Pn Lebedev Physics Institute

Moscow, Russia

Pn Lebedev Physics Institute

Moscow, Russia
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Adorno T.C.,University of Sao Paulo | Gitman D.M.,University of Sao Paulo | Shabad A.E.,Pn Lebedev Physics Institute | Vassilevich D.V.,Federal University of ABC | Vassilevich D.V.,Saint Petersburg State University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

It has been argued that in noncommutative field theories, the sizes of physical objects cannot be taken smaller than an "elementary length" related to noncommutativity parameters. By gauge covariantly extending field equations of noncommutative U(1) theory to cover the presence of external sources, we find electric and magnetic fields produced by an extended static charge. We find that such a charge, apart from being an ordinary electric monopole, is also a magnetic dipole. By writing off the existing experimental clearance in the value of the lepton magnetic moments for the present effect, we get the bound on noncommutativity at the level of 104TeV. © 2011 American Physical Society.


Kalenkov M.S.,Pn Lebedev Physics Institute | Zaikin A.D.,Karlsruhe Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We formulate a quantitative theory of nonlocal electron transport in three-terminal disordered ferromagnet-superconductor-ferromagnet (FSF) structures. We demonstrate that magnetic effects have different implications. While strong exchange field suppresses disorder-induced electron interference in ferromagnetic electrodes, spin-sensitive electron scattering at superconductor-ferromagnet interfaces can drive the total nonlocal conductance g12 negative at sufficiently low energies. At higher energies, magnetic effects become less important and the nonlocal resistance behaves similarly to the nonmagnetic case. Our predictions can be directly tested in future experiments on nonlocal electron transport in hybrid FSF structures. © 2010 The American Physical Society.


Golubev D.S.,Karlsruhe Institute of Technology | Zaikin A.D.,Karlsruhe Institute of Technology | Zaikin A.D.,Pn Lebedev Physics Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We argue that Coulomb interaction can strongly influence nonlocal electron transport in normal-superconducting-normal structures and emphasize direct relation between Coulomb effects and nonlocal shot noise. In the tunneling limit nonlocal differential conductance is found to have an S-like shape and can turn negative at nonzero bias. At high transmissions crossed Andreev reflection yields positive noise cross correlations and Coulomb antiblockade of nonlocal electron transport. © 2010 The American Physical Society.


Galaktionov A.V.,Pn Lebedev Physics Institute | Zaikin A.D.,Karlsruhe Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We derive a microscopic effective action for superconducting contacts with arbitrary transmission distribution of conducting channels. Provided fluctuations of the Josephson phase remain sufficiently small our formalism allows to fully describe fluctuation and interaction effects in such systems. As compared to the well-studied tunneling limit our analysis yields a number of qualitatively distinct features which occur due to the presence of subgap Andreev bound states in the system. We investigate the equilibrium supercurrent noise and evaluate the electron-electron interaction correction to the Josephson current across superconducting contacts. At T=0 this correction is found to vanish for fully transparent contacts indicating the absence of Coulomb effects in this limit. © 2010 The American Physical Society.


Semenov A.G.,Pn Lebedev Physics Institute | Zaikin A.D.,Karlsruhe Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We analyze fluctuations of persistent current (PC) produced by a charged quantum particle moving in a ring and interacting with a dissipative environment formed by diffusive electron gas. We demonstrate that in the presence of interactions such PC fluctuations persist down to zero temperature. In the case of weak interactions and/or sufficiently small values of the ring radius R PC noise remains coherent and can be tuned by external magnetic flux Φx piercing the ring. In the opposite limit of strong interactions and/or large values of R fluctuations in the electronic bath strongly suppress quantum coherence of the particle down to T=0 and induce incoherent Φx-independent current noise in the ring, which persists even at Φx=0 when the average PC is absent. © 2011 American Physical Society.


Baranov S.P.,Pn Lebedev Physics Institute | Lipatov A.V.,Moscow State University | Zotov N.P.,Moscow State University
European Physical Journal C | Year: 2011

We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the kT - factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics. © Springer-Verlag / Società Italiana di Fisica 2011.


Baranov S.P.,Pn Lebedev Physics Institute | Lipatov A.V.,Moscow State University | Zotov N.P.,Moscow State University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

We investigate the prompt photon production in deep inelastic scattering at HERA in the framework of the kT-factorization QCD approach. Our study is based on the off-shell partonic amplitude eq*→eγq, where the photon radiation from the leptons as well as from the quarks is taken into account. The unintegrated quark densities in a proton are determined using the Kimber-Martin-Ryskin prescription. We investigate both inclusive and jet-associated prompt photon production rates. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS Collaborations. We demonstrate that in the kT-factorization approach the contribution from the quark radiation subprocess (QQ mechanism) is enhanced as compared to the leading-order collinear approximation. © 2010 The American Physical Society.


Shabad A.E.,Pn Lebedev Physics Institute | Usov V.V.,Weizmann Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

In nonlinear electrodynamics, by implementing the causality principle as the requirement that the group velocity of elementary excitations over a background field should not exceed the speed of light in the vacuum c=1, and the unitarity principle as the requirement that the residue of the propagator should be nonnegative, we establish the positive convexity of the effective Lagrangian on the class of constant fields, also the positivity of all characteristic dielectric and magnetic permittivity constants that are derivatives of the effective Lagrangian with respect to the field invariants. Violation of the general principles by the one-loop approximation in QED at exponentially large magnetic field is analyzed, resulting in complex energy ghosts that signal the instability of the magnetized vacuum. Superluminal excitations (tachyons) appear, too, but for the magnetic field exceeding its instability threshold. Also other popular Lagrangians are tested to establish that the ones leading to spontaneous vacuum magnetization possess wrong convexity. © 2011 American Physical Society.


Baranov S.P.,Pn Lebedev Physics Institute
AIP Conference Proceedings | Year: 2011

Diffractive production of D* mesons at HERA conditions is considered in the framework of collinear two-gluon exchange model. Theoretical results are compared with experimental data. © 2011 American Institute of Physics.


Shabad A.E.,Pn Lebedev Physics Institute | Usov V.V.,Weizmann Institute of Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

The photon behavior in an arbitrary superposition of constant magnetic and electric fields is considered on most general grounds based on the first principles like Lorentz, gauge, charge, and parity invariance. We make model-independent and approximation-independent, but still rather informative, statements about the behavior that the requirement of causal propagation prescribes to massive and massless branches of dispersion curves, and describe the way the eigenmodes are polarized. We find, as a consequence of Hermiticity in the transparency domain, that adding a smaller electric field to a strong magnetic field in parallel to the latter causes enhancement of birefringence. We find the magnetic field produced by a point electric charge far from it-a manifestation of magnetoelectric phenomenon. We establish degeneracies of the polarization tensor that-under special kinematical conditions-occur due to space-time symmetries of the vacuum left after the external field is imposed. © 2010 The American Physical Society.

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