569 research outputs found
Derivation of fluid dynamics from kinetic theory with the 14--moment approximation
We review the traditional derivation of the fluid-dynamical equations from
kinetic theory according to Israel and Stewart. We show that their procedure to
close the fluid-dynamical equations of motion is not unique. Their approach
contains two approximations, the first being the so-called 14-moment
approximation to truncate the single-particle distribution function. The second
consists in the choice of equations of motion for the dissipative currents.
Israel and Stewart used the second moment of the Boltzmann equation, but this
is not the only possible choice. In fact, there are infinitely many moments of
the Boltzmann equation which can serve as equations of motion for the
dissipative currents. All resulting equations of motion have the same form, but
the transport coefficients are different in each case.Comment: 15 pages, 3 figures, typos fixed and discussions added; EPJA: Topical
issue on "Relativistic Hydro- and Thermodynamics
Massive spinor fields in flat spacetimes with non-trivial topology
The vacuum expectation value of the stress-energy tensor is calculated for
spin massive fields in several multiply connected flat spacetimes.
We examine the physical effects of topology on manifolds such as , , , the Mobius strip and the Klein bottle.
We find that the spinor vacuum stress tensor has the opposite sign to, and
twice the magnitude of, the scalar tensor in orientable manifolds. Extending
the above considerations to the case of Misner spacetime, we calculate the
vacuum expectation value of spinor stress-energy tensor in this space and
discuss its implications for the chronology protection conjecture.Comment: 18 pages, Some of the equations in section VI as well as
typographical errors corrected, 5 figures, Revtex
Semiclassical Stability of the Extreme Reissner-Nordstrom Black Hole
The stress-energy tensor of a free quantized scalar field is calculated in
the extreme Reissner-Nordstr\"{o}m black hole spacetime in the zero temperature
vacuum state. The stress-energy appears to be regular on the event horizon,
contrary to the suggestion provided by two-dimensional calculations. An
analytic calculation on the event horizon for a thermal state shows that if the
temperature is nonzero then the stress-energy diverges strongly there.Comment: 10 pages, REVTeX, 4 figures in separate uuencoded compressed fil
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
Vanishing of Gravitational Particle Production in the Formation of Cosmic Strings
We consider the gravitationally induced particle production from the quantum
vacuum which is defined by a free, massless and minimally coupled scalar field
during the formation of a gauge cosmic string. Previous discussions of this
topic estimate the power output per unit length along the string to be of the
order of ergs/sec/cm in the s-channel. We find that this production
may be completely suppressed. A similar result is also expected to hold for the
number of produced photons.Comment: 10 pages, Plain LaTex. Minor improvements. To appear in PR
Exact metric around a wiggly cosmic string
The exact metric around a wiggly cosmic string is found by modifying the
energy momentum-tensor of a straight infinitely thin cosmic string to include
an electric current along the symmetry axis.Comment: 5 page
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
Second Order Dissipative Fluid Dynamics for Ultra-Relativistic Nuclear Collisions
The M\"uller-Israel-Stewart second order theory of relativistic imperfect
fluids based on Grad's moment method is used to study the expansion of hot
matter produced in ultra-relativistic heavy ion collisions. The temperature
evolution is investigated in the framework of the Bjorken boost-invariant
scaling limit. The results of these second-order theories are compared to those
of first-order theories due to Eckart and to Landau and Lifshitz and those of
zeroth order (perfect fluid) due to Euler.Comment: 5 pages, 4 figures, size of y-axis tick marks for Figs. 3 and 4 fixe
- …