1,303 research outputs found
Emergence of the fuzzy horizon through gravitational collapse
For a large enough Schwarzschild black hole, the horizon is a region of space
where gravitational forces are weak; yet it is also a region leading to
numerous puzzles connected to stringy physics. In this work, we analyze the
process of gravitational collapse and black hole formation in the context of
light-cone M theory. We find that, as a shell of matter contracts and is about
to reveal a black hole horizon, it undergoes a thermodynamic phase transition.
This involves the binding of D0 branes into D2's, and the new phase leads to
large membranes of the size of the horizon. These in turn can sustain their
large size through back-reaction and the dielectric Myers effect - realizing
the fuzzball proposal of Mathur and the Matrix black hole of M(atrix) theory.
The physics responsible for this phenomenon lies in strongly coupled 2+1
dimensional non-commutative dynamics. The phenomenon has a universal character
and appears generic.Comment: 24 pages, 4 figures; v2: minor clarifications, citations adde
From Surface Operators to Non-Abelian Volume Operators in Puff Field Theory
Puff Field Theory is a low energy decoupling regime of string theory that
still retains the non-local attributes of the parent theory - while preserving
isotropy for its non-local degrees of freedom. It realizes an extended
holographic dictionary at strong coupling and dynamical non-local states akin
to defects or the surface operators of local gauge theories. In this work, we
probe the non-local features of PFT using D3 branes. We find supersymmetric
configurations that end on defects endowed with non-Abelian degrees of freedom.
These are 2+1 dimensional defects in the 3+1 dimensional PFT that may be viewed
as volume operators. We determine their R-charge, vacuum expectation value,
energy, and gauge group structure.Comment: 39 pages, 6 figure
Which is the driver, the obsessions or the compulsions, in OCD?
The conventional view is that obsessive-compulsive disorder (OCD) is driven by irrational beliefs, which are a putative basis of obsessions. Compulsions are considered a coping mechanism, which neutralize anxiety or reduce the likelihood that these fears will be realized. Contrary to this view, recent data suggests that compulsions in OCD are a manifestation of a disruption in the neurobiologically well-defined balance between goal-directed action and automatic habits.This is the author's accepted manuscript. The final version is available from Nature Publishing Group in Neuropsychopharmacology at http://dx.doi.org/10.1038/npp.2014.20
D3 branes in a Melvin universe: a new realm for gravitational holography
The decoupling limit of a certain configuration of D3 branes in a Melvin
universe defines a sector of string theory known as Puff Field Theory (PFT) - a
theory with non-local dynamics but without gravity. In this work, we present a
systematic analysis of the non-local states of strongly coupled PFT using
gravitational holography. And we are led to a remarkable new holographic
dictionary. We show that the theory admits states that may be viewed as brane
protrusions from the D3 brane worldvolume. The footprint of a protrusion has
finite size - the scale of non-locality in the PFT - and corresponds to an
operator insertion in the PFT. We compute correlators of these states, and we
demonstrate that only part of the holographic bulk is explored by this
computation. We then show that the remaining space holographically encodes the
dynamics of the D3 brane tentacles. The two sectors are coupled: in this
holographic description, this is realized via quantum entanglement across a
holographic screen - a throat in the geometry - that splits the bulk into the
two regions in question. We then propose a description of PFT through a direct
product of two Fock spaces - akin to other non-local settings that employ
quantum group structures.Comment: 44 pages, 13 figures; v2: minor corrections, citations added; v3:
typos corrected in section on local operators, some asymptotic expansions
improved and made more consistent with rest of paper in section on non-local
operator
On black hole thermalization, D0 brane dynamics, and emergent spacetime
When matter falls past the horizon of a large black hole, the expectation
from string theory is that the configuration thermalizes and the information in
the probe is rather quickly scrambled away. The traditional view of a classical
unique spacetime near a black hole horizon conflicts with this picture. The
question then arises as to what spacetime does the probe actually see as it
crosses a horizon, and how does the background geometry imprint its signature
onto the thermal properties of the probe. In this work, we explore these
questions through an extensive series of numerical simulations of D0 branes. We
determine that the D0 branes quickly settle into an incompressible symmetric
state -- thermalized within a few oscillations through a process driven
entirely by internal non-linear dynamics. Surprisingly, thermal background
fluctuations play no role in this mechanism. Signatures of the background
fields in this thermal state arise either through fluxes, i.e. black hole hair;
or if the probe expands to the size of the horizon -- which we see evidence of.
We determine simple scaling relations for the D0 branes' equilibrium size, time
to thermalize, lifetime, and temperature in terms of their number, initial
energy, and the background fields. Our results are consistent with the
conjecture that black holes are the fastest scramblers as seen by Matrix
theory.Comment: 43 pages, 12 figures; v2: added analysis showing that results are
consistent with and confirm Susskind conjecture on black hole thermalization.
Added clarification about strong coupling regime. Citation adde
Branes wrapping black holes as a purely gravitational dielectric effect
In this paper we give a microscopical description of certain configurations
of branes wrapping black hole horizons in terms of dielectric gravitational
waves. Interestingly, the configurations are stable only due to the
gravitational background. Therefore, this constitutes a nice example of purely
gravitational dielectric effect.Comment: 17 pages, no figures. JHEP published versio
Using cognitive profiling to aid diagnosis and monitor or predict recovery in idiopathic normal pressure hydrocephalus
Generally Covariant Actions for Multiple D-branes
We develop a formalism that allows us to write actions for multiple D-branes
with manifest general covariance. While the matrix coordinates of the D-branes
have a complicated transformation law under coordinate transformations, we find
that these may be promoted to (redundant) matrix fields on the transverse space
with a simple covariant transformation law. Using these fields, we define a
covariant distribution function (a matrix generalization of the delta function
which describes the location of a single brane). The final actions take the
form of an integral over the curved space of a scalar single-trace action built
from the covariant matrix fields, tensors involving the metric, and the
covariant distribution function. For diagonal matrices, the integral localizes
to the positions of the individual branes, giving N copies of the single-brane
action.Comment: 34 pages, LaTeX. v2: comments and refs adde
Gravitational Radiation from Pulsating White Dwarfs
Rotating white dwarfs undergoing quasi-radial oscillations can emit
gravitational radiation in a frequency range from 0.1 - 0.3 Hz. Assuming that
the energy source for the gravitational radiation comes from the oblateness of
the white dwarf induced by the rotation, the strain amplitude is found to be
\sim 10^{-27} for a white dwarf at \sim 50 pc. The galactic population of these
sources is estimated to be \sim 10^7, and may produce a confusion limited
foreground for proposed advanced detectors in the frequency band between
space-based and ground-based interferometers. Nearby oscillating white dwarfs
may provide a clear enough signal to investigate white dwarf interiors through
gravitational wave asteroseismology.Comment: Accepted for Astrophysical Journal Letters. Changed value of
branching ratio resulting in an order of magnitude drop in gravitational wave
amplitude
Nuclear symmetry energy effects on neutron stars properties
We construct a class of nuclear equations of state based on a schematic
potential model, that originates from the work of Prakash et. al.
\cite{Prakash-88}, which reproduce the results of most microscopic
calculations. The equations of state are used as input for solving the
Tolman-Oppenheimer-Volkov equations for corresponding neutron stars. The
potential part contribution of the symmetry energy to the total energy is
parameterized in a generalized form both for low and high values of the baryon
density. Special attention is devoted to the construction of the symmetry
energy in order to reproduce the results of most microscopic calculations of
dense nuclear matter. The obtained nuclear equations of state are applied for
the systematic study of the global properties of a neutron star (masses, radii
and composition). The calculated masses and radii of the neutron stars are
plotted as a function of the potential part parameters of the symmetry energy.
A linear relation between these parameters, the radius and the maximum mass of
the neutron star is obtained. In addition, a linear relation between the radius
and the derivative of the symmetry energy near the saturation density is found.
We also address on the problem of the existence of correlation between the
pressure near the saturation density and the radius.Comment: 17 pages, 25 figure
- …