600 research outputs found
Entropic-gravity derivation of MOND
A heuristic entropic-gravity derivation has previously been given of the
gravitational two-body force of modified Newtonian dynamics (MOND). Here, it is
shown that also another characteristic of MOND can be recovered, namely, the
external field effect (implying a violation of the Strong Equivalence
Principle). In fact, the derivation gives precisely the modified Poisson
equation which Bekenstein and Milgrom proposed as a consistent nonrelativistic
theory of MOND.Comment: 6 pages; v5: published versio
New perspective on space and time from Lorentz violation
I present a brief review on space and time in different periods of physics,
and then talk on the nature of space and time from physical arguments. I
discuss the ways to test such a new perspective on space and time through
searching for Lorentz violation in some physical processes. I also make an
introduce to a newly proposed theory of Lorentz violation from basic
considerations.Comment: 10 latex pages. Plenary talk at First LeCosPA Symposium: Towards
Ultimate Understanding of the Universe (LeCosPA2012), National Taiwan
University, Taipei, Taiwan, February 6-9, 201
Entropic gravity, minimum temperature, and modified Newtonian dynamics
Verlinde's heuristic argument for the interpretation of the standard
Newtonian gravitational force as an entropic force is generalized by the
introduction of a minimum temperature (or maximum wave length) for the
microscopic degrees of freedom on the holographic screen. With the simplest
possible setup, the resulting gravitational acceleration felt by a test mass m
from a point mass M at a distance R is found to be of the form of the modified
Newtonian dynamics (MOND) as suggested by Milgrom. The corresponding MOND-type
acceleration constant is proportional to the minimum temperature, which can be
interpreted as the Unruh temperature of an emerging de-Sitter space. This
provides a possible explanation of the connection between local MOND-type
two-body systems and cosmology.Comment: 12 pages, v6: published versio
Quantum Black Hole Evaporation
We investigate a recently proposed model for a full quantum description of
two-dimensional black hole evaporation, in which a reflecting boundary
condition is imposed in the strong coupling region. It is shown that in this
model each initial state is mapped to a well-defined asymptotic out-state,
provided one performs a certain projection in the gravitational zero mode
sector. We find that for an incoming localized energy pulse, the corresponding
out-going state contains approximately thermal radiation, in accordance with
semi-classical predictions. In addition, our model allows for certain acausal
strong coupling effects near the singularity, that give rise to corrections to
the Hawking spectrum and restore the coherence of the out-state. To an
asymptotic observer these corrections appear to originate from behind the
receding apparent horizon and start to influence the out-going state long
before the black hole has emitted most of its mass. Finally, by putting the
system in a finite box, we are able to derive some algebraic properties of the
scattering matrix and prove that the final state contains all initial
information.Comment: 37 pages (figs 2 and 3 included as uuencoded compressed tar file),
Latex, needs epsf.tex, PUPT-1395, IASSNS-HEP-93/25 (revised version has minor
corrections, one reference added
Dilatonic Black Holes, Naked Singularities and Strings
We extend a previous calculation which treated Schwarschild black hole
horizons as quantum mechanical objects to the case of a charged, dilaton black
hole. We show that for a unique value of the dilaton parameter `a', which is
determined by the condition of unitarity of the S matrix, black holes transform
at the extremal limit into strings.Comment: 8 pages, REVTE
Newtonian gravity as an entropic force: Towards a derivation of G
It has been suggested that the Newtonian gravitational force may emerge as an
entropic force from a holographic microscopic theory. In this framework, the
possibility is reconsidered that Newton's gravitational coupling constant G can
be derived from the fundamental constants of the underlying microscopic theory.Comment: 10 pages. v6: published versio
The M five brane on a torus
The D-3 brane is examined from the point of view of the wrapped M-theory five
brane on a torus. In particular, the S-dual versions of the 3-brane are
identified as coming from different gauge choices of the auxiliary field that
is introduced in the PST description of the five brane world volume theory.Comment: 7 pages. To appear in proceedings of "Quantum aspects of gauge
theories, supergravity and unification", Corfu, September 1998, typos
correcte
Challenges Confronting Superluminal Neutrino Models
This talk opens the CosPA2011 session on OPERA's superluminal neutrino claim.
I summarize relevant observations and constraints from OPERA, MINOS, ICARUS,
KamLAND, IceCube and LEP as well as observations of SN1987A. I selectively
review some models of neutrino superluminality which have been proposed since
OPERA's announcement, focusing on a neutrino dark energy model. Powerful
theoretical constraints on these models arise from Cohen-Glashow bremsstrahlung
and from phase space requirements for the initial neutrino production. I
discuss these constraints and how they might be evaded in models in which the
maximum velocities of both neutrinos and charged leptons are equal but only
superluminal inside of a dense medium.Comment: 11 pages, proceedings for Oct 30th CosPA2011 talk, no figure
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