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Driencourt-Mangin, F., Rodrigo, G., & Sborlini, G. F. R. (2018). Universal dual amplitudes and asymptotic expansions for gg -> H and H -> gamma gamma in four dimensions. Eur. Phys. J. C, 78(3), 231–7pp.
Abstract: Though the one-loop amplitudes of the Higgs boson to massless gauge bosons are finite because there is no direct interaction at tree level in the Standard Model, a well-defined regularization scheme is still required for their correct evaluation. We reanalyze these amplitudes in the framework of the four-dimensional unsubtraction and the loop-tree duality (EDU/LTD), and show how a local renormalization solves potential regularization ambiguities. The Higgs boson interactions are also used to illustrate new additional advantages of this formalism. We show that LTD naturally leads to very compact integrand expressions in four space-time dimensions of the one-loop amplitude with virtual electroweak gauge bosons. They exhibit the same functional form as the amplitudes with top quarks and charged scalars, thus opening further possibilities for simplifications in higher-order computations. Another outstanding application is the straightforward implementation of asymptotic expansions by using dual amplitudes. One of the main benefits of the LTD representation is that it is supported in a Euclidean space. This characteristic feature naturally leads to simpler asymptotic expansions.
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Cottin, G., Helo, J. C., & Hirsch, M. (2018). Searches for light sterile neutrinos with multitrack displaced vertices. Phys. Rev. D, 97(5), 055025–6pp.
Abstract: We study discovery prospects for long-lived sterile neutrinos at the LHC with multitrack displaced vertices, with masses below the electroweak scale. We reinterpret current displaced vertex searches making use of publicly available, parametrized selection efficiencies for modeling the detector response to displaced vertices. We focus on the production of right-handed WR bosons and neutrinos N in a left-right symmetric model, and find poor sensitivity. After proposing a different trigger strategy ( considering the prompt lepton accompanying the neutrino displaced vertex) and optimized cuts in the invariant mass and track multiplicity of the vertex, we find that the LHC with root s = 13 TeV and 300 fb(-1) is able to probe sterile neutrino masses between 10 GeV < m(N) < 20 GeV ( for a right-handed gauge boson mass of 2 TeV < m(WR) < 3.5 TeV). To probe higher masses up to m(N) similar to 30 GeV and m(WR) < 5 TeV, 3000 fb(-1) will be needed. This work joins other efforts in motivating dedicated experimental searches to target this low sterile neutrino mass region.
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Caputo, A., Zavala, J., & Blas, D. (2018). Binary pulsars as probes of a Galactic dark matter disk. Phys. Dark Universe, 19, 1–11.
Abstract: As a binary pulsar moves through a wind of dark matter particles, the resulting dynamical friction modifies the binary's orbit. We study this effect for the double disk dark matter (DDDM) scenario, where a fraction of the dark matter is dissipative and settles into a thin disk. For binaries within the dark disk, this effect is enhanced due to the higher dark matter density and lower velocity dispersion of the dark disk, and due to its co-rotation with the baryonic disk. We estimate the effect and compare it with observations for two different limits in the Knudsen number (Kn). First, in the case where DDDM is effectively collisionless within the characteristic scale of the binary (Kn >> 1) and ignoring the possible interaction between the pair of dark matter wakes. Second, in the fully collisional case (Kn << 1), where a fluid description can be adopted and the interaction of the pair of wakes is taken into account. We find that the change in the orbital period is of the same order of magnitude in both limits. A comparison with observations reveals good prospects to probe currently allowed DDDM models with timing data from binary pulsars in the near future. We finally comment on the possibility of extending the analysis to the intermediate (rarefied gas) case with Kn similar to 1.
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n_TOF Collaboration(Barbagallo, M. et al), Domingo-Pardo, C., & Tain, J. L. (2018). Experimental setup and procedure for the measurement of the Be-7(n,p)Li-7 reaction at n_TOF. Nucl. Instrum. Methods Phys. Res. A, 887, 27–33.
Abstract: Following the completion of the second neutron beam line and the related experimental area (EAR2) at the n_TOF spallation neutron source at CERN, several experiments were planned and performed. The high instantaneous neutron flux available in EAR2 allows to investigate neutron induced reactions with charged particles in the exit channel even employing targets made out of small amounts of short-lived radioactive isotopes. After the successful measurement of the Be-7(n,alpha)alpha cross section, the Be-7(n,p)Li-7 reaction was studied in order to provide still missing cross section data of relevance for Big Bang Nucleosynthesis (BBN), in an attempt to find a solution to the cosmological Lithium abundance problem. This paper describes the experimental setup employed in such a measurement and its characterization.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). A search for pair-produced resonances in four-jet final states at root s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 78(3), 250–28pp.
Abstract: A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb(-1) of root s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, (t) over tilde, which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range 100 GeV < m((T) over tilde) < 410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV < m((t) over tilde) < 470 GeV and 480 GeV < m(<(t)over tilde>) < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.
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