[Jlab-seminars] Theory Center Seminar

[Mary Fox]

Theory Center Seminar
Wed., June 1, 2011
2:00 p.m. (coffee at 1:45 p.m.)
CEBAF Center, Room A110

Kirill Semenov-Tyan-Shanskiy
CPHT/Ecole Polytechnique
Cedex, France

*Introducing pi N Transition Distribution Amplitudes: Their Spectral
Representation, Symmetries and Constrains From Chiral Dynamics*

Baryon to meson Transition Distribution Amplitudes (TDAs) extend the
concept of generalized parton distributions. They appear as a building
block in the colinear factorized description of amplitudes for a class
of hard exclusive reactions prominent examples being hard exclusive pion
electroproduction off a nucleon in the backward region and
baryon-antibaryon annihilation into pion and a lepton pair.
We discuss general symmetry properties of these objects following from
the underlying symmetries of QCD. In particular, Lorentz symmetry
results in the polynomiality property of  the Mellin moments in the
corresponding longitudinal momentum fractions. We generalize the notion
of double distributions introduced in the context of GPDs for baryon to
meson TDAs and construct a spectral representation for baryon to meson
TDAs in terms of quadruple distributions. Using chiral symmetry and the
crossing relation between pi N TDAs and pi N generalized distribution
amplitudes we establish threshold soft pion theorems for $\pi N$ TDAs
which determine the magnitude of pi N TDAs. We argue that this
information may be used as input for realistic modeling of pi N TDA.
A possible approach may consist in "skewing" the \xi=1 limit for pi N
TDAs similarly to the fact  that "skewing" the forward limit for GPDs
provides the basis for the successful Ansatz for GPDs.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://mailman.jlab.org/pipermail/jlab-seminars/attachments/20110531/d6c1d301/attachment.html