Chiral perturbation theory for η→π0γγ

Abstract

An introduction to the methods and ideas of Chiral Perturbation Theory is presented in this talk. The discussion is illustrated with some phenomenological predictions that can be compared with available experimental results.

η→π0γγdecay within a chiral unitary approach revisited

“…The reason is that the tree-level amplitudes, both at O p 2 and O p 4 , vanish. The first nonvanishing contribution comes at O p 4 , either from loops involving kaons, largely suppressed due to the kaon masses, or from pion loops, again suppressed since they violate G parity and are thus proportional to m u ÿ m d [9]. The first sizable contribution comes at O p 6 , but the coefficients involved are not precisely determined and one must rely upon models.…”

“…The first sizable contribution comes at O p 6 , but the coefficients involved are not precisely determined and one must rely upon models. In this sense, either vector meson dominance (VMD) [9][10][11], the Nambu-Jona-Lasinio model (NJL) [12], or the extended Nambu-Jona-Lasinio model (ENJL) [13,14] has been used to determine these coefficients. However, the use of treelevel VMD to obtain the O p 6 chiral coefficients by expanding the vector meson propagators leads [9] to results about a factor of 2 smaller than the ''all order'' VMD term when one keeps the full vector meson propagator.…”

Light mesons at BESIII

“…The first sizable contribution comes at O(p 6 ) [22]. This decay provides a unique opportunity to test directly the correctness of the calculations of third order χPTh.…”

Goldstone boson production and decay

“…The different possibilities are distinguishable in the the E γ spectrum. The present experimental value for the width is 0.85±0.18 eV and the theoretical situation has despite some theoretical effort not really changed since (Ametller et al 1992). Adding all contributions in the table leads to Γ (η → π 0 γγ) =0.45-0.50 eV with a large uncertainty.…”

“…The loop effects at p 4 and p 6 are suppressed by either heavy intermediate states or G − (Ametller et al 1992). Those are in fact of the same size as the p 4 loops.…”