Corrections to Sirlin's Theorem in $O(p^6)$ Chiral Perturbation Theory

Abstract

We present the results of the first two-loop calculation of a form factor in full $SU(3)\times SU(3)$ Chiral Perturbation Theory. We choose a specific linear combination of ${\pi }^{+},K^{+},K^0$ and $K\pi$ form factors (the one appearing in Sirlin's theorem) which does not get contributions from order $p^6$ operators with unknown constants. For the charge radii, the correction to the previous one-loop result turns out to be significant, but still there is no agreement with the present data due to large experimental uncertainties in the kaon charge radii.

Comments: 6 pages, Latex, 2 LaTeX figures