13 research outputs found
Dynamics of Relativistic Interacting Gases : from a Kinetic to a Fluid Description
Starting from a microscopic approach, we develop a covariant formalism to
describe a set of interacting gases. For that purpose, we model the collision
term entering the Boltzmann equation for a class of interactions and then
integrate this equation to obtain an effective macroscopic description. This
formalism will be useful to study the cosmic microwave background
non-perturbatively in inhomogeneous cosmologies. It should also be useful for
the study of the dynamics of the early universe and can be applied, if one
considers fluids of galaxies, to the study of structure formation.Comment: Latex file, 28 pages, accepted for publication in Class. Quant. Gra
Electron-positron outflow from black holes
Gamma-ray bursts (GRBs) appear as the brightest transient phenomena in the
Universe. The nature of the central engine in GRBs is a missing link in the
theory of fireballs to their stellar mass progenitors. Here it is shown that
rotating black holes produce electron-positron outflow when brought into
contact with a strong magnetic field. The outflow is produced by a coupling of
the spin of the black hole to the orbit of the particles. For a nearly extreme
Kerr black hole, particle outflow from an initial state of electrostatic
equilibrium has a normalized isotropic emission of erg/s, where B is the
external magnetic field strength, B_c=4.4 x 10^{13}G, and M is the mass of the
black hole. This initial outflow has a half-opening angle
. A connection with fireballs in -ray bursts is
given.Comment: 10 pages LaTe
Casimir effect: running Newton constant or cosmological term
We argue that the instability of Euclidean Einstein gravity is an indication
that the vacuum is non perturbative and contains a condensate of the metric
tensor in a manner reminiscent of Yang-Mills theories. As a simple step toward
the characterization of such a vacuum the value of the one-loop effective
action is computed for Euclidean de Sitter spaces as a function of the
curvature when the unstable conformal modes are held fixed. Two phases are
found, one where the curvature is large and gravitons should be confined and
another one which appears to be weakly coupled and tends to be flat. The
induced cosmological constant is positive or negative in the strongly or weakly
curved phase, respectively. The relevance of the Casimir effect in
understanding the UV sensitivity of gravity is pointed out.Comment: Final, slightly extended version, to appear in Classical and Quantum
Gravit
A discrete nonetheless remarkable brick in de Sitter: the "massless minimally coupled field"
Over the last ten years interest in the physics of de Sitter spacetime has
been growing very fast. Besides the supposed existence of a "de sitterian
period" in inflation theories, the observational evidence of an acceleration of
the universe expansion (interpreted as a positive cosmological constant or a
"dark energy" or some form of "quintessence") has triggered a lot of attention
in the physics community. A specific de sitterian field called "massless
minimally coupled field" (mmc) plays a fundamental role in inflation models and
in the construction of the de sitterian gravitational field. A covariant
quantization of the mmc field, `a la Krein-Gupta-Bleuler was proposed in [1].
In this talk, we will review this construction and explain the relevance of
such a field in the construction of a massless spin 2 field in de Sitter
space-time.Comment: Proceedings of the XXVII Colloquium on Group Theoretical Methods in
Physics, Yerevan, August 200
Boson-fermion unification, superstrings, and Bohmian mechanics
Bosonic and fermionic particle currents can be introduced in a more unified
way, with the cost of introducing a preferred spacetime foliation. Such a
unified treatment of bosons and fermions naturally emerges from an analogous
superstring current, showing that the preferred spacetime foliation appears
only at the level of effective field theory, not at the fundamental superstring
level. The existence of the preferred spacetime foliation allows an objective
definition of particles associated with quantum field theory in curved
spacetime. Such an objective definition of particles makes the Bohmian
interpretation of particle quantum mechanics more appealing. The superstring
current allows a consistent Bohmian interpretation of superstrings themselves,
including a Bohmian description of string creation and destruction in terms of
string splitting. The Bohmian equations of motion and the corresponding
probabilistic predictions are fully relativistic covariant and do not depend on
the preferred foliation.Comment: 30 pages, 1 figure, revised, to appear in Found. Phy