11,900 research outputs found
Dilaton Black Holes Near the Horizon
Generic 4-d black holes with unbroken supersymmetry are shown
to tend to a Robinson-Bertotti type geometry with a linear dilaton and doubling
of unbroken supersymmetries near the horizon. Purely magnetic dilatonic black
holes, which have unbroken supersymmetry, behave near the horizon as a
2-d linear dilaton vacuum . This geometry is invariant under 8
supersymmetries, i.e. half of the original supersymmetries are unbroken.
The supersymmetric positivity bound, which requires the mass of the 4-d dilaton
black holes to be greater than or equal to the central charge, corresponds to
positivity of mass for a class of stringy 2-d black holes.Comment: 10 pages, SU-ITP-92-2
Black-Hole-Wave Duality in String Theory
Extreme 4-dimensional dilaton black holes embedded into 10-dimensional
geometry are shown to be dual to the gravitational waves in string theory. The
corresponding gravitational waves are the generalization of pp-fronted waves,
called supersymmetric string waves. They are given by Brinkmann metric and the
two-form field, without a dilaton. The non-diagonal part of the metric of the
dual partner of the wave together with the two-form field correspond to the
vector field in 4-dimensional geometry of the charged extreme black holes.Comment: 12 pages, LaTeX, preprint UG-3/94, SU-ITP-94-11, QMW-PH-94-1
Some Comments on Gravitational Entropy and the Inverse Mean Curvature Flow
The Geroch-Wald-Jang-Huisken-Ilmanen approach to the positive energy problem
to may be extended to give a negative lower bound for the mass of
asymptotically Anti-de-Sitter spacetimes containing horizons with exotic
topologies having ends or infinities of the form , in
terms of the cosmological constant. We also show how the method gives a lower
bound for for the mass of time-symmetric initial data sets for black holes with
vectors and scalars in terms of the mass, of the double extreme
black hole with the same charges. I also give a lower bound for the area of an
apparent horizon, and hence a lower bound for the entropy in terms of the same
function . This shows that the so-called attractor behaviour extends
beyond the static spherically symmetric case. and underscores the general
importance of the function . There are hints that higher dimensional
generalizations may involve the Yamabe conjectures.Comment: 13pp. late
Flux-Confinement in Dilatonic Cosmic Strings
We study dilaton-electrodynamics in flat spacetime and exhibit a set of
global cosmic string like solutions in which the magnetic flux is confined.
These solutions continue to exist for a small enough dilaton mass but cease to
do so above a critcal value depending on the magnetic flux. There also exist
domain wall and Dirac monopole solutions. We discuss a mechanism whereby
magnetic monopolesmight have been confined by dilaton cosmic strings during an
epoch in the early universe during which the dilaton was massless.Comment: 8 pages, DAMTP R93/3
Baryon Asymmetry, Supersymmetry and Gravitational Anomalies
We discuss two independent issues about the baryon asymmetry of the universe.
First, assuming that it is generated by an unspecified source at high
temperatures, we study the effects of non-perturbative dynamics above
the electroweak scale, in the context of supersymmetric models. We find that
there is a substantial difference with the nonsupersymmetric case with the net
effect of relaxing previous bounds on B and L violating interactions. In
particular supersymmetry allows neutrino masses as large as 10 eV (preferred by
solar neutrino and COBE data and measurable at future neutrino oscillation
experiments). Second, we argue that the existence of a mixed lepton
number-gravitational anomaly in the standard model will induce B-L violating
interactions. These transitions would be catalized by Einstein-Yang-Mills
instantons or sphalerons and could create a primordial B-L asymmetry at Planck
temperatures or lower. Gravity (and the anomaly structure of the standard
model) could then be the ultimate source of the baryon asymmetry. We analyze
the viability of the presently known gravitational instantons and sphalerons to
realize this scenario. (Talk presented by FQ at the Texas/Pascos Conference,
Berkeley Dec.1992.)Comment: 8 pages,FTUAM-93-07 NEIP93-001, harvma
Microstates of a Neutral Black Hole in M Theory
We consider vacuum solutions in M theory of the form of a five-dimensional
Kaluza-Klein black hole cross T^6. In a certain limit, these include the
five-dimensional neutral rotating black hole (cross T^6). From a IIA
standpoint, these solutions carry D0 and D6 charges. We show that there is a
weakly coupled D-brane description which precisely reproduces the
Hawking-Bekenstein entropy in the extremal limit, even though supersymmetry is
completely broken.Comment: 11 pages. v2: microstate counting extended to generic angular moment
Phases of 4D Scalar-tensor black holes coupled to Born-Infeld nonlinear electrodynamics
Recent results show that when non-linear electrodynamics is considered the
no-scalar-hair theorems in the scalar-tensor theories (STT) of gravity, which
are valid for the cases of neutral black holes and charged black holes in the
Maxwell electrodynamics, can be circumvented. What is even more, in the present
work, we find new non-unique, numerical solutions describing charged black
holes coupled to non-linear electrodynamics in a special class of scalar-tensor
theories. One of the phases has a trivial scalar field and coincides with the
corresponding solution in General Relativity. The other four phases that we
find are characterized by the value of the scalar field charge. The causal
structure and some aspects of the stability of the solutions have also been
studied. For the scalar-tensor theories considered, the black holes have a
single, non-degenerate horizon, i.e., their causal structure resembles that of
the Schwarzschild black hole. The thermodynamic analysis of the stability of
the solutions indicates that a phase transition may occur.Comment: 18 pages, 8 figures, new phases, figures, clarifying remarks and
acknowledgements adde
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HLA-B27 Positivity: associated health implications
HLA-B27 positivity makes the onset of autoimmune diseases such as uveitis, ankylosing spondylitis and Crohn's disease more likely to occur. Ankylosing spondylitis and Crohn's disease are two types of HLA-B27 positive diseases that demonstrate a direct association with uveitis. Although the possession of HLA-B27 positivity is not mandatory for autoimmune diseases such as uveitis to occur, HLA-B27 positivity not only makes it more likely but may modify the clinical picture in which a patient presents. In relation to assessment and diagnosis it is imperative that the medical history of patients is thoroughly examined to ensure pathological sequelae are appropriately treated. Nurses play an important role in assessing patients that have uveitis and should suspect ankylosing spondylitis or Crohn's disease may be present
Rational combinations of Betti diagrams of complete intersections
We investigate decompositions of Betti diagrams over a polynomial ring within
the framework of Boij-S\"oderberg theory. That is, given a Betti diagram, we
determine if it is possible to decompose it into the Betti diagrams of complete
intersections. To do so, we determine the extremal rays of the cone generated
by the diagrams of complete intersections and provide a rudimentary algorithm
for decomposition.Comment: This research was conducted at the Willamette Mathematics Consortium
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