605 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
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
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
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 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
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