Eur. Phys. J. C 69, 201-217 (2010)
https://doi.org/10.1140/epjc/s10052-010-1373-8

What if supersymmetry breaking unifies beyond the GUT scale?

¹ TH Division, PH Department, CERN, 1211, Geneva 23, Switzerland
² William I. Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, MN, 55455, USA

mustafayev@physics.umn.edu

Received: 1 April 2010
Revised: 17 May 2010
Published online: 9 July 2010

Abstract

We study models in which soft supersymmetry-breaking parameters of the MSSM become universal at some unification scale, M _in, above the GUT scale, M _GUT. We assume that the scalar masses and gaugino masses have common values, m ₀ and m _1/2 respectively, at M _in. We use the renormalisation-group equations of the minimal supersymmetric SU(5) GUT to evaluate their evolutions down to M _GUT, studying their dependences on the unknown parameters of the SU(5) superpotential. After displaying some generic examples of the evolutions of the soft supersymmetry-breaking parameters, we discuss the effects on physical sparticle masses in some specific examples. We note, for example, that near-degeneracy between the lightest neutralino and the lighter stau is progressively disfavoured as M _in increases. This has the consequence, as we show in (m _1/2,m ₀) planes for several different values of tan β, that the stau-coannihilation region shrinks as M _in increases, and we delineate the regions of the (M _in,tan β) plane where it is absent altogether. Moreover, as M _in increases, the focus-point region recedes to larger values of m ₀ for any fixed tan β and m _1/2. We conclude that the regions of the (m _1/2,m ₀) plane that are commonly favoured in phenomenological analyses tend to disappear at large M _in.