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M. J. Vicente Vacas

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

At least 73 records · Page 4Linked to original sources
arXiv2009

A study of nuclear effect in $F_3$ structure function in the deep inelastic $ν(\barν)$ reactions in nuclei

We study nuclear effect in the $F^A_3(x)$ structure function in the deep inelastic neutrino reactions on iron by taking into account Fermi motion, binding, target mass correction, shadowing and anti-shadowing corrections. Calculations have been done in a local density approximation using relativistic nuclear spectral functions which include nucleon correlations for nuclear matter. Results for $F^A_3(x)$ have been compared with the results reported at NuTeV and also with some of the older experiments reported in the literature.

nucl-th↗
arXiv2009

Electromagnetic structure of the lowest-lying decuplet resonances in covariant chiral perturbation theory

We present a calculation of the leading SU(3)-breaking $\mathcal{O}(p^3)$-corrections to the electromagnetic moments and charge radius (CR) of the lowest-lying decuplet resonances in covariant chiral perturbation theory. In particular, the magnetic dipole moment (MDM) of the members of the decuplet is predicted fixing the only low-energy constant (LEC) present up to this order with the well measured MDM of the $Ω^-$. We predict $μ_Δ^{++}=6.04(13)$ and $μ_Δ^+=2.84(2)$ which agree well with the current experimental information. For the electric quadrupole moment (EQM) and the CR we use state-of-the-art lattice QCD results to determine the corresponding LECs, whereas for the magnetic octupole moment (MOM) there is no unknown LEC up to the order considered here and we obtain a pure prediction. We compare our results with those reported in large $N_c$, lattice QCD, heavy-baryon chiral perturbation theory and other models.

hep-ph↗
arXiv2009

Dynamically generated resonances

In this talk I report on recent work related to the dynamical generation of baryonic resonances, some made up from pseudoscalar meson-baryon, others from vector meson-baryon and a third type from two meson-one baryon systems. We can establish a correspondence with known baryonic resonances, reinforcing conclusions previously drawn and bringing new light on the nature of some baryonic resonances of higher mass.

hep-ph↗
arXiv2009

Leading-order decuplet contributions to the baryon magnetic moments in Chiral Perturbation Theory

We extend an earlier study of the baryon magnetic moments in chiral perturbation theory by the explicit inclusion of the spin-3/2 decuplet resonances. We find that the corrections induced by these heavier degrees of freedom are relatively small in a covariant framework where unphysical spin-1/2 modes are removed. Consequently, implementing the leading SU(3)-breaking corrections given by both the baryon and decuplet contributions, we obtain a description of the baryon-octet magnetic moments that is better than the Coleman-Glashow relations. Finally, we discuss the uncertainties and compare between heavy baryon and covariant approaches.

hep-ph↗
arXiv2009

SU(3)-breaking corrections to the baryon-octet magnetic moments in chiral perturbation theory

We report a calculation of the baryon magnetic moments using covariant chiral perturbation theory within the extended-on-mass-shell renormalization scheme including intermediate octet and decuplet contributions. By fitting the two available low-energy constants, we improve the Coleman-Glashow description of the data when we include the leading SU(3) breaking effects coming from the lowest-order loops. We compare with previous attempts at the same order using heavy-baryon and covariant infrared chiral perturbation theory, and discuss the source of the differences.

hep-ph↗
arXiv2009

SU(3)-breaking corrections to the hyperon vector coupling $f_1(0)$ in covariant baryon chiral perturbation theory

We calculate the SU(3)-breaking corrections to the hyperon vector coupling $f_1(0)$ up to $\mathcal{O}(p^4)$ in covariant baryon chiral perturbation theory with dynamical octet and decuplet contributions. We find that the decuplet contributions are of similar or even larger size than the octet ones. Combining both, we predict positive SU(3)-breaking corrections to all the four independent $f_1(0)$'s (assuming isospin symmetry), which are consistent, within uncertainties, with the latest results form large $N_c$ fits, chiral quark models, and quenched lattice QCD calculations.

hep-ph↗
arXiv2008

Recent topics of mesic atoms and mesic nuclei -- $ϕ$ mesic nuclei exist ?--

We study $ϕ$-meson production in nuclei to investigate the in-medium modification of the $ϕ$-meson spectral function at finite density. We consider (${\bar p},ϕ$), ($γ,p$) and ($π^-,n$) reactions to produce a $ϕ$-meson inside the nucleus and evaluate the effects of the medium modifications to reaction cross sections. The structures of the bound states, $ϕ$-mesic nuclei, are also studied. For strong absorptive interaction cases, we need to know the spectrum shape in a wide energy region to deduce the properties of $ϕ$.

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arXiv2008

Leading SU(3)-breaking corrections to the baryon magnetic moments in Chiral Perturbation Theory

We calculate the baryon magnetic moments using covariant Chiral Perturbation Theory ($χ$PT) within the Extended-on-mass-shell (EOMS) renormalization scheme. By fitting the two available low-energy constants (LECs), we improve the Coleman-Glashow description of the data when we include the leading SU(3) breaking effects coming from the lowest-order loops. This success is in dramatic contrast with previous attempts at the same order using Heavy Baryon (HB) $χ$PT and covariant Infrared (IR) $χ$PT. We also analyze the source of this improvement with particular attention on the comparison between the covariant results.

hep-ph↗
arXiv2008

Nuclear effects in F_3 structure function of nucleon

We study nuclear effects in the $F^A_3(x)$ structure function in the deep inelastic neutrino reactions on iron by using a relativistic framework to describe the nucleon spectral functions in the nucleus. The results for the ratio $R(x,Q^2)=\frac{F^A_3(x,Q^2)}{AF^N_3(x, Q^2)}$ and the Gross-Llewellyn Smith(GLS) integral $G(x,Q^2)=\int_x^1 dx F^A_3(x,Q^2)$ in nuclei are discussed and compared with the recent results available in literature from theoretical and phenomenological analyses of experimental data.

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arXiv2008

Neutrino nucleus cross sections

We present the results of our calculation which has been performed to study the nuclear effects in the quasielastic, inelastic and deep inelastic scattering of neutrinos(antineutrinos) from nuclear targets. These calculations are done in the local density approximation. We take into account the effect of Pauli blocking, Fermi motion, Coulomb effect, renormalization of weak transition strengths in the nuclear medium in the case of the quasielastic reaction. The inelastic reaction leading to production of pions is calculated in a $Δ$- dominance model taking into account the renormalization of $Δ$ properties in the nuclear medium and the final state interaction effects of the outgoing pions with the residual nucleus. We discuss the nuclear effects in the $F_{3}^{A}(x)$ structure function in the deep inelastic neutrino(antineutrino) reaction using a relativistic framework to describe the nucleon spectral function in the nucleus.

nucl-th↗
arXiv2008

Study of the derivative expansions for the nuclear structure functions

We study the convergence of the series expansions sometimes used in the analysis of the nuclear effects in Deep Inelastic Scattering (DIS) proccesses induced by leptons. The recent advances in statistics and quality of the data, in particular for neutrinos calls for a good control of the theoretical uncertainties of the models used in the analysis. Using realistic nuclear spectral functions which include nucleon correlations, we find that the convergence of the derivative expansions to the full results is poor except at very low values of $x$.

nucl-th↗
arXiv2008

Nucleon-to-Delta axial transition form factors in relativistic baryon chiral perturbation theory

We report a theoretical study of the axial Nucleon to Delta(1232) ($N\toΔ$) transition form factors up to one-loop order in relativistic baryon chiral perturbation theory. We adopt a formalism in which the $Δ$ couplings obey the spin-3/2 gauge symmetry and, therefore, decouple the unphysical spin-1/2 fields. We compare the results with phenomenological form factors obtained from neutrino bubble chamber data and in quark models.

hep-ph↗
arXiv2008

Chiral Unitary Dynamics of Hadrons and Hadrons in a Nuclear Medium

In this talk I summarize recent findings around the description of axial vector mesons as dynamically generated states from the interaction of pseudoscalar mesons and vector mesons, dedicating some attention to the two $K_1(1270)$ states. Then I review the generation of open and hidden charm scalar and axial states, and how some recent experiment supports the existence of the new hidden charm scalar state predicted. I present recent results showing that the low lying $1/2^+$ baryon resonances for S=-1 can be obtained as bound states or resonances of two mesons and one baryon in coupled channels. Then show the differences with the S=0 case, where the $N^*(1710)$ appears also dynamically generated from the two pion one nucleon system, but the $N^*(1440)$ does not appear, indicating a more complex structure of the Roper resonance. Finally I shall show how the state X(2175), recently discovered at BABAR and BES, appears naturally as a resonance of the $ϕK \bar{K}$ system.

nucl-th↗
arXiv2008

Production of Two Pions Induced by Neutrinos

We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon pole, pion and contact terms is calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account.

hep-ph↗
arXiv2008

Nuclear effects in neutrino induced reactions

We discuss the relevance of nuclear medium effects in the analysis of some low and medium energy neutrino reactions of current interest. In particular, we study the Quasi-Elastic (QE) process, where RPA correlations and Final State Interactions (FSI) are shown to play a crucial role. We have also investigated the neutrino induced coherent pion production. We find a strong reduction of the cross section due to the distortion of the pion wave function and the modification of the production mechanisms in the nucleus. The sensitivity of the results to the axial $NΔ$ coupling $C_5^A(0)$ has been also investigated.

nucl-th↗
arXiv2008

Neutral current coherent pion production

We investigate the neutrino induced coherent pion production reaction at low and intermediate energies. The model includes pion, nucleon and Delta(1232) resonance as the relevant hadronic degrees of freedom. Nuclear medium effects on the production mechanisms and pion distortion are taken into account. We obtain that the dominance of the Delta excitation holds due to large cancellations among the background contributions. We consider two sets of vector and axial-vector N-Delta transition form-factors, evidencing the strong sensitivity of the results to the axial coupling C5A(0). The differences between neutrino and antineutrino cross sections, emerging from interference terms, are also discussed.

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