Low-energy photon and pion scattering in holographic QCD

Abstract

Using holographic models where chiral symmetry is broken through IR b.c.'s, we determine a novel set of relations between QCD matrix elements. In particular, we find that the amplitudes of the three processes pi pi->pi pi, gamma gamma->pi pi and gamma->pi pi pi involve a single scalar function h(Q^2) given by a suitable 5D integral of the EoM Green's function. In a phenomenological analysis of gamma gamma->pi pi we find an overall agreement with the experimental cross section for a broad range of energy. Moreover, the polarizabilities at low energies show a fair agreement between the holographic approach, previous computations and experiment.

24+1 pages, 3 png figures. The normalization of the cross section in Eq. (4.2) has been corrected in this version and extra comments have been added to the paragraphs before and after it. No additional modification introduced in the article. Erratum can be found at Erratum-ibid. 1408 (2014) 033 with DOI: 10.1007/JHEP08(2014)033