2,454 research outputs found
Study of the strong and in a non-relativistic quark model
We present results for the strong widths corresponding to the and decays. We apply our
model in Ref. Phys. Rev. D 72, 094022 (2005) where we previously studied the
corresponding transitions in the charmed sector. Our non-relativistic
constituent quark model uses wave functions that take advantage of the
constraints imposed by heavy quark symmetry. Partial conservation of axial
current hypothesis allows us to determine the strong vertices from an analysis
of the axial current matrix elements.Comment: 6 latex pages, 1 table, new references adde
Meson Resonances at large Nc: Complex Poles vs Breit-Wigner Masses
The rigorous quantum mechanical definition of a resonance requires
determining the pole position in the second Riemann sheet of the analytically
continued partial wave scattering amplitude in the complex Mandelstam
s-variable plane. For meson resonances we investigate the alternative
Breit-Wigner (BW) definition within the large Nc expansion. By assuming that
the pole position is and exploiting unitarity, we show
that the BW determination of the resonance mass differs from the pole position
by terms, which can be extracted from pi-pi scattering
data. For the case of the f0(600) pole, the BW scalar mass is predicted to
occur at about 700 MeV while the true value is located at about 800 MeV.Comment: 7 pages. No figures. (elsevier preprint
Thermal Field Theory in a wire: Applications of Thermal Field Theory methods to the propagation of photons in a one-dimensional plasma
We apply the Thermal Field Theory (TFT) methods to study the propagation of
photons in a plasma wire, that is, a system in which the electrons are confined
to a one-dimensional tube or wire, but are otherwise free. We find the
appropriate expression for the photon \emph{free-field} propagator in such a
medium, and write down the dispersion relation in terms of the free-field
propagator and the photon self-energy. The self-energy is then calculated in
the one-loop approximation and the corresponding dispersion relation is
determined and studied in some detail. Our work differs from previous work on
this subject in that we do not adopt any specific electronic wave functions in
the coordinates that are transverse to the idealized wire, or rely on
particular features of the electronic structure. We treat the electrons as a
free gas of particles, constrained to move in one dimension, but otherwise in a
model-independent way only following the rules of TFT adapted to the situation
at hand. For the appropriate conditions of the plasma the \emph{static
approximation} can be employed and the dispersion relation reduces to the
results obtained in previous works, but the formula that we obtain is valid
under more general conditions, including those in which the static
approximation is not valid. In particular, the dispersion relation has several
branches, which are not revealed if the static approximation is used. The
dispersion relations obtained reproduce several unique features of these
systems that have been observed in recent experiments.Comment: 17 pages Revised and extended discussion of the dispersion relation
The role of hyperfine mixing in semileptonic decays of doubly-heavy baryons
We analyze the effects of hyperfine mixing in semileptonic decays
of doubly heavy baryons. We qualitatively confirm the results by W. Roberts and
M. Pervin in Int. J. Mod. Phys. A, 2009, {\bf 24}: 2401-2413, finding that
mixing has a great impact on those transitions. However, predictions without
mixing differ by a factor of 2 and this discrepancy translates to the mixed
case where large differences in decay widths are observed between the two
calculations.Comment: 3 latex pages. Talk given at The 5-th International Conference on
Quarks and Nuclear Physics (QNP09), Beijing, September 200
Coherent pion production off nuclei at T2K and MiniBooNE energies revisited
As a result of a new improved fit to old bubble chamber data of the dominant
axial C_5^A nucleon-to-Delta form factor, and due to the relevance of this form
factor for neutrino induced coherent pion production, we re-evaluate our model
predictions in Phys. Rev. D79, 013002 (2009) for different observables of the
latter reaction. Central values for the total cross sections increase by 20% to
30%, while differential cross sections do not change their shape appreciably.
Furthermore, we also compute the uncertainties on total, differential and flux
averaged cross sections induced by the errors in the determination of C_5^A.
Our new results turn out to be compatible within about 1 sigma with the former
ones. Finally, we stress the existing tension between the recent experimental
determination of the sigma(CC coh \pi^+)/sigma(NC coh \pi^0) ratio by the
SciBooNE Collaboration and the theoretical predictions.Comment: 6 latex pages, 1 table, 2 figures. Shortened versio
The role of hyperfine mixing in semileptonic and electromagnetic decays of doubly-heavy baryons
We analyze the effects of hyperfine mixing in semileptonic and
electromagnetic decays of doubly heavy baryons.Comment: Talk given at the Chiral 10 Conferenc
The effect of hyperfine mixing in electromagnetic and semileptonic decays of doubly heavy baryons
We consider the role played by hyperfine mixing in electromagnetic and
semileptonic decays of doubly heavy baryons, which give rise to large
corrections to the decay widths in both cases.Comment: Talk given in Quark Confinement and the Hadron Spectrum IX, Madrid
September 201
Hyperfine mixing in semileptonic decay of doubly heavy baryons
We qualitatively corroborate the results of W. Roberts and M. Pervin in Int.
J. Mod. Phys. A 24, 2401 (2009) according to which hyperfine mixing greatly
affects the decay widths of semileptonic decays involving doubly heavy
baryons. However, our predictions for the decay widths of the unmixed
states differ from those reported in the work of Roberts and Pervin by a factor
of 2, and this discrepancy translates to the mixed case. We further show that
the predictions of heavy quark spin symmetry, might be used in the future to
experimentally extract information on the admixtures in the actual physical
baryons, in a model independent manner.Comment: 7 Latex pages, 4 Table
Wave functions for dynamically generated resonances; the two and
In this work we develop a formalism to evaluate wave functions in momentum
and coordinate space for the resonant states dynamically generated in a unitary
coupled channel approach. The on shell approach for the scattering matrix,
commonly used, is also obtained in Quantum Mechanics with a separable
potential, which allows one to write wave functions in a trivial way. We
develop useful relationships among the couplings of the dynamically generated
resonances to the different channels and the wave functions at the origin. The
formalism provides an intuitive picture of the resonances in the coupled
channel approach, as bound states of one bound channel, which decays into open
ones. It also provides an insight and practical rules for evaluating couplings
of the resonances to external sources and how to deal with final state
interaction in production processes. As an application of the formalism we
evaluate the wave functions of the two states in the , and other coupled channels. It also offers a practical way
to study three body systems when two of them cluster into a resonance.Comment: 5pages, 1 figure. To appear in the proceedings of the International
Workshop on Chiral Symmetry in Hadrons and Nuclei (Chiral10), Valencia,
Spain, Jun 21-24, 201
Heavy quark spin symmetric molecular states from and other coupled channels in the light of the recent LHCb pentaquarks
We consider the states, together with and other coupled channels, and take an interaction consistent with heavy
quark spin symmetry, with the dynamical input obtained from an extension of the
local hidden gauge approach. By fitting only one parameter to the recent three
pentaquark states reported by the LHCb collaboration, we can reproduce the
three of them in base to the mass and the width, providing for them the quantum
numbers and approximate molecular structure as ,
, and , and isospin
. We find another state around 4374 MeV, of
structure, for which indications appear in the experimental spectrum. Two other
near degenerate states of and nature are also found around 4520 MeV, which although less clear,
are not incompatible with the observed spectrum. In addition, a state at the same energy appears, which however does not couple
to in wave, and hence it is not expected to show up in the LHCb
experiment.Comment: 8 page
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