A radiation-like era before inflation

We employ the semiclassical approximation to the Wheeler-DeWitt equation in the spatially flat de Sitter Universe to investigate the dynamics of a minimally coupled scalar field near the Planck scale. We find that, contrary to naïve intuition, the effects of quantum gravitational fluctuations become negligible and the scalar field states asymptotically approach plane-waves at very early times. These states can then be used as initial conditions for the quantum states of matter to show that each mode essentially originated in the minimum energy vacuum. Although the full quantum dynamics cannot be solved exactly for the case at hand, our results can be considered as supporting the general idea of asymptotic safety in quantum gravity.

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“…See equation(2.39) below and[21].Journal ofCosmology and Astroparticle Physics 06 (2008) 014 (stacks.iop.org/JCAP/2008/i=06/a=014)…”

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confidence: 99%

“…A more complete analysis of the coupled gravity-matter dynamics is being performed[21].Journal ofCosmology and Astroparticle Physics 06 (2008) 014 (stacks.iop.org/JCAP/2008/i=06/a=014)…”

mentioning

confidence: 99%

Hints of (trans-Planckian) asymptotic freedom in semiclassical cosmology

Appignani

Casadio

2008

J. Cosmol. Astropart. Phys.

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“…In the present paper, we will show that fluctuation-dissipation dynamics during a radiation-dominated pre-inflationary epoch can indeed lead to such a thermalized state, where the homogeneous inflaton value naturally becomes localized within a flat plateau about the origin, thus setting the necessary conditions for the onset of inflation (see e.g. [56][57][58] for previous discussions of the role of the pre-inflationary dynamics in setting initial conditions for inflation).…”

Section: Introductionmentioning

confidence: 74%

The role of fluctuation-dissipation dynamics in setting initial conditions for inflation

Bastero-Gil

Berera

Brandenberger

et al. 2018

J. Cosmol. Astropart. Phys.

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Abstract.We study the problem of initial conditions for slow-roll inflation along a plateau-like scalar potential within the framework of fluctuation-dissipation dynamics. We consider, in particular, that inflation was preceded by a radiation-dominated epoch where the inflaton is coupled to light degrees of freedom and may reach a near-equilibrium state. We show that the homogeneous field component can be sufficiently localized at the origin to trigger a period of slow-roll if the interactions between the inflaton and the thermal degrees of freedom are sufficiently strong and argue that this does not necessarily spoil the flatness of the potential at the quantum level. We further conclude that the inflaton can still be held at the origin after its potential begins to dominate the energy balance, leading to a period of thermal inflation. This then suppresses the effects of nonlinear interactions between the homogeneous and inhomogeneous field modes that could prevent the former from entering a slow-roll regime. Finally, we discuss the possibility of an early period of chaotic inflation, at large field values, followed by a first stage of reheating and subsequently by a second inflationary epoch along the plateau about the origin. This scenario could prevent an early overclosure of the Universe, at the same time yielding a low tensor-to-scalar ratio in agreement with observations.

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“…We use this to make an argument that it is extremely likely that if the Universe had a period before inflation in which the semiclassical approximation was valid, then it expanded in approximately the same way as a radiation-dominated universe during that period. Evidence for a radiation dominated pre-inflationary era has also been found in a model in which the Wheeler-DeWitt equation is solved in the minisuperspace approximation which includes the Hamiltonian for the scale factor when a cosmological constant is present along with the Hamiltonian for a single mode of a massless minimally coupled scalar field [3].…”

Section: Introductionmentioning

confidence: 82%

Semiclassical predictions regarding a pre-inflationary era and its effects on the power spectrum

Anderson,

Carlson,

Ordines

et al. 2020

Preprint

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An investigation is undertaken into the properties and effects of a pre-inflationary era during at least part of which semiclassical gravity was valid. It is argued that if the Universe (or our part of it) was approximately homogeneous and isotropic during that era, then the Universe was likely to have been radiation dominated. A simple model in which the Universe contains classical radiation and a cosmological constant is used to investigate potential effects of such a pre-inflationary era on the cosmic microwave background. Various choices of state for a massless minimally coupled scalar field are considered, including adiabatic vacuum states of various orders and the vacuum state that would naturally occur if the Universe made a sudden transition from being radiation dominated to de Sitter space. In all cases considered there is a suppression of the power spectrum at large angles, and when plotted as a function of the momentum parameter, there are always oscillations with state-dependent amplitudes.

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A radiation-like era before inflation

Cited by 6 publications

References 20 publications

Hints of (trans-Planckian) asymptotic freedom in semiclassical cosmology

Hints of (trans-Planckian) asymptotic freedom in semiclassical cosmology

The role of fluctuation-dissipation dynamics in setting initial conditions for inflation

Semiclassical predictions regarding a pre-inflationary era and its effects on the power spectrum

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