234 research outputs found
Radiative Effects in the Standard Model Extension
The possibility of radiative effects induced by the Lorentz and CPT
non-invariant interaction term for fermions in the Standard Model Extension is
investigated. In particular, electron-positron photo-production and photon
emission by electrons and positrons are studied. The rates of these processes
are calculated in the Furry picture. It is demonstrated that the rates obtained
in the framework of the model adopted strongly depend on the polarization
states of the particles involved. As a result, ultra-relativistic particles
produced should occupy states with a preferred spin orientation, i.e., photons
have the sign of polarization opposite to the sign of the effective potential,
while charged particle are preferably in the state with the helicity coinciding
with the sign of the effective potential. This leads to evident spatial
asymmetries which may have certain consequences observable at high energy
accelerators, and in astrophysical and cosmological studies.Comment: 10 pages, 2 figures, Revtex4, to appear in Phys.Rev.D, misprints are
correcte
New bounds on neutrino magnetic moment and re-examination of plasma effect in neutrino spin light
Recent discussion on the possibility to obtain more stringent bounds on
neutrino magnetic moment has stimulated new interest to possible effects
induced by neutrino magnetic moment. In particular, in this note after a short
review on neutrino magnetic moment we re-examine the effect of plasmon mass on
neutrino spin light radiation in dense matter. We track the entry of the
plasmon mass quantity in process characteristics and found out that the most
substantial role it plays is the formation of the process threshold. It is
shown that far from this point the plasmon mass can be omitted in all the
corresponding physical quantities and one can rely on the results of massless
photon spin light radiation theory in matter.Comment: to appear in Nuovo Cimento 35 C, No. 1, 2012 (based on the talk
presented at the 25th Rencontres de Physique de la Vallee d'Aoste on "Results
and Perspectives in Particle Physics", La Thuile, February 27 - March 5, 201
Bound-state beta-decay of a neutron in a strong magnetic field
The beta-decay of a neutron into a bound state and an antineutrino
in the presence of a strong uniform magnetic field ( G) is
considered. The beta-decay process is treated within the framework of the
standard model of weak interactions. A Bethe-Salpeter formalism is employed for
description of the bound system in a strong magnetic field. For the
field strengths G G the estimate for the
ratio of the bound-state decay rate and the usual (continuum-state) decay
rate is derived. It is found that in such strong magnetic fields . This is in contrast to the field-free case, where [J. N. Bahcall, Phys. Rev. {\bf 124}, 495 (1961); L.
L. Nemenov, Sov. J. Nucl. Phys. {\bf 15}, 582 (1972); X. Song, J. Phys. G:
Nucl. Phys. {\bf 13}, 1023 (1987)]. The dependence of the ratio on
the magnetic field strength exhibits a logarithmic-like behavior. The
obtained results can be important for applications in astrophysics and
cosmology.Comment: 22 pages (revtex4), 1 figure; v2: more detailed discussion on
astrophysical applications in conclusion section, accepted for publication in
Phys. Rev.
Quantum treatment of neutrino in background matter
Motivated by the need of elaboration of the quantum theory of the spin light
of neutrino in matter (), we have studied in more detail the exact
solutions of the Dirac equation for neutrinos moving in the background matter.
These exact neutrino wavefunctions form a basis for a rather powerful method of
investigation of different neutrino processes in matter, which is similar to
the Furry representation of quantum electrodynamics in external fields. Within
this method we also derive the corresponding Dirac equation for an electron
moving in matter and consider the electromagnetic radiation ("spin light of
electron in matter", ) that can be emitted by the electron in this case.Comment: 10 pages, in: Proceedings of QFEXT'05 (The Seventh Workshop on
Quantum Field Theory under the Influence of External Conditions, IEEC, CSIC
and University of Barcelona, Barcelona, Catalonia, Spain, 5-9 September
2005.), ed. by Emilio Elizalde and Sergei Odintsov; published in Journal of
Physics
Neutrino spin oscillations in gravitational fields
We study neutrino spin oscillations in gravitational fields. The
quasi-classical approach is used to describe the neutrino spin evolution. First
we examine the case of a weak gravitational field. We obtain the effective
Hamiltonian for the description of neutrino spin oscillations. We also receive
the neutrino transition probability when a particle propagates in the
gravitational field of a rotating massive object. Then we apply the general
technique to the description of neutrino spin oscillations in the Schwarzschild
metric. The neutrino spin evolution equation for the case of the neutrino
motion in the vicinity of a black hole is obtained. The effective Hamiltonian
and the transition probability are also derived. We examine the neutrino
oscillations process on different circular orbits and analyze the frequencies
of spin transitions. The validity of the quasi-classical approach is also
considered.Comment: RevTeX4, 9 pages, 1 esp figure; article was revised, some misprints
were corrected, 6 references added; accepted for publication in
Int.J.Mod.Phys.
Modification of Coulomb law and energy levels of the hydrogen atom in a superstrong magnetic field
We obtain the following analytical formula which describes the dependence of
the electric potential of a point-like charge on the distance away from it in
the direction of an external magnetic field B: \Phi(z) = e/|z| [ 1-
exp(-\sqrt{6m_e^2}|z|) + exp(-\sqrt{(2/\pi) e^3 B + 6m_e^2} |z|) ]. The
deviation from Coulomb's law becomes essential for B > 3\pi B_{cr}/\alpha = 3
\pi m_e^2/e^3 \approx 6 10^{16} G. In such superstrong fields, electrons are
ultra-relativistic except those which occupy the lowest Landau level (LLL) and
which have the energy epsilon_0^2 = m_e^2 + p_z^2. The energy spectrum on which
LLL splits in the presence of the atomic nucleus is found analytically. For B >
3 \pi B_{cr}/\alpha, it substantially differs from the one obtained without
accounting for the modification of the atomic potential.Comment: version to be published in Physical Review D (incorrect "Keywords" in
previous version have been cancelled
The Exact Electron Propagator in a Magnetic Field as the Sum over Landau Levels on a Basis of the Dirac Equation Exact Solutions
The exact propagator for an electron in a constant uniform magnetic field as
the sum over Landau levels is obtained by the direct derivation by standard
methods of quantum field theory from exact solutions of the Dirac equation in
the magnetic field. The result can be useful for further development of the
calculation technique of quantum processes in an external active medium,
particularly in the conditions of moderately large field strengths when it is
insufficient to take into account only the ground Landau level contribution.Comment: 9 pages, LaTeX; v2: 3 misprints corrected, a note and 1 reference
added; to appear in Int. J. Mod. Phys.
Synchrotron Radiation in the Standard Model Extension
We obtain a system of exact solutions of the Dirac equation for an electron
moving in a constant homogeneous external magnetic field with account of its
vacuum magnetic moment and assumed Lorentz invariance violation in the minimal
CPT-odd form in the framework of the Standard Model Extension. Using these
solutions, characteristics of the particle synchrotron radiation are
calculated, and possible observable effects caused by the Lorentz non-invariant
interaction are described. We demonstrate that the angular distribution of the
radiation has specific asymmetry, which can be explained as a consequence of
non-conservation of transversal electron polarization in the presence of a
background Lorentz non-invariant condensate field.Comment: 14 pages, 2 figure
Chiral density waves in quark matter within the Nambu--Jona-Lasinio model in an external magnetic field
A possibility of formation of static dual scalar and pseudoscalar density
wave condensates in dense quark matter is considered for the
Nambu--Jona-Lasinio model in an external magnetic field. Within a mean-field
approximation, the effective potential of the theory is obtained and its minima
are numerically studied; a phase diagram of the system is constructed. It is
shown that the presence of a magnetic field favors the formation of spatially
inhomogeneous condensate configurations at low temperatures and arbitrary
non-zero values of the chemical potential.Comment: 13 pages, 4 figure
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