Out of Equilibrium Dynamics of Supersymmetry at High Energy Density

We investigate the out of equilibrium dynamics of global chiral supersymmetry at finite energy density. We concentrate on two specific models. The first is the massive Wess-Zumino model which we study in a selfconsistent one-loop approximation. We find that for energy densities above a certain threshold, the fields are driven dynamically to a point in field space at which the fermionic component of the superfield is massless. The state, however is found to be unstable, indicating a breakdown of the one-loop approximation. To investigate further, we consider an O(N) massive chiral model which is solved exactly in the large $N$ limit. For sufficiently high energy densities, we find that for late times the fields reach a nonperturbative minimum of the effective potential degenerate with the perturbative minimum. This minimum is a true attractor for O(N) invariant states at high energy densities, and this provides a mechanism for determining which of the otherwise degenerate vacua is chosen by the dynamics. The final state for large energy density is a cloud of massless particles (both bosons and fermions) around this new nonperturbative supersymmetric minimum. By introducing boson masses which softly break the supersymmetry, we demonstrate a see-saw mechanism for generating small fermion masses. We discuss some of the cosmological implications of our results.Comment: 31 pages, 15 figure

Self-consistent bounces in two dimensions

We compute bounce solutions describing false vacuum decay in a Phi**4 model in two dimensions in the Hartree approximation, thus going beyond the usual one-loop corrections to the decay rate. We use zero energy mode functions of the fluctuation operator for the numerical computation of the functional determinant and the Green's function. We thus avoid the necessity of discretizing the spectrum, as it is necessary when one uses numerical techniques based on eigenfunctions. Regularization is performed in analogy of standard perturbation theory; the renormalization of the Hartree approximation is based on the two-particle point-irreducible (2PPI) scheme. The iteration towards the self-consistent solution is found to converge for some range of the parameters. Within this range we find the corrections to the leading one-loop approximation to be relatively small, not exceeding one order of magnitude in the total transition rate.Comment: 30 pages, 12 figure

Nonequilibrium dynamics in scalar hybrid models

We study by numerical simulations the transition from the metastable "false vacuum" to the broken symmetry phase in the preheating stage after cosmic inflation in a scalar hybrid model. We take quantum fluctuations and their back reaction into account by applying a one-loop bubble-resummation.Comment: 5 pages, 4 figures, contribution to the conference Strong and Electroweak Matter (SEWM2004), Helsinki, Finland, 16-19 June 200

Scalar O(N) Model at Finite Temperature -- 2PI Effective Potential in Different Approximations

We calculate the two-particle irreducible (2PI) effective potential of the O(N) linear sigma model in 1+1 dimensions. The approximations we use are the next-to-leading order of a 1/N expansion (for arbitrary N) and a kind of "resummed loop approximation" for N=1. We show that the effective potential of the 1/N expansion is convex for N=4 and N=10 whereas it is not for the "loop" expansion and the case N=1 of the 1/N expansion.Comment: LaTeX, 5 pages. Contribution to the Proceedings of 6th Conference on Strong and Electroweak Matter 2004 (SEWM04), Helsinki, Finland, 16-19 Jun 200

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 3+1 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 in particular show that quantum corrections become smaller away from the thin-wall case. In the thin-wall limit the numerical results are found to join into those obtained by a gradient expansion.Comment: 31 pages, 7 figure

Quantum Fluctuations around the Electroweak Sphaleron

We present an analysis of the quantum fluctuations around the electroweak sphaleron and calculate the associated determinant which gives the 1--loop correction to the sphaleron transition rate. The calculation differs in various technical aspects from a previous analysis by Carson et al. 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.Comment: DO-TH-93/19 39 pages, 5 figures (available on request as Postscript files or via Fax or mail), LaTeX, no macros neede

Quantum fluctuations of the electroweak sphaleron: Erratum and Addendum

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.Comment: 4 pages, Dortmund preprint DO-TH-93/19E