28,689 research outputs found

    Inverse Neutrino-less Double Beta Decay Revisited: Neutrinos, Higgs Triplets and a Muon Collider

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    We revisit the process of inverse neutrino-less double beta decay (e e -> W W) at future linear colliders. The cases of Majorana neutrino and Higgs triplet exchange are considered. We also discuss the processes e mu -> W W and mu mu -> W W, which are motivated by the possibility of muon colliders. For heavy neutrino exchange and center-of-mass energies larger than 1 TeV, we show that masses up to 10^6 (10^5) GeV could be probed for e-e and e-mu machines, respectively. The stringent limits for mixing of heavy neutrinos with muons render mu mu -> W W less promising, even though this process is not constrained by limits from neutrino-less double beta decay. If Higgs triplets are responsible for inverse neutrino-less double beta decay, observable signals are only possible if a very narrow resonance is met. We also consider unitarity aspects of the process in case both Higgs triplets and neutrinos are exchanged. An exact see-saw relation connecting low energy data with heavy neutrino and triplet parameters is found.Comment: 19 pages, 6 figure

    K−K^- and pˉ\bar p Spectra for Au+Au Collisions at s\sqrt{s} = 200 GeV from STAR, PHENIX and BRAHMS in Comparison to Core-Corona Model Predictions

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    Based on results obtained with event generators we have launched the core-corona model. It describes in a simplified way but quite successfully the centrality dependence of multiplicity and of identified particles observed in heavy-ion reaction at beam energies between s\sqrt{s} = 17 GeV and 200 GeV. Also the centrality dependence of the elliptic flow, v2v_2, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single particle spectra of K−K^- and pˉ{\bar p} measured by the PHENIX, STAR and BRAHMS collaborations. We find that also for these particles the analysis of the spectra in the core-corona model suffers from differences in the data published by the different experimental groups, notably for the pp collisions. As for protons and K+K^+ for each experience the data agree well with the prediction of the core-corona model but the value of the two necessary parameters depends on the experiments. We show as well that the average momentum as a function of the centrality depends in a very sensitive way on the particle species and may be quite different for particles which have about the same mass. Therefore the idea to interpret this centrality dependence as a consequence of a collective expansion of the system, as done in blast way fits may be premature.Comment: Invited talk to the CPOD conference Dubna August 201

    Phase transitions and the internal noise structure of nonlinear Schr\"odi nger equation solitons

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    We predict phase-transitions in the quantum noise characteristics of systems described by the quantum nonlinear Schr\"odinger equation, showing them to be related to the solitonic field transition at half the fundamental soliton amplitude. These phase-transitions are robust with respect to Raman noise and scattering losses. We also describe the rich internal quantum noise structure of the solitonic fields in the vicinity of the phase-transition. For optical coherent quantum solitons, this leads to the prediction that eliminating the peak side-band noise due to the electronic nonlinearity of silica fiber by spectral filtering leads to the optimal photon-number noise reduction of a fundamental soliton.Comment: 10 pages, 5 figure

    Test of the Universality of Naive-time-reversal-odd Fragmentation Functions

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    We investigate the ''spontaneous'' hyperon transverse polarization in e+e−e^+e^- annihilation and semi-inclusive deep inelastic scattering processes as a test of the universality of the naive-time-reversal-odd transverse momentum dependent fragmentation functions. We find that universality implies definite sign relations among various observables. This provides a unique opportunity to study initial/final state interaction effects in the fragmentation process and test the associated factorization.Comment: 4 pages, 3 figure

    Probing Gluonic Spin-Orbit Correlations in Photon Pair Production

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    We consider photon pair production in hadronic collisions at large mass and small transverse momentum of the pair, assuming that factorization in terms of transverse momentum dependent parton distributions applies. The unpolarized cross section is found to have azimuthal angular dependencies that are generated by a gluonic version of the Boer-Mulders function. In addition, the single-transversely polarized cross section is sensitive to the gluon Sivers function. We present simple numerical estimates for the Boer-Mulders and Sivers effects in diphoton production at RHIC and find that the process would offer unique opportunities for exploring transverse momentum dependent gluon distributions.Comment: 5 pages, 2 figures, minor changes, final version, to be published in PR

    Mid-Cretaceous (Cenomanian) snakes from Wadi Abu Hashim, Sudan: the earliest snake assemblage

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    The Cenomanian (mid-Cretaceous) beds at Wadi Abu Hashim (Sudan) have yielded a snake assemblage that is very rich and diverse for its geological age. It is by far the oldest known snake fauna. As the assignment of the hitherto earliest presumed snake (Barremian) to the Serpentes may now be questioned, this diverse fauna is only slightly younger than the earliest certain appearance of snakes (late Albian). The fauna is a surprising mixture of very primitive and comparatively advanced snakes. It includes two forms belonging to the lapparentophiid-grade of snakes (‘ lapparentophiid-grade snake A ’ and ‘ lapparentophiid-grade snake B ’), an indeterminate Madtsoiidae, a possible Palaeophiidae, the aniliid Coniophis dabiebus sp. nov., Coniophis cf. C. dabiebus, the nigerophiid Nubianophis afaahus gen. et sp. nov., Nubianophis cf. N. afaahus, the russellophiid Krebsophis thobanus gen. et sp. nov., a Colubroidea incertae sedis (indeterminate family), and two indeterminate snakes. In sum, at least nine species, perhaps twelve, are present. They represent at least seven families: at least one family of lapparentophiid-grade (?Lapparentophiidae), Madtsoiidae, ?Palaeophiidae, Aniliidae, Nigerophiidae, Russellophiidae, and an indeterminate colubroid family. The presence of colubroid snakes (Russellophiidae and an indeterminate family) as early as the mid-Cretaceous is especially unexpected. It may be inferred from phylogenies that the higher taxa of snakes (Anilioidea, Booidea, Acrochordoidea, Colubroidea, and obviously Scolecophidia) were already present during mid-Cretaceous times. The diversity of this fauna, coupled with the presence of advanced forms (colubroids), suggest that the origin of snakes markedly antedates the Cenomanian. Africa played an important role in the early radiation and, probably, in the origin of snakes.The Council's Research Committe, University of the Witwatersrand; National Science Foundatio

    High-magnetic field phase diagram and failure of magnetic Gr\"uneisen scaling in LiFePO4_4

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    We report the magnetic phase diagram of single-crystalline LiFePO4_4 in magnetic fields up to 58~T and present a detailed study of magneto-elastic coupling by means of high-resolution capacitance dilatometry. Large anomalies at \tn\ in the thermal expansion coefficient α\alpha imply pronounced magneto-elastic coupling. Quantitative analysis yields the magnetic Gr\"uneisen parameter Îłmag=6.7(5)⋅10−7\gamma_{\rm mag}=6.7(5)\cdot 10^{-7}~mol/J. The positive hydrostatic pressure dependence dTN/dp=1.46(11)dT_{\rm N}/dp = 1.46(11)~K/GPa is dominated by uniaxial effects along the aa-axis. Failure of Gr\"uneisen scaling below ≈40\approx 40~K, i.e., below the peak temperature in the magneto-electric coupling coefficient [\onlinecite{toft2015anomalous}], implies several competing degrees of freedom and indicates relevance of recently observed hybrid excitations~[\onlinecite{yiu2017hybrid}]. A broad and strongly magnetic-field-dependent anomaly in α\alpha in this temperature regime highlight the relevance of structure changes. Upon application of magnetic fields B∣∣bB||b-axis, a pronounced jump in the magnetisation implies spin-reorientation at BSF=32B_{\rm SF} = 32~T as well as a precursing phase at 29~T and T=1.5T=1.5~K. In a two-sublattice mean-field model, the saturation field Bsat,b=64(2)B_{\rm sat,b} = 64(2)~T enables the determination of the effective antiferromagnetic exchange interaction Jaf=2.68(5)J_{\rm af} = 2.68(5)~meV as well as the anisotropies Db=−0.53(4)D_{\rm b} = -0.53(4)~meV and Dc=0.44(8)D_{\rm c} = 0.44(8)~meV

    Convergence rates in expectation for Tikhonov-type regularization of Inverse Problems with Poisson data

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    In this paper we study a Tikhonov-type method for ill-posed nonlinear operator equations \gdag = F( ag) where \gdag is an integrable, non-negative function. We assume that data are drawn from a Poisson process with density t\gdag where t>0t>0 may be interpreted as an exposure time. Such problems occur in many photonic imaging applications including positron emission tomography, confocal fluorescence microscopy, astronomic observations, and phase retrieval problems in optics. Our approach uses a Kullback-Leibler-type data fidelity functional and allows for general convex penalty terms. We prove convergence rates of the expectation of the reconstruction error under a variational source condition as t→∞t\to\infty both for an a priori and for a Lepski{\u\i}-type parameter choice rule
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