arXiv subjects

M. J. Vicente Vacas

Publications and source records attributed to M. J. Vicente Vacas.

148 records · Page 9Linked to original sources

arXiv1998

Chiral nonperturvative approach to the isoscalar s-wave pion-pion interaction in a nuclear medium

The s-wave isoscalar amplitude for pion-pion scattering in a nuclear medium is evaluated using a nonperturbative unitary coupled channels method and the standard chiral Lagrangians. The method has proved successful to describe the pion-pion properties in the scalar isoscalar channel up to 1.2 GeV giving rise to poles in the t matrix for the f0(980) and the sigma. The extension of the method to the nuclear medium implies not only the renormalization of the pions in the medium, but also the introduction of interaction terms related to contact terms in the pion-nucleon to pion-pion-nucleon interaction. Off shell effects are also shown to be important leading to cancellations which reduce the coupled channel integral equations to a set of algebraic equations. As the density increases we find a reduction of strength below the $σ$ region and a certain accumulation of strength at energies around pion threshold. Our results, based on chiral Lagrangians, provide similar results to those obtained with phenomenological models which impose minimal chiral constraints.

nucl-th↗

arXiv1998

$νd \to μ^- Δ^{++} n$ Reaction and Axial Vector $N-Δ$ Coupling

The reaction $νd \to μ^- Δ^{++} n$ is studied in the region of low $q^2$ to investigate the effect of deuteron structure and width of the $Δ$ resonance on the differential cross section. The results are used to extract the axial vector $N-Δ$ coupling $C^{A}_5$ from the experimental data on this reaction. The possibility to determine this coupling from electroweak interaction experiments with high intensity electron accelerators is discussed.

nucl-th↗

arXiv1997

Charged current weak electroproduction of Delta resonance

We study the weak production of $Δ$ (i.e. $e^{-} + p \to Δ^{0}+ ν_{e}$ and $e^{+} + p \to Δ^{++} + \barν_{e}$) in the intermediate energy range corresponding to the Mainz and TJNAF electron accelerators. The differential cross sections $σ(θ)$ are found to be of the order of $ 10^{-39}$ cm$^2$/sr, over a range of angles which increases with energy. The possibility of observing these reactions with the high luminosities available at these accelerators, and studying the weak N-$Δ$ transition form factors through these reactions is discussed. The production cross section of N$^*(1440)$ in the kinematic region of $Δ$ production is also estimated and found to be small.

nucl-th↗

arXiv1995

Recent Developments in one and two Pion Production in Elementary Reactions and Few Body Systems

In this talk we cover several issues concerning pion production. The first one is the p p ----> p p pi^0 reaction where an alternative explanation based on the off shell extrapolation of the pi N amplitude is offered. A recent model for the gamma N ----> pi pi N reaction is presented and a new kind of exchange current is constructed from it which allows one to address problems like double Delta photoproduction from the deuteron. Finally the (gamma, pi pi) reaction in nuclei is studied and shown to be highly sensitive to the renormalization of the pions in nuclei.

hep-ph↗