Constraints on just enough inflation preceded by a thermal era

2015/06/30 by Suratna Das, Gaurav Goswami, J. Prasad +2
Mathematics · Physics and Astronomy · #Astrophysics #Black Holes and Theoretical Physics #Classical mechanics #Cosmic microwave background #Cosmology #Cosmology and Gravitation Theories #Dark energy #Flatness (cosmology) #Galaxies: Formation, Evolution, Phenomena #Hubble's law #Inflation (cosmology) #Inflaton #Mathematical analysis #Mathematical physics #Mathematics #Physics #Quantum mechanics #Theoretical physics #Universe #Upper and lower bounds #astro-ph.CO #gr-qc #hep-ph #hep-th

paper · pdf · doi:10.1103/physrevd.93.023516

published as Phys. Rev. D 93, 023516 (2016) · Clearer presentation, agrees with published version

openalex publication_date 2016/01/22 · arxiv created 2016/01/24 · arxiv updated 2016/01/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

If the inflationary era is preceded by a radiation-dominated era in which the inflaton too was in thermal equilibrium at some very early time, then the CMB data places an upper bound on the comoving temperature of the (decoupled) inflaton quanta. In addition, if one considers models of ``just enough'' inflation, where the number of e-foldings of inflation is just enough to solve the horizon and flatness problems, then we get a lower bound on the Hubble parameter during inflation, H_inf, which is in severe conflict with the upper bound from tensor perturbations. Alternatively, imposing the upper bound on H_inf implies that such scenarios are compatible with the data only if the number of relativistic degrees of freedom in the thermal bath in the preinflationary Universe is extremely large (greater than 10⁹ or 10¹¹). We are not aware of scenarios in which this can be satisfied.

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