Jantzen, B., & Ruiz-Femenia, P. (2013). Next-to-next-to-leading order nonresonant corrections to threshold top-pair production from e(+)e(-) collisions: Endpoint-singular terms. Phys. Rev. D, 88(5), 054011–20pp.
Abstract: We analyze the subleading nonresonant contributions to the e(+)e(-) -> W(+)W(-)b (b) over bar cross section at energies near the top-antitop threshold. These correspond to next-to-next-to-leading-order (NNLO) corrections with respect to the leading-order resonant result. We show that these corrections produce 1/epsilon endpoint singularities which precisely cancel the finite-width divergences arising in the resonant production of the W(+)W(-)b (b) over bar final state from on-shell decays of the top and antitop quarks at the same order. We also provide analytic results for the (m(t)/Lambda)(2), (m(t)/Lambda) and (m(t)/Lambda)(0) log Lambda terms that dominate the expansion in powers of (Lambda/m(t)) of the complete set of NNLO nonresonant corrections, where Lambda is a cut imposed on the invariant masses of the bW pairs that is neither too tight nor too loose (m(t)Gamma(t) << Lambda(2) << m(t)(2)).
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Serodio, H. (2013). Yukawa sector of multi-Higgs-doublet models in the presence of Abelian symmetries. Phys. Rev. D, 88(5), 056015–48pp.
Abstract: A general method for classifying the possible quark models of a multi-Higgs-doublet model, in the presence of Abelian symmetries, is presented. All the possible sets of textures that can be present in a given sector are shown, thus turning the determination of the flavor models into a combinatorial problem. Several symmetry implementations are studied for two and three Higgs doublet models. Some models' implementations are explored in great detail, with a particular emphasis on models known as Branco-Grimus-Lavoura and nearest-neighbor-interaction. Several considerations on the flavor changing neutral currents of multi-Higgs models are also given.
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Helo, J. C., Kovalenko, S. G., Hirsch, M., & Pas, H. (2013). Short-range mechanisms of neutrinoless double beta decay at the LHC. Phys. Rev. D, 88(7), 073011–19pp.
Abstract: Lepton number violation (LNV) mediated by short- range operators can manifest itself in both neutrinoless double beta decay (0 nu beta beta) and in processes with same- sign dilepton final states at the LHC. We derive limits from existing LHC data at root s = 8 TeV and compare the discovery potential of the forthcoming root s = 14 TeV phase of the LHC with the sensitivity of current and future 0 nu beta beta decay experiments, assuming the short-range part of the 0 nu beta beta decay amplitude dominates. We focus on the first of two possible topologies triggered by one fermion and two bosons in the intermediate state. In all cases, except for the pure leptoquark mechanism, the LHC will be more sensitive than 0 nu beta beta decay in the future. In addition, we propose to search for a charge asymmetry in the final state leptons and to use different invariant mass peaks as a possible tool to discriminate the various possible mechanisms for LNV signals at the LHC.
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Roca, L., & Oset, E. (2013). Isospin 0 and 1 resonances from pi Sigma photoproduction data. Phys. Rev. C, 88(5), 055206–7pp.
Abstract: Recently we presented a successful strategy to extract the position of the two Lambda ( 1405) poles from experimental photoproduction data on the gamma p -> K+pi(0)Sigma(0) reaction at Jefferson Lab. Following a similar strategy, we extend the previous method to incorporate also the isospin 1 component which allows us to consider in addition the experimental data on gamma p -> K+pi(+/-)Sigma(-/+). The idea is based on considering a production mechanism as model independent as possible and implementing the final state interaction of the final meson-baryon pair based on small modifications of the unitary chiral perturbation theory amplitudes. Good fits to the data are obtained with this procedure, by means of which we can also predict the cross sections for the K- p -> (K) over barN, pi Sigma, and pi Lambda reactions for the different charge channels. Besides the two poles found for the Lambda(1405) resonance, we discuss the possible existence of an isospin 1 resonance in the vicinity of the (K) over barN threshold.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Measurement of top quark polarization in top-antitop events from proton-proton collisions at root s=7 TeV using the ATLAS detector. Phys. Rev. Lett., 111(23), 232002–19pp.
Abstract: This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4: 7 fb(-1) of proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at root s = 7 TeV. Final states containing one or two isolated leptons ( electrons or muons) and jets are considered. Two measurements of alpha P-l, the product of the leptonic spin-analyzing power and the top quark polarization, are performed assuming that the polarization is introduced by either a CP conserving or a maximally CP violating production process. The measurements obtained, alpha P-l(CPC) = -0: 035 +/- 0: 014(stat) +/- 0: 037(syst) and alpha P-l(CPV) = 0: 020 +/- 0: 016(stat)(-0.017)(+0.013)(syst), are in good agreement with the standard model prediction of negligible top quark polarization.
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Ruiz de Austri, R., & Perez de los Heros, C. (2013). Impact of nucleon matrix element uncertainties on the interpretation of direct and indirect dark matter search results. J. Cosmol. Astropart. Phys., 11(11), 049–19pp.
Abstract: We study in detail the impact of the current uncertainty in nucleon matrix elements on the sensitivity of direct and indirect experimental techniques for dark matter detection. We perform two scans in the framework of the cMSSM: one using recent values of the pion-sigma term obtained from Lattice QCD, and the other using values derived from experimental measurements. The two choices correspond to extreme values quoted in the literature and reflect the current tension between different ways of obtaining information about the structure of the nucleon. All other inputs in the scans, astrophysical and from particle physics, are kept unchanged. We use two experiments, XENON100 and IceCube, as benchmark cases to illustrate our case. We find that the interpretation of dark matter search results from direct detection experiments is more sensitive to the choice of the central values of the hadronic inputs than the results of indirect search experiments. The allowed regions of cMSSM parameter space after including XENON100 constrains strongly differ depending on the assumptions on the hadronic matrix elements used. On the other hand, the constraining potential of IceCube is almost independent of the choice of these values.
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Bernal, N., Colucci, S., Josse-Michaux, F. X., Racker, J., & Ubaldi, L. (2013). On baryogenesis from dark matter annihilation. J. Cosmol. Astropart. Phys., 10(10), 035–30pp.
Abstract: We study in detail the conditions to generate the baryon asymmetry of the universe from the annihilation of dark matter. This scenario requires a low energy mechanism for thermal baryogenesis, hence we first discuss some of these mechanisms together with the specific constraints due to the connection with the dark matter sector. Then we show that, contrary to what stated in previous studies, it is possible to generate the cosmological asymmetry without adding a light sterile dark sector, both in models with violation and with conservation of B – L. In addition, one of the models we propose yields some connection to neutrino masses.
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Gran, R., Nieves, J., Sanchez, F., & Vicente Vacas, M. J. (2013). Neutrino-nucleus quasi-elastic and 2p2h interactions up to 10 GeV. Phys. Rev. D, 88(11), 113007–10pp.
Abstract: We extend to 10 GeV results from a microscopic calculation of charged-current neutrino-nucleus reactions that do not produce a pion in the final state. For the class of events coming from neutrino interactions with two nucleons producing two holes (2p2h), limiting the calculation to three-momentum transfers less than 1.2 GeV produces a two-dimensional distribution in momentum and energy transfer that is roughly constant as a function of energy. The cross section for 2p2h interactions approximately scales with the number of nucleons for isoscalar nuclei, similar to the quasi-elastic cross section. When limited to momentum transfers below 1.2 GeV, the cross section is 26% of the quasi-elastic cross section at 3 GeV, but 14% if we neglect a Delta(1232) resonance absorption component. The same quantities are 33% and 17% for antineutrinos. For the quasi-elastic interactions, the full nuclear model with long range correlations produces an even larger, but approximately constant distortion of the shape of the four-momentum transfer at all energies above 2 GeV. The 2p2h enhancement and long-range correlation distortions to the cross section for these interactions are significant enough they should be observable in precision experiments to measure neutrino oscillations and neutrino interactions at these energies, but also balance out and produce less total distortion than each effect does individually.
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Hirsch, M., Lineros, R. A., Morisi, S., Palacio, J., Rojas, N., & Valle, J. W. F. (2013). WIMP dark matter as radiative neutrino mass messenger. J. High Energy Phys., 10(10), 149–18pp.
Abstract: The minimal seesaw extension of the Standard SU(3)(c)circle times SU(2)(L)circle times U(1)(Y) Model requires two electroweak singlet fermions in order to accommodate the neutrino oscillation parameters at tree level. Here we consider a next to minimal extension where light neutrino masses are generated radiatively by two electroweak fermions: one singlet and one triplet under SU(2)(L). These should be odd under a parity symmetry and their mixing gives rise to a stable weakly interactive massive particle (WIMP) dark matter candidate. For mass in the GeV-TeV range, it reproduces the correct relic density, and provides an observable signal in nuclear recoil direct detection experiments. The fermion triplet component of the dark matter has gauge interactions, making it also detectable at present and near future collider experiments.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2013). Measurement of Neutrino Oscillation Parameters from Muon Neutrino Disappearance with an Off-Axis Beam. Phys. Rev. Lett., 111(21), 211803–7pp.
Abstract: The T2K Collaboration reports a precision measurement of muon neutrino disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV. Near detector measurements are used to constrain the neutrino flux and cross section parameters. The Super-Kamiokande far detector, which is 295 km downstream of the neutrino production target, collected data corresponding to 3.01 x 10(20) protons on target. In the absence of neutrino oscillations, 205 +/- 17 (syst) events are expected to be detected while only 58 muon neutrino event candidates are observed. A fit to the neutrino rate and energy spectrum, assuming three neutrino flavors and normal mass hierarchy yields a best-fit mixing angle sin(2) (theta(23)) = 0.514 +/- 0.082 and mass splitting vertical bar Delta m(32)(2)vertical bar = 2.44(-0.15)(+0.17) x 10(-3) eV(2)/c(4). Our result corresponds to the maximal oscillation disappearance probability.
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