The European Physical Journal C (EPJ C)

Issue		Eur. Phys. J. C Volume 9, Number 4, July 1999
Page(s)		643 - 671
DOI		10.1007/s100520050565
Published online		18 June 1999

Contents | PDF_file_(370 Kb)

Eur. Phys. J. C 9, 643-671
DOI 10.1007/s100529900055

Baryon chiral perturbation theory in manifestly Lorentz invariant form

T. Becher - H. Leutwyler

Institute for Theoretical Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland

Received: 11 February 1999 / Published online: 18 June 1999

Abstract
We show that in the presence of massive particles, such as nucleons, the standard low-energy expansion, in powers of meson momenta and light-quark masses, in general converges in only part of the low-energy region. The expansion of the scalar form factor $\sigma(t)$ , for instance, breaks down in the vicinity of $t=4M_\pi^2$ . In the language of heavy baryon chiral perturbation theory, the proper behaviour in the threshold region results only if the multiple internal-line insertions generated by relativistic kinematics are summed up to all orders. We propose a method that yields a coherent representation throughout the low-energy region, while keeping Lorentz and chiral invariance explicit at all stages. The method is illustrated with a calculation of the nucleon mass and of the scalar form factor to order p⁴.

Contents | PDF_file_(370 Kb)

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