Constraints on just enough inflation preceded by a thermal era
Abstract
If the inflationary era is preceded by a radiationdominated 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 efoldings 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 10^{9} or 10^{11} ). We are not aware of scenarios in which this can be satisfied.
 Publication:

Physical Review D
 Pub Date:
 January 2016
 DOI:
 10.1103/PhysRevD.93.023516
 arXiv:
 arXiv:1506.04808
 Bibcode:
 2016PhRvD..93b3516D
 Keywords:

 High Energy Physics  Phenomenology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 Clearer presentation, agrees with published version