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Olmo, G. J., & Sanchis-Alepuz, H. (2011). Hamiltonian formulation of Palatini f(R) theories a la Brans-Dicke theory. Phys. Rev. D, 83(10), 104036–11pp.
Abstract: We study the Hamiltonian formulation of f(R) theories of gravity both in metric and in Palatini formalism using their classical equivalence with Brans-Dicke theories with a nontrivial potential. The Palatini case, which corresponds to the omega = -3/2 Brans-Dicke theory, requires special attention because of new constraints associated with the scalar field, which is nondynamical. We derive, compare, and discuss the constraints and evolution equations for the omega = -3/2 and omega not equal -3/2 cases. Based on the properties of the constraint and evolution equations, we find that, contrary to certain claims in the literature, the Cauchy problem for the omega = -3/2 case is well formulated and there is no reason to believe that it is not well posed in general.
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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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Molina, R., Nagahiro, H., Hosaka, A., & Oset, E. (2011). Decay of vector-vector resonances into gamma and a pseudoscalar meson. Phys. Rev. D, 83(9), 094030–12pp.
Abstract: We study the decay of dynamically generated resonances from the interaction of two vectors into a gamma and a pseudoscalar meson. The dynamics requires anomalous terms involving vertices with two vectors and a pseudoscalar, which renders it special. We compare our result with data on K-2*(+) (1430) -> K+ gamma and K-2*(0) (1430) -> K-0 gamma and find a good agreement with the data for the K-2*(+) (1430) case and a width considerably smaller than the upper bound measured for the K-2*(0) (1430) meson. We also investigate the decay into pi(+) gamma of one a(2) state, tentatively associated to the a(2)(1320), obtaining qualitative agreement with data.
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Achilli, A., Srivastava, Y., Godbole, R., Grau, A., Pancheri, G., & Shekhovtsova, O. (2011). Total and inelastic cross sections at LHC at root s=7 TeV and beyond. Phys. Rev. D, 84(9), 094009–14pp.
Abstract: We discuss expectations for the total and inelastic cross sections at LHC CM energies root s = 7 TeV and 14 TeV obtained in an eikonal minijet model augmented by soft gluon k(t)-resummation, which we describe in some detail. We present a band of predictions which encompass recent LHC data and suggest that the inelastic cross section described by two-channel eikonal models include only uncorrelated processes. We show that this interpretation of the model is supported by the LHC data.
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Cappiello, L., Cata, O., & D'Ambrosio, G. (2011). Hadronic light by light contribution to the (g-2)(mu) with holographic models of QCD. Phys. Rev. D, 83(9), 093006–19pp.
Abstract: We study the anomalous electromagnetic pion form factor F-pi 0 gamma*gamma* with a set of holographic models. By comparing with the measured value of the linear slope, some of these models can be ruled out. From the remaining models, we obtain predictions for the low-energy quadratic slope parameters of F-pi 0 gamma*gamma* , currently out of experimental reach but testable in the near future. We find it particularly useful to encode this low-energy information in a form factor able to satisfy also QCD short-distance constraints. We choose the form factor introduced by D'Ambrosio, Isidori, and Portoles in kaon decays, which has the right short distance for a particular value of the quadratic slope, which is later shown to be compatible with our holographic predictions. We then turn to a determination of the (dominant) pion exchange diagram in the hadronic light by light scattering contribution to the muon anomalous magnetic moment. We quantify the theoretical uncertainty in (g – 2)(mu) coming from the different input we use: QCD short distances, experimental input, and low-energy holographic predictions. We also test the pion-pole approximation. Our final result is a(mu)(pi 0) = 6: 54(25) x 10(-10), where the error is driven by the linear slope of F-pi 0 gamma*gamma* , soon to be measured with precision at KLOE-2. Our numerical analysis also indicates that large values of the magnetic susceptibility chi 0 are disfavored, therefore pointing at a mild effect from the pion off-shellness. However, in the absence of stronger bounds on chi 0, an additional (10-15)% systematic uncertainty on the previous value for a(mu)(pi 0) cannot be excluded.
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