222 research outputs found
Inelastic Scattering of Tritium-Source Antineutrinos on Electrons of Germanium Atoms
Processes of the inelastic magnetic and weak scattering of
tritium-beta-source antineutrinos on the bound electrons of a germanium atom
are considered. The results obtained by calculating the spectra and cross
sections are presented for the energy-transfer range between 1 eV and 18 keV.Comment: Latex, 7 pages, 8 ps figure
Super Star Clusters in SBS0335-052E
As one of the lowest metallicity star forming galaxies, with a nucleus of
several super star clusters, SBS0335-052E is the subject of substantial current
study. We present new insights on this galaxy based on new and archival high
spatial resolution NICMOS and ACS images. We provide new measurements and
limits on the size of several of the SSCs. The images have sufficient
resolution to divide the star formation into compact regions and newly
discovered extended regions, indicating a bi-modal form of star formation. The
star formation regions are dated via the equivalent width of the Pa alpha
emission and we find that two of the extended regions of star formation are
less than 10 million years old. Our previous finding that stellar winds confine
the photo-ionizing flux to small regions around individual stars is consistent
with the new observations. This may allow planet formation in what would
traditionally be considered a harsh environment and has implications for the
number of planets around globular cluster stars. In addition the images
pinpoint the regions of H2 emission as located in, but not at the center of the
two star forming super star clusters, S1 and S2.Comment: Accepted by the Astrophysical Journa
Nonphysician providers in hospital medicine: Not so fast
No abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64916/1/584_ftp.pd
Reactor-based Neutrino Oscillation Experiments
The status of neutrino oscillation searches employing nuclear reactors as
sources is reviewed. This technique, a direct continuation of the experiments
that proved the existence of neutrinos, is today an essential tool in
investigating the indications of oscillations found in studying neutrinos
produced in the sun and in the earth's atmosphere. The low-energy of the
reactor \nuebar makes them an ideal tool to explore oscillations with small
mass differences and relatively large mixing angles.
In the last several years the determination of the reactor anti-neutrino flux
and spectrum has reached a high degree of accuracy. Hence measurements of these
quantities at a given distance L can be readily compared with the expectation
at L = 0, thus testing \nuebar disappearance.
While two experiments, Chooz and Palo Verde, with baselines of about 1 km and
thus sensitive to the neutrino mass differences associated with the atmospheric
neutrino anomaly, have collected data and published results recently, an
ambitious project with a baseline of more than 100 km, Kamland, is preparing to
take data. This ultimate reactor experiment will have a sensitivity sufficient
to explore part of the oscillation phase space relevant to solar neutrino
scenarios. It is the only envisioned experiment with a terrestrial source of
neutrinos capable of addressing the solar neutrino puzzle.Comment: Submitted to Reviews of Modern Physics 34 pages, 39 figure
The first result of the neutrino magnetic moment measurement in the GEMMA experiment
The first result of the neutrino magnetic moment measurement at the
Kalininskaya Nuclear Power Plant (KNPP) with the GEMMA spectrometer is
presented. An antineutrino-electron scattering is investigated. A high-purity
germanium detector of 1.5 kg placed 13.9 m away from the 3 GW reactor core is
used in the spectrometer. The antineutrino flux is . The differential method is used to extract the -e
electromagnetic scattering events. The scattered electron spectra taken in 6200
and 2064 hours for the reactor ON and OFF periods are compared. The upper limit
for the neutrino magnetic moment Bohr magnetons
at 90{%} CL is derived from the data processing.Comment: 9 pages, 10 figures, 2 table
Evidence for Environmentally Dependent Cluster Disruption in M83
Using multi-wavelength imaging from the Wide Field Camera 3 on the Hubble
Space Telescope we study the stellar cluster populations of two adjacent fields
in the nearby face-on spiral galaxy, M83. The observations cover the galactic
centre and reach out to ~6 kpc, thereby spanning a large range of environmental
conditions, ideal for testing empirical laws of cluster disruption. The
clusters are selected by visual inspection to be centrally concentrated,
symmetric, and resolved on the images. We find that a large fraction of objects
detected by automated algorithms (e.g. SExtractor or Daofind) are not clusters,
but rather are associations. These are likely to disperse into the field on
timescales of tens of Myr due to their lower stellar densities and not due to
gas expulsion (i.e. they were never gravitationally bound). We split the sample
into two discrete fields (inner and outer regions of the galaxy) and search for
evidence of environmentally dependent cluster disruption. Colour-colour
diagrams of the clusters, when compared to simple stellar population models,
already indicate that a much larger fraction of the clusters in the outer field
are older by tens of Myr than in the inner field. This impression is quantified
by estimating each cluster's properties (age, mass, and extinction) and
comparing the age/mass distributions between the two fields. Our results are
inconsistent with "universal" age and mass distributions of clusters, and
instead show that the ambient environment strongly affects the observed
populations.Comment: 6 pages, 3 figures, MNRAS in pres
Solar Neutrinos: Radiative Corrections in Neutrino-Electron Scattering Experiments
Radiative corrections to the electron recoil-energy spectra and to total
cross sections are computed for neutrino-electron scattering by solar
neutrinos. Radiative corrections change monotonically the electron recoil
spectrum for incident \b8 neutrinos, with the relative probability of observing
recoil electrons being reduced by about 4 \% at the highest electron energies.
For and \be7 neutrinos, the recoil spectra are not affected
significantly. Total cross sections for solar neutrino-electron scattering are
reduced by about 2 \% compared to previously computed values. We also calculate
the recoil spectra from N and O neutrinos including radiative
corrections.Comment: 40 pages, uuencoded, Z-compress file
The galaxy’s gas content regulated by the dark matter halo mass results in a superlinear M BH–M ⋆ Relation
Supermassive black holes (SMBHs) are tightly correlated with their hosts, but the origin of such connection remains elusive. To explore the cosmic buildup of this scaling relation, we present an empirically motivated model that tracks galaxy and SMBH growth down to z = 0. Starting from a random mass seed distribution at z = 10, we assume that each galaxy evolves on the star-forming "main sequence" (MS) and each BH follows the recently derived stellar mass (M sstarf) dependent ratio between BH accretion rate and star formation rate, going as . Our simple recipe naturally describes the BH–galaxy buildup in two stages. At first, the SMBH lags behind the host that evolves along the MS. Later, as the galaxy grows in M sstarf, our M sstarf-dependent BHAR/SFR induces a superlinear BH growth, as . According to this formalism, smaller BH seeds increase their relative mass faster and earlier than bigger BH seeds, at fixed M sstarf, thus setting along a gradually tighter M BH–M sstarf locus toward higher M sstarf. Assuming reasonable values of the radiative efficiency epsilon ~ 0.1, our empirical trend agrees with both high-redshift model predictions and intrinsic M BH–M sstarf relations of local BHs. We speculate that the observed nonlinear BH–galaxy buildup is reflected in a twofold behavior with dark matter halo mass (M DM), displaying a clear turnover at M DM ~ 2 × 1012 M ⊙. While supernovae-driven feedback suppresses BH growth in smaller halos (), above the M DM threshold cold gas inflows possibly fuel both BH accretion and star formation in a similar fashion ()
A New Model of Solar Neutrinos in Manifest Violation of CPT Invariance
The large mixing (mass)(LMA)-MSW model of solar neutrinos (nue) is now widely
held to be near definitive, based on global consistency with data. No physical
effect, however, compels its uniqueness. The present search for an explicitly
testable competitive model was stimulated by a surprising finding--the high
energy part of the standard solar model (SSM) 8B nue spectrum can be scaled
very precisely to observed flux levels without measurable shape distortion via
sensitive combinations of long wavelength flavor conversion in vacuum and a 8B
flux f(B)<f(B:SSM).Pursuantly, a new "astroparticle" model with the relatively
specific parameters deltam2 = 76-78 mueV2 (10-12 eV2); sin2 2theta = 0.59-0.55;
f(B) =0.8f(B:SSM) coupled with modest changes in the SSM, offers a viable
solution consistent with data. Because KamLAND has set deltam2~50x106 mueV2,
sin2 2theta~1 for antineutrinos, our model manifestly violates CPT invariance.
The model predicts new distortional effects in solar neutrino spectra via nu-e
scattering signals in the window 3-5MeV, even though the spectrum is flat above
5 MeV. in This window that is accessible to experiment for the first time in
KamLAND. New experiments are proposed to observe the more dramatic
charged-current spectral effects.Comment: 25pages, 7 Fig and 4 Tables; Final JCAP Published version (text
improved, reference, footnotes added
An X-Ray-Selected Sample of Candidate Black Holes in Dwarf Galaxies
We present a sample of hard X-ray-selected candidate black holes (BHs) in 19 dwarf galaxies. BH candidates are identified by cross-matching a parent sample of ~44,000 local dwarf galaxies (M* = 3 × 10 9 M☉, z < 0.055) with the Chandra Source Catalog and subsequently analyzing the original X-ray data products for matched sources. Of the 19 dwarf galaxies in our sample, eight have X-ray detections reported here for the first time. We find a total of 43 point-like hard X-ray sources with individual luminosities L2-10 keV ~ 10 37 - 10 40 erg s-1. Hard X-ray luminosities in this range can be attained by stellar-mass X-ray binaries (XRBs) and by massive BHs accreting at low Eddington ratio. We place an upper limit of 53% (10/19) on the fraction of galaxies in our sample hosting a detectable hard X-ray source consistent with the optical nucleus, although the galaxy center is poorly defined in many of our objects. We also find that 42% (8/19) of the galaxies in our sample exhibit statistically significant enhanced hard X-ray emission relative to the expected galaxy-wide contribution from low-mass and high-mass XRBs, based on the [data] star formation rate relation defined by more massive and luminous systems. For the majority of these X-ray-enhanced dwarf galaxies, the excess emission is consistent with (but not necessarily due to) a nuclear X-ray source. Follow-up observations are necessary to distinguish between stellar-mass XRBs and active galactic nuclei powered by more massive BHs. In any case, our results support the notion that X-ray-emitting BHs in low-mass dwarf galaxies may have had an appreciable impact on reionization in the early universe
- …