37 research outputs found
On Witten's Instability and Winding Tachyons
We investigate, from a spacetime perspective, some aspects of Horowitz's
recent conjecture that black strings may catalyze the decay of Kaluza-Klein
spacetimes into a bubble of nothing. We identify classical configurations that
interpolate between flat space and the bubble, and discuss the energetics of
the transition. We investigate the effects of winding tachyons on the size and
shape of the barrier and find no evidence at large compactification radius that
tachyons enhance the tunneling rate. For the interesting radii, of order the
string scale, the question is difficult to answer due to the failure of the
expansion.Comment: 15 pages, 2 figures, Late
Non-relativistic metrics with extremal limits
We present solutions of type IIB supergravity with z=2 Schrodinger
asymptotics that admit an extremal limit, i.e. the black hole horizon has a
double zero. These solutions are obtained as TsT transformations of the charged
planar black hole in AdS_5 \times S^5. Unlike the uncharged solution, the
Ramond-Ramond two-form is turned on. We study the thermodynamic properties of
these new solutions, and we show that the ratio of shear viscosity to entropy
density is 1/4\pi even in the extremal limit. We also consider the
TsT-transformed soliton and show that, for a special radius of the compact
circle, there is a confinement-deconfinement phase transition at zero
temperature between the soliton and black hole phases.Comment: 23 pages, references and clarifications added, typos corrected,
restriction in phase transition due to equation 6.5 emphasized; published
versio
Some No-go Theorems for String Duals of Non-relativistic Lifshitz-like Theories
We study possibilities of string theory embeddings of the gravity duals for
non-relativistic Lifshitz-like theories with anisotropic scale invariance. We
search classical solutions in type IIA and eleven-dimensional supergravities
which are expected to be dual to (2+1)-dimensional Lifshitz-like theories.
Under reasonable ansaetze, we prove that such gravity duals in the
supergravities are not possible. We also discuss a possible physical reason
behind this.Comment: 18 pages, Latex, flux conditions clarified (v2), brief summary of
results added (v3
Thermal AdS(3), BTZ and competing winding modes condensation
We study the thermal physics of AdS(3) and the BTZ black hole when embedded
in String theory. The exact calculation of the Hagedorn temperature in TAdS(3)
is reinterpreted as the appearance of a winding tachyon both in AdS(3) and BTZ.
We construct a dual framework for analyzing the phases of the system. In this
dual framework, tachyon condensation and geometric capping appear on the same
footing, bridging the usual gap of connecting tachyon condensation to
modifications of geometry. This allows us to construct in a natural way a
candidate for the unstable phase, analogous to a small black hole in higher
dimensions. Additional peculiar effects associated with the Hagedorn
temperature and the Hawking-Page transition, some to do with the asymptotic
structure of AdS(3) and some with strong curvature effects, are analyzed and
explained.Comment: 40 pages, 5 figures, JHEP3 format. v2: added references, minor
corrections and clarification
Menus for Feeding Black Holes
Black holes are the ultimate prisons of the Universe, regions of spacetime
where the enormous gravity prohibits matter or even light to escape to
infinity. Yet, matter falling toward the black holes may shine spectacularly,
generating the strongest source of radiation. These sources provide us with
astrophysical laboratories of extreme physical conditions that cannot be
realized on Earth. This chapter offers a review of the basic menus for feeding
matter onto black holes and discusses their observational implications.Comment: 27 pages. Accepted for publication in Space Science Reviews. Also to
appear in hard cover in the Space Sciences Series of ISSI "The Physics of
Accretion onto Black Holes" (Springer Publisher
A human biomonitoring (HBM) Global Registry Framework: Further advancement of HBM research following the FAIR principles.
Data generated by the rapidly evolving human biomonitoring (HBM) programmes are providing invaluable opportunities to support and advance regulatory risk assessment and management of chemicals in occupational and environmental health domains. However, heterogeneity across studies, in terms of design, terminology, biomarker nomenclature, and data formats, limits our capacity to compare and integrate data sets retrospectively (reuse). Registration of HBM studies is common for clinical trials; however, the study designs and resulting data collections cannot be traced easily. We argue that an HBM Global Registry Framework (HBM GRF) could be the solution to several of challenges hampering the (re)use of HBM (meta)data. The aim is to develop a global, host-independent HBM registry framework based on the use of harmonised open-access protocol templates from designing, undertaking of an HBM study to the use and possible reuse of the resulting HBM (meta)data. This framework should apply FAIR (Findable, Accessible, Interoperable and Reusable) principles as a core data management strategy to enable the (re)use of HBM (meta)data to its full potential through the data value chain. Moreover, we believe that implementation of FAIR principles is a fundamental enabler for digital transformation within environmental health. The HBM GRF would encompass internationally harmonised and agreed open access templates for HBM study protocols, structured web-based functionalities to deposit, find, and access harmonised protocols of HBM studies. Registration of HBM studies using the HBM GRF is anticipated to increase FAIRness of the resulting (meta)data. It is also considered that harmonisation of existing data sets could be performed retrospectively. As a consequence, data wrangling activities to make data ready for analysis will be minimised. In addition, this framework would enable the HBM (inter)national community to trace new HBM studies already in the planning phase and their results once finalised. The HBM GRF could also serve as a platform enhancing communication between scientists, risk assessors, and risk managers/policy makers. The planned European Partnership for the Assessment of Risk from Chemicals (PARC) work along these lines, based on the experience obtained in previous joint European initiatives. Therefore, PARC could very well bring a first demonstration of first essential functionalities within the development of the HBM GRF
High pressure phase transition and elastic behaviour of lanthanum monochalcogenides
The Phase transition and elastic properties of La-monochalcogenides have been
investigated under pressure by means of a modified charge-transfer potential model which
incorporates the Coulomb interaction modified by Coulomb screening due to the
delocalization of electron of rare-earth atom leading to many-body interactions, covalency
effect and overlap repulsion extended up to second-nearest neighbours. Under high pressure
the coordination increases and they transform from rock-salt to CsCl structure. The
calculated values of cohesive energy, lattice constant, phase transition pressure,
relative volume collapse, harmonic and anharmonic elastic moduli and their first- and
second-order pressure derivatives agree well with the available measured data and better
than those computed by earlier workers. Present model is capable of explaining the
Cauchy’s discrepancy correctly