A Novel Probe of Supersymmetry in Light of Nanohertz Gravitational Waves

TL;DR

This paper proposes that nanohertz gravitational waves detected recently could originate from axion-induced gauge field instabilities in the MSSM, offering a novel probe of supersymmetry and early Universe physics.

Contribution

It introduces a new supersymmetric model where axion fields generate stochastic GWs during inflation, linking gravitational wave signals to supersymmetry and early Universe phenomena.

Findings

Nanohertz GWs may indicate supersymmetry.

Axion fields in MSSM can produce observable GWs.

Primordial magnetic fields could be generated in this scenario.

Abstract

A new era of exploring the early Universe may have begun with the recent strong evidence for the stochastic gravitational wave (GW) background from the data reported by NANOGrav, EPTA, PPTA, and CPTA. Inspired by this, we propose a new potential source of stochastic GWs in the minimal supersymmetric standard model (MSSM), which could be the theory at a very high energy scale. This source is the "axion" field in the Higgs multiplets when the Higgs field takes a large value along the D-flat direction in the early Universe, for example, during inflation. The axion motion triggers the instability of the standard model ${\rm U}(1)$ and/or ${\rm SU}(3)$ gauge fields, producing stochastic GWs during the inflation. This scenario can be seen as a simple UV completion of the commonly studied models where an axion spectator/inflaton is coupled to a hidden ${\rm U}(1)$ or ${\rm SU}(N)$ gauge field without matter fields. Thus the nanohertz GWs may be a sign of supersymmetry. Primordial magnetic field production is also argued. In addition, we point out the simple possibility that this axion within the MSSM drives inflation.