660 research outputs found
The information paradox: conflicts and resolutions
Many relativists have been long convinced that black hole evaporation leads
to information loss or remnants. String theorists have however not been too
worried about the issue, largely due to a belief that the Hawking argument for
information loss is flawed in its details. A recently derived inequality shows
that the Hawking argument for black holes with horizon can in fact be made
rigorous. What happens instead is that in string theory black hole microstates
have no horizons. Thus the evolution of radiation quanta with E ~ kT is
modified by order unity at the horizon, and we resolve the information paradox.
We discuss how it is still possible for E >> kT objects to see an approximate
black hole like geometry. We also note some possible implications of this
physics for the early Universe.Comment: 26 pages, 8 figures, Latex; (Expanded version of) proceedings for
Lepton-Photon 201
Comments on black holes I: The possibility of complementarity
We comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who
argue against black hole complementarity based on the claim that an infalling
observer 'burns' as he approaches the horizon. We show that in fact
measurements made by an infalling observer outside the horizon are
statistically identical for the cases of vacuum at the horizon and radiation
emerging from a stretched horizon. This forces us to follow the dynamics all
the way to the horizon, where we need to know the details of Planck scale
physics. We note that in string theory the fuzzball structure of microstates
does not give any place to 'continue through' this Planck regime. AMPS argue
that interactions near the horizon preclude traditional complementarity. But
the conjecture of 'fuzzball complementarity' works in the opposite way: the
infalling quantum is absorbed by the fuzzball surface, and it is the resulting
dynamics that is conjectured to admit a complementary description.Comment: 34 pages, 6 figures, v3: clarifications & references adde
Non-supersymmetric extremal multicenter black holes with superpotentials
Using the superpotential approach we generalize Denef's method of deriving
and solving first-order equations describing multicenter extremal black holes
in four-dimensional N = 2 supergravity to allow non-supersymmetric solutions.
We illustrate the general results with an explicit example of the stu model.Comment: 17 pages, v2: some clarifications adde
Excitations in the deformed D1D5 CFT
We perform some simple computations for the first order deformation of the
D1D5 CFT off its orbifold point. It had been shown earlier that under this
deformation the vacuum state changes to a squeezed state (with the further
action of a supercharge). We now start with states containing one or two
initial quanta and write down the corresponding states obtained under the
action of deformation operator. The result is relevant to the evolution of an
initial excitation in the CFT dual to the near extremal D1D5 black hole: when a
left and a right moving excitation collide in the CFT, the deformation operator
spreads their energy over a larger number of quanta, thus evolving the state
towards the infrared.Comment: 26 pages, Latex, 4 figure
Deforming the D1D5 CFT away from the orbifold point
The D1D5 brane bound state is believed to have an `orbifold point' in its
moduli space which is the analogue of the free Yang Mills theory for the D3
brane bound state. The supergravity geometry generated by D1 and D5 branes is
described by a different point in moduli space, and in moving towards this
point we have to deform the CFT by a marginal operator: the `twist' which links
together two copies of the CFT. In this paper we find the effect of this
deformation operator on the simplest physical state of the CFT -- the Ramond
vacuum. The twist deformation leads to a final state that is populated by pairs
of excitations like those in a squeezed state. We find the coefficients
characterizing the distribution of these particle pairs (for both bosons and
fermions) and thus write this final state in closed form.Comment: 30 pages, 4 figures, Late
Non-extremal Black Hole Microstates: Fuzzballs of Fire or Fuzzballs of Fuzz ?
We construct the first family of microstate geometries of near-extremal black
holes, by placing metastable supertubes inside certain scaling supersymmetric
smooth microstate geometries. These fuzzballs differ from the classical black
hole solution macroscopically at the horizon scale, and for certain probes the
fluctuations between various fuzzballs will be visible as thermal noise far
away from the horizon. We discuss whether these fuzzballs appear to infalling
observers as fuzzballs of fuzz or as fuzzballs of fire. The existence of these
solutions suggests that the singularity of non-extremal black holes is resolved
all the way to the outer horizon and this "backwards in time" singularity
resolution can shed light on the resolution of spacelike cosmological
singularities.Comment: 34 pages, 10 figure
Emission from the D1D5 CFT: Higher Twists
We study a certain class of nonextremal D1D5 geometries and their ergoregion
emission. Using a detailed CFT computation and the formalism developed in
arXiv:0906.2015 [hep-th], we compute the full spectrum and rate of emission
from the geometries and find exact agreement with the gravity answer.
Previously, only part of the spectrum had been reproduced using a CFT
description. We close with a discussion of the context and significance of the
calculation.Comment: 39 pages, 6 figures, late
Cognitive appraisal of environmental stimuli induces emotion-like states in fish
The occurrence of emotions in non-human animals has been the focus of debate over the years. Recently, an interest in expanding this debate to non-tetrapod vertebrates and to invertebrates has emerged. Within vertebrates, the study of emotion in teleosts is particularly interesting since they represent a divergent evolutionary radiation from that of tetrapods, and thus they provide an insight into the evolution of the biological mechanisms of emotion. We report that Sea Bream exposed to stimuli that vary according to valence (positive, negative) and salience (predictable, unpredictable) exhibit different behavioural, physiological and neuromolecular states. Since according to the dimensional theory of emotion valence and salience define a two-dimensional affective space, our data can be interpreted as evidence for the occurrence of distinctive affective states in fish corresponding to each the four quadrants of the core affective space. Moreover, the fact that the same stimuli presented in a predictable vs. unpredictable way elicited different behavioural, physiological and neuromolecular states, suggests that stimulus appraisal by the individual, rather than an intrinsic characteristic of the stimulus, has triggered the observed responses. Therefore, our data supports the occurrence of emotion-like states in fish that are regulated by the individual's perception of environmental stimuli.European Commission [265957 Copewell]; Fundacao para a Ciencia e Tecnologia [SFRH/BD/80029/2011, SFRH/BPD/72952/2010]info:eu-repo/semantics/publishedVersio
Key clinical benefits of neuroimaging at 7 T
The growing interest in ultra-high field MRI, with more than 35.000 MR examinations already performed at 7 T, is related to improved clinical results with regard to morphological as well as functional and metabolic capabilities. Since the signal-to-noise ratio increases with the field strength of the MR scanner, the most evident application at 7 T is to gain higher spatial resolution in the brain compared to 3 T. Of specific clinical interest for neuro applications is the cerebral cortex at 7 T, for the detection of changes in cortical structure, like the visualization of cortical microinfarcts and cortical plaques in Multiple Sclerosis. In imaging of the hippocampus, even subfields of the internal hippocampal anatomy and pathology may be visualized with excellent spatial resolution. Using Susceptibility Weighted Imaging, the plaque-vessel relationship and iron accumulations in Multiple Sclerosis can be visualized, which may provide a prognostic factor of disease. Vascular imaging is a highly promising field for 7 T which is dealt with in a separate dedicated article in this special issue. The static and dynamic blood oxygenation level-dependent contrast also increases with the field strength, which significantly improves the accuracy of pre-surgical evaluation of vital brain areas before tumor removal. Improvement in acquisition and hardware technology have also resulted in an increasing number of MR spectroscopic imaging studies in patients at 7 T. More recent parallel imaging and short-TR acquisition approaches have overcome the limitations of scan time and spatial resolution, thereby allowing imaging matrix sizes of up to 128×128. The benefits of these acquisition approaches for investigation of brain tumors and Multiple Sclerosis have been shown recently. Together, these possibilities demonstrate the feasibility and advantages of conducting routine diagnostic imaging and clinical research at 7 T
Supergravity Solutions from Floating Branes
We solve the equations of motion of five-dimensional ungauged supergravity
coupled to three U(1) gauge fields using a floating-brane Ansatz in which the
electric potentials are directly related to the gravitational warp factors. We
find a new class of non-BPS solutions, that can be obtained linearly starting
from an Euclidean four-dimensional Einstein-Maxwell base. This class - the
largest known so far - reduces to the BPS and almost-BPS solutions in certain
limits. We solve the equations explicitly when the base space is given by the
Israel-Wilson metric, and obtain solutions describing non-BPS D6 and anti-D6
branes kept in equilibrium by flux. We also examine the action of spectral flow
on solutions with an Israel-Wilson base and show that it relates these
solutions to almost-BPS solutions with a Gibbons-Hawking base.Comment: 24 pages, 1 figur
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