3,193 research outputs found
The non-linear Glasma
We study the evolution of quantum fluctuations in the Glasma created
immediately after the collision of heavy nuclei. It is shown how the presence
of instabilities leads to an enhancement of non-linear interactions among
initially small fluctuations. The non-linear dynamics leads to an enhanced
growth of fluctuations in a large momentum region exceeding by far the
originally unstable band. We investigate the dependence on the coupling
constant at weak coupling using classical statistical lattice simulations for
SU(2) gauge theory and show how these non-linearities can be analytically
understood within the framework of two-particle irreducible (2PI) effective
action techniques. The dependence on the coupling constant is only logarithmic
in accordance with analytic expectations. Concerning the isotropization of bulk
quantities, our results indicate that the system exhibits an order-one
anisotropy on parametrically large time scales. Despite this fact, we find that
gauge invariant pressure correlation functions seem to exhibit a power law
behavior characteristic for wave turbulence.Comment: 16 pages, 7 figures, to appear in Phys. Rev.
Dynamic critical phenomena from spectral functions on the lattice
We investigate spectral functions in the vicinity of the critical temperature
of a second-order phase transition. Since critical phenomena in quantum field
theories are governed by classical dynamics, universal properties can be
computed using real-time lattice simulations. For the example of a relativistic
single-component scalar field theory in 2+1 dimensions, we compute the spectral
function described by universal scaling functions and extract the dynamic
critical exponent z. Together with exactly known static properties of this
theory, we obtain a verification from first principles that the relativistic
theory is well described by the dynamic universality class of relaxational
models with conserved density (Model C).Comment: 18 pages, 6 figures, NPB version, minor change
Basin of attraction for turbulent thermalization and the range of validity of classical-statistical simulations
Different thermalization scenarios for systems with large fields have been
proposed in the literature based on classical-statistical lattice simulations
approximating the underlying quantum dynamics. We investigate the range of
validity of these simulations for condensate driven as well as fluctuation
dominated initial conditions for the example of a single component scalar field
theory. We show that they lead to the same phenomenon of turbulent
thermalization for the whole range of (weak) couplings where the
classical-statistical approach is valid. In the turbulent regime we establish
the existence of a dual cascade characterized by universal scaling exponents
and scaling functions. This complements previous investigations where only the
direct energy cascade has been studied for the single component theory. A
proposed alternative thermalization scenario for stronger couplings is shown to
be beyond the range of validity of classical-statistical simulations.Comment: 11 pages, 10 figures; version published in JHEP (minor revisions
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