39,879 research outputs found
Baryon states with open beauty in the extended local hidden gauge approach
In this paper we examine the interaction of \bar B N, \bar B \Delta, \bar B^*
N and \bar B^* \Delta states, together with their coupled channels, using a
mapping from the light meson sector. The assumption that the heavy quarks act
as spectators at the quark level automatically leads us to the results of the
heavy quark spin symmetry for pion exchange and reproduces the results of the
Weinberg Tomozawa term, coming from light vector exchanges in the extended
local hidden gauge approach. With this dynamics we look for states dynamically
generated from the interaction and find two states with nearly zero width,
which we associate to the \Lambda_b(5912) and \Lambda_b(5920) states. The
states couple mostly to \bar B^* N, which are degenerate with the Weinberg
Tomozawa interaction. The difference of masses between these two states, with
J=1/2, 3/2 respectively, is due to pion exchange connecting these states to
intermediate \bar B N states. In addition to these two \Lambda_b states, we
find three more states with I=0, one of them nearly degenerate in two states of
J=1/2,3/2. Furthermore we also find eight more states in , two of them
degenerate in J=1/2, 3/2, and other two degenerate in J=1/2, 3/2, 5/2.Comment: 26 pages, 9 figures, 24 table
Baryon states with open charm in the extended local hidden gauge approach
In this paper we examine the interaction of and states,
together with their coupled channels, by using an extension of the local hidden
gauge formalism from the light meson sector, which is based on heavy quark spin
symmetry. The scheme is based on the use of the impulse approximation at the
quark level, with the heavy quarks acting as spectators, which occurs for the
dominant terms where there is the exchange of a light meson. The pion exchange
and the Weinberg-Tomozawa interactions are generalized and with this dynamics
we look for states generated from the interaction, with a unitary coupled
channels approach that mixes the pseudoscalar-baryon and vector-baryon states.
We find two states with nearly zero width which are associated to the
and . The lower state, with ,
couples to and , and the second one, with , to . In addition to these two states, we find four more states with
, one of them nearly degenerate in two states of .
Furthermore we find three states in , two of them degenerate in .Comment: v3: version to appear in Eur.Phys.J.
J06587-5558 -- A Very Unusual Polarised Radio Source
We have found a peculiar radio source in the field of one of the hottest
known clusters of galaxies 1E0657-56. It is slightly extended, highly polarised
(54% at 8.8GHz) and has a very steep spectrum, with alpha ~ -1 at 1.3 GHz,
steepening to ~ -1.5 at 8.8GHz (S \propto nu^alpha). No extragalactic sources
are known with such high integrated polarisation, and sources with spectra as
steep as this are rare. In this paper, we report the unusual properties of the
source J06587-5558 and speculate on its origin and optical identification.Comment: 5 pages, 6 figures, accepted by MNRAS letter
Calibration of GRB Luminosity Relations with Cosmography
For the use of Gamma-Ray Bursts (GRBs) to probe cosmology in a
cosmology-independent way, a new method has been proposed to obtain luminosity
distances of GRBs by interpolating directly from the Hubble diagram of SNe Ia,
and then calibrating GRB relations at high redshift. In this paper, following
the basic assumption in the interpolation method that objects at the same
redshift should have the same luminosity distance, we propose another approach
to calibrate GRB luminosity relations with cosmographic fitting directly from
SN Ia data. In cosmography, there is a well-known fitting formula which can
reflect the Hubble relation between luminosity distance and redshift with
cosmographic parameters which can be fitted from observation data. Using the
Cosmographic fitting results from the Union set of SNe Ia, we calibrate five
GRB relations using GRB sample at and deduce distance moduli of GRBs
at by generalizing above calibrated relations at high
redshift. Finally, we constrain the dark energy parameterization models of the
Chevallier-Polarski-Linder (CPL) model, the Jassal-Bagla-Padmanabhan (JBP)
model and the Alam model with GRB data at high redshift, as well as with the
Cosmic Microwave Background radiation (CMB) and the baryonic acoustic
oscillation (BAO) observations, and we find the CDM model is
consistent with the current data in 1- confidence region.Comment: 15 pages, 4 figures, 2 tables; accepted for publication in IJMP
Winding number transitions at finite temperature in the Abelian-Higgs model
Following our earlier investigations we examine the quantum-classical winding
number transition in the Abelian-Higgs system. It is demonstrated that the
sphaleron transition in this system is of the smooth second order type in the
full range of parameter space. Comparison of the action of classical vortices
with that of the sphaleron supports our finding.Comment: final version, to appear in J. Phys.
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