[Theory-seminars] cake seminar today: Kirill Semenov-Tyan-Shanskiy, 2:00pm, room A110

[Bernhard Musch]

Dear all,

our visitor Kirill Semenov-Tyan-Shanskiy will speak today, June 1, at 
2:00 pm in room A110. Since our autonomous nervous systems are 
accustomed to cake on Wednesday, Wally Melnitchouk has volunteered to 
sponsor a cake. Here is the information for the talk:

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

*Introducing pi N transition distribution amplitudes: their spectral 
representation, symmetries and constrains from chiral dynamics*

Abstract:

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.

cake sponsor:  Wally M.



-----

A complete list of upcoming theory seminars and talks from previous
seminars are available from:
http://www.jlab.org/~prokudin/seminars/

Alexei, Berni and Satoshi
JLab Theory Seminar Organizers