ρ PARAMETER CONSTRAINTS ON FOURTH GENERATION QUARK MASSES

Constraints on the masses of possible fourth generation quarks (a, υ) are obtained from measurements of the ρ parameter and the elements of the quark mixing matrix. Stringent mass limits are found when the off-diagonal elements V_tυ and V_ab are large. For example, with m_t=90 GeV and |V_tυ|≃0.5 we find m_a,v≤ 300 GeV. Stronger constraints are obtained as m_t or |V_tυ| increase.