420 research outputs found

    Stability of multiquarks in a simple string model

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    A simple string model inspired by the strong-coupling regime of Quantum ChromoDynamics is used as a potential for studying the spectrum of multiquark systems with two quarks and two antiquarks, with a careful treatment of the four-body problem. It is found that the ground state is stable, lying below the threshold for dissociation into two isolated mesons.Comment: 4 pages, 2 figures, Refs. added, typos corrected, discussion improved, to appear in Phys. Rev.

    Quark Cluster Model Study of Isospin-Two Dibaryons

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    Based on a quark cluster model for the non-strange sector that reproduces reasonably well the nucleon-nucleon system and the excitation of the Δ\Delta isobar, we generate a nucleon-Δ\Delta interaction and present the predictions for the several isospin two channels. The only attractive channels are 0+0^+ and 0−0^-, but not attractive enough to generate a resonance. If a resonance is artificially generated and is required to have the observed experimental mass, then our model predicts a width that agrees with the experimental result.Comment: 12 pages, 5 poscript figures available under request. To appear in Phys. Rev.

    Open-charm meson spectroscopy

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    We present a theoretical framework that accounts for the new DJD_J and DsJD_{sJ} mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional P−P-wave quark-antiquark states and four-quark components. The narrowest states are basically P−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.Comment: 15 pages, 5 tables. Accepted for publication in Phys. Rev.

    Nonlocal calculation for nonstrange dibaryons and tribaryons

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    We study the possible existence of nonstrange dibaryons and tribaryons by solving the bound-state problem of the two- and three-body systems composed of nucleons and deltas. The two-body systems are NNNN, NΔN\Delta, and ΔΔ\Delta\Delta, while the three-body systems are NNNNNN, NNΔNN\Delta, NΔΔN\Delta\Delta, and ΔΔΔ\Delta\Delta\Delta. We use as input the nonlocal NNNN, NΔN\Delta, and ΔΔ\Delta\Delta potentials derived from the chiral quark cluster model by means of the resonating group method. We compare with previous results obtained from the local version based on the Born-Oppenheimer approximation.Comment: 19 pages. To be published in Physical Review

    Pulsation Period Changes as a Tool to Identify Pre-Zero Age Horizontal Branch Stars

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    One of the most dramatic events in the life of a low-mass star is the He flash, which takes place at the tip of the red giant branch (RGB) and is followed by a series of secondary flashes before the star settles into the zero-age horizontal branch (ZAHB). Yet, no stars have been positively identified in this key evolutionary phase, mainly for two reasons: first, this pre-ZAHB phase is very short compared to other major evolutionary phases in the life of a star; and second, these pre-ZAHB stars are expected to overlap the loci occupied by asymptotic giant branch (AGB), HB and RGB stars observed in the color-magnitude diagram (CMD). We investigate the possibility of detecting these stars through stellar pulsations, since some of them are expected to rapidly cross the Cepheid/RR Lyrae instability strip in their route from the RGB tip to the ZAHB, thus becoming pulsating stars along the way. As a consequence of their very high evolutionary speed, some of these stars may present anomalously large period change rates. We constructed an extensive grid of stellar models and produced pre-ZAHB Monte Carlo simulations appropriate for the case of the Galactic globular cluster M3 (NGC 5272), where a number of RR Lyrae stars with high period change rates are found. Our results suggest that some -- but certainly not all -- of the RR Lyrae stars in M3 with large period change rates are in fact pre-ZAHB pulsators.Comment: Conference Proceedings HELAS Workshop on 'Synergies between solar and stellar modelling', Rome, June 2009, Astrophys. Space Sci., in the pres

    Mass and width of the d′d' resonance in nuclei

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    We calculated the mass and width of the d′d' resonance inside nuclei within a nucleon-Δ\Delta model by including the self-energy of the Δ\Delta in the NΔN\Delta propagator. We found that in the nuclear medium the width of the d′d' is increased by one order of magnitude while its mass changes only by a few MeV. This broadening of the width of the d′d' resonance embedded in nuclei is consistent with the experimental observations so that the d′d' can be understood as a NΔN\Delta resonance. Thus, given the freedom between either isospin 0 or isospin 2 for the d′d', our results give weigth to the isospin-2 assignment.Comment: 14 pages, RevteX type, 2 eps figures. To be published in Phys. Rev. C (September

    Faddeev study of heavy baryon spectroscopy

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    We investigate the structure of heavy baryons containing a charm or a bottom quark. We employ a constituent quark model successful in the description of the baryon-baryon interaction which is consistent with the light baryon spectra. We solve exactly the three-quark problem by means of the Faddeev method in momentum space. Heavy baryon spectrum shows a manifest compromise between perturbative and nonperturbative contributions. The flavor dependence of the one-gluon exchange is analyzed. We assign quantum numbers to some already observed resonances and we predict the first radial and orbital excitations of all states with J=1/2J=1/2 or 3/2. We combine our results with heavy quark symmetry and lowest-order SU(3) symmetry breaking to predict the masses and quantum numbers of six still non-measured ground-state beauty baryons.Comment: 22 pages, 4 figures, 8 tables. Accepted for publication in J. Phys.

    Spectroscopy of doubly charmed baryons

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    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.Comment: 6 pages, 1 figure, accepted for publication in Phys. Rev.
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