Against Tachyophobia

TL;DR

This paper explores the viability of extending the MSSM parameter space to include negative scalar masses, analyzing the implications for vacuum stability and cosmology through numerical searches for deep vacua.

Contribution

It demonstrates that negative scalar masses at the unification scale can evolve to acceptable values and identifies conditions for avoiding problematic vacua in MSSM models.

Findings

Negative scalar masses can evolve to positive values at the electroweak scale.

Deep charge- and color-breaking vacua can exist but may be cosmologically acceptable.

Inflation-induced scalar masses influence vacuum stability.

Abstract

We examine the possible extension of the parameter space of the minimal supersymmetric extension of the Standard Model (MSSM), as expressed via the renormalization-group equations in terms of universal soft supersymmetry-breaking terms at the unification scale, to include tachyonic input scalar masses. Many models with negative masses-squared for scalars at the unification scale may be viable because the small sizes of the masses-squared allow them to change signs during the renormalization-group evolution to the electroweak scale. However, in many cases, there is, in addition to the electroweak vacuum, a much deeper high-scale vacuum located along some F- and D-flat direction in the effective potential for the MSSM. We perform a numerical search for such vacua in both the CMSSM and the NUHM. We discuss the circumstances under which the existence of such a deep charge- and color-breaking vacuum is consistent with standard cosmology. A crucial role is played by the inflation--induced scalar masses, whereas thermal effects are often irrelevant.