638 research outputs found
Taking the Temperature of a Black Hole
We use the global embedding of a black hole spacetime into a higher
dimensional flat spacetime to define a local temperature for observers in free
fall outside a static black hole. The local free-fall temperature remains
finite at the event horizon and in asymptotically flat spacetime it approaches
the Hawking temperature at spatial infinity. Freely falling observers outside
an AdS black hole do not see any high-temperature thermal radiation even if the
Hawking temperature of such black holes can be arbitrarily high.Comment: latex, 14 pages, 4 figures, v3: added references, matches published
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Quantum information erasure inside black holes
An effective field theory for infalling observers in the vicinity of a
quasi-static black hole is given in terms of a freely falling lattice
discretization. The lattice model successfully reproduces the thermal spectrum
of outgoing Hawking radiation, as was shown by Corley and Jacobson, but can
also be used to model observations made by a typical low-energy observer who
enters the black hole in free fall at a prescribed time. The explicit short
distance cutoff ensures that, from the viewpoint of the infalling observer, any
quantum information that entered the black hole more than a scrambling time
earlier has been erased by the black hole singularity. This property, combined
with the requirement that outside observers need at least of order the
scrambling time to extract quantum information from the black hole, ensures
that a typical infalling observer does not encounter drama upon crossing the
black hole horizon in a theory where black hole information is preserved for
asymptotic observers.Comment: 20 pages, 3 figures, some minor correction
Black hole holography and mean field evolution
Holographic theories representing black holes are expected to exhibit quantum
chaos. We argue if the laws of quantum mechanics are expected to hold for
observers inside such black holes, then such holographic theories must have a
mean field approximation valid for typical black hole states, and for
timescales approaching the scrambling time. Using simple spin models as
examples, we examine the predictions of such an approach for observers inside
black holes, and more speculatively inside cosmological horizons.Comment: 11 pages, 5 figure
Efficient Logging in Non-Volatile Memory by Exploiting Coherency Protocols
Non-volatile memory (NVM) technologies such as PCM, ReRAM and STT-RAM allow
processors to directly write values to persistent storage at speeds that are
significantly faster than previous durable media such as hard drives or SSDs.
Many applications of NVM are constructed on a logging subsystem, which enables
operations to appear to execute atomically and facilitates recovery from
failures. Writes to NVM, however, pass through a processor's memory system,
which can delay and reorder them and can impair the correctness and cost of
logging algorithms.
Reordering arises because of out-of-order execution in a CPU and the
inter-processor cache coherence protocol. By carefully considering the
properties of these reorderings, this paper develops a logging protocol that
requires only one round trip to non-volatile memory while avoiding expensive
computations. We show how to extend the logging protocol to building a
persistent set (hash map) that also requires only a single round trip to
non-volatile memory for insertion, updating, or deletion
Probing emergent geometry through phase transitions in free vector and matrix models
Boundary correlation functions provide insight into the emergence of an
effective geometry in higher spin gravity duals of O(N) or U(N) symmetric field
theories. On a compact manifold, the singlet constraint leads to nontrivial
dynamics at finite temperature and large N phase transitions even at vanishing
't Hooft coupling. At low temperature, the leading behavior of boundary
two-point functions is consistent with propagation through a bulk thermal anti
de Sitter space. Above the phase transition, the two-point function shows
significant departure from thermal AdS space and the emergence of localized
black hole like objects in the bulk. In adjoint models, these objects appear at
length scales of order of the AdS radius, consistent with a Hawking-Page
transition, but in vector models they are parametrically larger than the AdS
scale. In low dimensions, we find another crossover at large distances beyond
which the correlation function again takes a thermal AdS form, albeit with a
temperature dependent normalization factor.Comment: 24 pages, 1 table, 3 figure
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