363 research outputs found
Bound on the Photon Charge from the Phase Coherence of Extragalactic Radiation
If the photon possessed a nonzero charge, then electromagnetic waves
traveling along different paths would acquire Aharonov-Bohm phase differences.
The fact that such an effect has not hindered interferometric astronomy places
a bound on the photon charge estimated to be at the 10^(-32) e level if all
photons have the same charge and 10^(-46) e if different photons can carry
different charges.Comment: 8 pages, new bound added, version appearing in Phys. Rev. Let
Nonlinear Evolution of Anisotropic Cosmological Power
There has been growing interest in the possibility of testing more precisely
the assumption of statistical isotropy of primordial density perturbations. If
it is to be tested with galaxy surveys at distance scales <~ 10 Mpc, then
nonlinear evolution of anisotropic power must be understood. To this end, we
calculate the angular dependence of the power spectrum to third order in
perturbation theory for a primordial power spectrum with a quadrupole
dependence on the wavevector direction. Our results suggest that primordial
power anisotropies will be suppressed by <~ 7% in the quasilinear regime. We
also show that the skewness in the statistically anisotropic theory differs by
no more than 1% from that in the isotropic theory.Comment: 4 pages, 1 figure; accepted for publication in Physical Review
Letter
Domain Walls in Strongly Coupled Theories
Domain walls in strongly coupled gauge theories are discussed. A general
mechanism is suggested automatically leading to massless gauge bosons localized
on the wall. In one of the models considered, outside the wall the theory is in
the non-Abelian confining phase, while inside the wall it is in the Abelian
Coulomb phase. Confining property of the non-Abelian theories is a key
ingredient of the mechanism which may be of practical use in the context of the
dynamic compactification scenarios.
In supersymmetric (N=1) Yang-Mills theories the energy density of the wall
can be exactly calculated in the strong coupling regime. This calculation
presents a further example of non-trivial physical quantities that can be found
exactly by exploiting specific properties of supersymmetry. A key observation
is the fact that the wall in this theory is a BPS-saturated state.Comment: Several typos correcte
Radiatively Induced Lorentz and Gauge Symmetry Violation in Electrodynamics with Varying alpha
A time-varying fine structure constant alpha(t) could give rise to Lorentz-
and CPT-violating changes to the vacuum polarization, which would affect photon
propagation. Such changes to the effective action can violate gauge invariance,
but they are otherwise permitted. However, in the minimal theory of varying
alpha, no such terms are generated at lowest order. At second order, vacuum
polarization can generate an instability--a Lorentz-violating analogue of a
negative photon mass squared -m^2 proportional to alpha [(d alpha/dt) /
alpha]^2 log (Lambda^2), where Lambda is the cutoff for the low-energy
effective theory.Comment: 14 page
Operator Product Expansion, Heavy Quarks, QCD Duality and its Violations
The quark (gluon)-hadron duality constitutes a basis for the theoretical
treatment of a wide range of inclusive processes -- from hadronic \tau decays
and R_{e^+e^-}, to semileptonic and nonleptonic decay rates of heavy flavor
hadrons. A theoretical analysis of these processes is carried out by using the
operator product expansion in the Euclidean domain, with subsequent analytic
continuation to the Minkowski domain. We formulate the notion of the quark
(gluon)-hadron duality in quantitative terms, then classify various
contributions leading to violations of duality. A prominent role in the
violations of duality seems to belong to the so called exponential terms which,
conceptually, may represent the (truncated) tail of the power series. A
qualitative model, relying on an instanton background field, is developed,
allowing one to get an estimate of the exponential terms. We then discuss a
number of applications, mostly from heavy quark physics.Comment: 59 pages, 6 figures, epsf.sty required. Revised: Styllistic changes;
minor clarifications added; three references corrected; minor changes in the
color-related factor
Cosmic Microwave Background Statistics for a Direction-Dependent Primordial Power Spectrum
Statistical isotropy of primordial perturbations is a common assumption in
cosmology, but it is an assumption that should be tested. To this end, we
develop cosmic microwave background statistics for a primordial power spectrum
that depends on the direction, as well as the magnitude, of the Fourier
wavevector. We first consider a simple estimator that searches in a
model-independent way for anisotropy in the square of the temperature (and/or
polarization) fluctuation. We then construct the minimum-variance estimators
for the coefficients of a spherical-harmonic expansion of the
direction-dependence of the primordial power spectrum. To illustrate, we apply
these statistics to an inflation model with a quadrupole dependence of the
primordial power spectrum on direction and find that a power quadrupole as
small as 2.0% can be detected with the Planck satellite.Comment: Published in Phys. Rev. D; 8 pages; 1 table; Table 1 corrected;
references adde
Top quark longitudinal polarization near the threshold in l+ l- annihilation
We show that the longitudinal polarization of the top quarks produced in the
annihilation of e+ e- or mu+ mu- into tbar t at energies near the threshold is
not affected by the large Coulomb-type corrections, which greatly modify the
total cross section. Thus the longitudinal polarization, although small, may
provide an independent information on the mass and the width of the top quark,
largely independent of the uncertainty in alpha_s.Comment: 6 pages, LaTeX, no figures, added references, corrected typo
BPS Saturated Vacua Interpolation along One Compact Dimension
A class of generalized Wess-Zumino models with distinct vacua is
investigated. These models allow for BPS saturated vacua interpolation along
one compact spatial dimension. The properties of these interpolations are
studied.Comment: 8 pages, 4 figure
Domain walls in supersymmetric QCD: from weak to strong coupling
We consider domain walls that appear in supersymmetric QCD with Nf < Nc
massive flavours. In particular, for 2 Nf < Nc we explicitly construct the
domain walls that interpolate between vacua labeled by i and (i+ N_f). We show
that these solutions are Bogomol'nyi-Prasad-Sommerfield (BPS) saturated for any
value of the mass of the matter fields. This fact allows us to evaluate the
large mass limit of these domain walls. We comment on the relevance of these
solutions for supersymmetric gluodynamics.Comment: 4 pages, 4 figures, LaTex, uses psfig.st
Modified mode-expansion on a BPS wall related to the nonlinear realization
We propose a modified mode-expansion of the bulk fields in a BPS domain wall
background to obtain the effective theory on the wall. The broken SUSY is
nonlinearly realized on each mode defined by our mode-expansion. Our work
clarifies a relation between two different approaches to derive the effective
theory on a BPS wall, {\it i.e.} the nonlinear realization approach and the
mode-expansion approach. We also discuss a further modification that respects
the Lorentz and symmetries broken by the wall.Comment: LaTeX file, 21 pages, no figure
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