17,014 research outputs found
Above-Threshold Poles in Model-Independent Form Factor Parametrizations
The model-independent parametrization for exclusive hadronic form factors
commonly used for semileptonic decays is generalized to allow for the inclusion
of above-threshold resonant poles of known mass and width. We discuss the
interpretation of such poles, particularly with respect to the analytic
structure of the relevant two-point Green's function in which they reside.
Their presence has a remarkably small effect on the parametrization, as we show
explicitly for the case of .Comment: 8 pages, no figures, REVTeX. Version accepted by Phys. Rev. D.
References and clarifying remarks adde
Technological systems and momentum change: American electric utilities, restructuring, and distributed generation
No description supplie
Librational response of a deformed 3-layer Titan perturbed by non-keplerian orbit and atmospheric couplings
The analyses of Titan's gravity field obtained by Cassini space mission
suggest the presence of an internal ocean beneath its icy surface. The
characterization of the geophysical parameters of the icy shell and the ocean
is important to constrain the evolution models of Titan. The knowledge of the
librations, that are periodic oscillations around a uniform rotational motion,
can bring piece of information on the interior parameters. The objective of
this paper is to study the librational response in longitude from an analytical
approach for Titan composed of a deep atmosphere, an elastic icy shell, an
internal ocean, and an elastic rocky core perturbed by the gravitational
interactions with Saturn. We start from the librational equations developed for
a rigid satellite in synchronous spin-orbit resonance. We introduce explicitly
the atmospheric torque acting on the surface computed from the Titan IPSL GCM
(Institut Pierre Simon Laplace General Circulation Model) and the periodic
deformations of elastic solid layers due to the tides. We investigate the
librational response for various interior models in order to compare and to
identify the influence of the geophysical parameters and the impact of the
elasticity. The main librations arise at two well-separated forcing frequency
ranges: low forcing frequencies dominated by the Saturnian annual and
semi-annual frequencies, and a high forcing frequency regime dominated by
Titan's orbital frequency around Saturn. We find that internal structure models
including an internal ocean with elastic solid layers lead to the same order of
libration amplitude than the oceanless models, which makes more challenging to
differentiate them by the interpretation of librational motion.Comment: 38 pages, 4 figures. Accepted for publication in Planetary and Space
Scienc
Model-independent constraints on hadronic form factors with above-threshold poles
Model-independent constraints on hadronic form factors, in particular those
describing exclusive semileptonic decays, can be derived from the knowledge of
field correlators calculated in perturbative QCD, using analyticity and
unitarity. The location of poles corresponding to below-threshold resonances,
i.e., stable states that cannot decay into a pair of hadrons from the crossed
channel of the form factor, must be known a priori, and their effect, accounted
for through the use of Blaschke factors, is to reduce the strength of the
constraints in the semileptonic region. By contrast, above-threshold resonances
appear as poles on unphysical Riemann sheets, and their presence does not
affect the original model-independent constraints. We discuss the possibility
that the above-threshold poles can provide indirect information on the form
factors on the first Riemann sheet, either through information from their
residues or by constraining the discontinuity function. The bounds on form
factors can be improved by imposing, in an exact way, the additional
information in the extremal problem. The semileptonic and
decays are considered as illustrations.Comment: 9 pages, 1 pdf figure. Illustrative numerical results included.
Version accepted for publication in Phys. Rev.
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