5,123 research outputs found
Commercial air transport hazard warning and avoidance system. Volume 3 - Radar performance studies Final report
Technology and system analysis of radar performance for hazard warning and avoidance syste
Gravity: A New Holographic Perspective
A general paradigm for describing classical (and semiclassical) gravity is
presented. This approach brings to the centre-stage a holographic relationship
between the bulk and surface terms in a general class of action functionals and
provides a deeper insight into several aspects of classical gravity which have
no explanation in the conventional approach. After highlighting a series of
unresolved issues in the conventional approach to gravity, I show that (i)
principle of equivalence, (ii) general covariance and (iii)a reasonable
condition on the variation of the action functional, suggest a generic
Lagrangian for semiclassical gravity of the form with
. The expansion of in terms of the
derivatives of the metric tensor determines the structure of the theory
uniquely. The zeroth order term gives the Einstein-Hilbert action and the first
order correction is given by the Gauss-Bonnet action. Any such Lagrangian can
be decomposed into a surface and bulk terms which are related holographically.
The equations of motion can be obtained purely from a surface term in the
gravity sector. Hence the field equations are invariant under the
transformation and gravity does not
respond to the changes in the bulk vacuum energy density. The cosmological
constant arises as an integration constant in this approach. The implications
are discussed.Comment: Plenary talk at the International Conference on Einstein's Legacy in
the New Millennium, December 15 - 22, 2005, Puri, India; to appear in the
Proceedings to be published in IJMPD; 16 pages; no figure
Calculation of High Energy Neutrino-Nucleon Cross Sections and Uncertainties Using the MSTW Parton Distribution Functions and Implications for Future Experiments
We present a new calculation of the cross sections for charged current (CC)
and neutral current (NC) and interactions in the neutrino
energy range GeV using the most recent MSTW parton
distribution functions (PDFs), MSTW 2008. We also present the associated
uncertainties propagated from the PDFs, as well as parametrizations of the
cross section central values, their uncertainty bounds, and the inelasticity
distributions for ease of use in Monte Carlo simulations. For the latter we
only provide parametrizations for energies above GeV. Finally, we assess
the feasibility of future neutrino experiments to constrain the cross
section in the ultra-high energy (UHE) regime using a technique that is
independent of the flux spectrum of incident neutrinos. A significant deviation
from the predicted Standard Model cross sections could be an indication of new
physics, such as extra space-time dimensions, and we present expected
constraints on such models as a function of the number of events observed in a
future subterranean neutrino detector.Comment: 20 pages, 13 figures, 5 tables, published in Phys.Rev.D. This version
fixes a typo in Equation 16 of the publication. Also since version v1, the
following changes are in v2 and also in the published version: tables with cs
values, parametrization of the y distribution at low-y improved, the
discussions on likelihood and also earth absorption are expanded, added a
needed minus sign in Eq. 17 of v
Commercial air transport hazard warning and avoidance system. Volume 2 - Requirements studies Final report
Operational requirements and cost effectiveness of commercial air transport hazard warning and avoidance syste
Periodic Solutions of the Einstein Equations for Binary Systems
This revision includes clarified exposition and simplified analysis.
Solutions of the Einstein equations which are periodic and have standing
gravitational waves are valuable approximations to more physically realistic
solutions with outgoing waves. A variational principle is found which has the
power to provide an accurate estimate of the relationship between the mass and
angular momentum of the system, the masses and angular momenta of the
components, the rotational frequency of the frame of reference in which the
system is periodic, the frequency of the periodicity of the system, and the
amplitude and phase of each multipole component of gravitational radiation.
Examination of the boundary terms of the variational principle leads to
definitions of the effective mass and effective angular momentum of a periodic
geometry which capture the concepts of mass and angular momentum of the source
alone with no contribution from the gravitational radiation. These effective
quantities are surface integrals in the weak-field zone which are independent
of the surface over which they are evaluated, through second order in the
deviations of the metric from flat space.Comment: 18 pages, RevTeX 3.0, UF-RAP-93-1
Locality in quantum gravity and string theory
Breakdown of local physics in string theory at distances longer than the
string scale is investigated. Such nonlocality would be expected to be visible
in ultrahigh-energy scattering. The results of various approaches to such
scattering are collected and examined. No evidence is found for non-locality
from strings whose length grows linearly with the energy. However, local
quantum field theory does apparently fail at scales determined by gravitational
physics, particularly strong gravitational dynamics. This amplifies locality
bound arguments that such failure of locality is a fundamental aspect of
physics. This kind of nonlocality could be a central element of a possible
loophole in the argument for information loss in black holes.Comment: 26 pages, 3 figures, harvmac. v2: minor changes to bring into accord
with revised paper hep-th/060519
Gedanken Experiments involving Black Holes
Analysis of several gedanken experiments indicates that black hole
complementarity cannot be ruled out on the basis of known physical principles.
Experiments designed by outside observers to disprove the existence of a
quantum-mechanical stretched horizon require knowledge of Planck-scale effects
for their analysis. Observers who fall through the event horizon after sampling
the Hawking radiation cannot discover duplicate information inside the black
hole before hitting the singularity. Experiments by outside observers to detect
baryon number violation will yield significant effects well outside the
stretched horizon.Comment: 22 pages (including 7 figures), SU-ITP-93-1
Comments on the black hole information problem
String theory provides numerous examples of duality between gravitational
theories and unitary gauge theories. To resolve the black hole information
paradox in this setting, it is necessary to better understand how unitarity is
implemented on the gravity side. We argue that unitarity is restored by
nonlocal effects whose initial magnitude is suppressed by the exponential of
the Bekenstein-Hawking entropy. Time-slicings for which effective field theory
is valid are obtained by demanding the mutual back-reaction of quanta be small.
The resulting bounds imply that nonlocal effects do not lead to observable
violations of causality or conflict with the equivalence principle for
infalling observers, yet implement information retrieval for observers who stay
outside the black hole.Comment: 18 pages, 2 figures, revtex, v2 figure added and some improvements to
presentatio
Model of black hole evolution
From the postulate that a black hole can be replaced by a boundary on the
apparent horizon with suitable boundary conditions, an unconventional scenario
for the evolution emerges. Only an insignificant fraction of energy of order
is radiated out. The outgoing wave carries a very small part of the
quantum mechanical information of the collapsed body, the bulk of the
information remaining in the final stable black hole geometry.Comment: 9 pages, harvmac, 3 figures, minor addition
Model of black hole evolution
From the postulate that a black hole can be replaced by a boundary on the
apparent horizon with suitable boundary conditions, an unconventional scenario
for the evolution emerges. Only an insignificant fraction of energy of order
is radiated out. The outgoing wave carries a very small part of the
quantum mechanical information of the collapsed body, the bulk of the
information remaining in the final stable black hole geometry.Comment: 9 pages, harvmac, 3 figures, minor addition
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