1,685,731 research outputs found
Finite-temperature phase transitions in the quantum fully frustrated Ising models
The quantum antiferromagnetic spin-1/2 Ising model on a triangular lattice
and analogous fully frustrated Ising model on a square lattice with quantum
fluctuations induced by the application of the transverse magnetic field are
studied at finite temperatures by constructing an exact mapping onto a purely
classical model with a more complex interaction. It is shown that in weak
fields the temperatures of the phase transitions separating the critical phase
from the ordered and disordered phases in both models are proportional to the
magnitude of the field.Comment: 5 pages, RevTex
Radiative Corrections to QCD Amplitudes in Quasi-Multi-Regge Kinematics
Radiative corrections to QCD amplitudes in the quasi-multi-Regge kinematics
are interesting in particular since the Reggeized form of these amplitudes is
used in the derivation of the NLO BFKL. This form is a hypothesis which must be
at least carefully checked, if not proved. We calculate the radiative
corrections in the one-loop approximation using the s-channel unitarity.
Compatibility of the Reggeized form of the amplitudes with the s-channel
unitarity requires fulfillment of the set of nonlinear equations for the
Reggeon vertices. We show that these equations are satisfied.Comment: 28 pages,3 figure
Scaling, Finite Size Effects, and Crossovers of the Resistivity and Current-Voltage Characteristics in Two-Dimensional Superconductors
We revisit the scaling properties of the resistivity and the current-voltage
characteristics at and below the Berezinskii-Kosterlitz-Thouless transition,
both in zero and nonzero magnetic field. The scaling properties are derived by
integrating the renormalization group flow equations up to a scale where they
can be reliably matched to simple analytic expressions. The vortex fugacity
turns out to be dangerously irrelevant for these quantities below Tc, thereby
altering the scaling behavior. We derive the possible crossover effects as the
current, magnetic field, or system size is varied, and find a strong
multiplicative logarithmic correction near Tc, all of which is necessary to
account for when interpreting experiments and simulation data. Our analysis
clarifies a longstanding discrepancy between the finite size dependence found
in many simulations and the current-voltage characteristics of experiments. We
further show that the logarithmic correction can be avoided by approaching the
transition in a magnetic field, thereby simplifying the scaling analysis. We
confirm our results by large-scale numerical simulations, and calculate the
dynamic critical exponent z, for relaxational Langevin dynamics and for
resistively and capacitively shunted Josephson junction dynamics.Comment: 5 pages, 2 figure
To the modification of methods of nuclear chronometry in astrophysics and geophysics
In practically all known till now methods of nuclear chronometry there were
usually taken into account the life-times of only fundamental states of
-radioactive nuclei. But in the processes of nuclear synthesis in stars
and under the influence of the constant cosmic radiation on surfaces of planets
the excitations of the -radioactive nuclei are going on. Between them
there are the states with the excited -particles inside the parent
nuclei and so with much smaller life-times. And inside the large masses of
stellar, terrestrial and meteoric substances the transitions between different
internal conditions of radioactive nuclei are accompanied by infinite chains of
the -radiations with the subsequent -absorptions, the further
-radiations etc. For the description of the -decay evolution
with considering of such excited states and multiple -radiations and
-absorptions inside stars and under the influence of the cosmic
radiation on the earth surface we present the quantum-mechanical approach,
which is based on the generalized Krylov-Fock theorem.
Some simple estimations are also presented. They bring to the conclusion that
the usual (non-corrected) "nuclear clocks" do really indicate not to realistic
values but to the \emph{upper limits} of the durations of the -decay
stellar and planet processes.Comment: 6 pages, Standard LaTeX v.2
Dunajski generalization of the second heavenly equation: dressing method and the hierarchy
Dunajski generalization of the second heavenly equation is studied. A
dressing scheme applicable to Dunajski equation is developed, an example of
constructing solutions in terms of implicit functions is considered. Dunajski
equation hierarchy is described, its Lax-Sato form is presented. Dunajsky
equation hierarchy is characterized by conservation of three-dimensional volume
form, in which a spectral variable is taken into account.Comment: 13 page
Role of quark-instanton liquid interactions in colour superconductivity phase
The interaction of light quarks and instanton liquid is analyzed at finite
density of quark/baryon matter and in the phase of nonzero values of diquark
(colour) condensate. It is shown that instanton liquid perturbation produced by
such an interaction results in an essential increase of the critical value of
quark chemical potential which provokes the perceptible increase of
quark matter density around the expected onset of the colour superconductivity
phase.Comment: 11 pages, 5 figure
Magnetocaloric effect and nature of magnetic transition in nanoscale Pr0.5Ca0.5MnO3
Systematic measurements pertinent to the magnetocaloric effect and nature of
magnetic transition around the transition temperature are performed in the 10
nm Pr0.5Ca0.5MnO3 nanoparticles (PCMO10) . Maxwell relation is employed to
estimate the change in magnetic entropy. At Curie temperature TC, 83.5 K, the
change in magnetic entropy discloses a typical variation with a value 0.57 J/kg
K, and is found to be magnetic field dependent. From the area under the curve
Delta S vs T, the refrigeration capacity is calculated at TC, 83.5 K and it is
found to be 7.01 J/kg. Arrott plots infer that due to the competition between
the ferromagnetic and anti ferromagnetic interactions, the magnetic phase
transition in PCMO10 is broadly spread over both in temperature as well as in
magnetic field coordinates. Upon tuning the particle size, size distribution,
morphology, and relative fraction of magnetic phases, it may be possible to
enhance the magnetocalorific effect further in PCMO10.Comment: Accepted (Journal of Applied Physics) (In press
Photon-Reggeon Interaction Vertices in the Nla
We calculate the effective vertices for the quark-antiquark and the
quark-antiquark-gluon production in the virtual photon - Reggeized gluon
interaction. The last vertex is considered at the Born level; for the first one
the one-loop corrections are obtained. These vertices have a number of
applications; in particular, they are necessary for calculation of the virtual
photon impact factor in the next-to-leading logarithmic approximation.Comment: 20 pages, references adde
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