92 research outputs found
Particle Production in Strong Time-dependent Fields
In these lecture notes we give an introduction to the kinetic equation
approach to pair production form the vacuum in strong, time-dependent external
fields (dynamical Schwinger process). We first give a derivation of the kinetic
equation with the source term for the case of fermions starting from the Dirac
equation and for bosons from the Klein-Gordon equation. In a second part we
discuss the application of the approach to the situation of external field
pulses as single-sheeted functions of time (like the Sauter-pulse) and as
multi- sheeted functions approximating the situation in the focal point of
counter-propagating laser beams. Special emphasis is on the discussion of the
time evolution of the system that exhibits the characteristics of a
field-induced phase transition for which we discuss the behaviour of the
entropy and particle density of the system. We give an outlook to applications
of the approach in describing particle production in strong fields formed in
particle and nuclear collisions.Comment: 23 pages, 7 figures, Lecture Notes based on arXiv:hep-ph/9809227 and
arxiv:1607.08775; to appear in Proceedings of the Helmholtz International
Summer School on "Quantum Field Theory at the Limits: From Strong Fields to
Heavy Quarks", July 18-30, 2016, Dubna, Russi
On the kinetic equation approach to pair production by time-dependent electric field
We investigate the quantum kinetic approach to pair production from vacuum by
time-dependent electric field. Equivalence between this approach and the more
familiar S-matrix approach is explicitly established for both scalar and
fermion cases. For the particular case of a constant electric field exact
solution for kinetic equations is provided and the accuracy of low-density
approximation is estimated.Comment: 8 pages, 4 figure
Strange and charm quark-pair production in strong non-Abelian field
We have investigated strange and charm quark-pair production in the early
stage of heavy ion collisions. Our kinetic model is based on a Wigner function
method for fermion-pair production in strong non-Abelian fields. To describe
the overlap of two colliding heavy ions we have applied the time-dependent
color field with a pulse-like shape. The calculations have been performed in an
SU(2)-color model with finite current quark masses. For strange quark-pair
production the obtained results are close to the Schwinger limit, as we
expected. For charm quark the large inverse temporal width of the field pulse,
instead of the large charm quark mass, determines the efficiency of the
quark-pair production. Thus we do not observe the expected suppression of charm
quark-pair production connecting to the usual Schwinger-formalism, but our
calculation results in a relatively large charm quark yield. This effect
appears in Abelian models as well, demonstrating that particle-pair production
for fast varying non-Abelian gluon field strongly deviates from the Schwinger
limit for charm quark. We display our results on number densities for light,
strange, charm quark-pairs, and different suppression factors as the function
of characteristic time of acting chromo-electric field.Comment: 6 pages, 2 figures; to appear in the proceedings of the International
Conference on Strangeness in Quark matter (SQM2008), Beijing, China, Oct
6-10, 2008; version accepted to J. Phys.
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