50 research outputs found
Constructing Time Machines
The existence of time machines, understood as spacetime constructions
exhibiting physically realised closed timelike curves (CTCs), would raise
fundamental problems with causality and challenge our current understanding of
classical and quantum theories of gravity. In this paper, we investigate three
proposals for time machines which share some common features: cosmic strings in
relative motion, where the conical spacetime appears to allow CTCs; colliding
gravitational shock waves, which in Aichelburg-Sexl coordinates imply
discontinuous geodesics; and the superluminal propagation of light in
gravitational radiation metrics in a modified electrodynamics featuring
violations of the strong equivalence principle. While we show that ultimately
none of these constructions creates a working time machine, their study
illustrates the subtle levels at which causal self-consistency imposes itself,
and we consider what intuition can be drawn from these examples for future
theories.Comment: 36 pages, 14 figures, TeX with harvmac; Review article prepared for
Int. J. Mod. Phys.
Ultrarelativistic boost of spinning black rings
We study the D=5 Emparan-Reall spinning black ring under an ultrarelativistic
boost along an arbitrary direction. We analytically determine the resulting
shock pp-wave, in particular for boosts along axes orthogonal and parallel to
the plane of rotation. The solution becomes physically more interesting and
simpler if one enforces equilibrium between the forces on the ring. We also
comment on the ultrarelativistic limit of recently found supersymmetric black
rings with two independent angular momenta. Essential distinct features with
respect to the boosted Myers-Perry black holes are pointed out.Comment: 15 pages, 2 figures. v2: added multipole expansions at spatial
infinity, and a comparison with the boosted Myers-Perry solution in a new
appendix. To appear in JHE
Effect of charged partons on black hole production at the Large Hadron Collider
The cross section for black hole production in hadron colliders is calculated
using a factorization hypothesis in which the parton-level process is
integrated over the parton density functions of the protons. The mass, spin,
charge, colour, and finite size of the partons are usually ignored. We examine
the effects of parton electric charge on black hole production using the
trapped-surface approach of general relativity. Accounting for electric charge
of the partons could reduce the black hole cross section by one to four orders
of magnitude at the Large Hadron Collider. The cross section results are
sensitive to the Standard Model brane thickness. Lower limits on the amount of
energy trapped behind the event horizon in the collision of charged particles
are also calculated.Comment: corrected typo in figure 1b; added some clarification in 3 places; 21
pages, 9 figures, JHEP3 forma
Black Hole Cross Section at the Large Hadron Collider
Black hole production at the Large Hadron Collider (LHC) was first discussed
in 1999. Since then, much work has been performed in predicting the black hole
cross section. In light of the start up of the LHC, it is now timely to review
the state of these calculations. We review the uncertainties in estimating the
black hole cross section in higher dimensions. One would like to make this
estimate as precise as possible since the predicted values, or lower limits,
obtain for the fundamental Planck scale and number of extra dimensions from
experiments will depend directly on the accuracy of the cross section. Based on
the current knowledge of the cross section, we give a range of lower limits on
the fundamental Planck scale that could be obtained at LHC energies.Comment: 28 pages, 9 figures, LaTeX; added references, corrected typos,
expanded discussio
Head-on collision of ultrarelativistic charges
We consider the head-on collision of two opposite-charged point particles
moving at the speed of light. Starting from the field of a single charge we
derive in a first step the field generated by uniformly accelerated charge in
the limit of infinite acceleration. From this we then calculate explicitly the
burst of radiation emitted from the head-on collision of two charges and
discuss its distributional structure. The motivation for our investigation
comes from the corresponding gravitational situation where the head-on
collision of two ultrarelativistic particles (black holes) has recently aroused
renewed interest.Comment: 4 figures, uses the AMSmat
Black Hole Production at the Large Hadron Collider
Black hole production at the Large Hadron Collider (LHC) is an interesting
consequence of TeV-scale gravity models. The predicted values, or lower limits,
for the fundamental Planck scale and number of extra dimensions will depend
directly on the accuracy of the black hole production cross-section. We give a
range of lower limits on the fundamental Planck scale that could be obtained at
LHC energies. In addition, we examine the effects of parton electric charge on
black hole production using the trapped-surface approach of general relativity.
Accounting for electric charge of the partons could reduce the black hole
cross-section by one to four orders of magnitude at the LHC.Comment: CTP Symposium on Supersymmetry at LHC: Theoretical and Experimental
Perspectives at the British University in Egypt 11-14 March 200
Large-N bounds on, and compositeness limit of, gauge and gravitational interactions
In a toy model of gauge and gravitational interactions in
dimensions, endowed with an invariant UV cut-off , and containing a
large number of non-self-interacting matter species, the physical gauge and
gravitational couplings at the cut-off, and
, are shown to be bounded by appropriate
powers of . This implies that the infinite-bare-coupling (so-called
compositeness) limit of these theories is smooth, and can even resemble our
world. We argue that such a result, when extended to more realistic situations,
can help avoid large-N violations of entropy bounds, solve the dilaton
stabilization and GUT-scale problems in superstring theory, and provide a new
possible candidate for quintessence.Comment: 8 pages, Latex, minor modifications in notations and reference
Gravitational anomalies in a dispersive approach
The gravitational anomalies in two dimensions, specifically the Einstein
anomaly and the Weyl anomaly, are fully determined by means of dispersion
relations. In this approach the anomalies originate from the peculiar infrared
feature of the imaginary part of the relevant formfactor which approaches a
-function singularity at zero momentum squared when .Comment: 10 page
Charge and mass effects on the evaporation of higher-dimensional rotating black holes
To study the dynamics of discharge of a brane black hole in TeV gravity
scenarios, we obtain the approximate electromagnetic field due to the charged
black hole, by solving Maxwell's equations perturbatively on the brane. In
addition, arguments are given for brane metric corrections due to backreaction.
We couple brane scalar and brane fermion fields with non-zero mass and charge
to the background, and study the Hawking radiation process using well known low
energy approximations as well as a WKB approximation in the high energy limit.
We argue that contrary to common claims, the initial evaporation is not
dominated by fast Schwinger discharge.Comment: Published version. Minor typos corrected. 29 pages, 5 figure