164 research outputs found
The fully differential single-top-quark cross section in next-to-leading order QCD
We present a new next-to-leading order calculation for fully differential
single-top-quark final states. The calculation is performed using phase space
slicing and dipole subtraction methods. The results of the methods are found to
be in agreement. The dipole subtraction method calculation retains the full
spin dependence of the final state particles. We show a few numerical results
to illustrate the utility and consistency of the resulting computer
implementations.Comment: 37 pages, latex, 2 ps figure
Topological and geometrical restrictions, free-boundary problems and self-gravitating fluids
Let (P1) be certain elliptic free-boundary problem on a Riemannian manifold
(M,g). In this paper we study the restrictions on the topology and geometry of
the fibres (the level sets) of the solutions f to (P1). We give a technique
based on certain remarkable property of the fibres (the analytic representation
property) for going from the initial PDE to a global analytical
characterization of the fibres (the equilibrium partition condition). We study
this analytical characterization and obtain several topological and geometrical
properties that the fibres of the solutions must possess, depending on the
topology of M and the metric tensor g. We apply these results to the classical
problem in physics of classifying the equilibrium shapes of both Newtonian and
relativistic static self-gravitating fluids. We also suggest a relationship
with the isometries of a Riemannian manifold.Comment: 36 pages. In this new version the analytic representation hypothesis
is proved. Please address all correspondence to D. Peralta-Sala
Single Top Production as a Window to Physics Beyond the Standard Model
Production of single top quarks at a high energy hadron collider is studied
as a means to identify physics beyond the standard model related to the
electroweak symmetry breaking. The sensitivity of the -channel mode,
the -channel -gluon fusion mode, and the \tw mode to various possible
forms of new physics is assessed, and it is found that the three modes are
sensitive to different forms of new physics, indicating that they provide
complimentary information about the properties of the top quark. Polarization
observables are also considered, and found to provide potentially useful
information about the structure of the interactions of top.Comment: References added and minor discussion improvements; results
unchanged; Version to be published in PR
The Kuiper Belt and Other Debris Disks
We discuss the current knowledge of the Solar system, focusing on bodies in
the outer regions, on the information they provide concerning Solar system
formation, and on the possible relationships that may exist between our system
and the debris disks of other stars. Beyond the domains of the Terrestrial and
giant planets, the comets in the Kuiper belt and the Oort cloud preserve some
of our most pristine materials. The Kuiper belt, in particular, is a
collisional dust source and a scientific bridge to the dusty "debris disks"
observed around many nearby main-sequence stars. Study of the Solar system
provides a level of detail that we cannot discern in the distant disks while
observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book
"Astrophysics in the Next Decade
Thermal desorption of CH4 retained in CO2 ice
CO2 ices are known to exist in different astrophysical environments. In spite
of this, its physical properties (structure, density, refractive index) have
not been as widely studied as those of water ice. It would be of great value to
study the adsorption properties of this ice in conditions related to
astrophysical environments. In this paper, we explore the possibility that CO2
traps relevant molecules in astrophysical environments at temperatures higher
than expected from their characteristic sublimation point. To fulfil this aim
we have carried out desorption experiments under High Vacuum conditions based
on a Quartz Crystal Microbalance and additionally monitored with a Quadrupole
Mass Spectrometer. From our results, the presence of CH4 in the solid phase
above the sublimation temperature in some astrophysical scenarios could be
explained by the presence of several retaining mechanisms related to the
structure of CO2 ice.Comment: 8 pages, accepted for publication in Astrophysics & Space Scienc
Refining and regaining skills in fixation/diversification stage performers: The Five-A Model
Technical change is one of many factors underpinning success in elite, fixation/diversification stage performers. Surprisingly, however, there is a dearth of research pertaining to this process or the most efficacious methods used to bring about such a change. In this paper we highlight the emergent processes, yet also the lack in mechanistic comprehension surrounding technical change, addressing issues within the motor control, sport psychology, coaching and choking literature. More importantly, we seek an understanding of how these changes can be made more secure to competitive pressure, and how this can be embedded within the process of technical change. Following this review, we propose The Five-A Model based on successful coaching techniques, psychosocial concomitants, the avoidance of choking and principles of effective behaviour change. Specific mechanisms for each stage are discussed, with a focus on the use of holistic rhythm-based cues as a possible way of internalising changes. Finally, we suggest the need for further research to examine these five stages, to aid a more comprehensive construction of the content and delivery of such a programme within the applied setting
A Theory for the High-T_c Cuprates: Anomalous Normal-State and Spectroscopic Properties, Phase Diagram, and Pairing
A theory of highly correlated layered superconducting materials isapplied for
the cuprates. Differently from an independent-electron approximation, their
low-energy excitations are approached in terms of auxiliary particles
representing combinations of atomic-like electron configurations, where the
introduction of a Lagrange Bose field enables treating them as bosons or
fermions. The energy spectrum of this field accounts for the tendency of
hole-doped cuprates to form stripe-like inhomogeneities. Consequently, it
induces a different analytical behavior for auxiliary particles corresponding
to "antinodal" and "nodal" electrons, enabling the existence of different
pairing temperatures at T^* and T_c. This theory correctly describes the
observed phase diagram of the cuprates, including the non-Fermi-liquid to FL
crossover in the normal state, the existence of Fermi arcs below T^* and of a
"marginal-FL" critical behavior above it. The qualitative anomalous behavior of
numerous physical quantities is accounted for, including kink- and
waterfall-like spectral features, the drop in the scattering rates below T^*
and more radically below T_c, and an effective increase in the density of
carriers with T and \omega, reflected in transport, optical and other
properties. Also is explained the correspondence between T_c, the
resonance-mode energy, and the "nodal gap".Comment: 28 pages, 7 figure
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