39,297 research outputs found
Black Hole Formation and Classicalization in Ultra-Planckian 2 -> N Scattering
We establish a connection between the ultra-Planckian scattering amplitudes
in field and string theory and unitarization by black hole formation in these
scattering processes. Using as a guideline an explicit microscopic theory in
which the black hole represents a bound-state of many soft gravitons at the
quantum critical point, we were able to identify and compute a set of
perturbative amplitudes relevant for black hole formation. These are the
tree-level N-graviton scattering S-matrix elements in a kinematical regime
(called classicalization limit) where the two incoming ultra-Planckian
gravitons produce a large number N of soft gravitons. We compute these
amplitudes by using the Kawai-Lewellen-Tye relations, as well as scattering
equations and string theory techniques. We discover that this limit reveals the
key features of the microscopic corpuscular black hole N-portrait. In
particular, the perturbative suppression factor of a N-graviton final state,
derived from the amplitude, matches the non-perturbative black hole entropy
when N reaches the quantum criticality value, whereas final states with
different value of N are either suppressed or excluded by non-perturbative
corpuscular physics. Thus we identify the microscopic reason behind the black
hole dominance over other final states including non-black hole classical
object. In the parameterization of the classicalization limit the scattering
equations can be solved exactly allowing us to obtain closed expressions for
the high-energy limit of the open and closed superstring tree-level scattering
amplitudes for a generic number N of external legs. We demonstrate matching and
complementarity between the string theory and field theory in different large-s
and large-N regimes.Comment: 55 pages, 7 figures, LaTeX; v2: typos removed; final version to
appear in Nucl. Phys.
Molecular Realism in Default Models for Information Theories of Hydrophobic Effects
This letter considers several physical arguments about contributions to
hydrophobic hydration of inert gases, constructs default models to test them
within information theories, and gives information theory predictions using
those default models with moment information drawn from simulation of liquid
water. Tested physical features include: packing or steric effects, the role of
attractive forces that lower the solvent pressure, and the roughly tetrahedral
coordination of water molecules in liquid water. Packing effects (hard sphere
default model) and packing effects plus attractive forces (Lennard-Jones
default model) are ineffective in improving the prediction of hydrophobic
hydration free energies of inert gases over the previously used Gibbs and flat
default models. However, a conceptually simple cluster Poisson model that
incorporates tetrahedral coordination structure in the default model is one of
the better performers for these predictions. These results provide a partial
rationalization of the remarkable performance of the flat default model with
two moments in previous applications. The cluster Poisson default model thus
will be the subject of further refinement.Comment: 5 pages including 3 figure
Dark Matter, Sparticle Spectroscopy and Muon in
We explore the sparticle mass spectra including LSP dark matter within the
framework of supersymmetric (422)
models, taking into account the constraints from extensive LHC and cold dark
matter searches. The soft supersymmetry-breaking parameters at can be
non-universal, but consistent with the 422 symmetry. We identify a variety of
coannihilation scenarios compatible with LSP dark matter, and study the
implications for future supersymmetry searches and the ongoing muon g-2
experiment.Comment: 21 pages, 8 fig
Two-Higgs-Doublet type-II and -III models and at the LHC
We study the constraints of the generic two-Higgs-doublet model (2HDM)
type-III and the impacts of the new Yukawa couplings. For comparisons, we
revisit the analysis in the 2HDM type-II. To understand the influence of all
involving free parameters and to realize their correlations, we employ
-square fitting approach by including theoretical and experimental
constraints, such as S, T, and U oblique parameters, the production of standard
model Higgs and its decay to , , , etc.
The errors of analysis are taken at , , and confidence
levels. Due to the new Yukawa couplings being associated with
and , we find that the allowed
regions for and in the type-III model can be broader
when the dictated parameter is positive; however, for negative
, the limits are stricter than those in the type-II model. By using the
constrained parameters, we find that the deviation from the SM in the can be of . Additionally, we also study the top-quark
flavor-changing processes induced at the tree level in the type-III model and
find that when all current experimental data are considered, we get for and GeV and
slightly exceeds for GeV.Comment: 22 pages, 11 figures. v3: Slight change in the abstract, Figure.1
added and commented, the conclusion remains unchange
Collective resonances in plasmonic crystals: Size matters
Periodic arrays of metallic nanoparticles may sustain Surface Lattice
Resonances (SLRs), which are collective resonances associated with the
diffractive coupling of Localized Surface Plasmon Resonances (LSPRs). By
investigating a series of arrays with varying number of particles, we traced
the evolution of SLRs to its origins. Polarization resolved extinction spectra
of arrays formed by a few nanoparticles were measured, and found to be in very
good agreement with calculations based on a coupled dipole model. Finite size
effects on the optical properties of the arrays are observed, and our results
provide insight into the characteristic length scales for collective plasmonic
effects: for arrays smaller than 5 x 5 particles, the Q-factors of SLRs are
lower than those of LSPRs; for arrays larger than 20 x 20 particles, the
Q-factors of SLRs saturate at a much larger value than those of LSPRs; in
between, the Q-factors of SLRs are an increasing function of the number of
particles in the array.Comment: 4 figure
Tramp Novae Between Galaxies in the Fornax Cluster: Tracers of Intracluster Light
We report the results of a survey for novae in and between the galaxies of
the Fornax cluster. Our survey provides strong evidence that intracluster novae
exist and that they provide a useful, independent measure of the intracluster
light in Fornax. We discovered six strong nova candidates in six distinct
epochs spanning eleven years from 1993 to 2004. The data were taken with the 4m
and the 1.5m telescopes at CTIO. The spatial distribution of the nova
candidates is consistent with 16-41% of the total light in the cluster
being in the intracluster light, based on the ratio of the number of novae we
discovered in intracluster space over the total number of novae discovered plus
a simple completeness correction factor. This estimate is consistent with
independent measures of intracluster light in Fornax and Virgo using
intracluster planetary nebulae. The accuracy of the intracluster light
measurement improves with each survey epoch as more novae are discovered.Comment: 30 pages, 10 figures, accepted for publication in the Astrophysical
Journal (Sep 9, 2004). Version 2: Added references. Full resolution versions
of figures 1-7 and 10 can be found at
http://astrowww.phys.uvic.ca/~neill/fnx
A Hydrogen-Poor Superluminous Supernova with Enhanced Iron-Group Absorption: A New Link Between SLSNe and Broad-Lined Type Ic SNe
We present optical observations of the Type I superluminous supernova
(SLSN-I) SN2017dwh at , which reached
mag at peak. Spectra taken a few days after peak show an unusual and strong
absorption line centered near 3200\AA\ that we identify with Co II, suggesting
a high fraction of synthesized Ni in the ejecta. By month
after peak, SN2017dwh became much redder than other SLSNe-I, instead strongly
resembling broad-lined Type Ic supernovae (Ic-BL SNe) with clear suppression of
the flux redward of \AA, providing further evidence for a large
mass of Fe-group elements. Late-time upper limits indicate a Ni mass of
M, leaving open the possibility that SN2017dwh produced
a Ni mass comparable to SN1998bw ( M). Fitting the
light curve with a combined magnetar and Ni model using ,
we find that the light curve can easily accommodate such masses without
affecting the inferred magnetar parameters. We also find that SN2017dwh
occurred in the least-luminous detected host galaxy to date for a SLSN-I, with
mag and an implied metallicity of .
The spectral properties of SN2017dwh provide new evidence linking SLSNe-I with
Type Ic-BL SNe, and in particular the high Fe-group abundance may be due to
enhanced Ni production or mixing due to asphericity. Finally, we find
that SN2017dwh represents the most extreme end of a correlation between
continuum shape and Co II absorption strength in the near-peak spectra of
SLSNe-I, indicating that Fe-group abundance likely accounts for some of the
variation in their spectral shapes.Comment: 16 pages, 7 figures, Submitted to Ap
Brans-Dicke DGP Brane Cosmology
We consider a five dimensional DGP-brane scenario endowed with a
non-minimally coupled scalar field within the context of Brans-Dicke theory.
This theory predicts that the mass appearing in the gravitational potential is
modified by the addition of the mass of the effective intrinsic curvature on
the brane. We also derive the effective four dimensional field equations on a
3+1 dimensional brane where the fifth dimension is assumed to have an orbifold
symmetry. Finally, we discuss the cosmological implications of this setup,
predicting an accelerated expanding universe with a value of the Brans-Dicke
parameter consistent with values resulting from the solar system
observations.Comment: 12 pages, 1 figure, to appear in JCA
Ill-posedness in the Einstein equations
It is shown that the formulation of the Einstein equations widely in use in
numerical relativity, namely, the standard ADM form, as well as some of its
variations (including the most recent conformally-decomposed version), suffers
from a certain but standard type of ill-posedness. Specifically, the norm of
the solution is not bounded by the norm of the initial data irrespective of the
data. A long-running numerical experiment is performed as well, showing that
the type of ill-posedness observed may not be serious in specific practical
applications, as is known from many numerical simulations.Comment: 13 pages, 3 figures, accepted for publication in Journal of
Mathematical Physics (to appear August 2000
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