5,146 research outputs found
Constraints on Scalar Asymmetric Dark Matter from Black Hole Formation in Neutron Stars
We consider possibly observable effects of asymmetric dark matter (ADM) in
neutron stars. Since dark matter does not self-annihilate in the ADM scenario,
dark matter accumulates in neutron stars, eventually reaching the Chandrasekhar
limit and forming a black hole. We focus on the case of scalar ADM, where the
constraints from Bose-Einstein condensation and subsequent black hole formation
are most severe due to the absence of Fermi degeneracy pressure. We also note
that in some portions of this constrained parameter space, non-trivial effects
from Hawking radiation can modify our limits. We find that for scalar ADM with
mass between 100 keV and 10^5 GeV, the constraint from pulsars in globular
clusters on the scattering cross-section with neutrons ranges from \sigma_n <
10^{-45} cm^2 to 10^{-52} cm}^2. In particular, for scalar ADM with mass
between 1 GeV and 1 TeV (in the case where black hole evaporation due to
Hawking radiation is unimportant), the constraint on the scattering
cross-section is below what is reachable with ton scale direct detection
experiments.Comment: 24 pages, 5 figures; updated to match published versio
Ground state properties of a Tonks-Girardeau Gas in a periodic potential
In this paper, we investigate the ground-state properties of a bosonic
Tonks-Girardeau gas confined in a one-dimensional periodic potential. The
single-particle reduced density matrix is computed numerically for systems up
to bosons. Scaling analysis of the occupation number of the lowest
orbital shows that there are no Bose-Einstein Condensation(BEC) for the
periodically trapped TG gas in both commensurate and incommensurate cases. We
find that, in the commensurate case, the scaling exponents of the occupation
number of the lowest orbital, the amplitude of the lowest orbital and the
zero-momentum peak height with the particle numbers are 0, -0.5 and 1,
respectively, while in the incommensurate case, they are 0.5, -0.5 and 1.5,
respectively. These exponents are related to each other in a universal
relation.Comment: 9 pages, 10 figure
X-ray Properties of Radio-Selected Dual Active Galactic Nuclei
Merger simulations predict that tidally induced gas inflows can trigger
kpc-scale dual active galactic nuclei (dAGN) in heavily obscured environments.
Previously with the Very Large Array, we have confirmed four dAGN with
redshifts between and projected separations between 4.3 and
9.2 kpc in the SDSS Stripe 82 field. Here, we present X-ray
observations that spatially resolve these dAGN and compare their
multi-wavelength properties to those of single AGN from the literature. We
detect X-ray emission from six of the individual merger components and obtain
upper limits for the remaining two. Combined with previous radio and optical
observations, we find that our dAGN have properties similar to nearby
low-luminosity AGN, and they agree well with the black hole fundamental plane
relation. There are three AGN-dominated X-ray sources, whose X-ray
hardness-ratio derived column densities show that two are unobscured and one is
obscured. The low obscured fraction suggests these dAGN are no more obscured
than single AGN, in contrast to the predictions from simulations. These three
sources show an apparent X-ray deficit compared to their mid-infrared continuum
and optical [OIII] line luminosities, suggesting higher levels of obscuration,
in tension with the hardness-ratio derived column densities. Enhanced
mid-infrared and [OIII] luminosities from star formation may explain this
deficit. There is ambiguity in the level of obscuration for the remaining five
components since their hardness ratios may be affected by non-nuclear X-ray
emissions, or are undetected altogether. They require further observations to
be fully characterized.Comment: 11 pages, 5 figures, Accepted for publication in the Astrophysical
Journa
Holographic Superconductors with Ho\v{r}ava-Lifshitz Black Holes
We discuss the phase transition of planar black holes in Ho\v{r}ava-Lifshitz
gravity by introducing a Maxwell field and a complex scalar field. We calculate
the condensates of the charged operators in the dual CFTs when the mass square
of the complex scalar filed is and , respectively. We
compute the electrical conductivity of the \hl superconductor in the probe
approximation. In particular, it is found that there exists a spike in the
conductivity for the case of the operator with scaling dimension one. These
results are quite similar to those in the case of Schwarzschild-AdS black
holes, which demonstrates that the holographic superconductivity is a robust
phenomenon associated with asymptotic AdS black holes.Comment: 12 pages, 7 figures,refs adde
Checkerboard charge density wave and pseudogap in high- cuprates
We consider the scenario where a 4-lattice constant, rotationally symmetric
charge density wave (CDW) is present in the underdoped cuprates. We prove a
theorem that puts strong constraint on the possible form factor of such a CDW.
We demonstrate, within mean-field theory, that a particular form factor within
the allowed class describes the angle-resolved photoemission and scan tunneling
spectroscopy well. We conjecture that the ``large pseudogap'' in cuprates is
the consequence of this type of charge density wave.Comment: We add a new section II on the symmetry property of the checkerboard
CD
Turning off the Lights: How Dark is Dark Matter?
We consider current observational constraints on the electromagnetic charge
of dark matter. The velocity dependence of the scattering cross-section through
the photon gives rise to qualitatively different constraints than standard dark
matter scattering through massive force carriers. In particular, recombination
epoch observations of dark matter density perturbations require that
, the ratio of the dark matter to electronic charge, is less than
for , rising to for .
Though naively one would expect that dark matter carrying a charge well below
this constraint could still give rise to large scattering in current direct
detection experiments, we show that charged dark matter particles that could be
detected with upcoming experiments are expected to be evacuated from the
Galactic disk by the Galactic magnetic fields and supernova shock waves, and
hence will not give rise to a signal. Thus dark matter with a small charge is
likely not a source of a signal in current or upcoming dark matter direct
detection experiments.Comment: 19 pages, 2 figures; v2 - figures fixed, references adde
Complex Correspondence Principle
Quantum mechanics and classical mechanics are two very different theories,
but the correspondence principle states that quantum particles behave
classically in the limit of high quantum number. In recent years much research
has been done on extending both quantum mechanics and classical mechanics into
the complex domain. This letter shows that these complex extensions continue to
exhibit a correspondence, and that this correspondence becomes more pronounced
in the complex domain. The association between complex quantum mechanics and
complex classical mechanics is subtle and demonstrating this relationship
prequires the use of asymptotics beyond all orders.Comment: 4 pages, 6 figure
Instantons, supersymmetric vacua, and emergent geometries
We study instanton solutions and superpotentials for the large number of
vacua of the plane-wave matrix model and a 2+1 dimensional Super Yang-Mills
theory on with sixteen supercharges. We get the superpotential in
the weak coupling limit from the gauge theory description. We study the gravity
description of these instantons. Perturbatively with respect to a background,
they are Euclidean branes wrapping cycles in the dual gravity background.
Moreover, the superpotential can be given by the energy of the electric charge
system characterizing each vacuum. These charges are interpreted as the
eigenvalues of matrices from a reduction for the 1/8 BPS sector of the gauge
theories. We also discuss qualitatively the emergence of the extra spatial
dimensions appeared on the gravity side.Comment: 29 pages, 3 figures, latex. v2: references added, comments added. v3:
accepted version in PR
A Comprehensive View of a Strongly Lensed Planck-Associated Submillimeter Galaxy
We present high-resolution maps of stars, dust, and molecular gas in a strongly lensed submillimeter galaxy (SMG) at z = 3.259. HATLAS J114637.9–001132 is selected from the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) as a strong lens candidate mainly based on its unusually high 500 μm flux density (~300 mJy). It is the only high-redshift Planck detection in the 130 deg^2 H-ATLAS Phase-I area. Keck Adaptive Optics images reveal a quadruply imaged galaxy in the K band while the Submillimeter Array and the Jansky Very Large Array show doubly imaged 880 μm and CO(1→0) sources, indicating differentiated distributions of the various components in the galaxy. In the source plane, the stars reside in three major kpc-scale clumps extended over ~1.6 kpc, the dust in a compact (~1 kpc) region ~3 kpc north of the stars, and the cold molecular gas in an extended (~7 kpc) disk ~5 kpc northeast of the stars. The emissions from the stars, dust, and gas are magnified by ~17, ~8, and ~7 times, respectively, by four lensing galaxies at z ~ 1. Intrinsically, the lensed galaxy is a warm (T_(dust) ~ 40-65 K), hyper-luminous (L_(IR) ~ 1.7 × 10^(13) L_☉; star formation rate (SFR) ~2000 M_☉ yr^(–1)), gas-rich (M_(gas)/M_(baryon) ~ 70%), young (M_(stellar)/SFR ~ 20 Myr), and short-lived (M_(gas)/SFR ~ 40 Myr) starburst. With physical properties similar to unlensed z > 2 SMGs, HATLAS J114637.9–001132 offers a detailed view of a typical SMG through a powerful cosmic microscope
Possible Superconductivity at 37 K in Graphite-Sulfur Composite
Sulfur intercalated graphite composites with diamagnetic transitions at 6.7 K
and 37 K are prepared. The magnetization hysteresis loops (MHL), Xray
diffraction patterns, and resistance were measured. From the MHL, a slight
superconducting like penetration process is observed at 15 K in low field
region. The XRD shows no big difference from the mixture of graphite and sulfur
indicating that the volume of the superconducting phase (if any) is very small.
The temperature dependence of resistance shows a typical semiconducting
behavior with a saturation in low temperature region. This saturation is either
induced by the de-localization of conducting electrons or by possible
superconductivity in this system.Comment: CHIN. PHYS.LETT v18 1648 (2001
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