Adiabatic out-of-equilibrium solutions to the Boltzmann equation in warm inflation

Journal of High Energy Physics, Feb 2018

Mar Bastero-Gil, Arjun Berera, Rudnei O. Ramos, João G. Rosa

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Adiabatic out-of-equilibrium solutions to the Boltzmann equation in warm inflation

HJE Adiabatic out-of-equilibrium solutions to the Boltzmann equation in warm in ation Mar Bastero-Gil 0 1 2 4 5 Arjun Berera 0 1 2 3 5 Rudnei O. Ramos 0 1 2 5 Jo~ao G. Rosa 0 1 2 5 0 20550-013 Rio de Janeiro, RJ , Brazil 1 Edinburgh , EH9 3FD , United Kingdom 2 Granada-18071 , Spain 3 School of Physics and Astronomy, University of Edinburgh 4 Departamento de F sica Teorica y del Cosmos, Universidad de Granada 5 Campus de Santiago , 3810-183 Aveiro , Portugal We show that, in warm in ation, the nearly constant Hubble rate and temperature lead to an adiabatic evolution of the number density of particles interacting with the thermal bath, even if thermal equilibrium cannot be maintained. In this case, the number density is suppressed compared to the equilibrium value but the associated phasespace distribution retains approximately an equilibrium form, with a smaller amplitude and a slightly smaller e ective temperature. As an application, we explicitly construct a baryogenesis mechanism during warm in ation based on the out-of-equilibrium decay of particles in such an adiabatically evolving state. We show that this generically leads to small baryon isocurvature perturbations, within the bounds set by the Planck satellite. These are correlated with the main adiabatic curvature perturbations but exhibit a distinct spectral index, which may constitute a smoking gun for baryogenesis during warm in ation. Finally, we discuss the prospects for other applications of adiabatically evolving out-of-equilibrium states. Cosmology of Theories beyond the SM; Thermal Field Theory 1 Introduction 2 3 4 5 Adiabatic baryogenesis during warm in ation Generation of baryon isocurvature perturbations Summary and future prospects A Boltzmann equation for scattering processes if strong dissipation is attained at the end of the slow-roll evolution regime (see, e.g., refs. [8{11]). The greatest appeal of warm in ation lies perhaps in the fact that thermal in aton uctuations are directly sourced by dissipative processes, changing the form of the primordial spectrum of curvature perturbations and thus providing a unique observational window into the particle physics behind in ation [11{18]. In addition, we have recently shown that warm in ation can be consistently realized in a simple quantum eld theory framework requiring very few elds, the Warm Little In aton scenario [19], where the required atness of the in aton potential is not spoiled by thermal e ects (see also refs. [20{26] for earlier alternative models), paving the way for developing a complete particle physics description of in ation that can be fully tested with CMB and Large-Scale Structure (LSS) observations and possibly have implications for collider and particle physics data. Independently of the particle physics involved in sustaining a thermal bath during ination, a generic feature of warm in ation is the slow evolution of both the temperature and the Hubble parameter for the usually required 50{60 e-folds of expansion. Since both scattering and particle decay rates typically depend on the former, this implies that the ratio =H will generically evolve slowly during in ation. Consequently, as we explicitly show in this work for the rst time, particle species in the warm in ationary plasma can maintain distributions that are slowly evolving and out-of-equilibrium throughout in ation, whether or not they are directly involved in the dissipative dynamics. This may have an important impact not only on the in ationary dynamics and predictions themselves but also on the present abundance of di erent components. As an example of application of this novel observation, we show that this can lead to the production of a baryon asymmetry during in ation, a possibility that can be tested in the near future with CMB and LSS observations. This work is organized as follows. In section 2 we analyze the Boltzmann equation for a particle species interacting with a thermal bath for an adiabatic evolution of the ratio =H, focusing explicitly on the case of decays and inverse decays for concreteness. We then show that this leads to slowly varying out-of-equilibrium con gurations, obtaining the overall particle number density and its phase space distribution. We brie y discuss how similar results can be obtained for scattering processes. In section 3 we use these results to develop a generic baryogenesis (or leptogenesis) mechanism during in ation. Then, in section 4, we discuss how this generically leads to baryon isocurvature modes that give a small contribution to the primordial curvature perturbation spectrum. In section 5 we summarize our results and discuss their potential impact on other aspects of the in ationary and post-in ationary history. An appendix is included where some technical details are given. 2 Adiabatic out-of-equilibrium dynamics Let us consider a particle X interacting with a thermal bath at temperature T in an expanding Universe.1 For concreteness, let u (...truncated)


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Mar Bastero-Gil, Arjun Berera, Rudnei O. Ramos, João G. Rosa. Adiabatic out-of-equilibrium solutions to the Boltzmann equation in warm inflation, Journal of High Energy Physics, 2018, pp. 63, Volume 2018, Issue 2, DOI: 10.1007/JHEP02(2018)063