Phase transition of decay rate from quantum tunneling to thermal activity
regimes is investigated in (3+1)-dimensional field theories with symmetry
breaking term fϕ. By applying the two independent criteria for the sharp
first-order transition to the same model, the upper and lower bounds of
critical value of the symmetry breaking parameter are obtained. Unlike two
dimensional case continuum states of the fluctuation operator near sphaleron
solution play an important role to determine the type of transition.Comment: Several mistakes including figures are corrected. Accepted version in
Phys. Lett.