13,159 research outputs found
Self-Gravitating Phase Transitions: Point Particles, Black Holes and Strings
We compute the quantum string entropy S_s(m,j) of the microscopic string
states of mass m and spin j in two physically relevant backgrounds: Kerr
(rotating) black holes and de Sitter (dS) space-time. We find a new formula for
the quantum gravitational entropy S_{sem} (M, J), as a function of the usual
Bekenstein-Hawking entropy S_{sem}^(0)(M, J). We compute the quantum string
emission by a black hole in de Sitter space-time (bhdS). In all these cases:
(i) strings with the highest spin, and (ii) in dS space-time, (iii) quantum
rotating black holes, (iv) quantum dS regime, (v) late bhdS evaporation, we
find a new gravitational phase transition with a common distinctive universal
feature: A square root branch point singularity in any space-time dimensions.
This is the same behavior as for the thermal self-gravitating gas of point
particles (de Vega-Sanchez transition), thus describing a new universality
class.Comment: Invited lecture at `Statistical Mechanics of Non-Extensive Systems',
Observatoire de Paris, 24-25 October 2005, to be published in a Special issue
of `Les Comptes rendus de l'Academie des sciences', Elsevie
Strings in Cosmological and Black Hole Backgrounds: Ring Solutions
The string equations of motion and constraints are solved for a ring shaped
Ansatz in cosmological and black hole spacetimes. In FRW universes with
arbitrary power behavior [R(X^0) = a\;|X^0|^{\a}\, ], the asymptotic form of
the solution is found for both and and we plot the
numerical solution for all times. Right after the big bang (), the
string energy decreasess as and the string size grows as for . Very
soon [ ] , the ring reaches its oscillatory regime with frequency
equal to the winding and constant size and energy. This picture holds for all
values of \a including string vacua (for which, asymptotically, \a = 1).
In addition, an exact non-oscillatory ring solution is found. For black hole
spacetimes (Schwarzschild, Reissner-Nordstr\oo m and stringy), we solve for
ring strings moving towards the center. Depending on their initial conditions
(essentially the oscillation phase), they are are absorbed or not by
Schwarzschild black holes. The phenomenon of particle transmutation is
explicitly observed (for rings not swallowed by the hole). An effective horizon
is noticed for the rings. Exact and explicit ring solutions inside the
horizon(s) are found. They may be interpreted as strings propagating between
the different universes described by the full black hole manifold.Comment: Paris preprint PAR-LPTHE-93/43. Uses phyzzx. Includes figures. Text
and figures compressed using uufile
Planetoid String Solutions in 3 + 1 Axisymmetric Spacetimes
The string propagation equations in axisymmetric spacetimes are exactly
solved by quadratures for a planetoid Ansatz. This is a straight
non-oscillating string, radially disposed, which rotates uniformly around the
symmetry axis of the spacetime. In Schwarzschild black holes, the string stays
outside the horizon pointing towards the origin. In de Sitter spacetime the
planetoid rotates around its center. We quantize semiclassically these
solutions and analyze the spin/(mass) (Regge) relation for the planetoids,
which turns out to be non-linear.Comment: Latex file, 14 pages, two figures in .ps files available from the
author
Strings Next To and Inside Black Holes
The string equations of motion and constraints are solved near the horizon
and near the singularity of a Schwarzschild black hole. In a conformal gauge
such that ( = worldsheet time coordinate) corresponds to the
horizon () or to the black hole singularity (), the string
coordinates express in power series in near the horizon and in power
series in around . We compute the string invariant size and
the string energy-momentum tensor. Near the horizon both are finite and
analytic. Near the black hole singularity, the string size, the string energy
and the transverse pressures (in the angular directions) tend to infinity as
. To leading order near , the string behaves as two dimensional
radiation. This two spatial dimensions are describing the sphere in the
Schwarzschild manifold.Comment: RevTex, 19 pages without figure
Warm Dark Matter Galaxies with Central Supermassive Black-Holes
We generalize the Thomas-Fermi approach to galaxy structure to include
self-consistently and non-linearly central supermassive black holes. This
approach naturally incorporates the quantum pressure of the warm dark matter
(WDM) particles and shows its full powerful and clearness in the presence of
supermassive black holes (SPMHs). We find the main galaxy and central black
hole magnitudes: halo radius r_h , halo mass M_h, black hole mass M_BH,
velocity dispersion, phase space density, with their realistic astrophysical
values, masses and sizes over a wide galaxy range. The SMBH masses arise
naturally in this framework. Our extensive numerical calculations and detailed
analytic resolution show that with SMBH's, both WDM regimes: classical
(Boltzmann dilute) and quantum (compact) do necessarily co-exist in any galaxy:
from the smaller and compact galaxies to the largest ones. The transition from
the quantum to the classical region occurs precisely at the same point r_A
where the chemical potential vanishes. A novel halo structure with three
regions shows up: A small quantum compact core of radius r_A around the SMBH,
followed by a less compact region till the BH influence radius r_i, and then
for r> r_i the known halo galaxy shows up with its astrophysical size. Three
representative families of galaxy plus central SMBH solutions are found and
analyzed:small, medium and large galaxies having SMBH masses of 10^5, 10^7 and
10^9 M_sun respectively. A minimum galaxy size and mass ~ 10^7 M_sun larger
than the one without SMBH is found. Small galaxies in the range 10^4 M_sun <
M_h < 10^7 M_sun cannot harbor central SMBHs. We find novel scaling M_BH - r_h
- M_h relations. The galaxy equation of state is derived: The pressure P(r)
takes huge values in the SMBH vecinity and then sharply decreases entering the
classical region following a local perfect gas behaviour.(Abridged)Comment: 31 pages, 14 figures, new materia
Effects of regulation on a self-organized market
Adapting a simple biological model, we study the effects of control on the
market. Companies are depicted as sites on a lattice and labelled by a fitness
parameter (some `company-size' indicator). The chance of survival of a company
on the market at any given time is related to its fitness, its position on the
lattice and on some particular external influence, which may be considered to
represent regulation from governments or central banks. The latter is rendered
as a penalty for companies which show a very fast betterment in fitness space.
As a result, we find that the introduction of regulation on the market
contributes to lower the average fitness of companies.Comment: 7 pages, 2 figure
Galaxy phase-space density data exclude Bose-Einstein condensate Axion Dark Matter
Light scalars (as the axion) with mass m ~ 10^{-22} eV forming a
Bose-Einstein condensate (BEC) exhibit a Jeans length in the kpc scale and were
therefore proposed as dark matter (DM) candidates. Our treatment here is
generic, independent of the particle physics model and applies to all DM BEC,
in or out of equilibrium. Two observed quantities crucially constrain DM in an
inescapable way: the average DM density rho_{DM} and the phase-space density Q.
The observed values of rho_{DM} and Q in galaxies today constrain both the
possibility to form a BEC and the DM mass m. These two constraints robustly
exclude axion DM that decouples just after the QCD phase transition. Moreover,
the value m ~ 10^{-22} eV can only be obtained with a number of
ultrarelativistic degrees of freedom at decoupling in the trillions which is
impossible for decoupling in the radiation dominated era. In addition, we find
for the axion vacuum misalignment scenario that axions are produced strongly
out of thermal equilibrium and that the axion mass in such scenario turns to be
17 orders of magnitude too large to reproduce the observed galactic structures.
Moreover, we also consider inhomogenous gravitationally bounded BEC's supported
by the bosonic quantum pressure independently of any particular particle
physics scenario. For a typical size R ~ kpc and compact object masses M ~ 10^7
Msun they remarkably lead to the same particle mass m ~ 10^{-22} eV as the BEC
free-streaming length. However, the phase-space density for the gravitationally
bounded BEC's turns to be more than sixty orders of magnitude smaller than the
galaxy observed values. We conclude that the BEC's and the axion cannot be the
DM particle. However, an axion in the mili-eV scale may be a relevant source of
dark energy through the zero point cosmological quantum fluctuations.Comment: 8 pages, no figures. Expanded versio
Data reduction in the ITMS system through a data acquisition model with self-adaptive sampling rate
Long pulse or steady state operation of fusion experiments require data acquisition and processing systems that reduce the volume of data involved. The availability of self-adaptive sampling rate systems and the use of real-time lossless data compression techniques can help solve these problems. The former is important for continuous adaptation of sampling frequency for experimental requirements. The latter allows the maintenance of continuous digitization under limited memory conditions. This can be achieved by permanent transmission of compressed data to other systems. The compacted transfer ensures the use of minimum bandwidth. This paper presents an implementation based on intelligent test and measurement system (ITMS), a data acquisition system architecture with multiprocessing capabilities that permits it to adapt the system’s sampling frequency throughout the experiment. The sampling rate can be controlled depending on the experiment’s specific requirements by using an external dc voltage signal or by defining user events through software. The system takes advantage of the high processing capabilities of the ITMS platform to implement a data reduction mechanism based in lossless data compression algorithms which are themselves based in periodic deltas
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