13,218 research outputs found
Integrability of a Generalized Ito System: the Painleve Test
It is shown that a generalized Ito system of four coupled nonlinear evolution
equations passes the Painleve test for integrability in five distinct cases, of
which two were introduced recently by Tam, Hu and Wang. A conjecture is
formulated on integrability of a vector generalization of the Ito system.Comment: LaTeX, 5 page
Axion Dark Matter and Cosmological Parameters
We observe that photon cooling after big bang nucleosynthesis (BBN) but
before recombination can remove the conflict between the observed and
theoretically predicted value of the primordial abundance of Li. Such
cooling is ordinarily difficult to achieve. However, the recent realization
that dark matter axions form a Bose-Einstein condensate (BEC) provides a
possible mechanism, because the much colder axions may reach thermal contact
with the photons. This proposal predicts a high effective number of neutrinos
as measured by the cosmic microwave anisotropy spectrum.Comment: 4 pages, one figure. Version to appear in Phys. Rev. Lett.,
incorporating useful comments by the referees and emphasizing that photon
cooling by axion BEC is a possibility, not a certaint
Discovery of {\gamma}-ray pulsation and X-ray emission from the black widow pulsar PSR J2051-0827
We report the discovery of pulsed {\gamma}-ray emission and X-ray emission
from the black widow millisecond pulsar PSR J2051-0827 by using the data from
the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope and
the Advanced CCD Imaging Spectrometer array (ACIS-S) on the Chandra X-ray
Observatory. Using 3 years of LAT data, PSR J2051-0827 is clearly detected in
{\gamma}-ray with a signicance of \sim 8{\sigma} in the 0.2 - 20 GeV band. The
200 MeV - 20 GeV {\gamma}-ray spectrum of PSR J2051-0827 can be modeled by a
simple power- law with a photon index of 2.46 \pm 0.15. Significant (\sim
5{\sigma}) {\gamma}-ray pulsations at the radio period were detected. PSR
J2051-0827 was also detected in soft (0.3-7 keV) X-ray with Chandra. By
comparing the observed {\gamma}-rays and X-rays with theoretical models, we
suggest that the {\gamma}-ray emission is from the outer gap while the X-rays
can be from intra-binary shock and pulsar magnetospheric synchrotron emissions.Comment: 10 pages, 4 figures, accepted by ApJ on Jan 28, 201
A NuSTAR Observation of the Gamma-ray Emitting Millisecond Pulsar PSR J1723-2837
We report on the first NuSTAR observation of the gamma-ray emitting
millisecond pulsar binary PSR J1723-2837. X-ray radiation up to 79 keV is
clearly detected and the simultaneous NuSTAR and Swift spectrum is well
described by an absorbed power-law with a photon index of ~1.3. We also find
X-ray modulations in the 3-10 keV, 10-20 keV, 20-79 keV, and 3-79 keV bands at
the 14.8-hr binary orbital period. All these are entirely consistent with
previous X-ray observations below 10 keV. This new hard X-ray observation of
PSR J1723-2837 provides strong evidence that the X-rays are from the
intrabinary shock via an interaction between the pulsar wind and the outflow
from the companion star. We discuss how the NuSTAR observation constrains the
physical parameters of the intrabinary shock model.Comment: Accepted for publication in ApJ. 5 pages, 3 figure
Study of off-diagonal disorder using the typical medium dynamical cluster approximation
We generalize the typical medium dynamical cluster approximation (TMDCA) and
the local Blackman, Esterling, and Berk (BEB) method for systems with
off-diagonal disorder. Using our extended formalism we perform a systematic
study of the effects of non-local disorder-induced correlations and of
off-diagonal disorder on the density of states and the mobility edge of the
Anderson localized states. We apply our method to the three-dimensional
Anderson model with configuration dependent hopping and find fast convergence
with modest cluster sizes. Our results are in good agreement with the data
obtained using exact diagonalization, and the transfer matrix and kernel
polynomial methods.Comment: 10 pages, 8 figure
Swift, XMM-Newton, and NuSTAR observations of PSR J2032+4127/MT91 213
We report our recent Swift, NuSTAR, and XMM-Newton X-ray and Lijiang optical
observations on PSR J2032+4127/MT91 213, the gamma-ray binary candidate with a
period of 45-50 years. The coming periastron of the system was predicted to be
in November 2017, around which high-energy flares from keV to TeV are expected.
Recent studies with Chandra and Swift X-ray observations taken in 2015/16
showed that its X-ray emission has been brighter by a factors of ~10 than that
before 2013, probably revealing some on-going activities between the pulsar
wind and the stellar wind. Our new Swift/XRT lightcurve shows no strong
evidence of a single vigorous brightening trend, but rather several strong
X-ray flares on weekly to monthly timescales with a slowly brightening
baseline, namely the low state. The NuSTAR and XMM-Newton observations taken
during the flaring and the low states, respectively, show a denser environment
and a softer power-law index during the flaring state, implying that the pulsar
wind interacted with stronger stellar winds of the companion to produce the
flares. These precursors would be crucial in studying the predicted giant
outburst from this extreme gamma-ray binary during the periastron passage in
late 2017.Comment: 6 pages, including 3 figures and 2 tables. Accepted for publication
in Ap
A Typical Medium Dynamical Cluster Approximation for the Study of Anderson Localization in Three Dimensions
We develop a systematic typical medium dynamical cluster approximation that
provides a proper description of the Anderson localization transition in three
dimensions (3D). Our method successfully captures the localization phenomenon
both in the low and large disorder regimes, and allows us to study the
localization in different momenta cells, which renders the discovery that the
Anderson localization transition occurs in a cell-selective fashion. As a
function of cluster size, our method systematically recovers the re-entrance
behavior of the mobility edge and obtains the correct critical disorder
strength for Anderson localization in 3D.Comment: 5 Pages, 4 Figures and Supplementary Material include
Dual Fermion Dynamical Cluster Approach for Strongly Correlated Systems
We have designed a new multi-scale approach for Strongly Correlated Systems
by combining the Dynamical Cluster Approximation (DCA) and the recently
introduced dual-fermion formalism. This approach employs an exact mapping from
a real lattice to a DCA cluster of linear size Lc embedded in a dual fermion
lattice. Short-length-scale physics is addressed by the DCA cluster
calculation, while longer-length-scale physics is addressed diagrammatically
using dual fermions. The bare and dressed dual Fermionic Green functions scale
as O(1/Lc) so perturbation theory on the dual lattice converges very quickly.
E.g., the dual Fermion self-energy calculated with simple second order
perturbation theory is of order O(1/Lc^3), with third order and three body
corrections down by an additional factor of O(1/Lc^2)
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