245 research outputs found
Pair Creation of Massless Fermions in Electric Flux Tube
Using chiral anomaly, we discuss the pair creation of massless fermions in an
electric flux tube under homogeneous magnetic field
parallel to . The tube is axial symmetric and infinitely long in
longitudinal direction. In the limit , we can analytically obtain the
spatial and temporal behaviors of the electric field and azimuthal magnetic
field generated by the produced fermions. We find that the life time of
the electric field is shorter as the width of the tube is narrower. Applying it
to the glasma in high-energy heavy-ion collisions, we find that color electric
field decays fast such as with saturation momentum .Comment: 6 pages, 4 figure
Acceleration and vacuum temperature
The quantum fluctuations of an "accelerated" vacuum state, that is vacuum
fluctuations in the presence of a constant electromagnetic field, can be
described by the temperature \TEH. Considering \TEH for the gyromagnetic
factor we show that \TEH(g=1)=\THU, where \THU is the Unruh
temperature experienced by an accelerated observer. We conjecture that both
particle production and nonlinear field effects inherent in the Unruh
accelerated observer case are described by the case QED of strong fields.
We present rates of particle production for and show that the case
is experimentally distinguishable from . Therefore, either
accelerated observers are distinguishable from accelerated vacuum or there is
unexpected modification of the theoretical framework.Comment: 4 pages, 1 figure; expanded discussion of experimental observables,
added references, version appearing in Phys Rev
Anomalous magnetic ordering in PrBa_2Cu_3O_{7-y} single crystals: Evidence for magnetic coupling between the Cu and Pr sublattices
In Al-free PrBa_2Cu_3O_{7-y} single crystals the kink in the temperature
dependence of magnetic susceptibility chi_{ab}(T), connected with Pr
antiferromagnetic ordering, disappears after field cooling (FC) in a field H ||
ab-plane. The kink in chi_c(T) remains unchanged after FC in H || c-axis. As a
possible explanation, freezing of the Cu magnetic moments, lying in the
ab-plane, caused by FC in H || ab, hinders their reorientation and, due to
coupling between the Pr and Cu(2) sublattices, ordering of the Pr^{3+} moments.
A field induced phase transition and a field dependence of the Pr^{3+} ordering
temperature have been found for both H || c and H || ab.Comment: 11 pages (LaTex with elsart.sty), 5 EPS figs. Accepted to Physica
Non-Linear Compton Scattering of Ultrashort and Ultraintense Laser Pulses
The scattering of temporally shaped intense laser pulses off electrons is
discussed by means of manifestly covariant quantum electrodynamics. We employ a
framework based on Volkov states with a time dependent laser envelope in
light-cone coordinates within the Furry picture. An expression for the cross
section is constructed, which is independent of the considered pulse shape and
pulse length. A broad distribution of scatted photons with a rich pattern of
subpeaks like that obtained in Thomson scattering is found. These broad peaks
may overlap at sufficiently high laser intensity, rendering inappropriate the
notion of individual harmonics. The limit of monochromatic plane waves as well
as the classical limit of Thomson scattering are discussed. As a main result, a
scaling law is presented connecting the Thomson limit with the general result
for arbitrary kinematics. In the overlapping regions of the spectral density,
the classical and quantum calculations give different results, even in the
Thomson limit. Thus, a phase space region is identified where the differential
photon distribution is strongly modified by quantum effects.Comment: 31 pages, 10 figure
Schwinger Pair Production at Finite Temperature in Scalar QED
In scalar QED we study the Schwinger pair production from an initial ensemble
of charged bosons when an electric field is turned on for a finite period
together with or without a constant magnetic field. The scalar QED Hamiltonian
depends on time through the electric field, which causes the initial ensemble
of bosons to evolve out of equilibrium. Using the Liouville-von Neumann method
for the density operator and quantum states for each momentum mode, we
calculate the Schwinger pair-production rate at finite temperature, which is
the pair-production rate from the vacuum times a thermal factor of the
Bose-Einstein distribution.Comment: RevTex 10 pages, no figure; replaced by the version accepted in Phys.
Rev. D; references correcte
Pair Production of Arbitrary Spin Particles by Electromagnetic Fields
The exact solutions of the wave equation for arbitrary spin particles in the
field of the soliton-like electric impulse were obtained. The differential
probability of pair production of particles by electromagnetic fields has been
evaluated on the basis of the exact solutions. As a particular case, the
particle pair producing in the constant and uniform electric field were
studied.Comment: 13 pages, no figure
Anisotropic magnetic behavior of GdBa_2Cu_3O_{6+y} single crystals
Magnetic properties of high-quality Al-free nonsuperconducting
GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The
magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the
direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N
clear indications of spin-flop transitions for H||c have been observed on
magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been
obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic
susceptibility (unexpected for Gd-based compounds) has been found above T_N.Comment: 2 pages, 3 figures; LT23 (Aug. 2002; Hiroshima), accepted to Physica
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