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Beltran Jimenez, J., & Delhom, A. (2020). Instabilities in metric-affine theories of gravity with higher order curvature terms. Eur. Phys. J. C, 80(6), 585–27pp.
Abstract: We discuss the presence of ghostly instabilities for metric-affine theories constructed with higher order curvature terms. We mainly focus on theories containing only the Ricci tensor and show the crucial role played by the projective symmetry. The pathological modes arise from the absence of a pure kinetic term for the projective mode and the non-minimal coupling of a 2-form field contained in the connection, and which can be related to the antisymmetric part of the metric in non-symmetric gravity theories. The couplings to matter are considered at length and cannot be used to render the theories stable. We discuss different procedures to avoid the ghosts by adding additional constraints. We finally argue how these pathologies are expected to be present in general metric-affine theories unless much care is taken in their construction.
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de Florian, D., Sborlini, G. F. R., & Rodrigo, G. (2016). QED corrections to the Altarelli-Parisi splitting functions. Eur. Phys. J. C, 76(5), 282–6pp.
Abstract: We discuss the combined effect of QED and QCD corrections to the evolution of parton distributions. We extend the available knowledge of the Altarelli-Parisi splitting functions to one order higher in QED, and we provide explicit expressions for the splitting kernels up to O(alpha alpha(S)). The results presented in this article allow one to perform a parton distribution function analysis reaching full NLO QCD-QED combined precision.
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Bossingham, T., Mavromatos, N. E., & Sarkar, S. (2018). Leptogenesis from heavy right-handed neutrinos in CPT violating backgrounds. Eur. Phys. J. C, 78(2), 113–33pp.
Abstract: We discuss leptogenesis in a model with heavy right-handed Majorana neutrinos propagating in a constant but otherwise generic CPT-violating axial time-like background (motivated by string theory). At temperatures much higher than the temperature of the electroweak phase transition, we solve approximately, but analytically (using Pade approximants), the corresponding Boltzmann equations, which describe the generation of lepton asymmetry from the tree-level decays of heavy neutrinos into Standard Model leptons. At such temperatures these leptons are effectively massless. The current work completes in a rigorous way a preliminary treatment of the same system, by some of the present authors. In this earlier work, lepton asymmetry was crudely estimated considering the decay of a righthanded neutrino at rest. Our present analysis includes thermal momentum modes for the heavy neutrino and this leads to a total lepton asymmetry which is bigger by a factor of two as compared to the previous estimate. Nevertheless, our current and preliminary results for the freezeout are found to be in agreement (within a similar to 12.5% uncertainty). Our analysis depends on a novel use of Pade approximants to solve the Boltzmann equations and may be more widely useful in cosmology.
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Albaladejo, M., & Nieves, J. (2022). Compositeness of S-wave weakly-bound states from next-to-leading order Weinberg's relations. Eur. Phys. J. C, 82(8), 724–12pp.
Abstract: We discuss a model-independent estimator of the likelihood of the compositeness of a shallow S-wave bound or virtual state. The approach is based on an extension of Weinberg's relations in Weinberg (Phys Rev 137:B672, 1965) and it relies only on the proximity of the energy of the state to the two-hadron threshold to which it significantly couples. The scheme only makes use of the experimental scattering length and the effective range low energy parameters, and it is shown to be fully consistent for predominantly molecular hadrons. As explicit applications, we analyse the case of the deuteron, the S-1(0) nucleon virtual state and the exotic D-so(*)(2317)(+/-) , and find strong support to the molecular interpretation in all cases. Results are less conclusive for the D* (s0)(2317)+/-, since the binding energy of this state would be significantly higher than that of the deuteron, and the approach employed here is at the limit of its applicability. We also qualitatively address the case of the recently discovered T + cc state, within the isospin limit to avoid the complexity of the very close thresholds (DD)-D-0*+ and D + D*(0), which could mask the ingredients of the approach proposed in this work.
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Toledo, G., Ikeno, N., & Oset, E. (2021). Theoretical study of the D-0 -> K-pi(+)eta reaction. Eur. Phys. J. C, 81(3), 268–11pp.
Abstract: We develop a model to study the D-0 -> K-pi(+)eta weak decay, starting with the color favored external emission and Cabibbo favored mode at the quark level. A less favored internal emission decay mode is also studied as a source of small corrections. Some pairs of quarks are allowed to hadronize producing two pseudoscalar mesons, which posteriorly are allowed to interact to finally provide the K-pi(+)eta state. The chiral unitary approach is used to take into account the final state interaction of pairs of mesons, which has as a consequence the production of the kappa (K-0*(700)) and the a(0)(980) resonances, well visible in the invariant mass distributions. We also introduce the (K) over bar*(0)eta production in a phenomenological way and show that the s-wave pseudoscalar interaction together with this vector excitation mode are sufficient to provide a fair reproduction of the experimental data. The model provides the relative weight of the a(0)(980) to the kappa excitation, and their strength is clearly visible in the low energy part of the K pi spectrum.
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