7,331 research outputs found
Spectra of Nearby Galaxies Measured with a New Very Broadband Receiver
Three-millimeter-wavelength spectra of a number of nearby galaxies have been
obtained at the Five College Radio Astronomy Observatory (FCRAO) using a new,
very broadband receiver. This instrument, which we call the Redshift Search
Receiver, has an instantaneous bandwidth of 36 GHz and operates from 74 to
110.5 GHz. The receiver has been built at UMass/FCRAO to be part of the initial
instrumentation for the Large Millimeter Telescope (LMT) and is intended
primarily for determination of the redshift of distant, dust-obscured galaxies.
It is being tested on the FCRAO 14m by measuring the 3mm spectra of a number of
nearby galaxies. There are interesting differences in the chemistry of these
galaxies.Comment: published in the Proceedings of the International Astronomical Union
(2008), 4. Vol 251, pp 251-256 Cambridge University Pres
Reconstructing the primordial power spectrum - a new algorithm
We propose an efficient and model independent method for reconstructing the
primordial power spectrum from Cosmic Microwave Background (CMB) and large
scale structure observations. The algorithm is based on a Monte Carlo principle
and therefore very simple to incorporate into existing codes such as Markov
Chain Monte Carlo. The algorithm has been used on present cosmological data to
test for features in the primordial power spectrum. No significant evidence for
features is found, although there is a slight preference for an overall bending
of the spectrum, as well as a decrease in power at very large scales. We have
also tested the algorithm on mock high precision CMB data, calculated from
models with non-scale invariant primordial spectra. The algorithm efficiently
extracts the underlying spectrum, as well as the other cosmological parameters
in each case. Finally we have used the algorithm on a model where an artificial
glitch in the CMB spectrum has been imposed, like the ones seen in the WMAP
data. In this case it is found that, although the underlying cosmological
parameters can be extracted, the recovered power spectrum can show significant
spurious features, such as bending, even if the true spectrum is scale
invariant.Comment: 22 pages, 12 figures, matches JCAP published versio
Supercollider Signatures of Supergravity Models with Yukawa Unification
We study the predictions of the simplest SU(5) grand unified model within the
framework of minimal supergravity, including constraints from the radiative
breaking of electroweak symmetry. As a consequence of the unification of the
-quark and -lepton Yukawa couplings, the top quark mass is predicted
to be close to its fixed point value. We delineate the regions of the
supergravity parameter space allowed by constraints from the non-observation of
proton decay and from the requirement that the LSP does not overclose the
universe. These constraints lead to a definite pattern of sparticle masses: the
feature unique to Yukawa unified models is that some of the third generation
squarks are much lighter than those of the first two generations. Despite the
fact that all sparticle masses and mixings are determined by just four SUSY
parameters at the GUT scale (in addition to ), we find that the signals
for sparticle production can vary substantially over the allowed parameter
space. We identify six representative scenarios and study the signals from
sparticle production at the LHC. We find that by studying the signal in various
channels, these scenarios may be distinguished from one another, and also from
usually studied ``minimal models'' where squarks and sleptons are taken to be
degenerate. In particular, our studies allow us to infer that some third
generation squarks are lighter than other squarks---a feature that could
provide the first direct evidence of supergravity grand unification.Comment: 28 pages Revtex files with 5 PS figures available from
[email protected], Preprint nos. FSU-HEP-940311, KEK-TH-392,
MAD/PH/825, UH-511-785-9
Detecting Higgs Boson Decay to Neutralinos at Hadron Supercolliders
We examine prospects for detecting the neutral Higgs bosons of minimal
supersymmetric models (MSSM) when their decays into neutralino pairs are
kinematically allowed. The best signature appears to be
H_h,H_p\to\tz_2\tz_2\to 4\ell +\eslt. We argue that Standard Model
contributions to this signature are negligible, and examine regions of MSSM
parameter space where the four lepton mode should be observable at the Large
Hadron Collider. The same signal can also come from continuum neutralino pair
production. We propose a set of cuts to illustrate that the neutralino decay
mode of the Higgs bosons provides a viable signal over a substantial range of
model parameters, and show that it may be separable from continuum neutralino
production if sufficient integrated luminosity can be accumulated.Comment: 15 pages (REVTEX), 7 figures available by regular mail,
FSU-HEP-940204, UH-511-781-9
The Combined Effect of Air Layers and Membrane Superhydrophobicity on Biofouling in Membrane Distillation
Previous studies of membrane distillation (MD) have shown that superhydrophobic membranes experience dramatically less inorganic and particulate fouling. However, little explanation for this improved performance has been given in the literature. Furthermore, studies comparing membrane superhydrophobicity and biofouling are lacking, though superhydrophobic surfaces are known to be more vulnerable to biofouling than other types. In non-membrane surfaces, visible air layers on superhydrophobic surfaces have been correlated with
significant decreases in biofouling. Therefore, it was proposed here to use superhydrophobic MD membranes with periodic introduction of air to maintain an air layer on the membrane surface. Superhydrophobic membranes were created with initiated chemical vapor deposition (iCVD) of a fluorinated compound, perfluorodecyl acrylate (PFDA). The substrate membrane was PVDF. To test MD fouling, an MD membrane was placed on top of a fouling solution, with a heater and stirrer to caus
e evaporation of water through the membrane. Results were analyzed with foulant mass measurements. Alginate gel fouling was examined, as this compound is a common proxy for biological fouling in ocean w
ater. The introduction of air layers was found to dramatically decrease foulant adhesion to the membrane, by 95-97%. Membrane superhydrophobicity made a much smaller impact in reducing fouling.
Keywords
membrane distillation, superhydrophobic surfaces, alginate, air layers, anti-foulin
Point-Form Analysis of Elastic Deuteron Form Factors
Point-form relativistic quantum mechanics is applied to elastic
electron-deuteron scattering. The deuteron is modeled using relativistic
interactions that are scattering-equivalent to the nonrelativistic Argonne
and Reid '93 interactions. A point-form spectator approximation (PFSA)
is introduced to define a conserved covariant current in terms of
single-nucleon form factors. The PFSA is shown to provide an accurate
description of data up to momentum transfers of 0.5 , but falls
below the data at higher momentum transfers. Results are sensitive to the
nucleon form factor parameterization chosen, particularly to the neutron
electric form factor.Comment: RevTex, 31 pages, 1 table, 13 figure
Holographic bounds on the UV cutoff scale in inflationary cosmology
We discuss how holographic bounds can be applied to the quantum fluctuations
of the inflaton. In general the holographic principle will lead to a bound on
the UV cutoff scale of the effective theory of inflation, but it will depend on
the coarse-graining prescription involved in calculating the entropy. We
propose that the entanglement entropy is a natural measure of the entropy of
the quantum perturbations, and show which kind of bound on the cutoff it leads
to. Such bounds are related to whether the effects of new physics will show up
in the CMB.Comment: 19 pages, 2 figures;(V3):Comments and references adde
Phenomenological Implications of Deflected Mirage Mediation: Comparison with Mirage Mediation
We compare the collider phenomenology of mirage mediation and deflected
mirage mediation, which are two recently proposed "mixed" supersymmetry
breaking scenarios motivated from string compactifications. The scenarios
differ in that deflected mirage mediation includes contributions from gauge
mediation in addition to the contributions from gravity mediation and anomaly
mediation also present in mirage mediation. The threshold effects from gauge
mediation can drastically alter the low energy spectrum from that of pure
mirage mediation models, resulting in some cases in a squeezed gaugino spectrum
and a gluino that is much lighter than other colored superpartners. We provide
several benchmark deflected mirage mediation models and construct model lines
as a function of the gauge mediation contributions, and discuss their discovery
potential at the LHC.Comment: 29 pages, 9 figure
Trilepton Signature of Minimal Supergravity at the Upgraded Tevatron
The prospects for detecting trilepton events ( or ) from
chargino-neutralino () associated production are
investigated for the upgraded Fermilab Tevatron Collider in the context of the
minimal supergravity model (mSUGRA). In some regions of parameter space,
and decay dominantly into final states with
leptons and the contributions from leptonic decays enhance the trilepton
signal substantially when soft cuts on lepton transverse momenta are used.
Additional sources of the mSUGRA trilepton signal and dominant irreducible
backgrounds are discussed. The dilepton () invariant mass
distribution near the endpoint is considered as a test of mSUGRA mass
relations. Discovery contours for at 2 TeV with an
integrated luminosity of 2 fb to 30 fb are presented in the
mSUGRA parameter space of for several choices of .Comment: Version to appear in Physical Review
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