113 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
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
Worldline approach to helicity flip in plane waves
We apply worldline methods to the study of vacuum polarisation effects in
plane wave backgrounds, in both scalar and spinor QED. We calculate
helicity-flip probabilities to one loop order and treated exactly in the
background field, and provide a toolkit of methods for use in investigations of
higher-order processes. We also discuss the connections between the worldline,
S-matrix, and lightfront approaches to vacuum polarisation effects.Comment: 11 pages, 1 figur
Effective Action of QED in Electric Field Backgrounds II: Spatially Localized Fields
We find the Bogoliubov coefficient from the tunneling boundary condition on a
charged particle coupled to a static electric field and,
using the regularization scheme in Phys. Rev. D 78, 105013 (2008), obtain the
exact one-loop effective action in scalar and spinor QED. It is shown that the
effective action satisfies the general relation between the vacuum persistence
and the mean number of produced pairs. We advance an approximation method for
general electric fields and show the duality between the space-dependent and
time-dependent electric fields of the same form at the leading order of the
effective actions.Comment: RevTex 7 pages, no figure; extension of arXiv:0807.2696 to
space-dependent electric fields; new section added on approximate effective
actions in general electric fields and conclusion shortened; references
added; replaced by the version to be published in Phys. Rev.
Dynamics of the Chiral Magnetic Effect in a weak magnetic field
We investigate the real-time dynamics of the chiral magnetic effect in
quantum electrodynamics (QED) and quantum chromodynamics (QCD). We consider a
field configuration of parallel (chromo)electric and (chromo)magnetic fields
with a weak perpendicular electromagnetic magnetic field. The chiral magnetic
effect induces an electromagnetic current along this perpendicular magnetic
field, which we will compute using linear response theory. We discuss specific
results for a homogeneous sudden switch-on and a pulsed (chromo)electric field
in a static and homogeneous (chromo)magnetic field. Our methodology can be
easily extended to more general situations. The results are useful for
investigating the chiral magnetic effect with heavy ion collisions and with
lasers that create strong electromagnetic fields. As a side result we obtain
the rate of chirality production for massive fermions in parallel electric and
magnetic fields that are static and homogeneous.Comment: 13 pages, 7 figures, revte
Renormalized Effective Actions in Radially Symmetric Backgrounds I: Partial Wave Cutoff Method
The computation of the one-loop effective action in a radially symmetric
background can be reduced to a sum over partial-wave contributions, each of
which is the logarithm of an appropriate one-dimensional radial determinant.
While these individual radial determinants can be evaluated simply and
efficiently using the Gel'fand-Yaglom method, the sum over all partial-wave
contributions diverges. A renormalization procedure is needed to unambiguously
define the finite renormalized effective action. Here we use a combination of
the Schwinger proper-time method, and a resummed uniform DeWitt expansion. This
provides a more elegant technique for extracting the large partial-wave
contribution, compared to the higher order radial WKB approach which had been
used in previous work. We illustrate the general method with a complete
analysis of the scalar one-loop effective action in a class of radially
separable SU(2) Yang-Mills background fields. We also show that this method can
be applied to the case where the background gauge fields have asymptotic limits
appropriate to uniform field strengths, such as for example in the Minkowski
solution, which describes an instanton immersed in a constant background.
Detailed numerical results will be presented in a sequel.Comment: 35 page
Fermion Pair Production From an Electric Field Varying in Two Dimensions
The Hamiltonian describing fermion pair production from an arbitrarily
time-varying electric field in two dimensions is studied using a
group-theoretic approach. We show that this Hamiltonian can be encompassed by
two, commuting SU(2) algebras, and that the two-dimensional problem can
therefore be reduced to two one-dimensional problems. We compare the group
structure for the two-dimensional problem with that previously derived for the
one-dimensional problem, and verify that the Schwinger result is obtained under
the appropriate conditions.Comment: Latex, 14 pages of text. Full postscript version available via the
worldwide web at http://nucth.physics.wisc.edu/ or by anonymous ftp from
ftp://nucth.physics.wisc.edu:/pub/preprints
The probability distribution of the number of electron-positron pairs produced in a uniform electric field
The probability-generating function of the number of electron-positron pairs
produced in a uniform electric field is constructed. The mean and variance of
the numbers of pairs are calculated, and analytical expressions for the
probability of low numbers of electron-positron pairs are given. A recursive
formula is derived for evaluating the probability of any number of pairs. In
electric fields of supercritical strength |eE| > \pi m^2/ \ln 2, where e is the
electron charge, E is the electric field, and m is the electron mass, a
branch-point singularity of the probability-generating function penetrates the
unit circle |z| = 1, which leads to the asymptotic divergence of the cumulative
probability. This divergence indicates a failure of the continuum limit
approximation. In the continuum limit and for any field strength, the positive
definiteness of the probability is violated in the tail of the distribution.
Analyticity, convergence, and positive definiteness are restored upon the
summation over discrete levels of electrons in the normalization volume.
Numerical examples illustrating the field strength dependence of the asymptotic
behavior of the probability distribution are presented.Comment: 7 pages, REVTeX, 4 figures; new references added; a short version of
this e-print has appeared in PR
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