3,849 research outputs found
The exclusive Drell-Yan process and deeply virtual pion production
In this talk it is reported on analyses of l p -> l pi+ n and pi- p -> l+ l-
n within the handbag approach. It is argued that recent measurements of hard
pion production performed by HERMES and CLAS clearly indicate the occurrence of
strong contributions from transversely polarized photons. The gamma*T -> pi
transitions are described by the transversity GPDs accompanied by twist-3 pion
wave functions. The experiments also require strong contributions from the pion
pole which can be modeled as a classical one-pion exchange. With these
extensions the handbag approach leads to results on cross sections and spin
asymmetries in fair agreement with experiment. This approach is also used for
an estimate of the partial cross sections for the exclusive Drell-Yan process.Comment: 8 pages, 6 figures, latex with style files jpsj-suppl.cls and
cite.sty invited talk presented at MENU2016, Kyoto (Japan), July 2016. arXiv
admin note: substantial text overlap with arXiv:1602.0380
Disorder-driven splitting of the conductance peak at the Dirac point in graphene
The electronic properties of a bricklayer model, which shares the same
topology as the hexagonal lattice of graphene, are investigated numerically. We
study the influence of random magnetic-field disorder in addition to a strong
perpendicular magnetic field. We found a disorder-driven splitting of the
longitudinal conductance peak within the narrow lowest Landau band near the
Dirac point. The energy splitting follows a relation which is proportional to
the square root of the magnetic field and linear in the disorder strength. We
calculate the scale invariant peaks of the two-terminal conductance and obtain
the critical exponents as well as the multifractal properties of the chiral and
quantum Hall states. We found approximate values for the
quantum Hall states, but for the divergence of the
correlation length of the chiral state at E=0 in the presence of a strong
magnetic field. Within the central Landau band, the multifractal
properties of both the chiral and the split quantum Hall states are the same,
showing a parabolic distribution with .
In the absence of the constant magnetic field, the chiral critical state is
determined by
Naive time-reversal odd phenomena in semi-inclusive deep-inelastic scattering from light-cone constituent quark models
We present results for leading-twist azimuthal asymmetries in semi-inclusive
lepton-nucleon deep-inelastic scattering due to naively time-reversal odd
transverse-momentum dependent parton distribution functions from the light-cone
constituent quark model. We carefully discuss the range of applicability of the
model, especially with regard to positivity constraints and evolution effects.
We find good agreement with available experimental data from COMPASS and
HERMES, and present predictions to be tested in forthcoming experiments at
Jefferson Lab.Comment: 10 pages, 7 figures, discussion of evolution effects extended, to
appear in Phys.Rev.
Pion mass dependence of the nucleon mass in the chiral quark soliton model
The dependence of the nucleon mass on the mass of the pion is studied in the
framework of the chiral quark-soliton model. A remarkable agreement is observed
with lattice data from recent full dynamical simulations. The possibility and
limitations to use the model results as a guideline for the chiral
extrapolation of lattice data are discussed.Comment: 14 pages, 12 figures, 4 tables. v2: References added, new figure
included, discussion improved, typos fixed, matches published versio
A shallow water model for magnetohydrodynamic flows with turbulent Hartmann layers
We establish a shallow water model for flows of electrically conducting
fluids in homogeneous static magnetic fields that are confined between two
parallel planes where turbulent Hartmann layers are present. This is achieved
by modelling the wall shear stress in these layers using the Prandtl's mixing
length model, as did the authors of Albousssi\`ere \& Lingwood (Phys. Fluids,
2000). The idea for this new model arose from the failure of previous shallow
water models that assumed a laminar Hartmann layer to recover the correct
amount of dissipation found in some regimes of the MATUR experiment. This
experiment, conducted by the authors of Messadek \& Moreau (J. Fluid Mech.
2002), consisted of a thin layer of mercury electrically driven in differential
rotation in a transverse magnetic field. Numerical Simulations of our new model
in the configuration of this experiment allowed us to recover experimental
values of both the global angular momentum and the local velocity up to a few
percent when the Hartmann layer was in a sufficiently well developed turbulent
state. We thus provide an evidence that the unexplained level of dissipation
observed in MATUR in these specific regimes was caused by turbulence in the
Hartmann layers. A parametric analysis of the flow, made possible by the
simplicity of our model, also revealed that turbulent friction in the Hartmann
layer prevented quasi-2D turbulence from becoming more intense and limited the
size of the large scales
Critical regime of two dimensional Ando model: relation between critical conductance and fractal dimension of electronic eigenstates
The critical two-terminal conductance and the spatial fluctuations of
critical eigenstates are investigated for a disordered two dimensional model of
non-interacting electrons subject to spin-orbit scattering (Ando model). For
square samples, we verify numerically the relation between critical conductivity and
the fractal information dimension of the electron wave function, . Through a detailed numerical scaling analysis of the two-terminal
conductance we also estimate the critical exponent that
governs the quantum phase transition.Comment: IOP Latex, 7 figure
Intrinsic transverse parton momenta in deeply inelastic reactions
Intrinsic transverse parton momenta pT play an important role in the
understanding of azimuthal/spin asymmetries in semi-inclusive deep-inelastic
scattering (SIDIS) and the Drell-Yan process (DY). We review and update what is
presently known about pT from these processes. In particular, we address the
question to which extent data support the popular Gauss model for the
pT-distributions. We find that the Gauss model works very well, and observe
that the intrinsic transverse momenta in SIDIS and DY are compatible, which is
a support for the factorization approach. As a byproduct we recover a simple
but practical way of taking into account the energy dependence of
pT-distributions.Comment: 19 pages, 11 figure
Non-equilibrium dynamics of an active colloidal "chucker"
We report Monte Carlo simulations of the dynamics of a "chucker": a colloidal
particle which emits smaller solute particles from its surface, isotropically
and at a constant rate k_c. We find that the diffusion constant of the chucker
increases for small k_c, as recently predicted theoretically. At large k_c the
chucker diffuses more slowly due to crowding effects. We compare our simulation
results to those of a "point particle" Langevin dynamics scheme in which the
solute concentration field is calculated analytically, and in which
hydrodynamic effects can be included albeit in an approximate way. By
simulating the dragging of a chucker, we obtain an estimate of its apparent
mobility coefficient which violates the fluctuation-dissipation theorem. We
also characterise the probability density profile for a chucker which sediments
onto a surface which either repels or absorbs the solute particles, and find
that the steady state distributions are very different in the two cases. Our
simulations are inspired by the biological example of
exopolysaccharide-producing bacteria, as well as by recent experimental,
simulation and theoretical work on phoretic colloidal "swimmers".Comment: re-submission after referee's comment
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