Shear Viscosity in Weakly Coupled N-Component Scalar Field Theories

TL;DR

This paper investigates the behavior of shear viscosity to entropy density ratio in weakly coupled N-component scalar field theories, revealing complex temperature-dependent phenomena and improving computational methods.

Contribution

It introduces a systematic approach to compute shear viscosity using the Boltzmann equation and explores resonance and phase transition effects on eta/s.

Findings

eta/s exhibits a double dip due to resonances and phase transitions

Adding a goldstone mass term causes eta/s to decrease monotonically or reach a minimum

Enhanced computational method for shear viscosity calculations

Abstract

The rich phenomena of the shear viscosity (eta) to entropy density (s) ratio, eta/s, in weakly coupled N-component scalar field theories are studied. eta/s can have a "double dip" behavior due to resonances and the phase transition. If an explicit goldstone mass term is added, then eta/s can either decrease monotonically in temperature or, as seen in many other systems, reach a minimum at the phase transition. We also show how to go beyond the original variational approach to make the Boltzmann equation computation of eta systematic.