Working in the context of the CMSSM, we argue that phenomenological constraints now require the universal soft supersymmetry-breaking scalar mass m 0 be non-zero at the input GUT scale. This conclusion is primarily imposed by the LEP lower limit on the Higgs mass and the requirement that the lightest supersymmetric particle not be charged. We find that m 0 > 0 for all tan β if µ < 0, and m 0 = 0 may be allowed for µ > 0 only when tan β ∼ 8 and one allows an uncertainty of 3+ GeV in the theoretical calculation of the Higgs mass. Upper limits on flavour-changing neutral interactions in the MSSM squark sector allow substantial violations of non-universality in the m 0 values, even if their magnitudes are comparable to the lower limit we find in the CMSSM. Also, we show that our lower limit on m 0 at the GUT scale in the CMSSM is compatible with the no-scale boundary condition m 0 = 0 at the Planck scale.
CERN-TH/2001-256 August 2001Motivated by the naturalness of the gauge hierarchy [1], TeV-scale supersymmetry is, perhaps, the most plausible scenario for low-energy physics beyond the Standard Model. Here we study the minimal supersymmetric extension of the Standard model (MSSM). Some of the greatest puzzles of supersymmetry are associated with its breaking. There is no consensus on the origin of supersymmetry breaking, even within string (or M) theory, and we do not know what fixes the scale of supersymmetry breaking (and how). Within this general area of puzzles, there are minor puzzles, such as questions whether soft supersymmetry-breaking scalar and gaugino masses, m 0 and m 1/2 , respectively, are universal. In particular, generationdependent scalar masses would threaten the observed suppression of flavour-changing neutral interactions (FCNI) [2], whereas differences between the scalar masses of sparticles with different gauge quantum numbers would be less problematic. In other words, one needsto a very good approximation, and similarly for the ℓ R and for the squarks. On the other hand, there is no strong phenomenological reason why m ℓ L 0 = m ℓ R 0 , or why squark and slepton masses should be equal. For the moment, however, we work in the context of the constrained MSSM (CMSSM), where this extended universality is assumed.Some proposed mechanisms for supersymmetry breaking in string theory yield generationdependent scalar masses, for example because they depend on moduli characterizing the string vacuum, whereas other mechanisms are naturally generation-independent. The former are a priori in conflict with the constraints imposed by FCNI. Many of the latter mechanisms achieve consistency with these limits by resuscitating no-scale gravity [3], in which the soft supersymmetry-breaking scalar masses vanish at the input supersymmetric grand-unification (GUT) scale. These input values are renormalized by gauge and Yukawa interactions at lower scales. The renormalizations by gauge interactions are generation-independent, whereas those by Yukawa interactions break universality by amounts related to quark ...