739 research outputs found
Gravity from the entropy of light
The holographic principle, considered in a semiclassical setting, is shown to
have direct consequences on physics at a fundamental level. In particular, a
certain relation is pointed out to be the expression of holography in basic
thermodynamics. It is argued moreover that through this relation holography can
be recognized to induce gravity, and an expression for the gravitational
lensing is obtained in terms of entropy over wavelength of black-body
radiation, or, at a deeper level, in terms of maximum entropy over associated
space to the elementary bit of information.Comment: 7 pages; v2: completion of the list of references; v3: the discussion
is divided in Sections and the argument is described in more detail; v4: a
statement is added (below eq.13) on what is the supposed difference between
Jacobson's work in ref.21 and this attempt; addition of a paragraph in last
Sectio
Entropy of gravitating systems: scaling laws versus radial profiles
Through the consideration of spherically symmetric gravitating systems
consisting of perfect fluids with linear equation of state constrained to be in
a finite volume, an account is given of the properties of entropy at conditions
in which it is no longer an extensive quantity (it does not scale with system's
size). To accomplish this, the methods introduced by Oppenheim [1] to
characterize non-extensivity are used, suitably generalized to the case of
gravitating systems subject to an external pressure. In particular when, far
from the system's Schwarzschild limit, both area scaling for conventional
entropy and inverse radius law for the temperature set in (i.e. the same
properties of the corresponding black hole thermodynamical quantities), the
entropy profile is found to behave like 1/r, being r the area radius inside the
system. In such circumstances thus entropy heavily resides in internal layers,
in opposition to what happens when area scaling is gained while approaching the
Schwarzschild mass, in which case conventional entropy lies at the surface of
the system. The information content of these systems, even if it globally
scales like the area, is then stored in the whole volume, instead of packed on
the boundary.Comment: 16 pages, 11 figures. v2: addition of some references; the stability
of equilibrium configurations is readdresse
From Unruh temperature to generalized Bousso bound
In a classical spacetime satisfying Einstein's equation and the null
convergence condition, the same quantum mechanical effects that cause black
holes to have a temperature are found to imply, if joined to the macroscopic
nature of entropy, the covariant entropy bound in its generalized form. This is
obtained from thermodynamics, as applied across the local Rindler causal
horizon through every point p of the null hypersurfaces L the covariant entropy
bound refers to, in the direction of the null geodesics generating L.Comment: 5 pages. v2: some changes to clarify the path to the obtained
results; two (final) paragraphs, the acknowledgments and a reference adde
Boundary layer model for vortex fingers in type II superconductors
Theoretical Physic
On the Origin of Entropic Gravity and Inertia
It was recently suggested that quantum field theory is not fundamental but
emerges from the loss of phase space information about matter crossing causal
horizons. Possible connections between this formalism and Verlinde's entropic
gravity and Jacobson's thermodynamic gravity are proposed.
The holographic screen in Verlinde's formalism can be identified as local
Rindler horizons and its entropy as that of the bulk fields beyond the
horizons.
This naturally resolves some issues on entropic gravity.
The quantum fluctuation of the fields is the origin of the thermodynamic
nature of entropic gravity.
It is also suggested that inertia is related to dragging
Rindler horizons.Comment: 9 pages, revtex4-1, 3 figures, accepted for publication in
Foundations of Physic
On the statistical-mechanical meaning of the Bousso bound
The Bousso entropy bound, in its generalized form, is investigated for the
case of perfect fluids at local thermodynamic equilibrium and evidence is found
that the bound is satisfied if and only if a certain local thermodynamic
property holds, emerging when the attempt is made to apply the bound to thin
layers of matter. This property consists in the existence of an ultimate lower
limit l* to the thickness of the slices for which a statistical-mechanical
description is viable, depending l* on the thermodynamical variables which
define the state of the system locally. This limiting scale, found to be in
general much larger than the Planck scale (so that no Planck scale physics must
be necessarily invoked to justify it), appears not related to gravity and this
suggests that the generalized entropy bound is likely to be rooted on
conventional flat-spacetime statistical mechanics, with the maximum admitted
entropy being however actually determined also by gravity.
Some examples of ideal fluids are considered in order to identify the
mechanisms which can set a lower limit to the statistical-mechanical
description and these systems are found to respect the lower limiting scale l*.
The photon gas, in particular, appears to seemingly saturate this limiting
scale and the consequence is drawn that for systems consisting of a single
slice of a photon gas with thickness l*, the generalized Bousso bound is
saturated. It is argued that this seems to open the way to a peculiar
understanding of black hole entropy: if an entropy can meaningfully (i.e. with
a second law) be assigned to a black hole, the value A/4 for it (where A is the
area of the black hole) is required simply by (conventional) statistical
mechanics coupled to general relativity.Comment: 6 pages. Some editing and the addition of a reference. This version,
ideally corresponding to the published one, contains 4 corrections to it,
with two of them (p.3, line 19 and p.6, line 10 of this version) with
semantic relevanc
Study of the effect of neutrino oscillation on the supernova neutrino signal with the LVD detector
We present an update of our previous study (astro-ph/0112312) on how
oscillations affect the signal from a supernova core collapse observed in the
LVD detector at LNGS. In this paper we use a recent, more precise determination
of the cross section (astro-ph/0302055) to calculate the expected number of
inverse beta decay events, we introduce in the simulation also the -{\rm
Fe} interactions, we include the Earth matter effects and, finally, we study
also the inverted mass hierarchy case.Comment: 4 pages, 4 figures, to appear in the Proceedings of ICRC 200
On-line recognition of supernova neutrino bursts in the LVD detector
In this paper we show the capabilities of the Large Volume Detector (INFN
Gran Sasso National Laboratory) to identify a neutrino burst associated to a
supernova explosion, in the absence of an "external trigger", e.g., an optical
observation. We describe how the detector trigger and event selection have been
optimized for this purpose, and we detail the algorithm used for the on-line
burst recognition. The on-line sensitivity of the detector is defined and
discussed in terms of supernova distance and electron anti-neutrino intensity
at the source.Comment: Accepted for pubblication on Astroparticle Physics. 13 pages, 10
figure
First CNGS events detected by LVD
The CERN Neutrino to Gran Sasso (CNGS) project aims to produce a high energy,
wide band beam at CERN and send it toward the INFN Gran Sasso
National Laboratory (LNGS), 732 km away. Its main goal is the observation of
the appearance, through neutrino flavour oscillation. The beam
started its operation in August 2006 for about 12 days: a total amount of
protons were delivered to the target. The LVD detector, installed
in hall A of the LNGS and mainly dedicated to the study of supernova neutrinos,
was fully operating during the whole CNGS running time. A total number of 569
events were detected in coincidence with the beam spill time. This is in good
agreement with the expected number of events from Montecarlo simulations.Comment: Accepted for publication by the European Physical Journal C ; 7
pages, 11 figure
Quantum criticality and black holes
Many condensed matter experiments explore the finite temperature dynamics of
systems near quantum critical points. Often, there are no well-defined
quasiparticle excitations, and so quantum kinetic equations do not describe the
transport properties completely. The theory shows that the transport
co-efficients are not proportional to a mean free scattering time (as is the
case in the Boltzmann theory of quasiparticles), but are completely determined
by the absolute temperature and by equilibrium thermodynamic observables.
Recently, explicit solutions of this quantum critical dynamics have become
possible via the AdS/CFT duality discovered in string theory. This shows that
the quantum critical theory provides a holographic description of the quantum
theory of black holes in a negatively curved anti-de Sitter space, and relates
its transport co-efficients to properties of the Hawking radiation from the
black hole. We review how insights from this connection have led to new results
for experimental systems: (i) the vicinity of the superfluid-insulator
transition in the presence of an applied magnetic field, and its possible
application to measurements of the Nernst effect in the cuprates, (ii) the
magnetohydrodynamics of the plasma of Dirac electrons in graphene and the
prediction of a hydrodynamic cyclotron resonance.Comment: 12 pages, 2 figures; Talk at LT25, Amsterda
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