A novel probe of supersymmetry in light of nanohertz gravitational waves

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 (including InPTA data), 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 U(1) and/or 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 U(1) or 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.

Automated summary

A new era of exploring the early Universe may have begun with the recent strong evidence for the stochastic gravitational wave (GW) background. This article proposes a new potential source of stochastic GWs in the minimal supersymmetric standard model (MSSM) by considering the axion field in the Higgs multiplets. The axion motion triggers the instability of the standard model gauge fields, producing stochastic GWs during inflation. The article also discusses the possibility of the axion within the MSSM driving inflation and the production of primordial magnetic fields.