Supergravity Grand Unification, Proton Decay and Cosmological Constraints

Abstract

Properties and experimental predictions of a broad class of supergravity grand unified models possessing an $SU(5)$-type proton decay and $R$ parity are described. Models of this type can be described in terms of four parameters at the Gut scale in addition to those of the Standard Model i.e. $m_o$ (universal scalar mass), $m_{1/2}$ (universal gaugino mass), $A_o$ (cubic soft breaking parameter) and $\tan\beta=<H_2>/<H_1>$. Thus the 32 SUSY masses can be expressed in terms of $m_o, m_{1/2}, A_o \tan\beta$ and the as yet unknown t-quark mass $m_t$. Gut thresholds are examined and a simple model leads to grand unification consistent with $p$-decay data when $0.114<\alpha_3 (M_z)<0.135$, in agreement with current values of $\alpha_3 (M_Z)$.Proton decay is examined for the superheavy Higgs triplet mass $M_{H_3}<10M_G(M_G\simeq 1.5 \times10^{16}$~GeV) and squarks and gluinos lighter than 1 TeV. Throughout most of the parameter space chargino-neutralino scaling relations are predicted to hold: $2m_{\tilde{Z}_1}\cong m_{\tilde{W}_1}\cong m_{\tilde{Z}_2}, m_{\tilde{W}_1}\simeq(1/4)m_{\tilde{g}}$ (for $\mu>0$) or $m_{\tilde{W}_1} \simeq(1/3)m_{\tilde{g}}$ (for $\mu<0$), while $m_{\tilde{W}_2}\cong m_{\tilde{Z}_3}\cong m_{\tilde{Z}_4}>>m_{\tilde{Z}_1}$. Future proton decay experiments combined with LEP2 lead to further predictions, e.g. for the entire parameter space either proton decay should be seen at these or the$\tilde{W}_1$ seen at LEP2. Relic density constraints on the $\tilde{Z}_1$ further constrain the parameter space e.g. so that $m_t<165$~GeV, $m_h<105$~GeV, $m_{\tilde{W}_1} <100$~GeV and $m_{\tilde{Z}_1}<50$~GeV when $M_{H_3}/M_G < 6$. (Invited talk at Les Rencontres de Physique de la Vallee D'Aoste}