Tübingen 2003 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 13: Poster-Sitzung: Theorie
HK 13.12: Poster
Dienstag, 18. März 2003, 13:30–15:30, Foyer
Induced pseudoscalar form factor of the nucleon at two-loop order — •Norbert Kaiser — Physik Department T39, Technische Universität München, D-85747 Garching
We calculate the imaginary part of the induced pseudoscalar form factor of the nucleon GP(t) in the framework of two-loop heavy baryon chiral perturbation theory. The effect of the calculated three-pion continuum on the pseudoscalar constant gP = (mµ/2M) GP(t=−0.877mµ2) measurable in ordinary muon capture µ−p→ nνµ turns out to be negligibly small. The magnitude of contributions from possible counterterms at two-loop order is smaller than the uncertainty of the dominant pion-pole term proportional to the pion-nucleon coupling constant gπ N= 13.2± 0.2. We conclude that a sufficiently accurate representation of the induced pseudoscalar form factor of the nucleon at low momentum transfers is given by the sum of the pion-pole term and the so-called Adler-Dothan-Wolfenstein term: GP(t) = 4gπ N M fπ/(mπ2 −t)− 2gA M2 ⟨ rA2 ⟩/3, with ⟨ rA2 ⟩ = (0.44± 0.02) fm2 the axial mean square radius of the nucleon. Work supported in part by BMBF, DFG and GSI.