8,111 research outputs found
Rare FCNC top, beauty and charm decays
Rare flavour changing neutral current (FCNC) decays of top, beauty and charm
quarks can provide a powerful probe for as yet unobserved particles. Recent
results on FCNC , and transitions from the LHC
experiments are reviewed. Particular attention is paid to the angular
distribution of the decay, where a
measurement performed by LHCb shows a local discrepancy of 3.7 standard
deviations with respect to the SM prediction. Using the decay , LHCb have also been able to demonstrate the
polarisation of photons produced in transitions. More work is
needed both experimentally and theoretically to understand if the Standard
Model description of these rare FCNC processes is correct.Comment: Proceedings for LHCP 2014 conferenc
Electroweak penguin decays at LHCb
Promising ways to search for New Physics effects in radiative penguin decays
are in the angular analysis of , in
the measurement of direct CP violation in \B_{d} \rightarrow
K^{*0}\mu^{+}\mu^{-} and a time dependent analysis of . All of these studies are being pursued at LHCb. First results will be
shown from the 2010 and early 2011 data, with particular emphasis on .Comment: Proceedings of the DPF-2011 Conferenc
Chord Diagrams and Gauss Codes for Graphs
Chord diagrams on circles and their intersection graphs (also known as circle
graphs) have been intensively studied, and have many applications to the study
of knots and knot invariants, among others. However, chord diagrams on more
general graphs have not been studied, and are potentially equally valuable in
the study of spatial graphs. We will define chord diagrams for planar
embeddings of planar graphs and their intersection graphs, and prove some basic
results. Then, as an application, we will introduce Gauss codes for immersions
of graphs in the plane and give algorithms to determine whether a particular
crossing sequence is realizable as the Gauss code of an immersed graph.Comment: 20 pages, many figures. This version has been substantially
rewritten, and the results are stronge
Performance Analysis of Spectral Clustering on Compressed, Incomplete and Inaccurate Measurements
Spectral clustering is one of the most widely used techniques for extracting
the underlying global structure of a data set. Compressed sensing and matrix
completion have emerged as prevailing methods for efficiently recovering sparse
and partially observed signals respectively. We combine the distance preserving
measurements of compressed sensing and matrix completion with the power of
robust spectral clustering. Our analysis provides rigorous bounds on how small
errors in the affinity matrix can affect the spectral coordinates and
clusterability. This work generalizes the current perturbation results of
two-class spectral clustering to incorporate multi-class clustering with k
eigenvectors. We thoroughly track how small perturbation from using compressed
sensing and matrix completion affect the affinity matrix and in succession the
spectral coordinates. These perturbation results for multi-class clustering
require an eigengap between the kth and (k+1)th eigenvalues of the affinity
matrix, which naturally occurs in data with k well-defined clusters. Our
theoretical guarantees are complemented with numerical results along with a
number of examples of the unsupervised organization and clustering of image
data
An Introduction to Virtual Spatial Graph Theory
Two natural generalizations of knot theory are the study of spatial graphs
and virtual knots. Our goal is to unify these two approaches into the study of
virtual spatial graphs. This paper is a survey, and does not contain any new
results. We state the definitions, provide some examples, and survey the known
results. We hope that this paper will help lead to rapid development of the
area.Comment: 9 pages, 7 figures, presented at the International Workshop on Knot
Theory for Scientific Objects at Osaka City University, March 200
Angular distribution of polarised baryons decaying to
Rare flavour-changing-neutral-current processes provide
important tests of the Standard Model of particle physics. Angular observables
in exclusive processes can be particularly powerful as
they allow hadronic uncertainties to be controlled. Amongst the exclusive
processes that have been studied by experiments, the decay is unique in that the baryon can be produced
polarised. In this paper, we derive an expression for the angular distribution
of the decay for the case where the
baryon is produced polarised. This extends the number of angular
observables in this decay from 10 to 34. Standard Model expectations for the
new observables are provided and the sensitivity of the observables is explored
under a variety of new physics models. At low-hadronic recoil, four of the new
observables have a new short distance dependence that is absent in the
unpolarised case. The remaining observables depend on the same short distance
contributions as the unpolarised observables, but with different dependence on
hadronic form-factors. These relations provide possibilities for novel tests of
the SM that could be carried out with the data that will become available at
the LHC or a future collider
A tidally interacting disk in the young triple system WL 20?
We present high-resolution λ = 2.7 mm imaging of the close triple pre-main-sequence system WL 20. Compact dust emission with integrated flux density of 12.9 ± 1.3 mJy is associated with two components of the triple system, WL 20W and WL 20S. No emission above a 3 σ level of 3.9 mJy is detected toward the third component, WL 20E, which lies 3."17 (400 AU) due east in projection from its neighbors. A possibly warped structure of ~0.1 M_☉ and ≤3."2 extent encompasses WL 20W and WL 20S, which have a projected separation of 2."25 (~280 AU) along a north-south axis. This structure is most likely a tidally disrupted disk surrounding WL 20S. New near-infrared spectra of the individual components show a remarkable similarity between the two T Tauri stars of the system: WL 20E has a K7 spectral type (T_eff = 4040 K) with r_K = 0.2, and WL 20W has an M0 spectral type (T_eff = 3800 K) with r_K = 0.2. The spectrum of WL 20S is consistent with that of a source intrinsically similar to WL 20W, with r_K < 0.9, but seen through an A_V = 25 in addition to the A_V = 16.3 to the system as a whole. Taken together, these millimeter and infrared data help explain the peculiar nature of the infrared companion, WL 20S, as resulting from a large enhancement in its dusty, circumstellar environment in relation to its companions
Intrinsic Linking and Knotting in Virtual Spatial Graphs
We introduce a notion of intrinsic linking and knotting for virtual spatial
graphs. Our theory gives two filtrations of the set of all graphs, allowing us
to measure, in a sense, how intrinsically linked or knotted a graph is; we show
that these filtrations are descending and non-terminating. We also provide
several examples of intrinsically virtually linked and knotted graphs. As a
byproduct, we introduce the {\it virtual unknotting number} of a knot, and show
that any knot with non-trivial Jones polynomial has virtual unknotting number
at least 2.Comment: 13 pages, 13 figure
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