Charge asymmetry for electron (positron)-proton elastic scattering at large angle

Charge asymmetry in electron (positron) scattering arises from the interference of the Born amplitude and the box-type amplitude corresponding to two virtual photons exchange. It can be extracted from electron proton and positron proton scattering experiments, in the same kinematical conditions. Considering the virtual photon Compton scattering tensor, which contributes to the box-type amplitude, we separate proton and inelastic contributions in the intermediate state and parametrize the proton form-factors as the sum of a pure QED term and a strong interaction term. Arguments based on analyticity are given in favor of cancellation of contributions from proton strong interaction form factors and of inelastic intermediate states in the box type amplitudes. In frame of this model, with a realistic expression for nucleon form-factors, numerical estimations are given for moderately high energies.Comment: 14 pages, 4 figure

How to reconcile the Rosenbluth and the polarization transfer method in the measurement of the proton form factors

The apparent discrepancy between the Rosenbluth and the polarization transfer method for the ratio of the electric to magnetic proton form factors can be explained by a two-photon exchange correction which does not destroy the linearity of the Rosenbluth plot. Though intrinsically small, of the order of a few percent of the cross section, this correction is kinematically enhanced in the Rosenbluth method while it is small for the polarization transfer method, at least in the range of (Q^2) where it has been used until now.Comment: 4 pages, 4 figures. Version accepted for publication in Phys. Rev. Let

Two-component model for the deuteron electromagnetic structure

We suggest a simple phenomenological parametrization for all three deuteron electromagnetic form factors, and show that a good fit on the available data, with a minimal number of parameters, can be obtained. The present description of the deuteron electromagnetic structure is based on two components with different radii, one corresponding to two nucleons separated by $\simeq$2 fm, and a standard isoscalar contribution, saturated by $\omega$ and $\phi$ mesons, only.Comment: 5 pages, 6 fig. 2 table

Polarization effects in the reaction e++e−→ρ++ρ−e^++e^-\to \rho^+ +\rho^- and determination of the ρ−\rho - meson form factors in the time--like region

The electron positron annihilation reaction into four pion production has been studied, through the channel $e^++e^-\to \bar \rho+\rho$. The differential (and total) cross sections and various polarization observables for this reaction have been calculated in terms of the electromagnetic form factors of the corresponding $\gamma^*\rho\rho$ current. The elements of the spin--density matrix of the $\rho -$meson were also calculated. Numerical estimations have been done, with the help of phenomenological form factors obtained in the space--like region of the momentum transfer squared and analytically extended to the time-like region.Comment: 19 pages, 2 figures, to appear in Phys Rev

Search for evidence of two photon contribution in elastic electron proton data

We reanalyze the most recent data on elastic electron proton scattering. We look for a deviation from linearity of the Rosenbluth fit to the differential cross section, which would be the signature of the presence of two photon exchange. The two photon contribution is parametrized by a one parameter formula, based on symmetry arguments. The present data do not show evidence for such deviation.Comment: 15 pages 3 figures More details on the fitting procedure, more explicit explanation

Superfluid states with moving condensate in nuclear matter

Superfluid states of symmetric nuclear matter with finite total momentum of Cooper pairs (nuclear LOFF phase) are studied with the use of Fermi-liquid theory in the model with Skyrme effective forces. It is considered the case of four-fold splitting of the excitation spectrum due to finite superfluid momentum and coupling of T=0 and T=1 pairing channels. It has been shown that at zero temperature the energy gap in triplet-singlet (TS) pairing channel (in spin and isospin spaces) for the SkM$^*$ force demonstrates double-valued behavior as a function of superfluid momentum. As a consequence, the phase transition at the critical superfluid momentum from the LOFF phase to the normal state will be of a first order. Behavior of the energy gap as a function of density for TS pairing channel under increase of superfluid momentum changes from one-valued to universal two-valued. It is shown that two-gap solutions, describing superposition of states with singlet-triplet (ST) and TS pairing of nucleons appear as a result of branching from one-gap ST solution. Comparison of the free energies shows that the state with TS pairing of nucleons is thermodynamically most preferable.Comment: Report on DAAD summer school "Dense matter in Particle- and Astrophysics". Prepared with RevTeX4, 5p., 4 eps figure

Second quantization method in the presence of bound states of particles

We develop an approximate second quantization method for describing the many-particle systems in the presence of bound states of particles at low energies (the kinetic energy of particles is small in comparison to the binding energy of compound particles). In this approximation the compound and elementary particles are considered on an equal basis. This means that creation and annihilation operators of compound particles can be introduced. The Hamiltonians, which specify the interactions between compound and elementary particles and between compound particles themselves are found in terms of the interaction amplitudes for elementary particles. The nonrelativistic quantum electrodynamics is developed for systems containing both elementary and compound particles. Some applications of this theory are considered.Comment: 35 page

Excitation of two-dimensional plasma wakefields by trains of equidistant particle bunches

Nonlinear effects responsible for elongation of the plasma wave period are numerically studied with the emphasis on two-dimensionality of the wave. The limitation on the wakefield amplitude imposed by detuning of the wave and the driver is found.Comment: 4 pages, 4 figure

Unusual temperature behavior of entropy of antiferromagnetic spin state in nuclear matter with effective finite range interaction

The unusual temperature behavior of the entropy of the antiferromagnetic (AFM) spin state in symmetric nuclear matter with the Gogny D1S interaction, being larger at low temperatures than the entropy of nonpolarized matter, is related to the dependence of the entropy on the effective masses of nucleons in a spin polarized state. The corresponding conditions for comparing the entropies of the AFM and nonpolarized states in terms of the effective masses are formulated, including low and high temperature limits. It is shown that the unexpected temperature behavior of the entropy of the AFM spin state at low temperatures is caused by the violation of the corresponding low temperature criterium.Comment: version accepted for publication in PR