703 research outputs found
Dynamic Dilatonic Domain Walls
Motivated by the ``universe as a brane'' idea, we investigate the motion of a
-brane (or domain wall) that couples to bulk matter. Usually one would
expect the spacetime outside such a wall to be time dependent however we show
that in certain cases it can be static, with consistency of the Israel
equations yielding relationships between the bulk metric and matter that can be
used as ans\"atze to solve the Einstein equations. As a concrete model we study
a domain wall coupled to a bulk dilaton with Liouville potentials for the
dilaton both in the bulk and on the wall. The bulk solutions we find are all
singular but some have black hole or cosmological horizons, beyond which our
solutions describe domain walls moving in time dependent bulks. A significant
period of world volume inflation occurs if the potential on the wall is not too
steep; in some cases the bulk also inflates (with the wall comoving) while in
others the wall moves relative to a non-inflating bulk. We apply our method to
obtain cosmological solutions of Ho\v{r}ava-Witten theory compactified on a
Calabi-Yau space. tive to a non-inflating bulk. We apply our method to obtain
cosmological solutions of Ho\v{r}ava-Witten theory compactified on a Calabi-Yau
space.Comment: 32 pages LaTeX, 5 .eps figures, corrected some typo
Consistent histories, the quantum Zeno effect, and time of arrival
We present a decomposition of the general quantum mechanical evolution
operator, that corresponds to the path decomposition expansion, and interpret
its constituents in terms of the quantum Zeno effect (QZE). This decomposition
is applied to a finite dimensional example and to the case of a free particle
in the real line, where the possibility of boundary conditions more general
than those hitherto considered in the literature is shown. We reinterpret the
assignment of consistent probabilities to different regions of spacetime in
terms of the QZE. The comparison of the approach of consistent histories to the
problem of time of arrival with the solution provided by the probability
distribution of Kijowski shows the strength of the latter point of view
General Static Solutions of 2-dimensional Einstein-Dilaton-Maxwell-Scalar Theories
General static solutions of effectively 2-dimensional
Einstein-Dilaton-Maxwell-Scalar theories are obtained. Our model action
includes a class of 2-d dilaton gravity theories coupled with a gauge
field and a massless scalar field. Therefore it also describes the spherically
symmetric reduction of -dimensional Einstein-Scalar-Maxwell theories. The
properties of the analytic solutions are briefly discussed.Comment: 16 pages, Latex fil
Unstable particles in matter at a finite temperature: the rho and omega mesons
Unstable particles (such as the vector mesons) have an important role to play
in low mass dilepton production resulting from heavy ion collisions and this
has been a subject of several investigations. Yet subtleties, such as the
implications of the generalization of the Breit-Wigner formula for nonzero
temperature and density, e.g. the question of collisional broadening, the role
of Bose enhancement, etc., the possibility of the kinematic opening (or
closing) of decay channels due to environmental effects, the problem of double
counting through resonant and direct contributions, are often given
insufficient emphasis. The present study attempts to point out these features
using the rho and omega mesons as illustrative examples. The difference between
the two versions of the Vector Meson Dominance Model in the present context is
also presented. Effects of non-zero temperature and density, through vector
meson masses and decay widths, on dilepton spectra are studied, for
concreteness within the framework of a Walecka-type model, though most of the
basic issues highlighted apply to other scenarios as well.Comment: text and figures modifie
Dust detection by the wave instrument on STEREO: nanoparticles picked up by the solar wind?
The STEREO/WAVES instrument has detected a very large number of intense
voltage pulses. We suggest that these events are produced by impact ionisation
of nanoparticles striking the spacecraft at a velocity of the order of
magnitude of the solar wind speed. Nanoparticles, which are half-way between
micron-sized dust and atomic ions, have such a large charge-to-mass ratio that
the electric field induced by the solar wind magnetic field accelerates them
very efficiently. Since the voltage produced by dust impacts increases very
fast with speed, such nanoparticles produce signals as high as do much larger
grains of smaller speeds. The flux of 10-nm radius grains inferred in this way
is compatible with the interplanetary dust flux model. The present results may
represent the first detection of fast nanoparticles in interplanetary space
near Earth orbit.Comment: In press in Solar Physics, 13 pages, 5 figure
Algebraic approach to quantum black holes: logarithmic corrections to black hole entropy
The algebraic approach to black hole quantization requires the horizon area
eigenvalues to be equally spaced. As shown previously, for a neutral
non-rotating black hole, such eigenvalues must be -fold degenerate if
one constructs the black hole stationary states by means of a pair of creation
operators subject to a specific algebra. We show that the algebra of these two
building blocks exhibits symmetry, where the area
operator generates the U(1) symmetry. The three generators of the SU(2)
symmetry represent a {\it global} quantum number (hyperspin) of the black hole,
and we show that this hyperspin must be zero. As a result, the degeneracy of
the -th area eigenvalue is reduced to for large , and
therefore, the logarithmic correction term should be added to the
Bekenstein-Hawking entropy. We also provide a heuristic approach explaining
this result, and an evidence for the existence of {\it two} building blocks.Comment: 15 pages, Revtex, to appear in Phys. Rev.
Sneutrino cold dark matter, a new analysis: relic abundance and detection rates
We perform a new and updated analysis of sneutrinos as dark matter
candidates, in different classes of supersymmetric models. We extend previous
analyses by studying sneutrino phenomenology for full variations of the
supersymmetric parameters which define the various models. We first revisit the
standard Minimal Supersymmetric Standard Model, concluding that sneutrinos are
marginally compatible with existing experimental bounds, including direct
detection, provided they compose a subdominant component of dark matter. We
then study supersymmetric models with the inclusion of right-handed fields and
lepton-number violating terms. Simple versions of the lepton-number-violating
models do not lead to phenomenology different from the standard case when the
neutrino mass bounds are properly included. On the contrary, models with
right-handed fields are perfectly viable: they predict sneutrinos which are
compatible with the current direct detection sensitivities, both as subdominant
and dominant dark matter components. We also study the indirect detection
signals for such successful models: predictions for antiproton, antideuteron
and gamma-ray fluxes are provided and compared with existing and future
experimental sensitivities. The neutrino flux from the center of the Earth is
also analyzed.Comment: 72 pages, 50 figures. The version on the archive has low-resolution
figures. The paper with high resolution figures may be found through
http://www.to.infn.it/~arina/papers or
http://www.to.infn.it/~fornengo/Research/paperlist.htm
The Oedipal Paradigm in Group Development
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68383/2/10.1177_104649647300400302.pd
Procoagulant Adaptation of a Blood Coagulation Prothrombinase-like Enzyme Complex in Australian Elapid Venom
The macromolecular enzyme complex prothrombinase serves an indispensable role in blood coagulation as it catalyzes the conversion of prothrombin to thrombin, a key regulatory enzyme in the formation of a blood clot. Interestingly, a virtually identical enzyme complex is found in the venom of some Australian elapid snakes, which is composed of a cofactor factor Va-component and a serine protease factor Xa-like subunit. This review will provide an overview of the identification and characterization of the venom prothrombinase complex and will discuss the rationale for its powerful procoagulant nature responsible for the potent hemostatic toxicity of the elapid venom
Absorption cross section in Lifshitz black hole
We derive the absorption cross section of a minimally coupled scalar in the
Lifshitz black hole obtained from the new massive gravity. The absorption cross
section reduces to the horizon area in the low energy and massless limit of
s-wave mode propagation, indicating that the Lifshitz black hole also satisfies
the universality of low energy absorption cross section for black holes.Comment: 13 pages, 1 figure, version to appear in EPJ
- …