Chiral gravitational waves from multi-phase magnetogenesis

TL;DR

This paper proposes a novel inflationary mechanism with parity-violating interactions that amplifies primordial magnetic fields and produces chiral gravitational waves, offering potential observational signatures for future gravitational-wave detectors.

Contribution

It introduces a non-slow-roll inflationary framework with parity violation that enhances magnetic fields and predicts detectable chiral gravitational-wave signals.

Findings

Chiral magnetic fields can be significantly amplified during brief non-slow-roll phases.

Distinct polarization-dependent spectral features are imprinted in the magnetic fields.

Chiral gravitational-wave backgrounds with characteristic frequency profiles are predicted.

Abstract

Cosmological vector fields are central to many early-Universe phenomena, including inflationary dynamics, primordial magnetogenesis, and dark-matter scenarios. However, constructing models able to generate cosmological magnetic fields while avoiding strong coupling, backreaction, and cosmic microwave background constraints remains challenging. We study a novel mechanism in which brief non--slow-roll phases during inflation amplify primordial magnetic fields at small scales, while maintaining theoretical consistency and observational viability. We incorporate parity-violating interactions in the vector sector and demonstrate, for the first time in a non--slow-roll framework, that chirality can significantly boost magnetic-field amplitudes and imprint distinctive polarization-dependent spectral features. We complement detailed numerical computations with an analytical treatment yielding compact expressions for chiral vector mode functions that reproduce the main spectral properties. We then develop a systematic formalism to evaluate the stochastic gravitational-wave background naturally induced at second order by these amplified fields, identifying both an intensity component and a circularly polarized contribution with characteristic frequency profiles. We discuss detection prospects with future multiband gravitational-wave observatories, showing that chiral signatures could provide a distinctive observational probe. Our results introduce new avenues for enhancing primordial magnetic fields and their associated gravitational-wave signals, opening promising possibilities for their future detection and interpretation, both with cosmological and gravitational wave probes.