Baryon chiral perturbation theory: an update

The issue of consistent power counting in baryon chiral perturbation theory is revisited.Comment: 5 pp, 1 fig; contributed to BARYONS 2010, Osaka, Japan, Dec 7-11, 201

A Statistical Analysis of Hadron Spectrum: Quantum Chaos in Hadrons

The nearest-neighbor mass-spacing distribution of the meson and baryon spectrum (up to 2.5 GeV) is described by the Wigner surmise corresponding to the statistics of the Gaussian orthogonal ensemble of random matrix theory. This can be viewed as a manifestation of quantum chaos in hadrons.Comment: 9 pages, 3 figures, revise

Proton polarizabilities: status, relevance, prospects

This is a brief review of the status of understanding the proton polarizabilities in chiral perturbation theory and of their relevance to the `proton charge radius puzzle'.Comment: 4 pages, 1 figure; contribution to proceedings of the Workshop to Explore Physics Opportunities with Intense, Polarized Electron Beams up to 300 MeV, March 14-16, 2013 MIT, Cambridge, Massachusett

Reply to "Comment on `Breakdown of the expansion of finite-size corrections to the hydrogen Lamb shift in moments of charge distribution'"

To comply with the critique of the Comment [J. Arrington, arXiv:1602.01461], we consider another modification of the proton electric form factor, which resolves the "proton-radius puzzle". The proposed modification satisfies all the consistency criteria put forward in the Comment, and yet has a similar impact on the puzzle as that of the original paper. Contrary to the concluding statement of the Comment, it is not difficult to find an ad hoc modification of the form factor at low $Q$ that resolves the discrepancy and is consistent with analyticity constraints. We emphasize once again that we do not consider such an ad hoc modification of the proton form factor to be a solution of the puzzle until a physical mechanism for it is found.Comment: 3 pages, 3 figures, 1 table, to appear in Phys. Rev. A, corrected typo in caption of fig.

Dissecting the hadronic contributions to (g−2)μ(g-2)_\mu by Schwinger's sum rule

The theoretical uncertainty of $(g-2)_\mu$ is currently dominated by hadronic contributions. In order to express those in terms of directly measurable quantities, we consider a sum rule relating $g-2$ to an integral of a photo-absorption cross section. The sum rule, attributed to Schwinger, can be viewed as a combination of two older sum rules: Gerasimov-Drell-Hearn and Burkhardt-Cottingham. The Schwinger sum rule has an important feature, distinguishing it from the other two: the relation between the anomalous magnetic moment and the integral of a photo-absorption cross section is linear, rather than quadratic. The linear property makes it suitable for a straightforward assessment of the hadronic contributions to $(g-2)_\mu$. From the sum rule we rederive the Schwinger $\alpha/2\pi$ correction, as well as the formula for the hadronic vacuum-polarization contribution. As an example of the light-by-light contribution we consider the single-meson exchange.Comment: 6 pages, 10 figures, published version extended by a few clarifying remarks and an Appendi

Large-NcN_c relations for the electromagnetic N to Delta(1232) transition

We examine the large-$N_c$ relations which express the electromagnetic $N$-to-$\Delta$ transition quantities in terms of the electromagnetic properties of the nucleon. These relations are based on the known large-$N_c$ relation between the $N\to \Delta$ electric quadrupole moment and the neutron charge radius, and a newly derived large-$N_c$ relation between the electric quadrupole ($E2$) and Coulomb quadrupole ($C2$) transitions. Extending these relations to finite, but small, momentum transfer we find that the description of the electromagnetic $N\to\Delta$ ratios ($R_{EM}$ and $R_{SM}$) in terms of the nucleon form factors predicts a structure which may be ascribed to the effect of the ``pion cloud''. These relations also provide useful constraints for the $N \to \Delta$ generalized parton distributions.Comment: 4 pages, 1 figure; to appear in PRD, Rapid Communication