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Update on Overleaf.

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Javier Gustavo Vela Castro 2025-03-21 12:05:25 +00:00 committed by node
parent 909e0b03db
commit ec4b25adbd
2 changed files with 28 additions and 8 deletions

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@ -33,6 +33,7 @@
\begin{frame}{The silver lining} \begin{frame}{The silver lining}
\begin{itemize} \begin{itemize}
\item Isospectral pairs are cool and all, but they cannot occur in dimension $3$. \item Isospectral pairs are cool and all, but they cannot occur in dimension $3$.
\item We can thus attempt to infer the shape of our universe based on its spectrum. \item We can thus attempt to infer the shape of our universe based on its spectrum.
\end{itemize} \end{itemize}

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@ -84,16 +84,18 @@ code-for-last-col = \color{blue}
\begin{frame}[fragile]{Homogeneous Spherical Spaces} \begin{frame}[fragile]{Homogeneous Spherical Spaces}
\begin{itemize} \begin{itemize}
\pause
\item Finite subgroup $\Gamma \leq \so 4.$ \item Finite subgroup $\Gamma \leq \so 4.$
\pause
\item The Helmholtz equation on $\textcolor{blue}{M}$ has the spectrum of the underlying manifold as its solutions, and is given by \item The Helmholtz equation on $\textcolor{blue}{M}$ has the spectrum of the underlying manifold as its solutions, and is given by
\begin{align*} \begin{align*}
(\Delta + E_{\textcolor{red}{\beta}}^{\textcolor{blue}{M}})\psi_{\textcolor{red}{\beta}}^{{\textcolor{blue}{M}}, i} = 0. (\Delta + E_{\textcolor{red}{\beta}}^{\textcolor{blue}{M}})\psi_{\textcolor{red}{\beta}}^{{\textcolor{blue}{M}}, i} = 0.
\end{align*} \end{align*}
\pause
\item In fact $E_{\textcolor{red}{\beta}}^m = {\textcolor{red}{\beta}}^2-1$ for $\textcolor{red}{\beta} \in \mathbb{N}$. We call $\textcolor{red}{\beta}$ a wave number. \item In fact $E_{\textcolor{red}{\beta}}^m = {\textcolor{red}{\beta}}^2-1$ for $\textcolor{red}{\beta} \in \mathbb{N}$. We call $\textcolor{red}{\beta}$ a wave number.
\pause
\item The set of all possible wave numbers [for which a nonzero solution exists] depends on $\Gamma$ - usually a proper subset of $\mathbb{{N}}$. \item The set of all possible wave numbers [for which a nonzero solution exists] depends on $\Gamma$ - usually a proper subset of $\mathbb{{N}}$.
\pause
\item Solutions to the Helmholtz equation are calculated for each $\Gamma$ and CMB anisotropy $\frac{\delta T}{T}$ computed as a sum of spherical harmonics. \item Solutions to the Helmholtz equation are calculated for each $\Gamma$ and CMB anisotropy $\frac{\delta T}{T}$ computed as a sum of spherical harmonics.
\end{itemize} \end{itemize}
\end{frame} \end{frame}
@ -114,9 +116,11 @@ code-for-last-col = \color{blue}
\begin{frame}[fragile]{Homogenous Spherical Spaces --- Results} \begin{frame}[fragile]{Homogenous Spherical Spaces --- Results}
\begin{itemize} \begin{itemize}
\pause
\item For the majority of groups $\Gamma$, the anisotropies $\frac{\delta T}{T}$ do not coincide with observations. \item For the majority of groups $\Gamma$, the anisotropies $\frac{\delta T}{T}$ do not coincide with observations.
\pause
\item The only groups for which it does are $\Gamma = O^*$ and $\Gamma = I^*$ — the \textcolor{red}{binary octahedral} and \textcolor{red}{binary icosahedral} groups of order 48 and 120 respectively. \item The only groups for which it does are $\Gamma = O^*$ and $\Gamma = I^*$ — the \textcolor{red}{binary octahedral} and \textcolor{red}{binary icosahedral} groups of order 48 and 120 respectively.
\pause
\end{itemize} \end{itemize}
\begin{figure}[H] \begin{figure}[H]
\centering \centering
@ -135,11 +139,13 @@ code-for-last-col = \color{blue}
\item Manifolds of the form $\S^3/\Gamma$ with $\Gamma$ a group acting on $\S^3$. \item Manifolds of the form $\S^3/\Gamma$ with $\Gamma$ a group acting on $\S^3$.
\item Multi-connected space: it has non-contractable loops \item Multi-connected space: it has non-contractable loops
\item Inhomogeneous space: it does not look identical from every point in space \item Inhomogeneous space: it does not look identical from every point in space
\item Fixing $|\Gamma|=8$, we have three multi-connected manifolds, up to equivalence: \pause
\item Fixing $|\Gamma|=8$, we have three multi-connected manifolds, up to equivalence: \pause
\begin{enumerate} \begin{enumerate}
\item homogeneous: $N3$ and $L(8,1)$ \item homogeneous: $N3$ and $L(8,1)$
\item inhomogeneous: $N2 \equiv L(8,3)$ \item inhomogeneous: $N2 \equiv L(8,3)$
\end{enumerate} \end{enumerate}
\pause
\item Results: inhomogeneous spaces have more variety in the CMB anisotropies than homogeneous spaces, because the strength of anisotropy suppression is observer dependent. \item Results: inhomogeneous spaces have more variety in the CMB anisotropies than homogeneous spaces, because the strength of anisotropy suppression is observer dependent.
\end{itemize} \end{itemize}
@ -153,16 +159,18 @@ code-for-last-col = \color{blue}
\textbf{Theoretical Expectation:}\\ \textbf{Theoretical Expectation:}\\
From the perspective of an Earth-based observer, we can view the CMB as a function defined on the celestial sphere $\mathbb{S}^2$.\\ From the perspective of an Earth-based observer, we can view the CMB as a function defined on the celestial sphere $\mathbb{S}^2$.\\
\begin{itemize} \begin{itemize}
\pause
\item The CMB temperature fluctuations can be expanded as: \item The CMB temperature fluctuations can be expanded as:
\[ \[
\Delta T(\hat{n}) = \sum_{\ell=0}^{\infty} \sum_{m=-\ell}^{\ell} a_{\ell m} Y_{\ell m}(\hat{n}) \Delta T(\hat{n}) = \sum_{\ell=0}^{\infty} \sum_{m=-\ell}^{\ell} a_{\ell m} Y_{\ell m}(\hat{n})
\] \]
\pause
\item If the universe is isotropic, the \textbf{mean of the harmonic coefficients} should satisfy: \item If the universe is isotropic, the \textbf{mean of the harmonic coefficients} should satisfy:
\[ \[
\langle a_{\ell m} \rangle = 0 \langle a_{\ell m} \rangle = 0
\] \]
\end{itemize} \end{itemize}
\pause
\textbf{Key Question:} \textbf{Key Question:}
- Does the observed CMB data deviate from statistical isotropy? - Does the observed CMB data deviate from statistical isotropy?
- If \( \langle a_{\ell m} \rangle \neq 0 \), this suggests a preferred cosmic direction. - If \( \langle a_{\ell m} \rangle \neq 0 \), this suggests a preferred cosmic direction.
@ -173,13 +181,15 @@ code-for-last-col = \color{blue}
\textbf{Challenges in Real Observations:} \textbf{Challenges in Real Observations:}
\begin{itemize} \begin{itemize}
\item We cannot observe the full CMB sky due to foreground contamination. \item We cannot observe the full CMB sky due to foreground contamination.
\item A \textbf{sky mask function} \( A(\hat{n}) \) removes contaminated regions, but introduces bias. \item A \textbf{sky mask function} \( A(\hat{n}) \) removes contaminated regions, but introduces bias.
\pause
\item The test statistic \( S_i \) is used, with a matrix $W$ to correct for these effects: \item The test statistic \( S_i \) is used, with a matrix $W$ to correct for these effects:
\[ \[
S_i = \sum_{j} W_{ij} M_j S_i = \sum_{j} W_{ij} M_j
\] \]
\end{itemize} \end{itemize}
\pause
\textbf{Monte Carlo Simulations:} \textbf{Monte Carlo Simulations:}
\begin{itemize} \begin{itemize}
\item We generate thousands of \textbf{simulated CMB skies} assuming isotropy. \item We generate thousands of \textbf{simulated CMB skies} assuming isotropy.
@ -202,12 +212,13 @@ code-for-last-col = \color{blue}
\caption{The decorrelated band mean test statistic values over multipole ranges [9].} \caption{The decorrelated band mean test statistic values over multipole ranges [9].}
\end{figure} \end{figure}
\column{0.5\textwidth} \column{0.5\textwidth}
\pause
\textbf{Key Findings:} \textbf{Key Findings:}
\begin{itemize} \begin{itemize}
\item A statistically significant deviation was found in \( 221 \leq \ell \leq 240 \). \item A statistically significant deviation was found in \( 221 \leq \ell \leq 240 \).
\item This suggests a potential \textcolor{red}{preferred cosmic direction}. \item This suggests a potential \textcolor{red}{preferred cosmic direction}.
\end{itemize} \end{itemize}
\pause
\textbf{Possible Explanations:} \textbf{Possible Explanations:}
\begin{itemize} \begin{itemize}
\item A real cosmological signal? → A finite universe or new physics. \item A real cosmological signal? → A finite universe or new physics.
@ -219,10 +230,18 @@ code-for-last-col = \color{blue}
\section{Conclusion} \section{Conclusion}
\begin{frame}{Conclusion} \begin{frame}{Conclusion}
\pause
\begin{enumerate} \begin{enumerate}
\item We can infer the shape of the universe from its spectrum \item We can infer the shape of the universe from its spectrum
\pause
\item There are two homogeneous spherical manifolds obtained as $\S^3/\Gamma$ which produce CMB similar to observations \item There are two homogeneous spherical manifolds obtained as $\S^3/\Gamma$ which produce CMB similar to observations
\pause
\item Inhomogeneous spherical spaces exhibit varied behavior of CMB anisotropies \item Inhomogeneous spherical spaces exhibit varied behavior of CMB anisotropies
\pause
\item Statistical test results suggest possibilities of finite multi-connected topology \item Statistical test results suggest possibilities of finite multi-connected topology
\end{enumerate} \end{enumerate}
\end{frame} \end{frame}