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A. V. Kuznetsov

Publications and source records attributed to A. V. Kuznetsov.

At least 55 records · Page 3Linked to original sources
arXiv2006

Neutrino propagation in magnetized plasma

The process of neutrino propagation through an active medium consisting of magnetic field and plasma is analysed. We consider in detail the contribution of a magnetic field B into the neutrino self-energy operator Sigma (p). The results for this contribution were contradictory in the previous literature. For the conditions of the early universe where the background medium consists of a charge-symmetric plasma, the pure B-field contribution to the neutrino dispersion relation is proportional to (e B)^2 and thus comparable to the contribution of the magnetized plasma. The neutrino self-energy operator Sigma (p) is calculated also for the case of high-energy neutrinos, which corresponds to the crossed field approximation. The probability of the neutrino decay nu to e^- W^+ is calculated from the imaginary part of the Sigma (p) operator. A simple analytical result is obtained for the most interesting region of parameters which was not considered earlier. The external magnetic field contribution into the neutrino magnetic moment is calculated. The result obtained corrects the formulas existed earlier. We show qualitatively that the effect of ``neutrino spin light'' discussed in the literature has no physical region of realization because of the medium influence on photon dispersion.

hep-ph↗
arXiv2006

Magnetic properties of collinear structures of compound La1-xCaxMnO3

With use of homogeneous model for magnetic sub-lattice of compound La1-x CaxMnO3 allowing for Heisenberg superexchange and double exchange between nearest neighbors the temperature dependence of spontaneous magnetization on a separate site is investigated in molecular field approximation. The difference from the usual magnets with one type of magnetic ions is in the fact that system of equations appears with two unknowns, being the mean spin values of ions Mn3+ and Mn4+, correspondingly. Near ordering temperature this system can be solved analytically and at the same time the expression for the ordering temperature can be obtained. To find the temperature dependence of magnetization in the whole temperature range we used the exact expression for double exchange operator containing spin operators under the square root. The numerical solutions were found in this case.

cond-mat.str-el↗
arXiv2005

Neutrino dispersion in external magnetic fields

We calculate the neutrino self-energy operator Sigma (p) in the presence of a magnetic field B. In particular, we consider the weak-field limit e B << m_\ell^2, where m_\ell is the charged-lepton mass corresponding to the neutrino flavor ν_\ell, and we consider a "moderate field" m_\ell^2 << e B << m_W^2. Our results differ substantially from the previous literature. For a moderate field, we show that it is crucial to include the contributions from all Landau levels of the intermediate charged lepton, not just the ground-state. For the conditions of the early universe where the background medium consists of a charge-symmetric plasma, the pure B-field contribution to the neutrino dispersion relation is proportional to (e B)^2 and thus comparable to the contribution of the magnetized plasma.

hep-ph↗
arXiv2005

Magnetic structure and double exchange in hypothetical compound La1-xCaxMnO3

Question about the appearance of different magnetic structures in the family of compounds La1-xCaxMnO3,is investigated theoretically. It is supposed that the whole series has GdFeO3 structure type. The problem is considered at absolute zero temperature in the nearest neighbor approximation. Superexchange, double exchange and anisotropy energy are taken into account-all together 10 interaction parameters. The spin operator of double exchange interaction in crystal between ions with different valence Mn3+ and Mn4+ is the straight generalization of two-spin operator in the known problem of Anderson and Hasegawa molecule. Minimization of the ground state energy with respect to direction angles of magnetic sub-lattices leads to a system of transcendental equations whose solutions give 11 types of magnetic configurations: two ferromagnetic, three collinear antiferromagnetic and six non-collinear. When the concentration of Ca ions x changes one spin configuration replaces another as the ground state. As a whole the sequence of configurations when x changes from 0 till 1 can be brought in correspondence to those observed on the experiment. The comparison with experiment was made by means of mixed procedure: part of numerical values of interaction parameters and transition concentrations x from one configuration to another were taken from experiment while the missing values of these parameters were calculated with the help of the corresponding theoretical relations representing the conditions of equality of different phases energies at the concentration crossing.

cond-mat.str-el↗
arXiv2004

Quantum Critiality and Collective Effects in Low Dimensional Magnet CuGeO3 Probed by High Frequency EPR

For the CuGeO3 single crystals doped with 1% of Fe the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: a=0.34 (B //a and B //c) and a=0.31 (B //b). The description of the temperature dependences of the line width and g-factor could be obtained in the OA theory assuming that staggered component of the magnetic moment is located predominantly along b axis. Possible arguments favoring the competition between effects of the staggered field and antiferromagnetic ordering are provided.

cond-mat.str-el↗
arXiv2004

Disorder driven quantum critical behavior in CuGeO3 doped with magnetic impurity

For the CuGeO3 doped with 1% of Fe the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: a=0.34 (B//a and B//c) and a=0.31 (B//b). New effect of the frequency dependence of the critical exponent is discussed.

cond-mat.str-el↗
arXiv2003

General amplitude of the n - vertex one-loop process in a strong magnetic field

A general analysis of the n-vertex loop amplitude in a strong magnetic field is performed, based on the asymptotic form of the electron propagator in the field. As an example, the photon-neutrino processes are considered, where one vertex in the amplitude is of a general type, and the other vertices are of the vector type. It is shown, that for odd numbers of vertices only the SV_1 ... V_{n-1} amplitude grows linearly with the magnetic field strength, while for even numbers of vertices the linear growth takes place only in the amplitudes PV_1 ... V_{n-1}, VV_1 ... V_{n-1} and AV_1 ... V_{n-1}. The general expressions for the amplitudes of the processes gamma gamma -> nu bar nu (in the framework of the model with the effective nu nu e e - coupling of a scalar type) and gamma gamma -> nu bar nu gamma (in the framework of the Standard Model) for arbitrary energies of particles are obtained. A comparison with existing results is performed.

hep-ph↗
arXiv2002

Could the process of neutrino photoproduction on nuclei, stimulated by a strong magnetic field, compete with URCA processes?

The recent studies is reported of the neutrino photoproduction on nuclei, gamma + Ze -> Ze + gamma + nu + anti-nu, in a strong magnetic field. It is shown that the catalyzing influence of the field on the process decreases essentially because of the modification of the photon dispersion properties in a strong magnetic field. Therefore, at any field magnitude, neutrino photoproduction cannot compete with the URCA processes. This conclusion contradicts a recent statement in the literature.

hep-ph↗
arXiv2002

Electron Mass Operator in a Strong Magnetic Field and Dynamical Chiral Symmetry Breaking

The electron mass operator in a strong magnetic field is calculated. The contribution of higher Landau levels of virtual electrons, along with the ground Landau level, is shown to be essential in the leading log approximation. The effect of the electron dynamical mass generation by a magnetic field is investigated. In a model with N charged fermions, it is shown that some critical number N_{cr} exists for any value of the electromagnetic coupling constant alpha, such that the fermion dynamical mass is generated with a doublet splitting for N < N_{cr}, and the dynamical mass does not arise at all for N > N_{cr}, thus leaving the chiral symmetry unbroken.

hep-ph↗
arXiv2002

Electron mass operator in a strong magnetic field

The electron mass operator in a strong magnetic field is calculated by summation of the leading log contributions in all orders of the perturbation theory. An influence of the strong field on the virtual photon polarization operator is taken into account. The contribution of higher Landau levels of virtual electrons, along with the ground Landau level, is shown to be essential in the leading log approximation.

hep-ph↗
arXiv2001

Cluster of Gamma-ray Bursts - Image of a Source. Catalog of Clusters (Sources) of Gamma-ray Bursts

The clusters of gamma-ray bursts are considered which are assumed to be images of the repeated gamma-ray burst (GRB) sources. It is shown, that localization of the cosmic gamma-ray burst sources (GBS) is determined by the clusters of GRBs. About 100 candidates in sources are presented in the form of the catalog, which is compiled relying on the base of the BATSE data up to middle of 2000. Gamma-ray bursts (from 5 to 13) of a cluster that display a source do not coincide in their position. The catalog table containing basic information about the GRB sources yields the possibility to research the GBS properties and their identification. The birth of GRBs in the clusters allows predicting the appearance of GRBs both in time and space. Most general properties of the supposed GRB sources are discussed. An attempt to compile the first GRB source catalog is made.

astro-ph↗
arXiv2001

Gamma-ray bursts and black holes. Interpretation of the observational data

The paper relies upon the (Kuznetsov 2000), where the cosmic gamma - ray bursts (GRBs) in clusters are shown to have an apparent shift relative to the position of the source. Hence the main conclusion follows: only cluster of GRBs ensures correct localization of the source whereas determining the direction of arrival of a single GRB practically carries no information about the position of its source. Generation of repeated GRBs in the activity phase of the source, which amounts to 3-4 months and with the period of repetition of activity equal to 4 years are most general properties of clusters. These properties precisely correspond to the characteristics of manifestation of activity of X-ray NOVAE (BHXN), thus pointing that the source of GRB clusters considered is a black hole (BH) in the XN. The direct identification of the GRB source with the BHXN GRO J0422+32 presented here this confirms. The investigated properties of GRB clusters permit a final solution of 2 main problems of astrophysics: search for black holes and origin of cosmic GRBs.

astro-ph↗
arXiv2001

Photon-pair conversion into neutrinos in a strong magnetic field

A general analysis of the three-vertex loop amplitude in a strong magnetic field, based on the asymptotic form of the electron propagator in the field, is performed. In order to investigate the photon-neutrino process gamma gamma -> nu bar nu, the vertex combinations of the scalar-vector-vector (SVV), pseudoscalar-vector-vector (PVV), 3-vector (VVV), and axial-vector-vector-vector (AVV) types are considered. It is shown that only the SVV amplitude grows linearly with the magnetic field strength, while in the other amplitudes, PVV, VVV, and AVV, the linearly growing terms are cancelled. The process gamma gamma -> nu bar nu is investigated in the left-right-symmetric extension of the standard model of electroweak interaction, where the effective scalar nu nu e e coupling could exist. Possible astrophysical manifestations of the considered process are discussed.

hep-ph↗
arXiv2001

Electric field gradients in MgB$_2$ synthesized at high pressure: $^111$Cd TDPAC study and ab initio calculation

We report the high-pressure synthesis of novel superconductor MgB$_2$ and some related compounds. The superconducting transition temperature of our samples of MgB$_2$ is equal to 36.6 K. The MgB$_2$ lattice parameters determined via X-ray diffraction are in excellent agreement with results of our ab initio calculations. The time-differential perturbed angular correlation (TDPAC) experiments demonstrate a small increase in quadrupole frequency of $^111$Cd probe with decreasing temperature from 293 to 4.2 K. The electric field gradient (EFG) at the B site calculated from first principles is in fair agreement with EFG obtained from $^11$B NMR spectra of MgB$_2$ reported in the literature. It is also very close to EFG found in our $^111$Cd TDPAC measurements, which suggests that the $^111$Cd probe substitutes for boron in the MgB$_2$ lattice.

cond-mat.mtrl-sci↗
arXiv2000

Compton-like interaction of massive neutrinos with virtual photons

The amplitude of a Compton-like process nu_i gamma^* -> nu_j gamma^* with virtual photons is calculated in the standard GWS theory with lepton mixing. The contribution of this process to the high energy neutrino scattering on the nucleus with single photon radiation nu N -> nu N gamma is discussed. The bremsspectrum and the total cross-section are estimated in the leading log approximation.

hep-ph↗
arXiv2000

Possible scenario of the spatially separated Fermi-Bose mixture in the superconductive bismuthates Ba_{1-x}K_xBiO_3

A new scenario for superconductivity in the bismuthates based on the concept of a spatially separated Fermi-Bose mixture is proposed. In the framework of this scenario we qualitatively explain the insulator-metal transition and the nature of the superconductivity which occur in Ba_{1-x}K_xBiO_3 under doping by K. We also analyze briefly an applicability of this scenario for the high-Tc superconductors. In conclusion some additional experiments required to elucidate more precisely the nature of the superconductivity in the bismuthates are discussed.

cond-mat.supr-con↗