S) \otimes H_{\bar{e}}). \end{align} -Here we have the one component of the algebra acting on $L^2(S) \otimes H_e$, -and the other one acting on $L^2(S) \otimes H_{\bar{e}}$ -\newline +Note that the one component of the algebra is acting on $L^2(S) \otimes H_e$, +and the other one acting on $L^2(S) \otimes H_{\bar{e}}$. In other words the components of +the decomposition of both the algebra and the Hilbertspace match by the action of +the algebra. -The derivation of the gauge theory is the same for $F_{ED}$ as for $F_X$, we -have $\mathfrak{B}(F) \simeq U(1)$ and for $B_\mu = A_\mu - J_F A_\mu -J_F^{-1}$ +The derivation of the gauge theory is the same for $F_{ED}$ as for the +Two-Point space $F_X$. We have $\mathfrak{B}(F) \simeq U(1)$ and for an +arbitrary gauge field $B_\mu = A_\mu - J_F A_\mu J_F^{-1}$ we can write \begin{align} \label{field} B_\mu = \begin{pmatrix} @@ -434,322 +434,321 @@ gauge group \text{$\mathfrak{B}$}(M\times F_{ED}) \simeq C^\infty(M, U(1)) \end{align} -Our space $N = M\times X \simeq M\sqcup M$ consists of two compies of $M$. -If $D_F = 0$ we have infinite distance between the two copies. Now we have $D_F$ -nonzero but $[D_F, a] = 0$ $\forall a \in A$ which still yields infinite -distance. -\begin{question} - What does this imply (physically, mathematically)? Why can we continue - even thought we have infinite distance between the same manifold? What do - we get if we fix this? -\end{question} -\subsubsection{The Spectral Action} -Here we calculate the Lagrangian of the almost commutative Manifold $M\times -F_{ED}$, which corresponds to the Lagrangian of Electrodynamics on a curved -background Manifold (+ gravitational Lagrangian). It consists of the spectral -action $S_b$ (bosonic) and of the fermionic action $S_f$. - -The simples spectral action of a spectral triple $(A, H, D)$ is given by the -trace of some function of $D$, we also allow inner fluctuations of the Dirac -operator $D_\omega = D + \omega + \varepsilon' J\omega J^{-1}$ where $\omega = -\omega ^* \in \Omega_D^1(A)$. -\begin{definition} - Let $f:\mathbb{R} \rightarrow \mathbb{R}$ be a suitable function - \textbf{positive and even}. The spectral action is then - \begin{align} - S_b [\omega] := \text{Tr}f(\frac{D_\omega}{\Lambda}) - \end{align} - where $\Lambda$ is a real cutoff parameter. The minimal condition on $f$ - is that $f(\frac{D_\omega}{\Lambda})$ is a traclass operator, which mean - that it should be compact operator with well defined finite trace - independent of the basis. The subscript $b$ of $S_b$ refers to bosonic, - because in physical applications $\omega$ will describe bosonic fields. - - Furthermore there is a topological spectral action, defined with the - grading $\gamma$ - \begin{align} - S_{\text{top}}[\omega] := \text{Tr}(\gamma\ - f(\frac{D_\omega}{\Lambda})). - \end{align} -\end{definition} -\begin{definition} - The fermionic action is defined by - \begin{align} - S_f[\omega, \psi] = (J\tilde{\psi}, D_\omega \tilde{\psi}) - \end{align} - with $\tilde{\psi} \in H_{cl}^+ := \{\tilde{\psi}: \psi \in H^+\}$. - $H_{cl}^+$ is the set of Grassmann variables in $H$ in the +1-eigenspace - of the grading $\gamma$. -\end{definition} -The grasmann variables are a set of Basis vectors of a vector space, they -form a unital algebra over a vector field say $V$ where the generators are anti commuting, that is for -$\theta _i, \theta _j$ some Grassmann variables we have -\begin{align} - &\theta _i \theta _j = -\theta _j \theta _i \\ - &\theta _i x = x\theta _j \;\;\;\; x\in V \\ - &(\theta_i)^2 = 0 \;\;\; (\theta _i \theta _i = -\theta _i \theta _i) -\end{align} -\begin{proposition} - The spectral action of the almost commutative manifold $M$ with $\dim(M) - =4$ with a fluctuated Dirac operator is. - \begin{align} - \text{Tr}(f\frac{D_\omega}{\Lambda}) \sim \int_M \mathcal{L}(g_{\mu\nu}, - B_\mu, \Phi) \sqrt{g}\ d^4x + O(\Lambda^{-1}) - \end{align} - with - \begin{align} - \mathcal{L}(g_{\mu\nu}, B_\mu, \Phi) = - N\mathcal{L}_M(g_{\mu\nu}) - \mathcal{L}_B(B_\mu)+ - \mathcal{L}_\phi(g_{\mu\nu}, B_\mu, \Phi) - \end{align} - where $N=4$ and $\mathcal{L}_M$ is the Lagrangian of the spectral triple - $(C^\infty(M) , L^2(S), D_M)$ - \begin{align}\label{lagr} - \mathcal{L}_M(g_{\mu\nu}) := \frac{f_4 \Lambda ^4}{2\pi^2} - - \frac{f_2 \Lambda^2}{24\pi ^2}s - \frac{f(0)}{320\pi^2} C_{\mu\nu - \varrho \sigma}C^{\mu\nu \varrho \sigma}. - \end{align} - Here $C^{\mu\nu \varrho \sigma}$ is defined in terms of the Riemannian - curvature tensor $R_{\mu\nu \varrho \sigma}$ and the Ricci tensor - $R_{\nu\sigma} = g^{\mu\varrho} R_{\mu\nu \varrho\sigma}$. - - - Furthermore $\mathcal{L}_B$ describes the kinetic term of the gauge field - \begin{align} - \mathcal{L}_B(B_\mu) := \frac{f(0)}{24\pi^2} - \text{Tr}(F_{\mu\nu}F^{\mu\nu}). - \end{align} - Last $\mathcal{L}_\phi$ is the scalar-field Lagrangian with a boundary - term. - \begin{align} - \mathcal{L}_\phi(g_{\mu\nu}, B_\mu, \Phi) := - &-\frac{2f_2\Lambda^2}{4\pi^2}\text{Tr}(\Phi^2) + \frac{f(0)}{8\pi^2} - \text{Tr}(\Phi^4) + \frac{f(0)}{24\pi^2} \Delta(\text{Tr}(\Phi^2))\\ - &+ \frac{f(0)}{48\pi^2}s\text{Tr}(\Phi^2) - \frac{f(0)}{8\pi^2}\text{Tr}((D_\mu \Phi)(D^\mu \Phi)). - \end{align} -\end{proposition} -\begin{proof} - the dimension of our manifold $m$ is $\dim(m) = \text{tr}(id) =4 $. let us - take a $x \in m$, we have an asymtotic expansion of - $\text{tr}(f(\frac{d_\omega}{\lambda}))$ as $\lambda \rightarrow \infty$ - \begin{align} - \text{tr}(f(\frac{d_\omega}{\lambda})) \simeq& \ 2f_4 \lambda ^4 - a_0(d_\omega ^2)+ 2f_2\lambda^2 a_2(d_\omega^2) \\&+ f(0) a_4(d_\omega^4) - +o(\lambda^{-1}). - \end{align} - note that the heat kernel coefficients are zero for uneven $k$, - furthermore they are dependent on the fluctuated dirac operator - $d_\omega$. we can rewrite the heat kernel coefficients in terms of $d_m$, - for the first two we note that $n:= \text{tr}\mathbbm{1_{h_f}})$ - \begin{align} - a_0(d_\omega^2) &= na_0(d_m^2)\\ - a_2(d_\omega^2 &= na_2(d_m^2) - \frac{1}{4\pi^2}\int_m - \text{tr}(\phi^2)\sqrt{g}d^4x - \end{align} - for $a_4$ we need to extend in terms of coefficients of $f$, look week9.pdf - for the standard version, - \begin{align} - &\frac{1}{360}\text{tr}(60sf)= -\frac{1}{6}s(ns + 4 - \text{tr}(\phi^2))\\ - \nonumber\\ - &f^2 = \frac{1}{16}s^2\otimes 1 + 1\otimes \phi^4 - \frac{1}{4} - \gamma^\mu\gamma^\nu \gamma^\varrho\gamma^\sigma f_{\mu\nu}f^{\mu\nu}+\\ - &\;\;\;\;\;\;\;+\gamma^\mu\gamma^\nu\otimes(d_\mu\phi)(d_\nu - \phi)+\frac{1}{2}s\otimes \phi^2 + \ \text{traceless terms}\\ - \nonumber\\ - &\frac{1}{360}\text{tr}(180f^2) = \frac{1}{8}s^2n + 2\text{tr}(\phi^4) - + \text{tr}(f_{\mu\nu}f^{\mu\nu}) +\\ - &\;\;\;\;\;\;\;+2\text{tr}((d_\mu\phi)(d^\mu\phi)) - + s\text{tr}(\phi^2)\\ - \nonumber\\ - &\frac{1}{360}\text{tr}(-60\delta f)= - \frac{1}{6}\delta(ns+4\text{tr}(\phi^2)). - \end{align} - now for the cross terms of $\omega_{\mu\nu}^e\omega^{e\mu\nu}$ the trace - vanishes because of the anti-symmetric properties of the riemannian - curvature tensor - \begin{align} - \omega_{\mu\nu}^e\omega^{e\mu\nu} = \omega_{\mu\nu}^s\omega^{s\mu\nu} - \otimes 1 - 1\otimes f_{\mu\nu}f^{\mu\nu} + 2i\omega_{\mu\nu}^s - \otimes f^{\mu\nu} - \end{align} - the trace of the cross term vanishes because - \begin{align} - \text{tr}(\omega^{s}_{\mu\nu} = \frac{1}{4} - r_{\mu\nu\varrho\sigma}\text{tr}(\gamma^\mu\gamma^\nu) = \frac{1}{4} - r_{\mu\nu\varrho\sigma}g^{\mu\nu} =0 - \end{align} - and the trace of the whole term is - \begin{align} - \frac{1}{360}\text{tr}(30\omega^e_{\mu\nu}\omega^{e\mu\nu}) = - \frac{n}{24}r_{\mu\nu\varrho\sigma}r^{\mu\nu\varrho\sigma} - -\frac{1}{3}\text{tr}(f_{\mu\nu}f^{\mu\nu}). - \end{align} - plugging the results into $a_4$ and simplifying we can write - \begin{align} - a_4(x, d_\omega^4) &= na_4(x, d_m^2) + \frac{1}{4\pi^2}\bigg(\frac{1}{12} s - \text{tr}(\phi^2) + \frac{1}{2}\text{tr}(\phi^4) \\ - &+ \frac{1}{4} - \text{tr}((d_\mu\phi)(d^\mu \phi)) + \frac{1}{6} - \delta\text{tr}(\phi^2) + \frac{1}{6} - \text{tr}(f_{\mu\nu}f^{\mu\nu})\bigg) - \end{align} - the only thing left is to plug in the heat kernel coefficients into the - heat kernel expansion above. -\end{proof} - -Here on we go and calculate the spectral action of $M\times F_{ED}$ -\begin{proposition} - The Spectral action of $M\times F_{ED}$ is - \begin{align} - \text{Tr}(f\frac{D_\omega}{\Lambda}) \sim \int_M \mathcal{L}(g_{\mu\nu}, - Y_\mu) \sqrt{g}\ d^4x + O(\Lambda^{-1}) - \end{align} - where the Lagrangian is - \begin{align} - \mathcal{L}(g_{\mu\nu}, Y_\mu) = - 4\mathcal{L}_M(g_{\mu\nu})+ - \mathcal{L}_Y(Y_\mu)+ - \mathcal{L}_\phi(g_{\mu\nu}, d) - \end{align} - here the $d$ in $\mathcal{L}_\phi$ is from $D_F$ in equation - \ref{dirac}. The Lagrangian $\mathcal{L}_M$ is like in equation - \ref{lagr}. The Lagrangian $\mathcal{L}_Y$ is the kinetic term of the - $U(1)$ gauge field $Y_\mu$ - \begin{align} - \mathcal{L}_Y(Y_\mu):= \frac{f(0)}{6\pi^2} - Y_{\mu\nu}Y^{\mu\nu}\;\;\;\;\;\;\;\;\text{with}\;\;\; Y_{\mu\nu} = - \partial_\mu Y_\nu - - \partial_\nu Y_\mu. - \end{align} - Then there is $\mathcal{L}_\phi$, which has two constant terms - (disregarding the boundary term) that add up to the Cosmological Constant - and a term that for the Einstein-Hilbert action - \begin{align} - \mathcal{L}_\phi(g_{\mu\nu}, d) := \frac{2f_2 \Lambda ^2}{\pi^2} - |d|^2 + \frac{f(0)}{2\pi^2} |d|^4 + \frac{f(0)}{12\pi ^2} s |d|^2. - \end{align} -\end{proposition} -\begin{proof} - The Trace of $\mathbb{C}^4$ (the Hilbertspace) gives $N=4$. With $B_\mu$ - like in equation \ref{field} we have $\text{Tr}(F_{\mu\nu} - F^{\mu\nu})=4Y_{\mu\nu}Y^{\mu\nu}$. This provides $\mathcal{L}_Y$. - Furthermore we have $\Phi^2 = D_F^2 = |d|^2$ and $\mathcal{L}_\phi$ only - give numerical contributions to the cosmological constant and the - Einstein-Hilbert action. - - The proof is relying itself on just plugging the terms into the previous - proposition, for which I didn't write the proof for. -\end{proof} - - -\subsection{fermionic action} -a quick reminder with what we are dealing with, the fermionic action is defined -in the following way. -\begin{definition} - the fermionic action is defined by - \begin{align} - s_f[\omega, \psi] = (j\tilde{\psi}, d_\omega \tilde{\psi}) - \end{align} - with $\tilde{\psi} \in h_{cl}^+ := \{\tilde{\psi}: \psi \in h^+\}$. - $h_{cl}^+$ is the set of grassmann variables in $h$ in the +1-eigenspace - of the grading $\gamma$. -\end{definition} - -the almostcommutative manifold we are dealing with is the following -\begin{align} - &m\times f_{ed} := \left(c^\infty(m,\mathbb{c}^2),\ l^2(s)\otimes - \mathbb{c}^4,\ - d_m\otimes 1 +\gamma _m \otimes d_f;\; j_m\otimes j_f,\ \gamma_m\otimes - \gamma _f\right).\\ - \nonumber\\ - &\text{where:} \nonumber \\ - &c^\infty(m,\mathbb{c}^2) = c^\infty(m) \otimes c^\infty(m) - &\mathcal{h} = \mathcal{h}^+ \otimes \mathcal{h}^-\\ - &\mathcal{h} = l^2(s)^+ \otimes h_f^+ \oplus l^2(s)^- \otimes h_f^-. -\end{align} -where $h_f$ is separated into the particle-anitparticle states with onb $\{e_r, -e_l, \bar{e}_r, \bar{e}_l\}$. the onb of $h_f^+$ is $\{e_l, \bar{e}_r\}$ and -for $h_f^-$ we have $\{e_r, \bar{e}_l\}$. furthermore we can decompose a spinor -$\psi \in l^2(s)$ for each of the eigenspaces $h_f^\pm$, $\psi = \psi_r -\psi_l$. thus we can write for an arbitrary $\psi \in \mathcal{h}^+$ -\begin{align} - \psi = \chi_r \otimes e_r + \chi_l \otimes e_l + \psi_l \otimes \bar{e}_r - \psi_r \otimes \bar{e}_l -\end{align} -for $\chi_l, \psi_l \in l^2(s)^+$ and $\chi_r, \psi_r \in l^2(s)^-$. -\begin{proposition} - we can define the action of the fermionic art of $m\times f_{ed}$ in the - following way - \begin{align} - s_f = -i\big(j_m\tilde{\chi}, \gamma(\nabla^s_\mu - i\gamma_\mu) - \tilde{\psi}\big) + \big(s_m\tilde{\chi}_l, \bar{d}\tilde{\psi}_l\big) - - \big(j_m\tilde{\chi}_r, d \tilde{\psi}_r\big) - \end{align} -\end{proposition} -\begin{proof} - we take the fluctuated dirac operator - \begin{align} - d_\omega = d_m \otimes i + \gamma^\mu \otimes b_\mu + \gamma_m \otimes - d_f - \end{align} -\end{proof} -the fermionic action is $s_f = (j\tilde{\xi}, d_\omega\tilde{\xi})$ for a $\xi -\in \mathcal{h}^+$, we can begin to calculate (note that we add the constant -$\frac{1}{2}$ to the action) -\begin{align} - \frac{1}{2}(j\tilde{\xi}, d_\omega\tilde{\xi}) =&\\ - &+\frac{1}{2}(j\tilde{\xi}, (d_m \otimes i)\tilde{\xi})\label{eq:1}\\ - &+\frac{1}{2}(j\tilde{\xi}, (\gamma^\mu \otimes b_\mu) - \tilde{\xi})\label{eq:2}\\ - &+\frac{1}{2}(j\tilde{\xi}, (\gamma_m\otimes - d_f)\tilde{\xi})\label{eq:3}. -\end{align} -for equation \ref{eq:1} we calculate -\begin{align} - \frac{1}{2}(j\tilde{\xi}, (d_m\otimes 1)\tilde{\xi}) &= - \frac{1}{2}(j_m\tilde{\chi}_r,d_m\tilde{\psi}_l)+ - \frac{1}{2}(j_m\tilde{\chi}_l,d_m\tilde{\psi}_r)+ - \\&+\frac{1}{2}(j_m\tilde{\psi}_l,d_m\tilde{\psi}_r)+ - \frac{1}{2}(j_m\tilde{\chi}_r,d_m\tilde{\chi}_l)\\ - &= (j_m\tilde{\chi},d_m\tilde{\chi}). -\end{align} -for equation \ref{eq:2} we have -\begin{align} - \frac{1}{2}(j\tilde{\xi}, (\gamma^\mu \otimes b_\mu)\tilde{\xi})&= - -\frac{1}{2}(j_m\tilde{\chi}_r, \gamma^\mu y_\mu\tilde{\psi}_r) - -\frac{1}{2}(j_m\tilde{\chi}_l, \gamma^\mu y_\mu\tilde{\psi}_r)+\\ - &+\frac{1}{2}(j_m\tilde{\psi}_l, \gamma^\mu y_\mu\tilde{\chi}_r)+ - \frac{1}{2}(j_m\tilde{\psi}_r, \gamma^\mu y_\mu\tilde{\chi}_l)=\\ - &= -(j_m\tilde{\chi}, \gamma^\mu y_\mu\tilde{\psi}). -\end{align} -for equation \ref{eq:3} we have -\begin{align} - \frac{1}{2}(j\tilde{\xi}, (\gamma_m\otimes d_f)\tilde{\xi})&= - +\frac{1}{2}(j_m\tilde{\chi}_r, d\gamma_m\tilde{\chi}_r) - +\frac{1}{2}(j_m\tilde{\chi}_l, \bar{d}\gamma_m\tilde{\chi}_l)+\\ - &+\frac{1}{2}(j_m\tilde{\chi}_l, \bar{d}\gamma_m\tilde{\chi}_l) - +\frac{1}{2}(j_m\tilde{\chi}_r, d\gamma_m\tilde{\chi}_r)=\\ - &= i(j_m\tilde{\chi}, m\tilde{\psi}) -\end{align} -note that we obtain a complex mass parameter $d$, so we write $d:=im$ for $m\in \mathbb{r}$, -which stands for the real mass and we obtain a nice result - -\begin{theorem} - the full lagrangian of $m\times f_{ed}$ is the sum of purely gravitational - lagrangian - \begin{align} - \mathcal{l}_{grav}(g_{\mu\nu})=4\mathcal{l}_m(g_{\mu\nu}) - \mathcal{l}_\phi (g_{\mu\nu}) - \end{align} - and the lagrangian of electrodynamics - \begin{align} - \mathcal{l}_{ed} = -i\bigg\langle - j_m\tilde{\chi},\big(\gamma^\mu(\nabla^s_\mu - iy_\mu) -m\big)\tilde{\psi}) - \bigg\rangle - +\frac{f(0)}{6\pi^2} y_{\mu\nu}y^{\mu\nu}. - \end{align} - -\end{theorem} +Our space $N = M\times X \simeq M\sqcup M$ consists of two copies of $M$. +If $D_F = 0$ we have infinite distance between the two copies. Now have +hacked the spectral triple to have nonzero Dirac operator $D_F$. The new +Dirac operator still has a commuting relation with the algebra $[D_F, a] = 0$ +$\forall a \in A$, and we should note that the distance between the two +copies of $M$ is still infinite. This is purely an mathematically abstract +observation and doesn't affect physical results. + +%\subsubsection{The Spectral Action} +%Here we calculate the Lagrangian of the almost commutative Manifold $M\times +%F_{ED}$, which corresponds to the Lagrangian of Electrodynamics on a curved +%background Manifold (+ gravitational Lagrangian). It consists of the spectral +%action $S_b$ (bosonic) and of the fermionic action $S_f$. +% +%The simples spectral action of a spectral triple $(A, H, D)$ is given by the +%trace of some function of $D$, we also allow inner fluctuations of the Dirac +%operator $D_\omega = D + \omega + \varepsilon' J\omega J^{-1}$ where $\omega = +%\omega ^* \in \Omega_D^1(A)$. +%\begin{definition} +% Let $f:\mathbb{R} \rightarrow \mathbb{R}$ be a suitable function +% \textbf{positive and even}. The spectral action is then +% \begin{align} +% S_b [\omega] := \text{Tr}f(\frac{D_\omega}{\Lambda}) +% \end{align} +% where $\Lambda$ is a real cutoff parameter. The minimal condition on $f$ +% is that $f(\frac{D_\omega}{\Lambda})$ is a traclass operator, which mean +% that it should be compact operator with well defined finite trace +% independent of the basis. The subscript $b$ of $S_b$ refers to bosonic, +% because in physical applications $\omega$ will describe bosonic fields. +% +% Furthermore there is a topological spectral action, defined with the +% grading $\gamma$ +% \begin{align} +% S_{\text{top}}[\omega] := \text{Tr}(\gamma\ +% f(\frac{D_\omega}{\Lambda})). +% \end{align} +%\end{definition} +%\begin{definition} +% The fermionic action is defined by +% \begin{align} +% S_f[\omega, \psi] = (J\tilde{\psi}, D_\omega \tilde{\psi}) +% \end{align} +% with $\tilde{\psi} \in H_{cl}^+ := \{\tilde{\psi}: \psi \in H^+\}$. +% $H_{cl}^+$ is the set of Grassmann variables in $H$ in the +1-eigenspace +% of the grading $\gamma$. +%\end{definition} +%The grasmann variables are a set of Basis vectors of a vector space, they +%form a unital algebra over a vector field say $V$ where the generators are anti commuting, that is for +%$\theta _i, \theta _j$ some Grassmann variables we have +%\begin{align} +% &\theta _i \theta _j = -\theta _j \theta _i \\ +% &\theta _i x = x\theta _j \;\;\;\; x\in V \\ +% &(\theta_i)^2 = 0 \;\;\; (\theta _i \theta _i = -\theta _i \theta _i) +%\end{align} +%\begin{proposition} +% The spectral action of the almost commutative manifold $M$ with $\dim(M) +% =4$ with a fluctuated Dirac operator is. +% \begin{align} +% \text{Tr}(f\frac{D_\omega}{\Lambda}) \sim \int_M \mathcal{L}(g_{\mu\nu}, +% B_\mu, \Phi) \sqrt{g}\ d^4x + O(\Lambda^{-1}) +% \end{align} +% with +% \begin{align} +% \mathcal{L}(g_{\mu\nu}, B_\mu, \Phi) = +% N\mathcal{L}_M(g_{\mu\nu}) +% \mathcal{L}_B(B_\mu)+ +% \mathcal{L}_\phi(g_{\mu\nu}, B_\mu, \Phi) +% \end{align} +% where $N=4$ and $\mathcal{L}_M$ is the Lagrangian of the spectral triple +% $(C^\infty(M) , L^2(S), D_M)$ +% \begin{align}\label{lagr} +% \mathcal{L}_M(g_{\mu\nu}) := \frac{f_4 \Lambda ^4}{2\pi^2} - +% \frac{f_2 \Lambda^2}{24\pi ^2}s - \frac{f(0)}{320\pi^2} C_{\mu\nu +% \varrho \sigma}C^{\mu\nu \varrho \sigma}. +% \end{align} +% Here $C^{\mu\nu \varrho \sigma}$ is defined in terms of the Riemannian +% curvature tensor $R_{\mu\nu \varrho \sigma}$ and the Ricci tensor +% $R_{\nu\sigma} = g^{\mu\varrho} R_{\mu\nu \varrho\sigma}$. +% +% +% Furthermore $\mathcal{L}_B$ describes the kinetic term of the gauge field +% \begin{align} +% \mathcal{L}_B(B_\mu) := \frac{f(0)}{24\pi^2} +% \text{Tr}(F_{\mu\nu}F^{\mu\nu}). +% \end{align} +% Last $\mathcal{L}_\phi$ is the scalar-field Lagrangian with a boundary +% term. +% \begin{align} +% \mathcal{L}_\phi(g_{\mu\nu}, B_\mu, \Phi) := +% &-\frac{2f_2\Lambda^2}{4\pi^2}\text{Tr}(\Phi^2) + \frac{f(0)}{8\pi^2} +% \text{Tr}(\Phi^4) + \frac{f(0)}{24\pi^2} \Delta(\text{Tr}(\Phi^2))\\ +% &+ \frac{f(0)}{48\pi^2}s\text{Tr}(\Phi^2) +% \frac{f(0)}{8\pi^2}\text{Tr}((D_\mu \Phi)(D^\mu \Phi)). +% \end{align} +%\end{proposition} +%\begin{proof} +% the dimension of our manifold $m$ is $\dim(m) = \text{tr}(id) =4 $. let us +% take a $x \in m$, we have an asymtotic expansion of +% $\text{tr}(f(\frac{d_\omega}{\lambda}))$ as $\lambda \rightarrow \infty$ +% \begin{align} +% \text{tr}(f(\frac{d_\omega}{\lambda})) \simeq& \ 2f_4 \lambda ^4 +% a_0(d_\omega ^2)+ 2f_2\lambda^2 a_2(d_\omega^2) \\&+ f(0) a_4(d_\omega^4) +% +o(\lambda^{-1}). +% \end{align} +% note that the heat kernel coefficients are zero for uneven $k$, +% furthermore they are dependent on the fluctuated dirac operator +% $d_\omega$. we can rewrite the heat kernel coefficients in terms of $d_m$, +% for the first two we note that $n:= \text{tr}\mathbbm{1_{h_f}})$ +% \begin{align} +% a_0(d_\omega^2) &= na_0(d_m^2)\\ +% a_2(d_\omega^2 &= na_2(d_m^2) - \frac{1}{4\pi^2}\int_m +% \text{tr}(\phi^2)\sqrt{g}d^4x +% \end{align} +% for $a_4$ we need to extend in terms of coefficients of $f$, look week9.pdf +% for the standard version, +% \begin{align} +% &\frac{1}{360}\text{tr}(60sf)= -\frac{1}{6}s(ns + 4 +% \text{tr}(\phi^2))\\ +% \nonumber\\ +% &f^2 = \frac{1}{16}s^2\otimes 1 + 1\otimes \phi^4 - \frac{1}{4} +% \gamma^\mu\gamma^\nu \gamma^\varrho\gamma^\sigma f_{\mu\nu}f^{\mu\nu}+\\ +% &\;\;\;\;\;\;\;+\gamma^\mu\gamma^\nu\otimes(d_\mu\phi)(d_\nu +% \phi)+\frac{1}{2}s\otimes \phi^2 + \ \text{traceless terms}\\ +% \nonumber\\ +% &\frac{1}{360}\text{tr}(180f^2) = \frac{1}{8}s^2n + 2\text{tr}(\phi^4) +% + \text{tr}(f_{\mu\nu}f^{\mu\nu}) +\\ +% &\;\;\;\;\;\;\;+2\text{tr}((d_\mu\phi)(d^\mu\phi)) +% + s\text{tr}(\phi^2)\\ +% \nonumber\\ +% &\frac{1}{360}\text{tr}(-60\delta f)= +% \frac{1}{6}\delta(ns+4\text{tr}(\phi^2)). +% \end{align} +% now for the cross terms of $\omega_{\mu\nu}^e\omega^{e\mu\nu}$ the trace +% vanishes because of the anti-symmetric properties of the Riemannian +% curvature tensor +% \begin{align} +% \omega_{\mu\nu}^e\omega^{e\mu\nu} = \omega_{\mu\nu}^s\omega^{s\mu\nu} +% \otimes 1 - 1\otimes f_{\mu\nu}f^{\mu\nu} + 2i\omega_{\mu\nu}^s +% \otimes f^{\mu\nu} +% \end{align} +% the trace of the cross term vanishes because +% \begin{align} +% \text{tr}(\omega^{s}_{\mu\nu} = \frac{1}{4} +% r_{\mu\nu\varrho\sigma}\text{tr}(\gamma^\mu\gamma^\nu) = \frac{1}{4} +% r_{\mu\nu\varrho\sigma}g^{\mu\nu} =0 +% \end{align} +% and the trace of the whole term is +% \begin{align} +% \frac{1}{360}\text{tr}(30\omega^e_{\mu\nu}\omega^{e\mu\nu}) = +% \frac{n}{24}r_{\mu\nu\varrho\sigma}r^{\mu\nu\varrho\sigma} +% -\frac{1}{3}\text{tr}(f_{\mu\nu}f^{\mu\nu}). +% \end{align} +% plugging the results into $a_4$ and simplifying we can write +% \begin{align} +% a_4(x, d_\omega^4) &= na_4(x, d_m^2) + \frac{1}{4\pi^2}\bigg(\frac{1}{12} s +% \text{tr}(\phi^2) + \frac{1}{2}\text{tr}(\phi^4) \\ +% &+ \frac{1}{4} +% \text{tr}((d_\mu\phi)(d^\mu \phi)) + \frac{1}{6} +% \delta\text{tr}(\phi^2) + \frac{1}{6} +% \text{tr}(f_{\mu\nu}f^{\mu\nu})\bigg) +% \end{align} +% the only thing left is to plug in the heat kernel coefficients into the +% heat kernel expansion above. +%\end{proof} +% +%Here on we go and calculate the spectral action of $M\times F_{ED}$ +%\begin{proposition} +% The Spectral action of $M\times F_{ED}$ is +% \begin{align} +% \text{Tr}(f\frac{D_\omega}{\Lambda}) \sim \int_M \mathcal{L}(g_{\mu\nu}, +% Y_\mu) \sqrt{g}\ d^4x + O(\Lambda^{-1}) +% \end{align} +% where the Lagrangian is +% \begin{align} +% \mathcal{L}(g_{\mu\nu}, Y_\mu) = +% 4\mathcal{L}_M(g_{\mu\nu})+ +% \mathcal{L}_Y(Y_\mu)+ +% \mathcal{L}_\phi(g_{\mu\nu}, d) +% \end{align} +% here the $d$ in $\mathcal{L}_\phi$ is from $D_F$ in equation +% \ref{dirac}. The Lagrangian $\mathcal{L}_M$ is like in equation +% \ref{lagr}. The Lagrangian $\mathcal{L}_Y$ is the kinetic term of the +% $U(1)$ gauge field $Y_\mu$ +% \begin{align} +% \mathcal{L}_Y(Y_\mu):= \frac{f(0)}{6\pi^2} +% Y_{\mu\nu}Y^{\mu\nu}\;\;\;\;\;\;\;\;\text{with}\;\;\; Y_{\mu\nu} = +% \partial_\mu Y_\nu - +% \partial_\nu Y_\mu. +% \end{align} +% Then there is $\mathcal{L}_\phi$, which has two constant terms +% (disregarding the boundary term) that add up to the Cosmological Constant +% and a term that for the Einstein-Hilbert action +% \begin{align} +% \mathcal{L}_\phi(g_{\mu\nu}, d) := \frac{2f_2 \Lambda ^2}{\pi^2} +% |d|^2 + \frac{f(0)}{2\pi^2} |d|^4 + \frac{f(0)}{12\pi ^2} s |d|^2. +% \end{align} +%\end{proposition} +%\begin{proof} +% The Trace of $\mathbb{C}^4$ (the Hilbertspace) gives $N=4$. With $B_\mu$ +% like in equation \ref{field} we have $\text{Tr}(F_{\mu\nu} +% F^{\mu\nu})=4Y_{\mu\nu}Y^{\mu\nu}$. This provides $\mathcal{L}_Y$. +% Furthermore we have $\Phi^2 = D_F^2 = |d|^2$ and $\mathcal{L}_\phi$ only +% give numerical contributions to the cosmological constant and the +% Einstein-Hilbert action. +% +% The proof is relying itself on just plugging the terms into the previous +% proposition, for which I didn't write the proof for. +%\end{proof} +% +% +%\subsection{fermionic action} +%a quick reminder with what we are dealing with, the fermionic action is defined +%in the following way. +%\begin{definition} +% the fermionic action is defined by +% \begin{align} +% s_f[\omega, \psi] = (j\tilde{\psi}, d_\omega \tilde{\psi}) +% \end{align} +% with $\tilde{\psi} \in h_{cl}^+ := \{\tilde{\psi}: \psi \in h^+\}$. +% $h_{cl}^+$ is the set of grassmann variables in $h$ in the +1-eigenspace +% of the grading $\gamma$. +%\end{definition} +% +%the almostcommutative manifold we are dealing with is the following +%\begin{align} +% &m\times f_{ed} := \left(c^\infty(m,\mathbb{c}^2),\ l^2(s)\otimes +% \mathbb{c}^4,\ +% d_m\otimes 1 +\gamma _m \otimes d_f;\; j_m\otimes j_f,\ \gamma_m\otimes +% \gamma _f\right).\\ +% \nonumber\\ +% &\text{where:} \nonumber \\ +% &c^\infty(m,\mathbb{c}^2) = c^\infty(m) \otimes c^\infty(m) +% &\mathcal{h} = \mathcal{h}^+ \otimes \mathcal{h}^-\\ +% &\mathcal{h} = l^2(s)^+ \otimes h_f^+ \oplus l^2(s)^- \otimes h_f^-. +%\end{align} +%where $h_f$ is separated into the particle-anitparticle states with onb $\{e_r, +%e_l, \bar{e}_r, \bar{e}_l\}$. the onb of $h_f^+$ is $\{e_l, \bar{e}_r\}$ and +%for $h_f^-$ we have $\{e_r, \bar{e}_l\}$. furthermore we can decompose a spinor +%$\psi \in l^2(s)$ for each of the eigenspaces $h_f^\pm$, $\psi = \psi_r +%\psi_l$. thus we can write for an arbitrary $\psi \in \mathcal{h}^+$ +%\begin{align} +% \psi = \chi_r \otimes e_r + \chi_l \otimes e_l + \psi_l \otimes \bar{e}_r +% \psi_r \otimes \bar{e}_l +%\end{align} +%for $\chi_l, \psi_l \in l^2(s)^+$ and $\chi_r, \psi_r \in l^2(s)^-$. +%\begin{proposition} +% we can define the action of the fermionic art of $m\times f_{ed}$ in the +% following way +% \begin{align} +% s_f = -i\big(j_m\tilde{\chi}, \gamma(\nabla^s_\mu - i\gamma_\mu) +% \tilde{\psi}\big) + \big(s_m\tilde{\chi}_l, \bar{d}\tilde{\psi}_l\big) - +% \big(j_m\tilde{\chi}_r, d \tilde{\psi}_r\big) +% \end{align} +%\end{proposition} +%\begin{proof} +% we take the fluctuated Dirac operator +% \begin{align} +% d_\omega = d_m \otimes i + \gamma^\mu \otimes b_\mu + \gamma_m \otimes +% d_f +% \end{align} +%\end{proof} +%the fermionic action is $s_f = (j\tilde{\xi}, d_\omega\tilde{\xi})$ for a $\xi +%\in \mathcal{h}^+$, we can begin to calculate (note that we add the constant +%$\frac{1}{2}$ to the action) +%\begin{align} +% \frac{1}{2}(j\tilde{\xi}, d_\omega\tilde{\xi}) =&\\ +% &+\frac{1}{2}(j\tilde{\xi}, (d_m \otimes i)\tilde{\xi})\label{eq:1}\\ +% &+\frac{1}{2}(j\tilde{\xi}, (\gamma^\mu \otimes b_\mu) +% \tilde{\xi})\label{eq:2}\\ +% &+\frac{1}{2}(j\tilde{\xi}, (\gamma_m\otimes +% d_f)\tilde{\xi})\label{eq:3}. +%\end{align} +%for equation \ref{eq:1} we calculate +%\begin{align} +% \frac{1}{2}(j\tilde{\xi}, (d_m\otimes 1)\tilde{\xi}) &= +% \frac{1}{2}(j_m\tilde{\chi}_r,d_m\tilde{\psi}_l)+ +% \frac{1}{2}(j_m\tilde{\chi}_l,d_m\tilde{\psi}_r)+ +% \\&+\frac{1}{2}(j_m\tilde{\psi}_l,d_m\tilde{\psi}_r)+ +% \frac{1}{2}(j_m\tilde{\chi}_r,d_m\tilde{\chi}_l)\\ +% &= (j_m\tilde{\chi},d_m\tilde{\chi}). +%\end{align} +%for equation \ref{eq:2} we have +%\begin{align} +% \frac{1}{2}(j\tilde{\xi}, (\gamma^\mu \otimes b_\mu)\tilde{\xi})&= +% -\frac{1}{2}(j_m\tilde{\chi}_r, \gamma^\mu y_\mu\tilde{\psi}_r) +% -\frac{1}{2}(j_m\tilde{\chi}_l, \gamma^\mu y_\mu\tilde{\psi}_r)+\\ +% &+\frac{1}{2}(j_m\tilde{\psi}_l, \gamma^\mu y_\mu\tilde{\chi}_r)+ +% \frac{1}{2}(j_m\tilde{\psi}_r, \gamma^\mu y_\mu\tilde{\chi}_l)=\\ +% &= -(j_m\tilde{\chi}, \gamma^\mu y_\mu\tilde{\psi}). +%\end{align} +%for equation \ref{eq:3} we have +%\begin{align} +% \frac{1}{2}(j\tilde{\xi}, (\gamma_m\otimes d_f)\tilde{\xi})&= +% +\frac{1}{2}(j_m\tilde{\chi}_r, d\gamma_m\tilde{\chi}_r) +% +\frac{1}{2}(j_m\tilde{\chi}_l, \bar{d}\gamma_m\tilde{\chi}_l)+\\ +% &+\frac{1}{2}(j_m\tilde{\chi}_l, \bar{d}\gamma_m\tilde{\chi}_l) +% +\frac{1}{2}(j_m\tilde{\chi}_r, d\gamma_m\tilde{\chi}_r)=\\ +% &= i(j_m\tilde{\chi}, m\tilde{\psi}) +%\end{align} +%note that we obtain a complex mass parameter $d$, so we write $d:=im$ for $m\in \mathbb{r}$, +%which stands for the real mass and we obtain a nice result +% +%\begin{theorem} +% the full lagrangian of $m\times f_{ed}$ is the sum of purely gravitational +% lagrangian +% \begin{align} +% \mathcal{l}_{grav}(g_{\mu\nu})=4\mathcal{l}_m(g_{\mu\nu}) +% \mathcal{l}_\phi (g_{\mu\nu}) +% \end{align} +% and the lagrangian of electrodynamics +% \begin{align} +% \mathcal{l}_{ed} = -i\bigg\langle +% j_m\tilde{\chi},\big(\gamma^\mu(\nabla^s_\mu - iy_\mu) -m\big)\tilde{\psi}) +% \bigg\rangle +% +\frac{f(0)}{6\pi^2} y_{\mu\nu}y^{\mu\nu}. +% \end{align} +% +%\end{theorem}