5,603 research outputs found
Muons with E_th >= 1 Gev and Mass Composition in the Energy Range 10^{18}-10^{20} ev Observed by Yakutsk Eas Array
The ratio of the muon flux density to charged particle flux density at
distances of 300 and 600 m from the shower axis (\rhom(300)/\rhos(300) and
\rhom(600)/\rhos(600)) is measured. In addition, the energy dependence of
\rhom(1000) is analysed for showers with energies above eV. A
comparison between the experimental data and calculations performed with the
QGSJET model is given for the cases of primary proton, iron nucleus and gamma-
ray. We conclude that the showers with \E\ge3\times10^{18} eV can be formed
by light nuclei with a pronounced fraction of protons and helium nuclei. It is
not excluded however that a small part of showers with energies above
eV could be initiated by primary gamma-rays.Comment: 19th European Cosmic Ray Symposium, Aug 30 - Sep 3 2004, Florence,
Italy. 3 pages, 1 figure. Submitted for publication in International Journal
of Modern Physics
Reverberation measurement of the inner radius of the dust torus in NGC 4151 during 2008-2013
We investigate the correlation between infrared (JHKL) and optical (B) fluxes
of the variable nucleus of the Seyfert galaxy NGC 4151 using partially
published data for the last 6 years (2008-2013.). Here we are using the same
data as in Oknyansky et al. (2014), but include also optical (B) data from Guo
et al. We find that the lag of flux in all the infrared bands is the same, 40
+- 6 days, to within the measurement accuracy. Variability in the J and K bands
is not quite simultaneous, perhaps due to the differing contributions of the
accretion disk in these bands. The lag found for the K band compared with the B
band is not significantly different from earlier values obtained for the period
2000-2007. However, finding approximately the same lags in all IR bands for
2008-2013 differs from previous results at earlier epochs when the lag
increased with increasing wavelength. Examples of almost the same lag in
different IR bands are known for some other active nuclei. In the case of NGC
4151 it appears that the relative lags between the IR bands may be different in
different years. The available data, unfortunately, do not allow us to
investigate a possible change in the lags during the test interval. We discuss
our results in the framework of the standard model where the variable infrared
radiation is mainly due to thermal re-emission from the part of the dusty torus
closest to the central source. There is also a contribution of some IR emission
from the accretion disk, and this contribution increases with decreasing
wavelength. Some cosmological applications of obtained results are discussed.Comment: 3 pages, 2 figures, 14-th Odessa International Astronomical Gamow
Conference-School Astronomy and beyond: Astrophysics, Cosmology and
Gravitation, Cosmomicrophysics, Radio-astronomy and Astrobiolog
Color Effects Associated with the 1999 Microlensing Brightness Peaks in Gravitationally Lensed Quasar Q2237+0305
Photometry of the Q2237+0305gravitational lens in VRI spectral bands with the
1.5-m telescope of the high-altitude Maidanak observatory in 1995-2000 is
presented. Monitoring of Q2237+0305 in July-October 2000, made at nearly daily
basis, did not reveal rapid (night-to-night and intranight) variations of
brightness of the components during this time period. Rather slow changes of
magnitudes of the components were observed, such as 0.08 mag fading of B and C
components and 0.05 mag brightening of D in R band during July 23 - October 7,
2000. By good luck three nights in 1999 were almost at the time of the strong
brightness peak of image C, and approximately in the middle of the ascending
slope of the image A brightness peak. The C component was the most blue one in
the system in 1998 and 1999, having changed its (V-I) color from 0.56 mag to
0.12 mag since August 1997, while its brightness increased almost 1.2 mag
during this time period. The A component behaved similarly between August 1998
and August 2000, having become 0.47 mag brighter in R, and at the same time,
0.15 mag bluer. A correlation between the color variations and variations of
magnitudes of the components is demonstrated to be significant and reaches
0.75, with a regression line slope of 0.33. A color (V-I) vrs color (V-R) plot
shows the components settled in a cluster, stretched along a line with a slope
of 1.31. Both slopes are noticeably smaller than those expected if a standard
galactic interstellar reddening law were responsible for the differences
between the colors of images and their variations over time. We attribute the
brightness and color changes to microlensing of the quasar's structure, which
we conclude is more compact at shorter wavelengths, as predicted by most quasar
models featuring an energizing central source.Comment: 14 pages, 7 figures, LaTeX, submitted to A&
Magnetoresistance of Highly Correlated Electron Liquid
The behavior in magnetic fields of a highly correlated electron liquid
approaching the fermion condensation quantum phase transition from the
disordered phase is considered. We show that at sufficiently high temperatures
the effective mass starts to depend on , . This dependence of the effective mass at elevated
temperatures leads to the non-Fermi liquid behavior of the resistivity,
and at higher temperatures . The
application of a magnetic field restores the common behavior of the
resistivity. The effective mass depends on the magnetic field, , being approximately independent of the temperature at . At , the dependence of the
effective mass is re-established. We demonstrate that this phase diagram
has a strong impact on the magnetoresistance (MR) of the highly correlated
electron liquid. The MR as a function of the temperature exhibits a transition
from the negative values of MR at to the positive values at . Thus, at , MR as a function of the temperature
possesses a node at .Comment: 7 pages, revtex, no figure
Theory of high-T_c superconductivity based on the fermion-condensation quantum phase transition
A theory of high temperature superconductivity based on the combination of
the fermion-condensation quantum phase transition and the conventional theory
of superconductivity is presented. This theory describes maximum values of the
superconducting gap which can be as big as , with
being the Fermi level. We show that the critical temperature
. If there exists the pseudogap above then
, and is the temperature at which the pseudogap
vanishes. A discontinuity in the specific heat at is calculated. The
transition from conventional superconductors to high- ones as a function
of the doping level is investigated. The single-particle excitations and their
lineshape are also considered.Comment: 6 pages, Revte
Ground state instability in systems of strongly interacting fermions
We analyze stability of a fermion system with model repulsive pair
interaction potential. The possibility for different types of restructuring of
the Fermi ground state (at sufficiently great coupling constant) is related to
the analytic properties of such potential. In particular, for the screened
Coulomb law it is shown that the restructuring cannot be of the Fermi
condensation type, known earlier for some exactly solvable models, and instead
it belongs to the class of topological transitions (TT). For this model, a
phase diagram has been built in the variables "screening parameter - coupling
constant" which displays two kinds of TT: a 5/2-kind similar to the known
Lifshitz transitions in metals, and a 2-kind characteristic for a uniform
strongly interacting system.Comment: The article has 11 pages, in Latex 2e (from Lyx), 3 eps figures or a
ps fil
Energy scales and the non-Fermi liquid behavior in YbRh2Si2
Multiple energy scales are detected in measurements of the thermodynamic and
transport properties in heavy fermion metals. We demonstrate that the
experimental data on the energy scales can be well described by the scaling
behavior of the effective mass at the fermion condensation quantum phase
transition, and show that the dependence of the effective mass on temperature
and applied magnetic fields gives rise to the non-Fermi liquid behavior. Our
analysis is placed in the context of recent salient experimental results. Our
calculations of the non-Fermi liquid behavior, of the scales and thermodynamic
and transport properties are in good agreement with the heat capacity,
magnetization, longitudinal magnetoresistance and magnetic entropy obtained in
remarkable measurements on the heavy fermion metal YbRh2Si2.Comment: 8 pages, 8 figure
Universal behavior of Ferromagnet at Quantum Critical Point
The heavy-fermion metal can be tuned from ferromagnetism
at to non-magnetic state at some critical concentration . The
non-Fermi liquid behavior (NFL) at is recognized by power low
dependence of the specific heat given by the electronic contribution,
magnetic susceptibility and volume expansion coefficient
at low temperatures: . We
also demonstrate that the behavior of normalized effective mass
observed in at agrees with that of
observed in paramagnetic and conclude that these alloys
exhibit the universal NFL thermodynamic behavior at their quantum critical
points. We show that the NFL behavior of can be accounted
for within frameworks of quasiparticle picture and fermion condensation quantum
phase transition, while this alloy exhibits a universal thermodynamic NFL
behavior which is independent of the characteristic features of the given alloy
such as its lattice structure, magnetic ground state, dimension etc.Comment: 5 pages, 3 figure
Two Scenarios of the Quantum Critical Point
Two different scenarios of the quantum critical point (QCP), a
zero-temperature instability of the Landau state, related to the divergence of
the effective mass, are investigated. Flaws of the standard scenario of the
QCP, where this divergence is attributed to the occurrence of some second-order
phase transition, are demonstrated. Salient features of a different {\it
topological} scenario of the QCP, associated with the emergence of bifurcation
points in equation that ordinarily determines the Fermi
momentum, are analyzed. The topological scenario of the QCP is applied to
three-dimensional (3D) Fermi liquids with an attractive current-current
interaction.Comment: 6 pages, added new discussion and 2 figure
Anomalous asymmetry of magnetoresistance in NbSe single crystals
A pronounced asymmetry of magnetoresistance with respect to the magnetic
field direction is observed for NbSe crystals placed in a magnetic field
perpendicular to their conducting planes. It is shown that the effect persists
in a wide temperature range and manifests itself starting from a certain
magnetic induction value , which at K corresponds to the
transition to the quantum limit, i.to the state where the Landay level
splitting exceeds the temperature.Comment: 4 pages, 6 figures, to be appeared in JETP Let
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