32,491 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.
Enhancement of Dark Matter Annihilation via Breit-Wigner Resonance
The Breit-Wigner enhancement of the thermally averaged annihilation cross
section is shown to provide a large boost factor when the dark
matter annihilation process nears a narrow resonance. We explicitly demonstrate
the evolution behavior of the Breit-Wigner enhanced as the function
of universe temperature for both the physical and unphysical pole cases. It is
found that both of the cases can lead an enough large boost factor to explain
the recent PAMELA, ATIC and PPB-BETS anomalies. We also calculate the coupling
of annihilation process, which is useful for an appropriate model building to
give the desired dark matter relic density.Comment: 4 pages, 4 figures, references added, accepted for publication in
Physical Review
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
Physical Model of the Immune Response of Bacteria Against Bacteriophage Through the Adaptive CRISPR-Cas Immune System
Bacteria and archaea have evolved an adaptive, heritable immune system that
recognizes and protects against viruses or plasmids. This system, known as the
CRISPR-Cas system, allows the host to recognize and incorporate short foreign
DNA or RNA sequences, called `spacers' into its CRISPR system. Spacers in the
CRISPR system provide a record of the history of bacteria and phage
coevolution. We use a physical model to study the dynamics of this coevolution
as it evolves stochastically over time. We focus on the impact of mutation and
recombination on bacteria and phage evolution and evasion. We discuss the
effect of different spacer deletion mechanisms on the coevolutionary dynamics.
We make predictions about bacteria and phage population growth, spacer
diversity within the CRISPR locus, and spacer protection against the phage
population.Comment: 37 pages, 13 figure
- …