1,387 research outputs found
Thermal Field Theory in a wire: Applications of Thermal Field Theory methods to the propagation of photons in a one-dimensional plasma
We apply the Thermal Field Theory (TFT) methods to study the propagation of
photons in a plasma wire, that is, a system in which the electrons are confined
to a one-dimensional tube or wire, but are otherwise free. We find the
appropriate expression for the photon \emph{free-field} propagator in such a
medium, and write down the dispersion relation in terms of the free-field
propagator and the photon self-energy. The self-energy is then calculated in
the one-loop approximation and the corresponding dispersion relation is
determined and studied in some detail. Our work differs from previous work on
this subject in that we do not adopt any specific electronic wave functions in
the coordinates that are transverse to the idealized wire, or rely on
particular features of the electronic structure. We treat the electrons as a
free gas of particles, constrained to move in one dimension, but otherwise in a
model-independent way only following the rules of TFT adapted to the situation
at hand. For the appropriate conditions of the plasma the \emph{static
approximation} can be employed and the dispersion relation reduces to the
results obtained in previous works, but the formula that we obtain is valid
under more general conditions, including those in which the static
approximation is not valid. In particular, the dispersion relation has several
branches, which are not revealed if the static approximation is used. The
dispersion relations obtained reproduce several unique features of these
systems that have been observed in recent experiments.Comment: 17 pages Revised and extended discussion of the dispersion relation
Calculating two- and three-body decays with FeynArts and FormCalc
The Feynman diagram generator FeynArts and the computer algebra program
FormCalc allow for an automatic computation of 2->2 and 2->3 scattering
processes in High Energy Physics. We have extended this package by four new
kinematical routines and adapted one existing routine in order to accomodate
also two- and three-body decays of massive particles. This makes it possible to
compute automatically two- and three-body particle decay widths and decay
energy distributions as well as resonant particle production within the
Standard Model and the Minimal Supersymmetric Standard Model at the tree- and
loop-level. The use of the program is illustrated with three standard examples:
h->b\bar{b}, \mu->e\bar{\nu}_e\nu_\mu, and Z->\nu_e\bar{\nu}_e.Comment: 8 pages, 1 figur
The effect of early dark matter halos on reionization
The annihilation of dark matter particles releases energy, ionizing some of
the gas in the Universe. We investigate the effect of dark matter halos on
reionization. We show that the effect depends on the assumed density profile,
the particle mass, and the assumed minimum halo mass. For NFW halos and typical
WIMPs, we find the effect to be quite small. However, light dark matter
candidates in the MeV range can contribute significantly to reionization and
can make an important contribution to the measured optical depth. This effect
may be used to constrain light dark matter models. We also study the effect of
varying the halo density profile on reionization.Comment: Minor changes from v2. Accepted for publication in Phys. Rev.
SU(3) Gauge Theory with Adjoint Fermions
We analyze the finite temperature phase diagram of QCD with fermions in the
adjoint representation. The simulations performed with four dynamical Majorana
fermions, which is equivalent to two Dirac fermions, show that the
deconfinement and chiral phase transitions occur at two distinct temperatures,
. While the deconfinement transition
is first order we find evidence for a continuous chiral transition. We also
present potentials for and both for fundamental and adjoint fermion-antifermion pairs.Comment: LATTICE98(hightemp), 3 pages LaTeX2e, espcrc2 style, 6 eps figure
Vacuum entanglement enhancement by a weak gravitational field
Separate regions in space are generally entangled, even in the vacuum state.
It is known that this entanglement can be swapped to separated Unruh-DeWitt
detectors, i.e., that the vacuum can serve as a source of entanglement. Here,
we demonstrate that, in the presence of curvature, the amount of entanglement
that Unruh-DeWitt detectors can extract from the vacuum can be increased.Comment: 6 pages, 1 figur
Hydrogen Atom in Relativistic Motion
The Lorentz contraction of bound states in field theory is often appealed to
in qualitative descriptions of high energy particle collisions. Surprisingly,
the contraction has not been demonstrated explicitly even in simple cases such
as the hydrogen atom. It requires a calculation of wave functions evaluated at
equal (ordinary) time for bound states in motion. Such wave functions are not
obtained by kinematic boosts from the rest frame. Starting from the exact
Bethe-Salpeter equation we derive the equal-time wave function of a
fermion-antifermion bound state in QED, i.e., positronium or the hydrogen atom,
in any frame to leading order in alpha. We show explicitly that the bound state
energy transforms as the fourth component of a vector and that the wave
function of the fermion-antifermion Fock state contracts as expected.
Transverse photon exchange contributes at leading order to the binding energy
of the bound state in motion. We study the general features of the
corresponding fermion-antifermion-photon Fock states, and show that they do not
transform by simply contracting. We verify that the wave function reduces to
the light-front one in the infinite momentum frame.Comment: 20 pages, 10 figures; v2: some changes in discussion, accepted for
publication in Phys.Rev.
Interactions of keV sterile neutrinos with matter
A sterile neutrino with mass of several keV is a well-motivated dark-matter
candidate, and it can also explain the observed velocities of pulsars via
anisotropic emission of sterile neutrinos from a cooling neutron star. We
discuss the interactions of such relic particles with matter and comment on the
prospects of future direct detection experiments. A relic sterile neutrino can
interact, via sterile-active mixing, with matter fermions by means of
electroweak currents, with the final state containing a relativistic active
neutrino. The recoil momentum impacted onto a matter fermion is determined by
the sterile neutrino mass and is enough to ionize atoms and flip the spins of
nuclei. While this suggests a possibility of direct experimental detection, we
calculate the rates and show that building a realistic detector of the required
size would be a daunting challenge.Comment: 5 pages, 1 figur
Renormalization group approach to 2D Coulomb interacting Dirac fermions with random gauge potential
We argue that massless Dirac particles in two spatial dimensions with
Coulomb repulsion and quenched random gauge field are described by a manifold
of fixed points which can be accessed perturbatively in disorder and
interaction strength, thereby confirming and extending the results of
arXiv:0707.4171. At small interaction and small randomness, there is an
infra-red stable fixed curve which merges with the strongly interacting
infra-red unstable line at a critical endpoint, along which the dynamical
critical exponent .Comment: 4 pages, 4 figure
V,W and X in Technicolour Models
Light techni-fermions and pseudo Goldstone bosons that contribute to the
electroweak radiative correction parameters V,W and X may relax the constraints
on technicolour models from the experimental values of the parameters S and T.
Order of magnitude estimates of the contributions to V,W and X from light
techni-leptons are made when the the techni-neutrino has a small Dirac mass or
a large Majorana mass. The contributions to V,W and X from pseudo Goldstone
bosons are calculated in a gauged chiral Lagrangian. Estimates of V,W and X in
one family technicolour models suggest that the upper bounds on S and T should
be relaxed by between 0.1 and 1 depending upon the precise particle spectrum.Comment: 19 pages + 2 pages of ps figs, SWAT/1
Three-Flavor Partially Quenched Chiral Perturbation Theory at NNLO for Meson Masses and Decay Constants
We discuss Partially Quenched Chiral Perturbation Theory (PQPT) and
possible fitting strategies to Lattice QCD data at next-to-next-to-leading
order (NNLO) in the mesonic sector. We also present a complete calculation of
the masses of the charged pseudoscalar mesons, in the supersymmetric
formulation of PQPT. Explicit analytical results are given for up to
three nondegenerate sea quark flavors, along with the previously unpublished
expression for the pseudoscalar meson decay constant for three nondegenerate
sea quark flavors. The numerical analysis in this paper demonstrates that the
corrections at NNLO are sizable, as expected from earlier work.Comment: 31 pages, numerical discussion extended including convergence NLO to
NNL
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