Threshold Neutral Pion Photoproduction on the Proton

The neutral pion photoproduction on the proton near threshold has a very small scattering cross section when compared to the charged channels, which in ChPT is explained by strong cancellations between the lowest order pieces. Therefore it is very sensitive to higher-order corrections of chiral perturbation theory. We perform a fully covariant calculation up to chiral order p^3 and we investigate the effect of the inclusion of the Delta(1232) resonance as an explicit degree of freedom. We show that the convergence improves, leading to a much better agreement with data at a wide range of energies.Comment: Proceedings to the NSTAR2015 conference, which will be published in JPS conference proceeding

Tensor properties of the nucleon

We report in the present talk recent results of the tensor properties of the nucleon within the framework of the chiral quark-soliton model. The tensor and anomalous tensor magnetic form factors are calculated for the momentum transfer up to $Q^{2}\leq1\,\mathrm{GeV}^{2}$ and at a renormalization scale of $0.36\,\mathrm{GeV}^{2}$. The main results are summarized as follows: the flavor tensor charges of the nucleon are yielded as $\delta u=1.08$, $\delta d=-0.31$, $\delta s=-0.01$, while the up and down anomalous tensor magnetic moments are evaluated as $\kappa_{T}^{u}=3.56$ and $\kappa_{T}^{d}=1.83$, respectively. The strange anomalous tensor magnetic moment turns out to be $\kappa_{T}^{s}=0.2\sim -0.2$, compatible with zero. We discuss their physical implications, comparing them in particular with those from the lattice QCD.Comment: 4 pages. 4 figures. A talk given at International Conference on the structure of baryons, BARYONS 2010, Dec. 7-11, 2010, Osaka, Japa

Hyperon forward spin polarizability gamma0 in baryon chiral perturbation theory

We present the calculation of the hyperon forward spin polarizability gamma0 using manifestly Lorentz covariant baryon chiral perturbation theory including the intermediate contribution of the spin 3/2 states. As at the considered order the extraction of gamma0 is a pure prediction of chiral perturbation theory, the obtained values are a good test for this theory. After including explicitly the decuplet states, our SU(2) results have a very good agreement with the experimental data and we extend our framework to SU(3) to give predictions to the hyperons' gamma0 values. Prominent are the Sigma^- and Xi^- baryons as their photon transition to the decuplet is forbidden in SU(3) symmetry and therefore they are not sensitive to the explicit inclusion of the decuplet in the theory

Background field approach to electromagnetic properties of baryons

We investigate the self-energies of particles in an external magnetic field $B$. The dependence is generally of the type $\sqrt{P(B)}$ with $P$ a polynomial in $B$ and the participating masses. The non-analytic point depends on the mass and charge constellations, is unproblematic for stable particles but constrains the linear energy shift approximation for resonances. We calculate the $B$ dependent self-energies of the nucleon and $\Delta(1232)$-isobar in the SU(2) covariant chiral perturbation theory and outline a way to obtain finite volume corrections to the nucleon anomalous magnetic moment without using the three point function method. We show that finite volume corrections might explain present discrepancies of lattice QCD and chiral perturbation theory results in the small pion mass region.Comment: revised, Refs adde

Electromagnetic properties of the Delta(1232) and decuplet baryons in the self-consistent SU(3) chiral quark-soliton model

We examine the electromagnetic properties of the Delta(1232) resonance within the self-consistent chiral quark-soliton model. In particular we present the Delta form factors of the vector-current GE0, GE2 and GM1 for a momentum-transfer range of $Q^{2} \leq 1GeV^{2}$. We apply the symmetry-conserving quantization of the soliton and take 1/N_c rotational corrections into account. Values for the magnetic moments of all decuplet baryons as well as for the N-Delta transition are given. Special interest is also given to the electric quadrupole moment of the Delta.Comment: 24 pages, 8 figure

Semileptonic hyperon decays in the self-consistent SU(3) chiral quark-soliton model

We investigate the semileptonic hyperon decays within the framework of the self-consistent SU(3) chiral quark-soliton model ($\chi$QSM). We take linear $1/N_c$ rotational as well as linear $m_s$ corrections into account and apply the symmetry conserving quantization. We present the results for the form factors $f_1(Q^2)$, $f_2(Q^2)$ and $g_1(Q^2)$ in addition to the semileptonic decay constants of hyperons. We also have calculated the radii and dipole masses of these form factors for all relevant strangeness-conserving and strangeness-changing transitions.Comment: 29 pages, 6 figure

Transverse strange quark spin structure of the nucleon

We investigate the transverse quark spin densities of the nucleon with the lowest moment within the framework of the SU(3) chiral quark-soliton model, emphasizing the strange quark spin density. Based on previous results of the vector and tensor form factors, we are able to determine the impact-parameter dependent probability densities of transversely polarized quarks in an unpolarized nucleon as well as those of unpolarized quarks in a transversely polarized nucleon. We find that the present numerical results for the transverse spin densities of the up and down quarks are in good agreement with those of the lattice calculation. We predict the transvere spin densities of the strange quark. It turns out that the polarized strange quark is noticeably distorted in an unpolarized proton.Comment: 10 pages. 16 figures. Submitted to Physical Review