Fermionic fluctuation corrections to bubble nucleation

We determine the fermionic corrections to the nucleation rate of bubbles at the electroweak phase transition. The fermion determinant is evaluated at finite temperature, both exactly and by using the gradient expansion. The gradient expansion is found to be a reliable approximation and is used to extrapolate to the large values of ${\nu }_{\mathit{n}}$=(2n+1)πT needed in the Matsubara sum. The contribution to the effective action is found to be negative. Only the top quark contribution is evaluated. It is smaller than the loop corrections from Higgs and W bosons and of opposite sign. © 1996 The American Physical Society.