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A. Valcarce

Publications and source records attributed to A. Valcarce.

At least 109 records · Page 6Linked to original sources
arXiv2006

Hyperspherical harmonic formalism for tetraquarks

We present a generalization of the hyperspherical harmonic formalism to study systems made of quarks and antiquarks of the same flavor. This generalization is based on the symmetrization of the $N-$body wave function with respect to the symmetric group using the Barnea and Novoselsky algorithm. Our analysis shows that four-quark systems with non-exotic $2^{++}$ quantum numbers may be bound independently of the quark mass. $0^{+-}$ and $1^{+-}$ states become attractive only for larger quarks masses.

hep-ph↗
arXiv2006

Nucleon sigma term and quark condensate in nuclear matter

We study the bound nucleon sigma term and the quark condensate in nuclear matter. In the quark-meson coupling (QMC) model the nuclear correction to the sigma term is small and negative, i.e., it decelerates the decrease of the quark condensate in nuclear matter. However, the quark condensate in nuclear matter is controlled primarily by the scalar-isoscalar $σ$ field. Compared to the leading term, it moderates the decrease more than that of the nuclear sigma term alone at densities around and larger than the normal nuclear matter density.

nucl-th↗
arXiv2006

Dynamical study of ${\bf QQ-\bar u \bar d}$ mesons

It has been recently conjectured by Selem and Wilczek \cite{Sel06} the existence of a $ss-[\bar u \bar d]$ meson due to strong correlations between the two light antiquarks. We make a detailed study of this system within a dynamical quark model which has proven to be successful in reproducing the most important features of low-energy hadron phenomenology. Our results, obtained within a parameter-free calculation, show that the antidiquark component of the $ss \bar u \bar d$ system indeed entails the stronger attraction, and drives its energy much lower than the $\bar{N}Ξ$ threshold, but still above the $\bar{K^0} {K^*}^-$ or $\bar{{K^*}^0} K^-$ thresholds. We have also studied the $cc \bar u \bar d$ and $bb \bar u \bar d$ systems. Exotic mesons are only expected to exist in the limit of large mass for the two-quark subsystem, $bb\bar u \bar d$, since the calculated mass is below the $\bar{B^0} {B^*}^-$ or $\bar{{B^*}^0} B^-$ thresholds.

hep-ph↗
arXiv2006

Spectral patterns in the nonstrange baryon spectrum

We extract, from a quark model potential that reproduces the number and ordering of nonstrange baryonic resonances up to 2.3 GeV, the quantum numbers for the dominant configurations in the ground and first non-radial excited states. From the pattern of quantum numbers we identify, from data, spectral regularities that allow us to predict the expected high spin low-lying spectrum from 2.3 to 3.0 GeV. $N-Δ$ degeneracies and $N$ parity doublets showing up can be interpreted in terms of a simple dynamics.

hep-ph↗
arXiv2006

Four-quark spectroscopy within the hyperspherical formalism

We present a generalization of the hyperspherical harmonic formalism to study systems made of quarks and antiquarks of the same flavor. This generalization is based on the symmetrization of the $N-$body wave function with respect to the symmetric group using the Barnea and Novoselsky algorithm. The formalism is applied to study four-quark systems by means of a constituent quark model successful in the description of the two- and three-quark systems. The results are compared to those obtained by means of variational approaches. Our analysis shows that four-quark systems with exotic $0^{+-}$ and non-exotic $2^{++}$ quantum numbers may be bound independently of the mass of the quark. $2^{+-}$ and $1^{+-}$ states become attractive only for larger mass of the quarks.

hep-ph↗
arXiv2006

Strange tribaryons

We use two-body potentials derived from a constituent quark cluster model to analyze the bound-state problem of the $ΣNN$ system. The observables of the two-body subsystems, $NN$ and $ΣN$, are well reproduced. We do not find $ΣNN$ bound states, but there are two attractive channels with a resonance close above the three-body threshold. These channels are the $(I,J)=(1,1/2)$ and $(0,1/2)$, their quantum numbers, widths and energy ordering consistent with the recently measured strange tribaryons from the $^{4}{\rm He}(K_{\rm stopped}^{-},N)$ reactions in the KEK PS E471 experiment.

hep-ph↗
arXiv2006

Open-charm meson spectroscopy

We present a theoretical framework that accounts for the new $D_J$ and $D_{sJ}$ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional $P-$wave quark-antiquark states and four-quark components. The narrowest states are basically $P-$wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold, being broad resonances. We study the electromagnetic decay widths as basic tools to scrutiny their nature. The proposed explanation incorporates in a natural way the most recently discovered mesons in charmonium spectroscopy.

hep-ph↗
arXiv2005

Nature of the light scalar mesons

Despite the apparent simplicity of meson spectroscopy, light scalar mesons cannot be accommodated in the usual $q\bar q$ structure. We study the description of the scalar mesons below 2 GeV in terms of the mixing of a chiral nonet of tetraquarks with conventional $q\bar q$ states. A strong diquark-antidiquark component is found for several states. The consideration of a glueball as dictated by quenched lattice QCD drives a coherent picture of the isoscalar mesons.

hep-ph↗
arXiv2005

Diquark-diquark correlations in the $^1S_0$ $ΛΛ$ potential

We derive a $ΛΛ$ potential from a chiral constituent quark model that has been successful in describing one, two and three nonstrange baryon systems. The resulting interaction at low energy is attractive at all distances due to the $σ$ exchange term. The attraction allows for a slightly bound state just below the $ΛΛ$ threshold. No short-range repulsive core is found. We extract the diquark-diquark contribution that turns out to be the most attractive and probable at small distances. At large distances the asymptotic behavior of the $ΛΛ$ interaction provides a prediction for the $σΛΛ$ coupling constant.

hep-ph↗
arXiv2005

Constituent quark model study of light- and strange-baryon spectra

We investigate the structure of the SU(3) octet and decuplet baryons employing a constituent quark model designed for the study of the baryon-baryon interaction and successfully applied to the meson spectra. The model considers through the interacting potential perturbative, one-gluon exchange, and non-perturbative, boson exchanges and confinement, aspects of the underlying theory, QCD. We solve the three-quark problem by means of the Faddeev method in momentum space. We analyze the effect of the different terms in the interaction and make contact with the use of relativistic kinematics. We find an explanation to the strong contribution of the pseudoscalar forces in the semirelativistic approach for the octet baryons. A phenomenological recipe for the regularization parameter of the one-gluon exchange is found.

hep-ph↗
arXiv2005

Constituent quark model study of the meson spectra

The $q\bar q$ spectrum is studied in a generalized constituent quark model constrained in the study of the $NN$ phenomenology and the baryon spectrum. An overall good fit to the available experimental data is obtained. A detailed analysis of all sectors from the light-pseudoscalar and vector mesons to bottomonium is performed paying special attention to the existence and nature of some non well-established states. These results should serve as a complementary tool in distinguishing conventional quark model mesons from glueballs, hybrids or multiquark states.

hep-ph↗
arXiv2005

Quark-model study of few-baryon systems

We review the application of non-relativistic constituent quark models to study one, two and three non-strange baryon systems. We present results for the baryon spectra, potentials and observables of the NN, N$Δ$, $ΔΔ$ and NN$^*(1440)$ systems, and also for the binding energies of three non-strange baryon systems. We make emphasis on observable effects related to quark antisymmetry and its interplay with quark dynamics.

hep-ph↗
arXiv2004

The meson spectra beyond a $q\bar q$ description

Despite the apparent simplicity of meson spectroscopy there are some states which cannot be accommodated in the usual $q\bar q$ structure. Among them there are either exotic states as the X(1600), or the recently measured charmed states $D_{sJ}^*$ and some of the light scalar mesons. We present a description of the light scalar mesons in terms of $q\bar q$ and $qq\bar q\bar q$ components.

hep-ph↗
arXiv2004

$b\bar b$ Description with a Screened Potential

Recent lattice QCD calculations suggest a rather abrupt transition in the confinig potential from a linear to a constant behavior. We analyze the effects of such a fast deconfinement in the simplest non-relativistic system, bottomonium.

hep-ph↗
arXiv2004

Spectroscopy of doubly charmed baryons

We study the mass spectrum of baryons with two and three charmed quarks. For double charm baryons the spin splitting is found to be smaller than standard quark-model potential predictions. This splitting is not influenced either by the particular form of the confining potential or by the regularization taken for the contact term of the spin-spin potential. We consistently predict the spectra for triply charmed baryons.

hep-ph↗
arXiv2004

Towards the understanding of the meson spectra

We present a quark-quark interaction for the complete study of the meson spectra, from the light to the heavy sector. We compare the quark model predictions against well-established $q\bar q$ experimental data. This allows to identify discrepancies between quark model results and experiment that may signal physics beyond conventional hadron spectroscopy.

hep-ph↗
arXiv2004

Describing non-$q\bar q$ candidates

Despite the apparent simplicity of meson spectroscopy there are some states which cannot be accommodated in the usual $q\bar q$ structure. Among them there are either exotic states as the X(1600) or the recently measured charm states $D_{sJ}^*$ and X(3872) and some of the light scalar mesons. In this work we present a possible description of these states in terms of tetraquarks.

hep-ph↗
arXiv2003

Screened potential and the baryon spectrum

We show that in a quark model scheme the use of a screened potential, suggested by lattice QCD, instead of an infinitely rising one with the interquark distance, provides a more adequate description of the high-energy baryon spectrum. In particular an almost perfect parallelism between the predicted and observed number of states comes out throwing new light about the so-called missing resonance problem.

hep-ph↗