1,480 research outputs found
Towards Realistic String Vacua From Branes At Singularities
We report on progress towards constructing string models incorporating both
realistic D-brane matter content and moduli stabilisation with dynamical
low-scale supersymmetry breaking. The general framework is that of local
D-brane models embedded into the LARGE volume approach to moduli stabilisation.
We review quiver theories on del Pezzo () singularities including
both D3 and D7 branes. We provide supersymmetric examples with three
quark/lepton families and the gauge symmetries of the Standard, Left-Right
Symmetric, Pati-Salam and Trinification models, without unwanted chiral
exotics. We describe how the singularity structure leads to family symmetries
governing the Yukawa couplings which may give mass hierarchies among the
different generations. We outline how these models can be embedded into compact
Calabi-Yau compactifications with LARGE volume moduli stabilisation, and state
the minimal conditions for this to be possible. We study the general structure
of soft supersymmetry breaking. At the singularity all leading order
contributions to the soft terms (both gravity- and anomaly-mediation) vanish.
We enumerate subleading contributions and estimate their magnitude. We also
describe model-independent physical implications of this scenario. These
include the masses of anomalous and non-anomalous U(1)'s and the generic
existence of a new hyperweak force under which leptons and/or quarks could be
charged. We propose that such a gauge boson could be responsible for the ghost
muon anomaly recently found at the Tevatron's CDF detector.Comment: 40 pages, 10 figure
Scale Dependence of Twist-3 Quark-Gluon Operators for Single Spin Asymmetries
We derive the scale dependence of twist-3 quark-gluon operators, or ETQS
matrix elements, at one-loop. These operators are used to factorize transverse
single spin asymmetries, which are studied intensively both in experiment and
theory. The scale dependence of two special cases are particularly interesting.
One is of soft-gluon-pole matrix elements, another is of soft-quark-pole matrix
elements. From our results the evolutions in the two cases can be obtained. A
comparison with existing results of soft-gluon-pole matrix elements is made.Comment: typo in Eq.(10) corrected, references adde
Limitations and challenges of EIT-based monitoring of stroke volume and pulmonary artery pressure.
Electrical impedance tomography (EIT) shows potential for radiation-free and noninvasive hemodynamic monitoring. However, many factors degrade the accuracy and repeatability of these measurements. Our goal is to estimate the impact of this variability on the EIT-based monitoring of two important central hemodynamic parameters: stroke volume (SV) and pulmonary artery pressure (PAP).
We performed simulations on a 4D ([Formula: see text]) bioimpedance model of a human volunteer to study the influence of four potential confounding factors (electrode belt displacement, electrode detachment, changes in hematocrit and lung air volume) on the performance of EIT-based SV and PAP estimation. Results were used to estimate how these factors affect the EIT measures of either absolute values or relative changes (i.e. trending).
Our findings reveal that the absolute measurement of SV via EIT is very sensitive to electrode belt displacements and lung conductivity changes. Nonetheless, the trending ability of SV EIT might be a promising alternative. The timing-based measurement of PAP is more robust to lung conductivity changes but sensitive to longitudinal belt displacements at severe hypertensive levels and to rotational displacements (independent of the PAP level).
We identify and quantify the challenges of EIT-based SV and PAP monitoring. Absolute SV via EIT is challenging, but trending is feasible, while both the absolute and trending of PAP via EIT are mostly impaired by belt displacements
Transverse Momentum Dependent Light-Cone Wave Function of B-Meson and Relation to the Momentum Integrated One
A direct generalization of the transverse momentum integrated(TMI) light-cone
wave function to define a transverse momentum dependent(TMD) light-cone wave
function will cause light-cone singularities and they spoil TMD factorization.
We motivate a definition in which the light-cone singularities are regularized
with non-light like Wilson lines. The defined TMD light-cone wave function has
some interesting relations to the corresponding TMI one. When the transverse
momentum is very large, the TMD light-cone wave function is determined
perturbatively in term of the TMI one. In the impact -space with a small
, the TMD light-cone wave function can be factorized in terms of the TMI
one. In this letter we study these relations. By-products of our study are the
renormalization evolution of the TMI light-cone wave function and the
Collins-Soper equation of the TMD light-cone wave function, the later will be
useful for resumming Sudakov logarithms.Comment: Minor change in text, 7 pages, two figure
Resummation of Large Logarithms in
In the collinear factorization of the form factor for the transition
the hard part contains double log terms as with as the momentum fraction of partons from 0 to 1. A simple
exponentiation for resummation leads to divergent results. We study the
resummation of these terms. We show that the terms come
partly from the light-cone wave function(LCWF) and partly from the form factor.
We introduce a jet factor to factorize the term in the form factor.
To handel the terms from the LCWF we introduce a nonstandard
light-cone wave function(NLCWF) with the gauge links off the light-cone
direction. An interesting relation between two wave function is found. With the
introduced NLCWF and the jet factor we can re-factorize the form factor and
obtain a new hard part which does not contain terms with . Beside the
renormalization scale the introduce NLCWF and jet factor have extra
scales to characterize their -behaviors. Using the evolutions of the extra
scales and the relation we can do the resummation perturbatively in sense that
the LCWF is the only nonpertubative object in the resumed formula. Our results
with some models of LCWF show that there is a significant difference between
numerical predictions with the resummation and that without the resummation,
and the resummed predictions can describe the experimental data.Comment: one reference adde
Regge Field Theory in zero transverse dimensions: loops versus "net" diagrams
Toy models of interacting Pomerons with triple and quaternary Pomeron
vertices in zero transverse dimension are investigated. Numerical solutions for
eigenvalues and eigenfunctions of the corresponding Hamiltonians are obtained,
providing the quantum solution for the scattering amplitude in both models. The
equations of motion for the Lagrangians of the theories are also considered and
the classical solutions of the equations are found. Full two-point Green
functions ("effective" Pomeron propagator) and amplitude of diffractive
dissociation process are calculated in the framework of RFT-0 approach. The
importance of the loops contribution in the amplitude at different values of
the model parameters is discussed as well as the difference between the models
with and without quaternary Pomeron vertex.Comment: 34 pages, 36 figure
Decoherence scenarios from micro- to macroscopic superpositions
Environment induced decoherence entails the absence of quantum interference
phenomena from the macroworld. The loss of coherence between superposed wave
packets depends on their separation. The precise temporal course depends on the
relative size of the time scales for decoherence and other processes taking
place in the open system and its environment. We use the exactly solvable model
of an harmonic oscillator coupled to a bath of oscillators to illustrate
various decoherence scenarios: These range from exponential golden-rule decay
for microscopic superpositions, system-specific decay for larger separations in
a crossover regime, and finally universal interaction-dominated decoherence for
ever more macroscopic superpositions.Comment: 11 pages, 7 figures, accompanying paper to quant-ph/020412
Thermal Equilibration and Expansion in Nucleus-Nucleus Collision at the AGS
The rather complete data set of hadron yields from central Si + A collisions
at the Brookhaven AGS is used to test whether the system at freeze-out is in
thermal and hadro-chemical equilibrium. Rapidity and transverse momentum
distributions are discussed with regards to the information they provide on
hydrodynamic flow.Comment: 11 pages + 2 uuencoded figure
Thermal and Hadrochemical Equilibration in Nucleus-Nucleus Collisions at the SPS
The currently available set of hadron abundances at the SPS for central
S+Au(W,Pb) collisions is compared to predictions from a scenario assuming local
thermal and hadrochemical equilibrium. The data are consistent with a
freeze-out temperature T = 160-170 MeV. Spectra are consistent with this
temperature range and a moderate transverse expansion. The freeze-out points at
the AGS and SPS are found to be close to the phase boundary between a hadron
gas and an ideal quark-gluon phase.Comment: 14 pages + 3 figures. Paper replaced with version accepted for
publication in Phys. Lett.
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