A walking dilaton inflation

Hiroyuki Ishida,Shinya Matsuzaki

doi:10.1016/j.physletb.2020.135390

Abstract

We propose an inflationary scenario based on a many-flavor hidden QCD with eight flavors, which realizes the almost scale-invariant (walking) gauge dynamics. The theory predicts two types of composite (pseudo) Nambu-Goldstone bosons, the pions and the lightest scalar (dilaton) associated with the spontaneous chiral symmetry breaking and its simultaneous violation of the approximate scale invariance. The dilaton acts as an inflaton, where the inflaton potential is induced by the nonperturbative-scale anomaly linked with the underlying theory. The inflaton potential parameters are highly constrained by the walking nature, which are evaluated by straightforward nonperturbative analyses including lattice simulations. Due to the pseudo Nambu-Goldstone boson's natures and the intrinsic property for the chiral symmetry breaking in the walking gauge dynamics, the inflaton coupled to the pions naturally undergoes the small field inflation consistently with all the cosmological and astrophysical constraints presently placed by Planck 2018 data. When the theory is vector-likely coupled to the standard model in part in a way to realize a dynamical electroweak symmetry breaking, the reheating temperature is determined by the pion decays to electroweak gauge bosons. The proposed inflationary scenario would provide a dynamical origin for the small field inflation as well as the light pions as a smoking-gun to be probed by future experiments.

Highlights

Expanded cosmological evolution, inflation, is one of the most attractive and plausible period of our Universe to dynamically and simultaneously solve crucial cosmological problems, such as the flatness, the homogeneous and isotropic, and the horizon problems
The inflationary scenario is fitted with all the cosmological and astrophysical constraints presently placed by Planck 2018 data [3] and theoretical requirements on the walking dilaton and chiral pion physics
We have proposed an inflationary scenario of the CW-small field inflation (SFI) type, dynamically arising from a large NF walking gauge theory, what we called the hidden walking gauge theory

Summary

Introduction

Expanded cosmological evolution, inflation, is one of the most attractive and plausible period of our Universe to dynamically and simultaneously solve crucial cosmological problems, such as the flatness, the homogeneous and isotropic, and the horizon problems. A possible inflationary history goes like: We start from the chiral-scale broken phase in the vacuum for a many flavor walking gauge theory, where we have the walking dilaton and its potential of a CW type. We find that the present inflationary scenario is highly constrained to give a stringent bound on the fermion dynamical mass scale (mF) to be greater than 1011 GeV, and the reheating temperature (TR) is fixed by chiral pion decays to EW gauge bosons including photons to be 102 GeV, where the masses of walking dilaton and pions are constrained by several theoretical and astrophysical limits to be 108 GeV and 105 GeV, respectively. The presently proposed inflationary scenario of the CW-SFI type would provide the dynamical origin and explanation for the tiny inflaton coupling and somewhat light particles (the walking pions) as a smokinggun to be probed by future experiments

Walking dilaton potential

F Ri F Li

Mp2l χini dχ χend

Embedding into a dynamical scalegenesis

Constraints and predictions

Summary and discussion