111 research outputs found
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
On leading order gravitational backreactions in de Sitter spacetime
Backreactions are considered in a de Sitter spacetime whose cosmological
constant is generated by the potential of scalar field. The leading order
gravitational effect of nonlinear matter fluctuations is analyzed and it is
found that the initial value problem for the perturbed Einstein equations
possesses linearization instabilities. We show that these linearization
instabilities can be avoided by assuming strict de Sitter invariance of the
quantum states of the linearized fluctuations. We furthermore show that quantum
anomalies do not block the invariance requirement. This invariance constraint
applies to the entire spectrum of states, from the vacuum to the excited states
(should they exist), and is in that sense much stronger than the usual Poincare
invariance requirement of the Minkowski vacuum alone. Thus to leading order in
their effect on the gravitational field, the quantum states of the matter and
metric fluctuations must be de Sitter invariant.Comment: 12 pages, no figures, typos corrected and some clarifying comments
added, version accepted by Phys. Rev.
How Black Holes Form in High Energy Collisions
We elucidate how black holes form in trans-Planckian collisions. In the rest
frame of one of the incident particles, the gravitational field of the other,
which is rapidly moving, looks like a gravitational shock wave. The shock wave
focuses the target particle down to a much smaller impact parameter. In turn,
the gravitational field of the target particle captures the projectile when the
resultant impact parameter is smaller than its own Schwarzschild radius,
forming a black hole. One can deduce this by referring to the original argument
of escape velocities exceeding the speed of light, which Michell and Laplace
used to discover the existence of black holes.Comment: 8 pages, 3 .eps figures, essa
An approximate binary-black-hole metric
An approximate solution to Einstein's equations representing two
widely-separated non-rotating black holes in a circular orbit is constructed by
matching a post-Newtonian metric to two perturbed Schwarzschild metrics. The
spacetime metric is presented in a single coordinate system valid up to the
apparent horizons of the black holes. This metric could be useful in numerical
simulations of binary black holes. Initial data extracted from this metric have
the advantages of being linked to the early inspiral phase of the binary
system, and of not containing spurious gravitational waves.Comment: 20 pages, 1 figure; some changes in Sec. IV B,C and Sec.
Radiation from a D-dimensional collision of shock waves: first order perturbation theory
We study the spacetime obtained by superimposing two equal Aichelburg-Sexl
shock waves in D dimensions traveling, head-on, in opposite directions.
Considering the collision in a boosted frame, one shock becomes stronger than
the other, and a perturbative framework to compute the metric in the future of
the collision is setup. The geometry is given, in first order perturbation
theory, as an integral solution, in terms of initial data on the null surface
where the strong shock has support. We then extract the radiation emitted in
the collision by using a D-dimensional generalisation of the Landau-Lifschitz
pseudo-tensor and compute the percentage of the initial centre of mass energy
epsilon emitted as gravitational waves. In D=4 we find epsilon=25.0%, in
agreement with the result of D'Eath and Payne. As D increases, this percentage
increases monotonically, reaching 40.0% in D=10. Our result is always within
the bound obtained from apparent horizons by Penrose, in D=4, yielding 29.3%,
and Eardley and Giddings, in D> 4, which also increases monotonically with
dimension, reaching 41.2% in D=10. We also present the wave forms and provide a
physical interpretation for the observed peaks, in terms of the null generators
of the shocks.Comment: 27 pages, 11 figures; v2 some corrections, including D dependent
factor in epsilon; matches version accepted in JHE
Quantum Black Holes from Cosmic Rays
We investigate the possibility for cosmic ray experiments to discover
non-thermal small black holes with masses in the TeV range. Such black holes
would result due to the impact between ultra high energy cosmic rays or
neutrinos with nuclei from the upper atmosphere and decay instantaneously. They
could be produced copiously if the Planck scale is in the few TeV region. As
their masses are close to the Planck scale, these holes would typically decay
into two particles emitted back-to-back. Depending on the angles between the
emitted particles with respect to the center of mass direction of motion, it is
possible for the simultaneous showers to be measured by the detectors.Comment: 6 pages, 3 figure
Exact Gravitational Shockwaves and Planckian Scattering on Branes
We obtain a solution describing a gravitational shockwave propagating along a
Randall-Sundrum brane. The interest of such a solution is twofold: on the one
hand, it is the first exact solution for a localized source on a
Randall-Sundrum three-brane. On the other hand, one can use it to study forward
scattering at Planckian energies, including the effects of the continuum of
Kaluza-Klein modes. We map out the different regimes for the scattering
obtained by varying the center-of-mass energy and the impact parameter. We also
discuss exact shockwaves in ADD scenarios with compact extra dimensions.Comment: 19 pages, 3 figures. v2: references added, minor improvements and
small errors correcte
Probing Exotic Physics With Cosmic Neutrinos
Traditionally, collider experiments have been the primary tool used in
searching for particle physics beyond the Standard Model. In this talk, I will
discuss alternative approaches for exploring exotic physics scenarios using
high energy and ultra-high energy cosmic neutrinos. Such neutrinos can be used
to study interactions at energies higher, and over baselines longer, than those
accessible to colliders. In this way, neutrino astronomy can provide a window
into fundamental physics which is highly complementary to collider techniques.
I will discuss the role of neutrino astronomy in fundamental physics,
considering the use of such techniques in studying several specific scenarios
including low scale gravity models, Standard Model electroweak instanton
induced interactions, decaying neutrinos and quantum decoherence.Comment: 11 pages, 6 figures; For the proceedings of From Colliders To Cosmic
Rays, Prague, Czech Republic, September 7-13, 200
Minimum black hole mass from colliding Gaussian packets
We study the formation of a black hole in the collision of two Gaussian
packets. Rather than following their dynamical evolution in details, we assume
a horizon forms when the mass function for the two packets becomes larger than
half the flat areal radius, as it would occur in a spherically symmetric
geometry. This simple approximation allows us to determine the existence of a
minimum black hole mass solely related to the width of the packets. We then
comment on the possible physical implications, both in classical and quantum
physics, and models with extra spatial dimensions.Comment: 11 pages, 4 figure
Gravitational Radiation from the radial infall of highly relativistic point particles into Kerr black holes
In this paper, we consider the gravitational radiation generated by the
collision of highly relativistic particles with rotating Kerr black holes. We
use the Sasaki-Nakamura formalism to compute the waveform, energy spectra and
total energy radiated during this process. We show that the gravitational
spectrum for high-energy collisions has definite characteristic universal
features, which are independent of the spin of the colliding objects. We also
discuss possible connections between these results and the black hole-black
hole collision at the speed of light process. With these results at hand, we
predict that during the high speed collision of a non-rotating hole with a
rotating one, about 35% of the total energy can get converted into
gravitational waves. Thus, if one is able to produce black holes at the Large
Hadron Collider, as much as 35% of the partons' energy should be emitted during
the so called balding phase. This energy will be missing, since we don't have
gravitational wave detectors able to measure such amplitudes. The collision at
the speed of light between one rotating black hole and a non-rotating one or
two rotating black holes turns out to be the most efficient gravitational wave
generator in the Universe.Comment: 15 pages, REVTEX4. Some comments and references adde
- âŠ