2,540 research outputs found
ABJM -Bremsstrahlung at four loops and beyond
In ABJ(M) theory a generalized cusp can be constructed out of the 1/6 BPS
Wilson line by introducing an angle in the spacial contour and/or an
angle in the internal R-symmetry space. The small angles limits of its
anomalous dimension are controlled by corresponding Bremsstrahlung functions.
In this note we compute the internal space -Bremsstrahlung function to
four loops at weak coupling in the planar limit. Based on this result, we
propose an all order conjecture for the -Bremsstrahlung function.Comment: 40 pages; v2: references added, JHEP published extended versio
ABJM -Bremsstrahlung at four loops and beyond: non-planar corrections
We consider the Bremsstrahlung function associated to a 1/6-BPS Wilson loop
in ABJM theory, with a cusp in the couplings to scalar fields. We non-trivially
extend its recent four-loop computation at weak coupling to include non-planar
corrections. We have recently proposed a conjecture relating this object to
supersymmetric circular Wilson loops with multiple windings, which can be
computed via localization. We find agreement between this proposal and the
perturbative computation of the Bremsstrahlung function, including color
sub-leading corrections. This supports the conjecture and hints at its validity
beyond the planar approximation.Comment: 22 page
Correlation Clustering with Adaptive Similarity Queries
In correlation clustering, we are given objects together with a binary
similarity score between each pair of them. The goal is to partition the
objects into clusters so to minimise the disagreements with the scores. In this
work we investigate correlation clustering as an active learning problem: each
similarity score can be learned by making a query, and the goal is to minimise
both the disagreements and the total number of queries. On the one hand, we
describe simple active learning algorithms, which provably achieve an almost
optimal trade-off while giving cluster recovery guarantees, and we test them on
different datasets. On the other hand, we prove information-theoretical bounds
on the number of queries necessary to guarantee a prescribed disagreement
bound. These results give a rich characterization of the trade-off between
queries and clustering error
A matrix model for the latitude Wilson loop in ABJM theory
In ABJ(M) theory, we propose a matrix model for the exact evaluation of BPS
Wilson loops on a latitude circular contour, so providing a new weak-strong
interpolation tool. Intriguingly, the matrix model turns out to be a particular
case of that computing torus knot invariants in Chern-Simons
theory. At weak coupling we check our proposal against a three-loop
computation, performed for generic framing, winding number and representation.
The matrix model is amenable of a Fermi gas formulation, which we use to
systematically compute the strong coupling and genus expansions. For the
fermionic Wilson loop the leading planar behavior agrees with a previous string
theory prediction. For the bosonic operator our result provides a clue for
finding the corresponding string dual configuration. Our matrix model is
consistent with recent proposals for computing Bremsstrahlung functions exactly
in terms of latitude Wilson loops. As a by-product, we extend the conjecture
for the exact Bremsstrahlung function to generic
representations and test it with a four-loop perturbative computation. Finally,
we propose an exact prediction for at unequal gauge group ranks.Comment: 73 pages; v2: several improvements, JHEP published versio
The soft X-ray polarization in obscured AGN
The soft X-ray emission in obscured active galactic nuclei (AGN) is dominated
by emission lines, produced in a gas photoionized by the nuclear continuum and
likely spatially coincident with the optical narrow line region (NLR). However,
a fraction of the observed soft X-ray flux appears like a featureless power law
continuum. If the continuum underlying the soft X-ray emission lines is due to
Thomson scattering of the nuclear radiation, it should be very highly
polarized. We calculated the expected amount of polarization assuming a simple
conical geometry for the NLR, combining these results with the observed
fraction of the reflected continuum in bright obscured AGN.Comment: 6 pages, 3 figures, to appear in 'X-ray Polarimetry: A New Window in
Astrophysics', edited by R. Bellazzini, E. Costa, G. Matt and G. Tagliaferr
False negativity to carbohydrate-deficient transferrin and drugs: a clinical case
Introduction: In this work we report on the possible effect of the medical therapy on CDT concentration in a chronic alcohol abuser, with known medical history (July 2007 – April 2012) and alcohol abuse confirmed by relatives.
Case history: At the end of 2007, patient displayed the following laboratory results: AST 137 U/L, ALT 120 U/L, GGT 434 U/L, MCV 101 fL and CDT 3.3%. On December 2007, after double coronary artery bypass surgery, he began a pharmacological treatment with amlodipine, perindopril, atorvastatin, isosorbide mononitrate, carvedilol, ticlopidine and pantoprazole. In the next months, until may 2011, the patient resumed alcohol abuse, as confirmed by relatives; however, CDT values were repeatedly found negative (0.8% and 1.1%) despite elevated transaminases and GGT, concurrent elevated ethyl glucuronide concentration (> 50 mg/L) and blood alcohol concentration (> 1 g/L). Alcohol consumption still continued despite increasing disulfiram doses ordered by an Alcohol Rehab Center. On May 2011, the patient was transferred to a private medical center where he currently lives.
Conclusions: This study suggests the possibility that a medical therapy including different drugs may hamper the identification of chronic alcohol abusers by CDT
The quantum 1/2 BPS Wilson loop in Chern-Simons-matter theories
In three dimensional Chern-Simons-matter theories two
independent fermionic Wilson loop operators can be defined, which preserve half
of the supersymmetry charges and are cohomologically equivalent at classical
level. We compute their three-loop expectation value in a convenient color
sector and prove that the degeneracy is uplifted by quantum corrections. We
expand the matrix model prediction in the same regime and by comparison we
conclude that the quantum 1/2 BPS Wilson loop is the average of the two
operators. We provide an all-loop argument to support this claim at any order.
As a by-product, we identify the localization result at three loops as a
correction to the framing factor induced by matter interactions. Finally, we
comment on the quantum properties of the non-1/2 BPS Wilson loop operator
defined as the difference of the two fermionic ones.Comment: 22 pages + appendixes, 4 figures, 1 Tabl
Towards the exact Bremsstrahlung function of ABJM theory
We present the three-loop calculation of the Bremsstrahlung function
associated to the 1/2-BPS cusp in ABJM theory, including color subleading
corrections. Using the BPS condition we reduce the computation to that of a
cusp with vanishing angle. We work within the framework of heavy quark
effective theory (HQET) that further simplifies the analytic evaluation of the
relevant cusp anomalous dimension in the near-BPS limit. The result passes
nontrivial tests, such as exponentiation, and is in agreement with the
conjecture made in [1] for the exact expression of the Bremsstrahlung function,
based on the relation with fermionic latitude Wilson loops.Comment: 46 pages, 15 figure
Epigenetic and posttranslational modifications in light signal transduction and the circadian clock in Neurospora crassa
Blue light, a key abiotic signal, regulates a wide variety of physiological processes in many organisms. One of these phenomena is the circadian rhythm presents in organisms sensitive to the phase-setting effects of blue light and under control of the daily alternation of light and dark. Circadian clocks consist of autoregulatory alternating negative and positive feedback loops intimately connected with the cellular metabolism and biochemical processes. Neurospora crassa provides an excellent model for studying the molecular mechanisms involved in these phenomena. The White Collar Complex (WCC), a blue-light receptor and transcription factor of the circadian oscillator, and Frequency (FRQ), the circadian clock pacemaker, are at the core of the Neurospora circadian system. The eukaryotic circadian clock relies on transcriptional/translational feedback loops: some proteins rhythmically repress their own synthesis by inhibiting the activity of their transcriptional factors, generating self-sustained oscillations over a period of about 24 h. One of the basic mechanisms that perpetuate self-sustained oscillations is post translation modification (PTM). The acronym PTM generically indicates the addition of acetyl, methyl, sumoyl, or phosphoric groups to various types of proteins. The protein can be regulatory or enzymatic or a component of the chromatin. PTMs influence protein stability, interaction, localization, activity, and chromatin packaging. Chromatin modification and PTMs have been implicated in regulating circadian clock function in Neurospora. Research into the epigenetic control of transcription factors such as WCC has yielded new insights into the temporal modulation of light-dependent gene transcription. Here we report on epigenetic and protein PTMs in the regulation of the Neurospora crassa circadian clock. We also present a model that illustrates the molecular mechanisms at the basis of the blue light control of the circadian clock
Correlation Clustering with Adaptive Similarity Queries
In correlation clustering, we are given n objects together with a binary similarity
score between each pair of them. The goal is to partition the objects into clusters
so to minimise the disagreements with the scores. In this work we investigate
correlation clustering as an active learning problem: each similarity score can be
learned by making a query, and the goal is to minimise both the disagreements
and the total number of queries. On the one hand, we describe simple active
learning algorithms, which provably achieve an almost optimal trade-off while
giving cluster recovery guarantees, and we test them on different datasets. On the
other hand, we prove information-theoretical bounds on the number of queries
necessary to guarantee a prescribed disagreement bound. These results give a rich
characterization of the trade-off between queries and clustering erro
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