376 research outputs found
Discovery of Blue Hook Stars in the Massive Globular Cluster M54
We present BV photometry centered on the globular cluster M54 (NGC 6715). The
color-magnitude diagram clearly shows a blue horizontal branch extending
anomalously beyond the zero age horizontal branch theoretical models. These
kinds of horizontal branch stars (also called ``blue hook'' stars), which go
beyond the lower limit of the envelope mass of canonical horizontal branch hot
stars, have so far been known to exist in only a few globular clusters: NGC
2808, Omega Centauri (NGC 5139), NGC 6273, and NGC 6388. Those clusters, like
M54, are among the most luminous in our Galaxy, indicating a possible
correlation between the existence of these types of horizontal branch stars and
the total mass of the cluster. A gap in the observed horizontal branch of M54
around T(eff)= 27000 K could be interpreted within the late helium flash
theoretical scenario, a possible explanation for the origin of those stars.Comment: 10 pages, 2 figures, accepted for publication in the Astrophysical
Journa
Structure of Lambda(1405) and chiral dynamics
We report on a recent theoretical work on the structure of the Lambda(1405)
resonance within a chiral unitary approach, in which the resonance is
dynamically generated in meson-baryon scattering. Studying the analytic
structure of the scattering amplitude, we have found that there are two poles
lying around energies of Lambda(1405) with different widths and couplings to
the meson-baryon states. We discuss reactions to conform the double pole
structure in experiment and elastic K^- p scattering at low energies.Comment: 4 pages, LaTeX, 2 eps figures. Talk given at 10th International
Conference on the Structure of Baryons (Baryon 2004) at Palaiseau (France),
25-29 October 200
In-medium modification of the isovector pion-nucleon amplitude
We study the in-medium modification of the isovector pi N amplitude using a
non-linear representation of the sigma model but keeping the scalar degree of
freedom. We check that our result does not depend on the representation. We
discuss the connection with other approaches based on chiral perturbation
theory.Comment: 7 page
Testing the nature of the resonance in proton-induced production
The resonance has been recently studied in a unitarized
coupled channel formalism with , , and
as constituents blocks. We provide a theoretical study of the
predictions of this model in physical observables of the and
reactions. In particular, we show that the ratio
between the and mass distributions can provide
valuable information on the ratio of the couplings of the
resonance to and that the theory predicts.
Calculations are done for energies which are accessible in an experimental
facility like COSY at J\"ulich or the developing CSR facility at Lanzhou.Comment: 8 pages, 4 figures. Submitted to Eur.Phys.J.
Self-consistent anisotropic oscillator with cranked angular and vortex velocities
The Kelvin circulation is the kinematical Hermitian observable that measures
the true character of nuclear rotation. For the anisotropic oscillator, mean
field solutions with fixed angular momentum and Kelvin circulation are derived
in analytic form. The cranking Lagrange multipliers corresponding to the two
constraints are the angular and vortex velocities. Self-consistent solutions
are reported with a constraint to constant volume.Comment: 12 pages, LaTex/RevTex, Phys. Rev. C4
Dynamical Generation of Hyperon Resonances
In this talk we report on how, using a chiral unitary approach for the
meson--baryon interactions, two octets of baryon states and a
singlet are generated dynamically, resulting in the case of strangeness
in two poles of the scattering matrix close to the nominal
resonance. We suggest experiments which could show evidence for the existence
of these states.Comment: Invited talk in the VIII International Conference on Hypernuclei and
Strange Particle Physic
DN interaction from meson exchange
A model of the DN interaction is presented which is developed in close
analogy to the meson-exchange KbarN potential of the Juelich group utilizing
SU(4) symmetry constraints. The main ingredients of the interaction are
provided by vector meson (rho, omega) exchange and higher-order box diagrams
involving D*N, D\Delta, and D*\Delta intermediate states. The coupling of DN to
the pi-Lambda_c and pi-Sigma_c channels is taken into account. The interaction
model generates the Lambda_c(2595) resonance dynamically as a DN quasi-bound
state. Results for DN total and differential cross sections are presented and
compared with predictions of an interaction model that is based on the
leading-order Weinberg-Tomozawa term. Some features of the Lambda_c(2595)
resonance are discussed and the role of the near-by pi-Sigma_c threshold is
emphasized. Selected predictions of the orginal KbarN model are reported too.
Specifically, it is pointed out that the model generates two poles in the
partial wave corresponding to the Lambda(1405) resonance.Comment: 14 pages, 8 figure
Effects of pseudoscalar-baryon channels in the dynamically generated vector-baryon resonances
We study the interaction of vector mesons with the octet of stable baryons in
the framework of the local hidden gauge formalism using a coupled channels
unitary approach, including also the pseudoscalar-baryon channels which couple
to the same quantum numbers. We examine the scattering amplitudes and their
poles, which can be associated to known baryon resonances,
and determine the role of the pseudoscalar-baryon channels, changing the width
and eventually the mass of the resonances generated with only the basis of
vector-baryon states
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