2,247 research outputs found
Proton Lifetime and Baryon Number Violating Signatures at the LHC in Gauge Extended Models
There exist a number of models in the literature in which the weak
interactions are derived from a chiral gauge theory based on a larger group
than SU(2)_L x U(1)_Y. Such theories can be constructed so as to be
anomaly-free and consistent with precision electroweak measurements, and may be
interpreted as a deconstruction of an extra dimension. They also provide
interesting insights into the issues of flavor and dynamical electroweak
symmetry breaking, and can help to raise the mass of the Higgs boson in
supersymmetric theories. In this work we show that these theories can also give
rise to baryon and lepton number violating processes, such as nucleon decay and
spectacular multijet events at colliders, via the instanton transitions
associated with the extended gauge group. For a particular model based on
SU(2)_1 x SU(2)_2, we find that the violating scattering cross sections
are too small to be observed at the LHC, but that the lower limit on the
lifetime of the proton implies an upper bound on the gauge couplings.Comment: 36 page
Novel technique for constraining r-process (n,) reaction rates
A novel technique has been developed, which will open exciting new
opportunities for studying the very neutron-rich nuclei involved in the
r-process. As a proof-of-principle, the -spectra from the -decay
of Ga have been measured with the SuN detector at the National
Superconducting Cyclotron Laboratory. The nuclear level density and
-ray strength function are extracted and used as input to
Hauser-Feshbach calculations. The present technique is shown to strongly
constrain the Ge()Ge cross section and reaction rate.Comment: 5 pages, 3 figure
Bubble wall velocities in the Standard Model and beyond
We present results for the bubble wall velocity and bubble wall thickness during a cosmological first-order phase transition in a condensed form. Our results are for minimal extensions of the Standard Model but in principle are applicable to a much broader class of settings. Our first assumption about the model is that only the electroweak Higgs is obtaining a vacuum expectation value during the phase transition. The second is that most of the friction is produced by electroweak gauge bosons and top quarks. Under these assumptions the bubble wall velocity and thickness can be deduced as a function of two equilibrium properties of the plasma: the strength of the phase transition and the pressure difference along the bubble wall
UV to IR SEDs of UV selected galaxies in the ELAIS fields: evolution of dust attenuation and star formation activity from z=0.7 to z=0.2
We study the ultraviolet to far-infrared (hereafter UV-to-IR) SEDs of a
sample of intermediate redshift (0.2 < z < 0.7) UV-selected galaxies from the
ELAIS-N1 and ELAIS-N2 fields by fitting a multi-wavelength dataset to a library
of GRASIL templates. Star formation related properties of the galaxies are
derived from the library of models by using the Bayesian statistics. We find a
decreasing presence of galaxies with low attenuation and low total luminosity
as redshift decreases, which does not hold for high total luminosity galaxies.
In addition the dust attenuation of low mass galaxies increases as redshift
decreases, and this trend seems to disappear for galaxies with M* > 10^11
M_sun. This result is consistent with a mass dependent evolution of the dust to
gas ratio, which could be driven by a mass dependent efficiency of star
formation in star forming galaxies. The specific star formation rates (SSFR)
decrease with increasing stellar mass at all redshifts, and for a given stellar
mass the SSFR decreases with decreasing redshift. The differences in the slope
of the M*--SSFR relation found between this work and others at similar redshift
could be explained by the adopted selection criteria of the samples which, for
a UV selected sample, favours blue, star forming galaxies.Comment: 21 figures, accepted for publication in Ap
Production cross sections from 82Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line
Production cross sections for neutron-rich nuclei from the fragmentation of a
82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions
of 126 neutron-rich isotopes of elements 11 <= Z <= 32 were scanned using an
experimental approach of varying the target thickness. Production cross
sections with beryllium and tungsten targets were determined for a large number
of nuclei including several isotopes first observed in this work. These are the
most neutron-rich nuclides of the elements 22 <= Z <= 25 (64Ti, 67V, 69Cr,
72Mn). One event was registered consistent with 70Cr, and another one with
75Fe. The production cross sections are correlated with Qg systematics to
reveal trends in the data. The results presented here confirm our previous
result from a similar measurement using a 76Ge beam, and can be explained with
a shell model that predicts a subshell closure at N = 34 around Z = 20. This is
demonstrated by systematic trends and calculations with the Abrasion-Ablation
model that are sensitive to separation energies.Comment: 13 pages, 11 figures, accepted to Phys.Rev.
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Active Sites Environmental Monitoring Program: Program plan
The Active Sites Environmental Monitoring Program (ASEMP), initiated in 1989, provides early detection and performance monitoring of transuranic (TRU) waste and active low-level waste (LLW) facilities at Oak Ridge National Laboratory (ORNL) in accordance with US Department of Energy (DOE) Order 5820.2A. Active LLW facilities in Solid Waste Storage Area (SWSA) 6 include Tumulus I and Tumulus II, the Interim Waste Management Facility (IWMF), LLW silos, high-range wells, asbestos silos, and fissile wells. The tumulus pads and IWMF are aboveground, high-strength concrete pads on which concrete vaults containing metal boxes of LLW are placed; the void space between the boxes and vaults is filled with grout. Eventually, these pads and vaults will be covered by an engineered multilayered cap. All other LLW facilities in SWSA 6 are below ground. In addition, this plan includes monitoring of the Hillcut Disposal Test Facility (HDTF) in SWSA 6, even though this facility was completed prior to the data of the DOE order. In SWSA 5 North, the TRU facilities include below-grade engineered caves, high-range wells, and unlined trenches. All samples from SWSA 6 are screened for alpha and beta activity, counted for gamma-emitting isotopes, and analyzed for tritium. In addition to these analytes, samples from SWSA 5 North are analyzed for specific transuranic elements
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Active Sites Environmental Monitoring Program: Mid-FY 1991 report
This report summarizes the activities of the Active Sites Environmental Monitoring Program (ASEMP) from October 1990 through March 1991. The ASEMP was established in 1989 by Solid Waste Operations and the Environmental Sciences Division to provide early detection and performance monitoring at active low-level radioactive waste (LLW) disposal sites in Solid Waste Storage Area (SWSA) 6 and transuranic (TRU) waste storage sites in SWSA 5 as required by chapters II and III of US Department of Energy Order 5820.2A. Monitoring results continue to demonstrate the no LLW is being leached from the storage vaults on the tumulus pads. Loading of vaults on Tumulus II began during this reporting period and 115 vaults had been loaded by the end of March 1991
Recommended from our members
Active Sites Environmental Monitoring Program: Program plan
DOE Order 5820.2A requires that low-level waste (LLW) disposal sites active on or after September 1988 and all transuranic (TRU) waste storage sites be monitored periodically to assure that radioactive contamination does not escape from the waste sites and pose a threat to the public or to the environment. This plan describes such a monitoring program for the active LLW disposal sites in SWSA 6 and the TRU waste storage sites in SWSA 5 North. 14 refs., 8 figs
The effect of environment on the UV colour-magnitude relation of early-type galaxies
We use \textit{GALEX} (Galaxy Evolution Explorer) near-UV (NUV) photometry of
a sample of early-type galaxies selected in \textit{SDSS} (Sloan Digital Sky
Survey) to study the UV color-magnitude relation (CMR). color is an
excellent tracer of even small amounts (% mass fraction) of recent
(\la 1 Gyr) star formation and so the CMR allows us to study the
effect of environment on the recent star formation history. We analyze a
volume-limited sample of 839 visually-inspected early-type galaxies in the
redshift range brighter than of -21.5 with any
possible emission-line or radio-selected AGN removed to avoid contamination. We
find that contamination by AGN candidates and late-type interlopers highly bias
any study of recent star formation in early-type galaxies and that, after
removing those, our lower limit to the fraction of massive early-type galaxies
showing signs of recent star formation is roughly This suggests
that residual star formation is common even amongst the present day early-type
galaxy population.
We find that the fraction of UV-bright early-type galaxies is 25% higher in
low-density environments. However, the density effect is clear only in the
lowest density bin. The blue galaxy fraction for the subsample of the brightest
early-type galaxies however shows a very strong density dependence, in the
sense that the blue galaxy fraction is lower in a higher density region.Comment: Accepted for publication in ApJ, paper with high-resolution figures
can be downloaded at:
http://www-astro.physics.ox.ac.uk/~kevins/PAPERS/uv_environment.p
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