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L. S. Geng

Publications and source records attributed to L. S. Geng.

At least 109 records · Page 6Linked to original sources
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↗
arXiv2009

Role of the $N^*$(1535) in the $J/ψ\to \bar{p}ηp$ and $J/ψ\to \bar{p}K^+Λ$ reactions

We study the $J/ψ\to \bar{p}ηp$ and $J/ψ\to \bar{p}K^+Λ$ reactions with a unitary chiral approach. We find that the unitary chiral approach, which generates the $N^*(1535)$ dynamically, can describe the data reasonably well, particularly the ratio of the integrated cross sections. This study provides further support for the unitary chiral description of the $N^*(1535)$. We also discuss some subtle differences between the coupling constants determined from the unitary chiral approach and those determined from phenomenological studies.

hep-ph↗
arXiv2009

Meson and Baryon resonances

In this talk I review recent advances on the structure of the meson and baryon resonances which can be dynamically generated from the interaction of mesons or mesons and baryons. Particular emphasis is put on results involving vector mesons, which bring new light into the nature of some of the observed higher mass mesons and baryons and make predictions for new states.

hep-ph↗
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

Testing the nature of the $Λ$(1520) in the $J/ψ\to\barΛK^-p$ and $J/ψ\to\barΛπ^+π^-Λ$ reactions

We study the reactions $J/ψ\to\barΛK^-p$ and $J/ψ\to\barΛπ^+π^-Λ$ with a unitary chiral approach. We predict the ratio of the invariant mass distributions of these two reactions at the $Λ(1520)$ peak position, which is free of the unknown production mechanism and reflects only the properties of the $Λ(1520)$. An experimental measurement of this ratio will provide the couplings of the $Λ(1520)$ to its decay channels, allowing to test the predictions of the chiral unitary approach on this resonance, which appears as dynamically generated in that approach.

hep-ph↗
arXiv2008

Nature of the axial-vector mesons from their Nc behavior within the chiral unitary approach

By describing within the chiral unitary approach the s-wave interaction of the vector meson nonet with the octet of pseudoscalar Goldstone Bosons, we find that the main component of the axial vector mesons b_1(1235), h_1(1170), h_1(1380), a_1(1260), f_1(1285) and the two states associated to the K_1(1270) does not follow the QCD dependence on the number of colors for ordinary qqbar mesons.

hep-ph↗
arXiv2008

X(2175) as a resonant state of the $ϕK \bar{K}$ system

We perform a Faddeev calculation for the three mesons system, $ϕK \bar{K}$, taking the interaction between two pseudoscalar mesons and between a vector and a pseudoscalar meson from the chiral unitary approach. We obtain a neat resonance peak around a total mass of 2150 MeV and an invariant mass for the $K \bar{K}$ system around 970 MeV, very close to the $f_0(980)$ mass. The state appears in I=0 and qualifies as a $ϕf_0(980)$ resonance. We enlarge the space of states including $ϕππ$, since $ππ$ and $K \bar{K}$ build up the $f_0$ (980), and find moderate changes that serve to quantify theoretical uncertainties. No state is seen in I=1. This finding provides a natural explanation for the recent state found at BABAR and BES, the X(2175), which decays into $ϕf_0(980)$.

nucl-th↗
arXiv2008

Application of the RMF mass model to the r-process and the influence of mass uncertainties

A new mass table calculated by the relativistic mean field approach with the state-dependent BCS method for the pairing correlation is applied for the first time to study r-process nucleosynthesis. The solar r-process abundance is well reproduced within a waiting-point approximation approach. Using an exponential fitting procedure to find the required astrophysical conditions, the influence of mass uncertainty is investigated. R-process calculations using the FRDM, ETFSI-Q and HFB-13 mass tables have been used for that purpose. It is found that the nuclear physical uncertainty can significantly influence the deduced astrophysical conditions for the r-process site. In addition, the influence of the shell closure and shape transition have been examined in detail in the r-process simulations.

astro-ph↗
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

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.

nucl-th↗
arXiv2008

The role of the $Λ(1405)$ in the $pp\to p K^+Λ(1405)$ reaction

We report a theoretical study of the $pp\to p K^+Λ(1405)$ reaction, which was recently investigated at COSY-Jülich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. The reaction is driven by single kaon exchange, single pion exchange, and single rho exchange terms which have very different shapes due to the two pole structure of the $Λ(1405)$ and the presence of background terms. The shape for the sum of the three contributions, as well as the total cross section, are consistent with present data within experimental and theoretical uncertainties, using reasonable form factors for the meson-baryon vertices.

hep-ph↗
arXiv2007

Recent Developments in Chiral Unitary Dynamics of Resonances

In this talk I summarize recent findings made on the description of axial vector mesons as dynamically generated states from the interaction of peseudoscalar 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. Finally, 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 dynamics.

nucl-th↗
arXiv2007

The WA3 data and the two $K_1(1270)$ resonances

Recent studies based on unitary chiral perturbation theory (U$χ$PT) found that the low-lying axial vector mesons can be dynamically generated due to the interaction of the pseudoscalar octet of the pion and the vector nonet of the rho. In particular, two poles in the second Riemann sheet have been associated to the nominal $K_1(1270)$ resonance. In this talk, we present a recent analysis of the WA3 data on $K^-p\to K^-π^+π^- p$ at 63 GeV using the U$χ$PT amplitudes, and show that it is in favor of the existence of two $K_1(1270)$'s [Phys. Rev. D 75, 014017 (2007)].

hep-ph↗
arXiv2007

The nature of the Lambda(1405)

We present here some results supporting the nature of the $Λ(1405)$ resonance as dynamically generated from the meson baryon interaction in coupled channels and resulting from the superposition of two close-by poles. We find support for this picture in the $K^- p \to π^0 π^0 Σ^0 $ reaction, which shows a different shape than the one obtained from the $π^- p \to K^0 πΣ$ reaction. We also call the attention to the $K^- p \to γπΣ$ with $πΣ$ in the $Λ(1405)$ region, which shows a narrow peak in the calculations around 1420 MeV. We also report on recent calculations of the radiative decay of the two $Λ(1405)$ states and on reactions to obtain information on these decay modes. Finally, we present results for the $pp\to p K^+Λ(1405)$ reaction recently measured at ANKE/COSY and compare them with theoretical results.

nucl-th↗
arXiv2007

Neutrino-induced coherent pion production

We have investigated the neutrino induced coherent pion production reaction at the energies of interest for recent experiments like K2K and MiniBooNE. The model includes pion, nucleon and the Delta(1232) resonance. Medium effects in the production mechanism and the distortion of the pion wave function are taken into account. We find a strong reduction of the cross section due to these effects and also substantial modifications in the energy distributions of the final pion. The sensitivity of the results on the axial N-Delta coupling C5A(0) and the coherent fraction in neutral-current pi0 production are discussed.

nucl-th↗