Small field axion inflation with sub-Planckian decay constant

Abstract

We study an axion inflation model recently proposed within the framework of type IIB superstring theory, where we pay a particular attention to a sub-Planckian axion decay constant. Our axion potential can lead to the small field inflation with a small tensor-to-scalar ratio, and a typical reheating temperature can be as low as GeV.

Constraints on small-field axion inflation

“…In the example of Refs. [12,13], we obtain q = 2. This behavior originates from sinusoidal functions in the axion inflation potential.…”

“…It is then possible to avoid the isocurvature constraint by the low-scale inflation, although the upper bound of f QCD depends on the initial misalignment angle of the axion and dilution mechanism after the inflation [9,10,11]. Recently, some of the authors conjectured that, in a certain class of small-field axion inflation derived from type IIB superstring theory [12], 1 the tensor-to-scalar ratio r correlates with the axion decay constant f as follows [13],…”

New forms of potential for string axion inflation

“…At any rate, it is quite interesting that one inflation model can lead to both the large-field inflation scenario and the small-field inflation scenario depending on parameter values. We would study more detail in further work [23].…”

Polyinstanton axion inflation

“…The inflation scenario with such modular function terms has also been studied [7,11,12]. Moreover, the mixture of polynomial functions and sinusoidal functions was derived by quantum corrections and studied to realize inflation models [13][14][15].…”

“…For example, we can analyze explicitly the reheating processes after the axion inflation. The axion couplings to the gauge bosons, quarks, and leptons may be rather weak, and the reheating temperature may be rather low [9,13,15]. The axions would also appear in phases of couplings among the quarks, leptons, and the Higgs fields.…”