Recent Developments in Warm Inflation

Abstract

Warm inflation, its different particle physics model implementations, and the implications of dissipative particle production for its cosmology are reviewed. First, we briefly present the background dynamics of warm inflation and contrast it with the cold inflation picture. An exposition of the space of parameters for different well-motivated potentials, which are ruled out, or severely constrained in the cold inflation scenario, but not necessarily in warm inflation, is provided. Next, the quantum field theory aspects in realizing explicit microscopic models for warm inflation are given. This includes the derivation of dissipation coefficients relevant in warm inflation for different particle field theory models. The dynamics of cosmological perturbations in warm inflation are then described. The general expression for the curvature scalar power spectrum is shown. We then discuss in detail the relevant regimes of warm inflation, the weak and strong dissipative regimes. We also discuss the results predicted in these regimes of warm inflation and how they are confronted with the observational data. We explain how the dissipative dynamics in warm inflation can address several long-standing issues related to (post-) inflationary cosmology. This includes recent discussions concerning the so-called swampland criteria and how warm inflation can belong to the landscape of string theory.

Defying eternal inflation in warm inflation with a negative running

“…As previously mentioned, in WI the addition of thermal effects has also a significant impact on the form of the primordial power spectrum which in WI is given by [14]:…”

“…where, in contrast to CI, we included a non-negligible dissipation rate Υ ≡ Υ(ϕ, T ), which accounts for the energy transfer between the inflaton field and the radiation bath (at temperature T ) present during inflation. 4 In addition, we also introduced two stochastic Gaussian noise terms, ξ q and ξ T , which account for the quantum and thermal fluctuations, respectively, with two-point correlation functions given by [14,44,45]:…”

“…A well-established alternative framework to this standard picture is warm inflation (WI) [11] (see also refs. [12][13][14] for reviews), where instead the inflaton field is thermally coupled to a bath of radiation, continuously sourcing its production throughout the accelerated expansion. Via these dissipative effects, WI is able to smoothly route the Universe to a radiation dominated era, alleviating the need for a separate reheating phase.…”

Monomial warm inflation revisited

“…1. An additive cold-like piece of the form H 4 /(2π φ) 2 . We call it cold-like because although it has the same form as in standard cold inflation, H and φ are evaluated on the background solution of warm inflation.…”

“…In this paper we will entertain the possibility that particle production during inflation is strong enough that it becomes necessary to consider a thermal bath during inflation. The thermal bath is thought to originate from the inflation gradually releasing part of its energy into other species, which then thermalize (or, more commonly in concrete implementations, lead to yet other particles which finalize thermalize, see [2] for a review). This scenario is known as warm inflation [3], as opposed to the standard picture of (cold) inflation.…”