2,050 research outputs found
Flat-space Quantum Gravity in AdS/CFT
Motivated by the task of understanding microscopic dynamics of an evolving
black hole, we present a scheme describing gauge-fixed continuous time
evolution of quantum gravitational processes in asymptotically flat spacetime
using the algebra of CFT operators. This allows us to study the microscopic
dynamics of the Hawking emission process, although obtaining a full S-matrix
may require a modification of the minimal scheme. The role of the operator
product expansion is to physically interpret the resulting time evolution by
decomposing the Hilbert space of the states for the entire system into those
for smaller subsystems. We translate the picture of an evaporating black hole
previously proposed by the authors into predictions for nonperturbative
properties of the CFTs that have weakly coupled dual gravitational
descriptions. We also discuss a possible relationship between the present
scheme and a reference frame change in the bulk.Comment: 31 pages, 2 figures; clarifications adde
The Black Hole Interior in Quantum Gravity
We discuss the interior of a black hole in quantum gravity, in which black
holes form and evaporate unitarily. The interior spacetime appears in the sense
of complementarity because of special features revealed by the microscopic
degrees of freedom when viewed from a semiclassical standpoint. The relation
between quantum mechanics and the equivalence principle is subtle, but they are
still consistent.Comment: 5 pages; text shortened, references added, Phys. Rev. Lett. in pres
Relativeness in Quantum Gravity: Limitations and Frame Dependence of Semiclassical Descriptions
Consistency between quantum mechanical and general relativistic views of the
world is a longstanding problem, which becomes particularly prominent in black
hole physics. We develop a coherent picture addressing this issue by studying
the quantum mechanics of an evolving black hole. After interpreting the
Bekenstein-Hawking entropy as the entropy representing the degrees of freedom
that are coarse-grained to obtain a semiclassical description from the
microscopic theory of quantum gravity, we discuss the properties these degrees
of freedom exhibit when viewed from the semiclassical standpoint. We are led to
the conclusion that they show features which we call extreme relativeness and
spacetime-matter duality---a nontrivial reference frame dependence of their
spacetime distribution and the dual roles they play as the "constituents" of
spacetime and as thermal radiation. We describe black hole formation and
evaporation processes in distant and infalling reference frames, showing that
these two properties allow us to avoid the arguments for firewalls and to make
the existence of the black hole interior consistent with unitary evolution in
the sense of complementarity. Our analysis provides a concrete answer to how
information can be preserved at the quantum level throughout the evolution of a
black hole, and gives a basic picture of how general coordinate transformations
may work at the level of full quantum gravity beyond the approximation of
semiclassical theory.Comment: 44 pages, 4 figures; typos correcte
Spacetime Equals Entanglement
We study the Hilbert space structure of classical spacetimes under the
assumption that entanglement in holographic theories determines semiclassical
geometry. We show that this simple assumption has profound implications; for
example, a superposition of classical spacetimes may lead to another classical
spacetime. Despite its unconventional nature, this picture admits the standard
interpretation of superpositions of well-defined semiclassical spacetimes in
the limit that the number of holographic degrees of freedom becomes large. We
illustrate these ideas using a model for the holographic theory of cosmological
spacetimes.Comment: 6 pages, 2 figures; v2: remarks on time evolution revised, v3:
matches published versio
A produção comercial de Achigãs (Micropterus salmoides)
A produção comercial de achigãs (Micropterus salmoides) poderá ser uma opção interessante para as pisciculturas de águas interiores localizadas em regiões do país onde aquela espécie tem elevado interesse comercial. Os achigãs são muito valorizados para gastronomia e para repovoamentos de lagos e barragens de rega utilizadas para pesca desportiva. A utilização de alimento composto comercial permitirá o crescimento mais rápido dos achigãs que conseguem atingir o peso de mercado ao fim de 24 meses. Com este trabalho, pretendemos divulgar técnicas para criação de achigãs em que se utilizam tanques de reprodução, tanques de alevinagem, tanques de adaptação ao alimento composto e tanques de crescimento. No trabalho também são referidos aspetos práticos relativos ao maneio alimentar do achigã. Enquanto no nosso país houve produção desta espécie em cativeiro, os alevins obtidos destinavam-se ao repovoamento. O plano de negócio apresentado na parte final do trabalho realça o interesse económico que pode ter a produção de alevins de achigãs para repovoamento de locais de pesca. Um sistema de produção muito simples poderá originar receitas superiores a 2.500€/ha/ano
Disordered Bose Einstein Condensates with Interaction in One Dimension
We study the effects of random scatterers on the ground state of the
one-dimensional Lieb-Liniger model of interacting bosons on the unit interval
in the Gross-Pitaevskii regime. We prove that Bose Einstein condensation
survives even a strong random potential with a high density of scatterers. The
character of the wave function of the condensate, however, depends in an
essential way on the interplay between randomness and the strength of the
two-body interaction. For low density of scatterers or strong interactions the
wave function extends over the whole interval. High density of scatterers and
weak interaction, on the other hand, leads to localization of the wave function
in a fragmented subset of the interval
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