659 research outputs found

### Thermal Quantum Fields in Static Electromagnetic Backgrounds

We present and discuss, at a general level, new mathematical results on the
spatial nonuniformity of thermal quantum fields coupled minimally to static
background electromagnetic potentials. Two distinct examples are worked through
in some detail: uniform (parallel and perpendicular) background electric and
magnetic fields coupled to a thermal quantum scalar field.Comment: 22 page

### Chemical potential as a source of stability for gravitating Skyrmions

A discussion of the stability of self gravitating Skyrmions, with a large
winding number N, in a Schwarzschild type of metric, is presented for the case
where an isospin chemical potential is introduced. It turns out that the
chemical potential stabilizes the behavior of the Skyrmion discussed previously
in the literature. This analysis is carried on in the framework of a
variational approach using different ansaetze for the radial profile of the
Skyrmion. We found a divergent behavior for the size of the Skyrmion,
associated to a certain critical value $\mu_c$ of the chemical potential. At
this point, the mass of the Skyrmion vanishes. $\mu_c$ is essentialy
independent of gravitating effects. The stability of a large N skyrmion against
decays into single particles is also discussed.Comment: 10 pages, 4 figures Small changes to the previous version and a new
referenc

### Thermal Pions ns Isospin Chemical Potential Effects

The density corrections, in terms of the isospin chemical potential $\mu_I$,
to the mass of the pions are investigated in the framework of the SU(2) low
energy effective chiral invariant lagrangian. As a function of temperature and
$\mu_I =0$, the mass remains quite stable, starting to grow for very high
values of $T$, confirming previous results. However, the dependence for a
non-vanishing chemical potential turns out to be much more dramatic. In
particular, there are interesting corrections to the mass when both effects
(temperature and chemical potential) are simultaneously present. At zero
temperature the $\pi ^{\pm}$ should condensate when $\mu_{I} = \mp m_{\pi}$.
This is not longer valid anymore at finite $T$. The mass of the $\pi_0$
acquires also a non trivial dependence on $\mu_I$ at finite $T$.Comment: 5 pages, 2 figures. To appear in the proceedings of the International
High-Energy Physics Conference on Quantum Chromodynamics QCD02, Montpellier,
2-9 July (2002

### The effects of quantum instantons on the thermodynamics of the CP^(N-1) model

Using the 1/N expansion, we study the influence of quantum instantons on the
thermodynamics of the CP^(N-1) model in 1+1 dimensions. We do this by
calculating the pressure to next-to-leading order in 1/N, without quantum
instanton contributions. The fact that the CP^1 model is equivalent to the O(3)
nonlinear sigma model, allows for a comparison to the full pressure up to 1/N^2
corrections for N=3. Assuming validity of the 1/N expansion for the CP^1 model
makes it possible to argue that the pressure for intermediate temperatures is
dominated by the effects of quantum instantons. A similar conclusion can be
drawn for general N values by using the fact that the entropy should always be
positive.Comment: 7 pages, 5 figures, revtex. To appear in PRD. Some arguments and
conclusions reformulate

### Photon Propagation in Space-Time with a Compactified Spatial Dimension

The one-loop effects of vacuum polarization induced by untwisted fermions in
QED in a nonsimply connected space-time with topology $S^{1}\times R^{3}$ are
investigated. It is found that photon propagation in this system is
anisotropic, appearing several massive photon modes and a superluminal
transverse mode. For small compactification radius $a$, the superluminal
velocity increases logarithmically with $a$. At low energies the photon masses
lead to an effective confinement of the gauge fields into a (2+1)-dimensional
manifold transverse to the compactified direction. The system shows a
topologically induced directional superconductivity.Comment: 5 pages, to appear in PL

### Casimir piston for massless scalar fields in three dimensions

We study the Casimir piston for massless scalar fields obeying Dirichlet
boundary conditions in a three dimensional cavity with sides of arbitrary
lengths $a,b$ and $c$ where $a$ is the plate separation. We obtain an exact
expression for the Casimir force on the piston valid for any values of the
three lengths. As in the electromagnetic case with perfect conductor
conditions, we find that the Casimir force is negative (attractive) regardless
of the values of $a$, $b$ and $c$. Though cases exist where the interior
contributes a positive (repulsive) Casimir force, the total Casimir force on
the piston is negative when the exterior contribution is included. We also
obtain an alternative expression for the Casimir force that is useful
computationally when the plate separation $a$ is large.Comment: 19 pages,3 figures; references updated and typos fixed to match
published versio

### Applications of the Mellin-Barnes integral representation

We apply the Mellin-Barnes integral representation to several situations of
interest in mathematical-physics. At the purely mathematical level, we derive
useful asymptotic expansions of different zeta-functions and partition
functions. These results are then employed in different topics of quantum field
theory, which include the high-temperature expansion of the free energy of a
scalar field in ultrastatic curved spacetime, the asymptotics of the $p$-brane
density of states, and an explicit approach to the asymptotics of the
determinants that appear in string theory.Comment: 20 pages, LaTe

### Skyrme model and Isospin Chemical Potential

We discuss the stability of the Skyrmion solution in the presence of a finite
isospin chemical potential $\mu$. Solving numerically the mass of the Skyrmion
as function of $\mu$, we find a critical value $\mu_c=222.8$ MeV where the
Skyrmion mass vanishes. We compare the exact numerical treatment with an
analytical discussion based on a special shape for the profile of the Skyrmion
due to Atiyah and Manton. The extension of this ansatz for finite $\mu$ works
quite well for $\mu<121$ MeV. Then, for small values of $\mu$, where the
analytical approach is valid, we consider the possibility of having an angular
deformation for the Skyrmionic profile, which is possible for finite values of
$\mu$. This is however, a small effect. Finally we introduce finite temperature
corrections, which strength the instability induced by the chemical potential,
finding the dependence of the critical temperature on $\mu$.Comment: 13 pages, 7 figure

### Skyrmions, Hadrons and isospin chemical potential

Using the Hamiltonian formulation, in terms of collective variables, we
explore the evolution of different skyrmionic parameters as function of the
isospin chemical potential ($\mu$), such as the energy density, the charge
density, the isoscalar radius and the isoscalar magnetic radius. We found that
the radii start to grow very fast for $\mu \gtrsim 140$ MeV, suggesting the
occurrence of a phase transition.Comment: 10 pages, 5 figure

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