5,050 research outputs found
Evidence for two spatially separated UV continuum emitting regions in the Cloverleaf broad absorption line quasar
Testing the standard Shakura-Sunyaev model of accretion is a challenging task
because the central region of quasars where accretion takes place is unresolved
with telescopes. The analysis of microlensing in gravitationally lensed quasars
is one of the few techniques that can test this model, yielding to the
measurement of the size and of temperature profile of the accretion disc. We
present spectroscopic observations of the gravitationally lensed broad
absorption line quasar H1413+117, which reveal partial microlensing of the
continuum emission that appears to originate from two separated regions: a
microlensed region, corresponding to the compact accretion disc; and a
non-microlensed region, more extended and contributing to at least 30\% of the
total UV-continuum flux. Because this extended continuum is occulted by the
broad absorption line clouds, it is not associated with the host galaxy, but
rather with light scattered in the neighbourhood of the central engine. We
measure the amplitude of microlensing of the compact continuum over the
rest-frame wavelength range 1000-7000 \AA. Following a Bayesian scheme, we
confront our measurements to microlensing simulations of an accretion disc with
a temperature varying as . We find a most likely source
half-light radius of cm (i.e., 0.002\,pc) at
0.18\,m, and a most-likely index of . The standard disc
() model is not ruled out by our data, and is found within the 95\%
confidence interval associated with our measurements. We demonstrate that, for
H1413+117, the existence of an extended continuum in addition to the disc
emission only has a small impact on the inferred disc parameters, and is
unlikely to solve the tension between the microlensing source size and standard
disc sizes, as previously reported in the literature.Comment: Accepted for publication in Astronomy and Astrophysics. 12 pages.
Minor changes w.r.t. v1 (language editing, Fig. 5-6
Microlensing of the broad-line region in the quadruply imaged quasar HE0435-1223
Using infrared spectra of the z = 1.693 quadruply lensed quasar HE0435-1223
acquired in 2009 with the spectrograph SINFONI at the ESO Very Large Telescope,
we have detected a clear microlensing effect in images A and D. While
microlensing affects the blue and red wings of the H{\alpha} line profile in
image D very differently, it de-magnifies the line core in image A. The
combination of these different effects sets constraints on the line-emitting
region; these constraints suggest that a rotating ring is at the origin of the
H{\alpha} line. Visible spectra obtained in 2004 and 2012 indicate that the
MgII line profile is microlensed in the same way as the H{\alpha} line. Our
results therefore favour flattened geometries for the low-ionization
line-emitting region, for example, a Keplerian disk. Biconical models cannot be
ruled out but require more fine-tuning. Flux ratios between the different
images are also derived and confirm flux anomalies with respect to estimates
from lens models with smooth mass distributions.Comment: 6 pages, 4 figures, 3 tables, accepted by A&A on 10 April 201
Electroweak bubbles and sphalerons
We consider non-perturbative solutions of the Weinberg-Salam model at finite
temperature. We employ an effective temperature-dependent potential yielding a
first order phase transition. In the region of the phase transition, there
exist two kinds of static, spherically symmetric solutions: sphalerons and
bubbles. We analyze these solutions as functions of temperature. We consider
the most general spherically symmetric fluctuations about the two solutions and
construct the discrete modes in the region of the phase transition. Sphalerons
and bubbles both possess a single unstable mode. We present simple
approximation formulae for these levels.Comment: 14 pages, plain tex, 9 figures appended as postscript files at the
end of the paper. THU-93/0
Trakhtenbrot's Theorem in Coq, A Constructive Approach to Finite Model Theory
We study finite first-order satisfiability (FSAT) in the constructive setting
of dependent type theory. Employing synthetic accounts of enumerability and
decidability, we give a full classification of FSAT depending on the
first-order signature of non-logical symbols. On the one hand, our development
focuses on Trakhtenbrot's theorem, stating that FSAT is undecidable as soon as
the signature contains an at least binary relation symbol. Our proof proceeds
by a many-one reduction chain starting from the Post correspondence problem. On
the other hand, we establish the decidability of FSAT for monadic first-order
logic, i.e. where the signature only contains at most unary function and
relation symbols, as well as the enumerability of FSAT for arbitrary enumerable
signatures. All our results are mechanised in the framework of a growing Coq
library of synthetic undecidability proofs
Sphaleron Effects Near the Critical Temperature
We discuss one-loop radiative corrections to the sphaleron-induced baryon
number-violating transition rate near the electroweak phase transition in the
standard model. We emphasize that in the case of a first-order transition a
rearrangement of the loop expansion is required close to the transition
temperature. The corresponding expansion parameter, the effective 3-dimensional
gauge coupling approaches a finite dependent value at the critical
temperature.
The
(Higgs mass) dependence of the 1-loop radiative corrections is discussed in
the framework of the heat kernel method. Radiative corrections are small
compared to the leading sphaleron contribution as long as the Higgs mass is
small compared to the W mass. To 1-loop accuracy, there is no Higgs mass range
compatible with experimental limits where washing-out of a B+L asymmetry could
be avoided for the minimal standard model with one Higgs doublet.Comment: 17 pages, RevTeX, (4 figures in a separate uuencoded file),
HD-THEP-93-23re
Sphalerons and the Electroweak Phase Transition in Models with Higher Scalar Representations
In this work we investigate the sphaleron solution in a
gauge theory, which also encompasses the Standard Model, with higher scalar
representation(s) (). We show that the field profiles
describing the sphaleron in higher scalar multiplet, have similar trends like
the doublet case with respect to the radial distance. We compute the sphaleron
energy and find that it scales linearly with the vacuum expectation value of
the scalar field and its slope depends on the representation. We also
investigate the effect of gauge field and find that it is small for the
physical value of the mixing angle, and resembles the case for the
doublet. For higher representations, we show that the criterion for strong
first order phase transition, , is relaxed with respect to
the doublet case, i.e. .Comment: 20 pages, 5 figures & 1 table, published versio
Baseline variability in onshore near surface gases and implications for monitoring at CO2 storage sites
The measurement of gas concentrations and fluxes in the soil and atmosphere is a powerful tool for monitoring geological carbon capture and storage (CCS) sites because the analyses are made directly in the biosphere in which we live. These methods can be used to both find and accurately quantifying leaks, and are visible and tangible data for public and ecosystem safety. To be most reliable and accurate, however, the measurements must be interpreted in the context of natural variations in gas concentration and flux. Such baseline data vary both spatially and temporally due to natural processes, and a clear understanding of their values and distributions is critical for interpreting near-surface gas monitoring techniques. The best example is CO2 itself, as the production of this gas via soil respiration can create a wide range of concentrations and fluxes that must be separated from, and not confused with, CO2 that may leak towards the surface from a storage reservoir. The present article summarizes baseline studies performed by the authors at various sites having different climates and geological settings from both Europe and North America, with focus given to the range of values that can result from near surface processes and how different techniques or data processing approaches can be used to help distinguish a leakage signal from an anomalous, shallow biogenic signal
Measurement of the hadronic photon structure function F_{2}^{γ} at LEP2
The hadronic structure function of the photon F_{2}^{γ} (x, Q²) is measured as a function of Bjorken x and of the photon virtuality Q² using deep-inelastic scattering data taken by the OPAL detector at LEP at e⁺e⁻ centre-of-mass energies from 183 to 209 GeV. Previous OPAL measurements of the x dependence of F_{2}^{γ} are extended to an average Q² of 〈Q²〉=780 GeV² using data in the kinematic range 0.15<x<0.98. The Q² evolution of F_{2}^{γ} is studied for 12.1<〈Q²〉<780 GeV² using three ranges of x. As predicted by QCD, the data show positive scaling violations in F_{2}^{γ} with F_{2}^{γ} (Q²)/α = (0.08±0.02⁺⁰·⁰⁵_₀.₀₃) + (0.13±0.01⁺⁰·⁰¹_₀.₀₁) lnQ², where Q² is in GeV², for the central x region 0.10–0.60. Several parameterisations of F_{2}^{γ} are in qualitative agreement with the measurements whereas the quark-parton model prediction fails to describe the data
Measurement of the charm structure function F_{2,c)^{γ} of the photon at LEP
The production of charm quarks is studied in deep-inelastic electron–photon scattering using data recorded by the OPAL detector at LEP at nominal e⁺e⁻ centre-of-mass energies from 183 to 209 GeV. The charm quarks have been identified by full reconstruction of charged D* mesons using their decays into D⁰π with the D⁰ observed in two decay modes with charged particle final states, Kπ and Kπππ. The cross-section σ^{D*} for production of charged D* in the reaction e⁺e⁻→e⁺e⁻D*Χ is measured in a restricted kinematical region using two bins in Bjorken x, 0.00140.1 the perturbative QCD calculation at next-to-leading order agrees perfectly with the measured cross-section. For x<0.1 the measured cross-section is 43.8±14.3±6.3±2.8 pb with a next-to-leading order prediction of 17.0⁺²·⁹_₂.₃ pb
Performance of a Large-Area GEM Detector Prototype for the Upgrade of the CMS Muon Endcap System
Gas Electron Multiplier (GEM) technology is being considered for the forward
muon upgrade of the CMS experiment in Phase 2 of the CERN LHC. Its first
implementation is planned for the GE1/1 system in the region of the muon endcap mainly to control muon level-1 trigger rates
after the second long LHC shutdown. A GE1/1 triple-GEM detector is read out by
3,072 radial strips with 455 rad pitch arranged in eight -sectors.
We assembled a full-size GE1/1 prototype of 1m length at Florida Tech and
tested it in 20-120 GeV hadron beams at Fermilab using Ar/CO 70:30 and
the RD51 scalable readout system. Four small GEM detectors with 2-D readout and
an average measured azimuthal resolution of 36 rad provided precise
reference tracks. Construction of this largest GEM detector built to-date is
described. Strip cluster parameters, detection efficiency, and spatial
resolution are studied with position and high voltage scans. The plateau
detection efficiency is [97.1 0.2 (stat)]\%. The azimuthal resolution is
found to be [123.5 1.6 (stat)] rad when operating in the center of
the efficiency plateau and using full pulse height information. The resolution
can be slightly improved by 10 rad when correcting for the bias due
to discrete readout strips. The CMS upgrade design calls for readout
electronics with binary hit output. When strip clusters are formed
correspondingly without charge-weighting and with fixed hit thresholds, a
position resolution of [136.8 2.5 stat] rad is measured, consistent
with the expected resolution of strip-pitch/ = 131.3 rad. Other
-sectors of the detector show similar response and performance.Comment: 8 pages, 32 figures, submitted to Proc. 2014 IEEE Nucl. Sci.
Symposium, Seattle, WA, reference adde
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