Collider and astrophysical signatures of light scalars with enhanced $\tau$ couplings

TL;DR

This paper investigates collider and astrophysical signals of light scalars coupled to tau leptons, proposing experimental strategies at Belle II and analyzing astrophysical constraints to identify new physics beyond the Standard Model.

Contribution

It introduces a comprehensive analysis of tau-coupled light scalars, combining collider signatures with astrophysical bounds, and discusses methods to distinguish different particle types.

Findings

Belle II can effectively probe tau-coupled scalars through multiple channels.

Astrophysical bounds from supernovae and neutron star mergers are highly constraining.

Distinct signatures can differentiate between axion-like, CP-even, and CP-odd particles.

Abstract

Beyond Standard Model scenarios addressing the flavor puzzle and the hierarchy problem generally predict dominant new physics couplings with fermions of the third generation. In this Letter, we explore the collider and astrophysical signatures of new light scalar and pseudoscalar particles dominantly coupled to the $\tau$-lepton. The best experimental prospects are expected at Belle II through the $e^+e^-\to\tau^+\tau^-\gamma\gamma$, $\tau^+\tau^-\gamma$, $3\gamma$, mono-$\gamma$ processes, and the $\tau$ anomalous magnetic moment. The correlated effects in these searches can unambiguously point toward the underlying new physics dynamics. Moreover, we study astrophysics bounds - especially from core-collapse supernovae and neutron star mergers - finding them particularly effective and complementary to collider bounds. We carry out this program in the well-motivated context of axion-like particles as well as generic CP-even and CP-odd particles, highlighting possible ways to discriminate among them.