New GUT predictions for quark and lepton mass ratios confronted with phenomenology

Abstract

Group theoretical factors from GUT symmetry breaking can lead to predictions for the ratios of quark and lepton masses (or Yukawa couplings) at the unification scale. Due to supersymmetric (SUSY) threshold corrections the viability of such predictions can depend strongly on the SUSY parameters. For three common minimal SUSY breaking scenarios with anomaly, gauge and gravity mediation we investigate which GUT scale ratios $m_e/m_d$, $m_{\mu }/m_s$, $y_{\tau }/y_b$ and $y_t/y_b$ are allowed when phenomenological constraints from electroweak precision observables, $B$ physics, $(g-2{)}_{\mu }$, mass-limits on sparticles from direct searches as well as, optionally, constraints from the observed dark matter density are taken into account. We derive possible new predictions for the GUT scale mass ratios and compare them with the phenomenologically allowed ranges. We find that new GUT scale predictions such as $m_{\mu }/m_s=9/2$ or 6 and $y_{\tau }/y_b=3/2$ or 2 are often favoured compared to the ubiquitous relations $m_{\mu }/m_s=3$ or $y_{\tau }/y_b=1$. They are viable for characteristic SUSY scenarios, testable at the CERN LHC and future colliders.

33 pages, 5 figures; references added; version to appear in Phys. Rev. D

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