A First Principles Warm Inflation Model that Solves the Cosmological Horizon and Flatness Problems

Abstract

A quantum field theory warm inflation model is presented that solves the horizon/flatness problems. The model obtains, from the elementary dynamics of particle physics, cosmological scale factor trajectories that begin in a radiation dominated regime, enter an inflationary regime and then smoothly exit back into a radiation dominated regime, with nonnegligible radiation throughout the evolution. PACS number(s): 98.80 Cq, 05.70.Ln, 11.10.Wx In Press Physical Review Letters 1999The resolution of the horizon problem, which underlies inflationary cosmology [1], is that at a very early time, the equation of state that dictates the expansion rate of the Universe was dominated by a vacuum energy density ρ v , so that a small causally connected patch could grow to a size that encompasses the comoving volume which becomes the observed universe today.In the standard (isentropic) inflationary scenarios, the radiation energy density ρ r scales with the inverse fourth power of the scale factor, becoming quickly negligible. In such case, a short time reheating period terminates the inflationary period and initiates the radiation dominated epoch. On the other hand, the only condition required by General Relativity for inflation is that ρ r < ρ v . Inflation in the presence of nonnegligible radiation is characterized by non-isentropic expansion [2,3] and thermal seeds of density perturbations [4]. This can be realized in warm inflation scenarios [5] where there is no reheating.The basic idea of our implementation of warm inflation is quite simple; a scalar field, which we call the inflaton, is coupled to several other fields. As the inflaton relaxes toward its minimum energy configuration, it will decay into lighter fields, generating an effective viscosity.

Inflationary initial conditions consistent with causality

“…For the cosmological setting, such damping terms are typically associated with systems involving a scalar field interacting with fields of a radiation bath. In this case, such damping terms have been found in first principles calculations for certain warm inflation models [24], although more work is needed along these lines. It is worth noting here that in the early stages of certain supercooled inflaton scenarios where radiation is present, in particular new [20] and thermal [27] inflation, a careful examination of the dynamics may reveal damping terms similar to this.…”

“…II, they also provide consistent spacetime embeddings, especially for Ω inf < 1. Furthermore, studies of warm inflation [21][22][23], including the first principles quantum field theory model [24], generally find that to obtain adequate inflationary e-folds, N e > ∼ 60, it requires Γ ≈ N e m 2 /H with m > ∼ H so that Γ > ∼ N e H and thus 1/Γ ≪ 1/H. As such, for warm inflationary conditions this simple analysis suggests that the smoothness requirement on the initial inflationary patch is at scales much smaller than the Hubble radius 1/H, which therefore imposes no violation of causality.…”

Particle creation and warm inflation

“…[5], we impose h 2 1 such that perturbation theory is reasonable. 4 From a standard one-loop calculation one can compute the (zero-temperature) onshell decay width for χ → ψψ, in the case that M χ > 2M ψ . Here the masses M χ,ψ include possible background field dependence.…”

“…In the most elementary setup, the dynamics of the inflaton mean field φ(t) = ϕ(t, x) is determined byφ (t) + 3H(t)φ(t) + V ′ [φ(t)] = 0, ( In warm inflation [2,3,4,5,6,7] the key idea is that interactions between the inflaton and other quantum fields are important during inflation and that they result in continuous energy transfer from the inflaton to these other fields. If this transfer is sufficiently fast and equilibration is rapid, a quasi-stable state could be achieved, different from the inflationary vacuum.…”

Chaotic symmetry breaking and dissipative two-field dynamics

“…While in all the previous works on chaotic dynamics of fields dealt with (conservative) Hamiltonian systems, here we will be mainly concerned with the effective field evolution equations, which are known to be intrinsically dissipative [3][4][5][6][7][8][9] and, therefore, the dynamical system we will be studying is non-Hamiltonian.…”