Warm inflation has been noted previously as a possible way to implement inflationary models compatible with the dS swampland bounds. But often in these discussions, the heat bath dynamics are kept largely unspecified. We point out that the recently introduced minimal warm inflation [K. V. Berghaus, P. W. Graham, and D. E. Kaplan, J. Cosmol. Astropart. Phys. 03 (2020) 034], where an axionic coupling of the inflaton leads to an explicit model for the thermal bath, yields models of inflation that can easily fit cosmological observations while satisfying de Sitter swampland bounds, as well as the swampland distance bound and trans-Planckian censorship.

India

Suratna Das

Gaurav Goswami

Chethan Krishnan

Swampland, axions, and minimal warm inflation

We investigate the possibility of enhancement of the effective axion decay constant in well-controlled constructions in string theory. To this end, we study the dynamics of axions arising in the compactifications of type IIA string theory on Calabi-Yau orientifolds with background fluxes (with nonperturbative effects included to ensure stabilization of all moduli). In this setup, we attempt to obtain the large effective axion decay constant in two different ways: by searching for a direction in field space in which the potential is sufficiently flat and by arriving at a very explicit stringy embedding of the Kim-Nilles-Peloso alignment mechanism. We do not find super-Planckian effective decay constants by either of the approaches. Furthermore, we find that the alignment angle of the Kim-Nilles-Peloso mechanism cannot be made arbitrarily small by adjusting the fluxes.

Enhancement of axion decay constants in type IIA theory?

If the Standard Model (SM) of elementary particle physics is assumed to hold good to arbitrarily high energies, then, for the best fit values of the parameters, the scalar potential of the Standard Model Higgs field turns negative at a high scale μinst . If the physics beyond the SM is such that it does not modify this feature of the Higgs potential and if the Hubble parameter during inflation ( Hinf ) is such that Hinf≫μinst , then, quantum fluctuations of the SM Higgs during inflation make it extremely unlikely that after inflation it will be found in the metastable vacuum at the weak scale. In this work, we assume that (i) during inflation, the SM Higgs is in Bunch–Davies vacuum state, and, (ii) the question about the stability of the effective potential must be answered in the frame of the freely falling observer (just like in Minkowski spacetime), and then use the well-known fact that the freely falling observer finds Bunch–Davies vacuum to be in thermal state to show that the probability to end up in the electroweak vacuum after inflation is reasonably high.