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Ballesteros, G., Carmona, A., & Chala, M. (2017). Exceptional composite dark matter. Eur. Phys. J. C, 77(7), 468–18pp.
Abstract: We study the darkmatter phenomenology of non-minimal composite Higgs models with SO(7) broken to the exceptional group G(2). In addition to the Higgs, three pseudo-Nambu-Goldstone bosons arise, one of which is electrically neutral. A parity symmetry is enough to ensure this resonance is stable. In fact, if the breaking of the Goldstone symmetry is driven by the fermion sector, this Z(2) symmetry is automatically unbroken in the electroweak phase. In this case, the relic density, as well as the expected indirect, direct and collider signals are then uniquely determined by the value of the compositeness scale, f. Current experimental bounds allow one to account for a large fraction of the dark matter of the Universe if the dark matter particle is part of an electroweak triplet. The totality of the relic abundance can be accommodated if instead this particle is a composite singlet. In both cases, the scale f and the dark matter mass are of the order of a few TeV.
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Ikeno, N., Bayar, M., & Oset, E. (2021). Combined theoretical study of the D+ -> pi(+) eta eta and D+ -> pi(+)pi(0) eta reactions. Eur. Phys. J. C, 81(4), 377–10pp.
Abstract: We study the D+ -> pi(+) eta eta and D+ -> pi(+)pi(0) eta reactions, which are single Cabibbo suppressed and can proceed both through internal and external emission. The primary mechanisms at quark level are considered, followed by hadronization to produce three mesons in the D+ decay, and after that the final state interaction of these mesons leads to the production of the a(0)(980) resonance, seen in the pi(+)eta, pi(0)eta mass distributions. The theory has three unknown parameters to determine the shape of the distributions and the ratio between the D+ -> pi(+) eta eta and D+ -> pi(+)pi(0) eta rates. This ratio restricts much the sets of parameters but there is still much freedom leading to different shapes in the mass distributions. We call for a measurement of these mass distributions that will settle the reaction mechanism, while at the same time provide relevant information on the way that the a(0)(980) resonance is produced in the reactions.
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Ikeno, N., Dias, J. M., Liang, W. H., & Oset, E. (2024). D+ → Ks0 π+ η reaction and a0(980)+. Eur. Phys. J. C, 84(5), 469–9pp.
Abstract: We study the D+ -> K- 0 pi (+) eta reaction where the a(0)(980) excitation plays a dominant role. We consider mechanisms of external and internal emission at the quark level, hadronize the qq components into two mesons and allow these mesons to undergo final state interaction where the a(0)(980) state is generated. While the a(0)(980) production is the dominant term, we also find other terms in the reaction that interfere with this production mode and, through interference with it, lead to a shape of the a(0)(980) significantly different from the one observed in other experiments, with an apparently much larger width.
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Guerrero, M., Olmo, G. J., & Rubiera-Garcia, D. (2023). Geodesic completeness of effective null geodesics in regular space-times with non-linear electrodynamics. Eur. Phys. J. C, 83(9), 785–8pp.
Abstract: We study the completeness of light trajectories in certain spherically symmetric regular geometries found in Palatini theories of gravity threaded by non-linear (electromagnetic) fields, which makes their propagation to happen along geodesics of an effective metric. Two types of geodesic restoration mechanisms are employed: by pushing the focal point to infinite affine distance, thus unreachable in finite time by any sets of geodesics, or by the presence of a defocusing surface associated to the development of a wormhole throat. We discuss several examples of such geometries to conclude the completeness of all such effective paths. Our results are of interest both for the finding of singularity-free solutions and for the analysis of their optical appearances e.g. in shadow observations.
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Liang, W. H., Xie, J. J., & Oset, E. (2016). f(0)(500), f(0)(980), and a(0)(980) production in the chi(c1) -> eta pi(+)pi(-) reaction. Eur. Phys. J. C, 76(12), 700–7pp.
Abstract: We study the chi(c1) -> eta pi(+)pi(-) decay, paying attention to the production of f(0)(500), f(0)(980), and a(0)(980) from the final state interaction of pairs of mesons that can lead to these three mesons in the final state, which is implemented using the chiral unitary approach. Very clean and strong signals are obtained for the a(0)(980) excitation in the eta pi invariant mass distribution and for the f(0)(500) in the pi(+)pi(-) mass distribution. A smaller, but also clear signal for the f(0)(980) excitation is obtained. The results are contrasted with experimental data and the agreement found is good, providing yet one more test in support of the picture where these resonances are dynamically generated from the meson-meson interaction.
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