891 research outputs found
Pion-to-vacuum vector and axial vector amplitudes and weak decays of pions in a magnetic field
We propose a model-independent parametrization for the one-pion-to-vacuum
matrix elements of the vector and axial vector hadronic currents in the
presence of an external uniform magnetic field. It is shown that, in general,
these hadronic matrix elements can be written in terms of several gauge
covariant Lorentz structures and form factors. Within this framework we obtain
a general expression for the weak decay and discuss
the corresponding limits of strong and weak external magnetic fields.Comment: 33 page
Constraints on economical 331 models from mixing of K, Bd and Bs neutral mesons
We analyze the effect of flavor changing neutral currents within 331 models.
In particular, we concentrate in the so-called "economical" models, which have
a minimal scalar sector. Taking into account the experimental measurements of
observables related to neutral K and B meson mixing, we study the resulting
bounds for angles and phases in the mixing matrix for the down quark sector,
and the mass and mixing parameters related to the new Z' gauge boson.Comment: 11 pages, 3 figures. Eqs. (8) and (9) corrected, to be published in
Phys. Rev.
Hadron structure in tau -> KKpi nu_tau decays
We analyse the hadronization structure of both vector and axial-vector
currents leading to tau -> KKpi nu_tau decays. At leading order in the 1/Nc
expansion, and considering only the contribution of the lightest resonances, we
work out, within the framework of the resonance chiral Lagrangian, the
structure of the local vertices involved in those processes. The couplings in
the resonance theory are constrained by imposing the asymptotic behaviour of
vector and axial-vector spectral functions ruled by QCD. In this way we predict
the hadron spectra and conclude that, contrarily to previous assertions, the
vector contribution dominates by far over the axial-vector one in all KKpi
charge channels.Comment: 32 pages, 7 figure
UV Emission line shifts of symbiotic binaries
Relative and absolute emission line shifts have been previously found for
symbiotic binaries, but their cause was not clear. This work aims to better
understand the emission line shifts. Positions of strong emission lines were
measured on archival UV spectra of Z And, AG Dra, RW Hya, SY Mus and AX Per and
relative shifts between the lines of different ions compared. Profiles of lines
of RW Hya and Z And were also examined. The reality of the relative shift
between resonance and intercombination lines of several times ionised atoms was
clearly shown except for AG Dra. This redshift shows a well defined variation
with orbital phase for Z And and RW Hya. In addition the intercombination lines
from more ionised atoms and especially OIV are redshifted with respect to those
from less ionised atoms. Other effects are seen in the profiles. The
resonance-intercombination line shift variation can be explained in quiescence
by P Cygni shorter wavelength component absorption, due to the wind of the cool
component, which is specially strong in inferior conjunction of this cool
giant. The velocity stratification permits absorption of line emission. The
relative intercombination line shifts may be connected with varying occultation
of line emission near an accretion disk, which is optically thick in the
continuum.Comment: 14 pages, 11 figures, to appear in A&
Quasiparticles at the verge of localization near the Mott metal-insulator transition in a two-dimensional material
The dynamics of charge carriers close to the Mott transition is explored
theoretically and experimentally in the quasi two-dimensional organic
charge-transfer salt -(BEDT-TTF)Cu[N(CN)]BrCl, with
varying Br content. The frequency dependence of the conductivity deviates
significantly from simple Drude model behavior: there is a strong
redistribution of spectral weight as the Mott transition is approached and with
temperature. The effective mass of the quasiparticles increases considerably
when coming close to the insulating phase. A dynamical mean-field-theory
treatment of the relevant Hubbard model gives a good quantitative description
of the experimental data.Comment: 5 pages, 4 figure
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