14,193 research outputs found
History of vertical displacement of Kerepehi Fault at Kopouatai bog, Hauraki Lowlands, New Zealand, since c. 10 700 years ago
Thirteen tephra layers interbedded with peat, and a basal peathorizon, in four pairs of cores provide radiocarbon-dated reference horizons that indicate vertical displacement on the Kerepehi Fault at Kopouatai bog, Hauraki Lowlands. Progressive offset of the horizons with time shows that vertical fault movement, downthrown to the west, has been occurring for the past c. 10 700 radiocarbon years at an approximately uniform rate of c. 0.13 mm/yr. Step functions indicate faulting events earthquakes at c. 1400, c. 5600, c. 6800, and C. 9000 years ago, a mean recurrence interval of c. 2500 years. These findings support geophysical and geological evidence that the Hauraki Depression is an active rift, and show that active faulting occurs along the northern as well as southern extensions of the Kerepehi Fault.
If such earthquakes occur randomly in time, and based on the return period of 2500 years, there are 2%, 18%, and 33% probabilities of a major earthquake affecting the Kerepehi Fault at Kopouatai bog in the next 50, 500, and 1000 years, respectively
Naked and Thunderbolt Singularities in Black Hole Evaporation
If an evaporating black hole does not settle down to a non radiating remnant,
a description by a semi classical Lorentz metric must contain either a naked
singularity or what we call a thunderbolt, a singularity that spreads out to
infinity on a spacelike or null path. We investigate this question in the
context of various two dimensional models that have been proposed. We find that
if the semi classical equations have an extra symmetry that make them solvable
in closed form, they seem to predict naked singularities but numerical
calculations indicate that more general semi classical equations, such as the
original CGHS ones give rise to thunderbolts. We therefore expect that the semi
classical approximation in four dimensions will lead to thunderbolts. We
interpret the prediction of thunderbolts as indicating that the semi classical
approximation breaks down at the end point of black hole evaporation, and we
would expect that a full quantum treatment would replace the thunderbolt with a
burst of high energy particles. The energy in such a burst would be too small
to account for the observed gamma ray bursts.Comment: 21 pages (10 diagrams available on request
String Creation and Heterotic-Type I' Duality
The BPS spectrum of type I' string theory in a generic background is derived
using the duality with the nine-dimensional heterotic string theory with Wilson
lines. It is shown that the corresponding mass formula has a natural
interpretation in terms of type I', and it is demonstrated that the relevant
states in type I' preserve supersymmetry. By considering certain BPS states for
different Wilson lines an independent confirmation of the string creation
phenomenon in the D0-D8 system is found. We also comment on the
non-perturbative realization of gauge enhancement in type I', and on the
predictions for the quantum mechanics of type I' D0-branes.Comment: 24 pages, LaTex, 6 postscript figure
The Planckian Conspiracy: String Theory and the Black Hole Information Paradox
It has been argued that the consistency of quantum theory with black hole
physics requires nonlocality not present in ordinary effective field theory. We
examine the extent to which such nonlocal effects show up in the perturbative
S-matrix of string theory.Comment: 13 pages, harvma
QUANTUM CORRECTIONS AND EXTREMAL BLACK HOLES
We consider static solutions of two dimensional dilaton gravity models as toy
laboratories to address the question of the final fate of black holes. A non
perturbative correction to the CGHS potential term is shown to lead classically
to an extremal black hole geometry, thus providing a plausible solution to
Hawking evaporation paradox. However, the full quantum theory does not admit an
extremal solution.Comment: 12 pages, LaTex, no figures. We have improved the main argument
leading to the non-existence of an extremal black hole in the quantum theor
Bound States of Type I' D-particles and Enhanced Gauge Symmetry
Duality between the E_8 x E_8 heterotic string and Type I' theory predicts a
tower of D(irichlet)-particle bound states corresponding to perturbative
heterotic string states. In the limit of infinite Type I' coupling, some of
these bound states become massless, giving rise to enhanced E_8 x E_8 gauge
symmetry. By taking a different infinite coupling limit, one can recover the
E_8 x E_8 gauge bosons of M-theory, compactified on S^1/Z_2. In this paper we
use the matrix model description of the D-particle dynamics to study these
bound states. We find results consistent with the chain of dualities and
clarify a number of issues that arise in the application of the matrix
mechanics to this system.Comment: 11 pages, harvmac (b mode), minor correction
Higher-Order Black-Hole Solutions in N=2 Supergravity and Calabi-Yau String Backgrounds
Based on special geometry, we consider corrections to N=2 extremal black-hole
solutions and their entropies originating from higher-order derivative terms in
N=2 supergravity. These corrections are described by a holomorphic function,
and the higher-order black-hole solutions can be expressed in terms of
symplectic Sp(2+2) vectors. We apply the formalism to N=2 type-IIA
Calabi-Yau string compactifications and compare our results to recent related
results in the literature.Comment: 12 pages, LaTeX; reference added; minor changes, note added, version
to appear in Phys. Lett.
Heterotic Matrix String Theory
M-theory suggests the large N limit of the matrix description of a collection
of N Type IA D-particles should provide a nonperturbative formulation of
heterotic string theory. In this paper states in the matrix theory
corresponding to fundamental heterotic strings are identified, and their
interactions are studied. Comments are made about analogous states in Type IIA
string theory, which correspond to bound states of D-particles and
D-eightbranes.Comment: 13 pages, harvmac (b mode), references adde
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