Implications of an axino LSP for naturalness

TL;DR

This paper explores how an axino as the lightest supersymmetric particle influences electroweak naturalness and axion physics, with implications for collider searches and current experimental limits.

Contribution

It analyzes the impact of axino LSP on Higgsino mass parameter and axion scale, providing collider phenomenology and current experimental constraints.

Findings

Light Higgsinos decay to axinos, producing distinctive collider signatures.

Current LHC results set limits on the Higgsino mass parameter and axion scale.

Comparison with standard and extended spectra highlights unique axino phenomenology.

Abstract

Both the naturalness of the electroweak symmetry breaking and the resolution of the strong CP problem may require a small Higgsino mass $\mu$ generated by a realization of the DFSZ axion model. Assuming the axino is the lightest supersymmetric particle, we study its implications on $\mu$ and the axion scale. Copiously produced light Higgsinos at collider (effectively only neutral NLSP pairs) eventually decay to axinos leaving prompt multi-leptons or displaced vertices which are being looked for at the LHC. We use latest LHC7+8 results to derive current limits on $\mu$ and the axion scale. Various Higgsino-axino phenomenology is illustrated by comparing with a standard case without lightest axinos as well as with a more general case with additional light gauginos in the spectrum.