283 research outputs found
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 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
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
Gauge Fields Out-Of-Equilibrium: A Gauge Invariant Formulation and the Coulomb Gauge
We study the abelian Higgs model out-of-equilibrium in two different
approaches, a gauge invariant formulation, proposed by Boyanovsky et al.
\cite{Boyanovsky:1996dc} and in the Coulomb gauge. We show that both approaches
become equivalent in a consistent one loop approximation. Furthermore, we carry
out a proper renormalization for the model in order to prepare the equations
for a numerical implementation. The additional degrees of freedom, which arise
in gauge theories, influence the behavior of the system dramatically. A
comparison with results in the 't Hooft-Feynman background gauge found by us
recently, shows very good agreement.Comment: 32 pages, 8 figure
Nonequilibrium dynamics: a renormalized computation scheme
We present a regularized and renormalized version of the one-loop nonlinear
relaxation equations that determine the non-equilibrium time evolution of a
classical (constant) field coupled to its quantum fluctuations. We obtain a
computational method in which the evaluation of divergent fluctuation integrals
and the evaluation of the exact finite parts are cleanly separated so as to
allow for a wide freedom in the choice of regularization and renormalization
schemes. We use dimensional regularization here. Within the same formalism we
analyze also the regularization and renormalization of the energy-momentum
tensor. The energy density serves to monitor the reliability of our numerical
computation. The method is applied to the simple case of a scalar phi^4 theory;
the results are similar to the ones found previously by other groups.Comment: 15 pages, 9 postscript figures, revtex; version published in Phys.
Rev, with minor corrections; improves the first version of 1996 by including
the discussion of energy momentum tenso
Fluctuation corrections to bubble nucleation
The fluctuation determinant which determines the preexponential factor of the
transition rate for minimal bubbles is computed for the electroweak theory with
. As the basic action we use the three-dimensional
high-temperature action including, besides temperature dependent masses, the one-loop contribution which makes the phase transition first order. The
results show that this contribution (which has then to be subtracted from the
exact result) gives the dominant contribution to the one-loop effective action.
The remaining correction is of the order of, but in general larger than the
critical bubble action and suppresses the transition rate. The results for the
Higgs field fluctuations are compared with those of an approximate heat kernel
computation of Kripfganz et al., good agreement is found for small bubbles,
strong deviations for large thin-wall bubbles.Comment: 19 pages, LaTeX, no macros, no figure
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