1,178 research outputs found
Quantum fields and "Big Rip" expansion singularities
The effects of quantized conformally invariant massless fields on the
evolution of cosmological models containing a ``Big Rip'' future expansion
singularity are examined. Quantized scalar, spinor, and vector fields are found
to strengthen the accelerating expansion of such models as they approach the
expansion singularity.Comment: 7 pages; REVTeX
Renormalization of the charged scalar field in curved space
The DeWitt-Schwinger proper time point-splitting procedure is applied to a
massive complex scalar field with arbitrary curvature coupling interacting with
a classical electromagnetic field in a general curved spacetime. The scalar
field current is found to have a linear divergence. The presence of the
external background gauge field is found to modify the stress-energy tensor
results of Christensen for the neutral scalar field by adding terms of the form
to the logarithmic counterterms. These results are shown to be
expected from an analysis of the degree of divergence of scalar quantum
electrodynamics.Comment: 24 pages REVTe
Recommended from our members
Integration and Co-ordination of DDR and SALW Control Programming: Issues, Experience and Priorities. Thematic Working Paper 3.
This paper examines the inter-relationships in post-conflict contexts between DDR programmes and processes on the one hand, and wider arms management and SALW control programmes on the other. It is a contribution to the international project "on DDR and Human Security: Post-conflict security building and the interests of the poor‟, and aims to complement the four other Thematic working papers of this Project. It argues that greater co-coordination, and often integration, between DDR and civilian arms management/reduction programmes is needed to promote human security in most countries emerging from conflict, within the framework of a wider comprehensive strategy for enhancing security from fear and violence that also includes security sector reform
Inflation driven by causal heat flux
We find a simple inflationary solution in an inhomogeneous spacetime with
heat flux. The heat flux obeys a causal transport equation, and counteracts the
inflationary decrease of energy density. At late times, the heat flux tends to
zero and the fluid approaches the equation of state .Comment: Latex 5 pages; to appear Gen. Rel. Gra
Astrophysical Bounds on Global Strings
Global topological defects produce nonzero stress-energy throughout
spacetime, and as a result can have observable gravitational influence on
surrounding matter. Gravitational effects of global strings are used to place
bounds on their cosmic abundance. The minimum separation between global strings
is estimated by considering the defects' contribution to the cosmological
energy density. More rigorous constraints on the abundance of global strings
are constructed by examining the tidal forces such defects will have on
observable astrophysical systems. The small number of observed tidally
disrupted systems indicates there can be very few of these objects in the
observable universe.Comment: 14 pages, REVTe
Temperature Evolution Law of Imperfect Relativistic Fluids
The first-order general relativistic theory of a generic dissipative
(heat-conducting, viscous, particle-creating) fluid is rediscussed from a
unified covariant frame-independent point of view. By generalizing some
previous works in the literature, we derive a formula for the temperature
variation rate, which is valid both in Eckart's (particle) and in the
Landau-Lifshitz (energy) frames. Particular attention is paid to the case of
gravitational particle creation and its possible cross-effect with the bulk
viscosity mechanism.Comment: 14 pages, no figure, revte
Semiclassical Methods for Hawking Radiation from a Vaidya Black Hole
We derive the general form of Hawking temperature for Vaidya black hole in
the tunneling pictures. This kind of black hole is regarded as the description
of a more realistic one since it's time dependent decreasing mass due to the
evaporation process. Clearly, the temperature would be time dependent as our
findings. We use the semiclassical methods, namely radial null geodesic and
complex paths methods. Both methods are found to give the same results. Then,
we discuss the possible form of corresponding entropy.Comment: REVTeX 4, 11 pages, no figures, accepted for publication in IJMPA;
v2: eq.5 is correcte
Cosmic Censorship: The Role of Quantum Gravity
The cosmic censorship hypothesis introduced by Penrose thirty years ago is
still one of the most important open questions in {\it classical} general
relativity. In this essay we put forward the idea that cosmic censorship is
intrinsically a {\it quantum gravity} phenomena. To that end we construct a
gedanken experiment in which cosmic censorship is violated within the purely
{\it classical} framework of general relativity. We prove, however, that {\it
quantum} effects restore the validity of the conjecture. This suggests that
classical general relativity is inconsistent and that cosmic censorship might
be enforced only by a quantum theory of gravity.Comment: 7 pages. This essay received the Second Prize from the Gravity
Research Foundation 200
Exact inhomogeneous cosmologies whose source is a radiation-matter mixture with consistent thermodynamics
We derive a new class of exact solutions of Einstein's equations providing a
physically plausible hydrodynamical description of cosmological matter in the
radiative era (), between nucleosynthesis and decoupling.
The solutions are characterized by the Lema\^{\i}tre-Tolman -Bondi metric with
a viscous fluid source, subjected to the following conditions: (a) the
equilibrium state variables satisfy the equation of state of a mixture of an
ultra-relativistic and a non-relativistic ideal gases, where the internal
energy of the latter has been neglected, (b) the particle numbers of the
mixture components are independently conserved, (c) the viscous stress is
consistent with the transport equation and entropy balance law of Extended
Irreversible Thermodynamics, with the coefficient of shear viscosity provided
by Kinetic Theory for the `radiative gas' model. The fulfilment of (a), (b) and
(c) restricts initial conditions in terms of an initial value function,
, related to the average of spatial gradients of the
fluctuations of photon entropy per baryon in the initial hypersurface.
Constraints on the observed anisotropy of the microwave cosmic radiation and
the condition that decoupling occurs at K yield
an estimated value: which can be associated
with a bound on promordial entropy fluctuations. The Jeans mass at decoupling
is of the same order of magnitude as that of baryon dominated perturbation
models ()Comment: LaTeX with revtex (PRD macros). Contains 9 figures (ps). To be
published in Physics Review
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