Origins of the Universe Conference 2019

Paul Steinhardt

The talk will explain how combining intervals of slow contraction with a (non-singular) classical bounce naturally leads to a novel cyclic theory of the universe in which the Hubble parameter, energy density and temperature oscillate periodically, but the scale factor (and hence the size of the universe) grows by an exponential factor from one cycle to the next.

Anna Ijjas

In this talk, I will discuss the robustness of a slowly-contracting primordial epoch to initial conditions in realistic set-ups, using the full power of numerical general relativity. In addition, I will review recent progress on studying the generation of primordial perturbations as well as constructing smooth cosmological bounces.

Eva Silverstein

In this talk I will start by reviewing models of accelerated expansion in string theory (both existing ones and new examples under development), explaining the methodology behind the examples and their consistency. Most stress energy sources in string theory produce positive potential energy in four dimensions, with crucial and well-known negative contributions appearing at intermediate orders in the expansion in weak coupling and large curvature radius. Localized sources contribute calculable forces in a well-defined approximation scheme, whose nature depends on the strength of the gradients in the extra dimensions. In existing models as well as new ones under development, fluxes also play a key role in stabilizing the shape of the internal geometry. These have a standard generalized form in string theory which depends on the axion fields of the theory, often resulting in large field inflation whose phenomenology depends on back reaction on the geometry which was calculated in the models. In addition to applying to early universe phenomenology, this structure led to a framework for quantum gravity in de Sitter spacetime obtained by uplifting the AdS/CFT correspondence. This dual description became significantly more complete in the past year via its relation to a generalization of the T Tbar deformation, as detailed in Gorbenko’s talk at this meeting.

Victor Gorbenko

I will briefly review the existing approaches to holography for cosmological spacetimes, focusing on the dS/dS correspondence. This method relates a gravitational theory in de Sitter space to a theory in de Sitter space of lower dimension, which, in particular, allows to benefit from several novel exact results obtained in lower-dimensional quantum field theories. I will then discuss the calculations of correlation functions in cosmology with the help of stochastic differential equations as well as some properties of the wave function of the universe that these calculations highlight.

Dick Bond

Current CMB data, from our Planck 2019 Legacy work in particular. show a 2-parameter compression of nearly-Gaussian early Universe fluctuations, but novel primordial non- Gaussianities may arise that are not strongly 2D CMB-constrained in the ~10 e-folds we can probe, but may be more easily detected in 3D Large Scale Structure Surveys, or may reside as quite high nonG levels in the largely obscured 50 e-foldings from CMB/LSS scales to the end-of-inflation. An emphasis in our Modern Inflation group is to explore the theoretical possibilities and characterize them to test with new statistical methods on the huge CMB/LSS datasets soon to emerge, Simons Observatory being one major target. I will describe the use of highly-nonlinear pseudo-spectral lattice simulations and linear dynamical systems theory to understand the non-G possibilities, manifested by bursty particle and entropy creation in collective coordinates.  I will describe where we are at in our part of the MI non-G program, based on in-out state formulation for lattice simulations with the non-G arising from multi-field potential-surface features.  We are applying the framework to slow-growth instabilities after inflation ends and to short-lived instabilities while inflation is ongoing.

Guido D’Amico

We analyze the DR12 BOSS galaxy clustering data, using the EFTofLSS formalism. We assume ΛCDM, a fixed value of the baryon/dark-matter ratio, and of the tilt of the primordial power spectrum. After validating our technique against several sets of numerical simulations, we measure the primordial amplitude of the power spectrum, A_s , the abundance of matter, Ω_m , and the Hubble parameter, H₀ , to about 12.4%, 3.0% and 2.9% respectively. We find ln(10¹⁰ A_s ) = 2.79 ± 0.12, Ω_m = 0.309 ± 0.009, H₀ = 68.3 ± 2.0 km/(s Mpc) at 68% confidence level. Our results are a substantial qualitative and quantitative improvement with respect to former analyses.

Cumran Vafa

I review some of the recent developments in the Swampland program and how it relates to cosmology. In particular I discuss how the H0 tension is reduced in the context of extensions of LCDM which are compatible with the Swampland criteria.

Frans Pretorius

In this talk, I will describe some of the challenges applying modified gravity theories to scenarios that are of interest to both testing general relativity with gravitational wave observations, and to early universe cosmology. The issues can be most pronounced in the dynamical, strong-field regime, where numerical solution methods are often required. As a case study, I will describe new results on gravitational collapse and black hole formation within Einstein-dilaton-Gauss-Bonnet gravity.

Andrew Tolley

I will review how positivity bounds are used to put constraints on Effective field theories, and discuss in particular recent work on their application gravitational and cosmological context.

David Pirtskhalava

I will review proposals that aspire to describe a geodesically complete classical theory of early universe, either interpolating to inflation or replacing inflation by alternative phases. I will also review how similar theories can describe the late time cosmic acceleration of the universe.