88,499 research outputs found
Convergence and stability of the renormalisation group
Within the exact renormalisation group approach, it is shown that stability
properties of the flow are controlled by the choice for the regulator. Equally,
the convergence of the flow is enhanced for specific optimised choices for the
regularisation. As an illustration, we exemplify our reasoning for 3d scalar
theories at criticality. Implications for other theories are discussed.Comment: 8 pages, 4 figures, uses ActaStyle.cls, invited talk given at RG2002,
March 10-16, 2002, Strba, Slowaki
The Effects of Gravitational Slip on the Higher-Order Moments of the Matter Distribution
Cosmological departures from general relativity offer a possible explanation
for the cosmic acceleration. To linear order, these departures (quantified by
the model-independent parameter , referred to as a `gravitational
slip') amplify or suppress the growth of structure in the universe relative to
what we would expect to see from a general relativistic universe lately
dominated by a cosmological constant. As structures collapse and become more
dense, linear perturbation theory is an inadequate descriptor of their
behavior, and one must extend calculations to non-linear order. If the effects
of gravitational slip extend to these higher orders, we might expect to see a
signature of in the bispectrum of galaxies distributed on the sky. We
solve the equations of motion for non-linear perturbations in the presence of
gravitational slip and find that, while there is an effect on the bispectrum,
it is too weak to be detected with present galaxy surveys. We also develop a
formalism for incorporating scale dependence into our description of
gravitational slip.Comment: 25 pages, 9 figure
Recommended from our members
Delayed Circadian Rhythms and Pars Tuberalis Dysfunction in Mood Disorders
Transport theory and low energy properties of colour superconductors
The one-loop polarisation tensor and the propagation of ``in-medium'' photons
of colour superconductors in the 2SC and CFL phase is discussed. For a study of
thermal corrections to the low energy effective theory in the 2SC phase, a
classical transport theory for fermionic quasiparticles is invoked.Comment: 5 pages, talk given at the International Conference on "Statistical
QCD", Bielefeld, August 26-30, 200
Aspects of semi-classical transport theory for QCD
We discuss some aspects of a recently proposed semi-classical transport
theory for QCD plasmas based on coloured point particles. This includes the
derivation of effective transport equations for mean fields and fluctuations
which relies on the Gibbs ensemble average. Correlators of fluctuations are
interpreted as collision integrals for the effective Boltzmann equation. The
approach yields a recipe to integrate-out fluctuations. Systematic
approximations (first moment, second moment, polarisation approximation) based
on a small plasma parameter are discussed as well. Finally, the application to
a hot non-Abelian plasma close to thermal equilibrium is considered and the
consistency with the fluctuation-dissipation theorem established.Comment: Presented at Strong and Electroweak Matter (SEWM2000), Marseille,
France, 14-17 June 2000, 12 page
Derivative expansion and renormalisation group flows
We study the convergence of the derivative expansion for flow equations. The
convergence strongly depends on the choice for the infrared regularisation.
Based on the structure of the flow, we explain why optimised regulators lead to
better physical predictions. This is applied to O(N)-symmetric real scalar
field theories in 3d, where critical exponents are computed for all N. In
comparison to the sharp cut-off regulator, an optimised flow improves the
leading order result up to 10%. An analogous reasoning is employed for a proper
time renormalisation group. We compare our results with those obtained by other
methods.Comment: 15 pages, 5 figure
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