On the consistency and cosmological evolution of modified Higgs Inflation

Abstract

This thesis presents a detailed and self-consistent analysis of post-inflationary reheating for a modified model of Higgs inflation, where a curvature-squared term is present in addition to the usual nonminimal Higgs-curvature coupling. This modification raises the cutoff of the theory to the Planck scale and introduces a new ‘scalaron’ degree of freedom. While the inflationary stage reduces to single field dynamics, the postinflationary oscillations of the Higgs and scalaron are intrinsically multifield in nature, as is the reheating mechanism. For particular choices of the new parameters, the homogeneous Higgs and scalaron condensates display special ‘critical’ dynamics, leading to the violent tachyonic production of Higgs and longitudinal gauge bosons. We investigate this feature firstly using an approximation where inhomogeneous fluctuations are treated as perturbations of the homogeneous fields, and subsequently using a full nonlinear semiclassical analysis. We find that initially noncritical dynamics become critical after only a few inflaton oscillations, and that for ‘Higgs-like’ parameters resembling pure Higgs inflation, reheating is complete after a few oscillations. While the reheating is somewhat slower for '$R^$2-like’ parameters which resemble the pure curvature-squared theory, all parameter choices yield predictions for inflationary observables which are consistent with current experimental values at a 1σ confidence level. However, future 21cm tomography experiments may be able to determine the mixed Higgs-R2 model from its pure counterparts. We also reinforce the validity of Higgs inflationary theories by responding to a claim that an arbitrarily large number of physics sectors can exist between the electroweak and Planck scales, due to a proposed self-healing mechanism of the Standard Model. We show that this so-called ‘Higgspersion’ mechanism, which would compromise the minimalistic motivation for Higgs inflation, is incompatible with fundamental quantum field theory principles.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Apostolos Pilaftsis (Supervisor) & Fedor Bezrukov (Supervisor)