69 research outputs found
Renormalization of the Planck mass for type II superstrings on symmetric orbifolds
We compute the one-loop renormalization of the Planck mass for type II string
theories compactified to four dimensions on symmetric orbifolds that preserve
supersymmetry. Depending on the orbifold, the effect can be as
large as to compete with the standard tree-level value.Comment: 9 pages, reference added, counting of supersymmetries correcte
Schwinger terms in gravitation in two dimensions as a consequence of the gravitational anomaly
We compute the Schwinger term in the gravitational constraints in two
dimensions, starting from the path integral in Hamiltonian form and the
Einstein anomaly.Comment: 8 pages, Latex, additional reference
Localized gravity in non-compact superstring models
We discuss a string-theory-derived mechanism for localized gravity, which
produces a deviation from Newton's law of gravitation at cosmological
distances. This mechanism can be realized for general non-compact Calabi-Yau
manifolds, orbifolds and orientifolds. After discussing the cross-over scale
and the thickness in these models we show that the localized higher derivative
terms can be safely neglected at observable distances. We conclude by some
observations on the massless open string spectrum for the orientifold models.Comment: 12 Pages. Based on some unpublished work presented at Quarks-2004,
Pushkinskie Gory, Russia, May 24-3
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.
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
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