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Nieves, J., Pich, A., & Ruiz Arriola, E. (2011). Large-N(C) properties of the rho and f(0)(600) mesons from unitary resonance chiral dynamics. Phys. Rev. D, 84(9), 096002–20pp.
Abstract: We construct pi pi amplitudes that fulfill exact elastic unitarity, account for one-loop chiral perturbation theory contributions and include all 1/N(C) leading terms, with the only limitation of considering just the lowest-lying nonet of exchanged resonances. Within such a scheme, the N(C) dependence of sigma and rho masses and widths is discussed. Robust conclusions are drawn in the case of the rho resonance, confirming that it is a stable meson in the limit of a large number of QCD colors, N(C). Less definitive conclusions are reached in the scalar-isoscalar sector. With the present quality of data, we cannot firmly conclude whether or not the N(C) = 3 f(0)(600) resonance completely disappears at large N(C) or if it has a subdominant component in its structure, which would become dominant for a number of quark colors sufficiently large.
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Pavon Valderrama, M., & Ruiz Arriola, E. (2011). Renormalization of chiral two-pion exchange NN interactions with Delta excitations: Correlations in the partial-wave expansion. Phys. Rev. C, 83(4), 044002–19pp.
Abstract: In this work we consider the renormalization of the chiral two-pion exchange potential with explicit Delta excitations for nucleon-nucleon scattering at next-to-leading (NLO) and next-to-next-to-leading order (N(2)LO). Because of the singular nature of the chiral potentials, correlations between different partial waves are generated. In particular, we show that two-body scattering by a short distance power like singular attractive interaction can be renormalized in all partial waves with a single counterterm, provided the singularities are identical. A parallel statement holds in the presence of tensor interactions when the eigenpotentials in the coupled channel problem also coincide. Although this construction reduces the total number of counterterms to 11 in the case of nucleon-nucleon scattering with chiral two-pion exchange interactions with Delta degrees of freedom, the differences in the scattering phases as compared to the case with the uncorrelated partial-wave renormalization become smaller as the angular momentum is increased in the elastic scattering region.
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