Implications of an axino LSP for naturalness

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.