Polarization of Tau Leptons Produced in Quasielastic Neutrino--Nucleon Scattering

A numerical analysis of the polarization vector of tau leptons produced through quasielastic neutrino and antineutrino interactions with free nucleons is given with two models for vector electromagnetic form factors of proton and neutron. The impact of G parity violating axial and vector second-class currents is investigated by applying a simple heuristic model for the induced scalar and tensor form factors.Comment: Thesis of a talk given at the 8th Scientific Conference (SCYSS-04), Dubna, Russia, 2 - 6 Feb 2004. 11 pages, 6 figures; added references, figures and discussion; conclusions unchange

Mass and width of the d′d' resonance in nuclei

We calculated the mass and width of the $d'$ resonance inside nuclei within a nucleon-$\Delta$ model by including the self-energy of the $\Delta$ in the $N\Delta$ propagator. We found that in the nuclear medium the width of the $d'$ is increased by one order of magnitude while its mass changes only by a few MeV. This broadening of the width of the $d'$ resonance embedded in nuclei is consistent with the experimental observations so that the $d'$ can be understood as a $N\Delta$ resonance. Thus, given the freedom between either isospin 0 or isospin 2 for the $d'$, our results give weigth to the isospin-2 assignment.Comment: 14 pages, RevteX type, 2 eps figures. To be published in Phys. Rev. C (September

Nucleon form factors, B-meson factories and the radiative return

The feasibility of a measurement of the electric and magnetic nucleon form factors at $B$-meson factories through the radiative return is studied. Angular distributions allow a separation of the contributions from the two form factors. The distributions are presented for the laboratory and the hadronic rest frame, and the advantages of different coordinate systems are investigated. It is demonstrated that $Q^2$ values up to 8 or even 9 GeV$^2$ are within reach. The Monte Carlo event generator PHOKHARA is extended to nucleon final states, and results are presented which include Next-to-Leading Order radiative corrections from initial-state radiation. The impact of angular cuts on rates and distributions is investigated and the relative importance of radiative corrections is analysed.Comment: 9 pages, 11 figures. Final version to appear in Eur. Phys. J.

Renormalization of Singlet NN-Scattering with One Pion Exchange and Boundary Conditions

We present a simple and physically compelling boundary condition regularization scheme in the framework of effective field theory as applied to nucleon-nucleon interaction. It is free of off-shell ambiguities and ultraviolet divergences and provides finite results at any step of the calculation. Low energy constants and their non-perturbative evolution can directly be obtained from experimental threshold parameters in a completely unique and model independent way when the long range explicit pion effects are removed. This allows to compute scattering phase shifts which are, by construction consistent with effective range expansion to a given order in the CM momentum and are free from finite cut-off artifacts. We illustrate how the method works in the $^1S_0$ channel for the One Pion Exchange potential.Comment: (Latex, epsfig) 7 pages, 2 figure

Deuteron Magnetic and Quadrupole Moments with a Poincar\'e Covariant Current Operator in the Front-Form Dynamics

The deuteron magnetic and quadrupole moments are unambiguosly determined within the front-form Hamiltonian dynamics, by using a new current operator which fulfills Poincar\'e, parity and time reversal covariance, together with hermiticity and the continuity equation. For both quantities the usual disagreement between theoretical and experimental results is largely removed.Comment: To appear in Phys. Rev. Let

New empirical fits to the proton electromagnetic form factors

Recent measurements of the ratio of the elastic electromagnetic form factors of the proton, G_Ep/G_Mp, using the polarization transfer technique at Jefferson Lab show that this ratio decreases dramatically with increasing Q^2, in contradiction to previous measurements using the Rosenbluth separation technique. Using this new high quality data as a constraint, we have reanalyzed most of the world e-p elastic cross section data. In this paper, we present a new empirical fit to the reanalyzed data for the proton elastic magnetic form factor in the region 0 < Q^2 < 30 GeV^2. As well, we present an empirical fit to the proton electromagnetic form factor ratio, G_Ep/G_Mp, which is valid in the region 0.1 < Q^2 < 6 GeV^2

Renormalization Group Analysis of Boundary Conditions in Potential Scattering

We analyze how a short distance boundary condition for the Schrodinger equation must change as a function of the boundary radius by imposing the physical requirement of phase shift independence on the boundary condition. The resulting equation can be interpreted as a variable phase equation of a complementary boundary value problem. We discuss the corresponding infrared fixed points and the perturbative expansion around them generating a short distance modified effective range theory. We also discuss ultraviolet fixed points, limit cycles and attractors with a given fractality which take place for singular attractive potentials at the origin. The scaling behaviour of scattering observables can analytically be determined and is studied with some emphasis on the low energy nucleon-nucleon interaction via singular pion exchange potentials. The generalization to coupled channels is also studied.Comment: 31 pages, 8 figure

Effect of tensor couplings in a relativistic Hartree approach for finite nuclei

The relativistic Hartree approach describing the bound states of both nucleons and anti-nucleons in finite nuclei has been extended to include tensor couplings for the $\omega$- and $\rho$-meson. After readjusting the parameters of the model to the properties of spherical nuclei, the effect of tensor-coupling terms rises the spin-orbit force by a factor of 2, while a large effective nucleon mass $m^{*}/M_{N} \approx 0.8$ sustains. The overall nucleon spectra of shell-model states are improved evidently. The predicted anti-nucleon spectra in the vacuum are deepened about 20 -- 30 MeV.Comment: 31 pages, 4 postscript figures include