Understanding single-top-quark production and jets at hadron colliders

I present an analysis of fully differential single-top-quark production plus jets at next-to-leading order. I describe the effects of jet definitions, top-quark mass, and higher orders on the shapes and normalizations of the kinematic distributions, and quantify all theoretical uncertainties. I explain how to interpret next-to-leading-order jet calculations, and compare them to showering event generators. Using the program ZTOP, I show that HERWIG and PYTHIA significantly underestimate both s-channel and t-channel single-top-quark production, and propose a scheme to match the relevant samples to the next-to-leading-order predictions.Comment: 40 pgs., revtex4, 35 ps figs; added Fig. 4, 1 Ref., minor clarifications, to appear in Phys. Rev.

An Integrated Framework for Team Formation and Winner Prediction in the FIRST Robotics Competition: Model, Algorithm, and Analysis

This research work aims to develop an analytical approach for optimizing team formation and predicting team performance in a competitive environment based on data on the competitors' skills prior to the team formation. There are several approaches in scientific literature to optimize and predict a team's performance. However, most studies employ fine-grained skill statistics of the individual members or constraints such as teams with a set group of members. Currently, no research tackles the highly constrained domain of the FIRST Robotics Competition. This research effort aims to fill this gap by providing an analytical method for optimizing and predicting team performance in a competitive environment while allowing these constraints and only using metrics on previous team performance, not on each individual member's performance. We apply our method to the drafting process of the FIRST Robotics competition, a domain in which the skills change year-over-year, team members change throughout the season, each match only has a superficial set of statistics, and alliance formation is key to competitive success. First, we develop a method that could extrapolate individual members' performance based on overall team performance. An alliance optimization algorithm is developed to optimize team formation and a deep neural network model is trained to predict the winning team, both using highly post-processed real-world data. Our method is able to successfully extract individual members' metrics from overall team statistics, form competitive teams, and predict the winning team with 84.08% accuracy

Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058-5234

We present the analysis of a total of 177h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058-5234. The bulk of the observations (135h) were obtained during a WET campaign (XCOV15) in July 1997 that featured coordinated observing from 4 southern observatory sites over an 8-day period. The remaining data (42h) were obtained in June 2004 at Mt John Observatory in NZ over a one-week observing period. This work significantly extends the discovery observations of this low-amplitude (few percent) pulsator by increasing the number of detected frequencies from 8 to 18, and employs a simulation procedure to confirm the reality of these frequencies to a high level of significance (1 in 1000). The nature of the observed pulsation spectrum precludes identification of unique pulsation mode properties using any clearly discernable trends. However, we have used a global modelling procedure employing genetic algorithm techniques to identify the n, l values of 8 pulsation modes, and thereby obtain asteroseismic measurements of several model parameters, including the stellar mass (0.55 M_sun) and T_eff (~28200 K). These values are consistent with those derived from published spectral fitting: T_eff ~ 28400 K and log g ~ 7.86. We also present persuasive evidence from apparent rotational mode splitting for two of the modes that indicates this compact object is a relatively rapid rotator with a period of 2h. In direct analogy with the corresponding properties of the hydrogen (DAV) atmosphere pulsators, the stable low-amplitude pulsation behaviour of EC 20058 is entirely consistent with its inferred effective temperature, which indicates it is close to the blue edge of the DBV instability strip. (abridged)Comment: 19 pages, 8 figures, 5 tables, MNRAS accepte

Large Scale Electronic Structure Calculations with Multigrid Acceleration

We have developed a set of techniques for performing large scale ab initio calculations using multigrid accelerations and a real-space grid as a basis. The multigrid methods permit efficient calculations on ill-conditioned systems with long length scales or high energy cutoffs. The technique has been applied to systems containing up to 100 atoms, including a highly elongated diamond cell, an isolated C$_{60}$ molecule, and a 32-atom cell of GaN with the Ga d-states in valence. The method is well suited for implementation on both vector and massively parallel architectures.Comment: 4 pages, 1 postscript figur

GRBs as Cosmological Probes - Cosmic Chemical Evolution

Long-duration gamma-ray bursts (GRBs) are associated with the death of metal-poor massive stars. Even though they are highly transient events very hard to localize, they are so bright that they can be detected in the most difficult environments. GRB observations are unveiling a surprising view of the chemical state of the distant universe (redshifts z > 2). Contrary to what is expected for a high-z metal-poor star, the neutral interstellar medium (ISM) around GRBs is not metal poor (metallicities vary from ~1/10 solar at z = 6.3 to about solar at z = 2) and is enriched with dust (90-99% of iron is in solid form). If these metallicities are combined with those measured in the warm ISM of GRB host galaxies at z < 1, a redshift evolution is observed. Such an evolution predicts that the stellar masses of the hosts are in the range M* = 10^(8.6-9.8) Msun. This prediction makes use of the mass-metallicity relation (and its redshift evolution) observed in normal star-forming galaxies. Independent measurements coming from the optical-NIR photometry of GRB hosts indicate the same range of stellar masses, with a typical value similar to that of the Large Magellanic Cloud. This newly detected population of intermediate-mass galaxies is very hard to find at high redshift using conventional astronomy. However, it offers a compelling and relatively inexpensive opportunity to explore galaxy formation and cosmic chemical evolution beyond known borders, from the primordial universe to the present.Comment: Review article to be published in New Journal of Physics (http://www.njp.org), Focus Issue on Gamma Ray Burst

New Relations and Constraints on Quark Spin-flavor Contents in Symmetry-breaking Chiral Quark Model

New relations between the quark spin-flavor contents of the nucleon and axial weak coupling constants are obtained in the chiral quark model with both SU(3) and U(1)-breaking effects. Using the nonsinglet spin combinations, $\Delta_3$ and $\Delta_8$, all spin-flavor observables are functions of only one parameter $a$ $-$ probability for the chiral pionic fluctuation. The upper and lower bounds of these observables are given. The optimal range of $a$, determined by NMC data $\bar d-\bar u$, gives a constraint to the cutoff of the chiral quark field theory. The model predictions are in good agreement with the existing data in this range of $a$. The roles of kaon, $\eta$ and $\eta'$ are also discussed.Comment: 20 pages, Revtex, 3 tables, 4 figure

Osteology of the alvarezsauroid Linhenykus monodactylus from the Upper Cretaceous Wulansuhai Formation of Inner Mongolia, China, and comments on alvarezsauroid biogeography

published_or_final_versio

Search for very high energy gamma-rays from WIMP annihilations near the Sun with the Milagro Detector

The neutralino, the lightest stable supersymmetric particle, is a strong theoretical candidate for the missing astronomical ``dark matter''. A profusion of such neutralinos can accumulate near the Sun when they lose energy upon scattering and are gravitationally captured. Pair-annihilations of those neutralinos may produce very high energy (VHE, above $100 GeV$) gamma-rays. Milagro is an air shower array which uses the water Cherenkov technique to detect extensive air showers and is capable of observing VHE gamma-rays from the direction of the Sun with an angular resolution of $0.75^{\circ}$. Analysis of Milagro data with an exposure to the Sun of 1165 hours presents the first attempt to detect TeV gamma-rays produced by annihilating neutralinos captured by the Solar system and shows no statistically significant signal. Resulting limits that can be set on gamma-ray flux due to near-Solar neutralino annihilations and on neutralino cross-section are presented

Tautness for riemannian foliations on non-compact manifolds

For a riemannian foliation $\mathcal{F}$ on a closed manifold $M$, it is known that $\mathcal{F}$ is taut (i.e. the leaves are minimal submanifolds) if and only if the (tautness) class defined by the mean curvature form $\kappa_\mu$ (relatively to a suitable riemannian metric $\mu$) is zero. In the transversally orientable case, tautness is equivalent to the non-vanishing of the top basic cohomology group $H^{^{n}}(M/\mathcal{F})$, where n = \codim \mathcal{F}. By the Poincar\'e Duality, this last condition is equivalent to the non-vanishing of the basic twisted cohomology group $H^{^{0}}_{_{\kappa_\mu}}(M/\mathcal{F})$, when $M$ is oriented. When $M$ is not compact, the tautness class is not even defined in general. In this work, we recover the previous study and results for a particular case of riemannian foliations on non compact manifolds: the regular part of a singular riemannian foliation on a compact manifold (CERF).Comment: 18 page