5,152 research outputs found
The Migdal Effect and Photon Bremsstrahlung in effective field theories of dark matter direct detection and coherent elastic neutrino-nucleus scattering
Dark matter direct detection experiments have limited sensitivity to light
dark matter (below a few GeV), due to the challenges of lowering energy
thresholds for the detection of nuclear recoil to below
. While impressive progress has been made on this
front, light dark matter remains the least constrained region of dark-matter
parameter space. It has been shown that both ionization and excitation due to
the Migdal effect and coherently-emitted photon bremsstrahlung from the
recoiling atom can provide observable channels for light dark matter that would
otherwise have been missed owing to the resulting nuclear recoil falling below
the detector threshold. In this paper we extend previous work by calculating
the Migdal effect and photon bremmstrahlung rates for a general set of
interaction types, including those that are momentum-independent or -dependent,
spin-independent or -dependent, as well as examining the rates for a variety of
target materials, allowing us to place new experimental limits on some of these
interaction types. Additionally, we include a calculation of these effects
induced by the coherent scattering on nuclei of solar or atmospheric neutrinos.
We demonstrate that the Migdal effect dominates over the bremsstrahlung effect
for all targets considered for interactions induced by either dark matter or
neutrinos. This reduces photon bremsstrahlung to irrelevancy for future direct
detection experiments.Comment: 17 pages, 6 figure
Pulsar "Drifting"-Subpulse Polarization: No Evidence for Systematic Polarization-Angle Rotations
Polarization-angle density displays are given for pulsars B0809+74 and
B2303+30, which exhibit no evidence of the systematic polarization-angle
rotation within individual subpulses previously reported for these two stars.
The ``drifting'' subpulses of both pulsars exhibit strikingly linear and
circular polarization which appears to reflect the characteristics of two
nearly orthogonally polarized emission ``modes''--along which the severe
average-profile depolarization that is characteristic of their admixture at
comparable overall intensities.Comment: Accepted for publication in Astronomy & Astrophysic
G328.4+0.2 : A large and luminous Crab-like supernova remnant
We report on radio continuum and HI observations of the radio source
G328.4+0.2 using the Australia Telescope Compact Array. Our results confirm
G328.4+0.2 to be a filled-center nebula with no surrounding shell, showing
significant linear polarization and an almost flat spectral index. These
results lead us to conclude that G328.4+0.2 is a Crab-like, or ``plerionic'',
supernova remnant (SNR), presumably powered by an unseen central pulsar. HI
absorption towards G328.4+0.2 puts a lower limit on its distance of 17.4 +/-
0.9 kpc, making it the largest (D=25 pc) and most luminous (L_R = 3e35 erg/s)
Crab-like SNR in the Galaxy. We infer G328.4+0.2 to be significantly older than
the Crab Nebula, but powered by a pulsar which is fast spinning (P<20 ms) and
which has a comparatively low magnetic field (B<1e12 G). We propose G328.4+0.2,
G74.9+1.2 and N157B as a distinct group of large-diameter, high-luminosity
Crab-like SNRs, all powered by fast-spinning low-field pulsars.Comment: 7 pages, 3 embedded EPS figures, uses emulateapj.sty. Accepted to
ApJ. Abstract corrected so that distance is now in kpc, not pc
Real-Time Operating System/360
RTOS has a cost savings advantage for real-time applications, such as those with random inputs requiring a flexible data routing facility, display systems simplified by a device independent interface language, and complex applications needing added storage protection and data queuing
Acoustically driven ferromagnetic resonance
Surface acoustic waves (SAW) in the GHz frequency range are exploited for the
all-elastic excitation and detection of ferromagnetic resonance (FMR) in a
ferromagnetic/ferroelectric (nickel/lithium niobate) hybrid device. We measure
the SAW magneto-transmission at room temperature as a function of frequency,
external magnetic field magnitude, and orientation. Our data are well described
by a modified Landau-Lifshitz-Gilbert approach, in which a virtual,
strain-induced tickle field drives the magnetization precession. This causes a
distinct magnetic field orientation dependence of elastically driven FMR that
we observe in both model and experiment.Comment: 4 page
Results of the studies on energy deposition in IR6 superconducting magnets from continuous beam loss on the TCDQ system
A single sided mobile graphite diluter block TCDQ, in combination with a two-sided secondary collimator TCS and an iron shield TCDQM, will be installed in front of the superconducting quadrupole Q4 magnets in IR6, in order to protect it and other downstream LHC machine elements from destruction in the event of a beam dump that is not synchronised with the abort gap. The TCDQ will be positioned close to the beam, and will intercept the particles from the secondary halo during low beam lifetime. Previous studies (1-4) have shown that the energy deposited in the Q4 magnet coils can be close to or above the quench limit. In this note the results of the latest FLUKA energy deposition simulations for Beam 2 are described, including an upgrade possibility for the TCDQ system with an additional shielding device. The results are discussed in the context of the expected performance levels for the different phases of LHC operation
The LWA1 Radio Telescope
LWA1 is a new radio telescope operating in the frequency range 10-88 MHz,
located in central New Mexico. The telescope consists of 258 pairs of
dipole-type antennas whose outputs are individually digitized and formed into
beams. Simultaneously, signals from all dipoles can be recorded using one of
the instrument's "all dipoles" modes, facilitating all-sky imaging. Notable
features of the instrument include high intrinsic sensitivity (about 6 kJy
zenith system equivalent flux density), large instantaneous bandwidth (up to 78
MHz), and 4 independently-steerable beams utilizing digital "true time delay"
beamforming. This paper summarizes the design of LWA1 and its performance as
determined in commissioning experiments. We describe the method currently in
use for array calibration, and report on measurements of sensitivity and
beamwidth.Comment: 9 pages, 14 figures, accepted by IEEE Trans. Antennas & Propagation.
Various minor changes from previous versio
Magnetic interference patterns in 0-Pi SIFS Josephson junctions: effects of asymmetry between 0 and Pi regions
We present a detailed analysis of the dependence of the critical current I_c
on the magnetic field B of 0, Pi, and 0-Pi
superconductor-insulator-ferromagnet-superconductor Josephson junctions. I_c(B)
of the 0 and Pi junction closely follows a Fraunhofer pattern, indicating a
homogeneous critical current density j_c(x). The maximum of I_c(B) is slightly
shifted along the field axis, pointing to a small remanent in-plane
magnetization of the F-layer along the field axis. I_c(B) of the 0-Pi junction
exhibits the characteristic central minimum. I_c however has a finite value
here, due to an asymmetry of j_c in the 0 and Pi part. In addition, this I_c(B)
exhibits asymmetric maxima and bumped minima. To explain these features in
detail, flux penetration being different in the 0 part and the Pi part needs to
be taken into account. We discuss this asymmetry in relation to the magnetic
properties of the F-layer and the fabrication technique used to produce the
0-Pi junctions
Seroprevalence of Zika virus in wild African green monkeys and baboons
ABSTRACT Zika virus (ZIKV) has recently spread through the Americas and has been associated with a range of health effects, including birth defects in children born to women infected during pregnancy. Although the natural reservoir of ZIKV remains poorly defined, the virus was first identified in a captive “sentinel” macaque monkey in Africa in 1947. However, the virus has not been reported in humans or nonhuman primates (NHPs) in Africa outside Gabon in over a decade. Here, we examine ZIKV infection in 239 wild baboons and African green monkeys from South Africa, the Gambia, Tanzania, and Zambia using combinations of unbiased deep sequencing, quantitative reverse transcription-PCR (qRT-PCR), and an antibody capture assay that we optimized using serum collected from captive macaque monkeys exposed to ZIKV, dengue virus, and yellow fever virus. While we did not find evidence of active ZIKV infection in wild NHPs in Africa, we found variable ZIKV seropositivity of up to 16% in some of the NHP populations sampled. We anticipate that these results and the methodology described within will help in continued efforts to determine the prevalence, natural reservoir, and transmission dynamics of ZIKV in Africa and elsewhere. IMPORTANCE Zika virus (ZIKV) is a mosquito-borne virus originally discovered in a captive monkey living in the Zika Forest of Uganda, Africa, in 1947. Recently, an outbreak in South America has shown that ZIKV infection can cause myriad health effects, including birth defects in the children of women infected during pregnancy. Here, we sought to investigate ZIKV infection in wild African primates to better understand its emergence and spread, looking for evidence of active or prior infection. Our results suggest that up to 16% of some populations of nonhuman primate were, at some point, exposed to ZIKV. We anticipate that this study will be useful for future studies that examine the spread of infections from wild animals to humans in general and those studying ZIKV in primates in particular. Podcast: A podcast concerning this article is available
Beam Halo on the LHC TCDQ Diluter System and Thermal Load on the Downstream Superconducting Magnets
The moveable single-jawed graphite TCDQ diluter must be positioned very close to the circulating LHC beam in order to prevent damage to downstream components in the event of an unsynchronised beam abort. A two-jawed graphite TCS.IR6 collimator forms part of the TCDQ system. The requirement to place the jaws close to the beam means that the system can intercept a substantial beam halo load. Initial investigations indicated a worryingly high heat load on the Q4 coils. This paper presents the updated load cases, shielding and simulation geometry, and the results of simulations of the energy deposition in the TCDQ system and in the downstream superconducting Q4 magnet. The implications for the operation of the LHC are discussed
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