Calibbi, L., Lopez-Ibañez, M. L., Melis, A., & Vives, O. (2021). Implications of the Muon g-2 result on the flavour structure of the lepton mass matrix. Eur. Phys. J. C, 81(10), 929–11pp.
Abstract: The confirmation of the discrepancy with the Standard Model predictions in the anomalous magnetic moment by theMuon g-2 experiment at Fermilab points to a low scale of new physics. Flavour symmetries broken at low energies can account for this discrepancy but these models are much more restricted, as they would also generate offdiagonal entries in the dipole moment matrix. Therefore, if we assume that the observed discrepancy in the muon g – 2 is explained by the contributions of a low-energy flavor symmetry, lepton flavour violating processes can constrain the structure of the lepton mass matrices and therefore the flavour symmetries themselves predicting these structures. We apply these ideas to several discrete flavour symmetries popular in the leptonic sector, such as Delta(27), A(4), and A(5) proportional to CP.
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Albandea, D., Hernandez, P., Ramos, A., & Romero-Lopez, F. (2021). Topological sampling through windings. Eur. Phys. J. C, 81(10), 873–12pp.
Abstract: We propose a modification of the Hybrid Monte Carlo (HMC) algorithm that overcomes the topological freezing of a two-dimensional U(1) gauge theory with and without fermion content. This algorithm includes reversible jumps between topological sectors – winding steps – combined with standard HMC steps. The full algorithm is referred to as winding HMC (wHMC), and it shows an improved behaviour of the autocorrelation time towards the continuum limit. We find excellent agreement between the wHMC estimates of the plaquette and topological susceptibility and the analytical predictions in the U(1) pure gauge theory, which are known even at finite beta. We also study the expectation values in fixed topological sectors using both HMC and wHMC, with and without fermions. Even when topology is frozen in HMC – leading to significant deviations in topological as well as non-topological quantities – the two algorithms agree on the fixed-topology averages. Finally, we briefly compare the wHMC algorithm results to those obtained with master-field simulations of size L similar to 8 x 10(3).
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for dark matter produced in association with a single top quark in root s=13 TeV pp collisions with the ATLAS detector. Eur. Phys. J. C, 81(10), 860–37pp.
Abstract: This paper presents a search for dark matter in the context of a two-Higgs-doublet model together with an additional pseudoscalar mediator, a, which decays into the dark-matter particles. Processes where the pseudoscalar mediator is produced in association with a single top quark in the 2HDM+a model are explored for the first time at the LHC. Several final states which include either one or two charged leptons (electrons or muons) and a significant amount of missing transverse momentum are considered. The analysis is based on proton-proton collision data collected with the ATLAS experiment at root s = 13 TeV during LHC Run 2 (2015-2018), corresponding to an integrated luminosity of 139 fb(-1). No significant excess above the Standard Model predictions is found. The results are expressed as 95% confidence-level limits on the parameters of the signal models considered.
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Ling, P., Dai, X. H., Du, M. L., & Wang, Q. (2021). Prompt production of the hidden charm pentaquarks in the LHC. Eur. Phys. J. C, 81(9), 819–15pp.
Abstract: Motivated by the observation of the first hidden charm pentaquarks by the LHCb collaboration in 2015 and the updated analysis with an order-of-magnitude larger data set in 2019, we estimate their cross sections for the prompt production as well as their heavy quark spin partners, in the Sigma(()(c)*()) (D) over bar (()*()) hadronic molecular picture, at the center-of-mass energy 7 TeV in the pp collision. Their cross sections are several nb and we would expect several tens hidden charm pentaquark events in the LHC based on its current integrated luminosity. The cross sections show a sizable deviation of the cross sections for hidden charm pentaquarks with the third isospin component Iz = + 1/2 (P-c(+)) from those with Iz = – 1/2 (P-c(0)). The cross sections decrease dramatically with the increasing transverse momentum. Our study can also tell where to search for the missing hidden charm pentaquarks. The confirmation of the complete hidden charm pentaquarks in the heavy quark symmetry would further verify their Sigma(()(c)*()) (D) over bar (()*()) molecular interpretation. In addition, the relative strength among these cross sections for pentaquarks can help us to identify the quantum numbers of the P-c(4440) and P-c(4457).
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Molina, R., Doring, M., Liang, W. H., & Oset, E. (2021). The pi f(0)(500) decay of the a(1)(1260). Eur. Phys. J. C, 81(9), 782–9pp.
Abstract: We evaluate the a(1)(1260) -> pi sigma(f(0)(500)) decay width from the perspective that the a(1)(1260) resonance is dynamically generated from the pseudoscalar-vector interaction and the sigma arises from the pseudoscalar-pseudoscalar interaction. A triangle mechanism with a(1)(1260) -> p pi followed by rho -> pi pi and a fusion of two pions within the loop to produce the sigma provides the mechanism for this decay under these assumptions for the nature of the two resonances. We obtain widths of the order of 13-22 MeV. Present experimental results differ substantially from each other, suggesting that extra efforts should be devoted to the precise extraction of this important partial decay width, which should provide valuable information on the nature of the axial vector and scalar meson resonances and help clarify the role of the ps channel in recent lattice QCD calculations of the a(1).
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