Stringy effects during inflation and reheating

Abstract

We consider inflationary cosmology in the context of string compactifications with multiple throats. In scenarios where the warping differs significantly between throats, string and Kaluza-Klein physics can generate potentially observable corrections to the cosmology of inflation and reheating. First we demonstrate that a very low string scale in the ground state compactification is incompatible with a high Hubble scale during inflation, and we propose that the compactification geometry is altered during inflation. In this configuration, the lowest scale is just above the Hubble scale, which is compatible with the effective field theory but still leads to potentially observable cosmic microwave background corrections. Also in the appropriate region of parameter space, we find that reheating leads to a phase of long open strings in the standard model sector (before the usual radiation-dominated phase). We sketch the cosmology of the long string phase and we discuss possible observational consequences.

Inflation and String Theory

“…Reheating can then induce copious production of excited strings in the strongly warped throat [547]. Analyzing this process in detail remains challenging.…”

“…When the inflationary energy is also localized on a brane, one can take a modular approach, in which the inflationary sector and the visible sector constructed separately, in local geometries approximating regions of some unspecified compactification, and their interactions are then computed or parameterized. This strategy has been fruitful in extensive explorations [545][546][547][548][549][550][551][552][553][554][555][556] in the context of warped D-brane inflation [41], as we review in §5.1. Reheating in other models involving D-branes has been studied in e.g.…”

Gravitational wave constraints on Dirac–Born–Infeld inflation

“…One class of string-theoretic models that has received considerable attention is Dbrane inflation [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]. (For recent reviews, see, e.g., [27,28]).…”

Fine-tuning in DBI inflationary mechanism

“…Generally we expect a warped space with a very small minimum warp factor to be deformed in the IR side by the Hubble expansion, so the location where the deformation starts to be significant is crucial. So far there have been several kinds of such backreactions discussed in the literature [7,[9][10][11][12]. Particles such as strings can be created in the IR side by the spatial expansion because their mass scales are redshifted.…”

“…Only when the density of these particles exceeds certain critical value, its backreaction shortens the warped throat; but this still leaves a considerable portion of warped space for DBI inflation [7]. Various moduli that stabilize the IR warp factor in the flux compactification will fluctuate in the inflationary background and this also shortens the throat [9,10]. The analyses along this line so far has not been explicit enough for our purpose due to technical difficulties in solving equations of motion with large warping, and also it is likely to be model-dependent.…”