11,952 research outputs found
Symmetries in nonlinear Bethe-Heitler process
Nonlinear Bethe-Heitler process in a bichromatic laser field is investigated
using strong-field QED formalism. Symmetry properties of angular distributions
of created pairs are analyzed. These properties are showed to be
governed by a behavior of the vector potential characterizing the laser field,
rather than by the respective electric field component.Comment: 4 pages, 4 figure
From Popov-Fedotov trick to universal fermionization
We show that Popov-Fedotov trick of mapping spin-1/2 lattice systems on
two-component fermions with imaginary chemical potential readily generalizes to
bosons with a fixed (but not limited) maximal site occupation number, as well
as to fermionic Hamiltonians with various constraints on the site Fock states.
In a general case, the mapping---fermionization---is on multi-component
fermions with many-body non-Hermitian interactions. Additionally, the
fermionization approach allows one to convert large many-body couplings into
single-particle energies, rendering the diagrammatic series free of large
expansion parameters; the latter is essential for the efficiency and
convergence of the diagrammatic Monte Carlo method.Comment: 4 pages, no figures (v2 contains some improvements; the most
important one is the generic complex chemical potential trick for
spins/bosons
Comparative assessment of prognosis of the stop stimulus and trapezoidal rotation programs
For prognosis of the diagnostic possibilities of the stop stimulus and trapezoidal rotation programs with respect to the nystagmus response, 24 healthy young persons with normal auditory and vestibular analysers were studied experimentally. The trapezoidal program more accurately reflects the function and tone balance of the vestibular system than the stop stimulus program and causes the subject no unpleasant sensations during the study. Some optimum couples, acceleration and armchair rotation rate, necessary for effective deviation of the cupuloendolymphatic system were determined. The maximum angular velocity of the slow nystagmus component was more informative than nystagmus duration. The trapezoidal program is recommended for otoneurological practice and the maximum angular velocity of the slow nystagmus component as the basic index
Asymmetric tunneling, Andreev reflection and dynamic conductance spectra in strongly correlated metals
Landau Fermi liquid theory predicts that the differential conductivity
between metallic point and metal is a symmetric function of voltage bias V.
This symmetry holds if the particle-hole symmetry is preserved. We show that
the situation can be different when one of the two metals is a strongly
correlated one whose electronic system can be represented by a heavy fermion
liquid. When the heavy fermion liquid undergoes fermion condensation quantum
phase transition, the particle-hole symmetry is violated making both the
differential tunneling conductivity and dynamic conductance asymmetric as a
function of applied voltage. This asymmetry can be observed when the strongly
correlated metal is either normal or superconducting. We show that at small
values of $V the asymmetric part of the dynamic conductance is a linear
function of V and inversely proportional to the maximum value of the gap and
does not depend on temperature provided that metal is superconducting, when it
becomes normal the asymmetric part diminishes at elevated temperatures.Comment: 8 pages, 7 figure
Polarization of the electron and positron produced in combined Coulomb and strong laser fields
The process of production in the superposition of a Coulomb and a
strong laser field is considered. The pair production rate integrated over the
momentum and summed over the spin projections of one of the particles is
derived exactly in the parameters of the laser field and in the Born
approximation with respect to the Coulomb field. The case of a monochromatic
circularly polarized laser field is considered in detail. A very compact
analytical expression of the pair production rate and its dependence on the
polarization of one of the created particles is obtained in the quasiclassical
approximation for the experimentally relevant case of an undercritical laser
field. As a result, the polarization of the created electron (positron) is
derived.Comment: 16 pages, no figure
Tunneling through Color Glass Condensate and True Black Disks
We discover new vacuum solutions of the JIMWLK equation, which correspond to
center of a gauge group. We improve the color glass condensate (CGC) model by
an explicit usage of a density matrix. Studying scattering of CGC states in an
external color field, we observe that an amplitude is naturally expressed via
group characters. We construct an example that shows how new thin effects may
be potentially observed in peripheral collisions. We prove that at any parton
density a gluonic CGC state does not become a true black disk. We find a wave
function of a true black disk and show that it necessarily contains many
quarks. This result corresponds to the necessity of nonvacuum Reggeon loops in
a formation of a true black disk.Comment: 13 pages, 2 figures, revtex; final version, improved styl
Multidimensional Worldline Instantons
We extend the worldline instanton technique to compute the vacuum pair
production rate for spatially inhomogeneous electric background fields, with
the spatial inhomogeneity being genuinely two or three dimensional, both for
the magnitude and direction of the electric field. Other techniques, such as
WKB, have not been applied to such higher dimensional problems. Our method
exploits the instanton dominance of the worldline path integral expression for
the effective action.Comment: 22 pages, 13 figure
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