Search NASA⌕ Search

Engineering topics

Nieves, J

Publications and source records attributed to Nieves, J.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Large-N{sub C} properties of the {rho} and f{sub 0}(600) mesons from unitary resonance chiral dynamics

We construct {pi}{pi} amplitudes that fulfill exact elastic unitarity, account for one-loop chiral perturbation theory contributions and include all 1/N{sub C} leading terms, with the only limitation of considering just the lowest-lying nonet of exchanged resonances. Within such a scheme, the N{sub C} dependence of {sigma} and {rho} masses and widths is discussed. Robust conclusions are drawn in the case of the {rho} resonance, confirming that it is a stable meson in the limit of a large number of QCD colors, N{sub C}. Less definitive conclusions are reached in the scalar-isoscalar sector. With the present quality of data, we cannot firmly conclude whether or not the N{sub C}=3 f{sub 0}(600) resonance completely disappears at large N{sub C} or if it has a subdominant component in its structure, which would become dominant for a number of quark colors sufficiently large.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

New determination of the N-{Delta}(1232) axial form factors from weak pion production and coherent pion production off nuclei at T2K and MiniBooNE energies revisited

We re-evaluate our model predictions in Phys. Rev. D 79, 013002 (2009) for different observables in neutrino induced coherent pion production. This comes as a result of the new improved fit to old bubble chamber data of the dominant axial C{sub 5}{sup A} nucleon-to-Delta form factor. We find an increase of 20%{approx}30% in the values for the total cross sections. Uncertainties induced by the errors in the determination of C{sub 5}{sup A} are computed. Our new results turn out to be compatible within about 1{sigma} with the former ones. We also stress the existing tension between the recent experimental determination of the {sigma}(CCcoh{pi}{sup +})/{sigma}(NCcoh{pi}{sup 0}) ratio by the SciBooNE Collaboration and the theoretical predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Inclusive charged-current neutrino-nucleus reactions

We present a model for weak charged-current induced nuclear reactions at energies of interest for current and future neutrino oscillation experiments. This model is a natural extension of the work in Refs. [1,2], where the quasielastic contribution to the inclusive electron and neutrino scattering on nuclei was analyzed. The model is based on a systematic many-body expansion of the gauge boson absorption modes that includes one, two, and even three-body mechanisms, as well as the excitation of {Delta} isobars. The whole scheme has no free parameters, besides those previously adjusted to the weak pion production off the nucleon cross sections in the deuteron, since all nuclear effects were set up in previous studies of photon, electron, and pion interactions with nuclei. We have discussed at length the recent charged-current quasielastic MiniBooNE cross section data, and showed that two-nucleon knockout mechanisms are essential to describing these measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Couplings in coupled channels versus wave functions in the case of resonances: Application to the two {Lambda}(1405) states

In this paper 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 {Lambda}(1405) states in the {pi}{Sigma}, KN, and other coupled channels. It also offers a practical way to study three-body systems when two of them cluster into a resonance.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Low-lying even-parity meson resonances and spin-flavor symmetry

Based on a spin-flavor extension of chiral symmetry, a novel s-wave meson-meson interaction involving members of the {rho} nonet and of the {pi} octet is introduced, and its predictions are analyzed. The starting point is the SU(6) version of the SU(3)-flavor Weinberg-Tomozawa Lagrangian. SU(6) symmetry-breaking terms are then included to account for the physical meson masses and decay constants in a way that preserves (broken) chiral symmetry. Next, the T-matrix amplitudes are obtained by solving the Bethe-Salpeter equation in a coupled-channel scheme, and the poles are identified with their possible Particle Data Group counterparts. It is shown that most of the low-lying even-parity Particle Data Group meson resonances, especially in the J{sup P}=0{sup +} and 1{sup +} sectors, can be classified according to multiplets of SU(6). The f{sub 0}(1500), f{sub 1}(1420), and some 0{sup +}(2{sup ++}) resonances cannot be accommodated within this scheme, and thus they would be clear candidates to be glueballs or hybrids. Finally, we predict the existence of five exotic resonances (I{>=}3/2 and/or |Y|=2) with masses in the range of 1.4-1.6 GeV, which would complete the 27{sub 1}, 10{sub 3}, and 10{sub 3}* multiplets of SU(3) x SU(2).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Wave functions for dynamically generated resonances; the two {Lambda}(1405) and {Lambda}(1670)

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 {Lambda}(1405) states in the {pi}{Sigma}, K-barN and other coupled channels. It also offers a practical way to study three body systems when two of them cluster into a resonance.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Exotic dynamically generated baryons with C = -1

We follow a model based on the SU(8) symmetry for the interaction of mesons with baryons. The model treats on an equal footing the pseudo-scalars and the vector mesons, as required by heavy quark symmetry. The T-matrix calculated within an unitary scheme in coupled channels has poles which are interpreted as baryonic resonances.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗