2,968 research outputs found
Apparent horizon formation in the head-on collision of gyratons
The gyraton model describes a gravitational field of an object moving with
the velocity of light which has finite energy and spin distributed during some
finite time interval . A gyraton may be considered as a classical toy model
for a quantum wave packet of high-energy particles with spin. In this paper we
study a head-on collision of two gyratons and black hole formation in this
process. The goal of this study is to understand the role of the gravitational
spin-spin interaction in the process of mini-black-hole formation in particle
collisions. To simplify the problem we consider several gyraton models with
special profiles of the energy and spin density distribution. For these models
we study the apparent horizon (AH) formation on the future edge of a spacetime
region before interaction. We demonstrate that the AH forms only if the energy
duration and the spin are smaller than some critical values, while the length
of the spin distribution should be at least of the order of the system
gravitational radius. We also study gravitational spin-spin interaction in the
head-on collision of two gyratons under the assumption that the values of
gyraton spins are small. We demonstrate that the metric in the interaction
region for such gyratons depends on the relative helicities of incoming
gyratons, and the collision of gyratons with oppositely directed spins allows
the AH formation in a larger parameter region than in the collision of the
gyratons with the same direction of spins. Some applications of the obtained
results to the mini-black-hole production at the Large Hadron Collider in TeV
gravity scenarios are briefly discussed.Comment: 44 pages, 21 figures, published versio
Symmetrical Temperature-Chaos Effect with Positive and Negative Temperature Shifts in a Spin Glass
The aging in a Heisenberg-like spin glass Ag(11 at% Mn) is investigated by
measurements of the zero field cooled magnetic relaxation at a constant
temperature after small temperature shifts . A
crossover from fully accumulative to non-accumulative aging is observed, and by
converting time scales to length scales using the logarithmic growth law of the
droplet model, we find a quantitative evidence that positive and negative
temperature shifts cause an equivalent restart of aging (rejuvenation) in terms
of dynamical length scales. This result supports the existence of a unique
overlap length between a pair of equilibrium states in the spin glass system.Comment: 4 page
Absolute Transition Probabilities of Lines in the Spectra of Astrophysical Atoms, Molecules, and Ions
Progress in the investigation of absolute transition probabilities (A-values or F values) for ultraviolet lines is reported. A radio frequency ion trap was used for measurement of transition probabilities for intersystem lines seen in astronomical spectra. The intersystem line at 2670 A in Al II, which is seen in pre-main sequence stars and symbiotic stars, was studied
Temperature Chaos and Bond Chaos in the Edwards-Anderson Ising Spin Glass : Domain-Wall Free-Energy Measurements
Domain-wall free-energy , entropy , and the correlation
function, , of are measured independently in the
four-dimensional Edwards-Anderson (EA) Ising spin glass. The stiffness
exponent , the fractal dimension of domain walls and the
chaos exponent are extracted from the finite-size scaling analysis of
, and respectively well inside the
spin-glass phase. The three exponents are confirmed to satisfy the scaling
relation derived by the droplet theory within our
numerical accuracy. We also study bond chaos induced by random variation of
bonds, and find that the bond and temperature perturbations yield the universal
chaos effects described by a common scaling function and the chaos exponent.
These results strongly support the appropriateness of the droplet theory for
the description of chaos effect in the EA Ising spin glasses.Comment: 4 pages, 6 figures; The title, the abstract and the text are changed
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Black ring formation in particle systems
It is known that the formation of apparent horizons with non-spherical
topology is possible in higher-dimensional spacetimes. One of these is the
black ring horizon with topology where is the spacetime
dimension number. In this paper, we investigate the black ring horizon
formation in systems with -particles. We analyze two kinds of system: the
high-energy -particle system and the momentarily-static -black-hole
initial data. In the high-energy particle system, we prove that the black ring
horizon does not exist at the instant of collision for any . But there
remains a possibility that the black ring forms after the collision and this
result is not sufficient. Because calculating the metric of this system after
the collision is difficult, we consider the momentarily-static -black-hole
initial data that can be regarded as a simplified -particle model and
numerically solve the black ring horizon that surrounds all the particles. Our
results show that there is the minimum particle number that is necessary for
the black ring formation and this number depends on . Although many particle
number is required in five-dimensions, is sufficient for the black ring
formation in the cases. The black ring formation becomes easier for
larger . We provide a plausible physical interpretation of our results and
discuss the validity of Ida and Nakao's conjecture for the horizon formation in
higher-dimensions. Finally we briefly discuss the probable methods of producing
the black rings in accelerators.Comment: 26 pages, 7 figure
Improved analysis of black hole formation in high-energy particle collisions
We investigate formation of an apparent horizon (AH) in high-energy particle
collisions in four- and higher-dimensional general relativity, motivated by
TeV-scale gravity scenarios. The goal is to estimate the prefactor in the
geometric cross section formula for the black hole production. We numerically
construct AHs on the future light cone of the collision plane. Since this slice
lies to the future of the slice used previously by Eardley and Giddings
(gr-qc/0201034) and by one of us and Nambu (gr-qc/0209003), we are able to
improve the prefactor estimates. The black hole production cross section
increases by 40-70% in the higher-dimensional cases, indicating larger black
hole production rates in future-planned accelerators than previously estimated.
We also determine the mass and the angular momentum of the final black hole
state, as allowed by the area theorem.Comment: 28 pages, 14 figures, references and minor comments adde
Time evolution of a thin black ring via Hawking radiation
Black objects lose their mass and angular momenta through evaporation by
Hawking radiation, and the investigation of their time evolution has a long
history. In this paper, we study this problem for a five-dimensional doubly
spinning black ring. The black ring is assumed to emit only massless scalar
particles. We consider a thin black ring with a small thickness parameter,
, which can be approximated by a boosted Kerr string locally. We
show that a thin black ring evaporates with fixing its thickness parameter
. Further, in the case of an Emparan-Reall black ring, we derive
analytic formulas for the time evolution, which has one parameter to be
evaluated numerically. We find that the lifetime of a thin black ring is
shorter by a factor of compared to a five-dimensional
Schwarzschild black hole with the same initial mass. We also study detailed
properties of the Hawking radiation from the thin black ring, including the
energy and angular spectra of emitted particles.Comment: 28 pages, 6 figure
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