1,313 research outputs found
Search for a light dark sector particle at LHCb
A search is presented for a hidden-sector boson, , produced in the
decay , with and . The search is performed using a
-collision data sample collected at and 8 TeV with the LHCb
detector, corresponding to integrated luminosities of 1 and 2 fb
respectively. No significant signal is observed in the mass range MeV, and upper limits are placed on the branching fraction
product as a function of the mass and lifetime of the
boson. These limits place the most stringent constraints to date on many
theories that predict the existence of additional low-mass dark bosons.Comment: Presentation at the DPF 2015 Meeting of the American Physical Society
Division of Particles and Fields, Ann Arbor, Michigan, August 4-8, 201
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
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
A Hybrid Monte Carlo Ant Colony Optimization Approach for Protein Structure Prediction in the HP Model
The hydrophobic-polar (HP) model has been widely studied in the field of
protein structure prediction (PSP) both for theoretical purposes and as a
benchmark for new optimization strategies. In this work we introduce a new
heuristics based on Ant Colony Optimization (ACO) and Markov Chain Monte Carlo
(MCMC) that we called Hybrid Monte Carlo Ant Colony Optimization (HMCACO). We
describe this method and compare results obtained on well known HP instances in
the 3 dimensional cubic lattice to those obtained with standard ACO and
Simulated Annealing (SA). All methods were implemented using an unconstrained
neighborhood and a modified objective function to prevent the creation of
overlapping walks. Results show that our methods perform better than the other
heuristics in all benchmark instances.Comment: In Proceedings Wivace 2013, arXiv:1309.712
Towards establishing Lepton Flavour Universality violation in decays
Rare semileptonic transitions provide some of the
most promising frameworks to search for new physics effects. Recent analyses of
these decays have indicated an anomalous behaviour in measurements of angular
distributions of the decay and
lepton-flavour-universality observables. Unambiguously establishing if these
deviations have a common nature is of paramount importance in order to
understand the observed pattern. We propose a novel approach to independently
and complementary probe this hypothesis by performing a simultaneous amplitude
analysis of and decays. This method enables the direct determination of
observables that encode potential non-equal couplings of muons and electrons,
and are found to be insensitive to nonperturbative QCD effects. If current
hints of new physics are confirmed, our approach could allow an early discovery
of physics beyond the standard model with LHCb run II data sets.Comment: 6 pages, 7 figures. Matching the journal versio
New BPS Wilson loops in circular quiver Chern-Simons-matter theories
We construct new families of 1/4 BPS Wilson loops in circular quiver
superconformal Chern-Simons-matter (SCSM) theories in three
dimensions. They are defined as the holonomy of superconnections that contain
non-trivial couplings to scalar and fermions, and cannot be reduced to
block-diagonal matrices. Consequently, the new operators cannot be written in
terms of double-node Wilson loops, as the ones considered so far in the
literature. For particular values of the couplings the superconnection becomes
block-diagonal and we recover the known fermionic 1/4 and 1/2 BPS Wilson loops.
The new operators are cohomologically equivalent to bosonic 1/4 BPS Wilson
loops and are then amenable of exact evaluation via localization techniques.
Moreover, in the case of orbifold ABJM theory we identify the corresponding
gravity duals for some of the 1/4 and 1/2 BPS Wilson loops.Comment: 32 pages; v2: minor improvements, general classification of BPS WLs
added; v3: comments added, typos fixed, JHEP published versio
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