Extraction of Airways with Probabilistic State-space Models and Bayesian Smoothing

Segmenting tree structures is common in several image processing applications. In medical image analysis, reliable segmentations of airways, vessels, neurons and other tree structures can enable important clinical applications. We present a framework for tracking tree structures comprising of elongated branches using probabilistic state-space models and Bayesian smoothing. Unlike most existing methods that proceed with sequential tracking of branches, we present an exploratory method, that is less sensitive to local anomalies in the data due to acquisition noise and/or interfering structures. The evolution of individual branches is modelled using a process model and the observed data is incorporated into the update step of the Bayesian smoother using a measurement model that is based on a multi-scale blob detector. Bayesian smoothing is performed using the RTS (Rauch-Tung-Striebel) smoother, which provides Gaussian density estimates of branch states at each tracking step. We select likely branch seed points automatically based on the response of the blob detection and track from all such seed points using the RTS smoother. We use covariance of the marginal posterior density estimated for each branch to discriminate false positive and true positive branches. The method is evaluated on 3D chest CT scans to track airways. We show that the presented method results in additional branches compared to a baseline method based on region growing on probability images.Comment: 10 pages. Pre-print of the paper accepted at Workshop on Graphs in Biomedical Image Analysis. MICCAI 2017. Quebec Cit

Tracking Target Signal Strengths on a Grid using Sparsity

Multi-target tracking is mainly challenged by the nonlinearity present in the measurement equation, and the difficulty in fast and accurate data association. To overcome these challenges, the present paper introduces a grid-based model in which the state captures target signal strengths on a known spatial grid (TSSG). This model leads to \emph{linear} state and measurement equations, which bypass data association and can afford state estimation via sparsity-aware Kalman filtering (KF). Leveraging the grid-induced sparsity of the novel model, two types of sparsity-cognizant TSSG-KF trackers are developed: one effects sparsity through $\ell_1$-norm regularization, and the other invokes sparsity as an extra measurement. Iterative extended KF and Gauss-Newton algorithms are developed for reduced-complexity tracking, along with accurate error covariance updates for assessing performance of the resultant sparsity-aware state estimators. Based on TSSG state estimates, more informative target position and track estimates can be obtained in a follow-up step, ensuring that track association and position estimation errors do not propagate back into TSSG state estimates. The novel TSSG trackers do not require knowing the number of targets or their signal strengths, and exhibit considerably lower complexity than the benchmark hidden Markov model filter, especially for a large number of targets. Numerical simulations demonstrate that sparsity-cognizant trackers enjoy improved root mean-square error performance at reduced complexity when compared to their sparsity-agnostic counterparts.Comment: Submitted to IEEE Trans. on Signal Processin

Chiral-invariant CP-violating Effective Interactions in Z Decays to three Jets

Tests of CP violation by appropriate momentum correlations in $Z\to 3$ jets and in particular in $Z\to b\bar bX$ probe CP-violating effective couplings -- that manifest themselves as form factors -- which conserve the quark chirality and quark flavour. By giving two examples we show that such couplings can be induced at one-loop order in extensions of the Standard Model with CP violation beyond the Kobayashi-Maskawa phase. In one of the models we compute the chirality-conserving part of the CP-violating $Zb{\bar b}$-gluon amplitude for massless $b$ quarks, determine the resulting effective dimension $d=6$ couplings in the local limit, and discuss the possible size of the effects. Finally we show that in models with excited quarks the chiral-invariant CP-violating effective interactions could be quite large if appropriate couplings are of a size characteristic of a strong interactionComment: 14 pages, LaTeX with 4 postscript figures, epsf macro include

Implications of a W^+W^- (ZZ) - Higgs - t c-bar$ Interaction for e^+e^- -> t c-bar \nu_e \nu_e-bar, t c-bar e^+ e^-, t c-bar Z and for t -> cW^+W^-, cZZ in a Two Higgs Doublet Model

The Standard Model with one extra Higgs doublet may give rise to enhanced TREE-LEVEL flavor-changing-scalar coupling of a neutral Higgs to a pair of top-charm quarks. This coupling may drive a large TREE-LEVEL effective W^+W^-(ZZ) - Higgs - t c-bar interaction. As a result we find that the reactions e^+e^- -> t c-bar \nu_e \nu_e-bar, t c-bar e^+ e^-, t c-bar Z and the two rare top decays t -> cW^+W^-, t -> cZZ become very sensitive probes of such an effective interaction. The most promising ones, e^+e^- -> t c-bar \nu_e \nu_e-bar, t c-bar e^+ e^-, may yield several hundreds and up to thousands of such events at the Next Linear Collider with a center of mass energy of \sqrt{s}=0.5 - 2 TeV if the mass of the lightest neutral Higgs is a few hundred GeV. The rare decays t -> cW^+W^- and t -> cZZ may be accessible at the LHC if the mass of the lightest neutral Higgs lies in the narrow window 150 GeV < m_h < 200 GeV.Comment: 18 pages, plain latex, 12 figures embadded in the text using epsfi

Frequency Tracking and Parameter Estimation for Robust Quantum State-Estimation

In this paper we consider the problem of tracking the state of a quantum system via a continuous measurement. If the system Hamiltonian is known precisely, this merely requires integrating the appropriate stochastic master equation. However, even a small error in the assumed Hamiltonian can render this approach useless. The natural answer to this problem is to include the parameters of the Hamiltonian as part of the estimation problem, and the full Bayesian solution to this task provides a state-estimate that is robust against uncertainties. However, this approach requires considerable computational overhead. Here we consider a single qubit in which the Hamiltonian contains a single unknown parameter. We show that classical frequency estimation techniques greatly reduce the computational overhead associated with Bayesian estimation and provide accurate estimates for the qubit frequencyComment: 6 figures, 13 page

Flavor changing Z-decays from scalar interactions at a Giga-Z Linear Collider

The flavor changing decay Z -> d_I \bar{d}_J is investigated with special emphasis on the b \bar{s} final state. Various models for flavor violation are considered: two Higgs doublet models (2HDM's), supersymmetry (SUSY) with flavor violation in the up and down-type squark mass matrices and SUSY with flavor violation mediated by R-parity-violating interaction. We find that, within the SUSY scenarios for flavor violation, the branching ratio for the decay Z -> b \bar{s} can reach 10^{-6} for large \tan\beta values, while the typical size for this branching ratio in the 2HDM's considered is about two orders of magnitudes smaller at best. Thus, flavor changing SUSY signatures in radiative Z decays such as Z -> b \bar{s} may be accessible to future ``Z factories'' such as a Giga-Z version of the TESLA design.Comment: 27 pages, 15 figures, REVTeX4. A new section added and a few minor corrections were made in the tex

Flavourful Production at Hadron Colliders

We ask what new states may lie at or below the TeV scale, with sizable flavour-dependent couplings to light quarks, putting them within reach of hadron colliders via resonant production, or in association with Standard Model states. In particular, we focus on the compatibility of such states with stringent flavour-changing neutral current and electric-dipole moment constraints. We argue that the broadest and most theoretically plausible flavour structure of the new couplings is that they are hierarchical, as are Standard Model Yukawa couplings, although the hierarchical pattern may well be different. We point out that, without the need for any more elaborate or restrictive structure, new scalars with "diquark" couplings to standard quarks are particularly immune to existing constraints, and that such scalars may arise within a variety of theoretical paradigms. In particular, there can be substantial couplings to a pair of light quarks or to one light and one heavy quark. For example, the latter possibility may provide a flavour-safe interpretation of the asymmetry in top quark production observed at the Tevatron. We thereby motivate searches for diquark scalars at the Tevatron and LHC, and argue that their discovery represents one of our best chances for new insight into the Flavour Puzzle of the Standard Model.Comment: 18 pp., 8 figures, references adde

Flavor changing scalar couplings and tγ(Z)t\gamma(Z) production at hadron colliders

We calculate the contributions of the flavor changing scalar ($FCS$) couplings arised from topcolor-assisted technicolor ($TC2$) models at tree-level to the $t\gamma$ and $tZ$ production at the Tevatron and $LHC$ experiments. We find that the production cross sections are very small at the Tevatron with $\sqrt{s}=1.96TeV$, which is smaller than 5 fb in most of the parameter space of $TC2$ models. However, the virtual effects of the $FCS$ couplings on the $t\gamma(Z)$ production can be easily detected at the $LHC$ with $\sqrt{s}=14TeV$ via the final state $\gamma l\bar{\nu}b$ ($l^{+}l^{-}l\bar{\nu}b$).Comment: 10 pages,5 figure

Top-Charm Associated Production in High Energy e+e−e^+e^- Collisions

The possibility of exploring the flavor changing neutral current $tcZ/tc\gamma$ couplings in the production vertex for the reaction \epem\to t\bar c + \bar tc is examined. Using a model independent parameterization for the effective Lagrangian to describe the most general three-point interactions, production cross sections are found to be relatively small at LEP II, but potentially sizeable at higher energy \epem colliders. The kinematic characteristics of the signal are studied and a set of cuts are devised for clean separation of the signal from background. The resulting sensitivity to anomalous flavor changing couplings at LEP II with an integrated luminosity of $4\times 500$ pb$^{-1}$ is found to be comparable to their present indirect constraints from loop processes, while at higher energy colliders with $0.5-1$ TeV center-of-mass energy and 50-200 fb$^{-1}$ luminosity, one expects to reach a sensitivity at or below the percentage level.Comment: Latex, 22 page