46,235 research outputs found
Polarization as a Probe to the Production Mechanisms of Charmonium in Collisions
Measurements of the polarization of \jp produced in pion-nucleus collisions
are in disagreement with leading twist QCD prediction where \jp is observed
to have negligible polarization whereas theory predicts substantial
polarization. We argue that this discrepancy cannot be due to poorly known
structure functions nor the relative production rates of \jp and .
The disagreement between theory and experiment suggests important higher twist
corrections, as has earlier been surmised from the anomalous non-factorized
nuclear -dependence of the \jp cross section.Comment: 8 page
SATMC: Spectral Energy Distribution Analysis Through Markov Chains
We present the general purpose spectral energy distribution (SED) fitting
tool SED Analysis Through Markov Chains (SATMC). Utilizing Monte Carlo Markov
Chain (MCMC) algorithms, SATMC fits an observed SED to SED templates or models
of the user's choice to infer intrinsic parameters, generate confidence levels
and produce the posterior parameter distribution. Here we describe the key
features of SATMC from the underlying MCMC engine to specific features for
handling SED fitting. We detail several test cases of SATMC, comparing results
obtained to traditional least-squares methods, which highlight its accuracy,
robustness and wide range of possible applications. We also present a sample of
submillimetre galaxies that have been fitted using the SED synthesis routine
GRASIL as input. In general, these SMGs are shown to occupy a large volume of
parameter space, particularly in regards to their star formation rates which
range from ~30-3000 M_sun yr^-1 and stellar masses which range from
~10^10-10^12 M_sun. Taking advantage of the Bayesian formalism inherent to
SATMC, we also show how the fitting results may change under different
parametrizations (i.e., different initial mass functions) and through
additional or improved photometry, the latter being crucial to the study of
high-redshift galaxies.Comment: 17 pages, 11 figures, MNRAS accepte
Pinned modes in two-dimensional lossy lattices with local gain and nonlinearity
We introduce a system with one or two amplified nonlinear sites ("hot spots",
HSs) embedded into a two-dimensional linear lossy lattice. The system describes
an array of evanescently coupled optical or plasmonic waveguides, with gain
applied at selected HS cores. The subject of the analysis is discrete solitons
pinned to the HSs. The shape of the localized modes is found in
quasi-analytical and numerical forms, using a truncated lattice for the
analytical consideration. Stability eigenvalues are computed numerically, and
the results are supplemented by direct numerical simulations. In the case of
self-focusing nonlinearity, the modes pinned to a single HS are stable or
unstable when the nonlinearity includes the cubic loss or gain, respectively.
If the nonlinearity is self-defocusing, the unsaturated cubic gain acting at
the HS supports stable modes in a small parametric area, while weak cubic loss
gives rise to a bistability of the discrete solitons. Symmetric and
antisymmetric modes pinned to a symmetric set of two HSs are considered too.Comment: Philosophical Transactions of the Royal Society A, in press (a
special issue on "Localized structures in dissipative media"
The Nystrom plus Correction Method for Solving Bound State Equations in Momentum Space
A new method is presented for solving the momentum-space Schrodinger equation
with a linear potential. The Lande-subtracted momentum space integral equation
can be transformed into a matrix equation by the Nystrom method. The method
produces only approximate eigenvalues in the cases of singular potentials such
as the linear potential. The eigenvalues generated by the Nystrom method can be
improved by calculating the numerical errors and adding the appropriate
corrections. The end results are more accurate eigenvalues than those generated
by the basis function method. The method is also shown to work for a
relativistic equation such as the Thompson equation.Comment: Revtex, 21 pages, 4 tables, to be published in Physical Review
Indirect exchange of magnetic impurities in zigzag graphene ribbon
We use quantum Monte Carlo method to study the indirect coupling between two
magnetic impurities on the zigzag edge of graphene ribbon, with respect to the
chemical potential . We find that the spin-spin correlation between two
adatoms located on the nearest sites in the zigzag edge are drastically
suppressed around the zero-energy. As we switch the system away from
half-filling, the antiferromagnetic correlation is first enhanced and then
decreased. If the two adatoms are adsorbed on the sites belonging to the same
sublattice, we find similar behavior of spin-spin correlation except for a
crossover from ferromagnetic to antiferromagentic correlation in the vicinity
of zero-energy. We also calculated the weight of different components of
d-electron wave function and local magnet moment for various values of
parameters, and all the results are consistent with those of spin-spin
correlation between two magnetic impurities.Comment: 3 pages, 4 figures, conference proceedin
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