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  • 1. Bakhti, Pouya
    et al.
    Farzan, Yasaman
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Revisiting the quantum decoherence scenario as an explanation for the LSND anomaly2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 5, article id 007Article in journal (Refereed)
    Abstract [en]

    We propose an explanation for the LSND anomaly based on quantum decoherence, postulating an exponential behavior for the decoherence parameters as a function of the neutrino energy. Within this ansatz decoherence effects are suppressed for neutrino energies above 200 MeV as well as around and below few MeV, restricting deviations from standard three-flavour oscillations only to the LSND energy range of 20-50 MeV. The scenario is consistent with the global data on neutrino oscillations, alleviates the tension between LSND and KARMEN, and predicts a null-result for MiniBooNE. No sterile neutrinos are introduced, conflict with cosmology is avoided, and no tension between short-baseline appearance and disappearance data arises. The proposal can be tested at planned reactor experiments with baselines of around 50 km, such as JUNO or RENO-50.

  • 2. Bergström, Johannes
    et al.
    Gonzalez-Garcia, M. C.
    Maltoni, Michele
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Karlsruher Institut für Technologie (KIT), Germany.
    Bayesian global analysis of neutrino oscillation data2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, p. 1-25Article in journal (Refereed)
    Abstract [en]

    We perform a Bayesian analysis of current neutrino oscillation data. When estimating the oscillation parameters we find that the results generally agree with those of the chi (2) method, with some differences involving s (23) (2) and CP-violating effects. We discuss the additional subtleties caused by the circular nature of the CP-violating phase, and how it is possible to obtain correlation coefficients with s (23) (2) . When performing model comparison, we find that there is no significant evidence for any mass ordering, any octant of s (23) (2) or a deviation from maximal mixing, nor the presence of CP-violation.

  • 3. Blennow, Mattias
    et al.
    Coloma, Pilar
    Huber, Patrick
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max Planck Society, Germany.
    Quantifying the sensitivity of oscillation experiments to the neutrino mass ordering2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 3, p. 28-Article in journal (Refereed)
    Abstract [en]

    Determining the type of the neutrino mass ordering ( normal versus inverted) is one of the most important open questions in neutrino physics. In this paper we clarify the statistical interpretation of sensitivity calculations for this measurement. We employ standard frequentist methods of hypothesis testing in order to precisely define terms like the median sensitivity of an experiment. We consider a test statistic T which in a certain limit will be normal distributed. We show that the median sensitivity in this limit is very close to standard sensitivities based on Delta chi(2) values from a data set without statistical fluctuations, such as widely used in the literature. Furthermore, we perform an explicit Monte Carlo simulation of the INO, JUNO, LBNE, NO nu A, and PINGU experiments in order to verify the validity of the Gaussian limit, and provide a comparison of the expected sensitivities for those experiments.

  • 4. Blennow, Mattias
    et al.
    Herrero-Garcia, Juan
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A halo-independent lower bound on the dark matter capture rate in the Sun from a direct detection signal2015In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 5, article id 036Article in journal (Refereed)
    Abstract [en]

    We show that a positive signal in a dark matter (DM) direct detection experiment can be used to place a lower bound on the DM capture rate in the Sun, independent of the DM halo. For a given particle physics model and DM mass we obtain a lower bound on the capture rate independent of the local DM density, velocity distribution, galactic escape velocity, as well as the scattering cross section. We illustrate this lower bound on the capture rate by assuming that upcoming direct detection experiments will soon obtain a significant signal. When comparing the lower bound on the capture rate with limits on the high-energy neutrino flux from the Sun from neutrino telescopes, we can place upper limits on the branching fraction of DM annihilation channels leading to neutrinos. With current data from IceCube and Super-Kamiokande non-trivial limits can be obtained for spin-dependent interactions and direct annihilations into neutrinos. In some cases also annihilations into tau tau or bb start getting constrained. For spin-independent interactions current constraints are weak, but they may become interesting for data from future neutrino telescopes.

  • 5. Blennow, Mattias
    et al.
    Herrero-Garcia, Juan
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Vogl, Stefan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Halo-independent tests of dark matter direct detection signals: local DM density, LHC, and thermal freeze-out2015In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 8, article id 039Article in journal (Refereed)
    Abstract [en]

    From an assumed signal in a Dark Matter (DM) direct detection experiment a lower bound on the product of the DM-nucleon scattering cross section and the local DM density is derived, which is independent of the local DM velocity distribution. This can be combined with astrophysical determinations of the local DM density. Within a given particle physics model the bound also allows a robust comparison of a direct detection signal with limits from the LHC. Furthermore, the bound can be used to formulate a condition which has to be fulfilled if the particle responsible for the direct detection signal is a thermal relic, regardless of whether it constitutes all DM or only part of it. We illustrate the arguments by adopting a simplified DM model with a Z' mediator and assuming a signal in a future xenon direct detection experiment.

  • 6. Bozorgnia, Nassim
    et al.
    Catena, Riccardo
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max Planck Society, Germany.
    Anisotropic dark matter distribution functions and impact on WIMP direct detection2013In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 12, p. 050-Article in journal (Refereed)
    Abstract [en]

    Dark matter N-body simulations suggest that the velocity distribution of dark matter is anisotropic. In this work we employ a mass model for the Milky Way whose parameters are determined from a fit to kinematical data. Then we adopt an ansatz for the dark matter phase space distribution which allows to construct self-consistent halo models which feature a degree of anisotropy as a function of the radius such as suggested by the simulations. The resulting velocity distributions are then used for an analysis of current data from dark matter direct detection experiments. We find that velocity distributions which are radially biased at large galactocentric distances (up to the virial radius) lead to an increased high velocity tail of the local dark matter distribution. This affects the interpretation of data from direct detection experiments, especially for dark matter masses around 10 GeV, since in this region the high velocity tail is sampled. We find that the allowed regions in the dark matter mass-cross section plane as indicated by possible hints for a dark matter signal reported by several experiments as well as conflicting exclusion limits from other experiments shift in a similar way when the halo model is varied. Hence, it is not possible to improve the consistency of the data by referring to anisotropic halo models of the type considered in this work.

  • 7. Bozorgnia, Nassim
    et al.
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Is the effect of the Sun's gravitational potential on dark matter particles observable?2014In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 8, p. 013-Article in journal (Refereed)
    Abstract [en]

    We consider the effect of the Sun's gravitational potential on the local phase space distribution of dark matter particles, focusing on its implication for the annual modulation signal in direct detection experiments. We perform a fit to the modulation signal observed in DAMA/LIBRA and show that the allowed region shrinks if Solar gravitational focusing (GF) is included compared to the one without GF. Furthermore, we consider a possible signal in a generic future direct detection experiment, irrespective of the DAMA/LIBRA signal. Even for scattering cross sections close to the current bound and a large exposure of a xenon target with 270 ton yr it will be hard to establish the presence of GF from data. In the region of dark matter masses below 40 GeV an annual modulation signal can be established for our assumed experimental setup, however GF is negligible for low masses. In the high mass region, where GF is more important, the significance of annual modulation itself is very low. We obtain similar results for lighter targets such as Ge and Ar. We comment also on inelastic scattering, noting that GF becomes somewhat more important for exothermic scattering compared to the elastic case.

  • 8. Bozorgnia, Nassim
    et al.
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    What is the probability that direct detection experiments have observed dark matter?2014In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 12, p. 015-Article in journal (Refereed)
    Abstract [en]

    In Dark Matter direct detection we are facing the situation of some experiments reporting positive signals which are in conflict with limits from other experiments. Such conclusions are subject to large uncertainties introduced by the poorly known local Dark Matter distribution. We present a method to calculate an upper bound on the joint probability of obtaining the outcome of two potentially conflicting experiments under the assumption that the Dark Matter hypothesis is correct, but completely independent of assumptions about the Dark Matter distribution. In this way we can quantify the compatibility of two experiments in an astrophysics independent way. We illustrate our method by testing the compatibility of the hints reported by DAMA and CDMS-Si with the limits from the LUX and SuperCDMS experiments. The method does not require Monte Carlo simulations but is mostly based on using Poisson statistics. In order to deal with signals of few events we introduce the so-called signal length to take into account energy information. The signal length method provides a simple way to calculate the probability to obtain a given experimental outcome under a specified Dark Matter and background hypothesis.

  • 9.
    Elevant, Jessica
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    On the determination of the leptonic CP phase2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 016Article in journal (Refereed)
    Abstract [en]

    The combination of data from long-baseline and reactor oscillation experiments leads to a preference of the leptonic CP phase delta(CP) in the range between pi and 2 pi. We study the statistical significance of this hint by performing a Monte Carlo simulation of the relevant data. We find that the distribution of the standard test statistic used to derive confidence intervals for delta(CP) is highly non-Gaussian and depends on the unknown true values of theta(23) and the neutrino mass ordering. Values of delta(CP) around pi/2 are disfavored at between 2 sigma and 3 sigma, depending on the unknown true values of theta(23) and the mass ordering. Typically the standard chi(2) approximation leads to over-coverage of the confidence intervals for delta(CP). For the 2-dimensional confidence region in the (delta(CP), theta(23)) plane the usual chi(2) approximation is better justified. The 2-dimensional region does not include the value delta(CP) = pi/2 up to the 86.3% (89.2%) CL assuming a true normal (inverted) mass ordering. Furthermore, we study the sensitivity to delta(CP) and theta(23) of an increased exposure of the T2K experiment, roughly a factor 12 larger than the current exposure and including also anti-neutrino data. Also in this case deviations from Gaussianity may be significant, especially if the mass ordering is unknown.

  • 10. Gonzalez-Garcia, M. C.
    et al.
    Matoni, Michele
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Updated fit to three neutrino mixing: status of leptonic CP violation2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 11, article id 052Article in journal (Refereed)
    Abstract [en]

    We present a global analysis of solar, atmospheric, reactor and accelerator neutrino data in the framework of three-neutrino oscillations based on data available in summer 2014. We provide the allowed ranges of the six oscillation parameters and show that their determination is stable with respect to uncertainties related to reactor neutrino and solar neutrino flux predictions. We find that the maximal possible value of the Jarlskog invariant in the lepton sector is 0.033 +/- 0.010 (+/- 0.027) at the l sigma (3 sigma) level and we use leptonic unitarity triangles to illustrate the ability of global oscillation data to obtain information on CP violation. We discuss tendencies and tensions of the global fit related to the octant of theta 23 as well as the CP violating phase delta cp. The favored values of (delta cp are around 3 pi/2 while values around pi/2 are disfavored at about Delta chi(2) similar or equal to 6 . We comment on the non-trivial task to assign a confidence level to this Delta chi(2) value by performing a Monte Carlo study of T2K data.

  • 11. Schmidt, Daniel
    et al.
    Schwetz, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max-Planck-Institut für Kernphysik, Germany.
    Zhang, He
    Status of the Zee-Babu model for neutrino mass and possible tests at a like-sign linear collider2014In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 885, p. 524-541Article in journal (Refereed)
    Abstract [en]

    We provide an updated scan of the allowed parameter space of the two-loop Zee Babu model for neutrino mass. Taking into account most recent experimental data on mu -> e gamma as well as the mixing angle 13 we obtain lower bounds on the masses of the singly and doubly charged scalars of between 1 and 2 TeV, with some dependence on perturbativity and fine-tuning requirements. This makes the scalars difficult to observe at LHC with 14 TeV even with optimistic assumptions on the luminosity, and would require a multi-TeV linear collider to see the scalar resonances. We point out, however, that a sub-TeV linear collider in the like-sign mode may be able to observe lepton flavor violating processes such as e e pc due to contact interactions induced by the doubly charged scalar with masses up to around 10 TeV. We investigate the possibility to distinguish the Zee Babu model from the Higgs triplet model using such processes.

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