45 research outputs found
Counterterms for Linear Divergences in Real-Time Classical Gauge Theories at High Temperature
Real-time classical SU() gauge theories at non-zero temperature contain
linear divergences. We introduce counterterms for these divergences in the
equations of motion in the continuum and on the lattice. These counterterms can
be given in terms of auxiliary fields that satisfy local equations of motion.
We present a lattice model with 6+1D auxiliary fields that for IR-sensitive
quantities yields cut-off independent results to leading order in the coupling.
Also an approximation with 5+1D auxiliary fields is discussed.Comment: 10 pages, major change
Non-equilibrium field theory
I discuss various topics in relativistic non-equilibrium field theory related
to high energy physics and cosmology. I focus on non-perturbative problems and
how they can be treated on the lattice.Comment: Plenary talk given at the 18th International Symposium on Lattice
Field Theory (Lattice 2000), Bangalore, India, 17-22 Aug 200
Abelian hard thermal loops on a lattice
In Abelian theories, one can write for the hard thermal loop equations of
motions a local formulation that is more economical than the traditional Vlasov
formulation and is in explicitly canonical form. I show how this formulation
can be used for simulating non-equilibrium dynamics in the Abelian Higgs model.Comment: 3 pages. Talk given at LATTICE99 (electroweak), Pisa, Ital
The finite temperature real time \hbar^2 corrections in quantum mechanics
We study non-perturbative real time correlation functions at finite
temperature. In order to see whether the classical term gives a good
approximation in the high temperature limit T >> \hbar\omega, we consider the
first \hbar^2 quantum corrections. We find that for the simplest non-trivial
case, the quantum mechanical anharmonic oscillator, the classical result is
reliable only for moderately large times: after some time t_* the classical
approximation breaks down even at high temperatures. Moreover, the result for
the first quantum corrections cannot, in general, be reproduced by modifying
the parameters of the classical theory.Comment: 28 pages, 7 figure
Effective theory for real-time dynamics in hot gauge theories
For a high temperature non-Abelian plasma, we reformulate the hard thermal
loop approximation as an effective classical thermal field theory for the soft
modes. The effective theory is written in local Hamiltonian form, and the
thermal partition function is explicitly constructed. It involves an
ultraviolet cutoff which separates between hard and soft degrees of freedom in
a gauge-invariant way, together with counterterms which cancel the cutoff
dependence in the soft correlation functions. The effective theory is well
suited for numerical studies of the non-perturbative dynamics in real time, in
particular, for the computation of the baryon number violation rate at high
temperature.Comment: 11 pages, LaTeX, major rewriting, new title, new reference
Ultrasoft Amplitudes in Hot QCD
By using the Boltzmann equation describing the relaxation of colour
excitations in the QCD plasma, we obtain effective amplitudes for the ultrasoft
colour fields carrying momenta of order . These amplitudes are of the
same order in as the hard thermal loops (HTL), which they generalize by
including the effects of the collisions among the hard particles. The ultrasoft
amplitudes share many of the remarkable properties of the HTL's: they are gauge
invariant, obey simple Ward identities, and, in the static limit, reduce to the
usual Debye mass for the electric fields. However, unlike the HTL's, which
correspond effectively to one-loop diagrams, the ultrasoft amplitudes resum an
infinite number of diagrams of the bare perturbation theory. By solving the
linearized Boltzmann equation, we obtain a formula for the colour conductivity
which accounts for the contributions of the hard and soft modes beyond the
leading logarithmic approximation.Comment: 38 pages, 10 figures, LaTeX. An extension of the previous results is
included (in Sec. 4.2); also, some minor modifications here and there. Final
version, to appear in Nucl. Phys.
Isotropization by QCD Plasma Instabilities
Numerical solutions of the Wong-Yang-Mills equations with anisotropic
particle momentum distributions are presented. Their isotropization by
collective effects due to the classical Yang-Mills field is shown.Comment: 4 pages, 4 figures, contribution to the Quark Matter 2005 proceeding
Chern-Simons Number Diffusion and Hard Thermal Loops on the Lattice
We develop a discrete lattice implementation of the hard thermal loop
effective action by the method of added auxiliary fields. We use the resulting
model to measure the sphaleron rate (topological susceptibility) of Yang-Mills
theory at weak coupling. Our results give parametric behavior in accord with
the arguments of Arnold, Son, and Yaffe, and are in quantitative agreement with
the results of Moore, Hu, and Muller.Comment: 43 pages, 6 figure
From hard thermal loops to Langevin dynamics
In hot non-Abelian gauge theories, processes characterized by the momentum
scale (such as electroweak baryon number violation in the very early
universe) are non-perturbative. An effective theory for the soft
() field modes is obtained by integrating out momenta
larger than . Starting from the hard thermal loop effective theory,
which is the result of integrating out the scale , it is shown how to
integrate out the scale in an expansion in the gauge coupling . At
leading order in , one obtains Vlasov-Boltzmann equations for the soft field
modes, which contain a Gaussian noise and a collision term. The 2-point
function of the noise and the collision term are explicitly calculated in a
leading logarithmic approximation. In this approximation the Boltzmann equation
is solved. The resulting effective theory for the soft field modes is described
by a Langevin equation. It determines the parametric form of the hot baryon
number violation rate as , and it allows
for a calculation of on the lattice.Comment: 42 pages, 2 figures, uses elsart.sty; explanatory paragraph added to
the introduction, 4 references added, a few quotations added; to appear in
Nucl. Phys.
Effective Classical Theory for Real-Time SU(N) Gauge Theories at High Temperature
We derive an effective classical theory for real-time SU() gauge theories
at high temperature. By separating off and integrating out quantum fluctuations
we obtain a 3D classical path integral over the initial fields and conjugate
momenta. The leading hard mode contribution is incorporated in the equations of
motion for the classical fields. This yields the gauge invariant hard thermal
loop (HTL) effective equation of motion. No gauge-variant terms are generated
as in treatments with an intermediate momentum cut-off. Quantum corrections to
classical correlation functions can be calculated perturbatively. The 4D
renormalizability of the theory ensures that the 4D counterterms are sufficient
to render the theory finite. The HTL contributions of the quantum fluctuations
provide the counterterms for the linear divergences in the classical theory.Comment: 13 pages, 1 figure, title changed, discussion on the classical
approximation include