Journal Article

QCD-collapsed domain walls: QCD phase transition and gravitational wave spectroscopy

Bai, Yang, Korwar, Mrunal, Chen, Ting-Kuo

2023

Overview

A bstract For a discrete symmetry that is anomalous under QCD, the domain walls produced in the early universe from its spontaneous breaking can naturally annihilate due to QCD instanton effects. The gravitational waves generated from wall annihilation have their amplitude and frequency determined by both the discrete symmetry breaking scale and the QCD scale. The evidence of stochastic gravitational waves at nanohertz observed by pulsar timing array experiments suggests that the discrete-symmetry-breaking scale is around 100 TeV, assuming the domain-wall explanation. The annihilation temperature is about 100 MeV, which could naturally be below the QCD phase transition temperature. We point out that the QCD phase transition within some domains with an effective large QCD θ angle could be a first-order one. To derive the phase diagram in θ and temperature, we adopt a phenomenological linear sigma model with three quark flavors. The domain-wall explanation for the NANOGrav, EPTA, PPTA and CPTA results hints at a first-order QCD phase transition, which predicts additional gravitational waves at higher frequencies. If the initial formation of domain walls is also a first-order process, this class of domain-wall models predicts an interesting gravitational wave spectroscopy with frequencies spanning more than ten orders of magnitude, from nanohertz to 100 Hz.

• Publisher: Springer Berlin Heidelberg,Springer Nature B.V,Springer Nature,SpringerOpen
• Subject: Broken symmetry / Classical and Quantum Gravitation / Cosmology of Theories BSM / Domain walls / Early Universe Particle Physics / Elementary Particles / Flavor (particle physics) / Gravitational effects / Gravitational waves / High energy physics / Instantons / Phase diagrams / Phase transitions / Phase Transitions in the Early Universe / Physics / Physics and Astronomy / Pulsars / Quantum chromodynamics / Quantum Field Theories / Quantum Field Theory / Quantum Physics / Regular Article - Theoretical Physics / Relativity Theory / Spectroscopy / Spectrum analysis / String Theory / Symmetry / Transition temperature