655 research outputs found
Symmetry Nonrestoration at High Temperature in Little Higgs Models
A detailed study of the high temperature dynamics of the scalar sector of
Little Higgs scenarios, proposed to stabilize the electroweak scale, shows that
the electroweak gauge symmetry remains broken even at temperatures much larger
than the electroweak scale. Although we give explicit results for a particular
modification of the Littlest Higgs model, we expect that the main features are
generic. As a spin-off, we introduce a novel way of dealing with scalar
fluctuations in nonlinear sigma models, which might be of interest for
phenomenological applications.Comment: 23 pages, LaTeX, 4 figure
Phase Transitions at Preheating
Symmetry restoration processes during the non-equilibrium stage of
``preheating'' after inflation is studied. It is shown that symmetry
restoration is very efficient when the majority of created particles are
concentrated at energies much smaller than the temperature in equilibrium.
The strength of symmetry restoration measured in terms of the equivalent
temperature can exceed by many orders of magnitude. In some models the
effect can be equivalent to that if the temperature of instant reheating would
be close to the Planck scale. This can have an important impact on GUT and
axion models.Comment: Some statements are corrected. Also, comments of the referee of Phys.
Lett. B are taken into account; 12 pages, no figures, LaTe
The U.V. Price for Symmetry Non-Restoration
We study the non restoration of symmetries with a local order parameter in
field theory at finite temperature. After giving an interpretation of the
phenomenon, we show that hierarchy problems are a necessary condition for its
realization in renormalizable theories. We then use a large N treatment, and
find that high temperature symmetry can stay broken in this limit (in
opposition with a previous result), and further that the running of couplings
reinforces the effect in the simplest model with two scalars.Comment: 11 pages, 2 figs. Changes: added a discussion on trilinear couplings
in section 2 to meet referee's questio
1/N Expansion in Correlated Graphene
We examine the 1/N expansion, where N is the number of two-component Dirac
fermions, for Coulomb interactions in graphene with a gap of magnitude . We find that for , where is graphene's "fine
structure constant", there is a crossover as a function of distance from
the usual 3D Coulomb law, , to a 2D Coulomb interaction, , for . This effect
reflects the weak "confinement" of the electric field in the graphene plane.
The crossover also leads to unusual renormalization of the quasiparticle
velocity and gap at low momenta. We also discuss the differences between the
interaction potential in gapped graphene and usual QED for different coupling
regimes.Comment: 7 pages, 2 figures; expanded presentation, references adde
The Large N Limit and the High Temperature Phase Transition for the \phi^4 Theory
We study, with various methods (standard large N evaluation of the functional
integral for the effective potential, solution of the Schwinger-Dyson
equations), the high temperature phase transition for the -component
theory in the large limit. Our results fully confirm a previous
investigation of the problem, for arbitrary , with the method of the average
potential which employs renormalization group ideas. The phase transition is of
the second order with an effectively three-dimensional critical behaviour. }Comment: DESY-93-004, 23 pages, 2 figures available by fax upon reques
Soliton solutions of the improved quark mass density-dependent model at finite temperature
The improved quark mass density-dependent model (IQMDD) based on soliton bag
model is studied at finite temperature. Appling the finite temperature field
theory, the effective potential of the IQMDD model and the bag constant
have been calculated at different temperatures. It is shown that there is a
critical temperature . We also calculate the
soliton solutions of the IQMDD model at finite tmperature. It turns out that
when , there is a bag constant and the soliton solutions are
stable. However, when the bag constant and there is no
soliton solution, therefore, the confinement of quarks are removed quickly.Comment: 10 pages, 9 figures; Version to appear in Physical Review
Rayleigh-Ritz Variational Approximation and Symmetry Nonrestoration
The investigation of symmetry nonrestoration scenarios has led to a
controversy, with certain nonperturbative approximation schemes giving
indications in sharp disagreement with those found within conventional
perturbation theory. A Rayleigh-Ritz variational approach to the problem, which
might be useful in bridging the gap between perturbative and nonperturbative
viewpoints, is here proposed. As a first application, this approach is used in
the investigation of a -invariant thermal field theory with two
scalar fields, placing particular emphasis on the region of parameter space
that has been claimed to support symmetry nonrestoration.Comment: 9 pages, LaTex. To be published in Physics Letters
Extended Thomas-Fermi Density Functional for the Unitary Fermi Gas
We determine the energy density and the gradient
correction of the extended Thomas-Fermi
(ETF) density functional, where is number density and is Fermi
energy, for a trapped two-components Fermi gas with infinite scattering length
(unitary Fermi gas) on the basis of recent diffusion Monte Carlo (DMC)
calculations [Phys. Rev. Lett. {\bf 99}, 233201 (2007)]. In particular we find
that and give the best fit of the DMC data with an
even number of particles. We also study the odd-even splitting of the ground-state energy for the unitary gas in a
harmonic trap of frequency determining the constant . Finally
we investigate the effect of the gradient term in the time-dependent ETF model
by introducing generalized Galilei-invariant hydrodynamics equations.Comment: 7 pages, 3 figures, 1 table; corrected some typos; published in Phys.
Rev. A; added erratum: see also the unpublished diploma thesis of Marco
Manzoni (supervisors: N. Manini and L. Salasnich) at
http://www.mi.infm.it/manini/theses/manzoni.pd
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