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Reig, M. (2019). On the high-scale instanton interference effect: axion models without domain wall problem. J. High Energy Phys., 08(8), 167–13pp.
Abstract: We show that a new chiral, confining interaction can be used to break Peccei-Quinn symmetry dynamically and solve the domain wall problem, simultaneously. The resulting theory is an invisible QCD axion model without domain walls. No dangerous heavy relics appear.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Fernandez, P., Izmaylov, A., & Novella, P. (2019). Search for heavy neutrinos with the T2K near detector ND280. Phys. Rev. D, 100(5), 052006–10pp.
Abstract: This paper reports on the search for heavy neutrinos with masses in the range 140 < M-N < 493 MeV/c(2) using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are N -> l(alpha)(+/-)pi(-/+) and N -> l(alpha)(+)l(beta)nu (-(-))= (alpha, beta = e, mu). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavored currents (U-e(2), U-mu(2), U-tau(2)) as a function of the heavy neutrino mass, e.g., U-e(2) < 10(-9) at 90% C.L. for a mass of 390 MeV/c(2). These constraints are competitive with previous experiments.
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Bjorkeroth, F., de Medeiros Varzielas, I., Lopez-Ibañez, M. L., Melis, A., & Vives, O. (2019). Leptogenesis in Delta(27) with a universal texture zero. J. High Energy Phys., 09(9), 050–24pp.
Abstract: We investigate the possibility of viable leptogenesis in an appealing Delta(27) model with a universal texture zero in the (1,1) entry. The model accommodates the mass spectrum, mixing and CP phases for both quarks and leptons and allows for grand unification. Flavoured Boltzmann equations for the lepton asymmetries are solved numerically, taking into account both N-1 and N-2 right-handed neutrino decays. The N-1-dominated scenario is successful and the most natural option for the model, with M-1 is an element of [10(9), 10(12)] GeV, and M-1/M-2 is an element of [0.002, 0.1], which constrains the parameter space of the underlying model and yields lower bounds on the respective Yukawa couplings. Viable leptogenesis is also possible in the N-2-dominated scenario, with the asymmetry in the electron flavour protected from N-1 washout by the texture zero. However, this occurs in a region of parameter space which has a stronger mass hierarchy M-1/M-2< 0.002, and M-2 relatively close to M-3, which is not a natural expectation of the Delta(27) model.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Dijet azimuthal correlations and conditional yields in pp and p plus Pb collisions at root S-NN=5.02 TeV with the ATLAS detector. Phys. Rev. C, 100(3), 034903–24pp.
Abstract: This paper presents a measurement of forward-forward and forward-central dijet azimuthal angular correlations and conditional yields in proton-proton (pp) and proton-lead (p + Pb) collisions as a probe of the nuclear gluon density in regions where the fraction of the average momentum per nucleon carried by the parton entering the hard scattering is low. In these regions, gluon saturation can modify the rapidly increasing parton distribution function of the gluon. The analysis utilizes 25 pb(-1) of pp data and 360 μb(-1) of p + Pb data, both at root S-NN = 5.02 TeV, collected in 2015 and 2016, respectively, with the ATLAS detector at the Large Hadron Collider. The measurement is performed in the center-of-mass frame of the nucleon-nucleon system in the rapidity range between -4.0 and 4.0 using the two highest transverse-momentum jets in each event, with the highest transverse-momentum jet restricted to the forward rapidity range. No significant broadening of azimuthal angular correlations is observed for forward-forward or forward-central dijets in p + Pb compared to pp collisions. For forward-forward jet pairs in the proton-going direction, the ratio of conditional yields in p + Pb collisions to those in pp collisions is suppressed by approximately 20%, with no significant dependence on the transverse momentum of the dijet system. No modification of conditional yields is observed for forward-central dijets.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2019). Measurements of CP asymmetries in charmless four-body Lambda(0)(b) and Xi(0)(b) decays. Eur. Phys. J. C, 79(9), 745–19pp.
Abstract: Asearch for CP violation in charmless four-body decays of Lambda(0)(b) and Xi(0)(b) baryons with a proton and three charged mesons in the final state is performed. To cancel out production and detection charge-asymmetry effects, the search is carried out by measuring the difference between the CP asymmetries in a charmless decay and in a decay with an intermediate charmed baryon with the same particles in the final state. The data sample used was recorded in 2011 and 2012 with the LHCb detector and corresponds to an integrated luminosity of 3 fb(-1). A total of 18 CP asymmetries are considered, either accounting for the full phase space of the decays or exploring specific regions of the decay kinematics. No significant CP-violation effect is observed in any of the measurements.
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