468 research outputs found
Vector-axialvector mixing from a chiral effective field theory at finite temperature
We study the vector-axialvector mixing in a hot medium and its evolution
toward the chiral phase transition using different symmetry restoration
scenarios based on the generalized hidden local symmetry framework. We show
that the presence of the meson reduces the vector spectral function
around meson mass and enhances it around meson mass. The coupling
strength of to and vanishes at the critical temperature due
to the degenerate - masses. This feature holds rigorously in the
chiral limit and still stays intact to good approximation for the physical pion
mass.Comment: v2:11 pages, 6 figures, reorganized and expanded the text, new plots
and references added, main result and conclusions unchange
Mutually unbiased bases in dimension six: The four most distant bases
We consider the average distance between four bases in dimension six. The
distance between two orthonormal bases vanishes when the bases are the same,
and the distance reaches its maximal value of unity when the bases are
unbiased. We perform a numerical search for the maximum average distance and
find it to be strictly smaller than unity. This is strong evidence that no four
mutually unbiased bases exist in dimension six. We also provide a two-parameter
family of three bases which, together with the canonical basis, reach the
numerically-found maximum of the average distance, and we conduct a detailed
study of the structure of the extremal set of bases.Comment: 10 pages, 2 figures, 1 tabl
Equilibration in phi^4 theory in 3+1 dimensions
The process of equilibration in phi^4 theory is investigated for a
homogeneous system in 3+1 dimensions and a variety of out-of-equilibrium
initial conditions, both in the symmetric and broken phase, by means of the 2PI
effective action. Two Phi-derivable approximations including scattering effects
are used: the two-loop and the ``basketball'', the latter corresponding to the
truncation of the 2PI effective action at O(lambda^2). The approach to
equilibrium, as well as the kinetic and chemical equilibration is investigated.Comment: 32 pages, 14 figures, uses axodraw, minor corrections adde
Identity of the van der Waals Force and the Casimir Effect and the Irrelevance of these Phenomena to Sonoluminescence
We show that the Casimir, or zero-point, energy of a dilute dielectric ball,
or of a spherical bubble in a dielectric medium, coincides with the sum of the
van der Waals energies between the molecules that make up the medium. That
energy, which is finite and repulsive when self-energy and surface effects are
removed, may be unambiguously calculated by either dimensional continuation or
by zeta function regularization. This physical interpretation of the Casimir
energy seems unambiguous evidence that the bulk self-energy cannot be relevant
to sonoluminescence.Comment: 7 pages, no figures, REVTe
Characterization of quantum angular-momentum fluctuations via principal components
We elaborate an approach to quantum fluctuations of angular momentum based on
the diagonalization of the covariance matrix in two versions: real symmetric
and complex Hermitian. At difference with previous approaches this is SU(2)
invariant and avoids any difficulty caused by nontrivial commutators.
Meaningful uncertainty relations are derived which are nontrivial even for
vanishing mean angular momentum. We apply this approach to some relevant
states.Comment: 10 pages, Two column. New section II and some clarifying comment
Resonant photon creation in a three dimensional oscillating cavity
We analyze the problem of photon creation inside a perfectly conducting,
rectangular, three dimensional cavity with one oscillating wall. For some
particular values of the frequency of the oscillations the system is resonant.
We solve the field equation using multiple scale analysis and show that the
total number of photons inside the cavity grows exponentially in time. This is
also the case for slightly off-resonance situations. Although the spectrum of a
cavity is in general non equidistant, we show that the modes of the
electromagnetic field can be coupled, and that the rate of photon creation
strongly depends on this coupling. We also analyze the thermal enhancement of
the photon creation.Comment: 13 pages. New section on off-resonance motion is included. To appear
in Physical Review
Quantum electromagnetic field in a three dimensional oscillating cavity
We compute the photon creation inside a perfectly conducting, three
dimensional oscillating cavity, taking the polarization of the electromagnetic
field into account. As the boundary conditions for this field are both of
Dirichlet and (generalized) Neumann type, we analyze as a preliminary step the
dynamical Casimir effect for a scalar field satisfying generalized Neumann
boundary conditions. We show that particle production is enhanced with respect
to the case of Dirichlet boundary conditions. Then we consider the transverse
electric and transverse magnetic polarizations of the electromagnetic field.
For resonant frequencies, the total number of photons grows exponentially in
time for both polarizations, the rate being greater for transverse magnetic
modes.Comment: 11 pages, 1 figur
Steps on current-voltage characteristics of a silicon quantum dot covered by natural oxide
Considering a double-barrier structure formed by a silicon quantum dot
covered by natural oxide with two metallic terminals, we derive simple
conditions for a step-like voltage-current curve. Due to standard chemical
properties, doping phosphorus atoms located in a certain domain of the dot form
geometrically parallel current channels. The height of the current step
typically equals to (1.2 pA)N, where N=0,1,2,3... is the number of doping atoms
inside the domain, and only negligibly depends on the actual position of the
dopants. The found conditions are feasible in experimentally available
structures.Comment: 4 pages, 3 figure
Dynamical Casimir effect without boundary conditions
The moving-mirror problem is microscopically formulated without invoking the
external boundary conditions. The moving mirrors are described by the quantized
matter field interacting with the photon field, forming dynamical cavity
polaritons: photons in the cavity are dressed by electrons in the moving
mirrors. The effective Hamiltonian for the polariton is derived, and
corrections to the results based on the external boundary conditions are
discussed.Comment: 12 pages, 2 figure
Quantum fields in disequilibrium: neutral scalar bosons with long-range, inhomogeneous perturbations
Using Schwinger's quantum action principle, dispersion relations are obtained
for neutral scalar mesons interacting with bi-local sources. These relations
are used as the basis of a method for representing the effect of interactions
in the Gaussian approximation to field theory, and it is argued that a marked
inhomogeneity, in space-time dependence of the sources, forces a discrete
spectrum on the field. The development of such a system is characterized by
features commonly associated with chaos and self-organization (localization by
domain or cell formation). The Green functions play the role of an iterative
map in phase space. Stable systems reside at the fixed points of the map. The
present work can be applied to self-interacting theories by choosing suitable
properties for the sources. Rapid transport leads to a second order phase
transition and anomalous dispersion. Finally, it is shown that there is a
compact representation of the non-equilibrium dynamics in terms of generalized
chemical potentials, or equivalently as a pseudo-gauge theory, with an
imaginary charge. This analogy shows, more clearly, how dissipation and entropy
production are related to the source picture and transform a flip-flop like
behaviour between two reservoirs into the Landau problem in a constant
`magnetic field'. A summary of conventions and formalism is provided as a basis
for future work.Comment: 23 pages revte
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