Two-loop renormalization of tan beta and its gauge dependence

Renormalization of two-loop divergent corrections to the vacuum expectation values (v_1, v_2) of the two Higgs doublets in the minimal supersymmetric standard model, and their ratio tan beta=v_2/v_1, is discussed for general R_xi gauge fixings. When the renormalized (v_1, v_2) are defined to give the minimum of the loop-corrected effective potential, it is shown that, beyond the one-loop level, the dimensionful parameters in the R_xi gauge fixing term generate gauge dependence of the renormalized tan beta. Additional shifts of the Higgs fields are necessary to realize the gauge-independent renormalization of tan beta.