183 research outputs found
Gravitational instabilities and faster evolving density perturbations
The evolution of inhomogeneities in a spherical collapse model is studied by
expanding the Einstein equation in powers of inverse radial parameter. In the
linear regime, the density contrast is obtained for flat, closed and open
universes. In addition to the usual modes, an infinite number of new growing
modes are contained in the solutions for pressureless open and closed
universes. In the nonlinear regime, we obtain the leading growing modes in
closed forms for a flat universe and also, in the limits of small and large
times, for an open universe.Comment: latex, 17 pages; electronic address for programs correcte
Holographic Superconductors in a Rotating Spacetime
We consider holographic superconductors in a rotating black string spacetime.
In view of the mandatory introduction of the component of the
vector potential we are left with three equations to be solved. Their solutions
show that the effect of the rotating parameter influences the critical
temperature and the conductivity in a simple but not trivial
way.Comment: 9 pages, 5 figures, paper completely rewritten and improved. Version
to appear in EPJ
Decay amplitudes in two-dimensional QCD
Decay amplitudes for mesons in two-dimensional QCD are discussed. We show
that in spite of an infinite number of conserved charges, particle production
is not entirely suppressed. This phenomenon is explained in terms of quantum
corrections to the combined algebra of higher-conserved and spectrum-generating
currents. We predict the qualitative form of particle production probabilities
and verify that they are in agreement with numerical data. We also discuss
four-dimensional self-dual Yang-Mills theory in the light of our results.Comment: We discuss in more detail the background material and elaborate on
the consequences of the new results. New equations and text are added and the
figures are efficiently regenerated by a fortran program, latex file, 13
pages, 4 figures in encapsulated postscript files, uses epsf. minor changes,
version to appear in Physical Review
A precise formulation of the third law of thermodynamics
The third law of thermodynamics is formulated precisely: all points of the
state space of zero temperature are physically adiabatically
inaccessible from the state space of a simple system. In addition to implying
the unattainability of absolute zero in finite time (or "by a finite number of
operations"), it admits as corollary, under a continuity assumption, that all
points of are adiabatically equivalent. We argue that the third law
is universally valid for all macroscopic systems which obey the laws of quantum
mechanics and/or quantum field theory. We also briefly discuss why a precise
formulation of the third law for black holes remains an open problem.Comment: 24 pages, no figure
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