arXiv subjects
Publications and source records attributed to A. Valcarce.
By means of a NN to NN*(1440) transition potential derived in a parameter-free way from a quark-model based NN potential, we determine simultaneously the $πNN^*(1440)$ and $σNN^*(1440)$ coupling constants. We also present a study of the target Roper excitation diagram contributing to the $p(d,d')$ reaction.
The ${q}\bar{q}$ spectrum is studied within a chiral constituent quark model. It provides with a good fit of the available experimental data from light (vector and pseudoscalar) to heavy mesons including some recent results on charmonium. The $0^{++}$ light mesons and the new $D$ states measured at different factories cannot be described as $q\bar q$ pairs and a tetraquark structure is suggested.
We analyze the possibility of heavy-light tetraquark bound states by means of a chiral constituent quark model. The study is done in a variational approach. Special attention is paid to the contribution given by the different terms of the interacting potential and also to the role played by the different color channels. We find a stable state for both $qq\bar{c}\bar{c}$ and $qq\bar{b}\bar{b}$ configurations. Possible decay modes of these structures are analyzed.
The ${q}\bar{q}$ spectrum is studied within a chiral constituent quark model. It provides with a good fit of the available experimental data from light (vector and pseudoscalar) to heavy mesons. The new $D$ states measured at different factories are studied. The $0^{++}$ light mesons are analyzed as $q\bar q$ pairs or tetraquark structures.
We make use of a $NN \to NN^*(1440)$ transition potential derived from a quark-model in a parameter-free way, to study the Roper excitation diagram contributing to the reaction $p(d,d^{\prime})$. We also determine the $πNN^*(1440)$ and $σNN^*(1440)$ coupling constants.
The non-strange baryon spectrum is studied within a three-body model that incorporates relativistic kinematics. We found that the combined effect of relativistic kinematics together with the pion exchange between quarks is able to reverse the order of the first positive- and negative-parity nucleon excited states as observed experimentally. Including the chiral partner of the pion (the $σ$ meson) leads to an overall good description of the spectrum.
We perform a quark model calculation of the $b\bar{b}$ and $c\bar{c}$ spectra from a screened funnel potential form suggested by unquenched lattice calculations. A connection between the lattice screening parameter and an effective gluon mass directly derived from QCD is established. Spin-spin energy splittings, leptonic widths and radiative decays are also examined providing a test for the description of the states.
We review the actual state in the description of the NN interaction by means of chiral constituent quark models. We present a series of relevant features that are nicely explained within the quark model framework.
We present a nonrelativistic coupled-channel calculation of the deuteron structure including Delta Delta and NN^*(1440) channels, besides the standard NN S and D-wave components. All the necessary building blocks to perform the calculation have been obtained from the same underlying quark model. The calculated NN^*(1440) probabilities find support in the explanation given to different deuteron reactions.
A $NN\to NN^{\ast}(1440)$ transition potential, based on an effective quark-quark interaction and a constituent quark cluster model for baryons, is derived in the Born-Oppenheimer approach. The potential shows significant differences with respect to those obtained by a direct scaling of the nucleon-nucleon interaction. From its asymptotic behavior we extract the values of $πNN^{\ast}(1440)$ and $σNN^{\ast}(1440)$ coupling constants in a particular coupling scheme
By means of a $NN \to NN^*(1440)$ transition potential derived in a parameter-free way from a quark model, we determined simultaneously the $πNN^*(1440)$ and $σNN^*(1440)$ coupling constants.
In this work we study tetraquark bound states in the framework of the constituent quark model of Ref. [2], which has been used for the description of non-strange two- and three-baryon systems and later on applied to the hadron spectra.
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 $NN$, $NΔ$, and $ΔΔ$, while the three-body systems are $NNN$, $NNΔ$, $NΔΔ$, and $ΔΔΔ$. We use as input the nonlocal $NN$, $NΔ$, and $ΔΔ$ 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.
The three-nucleon bound state problem is studied employing a nucleon-nucleon potential obtained from a basic quark-quark interaction in a five-channel Faddeev calculation. The obtained triton binding energy is comparable to those predicted by conventional models of the $NN$ force.
The classical van Royen-Weisskopf formula for the decay width of a meson into a lepton-antilepton pair is modified in order to include non-zero quark momentum contributions within the meson as well as relativistic effects. Besides, a phenomenological electromagnetic density for quarks is introduced. The meson wave functions are obtained from two different models: a chiral constituent quark model and a quark potential model including instanton effects. The modified van Royen-Weisskopf formula is found to improve systematically the results for the widths, giving an overall good description of all known decays.
We have performed a Faddeev calculation of the baryon spectrum for the chiral constituent quark model including higher orbital angular momentum states. We have found that the effect of these states is important, although a description of the baryon spectrum of the same quality as the one given by including only the lowest-order configurations can be obtained. We have studied the effect of the pseudoscalar quark-quark interaction on the relative position of the positive- and negative-parity excitations of the nucleon as well as the effect of varying the strength of the color-magnetic interaction.
We present a calculation of the deuteron wave function including $NN$, $ΔΔ$, and $NN^*$(1440) channels. All the transition potentials, as well as the direct $NN$ potential, have been obtained from the same underlying quark model using standard techniques available in the literature. The calculated weights for the different channels are in agreement with previous theoretical estimations.
The three-nucleon bound state problem is studied employing nucleon-nucleon potentials derived from a basic quark-quark interaction. We analyze the effects of the nonlocalities generated by the quark model. The calculated triton binding energies indicate that quark-model nonlocalities can yield additional binding in the order of few hundred keV.