Longitudinal vector form factor in the pion β decay
Seminars
Seminar “QUANTUM FIELD THEORY”
Date and Time: Wednesday, 19 April 2017, at 11:00 AM
Venue: Blokhintsev Hall (4th floor), Bogoliubov Laboratory of Theoretical Physics
Seminar topic: «Longitudinal vector form factor in the pion β decay»
Speaker: M.I. Krivoruchenko (ITEP, BLTP, MIPT)
Abstract:
The generalized Ward-Takahashi identity (gWTI) in the pion sector for broken isotopic symmetry is derived and used for the model independent estimate of the longitudinal form factor f− of the pion β decay vector vertex. The on-shell form factor is found to be proportional to the mass difference of the pions and the difference between the isospin I = 1 and I = 2 pion radii. The isovector component of f− is obtained by rotating the isovector component of the electromagnetic current similarly to the weak magnetism [1]. The component I = 2 is not connected with isotopic rotations; it is determined by the gWTI. A numerical estimate of f− yields a value two times higher than the previous estimate from the quark model. Off-shell form factors are known to be ambiguous because of the gauge dependence and the freedom in the parameterization of the fields. The near-mass-shell form factor f− appears to be an exception, allowing for experimental verification of the consequences of the gWTI. We calculate f− near the mass shell using the gWTI and dispersion techniques.
M.I. Krivoruchenko, Adv. High Energy Phys. 2015, 656239 (2015).