329 research outputs found
VERITAS Search for VHE Gamma-ray Emission from Dwarf Spheroidal Galaxies
Indirect dark matter searches with ground-based gamma-ray observatories
provide an alternative for identifying the particle nature of dark matter that
is complementary to that of direct search or accelerator production
experiments. We present the results of observations of the dwarf spheroidal
galaxies Draco, Ursa Minor, Bootes 1, and Willman 1 conducted by VERITAS. These
galaxies are nearby dark matter dominated objects located at a typical distance
of several tens of kiloparsecs for which there are good measurements of the
dark matter density profile from stellar velocity measurements. Since the
conventional astrophysical background of very high energy gamma rays from these
objects appears to be negligible, they are good targets to search for the
secondary gamma-ray photons produced by interacting or decaying dark matter
particles. No significant gamma-ray flux above 200 GeV was detected from these
four dwarf galaxies for a typical exposure of ~20 hours. The 95% confidence
upper limits on the integral gamma-ray flux are in the range 0.4-2.2x10^-12
photons cm^-2s^-1. We interpret this limiting flux in the context of pair
annihilation of weakly interacting massive particles and derive constraints on
the thermally averaged product of the total self-annihilation cross section and
the relative velocity of the WIMPs. The limits are obtained under conservative
assumptions regarding the dark matter distribution in dwarf galaxies and are
approximately three orders of magnitude above the generic theoretical
prediction for WIMPs in the minimal supersymmetric standard model framework.
However significant uncertainty exists in the dark matter distribution as well
as the neutralino cross sections which under favorable assumptions could
further lower the limits.Comment: 21 pages, 2 figures, updated to reflect version published in ApJ.
NOTE: M.D. Wood added as autho
MiniBooNE and MicroBooNE Combined Fit to a 3+1 Sterile Neutrino Scenario
This letter presents the results from the MiniBooNE experiment within a full
"3+1" scenario where one sterile neutrino is introduced to the
three-active-neutrino picture. In addition to electron-neutrino appearance at
short-baselines, this scenario also allows for disappearance of the
muon-neutrino and electron-neutrino fluxes in the Booster Neutrino Beam, which
is shared by the MicroBooNE experiment. We present the 3+1 fit to the MiniBooNE
electron-(anti)neutrino and muon-(anti)neutrino data alone, and in combination
with MicroBooNE electron-neutrino data. The best-fit parameters of the combined
fit with the exclusive CCQE analysis (inclusive analysis) are , , , and . Comparing the
no-oscillation scenario to the 3+1 model, the data prefer the 3+1 model with a
, a
preference assuming the asymptotic approximation given by Wilks' theorem.Comment: 10 pages, 4 figures, 2 tabl
Study of the reaction e^{+}e^{-} -->J/psi\pi^{+}\pi^{-} via initial-state radiation at BaBar
We study the process with
initial-state-radiation events produced at the PEP-II asymmetric-energy
collider. The data were recorded with the BaBar detector at center-of-mass
energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454
. We investigate the mass
distribution in the region from 3.5 to 5.5 . Below 3.7
the signal dominates, and above 4
there is a significant peak due to the Y(4260). A fit to
the data in the range 3.74 -- 5.50 yields a mass value
(stat) (syst) and a width value (stat)(syst) for this state. We do not
confirm the report from the Belle collaboration of a broad structure at 4.01
. In addition, we investigate the system
which results from Y(4260) decay
Stellar kinematics and metallicities in the ultra-faint dwarf galaxy Reticulum II
Based on data obtained from the ESO Science Archive Facility under request number 157689
Updated MiniBooNE Neutrino Oscillation Results with Increased Data and New Background Studies
The MiniBooNE experiment at Fermilab reports a total excess of electron-like events () from a data sample corresponding to
protons-on-target in neutrino mode, which is a 46%
increase in the data sample with respect to previously published results, and
protons-on-target in antineutrino mode. The additional
statistics allow several studies to address questions on the source of the
excess. First, we provide two-dimensional plots in visible energy and cosine of
the angle of the outgoing lepton, which can provide valuable input to models
for the event excess. Second, we test whether the excess may arise from photons
that enter the detector from external events or photons exiting the detector
from decays in two model independent ways. Beam timing information
shows that almost all of the excess is in time with neutrinos that interact in
the detector. The radius distribution shows that the excess is distributed
throughout the volume, while tighter cuts on the fiducal volume increase the
significance of the excess. We conclude that models of the event excess based
on entering and exiting photons are disfavored.Comment: 22 pages, 18 figure
Constraints on the Physical Properties of GW190814 through Simulations Based on DECam Follow-up Observations by the Dark Energy Survey
On 2019 August 14, the LIGO and Virgo Collaborations detected gravitational waves from a black hole and a 2.6 solar mass compact object, possibly the first neutron star-black hole merger. In search of an optical counterpart, the Dark Energy Survey (DES) obtained deep imaging of the entire 90% confidence level localization area with Blanco/DECam 0, 1, 2, 3, 6, and 16 nights after the merger. Objects with varying brightness were detected by the DES Pipeline, and we systematically reduced the candidate counterparts through catalog matching, light-curve properties, host-galaxy photometric redshifts, Southern Astrophysical Research spectroscopic follow-up observations, and machine-learning-based photometric classification. All candidates were rejected as counterparts to the merger. To quantify the sensitivity of our search, we applied our selection criteria to full light-curve simulations of supernovae and kilonovae as they would appear in the DECam observations. Because the source class of the merger was uncertain, we utilized an agnostic, three-component kilonova model based on tidally disrupted neutron star (NS) ejecta properties to quantify our detection efficiency of a counterpart if the merger included an NS. We find that, if a kilonova occurred during this merger, configurations where the ejected matter is greater than 0.07 solar masses, has lanthanide abundance less than 10-8.56, and has a velocity between 0.18c and 0.21c are disfavored at the 2\u3c3 level. Furthermore, we estimate that our background reduction methods are capable of associating gravitational wave signals with a detected electromagnetic counterpart at the 4\u3c3 level in 95% of future follow-up observations
Searches for Neutrinos from Gamma-Ray Bursts Using the IceCube Neutrino Observatory
Gamma-ray bursts (GRBs) are considered as promising sources of ultra-high-energy cosmic rays (UHECRs) due to their large power output. Observing a neutrino flux from GRBs would offer evidence that GRBs are hadronic accelerators of UHECRs. Previous IceCube analyses, which primarily focused on neutrinos arriving in temporal coincidence with the prompt gamma-rays, found no significant neutrino excess. The four analyses presented in this paper extend the region of interest to 14 days before and after the prompt phase, including generic extended time windows and targeted precursor searches. GRBs were selected between 2011 May and 2018 October to align with the data set of candidate muon-neutrino events observed by IceCube. No evidence of correlation between neutrino events and GRBs was found in these analyses. Limits are set to constrain the contribution of the cosmic GRB population to the diffuse astrophysical neutrino flux observed by IceCube. Prompt neutrino emission from GRBs is limited to ≲1% of the observed diffuse neutrino flux, and emission on timescales up to 104 s is constrained to 24% of the total diffuse flux.Peer Reviewe
Succinate dehydrogenase inhibition leads to epithelial-mesenchymal transition and reprogrammed carbon metabolism
Have Atmospheric Cerenkov Telescopes Observed Dark Matter?
Two ground-based experiments have recently independently detected TeV
-rays from the direction of the Galactic center. The observations made
by the VERITAS and CANGAROO collaborations are unexpected, although not
impossible to interpret in terms of astrophysical sources. Here we examine in
detail whether the observed -rays may arise from the more exotic
alternative of annihilations of dark matter particles clustered in the center
of the Galaxy.Comment: 19 pages, 7 figure
Effects of Intermittent IL-2 Alone or with Peri-Cycle Antiretroviral Therapy in Early HIV Infection: The STALWART Study
The Study of Aldesleukin with and without antiretroviral therapy (STALWART) evaluated whether intermittent interleukin-2 (IL-2) alone or with antiretroviral therapy (ART) around IL-2 cycles increased CD4+ counts compared to no therapy
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