diff --git a/isospectral.tex b/isospectral.tex index ab9f9ff..7e67087 100644 --- a/isospectral.tex +++ b/isospectral.tex @@ -40,6 +40,7 @@ \fill[color=orange](0,0) rectangle (10pt,\paperheight); \end{tikzpicture} \begin{itemize} + \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. \end{itemize} diff --git a/main.tex b/main.tex index 0821640..b6d7d3d 100644 --- a/main.tex +++ b/main.tex @@ -81,16 +81,18 @@ code-for-last-col = \color{blue} \begin{frame}[fragile]{Homogeneous Spherical Spaces} \begin{itemize} + \pause \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 \begin{align*} (\Delta + E_{\textcolor{red}{\beta}}^{\textcolor{blue}{M}})\psi_{\textcolor{red}{\beta}}^{{\textcolor{blue}{M}}, i} = 0. \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. - + \pause \item The set of all possible wave numbers [for which a nonzero solution exists] depends on $\Gamma$ - usually a proper subset of $\mathbb{{N}}$. - + \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. \end{itemize} \end{frame} @@ -111,9 +113,11 @@ code-for-last-col = \color{blue} \begin{frame}[fragile]{Homogenous Spherical Spaces --- Results} \begin{itemize} + \pause \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. - + \pause \end{itemize} \begin{figure}[H] \centering @@ -132,11 +136,13 @@ code-for-last-col = \color{blue} \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 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} \item homogeneous: $N3$ and $L(8,1)$ \item inhomogeneous: $N2 \equiv L(8,3)$ \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. \end{itemize} @@ -150,16 +156,18 @@ code-for-last-col = \color{blue} \textbf{Theoretical Expectation:}\\ From the perspective of an Earth-based observer, we can view the CMB as a function defined on the celestial sphere $\mathbb{S}^2$.\\ \begin{itemize} + \pause \item The CMB temperature fluctuations can be expanded as: \[ \Delta T(\hat{n}) = \sum_{\ell=0}^{\infty} \sum_{m=-\ell}^{\ell} a_{\ell m} Y_{\ell m}(\hat{n}) \] + \pause \item If the universe is isotropic, the \textbf{mean of the harmonic coefficients} should satisfy: \[ \langle a_{\ell m} \rangle = 0 \] \end{itemize} - + \pause \textbf{Key Question:} - Does the observed CMB data deviate from statistical isotropy? - If \( \langle a_{\ell m} \rangle \neq 0 \), this suggests a preferred cosmic direction. @@ -170,13 +178,15 @@ code-for-last-col = \color{blue} \textbf{Challenges in Real Observations:} \begin{itemize} \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. + \pause \item The test statistic \( S_i \) is used, with a matrix $W$ to correct for these effects: \[ S_i = \sum_{j} W_{ij} M_j \] \end{itemize} - + \pause \textbf{Monte Carlo Simulations:} \begin{itemize} \item We generate thousands of \textbf{simulated CMB skies} assuming isotropy. @@ -199,12 +209,13 @@ code-for-last-col = \color{blue} \caption{The decorrelated band mean test statistic values over multipole ranges [9].} \end{figure} \column{0.5\textwidth} + \pause \textbf{Key Findings:} \begin{itemize} \item A statistically significant deviation was found in \( 221 \leq \ell \leq 240 \). \item This suggests a potential \textcolor{red}{preferred cosmic direction}. \end{itemize} - + \pause \textbf{Possible Explanations:} \begin{itemize} \item A real cosmological signal? → A finite universe or new physics. @@ -216,10 +227,18 @@ code-for-last-col = \color{blue} \section{Conclusion} \begin{frame}{Conclusion} + + \pause \begin{enumerate} \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 + + \pause \item Inhomogeneous spherical spaces exhibit varied behavior of CMB anisotropies + + \pause \item Statistical test results suggest possibilities of finite multi-connected topology \end{enumerate} \end{frame}