arXiv subjects

A. I. Milstein

Publications and source records attributed to A. I. Milstein.

At least 73 records · Page 4Linked to original sources

arXiv2014

Coulomb corrections to electron scattering on the extended source and the proton charge radius

It is shown that the account for the proton charge form factor in the Coulomb corrections to the electron-proton scattering cross section noticeably diminishes the difference between the value of the proton charge radius $r_{\mathrm{E}}$, extracted from the $ep$ scattering data, and that following from the muonic hydrogen data. For the electron energy much higher than the electron mass but much smaller than $r_{\mathrm{E}}^{-1}\approx 230$~MeV, the relative correction has the universal form $δr_{\mathrm{E}}/r_{\mathrm{E}}=-πα/2$, where $α$ is the fine structure constant.

hep-ph↗

arXiv2013

Charge asymmetry in high-energy $μ^+μ^-$ photoproduction in the electric field of a heavy atom

The charge asymmetry in the differential cross section of high-energy $μ^+μ^-$ photoproduction in the electric field of a heavy atom is obtained. This asymmetry arises due to the Coulomb corrections to the amplitude of the process (next-to-leading term with respect to the atomic field). The deviation of the nuclear electric field from the Coulomb field at small distances is crucially important for the charge asymmetry. Though the Coulomb corrections to the total cross section are negligibly small, the charge asymmetry is measurable for selected final states of $μ^+$ and $μ^-$. We further discuss the feasibility for experimental observation of this effect.

nucl-th↗

arXiv2013

Isoscalar amplitude dominance in $e^+e-$ annihilation to $N\bar{N}$ pair close to the threshold

We use the Paris nucleon-antinucleon optical potential for explanation of experimental data in the process $e^+e^- \rightarrow p\bar p$ near threshold. It turns out that final-state interaction due to Paris optical potential allows us to reproduce available experimental data. It follows from our consideration that the isoscalar form factor is much larger than the isovector one.

hep-ph↗

arXiv2013

Kinetics of polarization in non-relativistic scattering

An approach is developed, which essentially simplifies derivation of kinetic equation for polarization in non-relativistic scattering. This approach is applicable for collision of projectile particles with a target for any spins of colliding particles. The most detailed consideration is performed for the case of spin 1/2 projectile particle interacting with spin 1/2 particle of a target. The solution of the kinetic equation for the case of zero initial polarization is presented.

physics.atom-ph↗

arXiv2013

Final state Coulomb interaction and asymmetry of pair production close to threshold in $e^+e^-$ annihilation

We investigate a contribution of the $d$ wave to the cross section of $e^+e^-$ annihilation to the pair of charged leptons or nucleons close to threshold of the process. In contrast to the point of view accepted in literature, due to the Coulomb final state interaction this contribution does not vanish even at zero relative velocity of produced particles. This results in the nonzero asymmetry in angular distribution at threshold. Though value of the asymmetry is small, observation of this effect is not hopeless.

hep-ph↗

arXiv2012

Does the side jump effect exist?

The side-jump effect is a manifestation of the spin orbit interaction in electron scattering from an atom/ion/impurity. The effect has a broad interest because of its conceptual importance for generic spin-orbital physics, in particular the effect is widely discussed in spintronics. We reexamine the effect accounting for the exact nonperturbative electron wave function inside the atomic core. We find that value of the effect is much smaller than estimates accepted in literature. The reduction factor is 1/Z^2, where Z is the nucleus charge of the atom/impurity. This implies that the side-jump effect is practically irrelevant for spintronics, the skew scattering and/or the intrinsic mechanism always dominate the anomalous Hall and spin Hall effects.

cond-mat.mes-hall↗

arXiv2012

Quasiclassical approach to high-energy QED processes in strong laser and atomic fields

An approach, based on the use of the quasiclassical Green's function, is developed for investigating high-energy quantum electrodynamical processes in combined strong laser and atomic fields. Employing an operator technique, we derive the Green's function of the Dirac equation in an arbitrary plane wave and a localized potential. Then, we calculate the total cross section of high-energy electron-positron photoproduction in an atomic field of arbitrary charge number (Bethe-Heitler process) in the presence of a strong laser field. It is shown that the laser field substantially modifies the cross section at already available incoming photon energies and laser parameters. This makes it feasible to observe the analogous effect in a laser field of the Landau-Pomeranchuk-Migdal effect for the Bethe-Heitler process.

physics.atom-ph↗

arXiv2012

New quantum-mechanical phenomenon in a model of electron-electron interaction in graphene

A quantum mechanical model of two interacting electrons in graphene is considered. We concentrate on the case of zero total momentum of the pair. We show that the dynamics of the system is very unusual. Both stationary and time-dependent problems are considered. It is shown that the complete set of the wave functions with definite energy includes the new functions, previously overlooked. The time evolution of the wave packet, corresponding to the scattering problem setup, leads to the appearance of the localized state at large time. The asymptotics of this state is found analytically. We obtain the lower bound of the life time of this state, which is connected with the breakdown of the continuous model on the lattice scale. The estimate of this bound gives one a hope to observe the localized states in the experiment.

cond-mat.str-el↗

arXiv2012

Angular distribution of high-energy $e^+e^-$ photoproduction close to the end of spectrum

We consider the differential cross section of electron-positron pair production by a high-energy photon in a strong Coulomb field close to the end of the electron or positron spectrum. When the momentum transfer largely exceeds the electron mass, the cross section is obtained analytically in a compact form. Coulomb corrections essentially modify the cross section even for moderate values of the nuclear charge number $Z$. In the same kinematical region, the angular distribution for bound-free pair production, bremsstrahlung, and photorecombination is also obtained.

physics.atom-ph↗

arXiv2011

Charge asymmetry in the differential cross section of high-energy e+e- photoproduction in the field of a heavy atom

First quasiclassical correction to the differential cross section of high-energy electron-positron photoproduction in the electric field of a heavy atom is obtained with the exact account of the field. This correction is responsible for the charge asymmetry ${\cal A}$ in this process. When the transverse momentum of at least one of the produced particles is much larger than the electron mass $m$, the charge asymmetry can be as large as tens percent. We also estimate the contribution $\tilde{\cal A}$ to the charge asymmetry coming from the Compton-type diagram. For heavy nuclei, this contribution is negligible. For light nuclei, $\tilde{\cal A}$ is noticeable only when the angle between the momenta of electron and positron is of order of $m/ω$ ($ω$ is the photon energy) while the transverse momenta of both particles are much larger than $m$.

hep-ph↗

arXiv2011

Heavy quark spin structure in Z_b resonances

We discuss the heavy quark spin structure of the recently observed `twin' resonances $Z_b(10610)$ and $Z_b(10650)$ assuming that these are mostly of a `molecular' type, i.e. that their internal dynamics is dominated by the coupling to meson pairs $B^* \bar B - B {\bar B}^*$ and $B^* {\bar B}^*$. We find that the state of the $b \bar b$ pair within the $Z_b(10610)$ and $Z_b(10650)$ resonances is a mixture of a spin-triplet and a spin-singlet of equal amplitude and with the phase orthogonal between the two resonances. Such a structure gives rise to specific relations between observable amplitudes that are in agreement with the data obtained recently by Belle. We also briefly discuss possible properties of the isotopically singlet counterparts of the newly found resonances, and also of their $C$ ($G$) parity opposites that likely exist in the same mass range near the open $B$ flavor threshold.

hep-ph↗

arXiv2011

Effective field theories and spin-wave excitations in helical magnets

We consider two classes of helical magnets. The first one has magnetic ordering close to antiferromagnet and the second one has magnetic ordering close to ferromagnet. The first case is relevant to cuprate superconductors and the second case is realized in FeSrO$_3$ and FeCaO$_3$. We derive the effective field theories for these cases and calculate corresponding excitation spectra. We demonstrate that the "hourglass" spin-wave dispersion observed experimentally in cuprates is a fingerprint of the "antiferromagnetic spin spiral state". We also show that quantum fluctuations are important for the "ferromagnetic spin spiral", they influence qualitative features of the spin-wave dispersion.

cond-mat.str-el↗

arXiv2011

Relativistic Coulomb Green's function in $d$-dimensions

Using the operator method, the Green's functions of the Dirac and Klein-Gordon equations in the Coulomb potential $-Zα/r$ are derived for the arbitrary space dimensionality $d$. Nonrelativistic and quasiclassical asymptotics of these Green's functions are considered in detail.

physics.atom-ph↗

arXiv2010

Nucleon polarization in the process $e^+e^-\to N\bar{N}$ near threshold

The process $e^+e^- \rightarrow N\bar N$ is studied nearby a threshold with account for polarizations of all initial and final particles. The nucleon polarization $\bm ζ^N$ reveals a strong energy dependence due to that of the nucleon electromagnetic form factors $G_E(Q^2)$ and $G_M(Q^2)$ caused by the final-state interaction of nucleons. It is shown that the modulus of the ratio of these form factors and their relative phase can be determined by measuring $\bm ζ^N$ along with the differential cross section. The polarization degree is analyzed using Paris $N\bar N$ optical potential for calculation of the form factors. It turns out that $|\bm ζ^N|$ is high enough in a rather wide energy range above the threshold. Being especially high for longitudinally polarized beams, $|\bm ζ^N|$ is noticeable even if both $e^+e^-$ beams are unpolarized.

hep-ph↗

arXiv2010

Polarization of the electron and positron produced in combined Coulomb and strong laser fields

The process of $e^+e^-$ production in the superposition of a Coulomb and a strong laser field is considered. The pair production rate integrated over the momentum and summed over the spin projections of one of the particles is derived exactly in the parameters of the laser field and in the Born approximation with respect to the Coulomb field. The case of a monochromatic circularly polarized laser field is considered in detail. A very compact analytical expression of the pair production rate and its dependence on the polarization of one of the created particles is obtained in the quasiclassical approximation for the experimentally relevant case of an undercritical laser field. As a result, the polarization of the created electron (positron) is derived.

hep-ph↗

arXiv2010

Measurement of B(J/psi->eta_c gamma) at KEDR

We present a study of the inclusive photon spectrum from 6.3 million J/psi decays collected with the KEDR detector at the VEPP-4M e+e- collider. We measure the branching fraction of the radiative decay J/psi -> eta_c gamma, eta_c width and mass. Taking into account an asymmetric photon line shape we obtain: M(eta_c) = (2978.1 +- 1.4 +- 2.0) MeV/c^2, Gamma(eta_c) = (43.5 +- 5.4 +- 15.8) MeV, B(J/psi->eta_c gamma) = (2.59 +- 0.16 +- 0.31)%$.

hep-ex↗

arXiv2010

Effect of a strong laser field on $e^+ e^-$ photoproduction by relativistic nuclei

We study the influence of a strong laser field on the Bethe-Heitler photoproduction process by a relativistic nucleus. The laser field propagates in the same direction as the incoming high-energy photon and it is taken into account exactly in the calculations. Two cases are considered in detail. In the first case, the energy of the incoming photon in the nucleus rest frame is much larger than the electron's rest energy. The presence of the laser field may significantly suppress the photoproduction rate at soon available values of laser parameters. In the second case, the energy of the incoming photon in the rest frame of the nucleus is less than and close to the electron-positron pair production threshold. The presence of the laser field allows for the pair production process and the obtained electron-positron rate is much larger than in the presence of only the laser and the nuclear field. In both cases we have observed a strong dependence of the rate on the mutual polarization of the laser field and of the high-energy photon and the most favorable configuration is with laser field and high-energy photon linearly polarized in the same direction. The effects discussed are in principle measurable with presently available proton accelerators and laser systems.

hep-ph↗

arXiv2010

High-energy $e^+e^-$ photoproduction cross section close to the end of spectrum

We consider the cross section of electron-positron pair production by a high-energy photon in a strong Coulomb field close to the end of electron or positron spectrum. We show that the cross section essentially differs from the result obtained in the Born approximation as well as form the result which takes into account the Coulomb corrections under assumption that both electron and positron are ultrarelativistic. The cross section of bremsstrahlung in a strong Coulomb field by a high-energy electron is also obtained in the region where the final electron is not ultrarelativistic.

physics.atom-ph↗