Large $tan \beta$ from $SU(2)_R$ Gauge Symmetry
  Sufficient conditions for the relation $tan \beta \simeq m_t/m_b$ to hold in supersymmetric grand unified theories are formulated. Essential ingredients are the $SU(2)_R$ gauge symmetry and a discrete matter parity. The applicability of our conditions is illustrated by specific examples. Implications for neutrino masses are discussed. 
G.Lazarides and C.Panagiotakopoulos