258 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 of the chemical potential. At
this point, the mass of the Skyrmion vanishes. 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
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 and where 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 , and . 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 is large.Comment: 19 pages,3 figures; references updated and typos fixed to match
published versio
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
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 -brane
density of states, and an explicit approach to the asymptotics of the
determinants that appear in string theory.Comment: 20 pages, LaTe
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 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 , the superluminal
velocity increases logarithmically with . 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
Local Casimir Energies for a Thin Spherical Shell
The local Casimir energy density for a massless scalar field associated with
step-function potentials in a 3+1 dimensional spherical geometry is considered.
The potential is chosen to be zero except in a shell of thickness ,
where it has height , with the constraint . In the limit of zero
thickness, an ideal -function shell is recovered. The behavior of the
energy density as the surface of the shell is approached is studied in both the
strong and weak coupling regimes. The former case corresponds to the well-known
Dirichlet shell limit. New results, which shed light on the nature of surface
divergences and on the energy contained within the shell, are obtained in the
weak coupling limit, and for a shell of finite thickness. In the case of zero
thickness, the energy has a contribution not only from the local energy
density, but from an energy term residing entirely on the surface. It is shown
that the latter coincides with the integrated local energy density within the
shell. We also study the dependence of local and global quantities on the
conformal parameter. In particular new insight is provided on the reason for
the divergence in the global Casimir energy in third order in the coupling.Comment: 16 pages, revtex 4, no figures. Major additions, clarifications, and
corections, references adde
Complete High Temperature Expansions for One-Loop Finite Temperature Effects
We develop exact, simple closed form expressions for partition functions
associated with relativistic bosons and fermions in odd spatial dimensions.
These expressions, valid at high temperature, include the effects of a
non-trivial Polyakov loop and generalize well-known high temperature
expansions. The key technical point is the proof of a set of Bessel function
identities which resum low temperature expansions into high temperature
expansions. The complete expressions for these partition functions can be used
to obtain one-loop finite temperature contributions to effective potentials,
and thus free energies and pressures.Comment: 9 pages, RevTeX, no figures. To be published in Phys. Rev D. v2 has
revised introduction and conclusions, plus a few typographical errors are
corrected; v3 corrects one typ
Fermion Condensates of massless at Finite Density in non-trivial Topological Sectors
Vacuum expectation values of products of local bilinears are
computed in massless at finite density. It is shown that chiral
condensates exhibit an oscillatory inhomogeneous behaviour depending on the
chemical potential. The use of a path-integral approach clarifies the
connection of this phenomenon with the topological structure of the theory.Comment: 16 pages, no figures, To be published in Phys.Rev.
- …