Reply to Comment on ``Determination of pion-baryon coupling constants from QCD sum rules''

In response to Kim's comment (nucl-th/9903040) on the sum rules for pion-baryon coupling constants obtained in hep-ph/9512259 and hep-ph/9606471, we point out that our treatment of the continuum is consistent with duality and with the fact that the correlator in the presence of an external meson or field should be represented by a double dispersion relation.Comment: 5 pages (RevTeX), reply to nucl-th/990304

Renormalisation-group analysis of electromagnetic couplings in the pionless effective field theory

The Wilsonian renormalisation group is applied to a system of two nonrelativistic particles interacting via short-range forces and coupled to an external EM field. By demanding that a fully off-shell one-particle-irreducible 5-point amplitude is independent of the cutoff, a renormalisation group equation is derived for the interaction current density. This is solved to obtain the fixed point corresponding to the unitary limit. The scaling behaviour of perturbations around this point is analysed. Some of these terms are related by gauge invariance to terms in the effective-range expansion; others describe short-range physics that is not included in the two-body potential. We construct observables including the bound-state form factor and show how the scaling of the terms in the interaction current is reflected in the power counting for their contributions to observables.Comment: 14 pages; comments and references adde

Exact renormalization group and many-fermion systems

The exact renormalization group methods is applied to many fermion systems with short-range attractive force. The strength of the attractive fermion-fermion interaction is determined from the vacuum scattering length. A set of approximate flow equations is derived including fermionic and bosonic fluctuations. The numerical solutions show a phase transition to a gapped phase. The inclusion of bosonic fluctuations is found to be significant only in the small-gap regime.Comment: Talk, given by B. Krippa on the International Workshop "Meson2004", Cracow, Poland, 3 page

Proton polarisability contribution to the Lamb shift in muonic hydrogen at fourth order in chiral perturbation theory

We calculate the amplitude T_1 for forward doubly-virtual Compton scattering in heavy-baryon chiral perturbation theory, to fourth order in the chiral expansion and with the leading contribution of the gammaNDelta form factor. This provides a model-independent expression for the amplitude in the low-momentum region, which is the dominant one for its contribution to the Lamb shift. It allows us to significantly reduce the theoretical uncertainty in the proton polarisability contributions to the Lamb shift in muonic hydrogen. We also stress the importance of consistency between the definitions of the Born and structure parts of the amplitude. Our result leaves no room for any effect large enough to explain the discrepancy between proton charge radii as determined from muonic and normal hydrogen.Comment: 9 pages, 2 figures; added discussion of matching ChPT form factor onto dipole form at non-zero Q^2; no significant changes in result

Comment on soft-pion emission in DVCS

The soft-pion theorem for pion production in deeply virtual Compton scattering, derived by Guichon, Mosse and Vanderhaegen, is shown to be consistent with chiral perturbation theory. Chiral symmetry requires that the nonsinglet operators corresponding to spin-independent and spin-dependent parton distributions have the same anomalous dimensions in cases where those operators are related by chiral transformations. In chiral perturbation theory, their scale-dependences can thus be absorbed in the coefficents of the corresponding effective operators, without affecting their chiral structures.Comment: 2 pages, RevTe