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Plenter, J., & Rodrigo, G. (2021). Asymptotic expansions through the loop-tree duality. Eur. Phys. J. C, 81(4), 320–13pp.
Abstract: Asymptotic expansions of Feynman amplitudes in the loop-tree duality formalism are implemented at integrand-level in the Euclidean space of the loop three-momentum, where the hierarchies among internal and external scales are well-defined. The ultraviolet behaviour of the individual contributions to the asymptotic expansion emerges only in the first terms of the expansion and is renormalized locally in four space-time dimensions. These two properties represent an advantage over the method of Expansion by Regions. We explore different approaches in different kinematical limits, and derive explicit asymptotic expressions for several benchmark configurations.
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n_TOF Collaboration(Dietz, M. et al), Domingo-Pardo, C., & Tain, J. L. (2021). Measurement of the Ge-72(n, y) cross section over a wide neutron energy range at the CERN n_TOF facility. Phys. Rev. C, 103(4), 045809–8pp.
Abstract: The Ge-72(n, gamma) cross section was measured for neutron energies up to 300 keV at the neutron time-of-flight facility n_TOF (CERN), Geneva, for the first time covering energies relevant to heavy-element synthesis in stars. The measurement was performed at the high-resolution beamline EAR-1, using an isotopically enriched (GeO2)-Ge-72 sample. The prompt capture gamma rays were detected with four liquid scintillation detectors, optimized for low neutron sensitivity. We determined resonance capture kernels up to a neutron energy of 43 keV, and averaged cross sections from 43 to 300 keV. Maxwellian-averaged cross section values were calculated from kT = 5 to 100 keV, with uncertainties between 3.2% and 7.1%. The new results significantly reduce uncertainties of abundances produced in the slow neutron capture process in massive stars.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2021). Search for new phenomena with top quark pairs in final states with one lepton, jets, and missing transverse momentum in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 04(4), 174–66pp.
Abstract: A search for new phenomena with top quark pairs in final states with one isolated electron or muon, multiple jets, and large missing transverse momentum is performed. Signal regions are designed to search for two-, three-, and four-body decays of the directly pair-produced supersymmetric partner of the top quark (stop). Additional signal regions are designed specifically to search for spin-0 mediators that are produced in association with a pair of top quarks and decay into a pair of dark-matter particles. The search is performed using the Large Hadron Collider proton-proton collision dataset at a centre-of-mass energy of s = 13 TeV recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb(-1). No significant excess above the Standard Model background is observed, and limits at 95% confidence level are set in the stop-neutralino mass plane and as a function of the mediator mass or the dark-matter particle mass. Stops are excluded up to 1200 GeV (710 GeV) in the two-body (three-body) decay scenario. In the four-body scenario stops up to 640 GeV are excluded for a stop-neutralino mass difference of 60 GeV. Scalar and pseudoscalar dark-matter mediators are excluded up to 200 GeV when the coupling strengths of the mediator to Standard Model and dark-matter particles are both equal to one and when the mass of the dark-matter particle is 1 GeV.
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Moon, B. et al, & Montaner-Piza, A. (2021). Nuclear structure of Te isotopes beyond neutron magic number N=82. Phys. Rev. C, 103(3), 034320–15pp.
Abstract: Newly observed decay schemes of the nuclei Sb-137 and Sb-138 are reported. The neutron-rich Sb isotopes were produced by the in-flight fragmentation of a U-238 primary beam with an energy of 345 MeV/nucleon. Several new excited states of Te-137 with tentatively assigned spin-parities of (5/2(-)), (9/2(-)), and (7/2) have been established which play an important role in the evolution of neutron levels beyond N = 82. The study of the beta decay of Sb-138 led to a considerable extension of the level scheme of Te-138 including the identification of several nonyrast states. The structure of Te-137 and Te-138 is discussed on the basis of large-scale shell-model calculations performed using two different effective interactions.
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Barreiros, D. M., Joaquim, F. R., Srivastava, R., & Valle, J. W. F. (2021). Minimal scoto-seesaw mechanism with spontaneous CP violation. J. High Energy Phys., 04(4), 249–21pp.
Abstract: We propose simple scoto-seesaw models to account for dark matter and neutrino masses with spontaneous CP violation. This is achieved with a single horizontal Z8 discrete symmetry, broken to a residual Z2 subgroup responsible for stabilizing dark matter. CP is broken spontaneously via the complex vacuum expectation value of a scalar singlet, inducing leptonic CP-violating effects. We find that the imposed Z8 symmetry pushes the values of the Dirac CP phase and the lightest neutrino mass to ranges already probed by ongoing experiments, so that normal-ordered neutrino masses can be cornered by cosmological observations and neutrinoless double beta decay experiments.
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