381 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

### 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 $B(T)$
have been calculated at different temperatures. It is shown that there is a
critical temperature $T_{C}\simeq 110 \mathrm{MeV}$. We also calculate the
soliton solutions of the IQMDD model at finite tmperature. It turns out that
when $T<T_{C}$, there is a bag constant $B(T)$ and the soliton solutions are
stable. However, when $T>T_{C}$ the bag constant $B(T)=0$ 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

### 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 $\Delta
= 2 m$. We find that for $N\alpha\gg1$, where $\alpha$ is graphene's "fine
structure constant", there is a crossover as a function of distance $r$ from
the usual 3D Coulomb law, $V(r) \sim 1/r$, to a 2D Coulomb interaction, $V(r)
\sim \ln(N\alpha/mr)$, for $m^{-1} \ll r \ll m^{-1} N \alpha/6$. 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

### Extended Thomas-Fermi Density Functional for the Unitary Fermi Gas

We determine the energy density $\xi (3/5) n \epsilon_F$ and the gradient
correction $\lambda \hbar^2(\nabla n)^2/(8m n)$ of the extended Thomas-Fermi
(ETF) density functional, where $n$ is number density and $\epsilon_F$ 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 $\xi=0.455$ and $\lambda=0.13$ give the best fit of the DMC data with an
even number $N$ of particles. We also study the odd-even splitting $\gamma
N^{1/9} \hbar \omega$ of the ground-state energy for the unitary gas in a
harmonic trap of frequency $\omega$ determining the constant $\gamma$. 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

### Higgs Self-Coupling as a Probe of Electroweak Phase Transition

We argue that, within a broad class of extensions of the Standard Model,
there is a tight corellation between the dynamics of the electroweak phase
transition and the cubic self-coupling of the Higgs boson: Models which exhibit
a strong first-order EWPT predict a large deviation of the Higgs self-coupling
from the Standard Model prediction, as long as no accidental cancellations
occur. Order-one deviations are typical. This shift would be observable at the
Large Hadron Collider if the proposed luminosity or energy upgrades are
realized, as well as at a future electron-positron collider such as the
proposed International Linear Collider. These measurements would provide a
laboratory test of the dynamics of the electroweak phase transition.Comment: 20 pages, 6 figures; minor changes to clarify a few point

### Vector order parameter in general relativity. Covariant equations

Phase transitions with spontaneous symmetry breaking and vector order
parameter are considered in multidimensional theory of general relativity.
Covariant equations, describing the gravitational properties of topological
defects, are derived. The topological defects are classified in accordance with
the symmetry of the covariant derivative of the vector order parameter. The
abilities of the derived equations are demonstrated in application to the brane
world concept. New solutions of the Einstein equations with a transverse vector
order parameter are presented. In the vicinity of phase transition the
solutions are found analytically

### Three-dimensional Roton-Excitations and Supersolid formation in Rydberg-excited Bose-Einstein Condensates

We study the behavior of a Bose-Einstein condensate in which atoms are weakly
coupled to a highly excited Rydberg state. Since the latter have very strong
van der Waals interactions, this coupling induces effective, nonlocal
interactions between the dressed ground state atoms, which, opposed to dipolar
interactions, are isotropically repulsive. Yet, one finds partial attraction in
momentum space, giving rise to a roton-maxon excitation spectrum and a
transition to a supersolid state in three-dimensional condensates. A detailed
analysis of decoherence and loss mechanisms suggests that these phenomena are
observable with current experimental capabilities.Comment: 4 pages, 5 figure

- …