2,864 research outputs found
Black holes, quantum information, and unitary evolution
The unitary crisis for black holes indicates an apparent need to modify local
quantum field theory. This paper explores the idea that quantum mechanics and
in particular unitarity are fundamental principles, but at the price of
familiar locality. Thus, one should seek to parameterize unitary evolution,
extending the field theory description of black holes, such that their quantum
information is transferred to the external state. This discussion is set in a
broader framework of unitary evolution acting on Hilbert spaces comprising
subsystems. Here, various constraints can be placed on the dynamics, based on
quantum information-theoretic and other general physical considerations, and
one can seek to describe dynamics with "minimal" departure from field theory.
While usual spacetime locality may not be a precise concept in quantum gravity,
approximate locality seems an important ingredient in physics. In such a
Hilbert space approach an apparently "coarser" form of localization can be
described in terms of tensor decompositions of the Hilbert space of the
complete system. This suggests a general framework in which to seek a
consistent description of quantum gravity, and approximate emergence of
spacetime. Other possible aspects of such a framework -- in particular
symmetries -- are briefly discussed.Comment: 39 pages, 5 figures. v2: refs added, very minor clarifications v3:
few small changes to agree with published version v4: corrected sign in eq.
3.3
Bulk shape of brane-world black holes
We propose a method to extend into the bulk asymptotically flat static
spherically symmetric brane-world metrics. We employ the multipole (1/r)
expansion in order to allow exact integration of the relevant equations along
the (fifth) extra coordinate and make contact with the parameterized
post-Newtonian formalism. We apply our method to three families of solutions
previously appeared as candidates of black holes in the brane world and show
that the shape of the horizon is very likely a flat ``pancake'' for
astrophysical sources.Comment: 10 pages, MPLA style, 5 figures, accepted for publication in MPL
The screwworm eradication data system archives
The archives accumulated during 1 year of operation of the Satellite Temperature-Monitoring System during development of the Screwworm Eradication Data System are reported. Brief descriptions of all the kinds of tapes, as well as their potential uses, are presented. Reference is made to other documents that explain the generation of these data
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
Braneworlds and Dark Energy
In the Randall-Sundrum scenario, we analyse the dynamics of an AdS5
braneworld when conformal matter fields propagate in five dimensions. We show
that conformal fields of weight -4 are associated with stable geometries which
describe the dynamics of inhomogeneous dust, generalized dark radiation and
homogeneous polytropic dark energy on a spherically symmetric 3-brane embedded
in the compact AdS5 orbifold. We discuss aspects of the radion stability
conditions and of the localization of gravity in the vicinity of the brane.Comment: 12 pages, latex, 3 eps figures. Talk given at the Seventh Workshop on
Quantum Field Theory under the Influence of External Conditions, IEEC, CSIC
and University of Barcelona, Barcelona, Catalonia, Spain, 5-9 September 2005.
Revised version published in the workshop proceedings, J. Phys. A:
Mathematical and General. Typos corrected and some changes introduced for
clarit
Dynamics of warped compactifications and the shape of the warped landscape
The dynamics of warped/flux compactifications is studied, including warping
effects, providing a firmer footing for investigation of the "landscape." We
present a general formula for the four-dimensional potential of warped
compactifications in terms of ten-dimensional quantities. This allows a
systematic investigation of moduli-fixing effects and potentials for mobile
branes. We provide a necessary criterion, "slope-dominance," for evading
"no-go" results for de Sitter vacua. We outline the ten-dimensional derivation
of the non-perturbative effects that should accomplish this in KKLT examples,
and outline a systematic discussion of their corrections. We show that
potentials for mobile branes receive generic contributions inhibiting slow-roll
inflation. We give a linearized analysis of general scalar perturbations of
warped IIB compactifications, revealing new features for both time independent
and dependent moduli, and new aspects of the kinetic part of the
four-dimensional effective action. The universal Kahler modulus is found_not_
to be a simple scaling of the internal metric, and a prescription is given for
defining holomorphic Kahler moduli, including warping effects. In the presence
of mobile branes, this prescription elucidates couplings between bulk and brane
fields. Our results are thus relevant to investigations of the existence of de
Sitter vacua in string theory, and of their phenomenology, cosmology, and
statistics.Comment: (80 pages; two appendices; harvmac. v3: minor corrections, and
references added. v4: argument that pure Kahler deformations are flat.
REAM intensity modulator-enabled 10Gb/s colorless upstream transmission of real-time optical OFDM signals in a single-fiber-based bidirectional PON architecture
Reflective electro-absorption modulation-intensity modulators (REAM-IMs) are utilized, for the first time, to experimentally demonstrate colorless ONUs in single-fiber-based, bidirectional, intensity-modulation and direct-detection (IMDD), optical OFDM PONs (OOFDM-PONs) incorporating 25km SSMFs and OLT-side-seeded CW optical signals. The colorlessness of the REAM-IMs is characterized, based on which optimum REAM-IM operating conditions are identified. In the aforementioned PON architecture, 10Gb/s colorless upstream transmissions of end-to-end realtime OOFDM signals are successfully achieved for various wavelengths within the entire C-band. Over such a wavelength window, corresponding minimum received optical powers at the FEC limit vary in a range as small as <0.5dB. In addition, experimental measurements also indicate that Rayleigh backscattering imposes a 2.8dB optical power penalty on the 10Gb/s over 25km upstream OOFDM signal transmission. Furthermore, making use of on-line adaptive bit and power loading, a linear trade-off between aggregated signal line rate and optical power budget is observed, which shows that, for the present PON system, a 10% reduction in signal line rate can improve the optical power budget by 2.6dB. © 2012 Optical Society of America
Quantum information transfer and models for black hole mechanics
General features of information transfer between quantum subsystems, via
unitary evolution, are investigated, with applications to the problem of
information transfer from a black hole to its surroundings. A particularly
direct form of quantum information transfer is "subspace transfer," which can
be characterized by saturation of a subadditivity inequality. We also describe
more general unitary quantum information transfer, and categorize different
models for black hole evolution. Evolution that only creates paired excitations
inside/outside the black hole is shown not to extract information, but
information-transferring models exist both in the "saturating" and
"non-saturating" category. The former more closely capture thermodynamic
behavior; the latter generically have enhanced energy flux, beyond that of
Hawking.Comment: 31 pages, harvmac. v2: nomenclature change, minor added explanation.
v3: small corrections/rewordings; improved figure; version to match
publication in PR
Braneworlds, Conformal Fields and the Gravitons
We investigate the dynamics of Randall-Sundrum AdS5 braneworlds with
5-dimensional conformal matter fields. In the scenario with a compact fifth
dimension the class of conformal fields with weight -4 is associated with exact
5-dimensional warped geometries which are stable under radion field
perturbations and describe on the brane the dynamics of inhomogeneous dust,
generalized dark radiation and homogeneous polytropic dark energy. We analyse
the graviton mode flutuations around this class of background solutions and
determine their mass eigenvalues and wavefunctions from a Sturm-Liouville
problem. We show that the localization of gravity is not sharp enough for large
mass hierarchies to be generated. We also discuss the physical bounds imposed
by experiments in particle physics, in astrophysics and in precise measurements
of the low energy gravitational interaction.Comment: LaTeX, 9 pages, 2 figures. Based on talk given in the Second
International Conference on Quantum Theories and the Renormalization Group in
Gravity and Cosmology, CSIC and University of Barcelona, Barcelona, Spain,
11-15 July 2006. Submitted to be published in the Conference Proceedings, J.
Phys. A: Math. Ge
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