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Available from: Mariam Tórtola, Aug 21, 2015
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    • "Solid lines indicate fermions, double lines Volkov states (which take the plane-wave background field exactly into account), wiggly lines photons and dashed lines the axial-vector current. energies in the GeV range [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] with strong optical lasers (ξ ∼ 10 2−3 ) [84] [85] [86] [87], the nonlinear quantum regime χ 1 could be entered, where also the production of real electron-positron pairs via the trident process becomes feasible [29] [30] [31] [32] [33] [34] [35]. As the energy and momentum required to bring the electron-positron pair on shell are provided by the laser field, the probability for trident pair production even exceeds the one for photon emission if χ 1 (the corresponding Feynman diagram contains only two interaction vertices, see Fig. 1). "
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    ABSTRACT: Even though neutrinos are neutral particles and interact only via the exchange of weak gauge bosons, charged leptons and quarks can mediate a coupling to the photon field beyond tree level. Inside a relativistically strong laser field nonlinear effects in the laser amplitude can play an important role, as electrons and positrons interact nonperturbatively with the coherent part of the photon field. Here, we calculate for the first time the leading-order contribution to the axial-vector--vector current-coupling tensor inside an arbitrary plane-wave laser field (which is taken into account exactly by employing the Furry picture). The current-coupling tensor appears in the calculation of various electroweak processes inside strong laser fields like photon emission or trident electron-positron pair production by a neutrino. Moreover, as we will see below, the axial-vector--vector current-coupling tensor contains the Adler-Bell-Jackiw (ABJ) anomaly. This occurrence renders the current-coupling tensor also interesting from a fundamental point of view, as it is the simplest Feynman diagram in an external field featuring this kind of anomaly.
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    • "But, the neutrino interactions involving the light fields are still assumed to be described by weak interactions within the SM and this is minimal SM extension for accomodating neutrino mass. However, once we invoke new physics in order to explain the non-zero neutrino masses, it seems rather unnatural to leave out the NSI which allow for flavor changing interactions as well as are new sources of CP violation which can affect production, detection and propagation of neutrinos [10] [11]. Some of the early attempts discussing new sources of lepton flavor violation (for instance, R-parity violating supersymmetry ) were geared towards providing an alternate explanation for the observed deficit of neutrinos coming from the Sun in the limiting case of zero neutrino mass and absence of vacuum mixing [12] [13] [14]. "
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    ABSTRACT: In vacuum or constant density matter, the two flavor neutrino oscillation formulae are insensitive to the presence of CP violating phases owing to the fact that the CP phase can be gauged away. In sharp contrast to the above case, we show that the CP violating phases can not be gauged away in presence of adiabatically changing background density accompanied by varying CP phases. We present a pure geometric visualization of this fact by exploiting Pancharatnam's prescription of cyclic quantum projections. Consequently the topological phase obtained in Phys. Rev. D 79, 096013 (2009) can become geometric if CP violation occurs in a varying density medium. Comment: v2 : modified version with new references
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    ABSTRACT: That neutrinos have mass and mix is now well established experimentally. Measurements of the properties of neutrinos from both natural and man-made sources have measured the large mixing angles and mass squared differences. In order to fully understand the nature of the neutrino, and ultimately the lepton sector, a number of measurements remain to be made. The Neutrino Factory would produce an intense beam of muon neutrino (muon antineutrino) and electron antineutrino (electron neutrino) from the decay of muons creating an intense flux of neutrinos. Such a facility would be capable of constraining the already measured mixing parameters to unprecedented accuracy while achieving sensitivity to the measurement of the third mixing angle and leptonic CP violating phase unrivaled by other facilities. The golden channel is characterised by the observation of a primary muon of the opposite charge to that decaying at the source, however, since this signal is subdominant the large data sample of correct sign muons have the potential to produce backgrounds to the desired signal channel and as such understanding the cross-sections to high accuracy enables a far better understanding of the response of the detector. Making these measurements requires the optimisation of all aspects of the detectors used for the measurement of the interaction properties as well as those which search for the appearance of neutrino flavours not present at the source. Pixellated silicon detectors are capable of high resolution three dimensional track reconstruction and vertexing. In studying active pixel sensors (APS) it was sought to understand the feasibility of commercially available technology to perform vertexing at a detector positioned within 1~km of the neutrino factory source. Using such technology at this near detector would improve significantly the ability of the experiment to constrain the cross-sections of neutrinos. These measurements would be particularly important in understanding neutrino induced charm production since the decays, in particular of charged D mesons, can produce penetrating muons with the potential to confuse the extraction of the appearance of muon neutrino (muon antineutrino). The capability to observe the impact parameter of the decaying meson significantly improves the accuracy of any measurement of the charm production cross-section. A Magnetised Iron Neutrino Detector (MIND) of large mass (50-100 ktonne) has been studied as the far detector where high suppression of the beam inherent backgrounds can be achieved due to the powerful suppression of hadronic particles in iron. Particular focus has been given to the introduction of a realistic reconstruction of the signal and analysis which optimises the signal efficiency below 5 GeV which has been identified by theoretical studies as key to the accurate measurement of the oscillation parameters down to low values. Studies of this detector have led to the extraction of the expected response of the detector to both golden channel signals and demonstration of the power of such an analysis to the measurement of the remaining oscillation parameters. Using minimal assumptions in the digitization of the simulated signal, the reconstruction and analysis of a large data-set of neutrino interactions, including deep-inelastic scattering (DIS), quasi-elastic scattering (QEL) and resonant pion production (RES), in MIND has led to the extraction of response matrices predicting signal efficiency for both muon neutrino and muon antineutrino appearance with thresholds between 2-3 GeV while suppressing key beam inherent backgrounds to at or below the 10^-4 level. Such a response has been shown to open the possiblity of sensitivity to the measurement of leptonic CP violation through the measurement of the mixing complex phase delta down to theta13 of order 0.2 degrees for maximal violation and to most possible values from theta13 of order 1 degrees. Sensitivity to the measurement of theta13 and to the determination of the true mass hierarchy is maintained down to theta13 of order 0.25 degrees.
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