Snowmass White Paper: Cosmology at the Theory Frontier

Abstract

The precision cosmological model describing the origin and expansion history of the universe, with observed structure seeded at the inflationary cosmic horizon, demands completion in the ultraviolet and in the infrared. The dynamics of the cosmic horizon also suggests an associated entropy, again requiring a microphysical theory. Recent years have seen enormous progress in understanding the structure of de Sitter space and inflation in string theory, and of cosmological observables captured by quantum field theory and solvable deformations thereof. The resulting models admit ongoing observational tests through measurements of the cosmic microwave background and large-scale structure, as well as through analyses of theoretical consistency by means of thought experiments. This paper, prepared for the TF01 and TF09 conveners of the Snowmass 2021 process, provides a synopsis of this important area, focusing on ongoing developments and opportunities.

TF1 Snowmass Report: Quantum gravity, string theory, and black holes

“…Others, involving non-perturbative effects, are still harder to understand in detail. Models of inflation and dark energy are discussed at greater length in §3 (on quantum gravity and cosmology) here, and in the white paper [8]. They require a level of theoretical control of effective po-tentials which remains just at the forefront of present technology.…”

“…In this section we summarize the conclusions of the white paper [8], where an extensive list of references can be found.…”

Detection of early-universe gravitational-wave signatures and fundamental physics

“…This includes the inflationary and other early phases in the evolution of the Universe that could have generated a stochastic GW background (SGWB). (For synergy, see Snowmass white papers on inflation [3] and high energy physics model-building of the early Universe [4,5].) Later, Section 5 is dedicated to the open problem of dark matter.…”

Effective field theories of gravity and compact binary dynamics: A Snowmass 2021 whitepaper

“…in [47,48,49,50,51,52,53,54,55,56,57]. These references only scratch the surface, see the Snowmass whitepaper [58], for a review of the role of fundamental theory in cosmology, and [59] more specifically for a summary of effective field theories.…”

“…Detailed reviews of EFT for other systems that include gravity can be found in the references, e.g. [58,59].…”