197 research outputs found
STM imaging of electronic waves on the surface of BiTe: topologically protected surface states and hexagonal warping effects
Scanning tunneling spectroscopy studies on high-quality BiTe crystals
exhibit perfect correspondence to ARPES data, hence enabling identification of
different regimes measured in the local density of states (LDOS). Oscillations
of LDOS near a step are analyzed. Within the main part of the surface band
oscillations are strongly damped, supporting the hypothesis of topological
protection. At higher energies, as the surface band becomes concave,
oscillations appear which disperse with a particular wave-vector that may
result from an unconventional hexagonal warping term.Comment: 4 pages, 4 figures. Revised manuscript with improved analysis and
figure
Cosmological Constant and Axions in String Theory
String theory axions appear to be promising candidates for explaining
cosmological constant via quintessence. In this paper, we study conditions on
the string compactifications under which axion quintessence can happen. For
sufficiently large number of axions, cosmological constant can be accounted for
as the potential energy of axions that have not yet relaxed to their minima. In
compactifications that incorporate unified models of particle physics, the
height of the axion potential can naturally fall close to the observed value of
cosmological constant.Comment: 22 page
Singularities and Closed String Tachyons
A basic problem in gravitational physics is the resolution of spacetime
singularities where general relativity breaks down. The simplest such
singularities are conical singularities arising from orbifold identifications
of flat space, and the most challenging are spacelike singularities inside
black holes (and in cosmology). Topology changing processes also require
evolution through classically singular spacetimes. I briefly review how a phase
of closed string tachyon condensate replaces, and helps to resolve, basic
singularities of each of these types. Finally I discuss some interesting
features of singularities arising in the small volume limit of compact
negatively curved spaces and the emerging zoology of spacelike singularities.Comment: 8 pages latex, based on comments at Solvay meetin
Analysis and Interpretation of Hard X-ray Emission from the Bullet Cluster (1E0657-56), the Most Distant Cluster of Galaxies Observed by RXTE
Evidence for non-thermal activity in clusters of galaxies is well established
from radio observations of synchrotron emission by relativistic electrons. New
windows in the Extreme Ultraviolet and Hard X-ray ranges have provided for more
powerful tools for the investigation of this phenomenon. Detection of hard
X-rays in the 20 to 100 keV range have been reported from several clusters of
galaxies, notably from Coma and others. Based on these earlier observations we
identified the relatively high redshift cluster 1E0657-56 (also known as RX
J0658-5557) as a good candidate for hard X-ray observations. This cluster, also
known as the bullet cluster, has many other interesting and unusual features,
most notably that it is undergoing a merger, clearly visible in the X-ray
images. Here we present results from a successful RXTE observations of this
cluster. We summarize past observations and their theoretical interpretation
which guided us in the selection process. We describe the new observations and
present the constraints we can set on the flux and spectrum of the hard X-rays.
Finally we discuss the constraints one can set on the characteristics of
accelerated electrons which produce the hard X-rays and the radio radiation.Comment: Accepted by the Astrophysical Journa
Magnetic fields above the surface of a superconductor with internal magnetism
The author presents a method for calculating the magnetic fields near a
planar surface of a superconductor with a given intrinsic magnetization in the
London limit. He computes solutions for various magnetic domain boundary
configurations and derives relations between the spectral densities of the
magnetization and the resulting field in the vacuum half space, which are
useful if the magnetization can be considered as a statistical quantity and its
features are too small to be resolved individually. The results are useful for
analyzing and designing magnetic scanning experiments. Application to existing
data from such experiments on SrRuO show that a domain wall would have
been detectable, but the magnetic field of randomly oriented small domains and
small defects may have been smaller than the experimental noise level.Comment: 8 pages, 2 figures. Journal version. Added one figure, some
discussion. A few typos correcte
Discovering the Higgs with Low Mass Muon Pairs
Many models of electroweak symmetry breaking have an additional light
pseudoscalar. If the Higgs boson can decay to a new pseudoscalar, LEP searches
for the Higgs can be significantly altered and the Higgs can be as light as 86
GeV. Discovering the Higgs boson in these models is challenging when the
pseudoscalar is lighter than 10 GeV because it decays dominantly into tau
leptons. In this paper, we discuss discovering the Higgs in a subdominant decay
mode where one of the pseudoscalars decays to a pair of muons. This search
allows for potential discovery of a cascade-decaying Higgs boson with the
complete Tevatron data set or early data at the LHC.Comment: 10 pages, 7 figure
It's On: Early Interpretations of ATLAS Results in Jets and Missing Energy Searches
The first search for supersymmetry from ATLAS with 70/nb of integrated
luminosity extends the Tevatron' s reach for colored particles that decay into
jets plus missing transverse energy. For gluinos that decay directly or through
a one step cascade into the LSP and two jets, the mass range m_g < 205 GeV is
disfavored by the ATLAS searches, regardless of the mass of the LSP. In some
cases the coverage extends up to m_g ~ 295 GeV, already surpassing the
Tevatron's reach for compressed supersymmetry spectra.Comment: 5 pages, 3 figures, 1 table; references and figure added; Physics
Letters B (2011
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Gravitational Wave Detection with Atom Interferometry
We propose two distinct atom interferometer gravitational wave detectors, one terrestrial and another satellite-based, utilizing the core technology of the Stanford 10m atom interferometer presently under construction. The terrestrial experiment can operate with strain sensitivity {approx} 10{sup -19}/{radical}Hz in the 1 Hz-10 Hz band, inaccessible to LIGO, and can detect gravitational waves from solar mass binaries out to megaparsec distances. The satellite experiment probes the same frequency spectrum as LISA with better strain sensitivity {approx} 10{sup -20}/{radical}Hz. Each configuration compares two widely separated atom interferometers run using common lasers. The effect of the gravitational waves on the propagating laser field produces the main effect in this configuration and enables a large enhancement in the gravitational wave signal while significantly suppressing many backgrounds. The use of ballistic atoms (instead of mirrors) as inertial test masses improves systematics coming from vibrations and acceleration noise, and reduces spacecraft control requirements
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Sequestering the Gravitino: Neutralino Dark Matter in Gauge Mediation
In conventional models of gauge-mediated supersymmetry breaking, the lightest supersymmetric particle (LSP) is invariably the gravitino. However, if the supersymmetry breaking sector is strongly coupled, conformal sequestering may raise the mass of the gravitino relative to the remaining soft supersymmetry-breaking masses. In this letter, we demonstrate that such conformal dynamics in gauge-mediated theories may give rise to satisfactory neutralino dark matter while simultaneously solving the flavor and {mu}/B{mu} problems
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Simple Stringy Dynamical SUSY Breaking
We present simple string models which dynamically break supersymmetry without non-Abelian gauge dynamics. The Fayet model, the Polonyi model, and the O'Raifeartaigh model each arise from D-branes at a specific type of singularity. D-brane instanton effects generate the requisite exponentially small scale of supersymmetry breaking
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