12 research outputs found
Quantum corrections to the Classical Statistical Approximation for the expanding quantum field
We found the deviation of the equation of state from ultrarelativistic one
due to quantum corrections for a nonequilibrium longitudinally expanding scalar
field. Relaxation of highly excited quantum field is usually described in terms
of Classical Statistical Approximation (CSA). However, the expansion of the
system reduces the applicability of such a semiclassical approach as the CSA
making quantum corrections important. We calculate the evolution of the trace
of the energy-momentum tensor within the Keldysh-Schwinger framework for static
and longitudinal expanding geometries. We provide analytical and numerical
arguments for the appearance of the nontrivial intermediate regime where
quantum corrections are significant
Semiclassical Approximation meets Keldysh-Schwinger diagrammatic technique: Scalar
We study the evolution of the non-equilibrium quantum fields from a highly
excited initial state in two approaches: the standard Keldysh-Schwinger diagram
technique and the semiclassical expansion. We demonstrate explicitly that these
two approaches coincide if the coupling constant and the Plank constant
are small simultaneously. Also, we discuss loop diagrams of the
perturbative approach, which are summed up by the leading order term of the
semiclassical expansion. As an example, we consider shear viscosity for the
scalar field theory at the leading semiclassical order. We introduce the new
technique that unifies both semiclassical and diagrammatic approaches and open
the possibility to perform the resummation of the semiclassical contributions.Comment: 10 pages, many diagram
Scaling laws for the elastic scattering amplitude
The partial differential equation for the imaginary part of the elastic
scattering amplitude is derived. It is solved in the black disk limit. The
asymptotical scaling behavior of the amplitude coinciding with the geometrical
scaling is proved. Its extension to preasymptotical region and modifications of
scaling laws for the differential cross section are considered.Comment: 6 p. arXiv admin note: substantial text overlap with arXiv:1206.547