Tübingen 2003 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 13: Poster-Sitzung: Theorie

HK 13.12: Poster

Tuesday, March 18, 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 G_P(t) in the framework of two-loop heavy baryon chiral perturbation theory. The effect of the calculated three-pion continuum on the pseudoscalar constant g_P = (m_µ/2M) G_P(t=−0.877m_µ²) measurable in ordinary muon capture µ⁻p→ nν_µ 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 g_{π 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: G_P(t) = 4g_{π N} M f_π/(m_π² −t)− 2g_A M² ⟨ r_A² ⟩/3, with ⟨ r_A² ⟩ = (0.44± 0.02)  fm² the axial mean square radius of the nucleon. Work supported in part by BMBF, DFG and GSI.