3,094 research outputs found
Light-Cone Representation of the Spin and Orbital Angular Momentum of Relativistic Composite Systems
The matrix elements of local operators such as the electromagnetic current,
the energy momentum tensor, angular momentum, and the moments of structure
functions have exact representations in terms of light-cone Fock state
wavefunctions of bound states such as hadrons. We illustrate all of these
properties by giving explicit light-cone wavefunctions for the two-particle
Fock state of the electron in QED, thus connecting the Schwinger anomalous
magnetic moment to the spin and orbital momentum carried by its Fock state
constituents. We also compute the QED one-loop radiative corrections for the
form factors for the graviton coupling to the electron and photon. Although the
underlying model is derived from elementary QED perturbative couplings, it in
fact can be used to simulate much more general bound state systems by applying
spectral integration over the constituent masses while preserving all of the
Lorentz properties, giving explicit realization of the spin sum rules and other
local matrix elements. The role of orbital angular momentum in understanding
the "spin crisis" problem for relativistic systems is clarified. We also prove
that the anomalous gravitomagnetic moment B(0) vanishes for any composite
system. This property is shown to follow directly from the Lorentz boost
properties of the light-cone Fock representation and holds separately for each
Fock state component. We show how the QED perturbative structure can be used to
model bound state systems while preserving all Lorentz properties. We thus
obtain a theoretical laboratory to test the consistency of formulae which have
been proposed to probe the spin structure of hadrons.Comment: Version to be published in Nuclear Physics B. Includes illustrations
of graviton-lepton form factors at one loop in QE
A dynamical model for longitudinal wave functions in light-front holographic QCD
We construct a Schrodinger-like equation for the longitudinal wave function
of a meson in the valence qq-bar sector, based on the 't Hooft model for
large-N two-dimensional QCD, and combine this with the usual transverse
equation from light-front holographic QCD, to obtain a model for mesons with
massive quarks. The computed wave functions are compared with the wave function
ansatz of Brodsky and De Teramond and used to compute decay constants and
parton distribution functions. The basis functions used to solve the
longitudinal equation may be useful for more general calculations of meson
states in QCD.Comment: 12 pages, 2 figures, RevTeX 4.1; expanded discussion, with
calculation details moved to appendice
A Shape-Aware Model for Discrete Texture Synthesis
International audienceWe present a novel shape-aware method for synthesizing 2D and 3D discrete element textures consisting of collections of distinct vector graphics objects. Extending the long-proven point process framework, we propose a shape process, a novel stochastic model based on spatial measurements that fully take into account the geometry of the elements. We demonstrate that our approach is well-suited for discrete texture synthesis by example. Our modelenables for both robust statistical parameter estimation and reliable output generation by Monte Carlo sampling. Our numerous experiments show that contrary to current state-of-the-art techniques, our algorithm manages to capture anisotropic element distributions and systematically prevents undesirable collisions between objects
Tests of the Standard Model Using Muon Polarization Asymmetries in Kaon Decays
We have examined the physics and the experimental feasibility of studying
various kaon decay processes in which the polarization of a muon in the final
state is measured. Valuable information on CP violation, the quark mixing (CKM)
matrix, and new physics can be obtained from such measurements. We have
considered muon polarization in K_L to mu+ mu- and K to pi mu+ mu- decays.
Although the effects are small, or difficult to measure because of the small
branching ratios involved, these studies could provide clean measurements of
the CKM parameters. The experimental difficulty appears comparable to the
observation of K to pi nu barnu. New sources of physics, involving non-standard
CP violation, could produce effects observable in these measurements. Limits
from new results on the neutron and electron electric dipole moment, and
epsilon-prime over epsilon in neutral kaon decays, do not eliminate certain
models that could contribute to the signal. A detailed examination of muon
polarization out of the decay plane in KMU3 and radiative KMU2 decays also
appears to be of interest. With current kaon beams and detector techniques, it
is possible to measure the T-violating polarization for KMU3 with uncertainties
approaching 0.0001. This level of sensitivity would provide an interesting
probe of new physics.Comment: 24 pages, 3 figures, To be published in the International Journal of
Modern Physics
Contributions from SUSY-FCNC couplings to the interpretation of the HyperCP events for the decay \Sigma^+ \to p \mu^+ \mu^-
The observation of three events for the decay
with a dimuon invariant mass of MeV by the HyperCP collaboration
imply that a new particle X may be needed to explain the observed dimuon
invariant mass distribution. We show that there are regions in the SUSY-FCNC
parameter space where the in the NMSSM can be used to explain the
HyperCP events without contradicting all the existing constraints from the
measurements of the kaon decays, and the constraints from the
mixing are automatically satisfied once the constraints from kaon decays are
satisfied.Comment: 18 pages, 7 figure
Experimental Evidence of a Haldane Gap in an S = 2 Quasi-linear Chain Antiferromagnet
The magnetic susceptibility of the quasi-linear chain Heisenberg
antiferromagnet (2,-bipyridine)trichloromanganese(III), MnCl_{3}(bipy), has
been measured from 1.8 to 300 K with the magnetic field, H, parallel and
perpendicular to the chains. The analyzed data yield and K. The magnetization, M, has been studied at 30 mK and 1.4 K in H up to 16
T. No evidence of long-range order is observed. Depending on crystal
orientation, at 30 mK until a critical field is achieved ( and $H_{c\bot} = 1.8\pm 0.2 T), where M increases continuously
as H is increased. These results are interpreted as evidence of a Haldane gap.Comment: 11 pages, 4 figure
Are diamonds a MEMS\u27 best friend?
Next-generation military and civilian communication systems will require technologies capable of handling data/ audio, and video simultaneously while supporting multiple RF systems operating in several different frequency bands from the MHz to the GHz range [1]. RF microelectromechanical/nanoelectromechanical (MEMS/NEMS) devices, such as resonators and switches, are attractive to industry as they offer a means by which performance can be greatly improved for wireless applications while at the same time potentially reducing overall size and weight as well as manufacturing costs
The Rare Decay D^0 -> gamma gamma
We present a calculation of the rare decay mode D^0 -> gamma gamma, in which
the long distance contributions are expected to be dominant. Using the Heavy
Quark Chiral Perturbation Theory Lagrangian with a strong g coupling as
recently determined by CLEO from the D^* -> D pi width, we consider both the
anomaly contribution which relates to the annihilation part of the weak
Lagrangian and the one-loop pi, K diagrams. The loop contributions which are
proportional to g and contain the a_1 Wilson coefficient are found to dominate
the decay amplitude, which turns out to be mainly parity violating. The
branching ratio is then calculated to be (1.0+-0.5)x10^(-8). Observation of an
order of magnitude larger branching ratio could be indicative of new physics.Comment: 16 pages, 5 figures, additional reference and several remarks added,
results unchange
Rare Z-decay into light CP-odd Higgs bosons: a comparative study in different new physics models
Various new physics models predict a light CP-odd Higgs boson (labeled as
) and open up new decay modes for Z-boson, such as ,
and , which could be explored at the GigaZ option of
the ILC. In this work we investigate these rare decays in several new physics
models, namely the type-II two Higgs doublet model (type-II 2HDM), the
lepton-specific two Higgs doublet model (L2HDM), the nearly minimal
supersymetric standard model (nMSSM) and the next-to-minimal supersymmetric
standard model (NMSSM). We find that in the parameter space allowed by current
experiments, the branching ratios can reach for
(), for and for , which
implies that the decays and may be accessible
at the GigaZ option. Moreover, since different models predict different
patterns of the branching ratios, the measurement of these rare decays at the
GigaZ may be utilized to distinguish the models.Comment: Version in JHEP (discussions added, errors corrected
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