4,790 research outputs found
Vector unparticle contributions to lepton g-2
The generic unparticle propagator may be modified in two ways. Breaking the
conformal symmetry effectively adds a mass term to the propagator, while
considering vacuum polarization corrections adds a width-like term. Both of
these modifications result naturally from the coupling of the unparticle to
standard model (SM) fields. We explore how these modifications to the
propagator affect the calculation of the lepton anomalous magnetic moment using
an integral approximation of the propagator that is accurate for
, where is the unparticle dimension. We find that for this
range of and various values of the conformal breaking scale , the
value of calculated when allowing various SM fermions to run in the
unparticle self-energy loops does not significantly deviate from the value of
when the width term is ignored. We also investigate the limits on a
characteristic mass scale for the unparticle sector as a function of and
.Comment: 16 pages, 11 figures, 2 tables. Included neutrinos in loops. Added
reference
Supernova Constraints and Systematic Uncertainties from the First Three Years of the Supernova Legacy Survey
We combine high-redshift Type Ia supernovae from the first three years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-z, 93 SDSS, 242 SNLS, and 14 Hubble Space Telescope). SN data alone require cosmic acceleration at >99.999% confidence, including systematic effects. For the dark energy equation of state parameter (assumed constant out to at least z = 1.4) in a flat universe, we find w = –0.91^(+0.16)_(–0.20)(stat)^(+0.07)_(–0.14)(sys) from SNe only, consistent with a cosmological constant. Our fits include a correction for the recently discovered relationship between host-galaxy mass and SN absolute brightness. We pay particular attention to systematic uncertainties, characterizing them using a systematic covariance matrix that incorporates the redshift dependence of these effects, as well as the shape-luminosity and color-luminosity relationships. Unlike previous work, we include the effects of systematic terms on the empirical light-curve models. The total systematic uncertainty is dominated by calibration terms. We describe how the systematic uncertainties can be reduced with soon to be available improved nearby and intermediate-redshift samples, particularly those calibrated onto USNO/SDSS-like systems
Is there Evidence for a Hubble bubble? The Nature of Type Ia Supernova Colors and Dust in External Galaxies
We examine recent evidence from the luminosity-redshift relation of Type Ia
Supernovae (SNe Ia) for the detection of a ``Hubble bubble'' --
a departure of the local value of the Hubble constant from its globally
averaged value \citep{Jha:07}. By comparing the MLCS2k2 fits used in that study
to the results from other light-curve fitters applied to the same data, we
demonstrate that this is related to the interpretation of SN color excesses
(after correction for a light-curve shape-color relation) and the presence of a
color gradient across the local sample. If the slope of the linear relation
() between SN color excess and luminosity is fit empirically, then the
bubble disappears. If, on the other hand, the color excess arises purely from
Milky Way-like dust, then SN data clearly favors a Hubble bubble. We
demonstrate that SN data give , instead of the
one would expect from purely Milky-Way-like dust. This suggests that either SN
intrinsic colors are more complicated than can be described with a single
light-curve shape parameter, or that dust around SN is unusual. Disentangling
these possibilities is both a challenge and an opportunity for large-survey SN
Ia cosmology.Comment: Further information and data at
http://qold.astro.utoronto.ca/conley/bubble/ Accepted for publication in ApJ
Measuring a Light Neutralino Mass at the ILC: Testing the MSSM Neutralino Cold Dark Matter Model
The LEP experiments give a lower bound on the neutralino mass of about 46 GeV
which, however, relies on a supersymmetric grand unification relation. Dropping
this assumption, the experimental lower bound on the neutralino mass vanishes
completely. Recent analyses suggest, however, that in the minimal
supersymmetric standard model (MSSM), a light neutralino dark matter candidate
has a lower bound on its mass of about 7 GeV. In light of this, we investigate
the mass sensitivity at the ILC for very light neutralinos. We study slepton
pair production, followed by the decay of the sleptons to a lepton and the
lightest neutralino. We find that the mass measurement accuracy for a few-GeV
neutralino is around 2 GeV, or even less if the relevant slepton is
sufficiently light. We thus conclude that the ILC can help verify or falsify
the MSSM neutralino cold dark matter model even for very light neutralinos.Comment: 7 pages, 1 figure; references adde
Evaluating Cropland N2O Emissions and Fertilizer Plant Greenhouse Gas Emissions With Airborne Observations
Agricultural activity is a significant source of greenhouse gas emissions. The fertilizer production process emits N2O, CO2, and CH4, and fertilized croplands emit N2O. We present continuous airborne observations of these trace gases in the Lower Mississippi River Basin to quantify emissions from both fertilizer plants and croplands during the early growing season. Observed hourly emission rates from two fertilizer plants are compared with reported inventory values, showing agreement for N2O and CO2 emissions but large underestimation in reported CH4 emissions by up to a factor of 100. These CH4 emissions are consistent with loss rates of 0.6–1.2%. We quantify regional emission fluxes (100 km) of N2O using the airborne mass balance technique, a first application for N2O, and explore linkages to controlling processes. Finally, we demonstrate the ability to use airborne measurements to distinguish N2O emission differences between neighboring fields, determining we can distinguish different emission behaviors of regions on the order of 2.5 km2 with emissions differences of approximately 0.026 μmol m−2 s−1. This suggests airborne approaches such as outlined here could be used to evaluate the impact of different agricultural practices at critical field‐size spatial scales.Key PointsReported N2O and CO2 emissions from fertilizer plants agree with observations, but CH4 is underestimated by orders of magnitudeWe demonstrate mass balance quantification of N2O emissions from agriculture at 10–100 km scalesAirborne measurements can observe and quantify N2O emission differences between agricultural fields of ∼2.5 km2Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156438/3/jgrd56401.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156438/2/jgrd5640-sup-0001-Figure_SI-S01.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156438/1/jgrd56401_am.pd
Supersymmetry Without Prejudice at the 7 TeV LHC
We investigate the model independent nature of the Supersymmetry search
strategies at the 7 TeV LHC. To this end, we study the
missing-transverse-energy-based searches developed by the ATLAS Collaboration
that were essentially designed for mSUGRA. We simulate the signals for ~71k
models in the 19-dimensional parameter space of the pMSSM. These models have
been found to satisfy existing experimental and theoretical constraints and
provide insight into general features of the MSSM without reference to a
particular SUSY breaking scenario or any other assumptions at the GUT scale.
Using backgrounds generated by ATLAS, we find that imprecise knowledge of these
estimated backgrounds is a limiting factor in the potential discovery of these
models and that some channels become systematics-limited at larger
luminosities. As this systematic error is varied between 20-100%, roughly half
to 90% of this model sample is observable with significance S>5 for 1 fb^{-1}
of integrated luminosity. We then examine the model characteristics for the
cases which cannot be discovered and find several contributing factors. We find
that a blanket statement that squarks and gluinos are excluded with masses
below a specific value cannot be made. We next explore possible modifications
to the kinematic cuts in these analyses that may improve the pMSSM model
coverage. Lastly, we examine the implications of a null search at the 7 TeV LHC
in terms of the degree of fine-tuning that would be present in this model set
and for sparticle production at the 500 GeV and 1 TeV Linear Collider.Comment: 51 pages, 26 figure
Constraining Type Ia Supernovae progenitors from three years of SNLS data
While it is generally accepted that Type Ia supernovae are the result of the
explosion of a carbon-oxygen White Dwarf accreting mass in a binary system, the
details of their genesis still elude us, and the nature of the binary companion
is uncertain. Kasen (2010) points out that the presence of a non-degenerate
companion in the progenitor system could leave an observable trace: a flux
excess in the early rise portion of the lightcurve caused by the ejecta impact
with the companion itself. This excess would be observable only under favorable
viewing angles, and its intensity depends on the nature of the companion. We
searched for the signature of a non-degenerate companion in three years of
Supernova Legacy Survey data by generating synthetic lightcurves accounting for
the effects of shocking and comparing true and synthetic time series with
Kolmogorov-Smirnov tests. Our most constraining result comes from noting that
the shocking effect is more prominent in rest-frame B than V band: we rule out
a contribution from white dwarf-red giant binary systems to Type Ia supernova
explosions greater than 10% at 2 sigma, and than 20% at 3 sigma level.Comment: 14 pages, 15 figures, resubmitted to ApJ, figure 15 modifie
Real-time Analysis and Selection Biases in the Supernova Legacy Survey
The Supernova Legacy Survey (SNLS) has produced a high-quality, homogeneous
sample of Type Ia supernovae (SNe Ia) out to redshifts greater than z=1. In its
first four years of full operation (to June 2007), the SNLS discovered more
than 3000 transient candidates, 373 of which have been confirmed
spectroscopically as SNe Ia. Use of these SNe Ia in precision cosmology
critically depends on an analysis of the observational biases incurred in the
SNLS survey due to the incomplete sampling of the underlying SN Ia population.
This paper describes our real-time supernova detection and analysis procedures,
and uses detailed Monte Carlo simulations to examine the effects of Malmquist
bias and spectroscopic sampling. Such sampling effects are found to become
apparent at z~0.6, with a significant shift in the average magnitude of the
spectroscopically confirmed SN Ia sample towards brighter values for z>0.75. We
describe our approach to correct for these selection biases in our three-year
SNLS cosmological analysis (SNLS3), and present a breakdown of the systematic
uncertainties involved.Comment: Accepted for publication in A
Recommended from our members
Application of Gauss's theorem to quantify localized surface emissions from airborne measurements of wind and trace gases
Airborne estimates of greenhouse gas emissions are becoming more
prevalent with the advent of rapid commercial development of trace gas
instrumentation featuring increased measurement accuracy, precision, and
frequency, and the swelling interest in the verification of current emission
inventories. Multiple airborne studies have indicated that emission
inventories may underestimate some hydrocarbon emission sources in US oil-
and gas-producing basins. Consequently, a proper assessment of the accuracy
of these airborne methods is crucial to interpreting the meaning of such
discrepancies. We present a new method of sampling surface sources of any
trace gas for which fast and precise measurements can be made and apply it to
methane, ethane, and carbon dioxide on spatial scales of ∼ 1000 m,
where consecutive loops are flown around a targeted source region at
multiple altitudes. Using Reynolds decomposition for the scalar
concentrations, along with Gauss's theorem, we show that the method
accurately accounts for the smaller-scale turbulent dispersion of the local
plume, which is often ignored in other average mass balance methods. With
the help of large eddy simulations (LES) we further show how the circling
radius can be optimized for the micrometeorological conditions encountered
during any flight. Furthermore, by sampling controlled releases of methane
and ethane on the ground we can ascertain that the accuracy of the method, in
appropriate meteorological conditions, is often better than 10 %, with
limits of detection below 5 kg h−1 for both methane and ethane. Because of the FAA-mandated minimum flight safe altitude of 150 m, placement of the aircraft is critical to preventing a large portion of the emission plume from flowing underneath the lowest aircraft sampling altitude, which is generally the leading source of uncertainty in these measurements. Finally, we show how the accuracy of the method is strongly dependent on the number of sampling loops and/or time spent sampling the source plume
Cosmology in massive gravity
We argue that more cosmological solutions in massive gravity can be obtained
if the metric tensor and the tensor defined by
St\"{u}ckelberg fields take the homogeneous and isotropic form. The standard
cosmology with matter and radiation dominations in the past can be recovered
and CDM model is easily obtained. The dynamical evolution of the
universe is modified at very early times.Comment: 4 pages, 1 figure,add more reference
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