4,608 research outputs found
Two-Loop Ultrasoft Running of the O(v^2) QCD Quark Potentials
The two-loop ultrasoft contributions to the next-to-leading logarithmic (NLL)
running of the QCD potentials at order v^2 are determined. The results
represent an important step towards the next-to-next-to-leading logarithmic
(NNLL) description of heavy quark pair production and annihilation close to
threshold.Comment: 13 pages, 3 figures; typos corrected, reference added, information on
cross checks added on page 7; acknowledgments adde
Two-Loop Massive Quark Jet Functions in SCET
We calculate the corrections to the primary massive
quark jet functions in Soft-Collinear Effective Theory (SCET). They are an
important ingredient in factorized predictions for inclusive jet mass cross
sections initiated by massive quarks emerging from a hard interaction with
smooth quark mass dependence. Due to the effects coming from the secondary
production of massive quark-antiquark pairs there are two options to define the
SCET jet function, which we call universal and mass mode jet functions. They
are related to whether or not a soft mass mode (zero) bin subtraction is
applied for the secondary massive quark contributions and differ in particular
concerning the infrared behavior for vanishing quark mass. We advocate that a
useful alternative to the common zero-bin subtraction concept is to define the
SCET jet functions through subtractions related to collinear-soft matrix
elements. This avoids the need to impose additional power counting arguments as
required for zero-bin subtractions. We demonstrate how the two SCET jet
function definitions may be used in the context of two recently developed
factorization approaches to treat secondary massive quark effects. We clarify
the relation between these approaches and in which way they are equivalent. Our
two-loop calculation involves interesting technical subtleties related to
spurious rapidity divergences and infrared regularization in the presence of
massive quarks.Comment: 51 pages + appendices, 8 figures, v2: journal versio
Rethinking CMB foregrounds: systematic extension of foreground parameterizations
Future high-sensitivity measurements of the cosmic microwave background (CMB)
anisotropies and energy spectrum will be limited by our understanding and
modeling of foregrounds. Not only does more information need to be gathered and
combined, but also novel approaches for the modeling of foregrounds,
commensurate with the vast improvements in sensitivity, have to be explored.
Here, we study the inevitable effects of spatial averaging on the spectral
shapes of typical foreground components, introducing a moment approach, which
naturally extends the list of foreground parameters that have to be determined
through measurements or constrained by theoretical models. Foregrounds are
thought of as a superposition of individual emitting volume elements along the
line of sight and across the sky, which then are observed through an
instrumental beam. The beam and line of sight averages are inevitable. Instead
of assuming a specific model for the distributions of physical parameters, our
method identifies natural new spectral shapes for each foreground component
that can be used to extract parameter moments (e.g., mean, dispersion,
cross-terms, etc.). The method is illustrated for the superposition of
power-laws, free-free spectra, gray-body and modified blackbody spectra, but
can be applied to more complicated fundamental spectral energy distributions.
Here, we focus on intensity signals but the method can be extended to the case
of polarized emission. The averaging process automatically produces
scale-dependent spectral shapes and the moment method can be used to propagate
the required information across scales in power spectrum estimates. The
approach is not limited to applications to CMB foregrounds but could also be
useful for the modeling of X-ray emission in clusters of galaxies.Comment: 19 pages, 8 figures, accepted by MNRAS, minor revision
Coherent Cancellation of Backaction Noise in optomechanical Force Measurements
Optomechanical detectors have reached the standard quantum limit in position
and force sensing where measurement backaction noise starts to be the limiting
factor for the sensitivity. A strategy to circumvent measurement backaction,
and surpass the standard quantum limit, has been suggested by M. Tsang and C.
Caves in Phys. Rev. Lett. 105 123601 (2010). We provide a detailed analysis of
this method and assess its benefits, requirements, and limitations. We conclude
that a proof-of-principle demonstration based on a micro-optomechanical system
is demanding, but possible. However, for parameters relevant to gravitational
wave detectors the requirements for backaction evasion appear to be
prohibitive.Comment: 9 pages, 6 figure
Quantum Transport through Nanostructures with Orbital Degeneracies
Geometric symmetries cause orbital degeneracies in a molecule's spectrum. In
a single-molecule junction, these degeneracies are lifted by various
symmetry-breaking effects. We study quantum transport through such
nanostructures with an almost degenerate spectrum. We show that the master
equation for the reduced density matrix must be derived within the
singular-coupling limit as opposed to the conventional weak-coupling limit.
This results in signatures of the density matrix's off-diagonal elements in the
transport characteristics
Prospects for Measuring Cosmic Microwave Background Spectral Distortions in the Presence of Foregrounds
Measurements of cosmic microwave background spectral distortions have
profound implications for our understanding of physical processes taking place
over a vast window in cosmological history. Foreground contamination is
unavoidable in such measurements and detailed signal-foreground separation will
be necessary to extract cosmological science. We present MCMC-based spectral
distortion detection forecasts in the presence of Galactic and extragalactic
foregrounds for a range of possible experimental configurations, focusing on
the Primordial Inflation Explorer (PIXIE) as a fiducial concept. We consider
modifications to the baseline PIXIE mission (operating 12 months in distortion
mode), searching for optimal configurations using a Fisher approach. Using only
spectral information, we forecast an extended PIXIE mission to detect the
expected average non-relativistic and relativistic thermal Sunyaev-Zeldovich
distortions at high significance (194 and 11, respectively),
even in the presence of foregrounds. The CDM Silk damping -type
distortion is not detected without additional modifications of the instrument
or external data. Galactic synchrotron radiation is the most problematic source
of contamination in this respect, an issue that could be mitigated by combining
PIXIE data with future ground-based observations at low frequencies (GHz). Assuming moderate external information on the synchrotron spectrum,
we project an upper limit of (95\% c.l.), slightly
more than one order of magnitude above the fiducial CDM signal from
the damping of small-scale primordial fluctuations, but a factor of improvement over the current upper limit from COBE/FIRAS. This limit could
be further reduced to (95\% c.l.) with more
optimistic assumptions about low-frequency information. (Abridged)Comment: (16 pages, 11 figures, submitted to MNRAS. Fisher code available at
https://github.com/mabitbol/sd_foregrounds. Updated with published version.
Recommended from our members
Studying the Effects of Galactic and Extragalactic Foregrounds on Cosmic Microwave Background Observations
Cosmic microwave background observations have been fundamental in forming the standard model of cosmology. Ongoing and upcoming cosmic microwave background experiments aim to confirm this model and push the boundaries of our knowledge to the very first moments of the Universe. Non-cosmological microwave radiation from the Galaxy and beyond, called foregrounds, obscures and contaminates these measurements. Understanding the sources and effects of foregrounds and removing their imprint in cosmic microwave background observations is a major obstacle to making cosmological inferences. This thesis contains my work studying these foregrounds. First, I will present observations of a well-known but poorly understood foreground called anomalous microwave emission. Second, I will present results forecasting the capability of a next-generation satellite experiment to detect cosmic microwave background spectral distortions in the presence of foregrounds. Third, I will present results studying the effect of foregrounds on the cosmic microwave background self-calibration method, which allows experiments to calibrate the telescope polarization angle using the cosmic microwave background itself. Fourth, I will present my analysis characterizing the performance of and producing maps for the E and B Experiment. Fifth, I will present my research contributions to the readout system that used in the laboratory to operate kinetic inductance detectors, which are being developed for cosmic microwave background observations. Lastly, I will conclude with future prospects in the field of foregrounds and cosmic microwave background cosmology
Utilizing weak pump depletion to stabilize squeezed vacuum states
We propose and demonstrate a pump-phase locking technique that makes use of
weak pump depletion (WPD) - an unavoidable effect that is usually neglected -
in a sub-threshold optical parametric oscillator (OPO). We show that the phase
difference between seed and pump beam is imprinted on both light fields by the
non-linear interaction in the crystal and can be read out without disturbing
the squeezed output. Our new locking technique allows for the first
experimental realization of a pump-phase lock by reading out the pre-existing
phase information in the pump field. There is no degradation of the detected
squeezed states required to implement this scheme.Comment: 11 pages, 7 figure
Constraining the Anomalous Microwave Emission Mechanism in the S140 Star Forming Region with Spectroscopic Observations Between 4 and 8 GHz at the Green Bank Telescope
Anomalous microwave emission (AME) is a category of Galactic signals that
cannot be explained by synchrotron radiation, thermal dust emission, or
optically thin free-free radiation. Spinning dust is one variety of AME that
could be partially polarized and therefore relevant for ongoing and future
cosmic microwave background polarization studies. The Planck satellite mission
identified candidate AME regions in approximately patches that were
found to have spectra generally consistent with spinning dust grain models. The
spectra for one of these regions, G107.2+5.2, was also consistent with
optically thick free-free emission because of a lack of measurements between 2
and 20 GHz. Follow-up observations were needed. Therefore, we used the C-band
receiver (4 to 8 GHz) and the VEGAS spectrometer at the Green Bank Telescope to
constrain the AME mechanism. For the study described in this paper, we produced
three band averaged maps at 4.575, 5.625, and 6.125 GHz and used aperture
photometry to measure the spectral flux density in the region relative to the
background. We found if the spinning dust description is correct, then the
spinning dust signal peaks at GHz, and it explains the excess
emission. The morphology and spectrum together suggest the spinning dust grains
are concentrated near S140, which is a star forming region inside our chosen
photometry aperture. If the AME is sourced by optically thick free-free
radiation, then the region would have to contain HII with an emission measure
of and a physical extent of
. This result suggests the HII
would have to be ultra or hyper compact to remain an AME candidate.Comment: 21 pages, 14 figures. Submitted to Ap
Rat Monoclonal Antibodies Specific for LST1 Proteins
The LST1 gene is located in the human MHC class III region and encodes transmembrane and soluble isoforms that have been suggested to play a role in the regulation of the immune response and are associated with inflammatory diseases such as rheumatoid arthritis. Here we describe the generation and characterization of the first monoclonal antibodies against LST1. Two hybridoma lines secreting monoclonal antibodies designated 7E2 and 8D12 were established. The 7E2 antibody detects recombinant and endogenous LST1 by Western blot analysis while 8D12 reacts with recombinant and endogenous LST1 in immunoprecipitation and flow cytometry procedures. The newly established antibodies were used to survey LST1 protein expression in human cell lines, which was found to be tightly regulated, allowing the expression of transmembrane isoforms but suppressing soluble isoforms
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