Inflation and primordial gravitational waves in scale-invariant quadratic gravity with Higgs
Anish Ghoshal (Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, Warsaw, 02-093, Poland); Debangshu Mukherjee (Department of Physics, Indian Institute of Technology Kanpur, Kanpur, 208016, India, School of Physics, Indian Institute of Science Education & Research Thiruvananthapuram, Vithura, Kerala, 695551, India); Massimiliano Rinaldi (Department of Physics, University of Trento, Via Sommarive 14, Trento, 38123, Italy, TIFPA-INFN, Via Sommarive 14, Trento, 38123, Italy)
In scale-invariant models of fundamental physics all mass scales are generated via spontaneous symmetry breaking. In this work, we study inflation in scale-invariant quadratic gravity, in which the Planck mass is generated classically by a scalar field, which evolves from an unstable fixed point to a stable one thus breaking scale-invariance. We investigate the dynamics by means of dynamical system standard techniques. By computing the spectral indices and comparing them with data, we put some constraints on the three dimensionless parameters of the theory. We show that certain regions of the parameter space will be within the range of future CMB missions like CMB-S4, LiteBIRD and STPol. The second half of the paper is dedicated to the analysis of inflationary first-order tensor perturbations and the calculation of the power spectrum of the gravitational waves. We comment on our results and compare them with the ones of mixed Starobinsky-Higgs inflation.
