Against tachyophobia

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 constrained MSSM (CMSSM) and a variant with nonuniversal Higgs masses (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.