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Register a new user$N^*(1535) rightarrow N $ transition form-factors due to the axial current
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The form-factors for the transition $ N^*(1535)to N $ induced by isovector and isoscalar axial currents within the framework of light-cone QCD sum rules by using the most general form of the interpolating current are calculated. In numerical calculations, we use two sets of values of input parameters. It is observed that the $ Q^2 $ dependence of the form-factor $ G_A $ can be described by the dipole form. Moreover, the form-factors $ G_P^{(S)} $ are found to be highly sensitive to the variations in the auxiliary parameter $ beta $.
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We calculate the axial $Nto Delta(1232)$ and $Nto N^{star}(1440)$ transition form factors in a chiral constituent quark model. As required by the partial conservation of axial current ($PCAC$) condition, we include one- and two-body axial exchange currents. For the axial $Nto Delta(1232)$ form factors we compare with previous quark model calculations that use only one-body axial currents, and with experimental analyses. The paper provides the first calculation of all weak axial $Nto N^{star}(1440)$ form factors. Our main result is that exchange currents are very important for certain axial transition form factors. In addition to improving our understanding of nucleon structure, the present results are relevant for neutrino-nucleus scattering cross section predictions needed in the analysis of neutrino mixing experiments.
We discuss how electromagnetic properties provide useful tests of the nature of resonances, and we study these properties for the N*(1535) which appears dynamically generated from the strong interaction of mesons and baryons. Within this coupled channel chiral unitary approach, we evaluate the A_1/2 and S_1/2 helicity amplitudes as a function of Q^2 for the electromagnetic N*(1535) to gamma* N transition. Within the same formalism we evaluate the cross section for the reactions gamma N to eta N. We find a fair agreement for the absolute values of the transition amplitudes, as well as for the Q^2 dependence of the amplitudes, within theoretical and experimental uncertainties discussed in the paper. The ratios obtained between the S_1/2 and A_1/2 for the neutron or proton states of the N*(1535) are in qualitative agreement with experiment and there is agreement on the signs. The same occurs for the ratio of cross sections for the eta photoproduction on neutron and proton targets in the vicinity of the N*(1535) energy. The global results support the idea of this resonance as being dynamically generated, hence, largely built up from meson baryon components. However, the details of the model indicate that an admixture with a genuine quark state is also demanded that could help obtain a better agreement with experimental data.
The form factors of $gamma^* N rightarrow Delta(1600)$ transition is calculated within the light-cone sum rules assuming that $Delta^+(1600)$ is the first radial excitation of $Delta(1232)$. The $Q^2$ dependence of the magnetic dipole $tilde{G}_M(Q^2)$, electric quadrupole $tilde{G}_E(Q^2)$, and Coulomb quadrupole $tilde{G}_c(Q^2)$ form factors are investigated. Moreover, the $Q^2$ dependence of the ratios $R_{EM} = -frac{tilde{G}_E(Q^2)}{tilde{G}_M{Q^2}}$ and $R_{SM} = - frac{1}{4 m_{Delta(1600)}^2} sqrt{4 m_{Delta(1600)}^2 Q^2 + (m_{Delta(1600)}^2 - Q^2 - m_N^2)^2} frac{tilde{G}_c(Q^2)}{tilde{G}_M(Q^2)}$ are studied. Finally, our predictions on $tilde{G}_M(Q^2)$, $tilde{G}_E(Q^2)$, and $tilde{G}_C(Q^2)$ are compared with the results of other theoretical approaches.
The C2/M1 ratio of the electromagnetic N->Delta(1232) transition, which is important for determining the geometric shape of the nucleon, is shown to be related to the neutron elastic form factor ratio G_C^n/G_M^n. The proposed relation holds with good accuracy for the entire range of momentum transfers where data are available.
We present a new method to determine the momentum dependence of the N to Delta transition form factors and demonstrate its effectiveness in the quenched theory at $beta=6.0$ on a $32^3 times 64$ lattice. We address a number of technical issues such as the optimal combination of matrix elements and the simultaneous overconstrained analysis of all lattice vector momenta contributing to a given momentum transfer squared, $Q^2$.
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