2,405 research outputs found
Black hole information, unitarity, and nonlocality
The black hole information paradox apparently indicates the need for a
fundamentally new ingredient in physics. The leading contender is nonlocality.
Possible mechanisms for the nonlocality needed to restore unitarity to black
hole evolution are investigated. Suggestions that such dynamics arises from
ultra-planckian modes in Hawking's derivation are investigated and found not to
be relevant, in a picture using smooth slices spanning the exterior and
interior of the horizon. However, no simultaneous description of modes that
have fallen into the black hole and outgoing Hawking modes can be given without
appearance of a large kinematic invariant, or other dependence on
ultra-planckian physics; a reliable argument for information loss thus has not
been constructed. This suggests that strong gravitational dynamics is
important. Such dynamics has been argued to be fundamentally nonlocal in
extreme situations, such as those required to investigate the fate of
information.Comment: 34 pages, 4 figures. Major revision of hep-th/0604047. v2: minor
corrections and added referenc
Is string theory a theory of quantum gravity?
Some problems in finding a complete quantum theory incorporating gravity are
discussed. One is that of giving a consistent unitary description of
high-energy scattering. Another is that of giving a consistent quantum
description of cosmology, with appropriate observables. While string theory
addresses some problems of quantum gravity, its ability to resolve these
remains unclear. Answers may require new mechanisms and constructs, whether
within string theory, or in another framework.Comment: Invited contribution for "Forty Years of String Theory: Reflecting on
the Foundations," a special issue of Found. Phys., ed. by G 't Hooft, E.
Verlinde, D. Dieks, S. de Haro. 32 pages, 5 figs., harvmac. v2: final version
to appear in journal (small revisions
A study of the performance, progress, and degree achievement of Iowa community college transfer students at Iowa\u27s state universities
The purpose of this study was to examine the performance, progress, and degree achievement of Iowa public community college transfer students at the three Iowa state universities and compare these students\u27 performance, progress, and degree achievement to that of transfer students from four-year colleges and students native to the universities. Data for this study were gathered from the permanent record of the individual students at each of the three Iowa state universities;Prior research reviewed was inconclusive in determining if the performance of community college students was equivalent to the performance of students who enroll directly from secondary schools to the university or the performance of students who transfer from other four-year colleges to the university. Some studies indicated that transfer students performed less well, while other studies indicated no difference in the performance of these groups;Comparisons were made among the student groups with regard to performance measured by upper-division grade point average; progress measured by the number of semesters enrolled, the number of upper-division credits earned, and the number of semester credits needed to graduate with a bachelor\u27s degree; and persistence measured by the rate of graduation. After making raw comparisons, students were then grouped by ACT composite score, sex, and and number of credits earned prior to transfer for community college students to determine if the same results were found using different methods of comparison;The results showed that students from each Iowa public community college had similar post-transfer success. Differences in transfer student success were found, however, among the three universities. The results also showed that community college transfers with 60 semester hours earned prior to transfer performed as well as four-year college transfers and better than other community college transfers;When students of similar ACT score were compared, no differences existed in performance and degree achievement between community college transfers with 60 semester hours prior to transfer and native students. It was concluded that different methods of comparison produce different results and grouped or matched comparisons should be used when comparing these student groups
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
System development of the Screwworm Eradication Data System (SEDS) algorithm
The use of remotely sensed data is reported in the eradication of the screwworm and in the study of the role of the weather in the activity and development of the screwworm fly. As a result, the Screwworm Eradication Data System (SEDS) algorithm was developed
UV-Completion by Classicalization
We suggest a novel approach to UV-completion of a class of non-renormalizable
theories, according to which the high-energy scattering amplitudes get
unitarized by production of extended classical objects (classicalons), playing
a role analogous to black holes, in the case of non-gravitational theories. The
key property of classicalization is the existence of a classicalizer field that
couples to energy-momentum sources. Such localized sources are excited in
high-energy scattering processes and lead to the formation of classicalons. Two
kinds of natural classicalizers are Nambu-Goldstone bosons (or, equivalently,
longitudinal polarizations of massive gauge fields) and scalars coupled to
energy-momentum type sources. Classicalization has interesting phenomenological
applications for the UV-completion of the Standard Model both with or without
the Higgs. In the Higgless Standard Model the high-energy scattering amplitudes
of longitudinal -bosons self-unitarize via classicalization, without the
help of any new weakly-coupled physics. Alternatively, in the presence of a
Higgs boson, classicalization could explain the stabilization of the hierarchy.
In both scenarios the high-energy scatterings are dominated by the formation of
classicalons, which subsequently decay into many particle states. The
experimental signatures at the LHC are quite distinctive, with sharp
differences in the two cases.Comment: 37 page
Information Loss and Anomalous Scattering
The approach of 't Hooft to the puzzles of black hole evaporation can be
applied to a simpler system with analogous features. The system is
dimensional electrodynamics in a linear dilaton background. Analogues of black
holes, Hawking radiation and evaporation exist in this system. In perturbation
theory there appears to be an information paradox but this gets resolved in the
full quantum theory and there exists an exact -matrix, which is fully
unitary and information conserving. 't Hooft's method gives the leading terms
in a systematic approximation to the exact result.Comment: 18 pages, 3 figures (postscript files available soon on request),
(earlier version got corrupted by mail system
Nonlocality vs. complementarity: a conservative approach to the information problem
A proposal for resolution of the information paradox is that "nice slice"
states, which have been viewed as providing a sharp argument for information
loss, do not in fact do so as they do not give a fully accurate description of
the quantum state of a black hole. This however leaves an information
*problem*, which is to provide a consistent description of how information
escapes when a black hole evaporates. While a rather extreme form of
nonlocality has been advocated in the form of complementarity, this paper
argues that is not necessary, and more modest nonlocality could solve the
information problem. One possible distinguishing characteristic of scenarios is
the information retention time. The question of whether such nonlocality
implies acausality, and particularly inconsistency, is briefly addressed. The
need for such nonlocality, and its apparent tension with our empirical
observations of local quantum field theory, may be a critical missing piece in
understanding the principles of quantum gravity.Comment: 11 pages of text and figures, + references. v2 minor text. v3 small
revisions to match final journal versio
Cosmological diagrammatic rules
A simple set of diagrammatic rules is formulated for perturbative evaluation
of ``in-in" correlators, as is needed in cosmology and other nonequilibrium
problems. These rules are both intuitive, and efficient for calculational
purposes.Comment: 7 pages, 3 figure
Interacting Strings in Matrix String Theory
It is here explained how the Green-Schwarz superstring theory arises from
Matrix String Theory. This is obtained as the strong YM-coupling limit of the
theory expanded around its BPS instantonic configurations, via the
identification of the interacting string diagram with the spectral curve of the
relevant configuration. Both the GS action and the perturbative weight
, where is the Euler characteristic of the world-sheet
surface and the string coupling, are obtained.Comment: 11 pages, no figures, two references adde
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