Past String Theory Journal Club

Motivated by string dualities we propose topological gravity as the early phase of our universe.  The topological nature of this phase naturally leads to the explanation of many of the puzzles of early universe cosmology.  A concrete realization of this scenario using Witten's four dimensional topological gravity is considered.  This model leads to the power spectrum of CMB fluctuations which is controlled by the conformal anomaly coefficients $a,c$.  In particular the strength of the fluctuation is controlled by $1/a$ and its tilt by $c g^2$ where $g$ is the coupling constant of topological gravity.  The positivity of $c$, a consequence of unitarity, leads automatically to an IR tilt for the power spectrum.   In contrast with standard inflationary models, this scenario predicts $\mathcal{O}(1)$ non-Gaussianities for four- and higher-point correlators and the absence of tensor modes in the CMB fluctuations.

https://arxiv.org/pdf/2004.06929.pdf

https://arxiv.org/abs/2003.02844

https://arxiv.org/abs/2003.10466

https://arxiv.org/abs/2004.00015

https://arxiv.org/abs/2004.06115

https://arxiv.org/abs/2003.02860

Discussion of https://arxiv.org/abs/1911.07895

Discussion of https://arxiv.org/abs/1812.04716

Discussin of https://arxiv.org/abs/1908.09858

We'll discuss the large charge expansion in CFTs with supersymmetry, focussing on 1908.10306 by Grassi, Komargodski and Tizzano.