L. Alvarez-Ruso

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 (chiPT) within the extended-on-mass-shell renormalization scheme. 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. This success is in dramatic contrast with previous attempts at the same order using heavy-baryon chiPT and covariant infrared chiPT. We also analyze the source of this improvement with particular attention to the comparison between the covariant results.

Nucleon mass and pion-nucleon sigma term from a chiral analysis of lattice QCD data

We investigate the pion-mass dependence of the nucleon mass within the covariant SU (2) baryon chiral perturbation theory up to order p 4 with and without explicit Δ (1232) degrees of freedom. We fit lattice QCD data from several collaborations for 2 and 2+1 flavor ensembles. Here, we emphasize our N f = 2 study where the inclusion the Δ (1232) contributions stabilizes the fits. We correct for finite volume and spacing effects, set independently the lattice QCD scale by a Sommer-scale of r 0 = 0.493(23) fm and also include one σ π N lQCD data point at M π ≈ 290 MeV. We obtain low-energy constants of natural size which are compatible with the rather linear pion-mass dependence observed in lattice QCD. We report a value of σ π N = 41(5)(4) MeV for the 2 flavor case and σ π N = 52(3)(8) MeV for 2+1 flavors.

Watson's theorem and the

We present a new determination of the

N\Delta(1232)

N\mathrm{\ensuremath{\Delta}}

axial transition

axial form factors from neutrino induced pion production data. For this purpose, the model of Hernandez et al. [Phys. Rev. D 76, 033005 (2007)] is improved by partially restoring unitarity. This is accomplished by imposing Watsons theorem on the dominant vector and axial multipoles. As a consequence, a larger

Photon emission in neutral current interactions at intermediate energies

{C}_{5}^{A}(0)

νd→μ−Δ++nreaction and axial vectorN−Δcoupling

, in good agreement with the prediction from the off-diagonal Goldberger-Treiman relation, is now obtained.

Single photon events from neutral current interactions at MiniBooNE

Neutral current photon emission reactions with nucleons and nuclei are studied. These processes are important backgrounds for nu_mu to nu_e (bar(nu)_mu to bar(nu)_e) appearance oscillation experiments where electromagnetic showers instigated by electrons (positrons) and photons are not distinguishable. At intermediate energies, these reactions are dominated by the weak excitation of the Delta(1232) resonance and its subsequent decay into Ngamma There are also non-resonant contributions that, close to threshold, are fully determined by the effective chiral Lagrangian of strong interactions. In addition, we have also included mechanisms mediated by nucleon excitations (N*) from the second resonance region above the Delta(1232). From these states, the contribution of the D13 N*(1520) turns out to be sizable for (anti)neutrino energies above 1.5 GeV. We have extended the model to nuclear targets taking, into account Pauli blocking, Fermi motion and the in-medium Delta resonance broadening. We present our predictions for both the incoherent and coherent channels, showing the relevance of the nuclear corrections. We also discuss the target mass dependence of the cross sections. This study is important in order to reduce systematic effects in neutrino oscillation experiments.

Antineutrino induced Λ ( 1405 ) production off the proton

The reaction

THE NUCLEON MASS AND PION-NUCLEON SIGMA TERM FROM A CHIRAL ANALYSIS OF Nf = 2 + 1 LATTICE QCD WORLD DATA

\nu d \to \mu^- \Delta^{++} n