QCD axion from a spontaneously broken B - L gauge symmetry

Area of Science:

• Particle Physics
• Cosmology
• Supersymmetry

Background:

• The Peccei-Quinn (PQ) symmetry is a theoretical concept proposed to solve the strong CP problem in quantum chromodynamics.
• The minimal supersymmetric standard model (MSSM) is a theoretical extension of the Standard Model that includes supersymmetry.
• B-L symmetry is a theoretical extension of the Standard Model that introduces a new gauge symmetry associated with baryon and lepton number conservation.

Purpose of the Study:

• To realize a high-quality Peccei-Quinn (PQ) symmetry within a simple B-L extension of the minimal supersymmetric standard model (MSSM).
• To investigate the implications of a light gravitino mass for baryogenesis and cosmological observables.
• To explore potential future tests of the proposed model through 21cm line observations.

Main Methods:

• The study utilizes theoretical calculations within the framework of supersymmetric gauge theories.
• It analyzes the conditions required for preserving the PQ symmetry through a non-anomalous discrete gauged R-symmetry.
• The research explores the consequences of a small gravitino mass (m3 ≪ 100 GeV) on reheating temperature and baryogenesis scenarios.

Main Results:

• A simple B-L extension of the MSSM naturally accommodates a good quality PQ symmetry.
• A viable mass range for a light gravitino is identified, allowing for high reheating temperatures.
• The proposed scenario supports thermal leptogenesis and other baryogenesis mechanisms without astrophysical or cosmological problems.

Conclusions:

• The Peccei-Quinn symmetry can be effectively realized in extensions of the Standard Model with B-L symmetry.
• A light gravitino is a key feature of this model, with significant implications for early universe cosmology.
• Future 21cm line observations offer a promising avenue for testing the existence of such a light gravitino.