Misalignment dynamics of Scalar Condensates with Yukawa coupling: Particle and Entropy Production

TL;DR

This paper investigates the non-equilibrium evolution of a Yukawa-coupled scalar condensate, revealing energy-conserving dynamics, particle production, and potential spontaneous symmetry breaking with implications for cosmology.

Contribution

It introduces a fully renormalized, energy-conserving framework for scalar condensate dynamics with Yukawa coupling, including derivative expansion and analysis of asymptotic states.

Findings

Emergence of highly excited stationary states with specific distribution functions

Identification of entropy with entanglement entropy in the system

Potential for spontaneous symmetry breaking driven by dynamics

Abstract

Misalignment dynamics, the non-equilibrium evolution of a scalar (or pseudoscalar) condensate in a potential landscape, broadly describes a solution to the strong CP problem, a mechanism for cold dark matter production and (pre) reheating post inflation. Often, radiative corrections are included phenomenologically by replacing the potential by the effective potential which is a \emph{static quantity}, its usefulness is restricted to (near) equilibrium situations. We study the misalignment dynamics of a scalar condensate Yukawa coupled to $N_f$ fermions in a manifestly energy conserving, fully renormalized Hamiltonian framework. A large $N_f$ limit allows us to focus on the fermion degrees of freedom, which yield a negative contribution to the effective potential, a radiatively induced instability and ultraviolet divergent field renormalization. We introduce an adiabatic basis and an adiabatic expansion that embodies the derivative expansion in the effective action, the zeroth order is identified with the effective potential, higher orders account for the derivative expansion including field renormalization and describe profuse particle production. Energy conserving dynamics leads to the conjecture of emergent asymptotic highly excited stationary states with a distribution function $n_k(\infty)\propto 1/k^6$ and an extensive entropy which is identified with an entanglement entropy. Subtle aspects of renormalization associated with the initial value problem are analyzed and resolved. Possible new manifestations of asymptotic spontaneous symmetry breaking (SSB) as a consequence of the dynamics even in absence of tree level (SSB), and cosmological inferences are discussed.