163 research outputs found
Systematic Resummed Perturbation Theory
A systematic loop expansion is formulated in terms of full propagators and
vertices. It is based on an expansion of the general solution of an exact
non-perturbative flow equation.Comment: 11 pages, LaTe
Conformal fixed point, Cosmological Constant and Quintessence
We connect a possible solution for the ``cosmological constant problem'' to
the existence of a (postulated) conformal fixed point in a fundamental theory.
The resulting cosmology leads to quintessence, where the present acceleration
of the expansion of the universe is linked to a crossover in the flow of
coupling constants.Comment: More detailed discussion of quantum fluctuations,update with
WMAP-data,4 pages,LaTe
Nonperturbative Condensates in the Electroweak Phase-Transition
We discuss the electroweak phase-transition in the early universe, using
non-perturbative flow equations for a computation of the free energy. For a
scalar mass above GeV, high-temperature perturbation theory cannot
describe this transition reliably. This is due to the dominance of
three-dimensional physics at high temperatures which implies that the effective
gauge coupling grows strong in the symmetric phase. We give an order of
magnitude-estimate of nonperturbative effects in reasonable agreement with
recent results from electroweak lattice simulations.
(Talk given by C. Wetterich at the 3rd Colloque Cosmologie, Paris, June 7-9,
1995, to appear in the proceedings)Comment: 20 pages, LaTeX, 4 figures, Talk given by C. Wetterich at the 3rd
Colloque Cosmologie, Paris, June 7-9, 1995, to appear in the proceedings, ***
Replaced figure 1 **
Isotropization from Color Field Condensate in heavy ion collisions
The expanding fireball shortly after a heavy ion collision may be
qualitatively described by a condensate of color fields or gluons which is
analogous to Bose-Einstein-condensation for massive bosonic particles. This
condensate is a transient non-equilibrium phenomenon and breaks Lorentz-boost
symmetry. The dynamics of color field condensates involves collective
excitations and is rather different from the perturbative scattering of gluons.
In particular, it provides for an efficient mechanism to render the local
pressure approximately isotropic after a short time of 0.2 fm/c. We suggest
that an isotropic color field condensate may play a central role for a simple
description of prethermalization and isotropization in the early stages of the
collision.Comment: 30 pages, 11 figures, published versio
Chiral tensor fields and spontaneous breaking of Lorentz symmetry
Antisymmetric tensor fields interacting with quarks and leptons have been
proposed as a possible solution to the gauge hierarchy problem. We compute the
one-loop beta function for a quartic self-interaction of the chiral
antisymmetric tensor fields. Fluctuations of the top quark drive the
corresponding running coupling to a negative value as the renormalization scale
is lowered. This may indicate a non-vanishing expectation value of the tensor
field, and thus a spontaneous breaking of Lorentz invariance. Settling this
issue will need the inclusion of tensor loops.Comment: 15 pages, 4 figure
Non-Equilibrium Time Evolution in Quantum Field Theory
The time development of equal-time correlation functions in quantum mechanics
and quantum field theory is described by an exact evolution equation for
generating functionals. This permits a comparison between classical and quantum
evolution in non-equilibrium systems.Comment: 7 pages, LaTe
Dark energy cosmologies for codimension-two branes
A six-dimensional universe with two branes in the "football-shaped" geometry
leads to an almost realistic cosmology. We describe a family of exact solutions
with time dependent characteristic size of internal space. After a short
inflationary period the late cosmology is either of quintessence type or turns
to a radiation dominated Friedmann universe where the cosmological constant
appears as a free integration constant of the solution. The radiation dominated
universe with relativistic fermions is analyzed in detail, including its
dimensional reduction.Comment: 18 page
- âŠ