39 research outputs found
Ground-state energy of pionic hydrogen to one loop
We investigate the ground-state energy of the pi- p atom (pionic hydrogen) in
the framework of QCD+QED. In particular, we evaluate the strong energy-level
shift. We perform the calculation at next-to-leading order in the low-energy
expansion in the framework of the relevant effective field theory. The result
provides a relation between the strong energy shift and the pion-nucleon S-wave
scattering lengths - evaluated in pure QCD - at next-to-leading order in
isospin breaking and in the low-energy expansion. We compare our result with
available model calculations.Comment: Version accepted for publication in Eur. Phys. J. C; Eq. (B8)
corrected, comment after Eq. (B11) changed, additional minor changes in the
text; preprint number adde
Can one see the number of colors in eta, eta-prime --> pi^+ pi^- gamma?
We investigate the decays eta, eta-prime --> pi^+ pi^- gamma up to
next-to-leading order in the framework of the combined 1/N_c and chiral
expansions. Counter terms of unnatural parity at next-to-leading order with
unknown couplings are important to acommodate the results both to the
experimental decay width and the photon spectrum. The presence of these
coefficients does not allow for a determination of the number of colors from
these decays.Comment: 8 pages, 2 figure
Hadronic potentials from effective field theories
We construct the potentials that describe the spectrum and decay of electromagnetic bound states of hadrons, and are consistent with ChPT. These potentials satisfy the matching condition which enables one to express the parameters of the potential through the threshold scattering amplitudes calculated in ChPT. We further analyze the ambiguity in the choice of the short-range hadronic potentials, which satisfy this matching condition
Electromagnetic corrections to p scattering length from pionic hydrogen
We derive a closed, model space independent, expression for the
electromagnetic correction factor to the scattering length
extracted from a hydrogenic atom with an extended charge to order
and in the limit of a short ranged hadronic interaction.Comment: 4 pages; PANIC02, XVIth Conference on Particles and Nuclei, Osaka, to
appear in Nuclear Physics
Perturbative framework for the pi(+)pi(-) atom
The perturbative framework is developed for the calculation of the pi(+)pi(-)
atom characteristics on the basis of the field-theoretical Bethe-Salpeter
approach. A closed expression for the first-order correction to the pi(+)pi(-)
atom lifetime has been obtained.Comment: 8 pages, LaTeX-fil
The pion-nucleon scattering lengths from pionic deuterium
We use the framework of effective field theories to discuss the determination
of the S-wave \pi N scattering lengths from the recent high-precision
measurements of pionic deuterium observables. The theoretical analysis proceeds
in several steps. Initially, the precise value of the pion-deuteron scattering
length a_{\pi d} is extracted from the data. Next, a_{\pi d} is related to the
S-wave \pi N scattering lengths a_+ and a_-. We discuss the use of this
information for constraining the values of these scattering lengths in the full
analysis, which also includes the input from the pionic hydrogen energy shift
and width measurements, and throughly investigate the accuracy limits for this
procedure. In this paper, we also give a detailed comparison to other effective
field theory approaches, as well as with the earlier work on the subject,
carried out within the potential model and multiple scattering framework.Comment: The replacement includes an erratum, which is published in Eur. Phys.
J.
QCD Short-distance Constraints and Hadronic Approximations
This paper discusses a general class of ladder resummation inspired hadronic
approximations. It is found that this approach naturally reproduces many
successes of single meson per channel saturation models (e.g. VMD) and NJL
based models. In particular the existence of a constituent quark mass and a gap
equation follows naturally. We construct an approximation that satisfies a
large set of QCD short-distance and large constraints and reproduces many
hadronic observables.
We show how there exists in general a problem between QCD short-distance
constraints for Green Functions and those for form factors and cross-sections
following from the quark-counting rule. This problem while expected for Green
functions that do not vanish in purely perturbative QCD also persists for many
Green functions that are order parameters.Comment: 27 page