16,643 research outputs found
Dispersive evaluation of the second-class amplitude in the standard model
We reevaluate the two form factors relevant for the second-class
decay mode, making systematic use of analyticity, unitarity, combined
with updated inputs to the NLO chiral constraints. We focus, in particular, on
the shape of the resonance peak which is a background-free signature of
a second-class current. Its dispersive construction requires the
scattering amplitude which we derive from a family of
Khuri-Treiman equations solutions constrained with accurate recent results on
the Dalitz plot.Comment: Presented at the 12th International workshop on Tau lepton physics
(TAU2012) in Nagoya, Japa
Solving integral equations in
A dispersive analysis of decays has been performed in the past
by many authors. The numerical analysis of the pertinent integral equations is
hampered by two technical difficulties: i) The angular averages of the
amplitudes need to be performed along a complicated path in the complex plane.
ii) The averaged amplitudes develop singularities along the path of integration
in the dispersive representation of the full amplitudes. It is a delicate
affair to handle these singularities properly, and independent checks of the
obtained solutions are demanding and time consuming. In the present article, we
propose a solution method that avoids these difficulties. It is based on a
simple deformation of the path of integration in the dispersive representation
(not in the angular average). Numerical solutions are then obtained rather
straightforwardly. We expect that the method also works for .Comment: 11 pages, 10 Figures. Version accepted for publication in EPJC. The
ancillary files contain an updated set of fundamental solutions. The
numerical differences to the former set are tiny, see the READMEv2 file for
detail
Long Distance Contribution to
We revisit the calculation of the long distance contribution to . We discuss this process within the framework of chiral
perturbation theory, and also using simple models for the vertex. We argue that it is unlikely that this mode can be used to
extract information on short distance parameters. The process
is also long-distance dominated and we find that .Comment: References added, one typo corrected. Version to appear in Nuclear
Physics
Radiation from accelerated perfect or dispersive mirrors following prescribed relativistic asymptotically inertial trajectories
We address the question of radiation emission from both perfect and
dispersive mirrors following prescribed relativistic trajectories. The
trajectories considered are asymptotically inertial: the mirror starts from
rest and eventually reverts to motion at uniform velocity. This enables us to
provide a description in terms of in and out states. We calculate exactly the
Bogolubov alpha and beta coefficients for a specific form of the trajectory,
and stress the analytic properties of the amplitudes and the constraints
imposed by unitarity. A formalism for the description of emission of radiation
from a dispersive mirror is presented.Comment: 7 figure
Towards a data-driven analysis of hadronic light-by-light scattering
The hadronic light-by-light contribution to the anomalous magnetic moment of
the muon was recently analyzed in the framework of dispersion theory, providing
a systematic formalism where all input quantities are expressed in terms of
on-shell form factors and scattering amplitudes that are in principle
accessible in experiment. We briefly review the main ideas behind this
framework and discuss the various experimental ingredients needed for the
evaluation of one- and two-pion intermediate states. In particular, we identify
processes that in the absence of data for doubly-virtual pion-photon
interactions can help constrain parameters in the dispersive reconstruction of
the relevant input quantities, the pion transition form factor and the helicity
partial waves for .Comment: 7 pages, 4 figures, 2 tables, journal versio
Finite volume methods for unidirectional dispersive wave models
We extend the framework of the finite volume method to dispersive
unidirectional water wave propagation in one space dimension. In particular we
consider a KdV-BBM type equation. Explicit and IMEX Runge-Kutta type methods
are used for time discretizations. The fully discrete schemes are validated by
direct comparisons to analytic solutions. Invariants conservation properties
are also studied. Main applications include important nonlinear phenomena such
as dispersive shock wave formation, solitary waves and their various
interactions.Comment: 25 pages, 12 figures, 51 references. Other authors papers can be
downloaded at http://www.lama.univ-savoie.fr/~dutykh
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