87 research outputs found
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
A renormalisation-group approach to two-body scattering with long-range forces
We apply the renormalisation-group to two-body scattering by a combination of
known long-range and unknown short-range forces. A crucial feature is that the
low-energy effective theory is regulated by applying a cut-off in the basis of
distorted waves for the long range potential. We illustrate the method by
applying it to scattering in the presence of a repulsive 1/r^2 potential. We
find a trivial fixed point, describing systems with weak short-range
interactions, and a unstable fixed point. The expansion around the latter
corresponds to a distorted-wave effective-range expansion.Comment: 4 pages (AIP style), talk presented at Mesons and Light Nuclei,
Prague, 200
Power counting for three-body decays of a near-threshold state
We propose a new power counting for the effective field theory describing a
near-threshold state with unstable constituents, such as the X(3872) meson. In
this counting, the momenta of the heavy particles, the pion mass and the
excitation energy of the unstable constituent -- the D* in the case of the X --
are treated as small scales, of order Q. The difference, delta, between the
excitation energy of the D* and the pion mass is smaller than either by a
factor ~20. We therefore assign delta an order Q^2 in our counting. This
provides a consistent framework for a double expansion in both delta/m_pi and
the ratio of m_pi to the high-energy scales in this system. It ensures that
amplitudes have the correct behaviour at the three-body threshold. It allows us
to derive, within an effective theory, various results which have previously
been obtained using physically-motivated approximations.Comment: 5 pages, 1 figure; more discussion of pion exchange adde
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