Jürgen Baacke

One loop corrections to the metastable vacuum decay

We evaluate the one-loop prefactor in the false vacuum decay rate in a theory of a self-interacting scalar field in

Quantum fluctuations around the electroweak sphaleron

3+1

The O(N) linear sigma model at finite temperature beyond the Hartree approximation

dimensions. We use a numerical method, established some time ago, which is based on a well-known theorem on functional determinants. The proper handling of zero modes and of renormalization is discussed. The numerical results show in particular that the quantum corrections strongly increase when one approaches the thin-wall case. In the thin-wall limit the numerical results are found to join into those obtained by a gradient expansion.

One-Loop Corrections to the Bubble Nucleation Rate at Finite Temperature

We present an analysis of the quantum fluctuations around the electroweak sphaleron and calculate the associated determinant which gives the one-loop correction to the sphaleron transition rate. The calculation differs in various technical aspects from a previous analysis by Carson and co-workers so that it can be considered as independent. The numerical results differ also, by several orders of magnitude, from those of this previous analysis; we find that the sphaleron transition rate is much less suppressed than found previously.

Quantum fluctuations of the electroweak sphaleron: Erratum and addendum

We study the O(N) linear sigma model with spontaneous symmetry breaking, using a Hartree-like ansatz with a classical field and variational masses. We go beyond the Hartree approximation by including the two-loop contribution, the sunset diagram, using the 2PPI expansion. We have computed numerically the effective potential at finite temperature. We find a phase transition of second order, while it is first order in the Hartree approximation. We also discuss some implications of the fact that in this order, the decay of the sigma into two pions affects the thermal diagrams.

Fluctuation corrections to bubble nucleation.

I present an evaluation of the 1-loop prefactor in the lifetime of a metastable state which decays at finite temperature by bubble nucleation. Such a state is considered in one-component ϕ4-model in three space dimensions. The calculation serves as a prototype application of a fast numerical method for evaluating the functional determinants that appear in semiclassical approximations.

Nonequilibrium evolution in scalarO(N)models with spontaneous symmetry breaking

We correct an error in our treatment of the tadpole contribution to the fluctuation determinant of the sphaleron, and also a minor mistake in a previous estimate. Thereby the overall agreement between the two existing exact computations and their consistency with the estimate is improved considerably.

Renormalization of nonequilibrium dynamics in FRW cosmology

I discuss the numerical computation of fluctuation corrections to instanton and sphaleron transition rates in quantum field theory. As an example of such a computation I will consider the bubble nucleation rate in the context of the electroweak phase transition. Some of the material presented here is based on work done in collaboration with V. G. Kiselev.

Renormalization of the nonequilibrium dynamics of fermions in a flat FRW universe

We consider the out-of-equilibrium evolution of a classical condensate field and its quantum fluctuations for a scalar O(N) model with spontaneously broken symmetry. In contrast to previous studies we do not consider the large N limit, but the case of finite N, including N=1, i.e., plain

Nonequilibrium evolution and symmetry structure of the large- N Φ 4 model at finite temperature

\lambda \phi^ 4