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  • 101.
    Bergström, Johannes
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Bayesian evidence for non-zero theta(13) and CP-violation in neutrino oscillations2012In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2012, no 8, p. 163-Article in journal (Refereed)
    Abstract [en]

    We present the Bayesian method for evaluating the evidence for a non-zero value of the leptonic mixing angle theta(13) and CP-violation in neutrino oscillation experiments. This is an application of the well-established method of Bayesian model selection, of which we give a concise and pedagogical overview. When comparing the hypothesis theta(13) = 0 with hypotheses where theta(13) > 0 using global data but excluding the recent reactor measurements, we obtain only a weak preference for a non-zero theta(13), even though the significance is over 3 sigma. We then add the reactor measurements one by one and show how the evidence for theta(13) > 0 quickly increases. When including the DOUBLE CHOOZ, DAYA BAY, and RENO data, the evidence becomes overwhelming with a posterior probability of the hypothesis theta(13) = 0 below 10(-11). Owing to the small amount of information on the CP-phase delta, very similar evidences are obtained for the CP-conserving and CP-violating hypotheses. Hence, there is, not unexpectedly, neither evidence for nor against leptonic CP-violation. However, when future experiments aiming to search for CP-violation have started taking data, this question will be of great importance and the method described here can be used as an important complement to standard analyses.

  • 102.
    Bergström, Johannes
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Combining and comparing neutrinoless double beta decay experiments using different nuclei2013In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, p. 093-Article in journal (Refereed)
    Abstract [en]

    We perform a global fit of the most relevant neutrinoless double beta decay experiments within the standard model with massive Majorana neutrinos. Using Bayesian inference makes it possible to take into account the theoretical uncertainties on the nuclear matrix elements in a fully consistent way. First, we analyze the data used to claim the observation of neutrinoless double beta decay in Ge-76, and find strong evidence (according to Jeffrey's scale) for a peak in the spectrum and moderate evidence for that the peak is actually close to the energy expected for the neutrinoless decay. We also find a significantly larger statistical error than the original analysis, which we include in the comparison with other data. Then, we statistically test the consistency between this claim with that of recent measurements using Xe-136. We find that the two data sets are about 40 to 80 times more probable under the assumption that they are inconsistent, depending on the nuclear matrix element uncertainties and the prior on the smallest neutrino mass. Hence, there is moderate to strong evidence of incompatibility, and for equal prior probabilities the posterior probability of compatibility is between 1.3% and 2.5%. If one, despite such evidence for incompatibility, combines the two data sets, we find that the total evidence of neutrinoless double beta decay is negligible. If one ignores the claim, there is weak evidence against the existence of the decay. We also perform approximate frequentist tests of compatibility for fixed ratios of the nuclear matrix elements, as well as of the no signal hypothesis. Generalization to other sets of experiments as well as other mechanisms mediating the decay is possible.

  • 103.
    Bergström, Johannes
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Models in Neutrino Physics: Numerical and Statistical Studies2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The standard model of particle physics can excellently describe the vast majorityof data of particle physics experiments. However, in its simplest form, it cannot account for the fact that the neutrinos are massive particles and lepton flavorsmixed, as required by the observation of neutrino oscillations. Hence, the standardmodel must be extended in order to account for these observations, opening up thepossibility to explore new and interesting physical phenomena.

    There are numerous models proposed to accommodate massive neutrinos. Thesimplest of these are able to describe the observations using only a small numberof effective parameters. Furthermore, neutrinos are the only known existing particleswhich have the potential of being their own antiparticles, a possibility that isactively being investigated through experiments on neutrinoless double beta decay.In this thesis, we analyse these simple models using Bayesian inference and constraintsfrom neutrino-related experiments, and we also investigate the potential offuture experiments on neutrinoless double beta decay to probe other kinds of newphysics.

    In addition, more elaborate theoretical models of neutrino masses have beenproposed, with the seesaw models being a particularly popular group of models inwhich new heavy particles generate neutrino masses. We study low-scale seesawmodels, in particular the resulting energy-scale dependence of the neutrino parameters,which incorporate new particles with masses within the reach of current andfuture experiments, such as the LHC.

  • 104.
    Bergström, Johannes
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Predictions of Effective Models in Neutrino Physics2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Experiments on neutrino oscillations have confirmed that neutrinos have small, but non-zero masses, and that the interacting neutrino states do not have definite masses, but are mixtures of such states.The seesaw models make up a group of popular models describing the small neutrino masses and the corresponding mixing.In these models, new, heavy fields are introduced and the neutrino masses are suppressed by the ratio between the electroweak scale and the large masses of the new fields. Usually, the new fields introduced have masses far above the electroweak scale, outside the reach of any foreseeable experiments, making these versions of seesaw models essentially untestable. However, there are also so-called low-scale seesaw models, where the new particles have masses above the electroweak scale, but within the reach of future experiments, such as the LHC.In quantum field theories, quantum corrections generally introduce an energy-scale dependence on all their parameters, described by the renormalization group equations. In this thesis, the energy-scale dependence of the neutrino parameters in two low-scale seesaw models, the low-scale type I and inverse seesaw models, are considered. Also, the question of whether the neutrinos are Majorana particles, \ie , their own antiparticles, has not been decided experimentally. Future experiments on neutrinoless double beta decay could confirm the Majorana nature of neutrinos. However, there could also be additional contributions to the decay, which are not directly related to neutrino masses. We have investigated the possible future bounds on the strength of such additional contributions to neutrinoless double beta decay, depending on the outcome of ongoing and planned experiments related to neutrino masses.

  • 105.
    Bergström, Johannes
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Signatures of Unparticle Self-Interactions at the Large Hadron Collider2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Unparticle physics is the physics of a hidden sector which is conformal in the infrared and coupled to the Standard Model. The concept of unparticle physics was introduced by Howard Georgi in 2007 and has since then received a lot of attention, including many studies of its phenomenology in different situations. After a review of the necessary background material, the implications of the self-interactions of the unparticle sector for LHC physics is studied. More specifically, analyses of four-body final states consisting of photons and leptons are performed. The results are upper bounds on the total cross sections as well as distributions of transverse momentum.

  • 106.
    Bergström, Johannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Malinský, Michal
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zhang, He
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Renormalization group running of neutrino parameters in the inverse seesaw model2010In: Physical Review D, ISSN 1550-7998, Vol. 81, no 11, p. 116006-Article in journal (Refereed)
    Abstract [en]

    We perform a detailed study of the renormalization group equations in the inverse seesaw model. Especially, we derive compact analytical formulas for the running of the neutrino parameters in the standard model and the minimal supersymmetric standard model, and illustrate that, due to large Yukawa coupling corrections, significant running effects on the leptonic mixing angles can be naturally obtained in the proximity of the electroweak scale, perhaps even within the reach of the LHC. In general, if the mass spectrum of the light neutrinos is nearly degenerate, the running effects are enhanced to experimentally accessible levels, well suitable for the investigation of the underlying dynamics behind the neutrino mass generation and the lepton flavor structure. In addition, the effects of the seesaw thresholds are discussed, and a brief comparison to other seesaw models is carried out.

  • 107.
    Bergström, Johannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Constraining new physics with a positive or negative signal of neutrino-less double beta decay2011In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2011, no 05, p. 122-Article in journal (Refereed)
    Abstract [en]

    We investigate numerically how accurately one could constrain the strengths of different short-range contributions to neutrino-less double beta decay in effective field theory. Depending on the outcome of near-future experiments yielding information on the neutrino masses, the corresponding bounds or estimates can be stronger or weaker. A particularly interesting case, resulting in strong bounds, would be a positive signal of neutrino-less double beta decay that is consistent with complementary information from neutrino oscillation experiments, kinematical determinations of the neutrino mass, and measurements of the sum of light neutrino masses from cosmological observations. The keys to more robust bounds are improvements of the knowledge of the nuclear physics involved and a better experimental accuracy.

  • 108.
    Bergström, Johannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Unparticle self-interactions at the Large Hadron Collider2009In: Physical Review D. Particles, fields, gravitation and cosmology, ISSN 1550-7998, Vol. 80, no 11, p. 115014-Article in journal (Refereed)
    Abstract [en]

    We investigate the effect of unparticle self-interactions at the Large Hadron Collider (LHC). Especially, we discuss the three-point correlation function, which is determined by conformal symmetry up to a constant, and study its relation to processes with four-particle final states. These processes could be used as a favorable way to look for unparticle physics, and for weak enough couplings to the standard model, even the only way. We find updated upper bounds on the cross sections for unparticle-mediated 4 gamma final states at the LHC and novel upper bounds for the corresponding 2 gamma 2l and 4l final states. The size of the allowed cross sections obtained are comparably large for large values of the scaling dimension of the unparticle sector, but they decrease with decreasing values of this parameter. In addition, we present relevant distributions for the different final states, enabling the possible identification of the unparticle scaling dimension if there was to be a large number of events of such final states at the LHC.

  • 109.
    Bergström, Johannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zhang, He
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Threshold effects on renormalization group running of neutrino parameters in the low-scale seesaw model2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 698, no 4, p. 297-305Article in journal (Refereed)
    Abstract [en]

    We show that, in the low-scale type-I seesaw model, renormalization group running of neutrino parameters may lead to significant modifications of the leptonic mixing angles in view of so-called seesaw threshold effects. Especially, we derive analytical formulas for radiative corrections to neutrino parameters in crossing the different seesaw thresholds, and show that there may exist enhancement factors efficiently boosting the renormalization group running of the leptonic mixing angles. We find that, as a result of the seesaw threshold corrections to the leptonic mixing angles, various flavor symmetric mixing patterns (e.g., bi-maximal and tri-bimaximal mixing patterns) can be easily accommodated at relatively low energy scales, which is well within the reach of running and forthcoming experiments (e.g., the LHC).

  • 110.
    Bergström, Johannes
    et al.
    Universitat de Barcelona.
    Riad, Riad
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Bayesian Model comparison of Higgs couplings2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 7, article id 075008Article in journal (Refereed)
    Abstract [en]

    We investigate the possibility of contributions from physics beyond the Standard Model (SM) to the Higgs couplings, in the light of the LHC data. The work is performed within an interim framework where the magnitude of the Higgs production and decay rates are rescaled through Higgs coupling scale factors. We perform Bayesian parameter inference on these scale factors, concluding that there is good compatibility with the SM. Furthermore, we carry out a Bayesian model comparison on all models where any combination of scale factors can differ from their SM values and find that typically models with fewer free couplings are strongly favored. We consider the evidence that each coupling individually equals the SM value, making the minimal assumptions on the other couplings. Finally, we make a comparison of the SM against a single "not-SM" model and find that there is moderate to strong evidence for the SM.

  • 111. Bergström, Lars
    et al.
    Botner, OlgaCarlson, PerHulth, Per OlofOhlsson, TommyKTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrino Physics: Proceedings of Nobel Symposium 1292006Conference proceedings (editor) (Refereed)
    Abstract [en]

    PREFACE

    Nobel Symposium 129 on Neutrino Physics was held at Haga Slott in Enköping, Sweden during August 19–24, 2004. Invited to the symposium were around 40 globally leading researchers in the field of neutrino physics, both experimental and theoretical. In addition to these participants, some 30 local researchers and graduate students participated in the symposium.

    The dominant theme of the lectures was neutrino oscillations, which after several years were recently verified by results from the Super-Kamiokande detector in Kamioka, Japan and the SNO detector in Sudbury, Canada. Discussion focused especially on effects of neutrino oscillations derived from the presence of matter and the fact that three different neutrinos exist. Since neutrino oscillations imply that neutrinos have mass, this is the first experimental observation that fundamentally deviates from the standard model of particle physics. This is a challenge to both theoretical and experimental physics. The various oscillation parameters will be determined with increased precision in new, specially designed experiments. Theoretical physics is working intensively to insert the knowledge that neutrinos have mass into the theoretical models that describe particle physics. It will probably turn out that the discovery of neutrino oscillations signifies a breakthrough in the description of the very smallest constituents of matter. The lectures provided a very good description of the intensive situation in the field right now. The topics discussed also included mass models for neutrinos, neutrinos in extra dimensions as well as the `seesaw mechanism', which provides a good description of why neutrino masses are so small.

    Also discussed, besides neutrino oscillations, was the new field of neutrino astronomy. Among the questions that neutrino astronomy hopes to answer are what the dark matter in the Universe consists of and where cosmic radiation at extremely high energies comes from. For this purpose, large neutrino telescopes are built deep in the Antarctic ice, in the Baikal Lake, and in the Mediterranean Sea.

    Among prominent unanswered questions, highlighted as one of the most important, was whether neutrinos are Dirac or Majorana particles. By studying neutrino double beta decay, researchers hope to answer this question, but it will put very large demands on detectors.

    The programme also included ample time for lively and valuable discussions, which cannot normally be held at ordinary conferences.

    The symposium concluded with a round-table discussion, where participants discussed the future of neutrino physics.Without a doubt, neutrino physics today is moving toward a very exciting and interesting period.

    An important contribution to the success of the symposium was the wonderful setting that the Haga Slott manor house hotel and conference center offered to the participants.

  • 112. Bertaccini, E. J.
    et al.
    Yoluk, Özge
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Lindahl, Erik R.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Trudell, James Robert
    Department of Anesthesia, Stanford University School of Medicine, United States .
    Assessment of homology templates and an anesthetic binding site within the ?-aminobutyric acid receptor2013In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 119, no 5, p. 1087-1095Article in journal (Refereed)
    Abstract [en]

    Background: Anesthetics mediate portions of their activity via modulation of the ?-aminobutyric acid receptor (GABAaR). Although its molecular structure remains unknown, significant progress has been made toward understanding its interactions with anesthetics via molecular modeling. Methods: The structure of the torpedo acetylcholine receptor (nAChR?), the structures of the ?4 and ?2 subunits of the human nAChR, the structures of the eukaryotic glutamate-gated chloride channel (GluCl), and the prokaryotic pH-sensing channels, from Gloeobacter violaceus and Erwinia chrysanthemi, were aligned with the SAlign and 3DMA algorithms. A multiple sequence alignment from these structures and those of the GABAaR was performed with ClustalW. The Modeler and Rosetta algorithms independently created three-dimensional constructs of the GABAaR from the GluCl template. The CDocker algorithm docked a congeneric series of propofol derivatives into the binding pocket and scored calculated binding affinities for correlation with known GABAaR potentiation EC50s. Results: Multiple structure alignments of templates revealed a clear consensus of residue locations relevant to anesthetic effects except for torpedo nAChR. Within the GABAaR models generated from GluCl, the residues notable for modulating anesthetic action within transmembrane segments 1, 2, and 3 converged on the intersubunit interface between ? and ? subunits. Docking scores of a propofol derivative series into this binding site showed strong linear correlation with GABAaR potentiation EC50. Conclusion: Consensus structural alignment based on homologous templates revealed an intersubunit anesthetic binding cavity within the transmembrane domain of the GABAaR, which showed a correlation of ligand docking scores with experimentally measured GABAaR potentiation.

  • 113. Bertolini, S.
    et al.
    Luzio, L. D.
    Malinský, Michal
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    The quantum vacuum of the minimal SO(10) GUT2010In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 259, no 1, p. 012098-Article in journal (Refereed)
    Abstract [en]

    We reexamine the longstanding no-go excluding all potentially viable SO(10) →SU(3)c⊗ SU(2)L ⊗ U(1)Y symmetry breaking patterns within the minimal renormalizable non-supersymmetric SO(10) GUT framework featuring the 45-dimensional adjoint representation in the Higgs sector. A simple symmetry argument indicates that quantum effects do change the vacuum structure of the model dramatically. A thorough analysis of the one-loop effective potential reveals that the phenomenologically favoured symmetry breaking chains passing through the SU(4)C ⊗ SU(2)L ⊗ U(1)R or SU(3)c ⊗ SU(2)L ⊗ SU(2)R ⊗ U(1)B-L intermediate stages are, indeed, supported at the quantum level. This brings the class of minimal non-supersymmetric SO(10) GUTs back from oblivion, providing a new ground for a potentially realistic model building.

  • 114. Bertolini, Stefano
    et al.
    Di Luzio, Luca
    Malinsky, Michal
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Intermediate mass scales in the nonsupersymmetric SO(10) grand unification: A reappraisal2009In: PHYSICAL REVIEW D, ISSN 1550-7998, Vol. 80, no 1, p. 015013-Article in journal (Refereed)
    Abstract [en]

    The constraints of gauge unification on intermediate mass scales in nonsupersymmetric SO(10) scenarios are systematically discussed. With respect to the existing reference studies we include the U(1) gauge mixing renormalization at the one- and two-loop level, and reassess the two-loop beta coefficients. We evaluate the effects of additional Higgs multiplets required at intermediate stages by a realistic mass spectrum and update the discussion to the present day data. On the basis of the obtained results, SO(10) breaking patterns with up to two intermediate mass scales are discussed for potential relevance and model predictivity.

  • 115. Bertolini, Stefano
    et al.
    Di Luzio, Luca
    Malinský, Michal
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    The vacuum of the minimal nonsupersymmetric SO(10) unification2010In: Physical Review D - Particles, Fields, Gravitation and Cosmology, ISSN 1550-7998, Vol. 81, no 3, p. 035015-Article in journal (Refereed)
    Abstract [en]

    We study a class of nonsupersymmetric SO(10) grand-unified scenarios where the first stage of the symmetry breaking is driven by the vacuum expectation values of the 45- dimensional adjoint representation. Three- decade- old results claim that such a Higgs setting may lead exclusively to the flipped SU(5) circle times U(1) intermediate stage. We show that this conclusion is actually an artifact of the tree- level potential. The study of the accidental global symmetries emerging in various limits of the scalar potential offers a simple understanding of the tree- level result and a rationale for the drastic impact of quantum corrections. We scrutinize in detail the simplest and paradigmatic case of the 45(H) circle plus 16(H) Higgs sector triggering the breaking of SO(10) to the standard electroweak model. We show that the minimization of the one- loop effective potential allows for intermediate SU(4)(C) circle times SU(2)(L) circle times U(1)(R) and SU(3)(c) circle times SU(2)(L) circle times SU(2)(R) circle times U(1)(B-L) symmetric stages as well. These are the options favored by gauge unification. Our results, that apply whenever the SO(10) breaking is triggered by < 45(H)>, open the path for hunting the simplest realistic scenario of nonsupersymmetric SO(10) grand unification.

  • 116.
    Biltmo, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Statics, Domain Structure and Dynamics in the Dilute Dipolar Magnet LiHoF42009Doctoral thesis, comprehensive summary (Other academic)
  • 117.
    Biltmo, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Glauber Dynamics of Dilute Ising DipolesManuscript (preprint) (Other academic)
  • 118.
    Biltmo, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Low-temperature properties of the dilute dipolar magnet LiHoxY1-xF42008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 5Article in journal (Refereed)
    Abstract [en]

    We analyze recent experiments on the dilute rare-earth compound LiHoxY1-xF4 in the context of an effective Ising dipolar model. Using a Monte Carlo method we calculate the low-temperature behavior of the specific heat and linear susceptibility and compare our results to measurements. In our model the susceptibility follows a Curie-Weiss law at high temperature, X similar to 1 / (T- T-cw), with a Curie-Weiss temperature that scales with dilution, T-cw similar to x, consistent with early experiments. We also find that the peak in the specific heat scales linearly with dilution, C-max(T)similar to x, in disagreement with recent experiments. This difference could be caused by the hyperfine interaction which is not included in our calculation. Experimental studies do not reach a consensus on the functional form of the susceptibility and specific heat, and in particular, we do not see reported scalings of the form X similar to T-0.75 and X similar to exp(-T/T-0). Furthermore, we calculate the ground-state magnetization as a function of dilution and re-examine the phase diagram around the critical dilution x, = 0.24 +/- 0.03. We find that the spin-glass susceptibility for the Ising model does not diverge below x, while some recent experiments give strong evidence for a stable spin-glass phase in LiHo0.167Y0.833F4.

  • 119.
    Biltmo, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Phase diagram of the dilute magnet LiHoxY1-xF42007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 5Article in journal (Refereed)
    Abstract [en]

    We study the effective long-range Ising dipole model with a local exchange interaction appropriate for the dilute magnetic compound LiHoxY1-xF4. Our calculations yield a value of 0.12 K for the nearest-neighbor exchange interaction. Using a Monte Carlo method, we calculate the phase boundary T-c(x) between the ferromagnetic and paramagnetic phases. We demonstrate that the experimentally observed linear decrease in T-c with dilution is not the simple mean-field result, but a combination of the effects of fluctuations and the exchange interaction. Furthermore, we find a critical dilution x(c)=0.21(2), below which there is no ordering. In agreement with recent Monte Carlo simulations on a similar model, we find no evidence of the experimentally observed freezing of the glassy state in our calculation. We apply the theory of Stephen and Aharony to LiHoxY1-xF4 and find that the theory does predict a finite-temperature freezing of the spin glass. Reasons for the discrepancies are discussed.

  • 120.
    Biltmo, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    The ferromagnetic transition and domain structure in LiHoF42009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, no 2Article in journal (Refereed)
    Abstract [en]

    Using Monte Carlo simulations we verify that the rare-earth compound LiHoF4 is a very good realization of a dipolar Ising model. With only one free parameter our calculations for the magnetization, specific heat and inverse susceptibility match experimental data at a quantitative level in the 0.5-3 kelvin range, including the ferromagnetic transition at 1.53 K. Using parallel tempering methods and reaching system sizes up to 32000 dipoles with periodic boundary conditions, we are able to give evidence of the logarithmic corrections predicted in renormalization group theory. Due to the long range and angular dependence of the dipolar model, sample shape and domains play a crucial role in the ordered state. We consider surface corrections to Griffiths's theorem, which arise infinite macroscopic samples and lead to a theory of magnetic domains. We find a domain wall energy of 0.059 erg/cm(2) and predict that the ground-state domain structure for cylinders with a demagnetization factor N > 0 consists of thin parallel sheets of opposite magnetization, with a width depending on the demagnetization factor.

  • 121.
    Biltmo, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Unreachable glass transition in dilute dipolar magnet2012In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 3, p. 857-Article in journal (Refereed)
    Abstract [en]

    In magnetic systems the combined effects of disorder and frustration may cause the moments to freeze into a disordered state at a spin-glass transition. Recent experiments have shown that the rare earth compound LiHo0.045Y0.955F4 freezes, but that the transition is unreachable because of dynamics that are 10(7) times slower than in ordinary spin-glass materials. This conclusion refutes earlier investigations reporting a speed-up of the dynamics into an exotic anti-glass phase caused by entanglement of quantum dipoles. Here we present a theory, backed by numerical simulations, which describes the material in terms of classical dipoles governed by Glauber dynamics. The dipoles freeze and we find that the ultra-slow dynamics are caused by rare, strongly ordered clusters, which give rise to a previously predicted, but hitherto unobserved, Griffths phase between the paramagnetic and spin-glass phases. In addition, the hyperfine interaction creates a high energy barrier to flipping the electronic spin, resulting in a clear signature in the dynamic correlation function.

  • 122.
    Birkne, Oskar
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Hanke, Jana
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Cooling a Bottle of Champagne: Mathematical Models for the Cooling Process2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 123. Biswas, A.
    et al.
    Choubey, S.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Khan, S.
    Galactic gamma ray excess and dark matter phenomenology in a U(1)B−L model2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2016, no 8, article id 114Article in journal (Refereed)
    Abstract [en]

    In this work, we have considered a gauged U(1)B−L extension of the Standard Model (SM) with three right handed neutrinos for anomaly cancellation and two additional SM singlet complex scalars with nontrivial B-L charges. One of these is used to spontaneously break the U(1)B−L gauge symmetry, leading to Majorana masses for the neutrinos through the standard Type I seesaw mechanism, while the other becomes the dark matter (DM) candidate in the model. We test the viability of the model to simultaneously explain the DM relic density observed in the CMB data as well as the Galactic Centre (GC) γ-ray excess seen by Fermi-LAT. We show that for DM masses in the range 40-55 GeV and for a wide range of U(1)B−L gauge boson masses, one can satisfy both these constraints if the additional neutral Higgs scalar has a mass around the resonance region. In studying the dark matter phenomenology and GC excess, we have taken into account theoretical as well as experimental constraints coming from vacuum stability condition, Planck bound on DM relic density, LHC and LUX and present allowed areas in the model parameter space consistent with all relevant data, calculate the predicted gamma ray flux from the GC and discuss the related phenomenology.

  • 124. Biswas, A.
    et al.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Harish-Chandra Research Institute, India.
    Khan, S.
    FIMP and muon (g − 2) in a U(1)Lμ−Lτ model2017In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2017, no 2, article id 123Article in journal (Refereed)
    Abstract [en]

    The tightening of the constraints on the standard thermal WIMP scenario has forced physicists to propose alternative dark matter (DM) models. One of the most popular alternate explanations of the origin of DM is the non-thermal production of DM via freeze-in. In this scenario the DM never attains thermal equilibrium with the thermal soup because of its feeble coupling strength (∼10−12) with the other particles in the thermal bath and is generally called the Feebly Interacting Massive Particle (FIMP). In this work, we present a gauged U(1)Lμ−Lτ extension of the Standard Model (SM) which has a scalar FIMP DM candidate and can consistently explain the DM relic density bound. In addition, the spontaneous breaking of the U(1)Lμ−Lτ gauge symmetry gives an extra massive neutral gauge boson Zμτ which can explain the muon (g − 2) data through its additional one-loop contribution to the process. Lastly, presence of three right-handed neutrinos enable the model to successfully explain the small neutrino masses via the Type-I seesaw mechanism. The presence of the spontaneously broken U(1)Lμ−Lτ gives a particular structure to the light neutrino mass matrix which can explain the peculiar mixing pattern of the light neutrinos.

  • 125. Biswas, Anirban
    et al.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Harish Chandra Res Inst, India.
    Khan, Sarif
    Neutrino mass, dark matter and anomalous magnetic moment of muon in a U(1)(L mu-LT) model2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 147Article in journal (Refereed)
    Abstract [en]

    The observation of neutrino masses, mixing and the existence of dark matter are amongst the most important signatures of physics beyond the Standard Model (SM). In this paper, we propose to extend the SM by a local L-mu-L-T gauge symmetry, two additional complex scalars and three right-handed neutrinos. The L-mu-L-T gauge symmetry is broken spontaneously when one of the scalars acquires a vacuum expectation value. The L-mu-L-T gauge symmetry is known to be anomaly free and can explain the beyond SM measurement of the anomalous muon (g - 2) through additional contribution arising from the extra Z(mu T) mediated diagram. Small neutrino masses are explained naturally through the Type-I seesaw mechanism, while the mixing angles are predicted to be in their observed ranges due to the broken L-mu-L-T symmetry. The second complex scalar is shown to be stable and becomes the dark matter candidate in our model. We show that while the Z(mu T) portal is ineffective for the parameters needed to explain the anomalous muon (g 2) data, the correct dark matter relic abundance can easily be obtained from annihilation through the Higgs portal. Annihilation of the scalar dark matter in our model can also explain the Galactic Centre gamma ray excess observed by Fermi-LAT. We show the predictions of our model for future direct detection experiments and neutrino oscillation experiments.

  • 126. Biswas, Anirban
    et al.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Harish-Chandra Research Institute, India.
    Khan, Sarif
    Neutrino mass, leptogenesis and FIMP dark matter in a U(1)(B-L) model2017In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 77, no 12, article id 875Article in journal (Refereed)
    Abstract [en]

    The Standard Model (SM) is inadequate to explain the origin of tiny neutrino masses, the dark matter (DM) relic abundance and the baryon asymmetry of the Universe. In this work, to address all three puzzles, we extend the SM by a local U(1)(B-L) gauge symmetry, three right-handed (RH) neutrinos for the cancellation of gauge anomalies and two complex scalars having non-zero U(1)(B-L) charges. All the newly added particles become massive after the breaking of the U(1)(B-L) symmetry by the vacuum expectation value (VEV) of one of the scalar fields phi(H). The other scalar field, phi(DM), which does not have any VEV, becomes automatically stable and can be a viable DM candidate. Neutrino masses are generated using the Type-I seesaw mechanism, while the required lepton asymmetry to reproduce the observed baryon asymmetry can be attained from the CP violating out of equilibrium decays of the RH neutrinos in TeV scale. More importantly within this framework, we study in detail the production of DM via the freeze-in mechanism considering all possible annihilation and decay processes. Finally, we find a situation when DM is dominantly produced from the annihilation of the RH neutrinos, which are at the same time also responsible for neutrino mass generation and leptogenesis.

  • 127.
    Björk, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Deng, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Discrete simulation models of surface growth2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this thesis the time evolution and scaling properties of different discrete models of

    surface growth using computer simulation is studied. The models are mainly using random

    deposition at a perpendicular angle to the substrates to model the adsorption process, and

    both one dimensional and two dimensional surfaces are considered. The Edwards-Wilkinson,

    Kardar-Parisi-Zhang and Mullins equations are also studied as analytical methods to describe

    the growth of surfaces. The scaling exponents derived from these equations are used as

    reference when analysing the exponents calculated from the simulation models studied in this

    thesis.

    We have found that the simulation models do not correspond perfectly with the analytical

    models for surface growth, suggesting possible flaws in our models or definitions. Despite the

    possible flaws, the models prove to be powerful tools for analysing the time evolution of surface

    growth. Furthermore, we have shown that most of the simulation models exhibit the expected

    scaling properties, which indicates that the surfaces do have the self-affine structure they are

    presumed to have.

  • 128.
    Blennow, M.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Choubey, S.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, T.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Pramanik, D.
    Raut, S. K.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    A combined study of source, detector and matter non-standard neutrino interactions at DUNE2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2016, no 8, article id 90Article in journal (Refereed)
    Abstract [en]

    We simultaneously investigate source, detector and matter non-standard neutrino interactions at the proposed DUNE experiment. Our analysis is performed using a Markov Chain Monte Carlo exploring the full parameter space. We find that the sensitivity of DUNE to the standard oscillation parameters is worsened due to the presence of non-standard neutrino interactions. In particular, there are degenerate solutions in the leptonic mixing angle θ23 and the Dirac CP-violating phase δ. We also compute the expected sensitivities at DUNE to the non-standard interaction parameters. We find that the sensitivities to the matter non-standard interaction parameters are substantially stronger than the current bounds (up to a factor of about 15). Furthermore, we discuss correlations between the source/detector and matter non-standard interaction parameters and find a degenerate solution in θ23. Finally, we explore the effect of statistics on our results.

  • 129.
    Blennow, Mattias
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Damping signatures in future neutrino oscillation experiments2006In: Nuclear physics B, Proceedings supplements, ISSN 0920-5632, E-ISSN 1873-3832, Vol. 155, p. 195-196Article in journal (Refereed)
    Abstract [en]

    In precision measurements of neutrino oscillation parameters and in the search for theta(13), it becomes important to study small effects which may alter the precision measurements or mimic a theta(13) signal. Here, I give an introduction to a common framework in which many of the possible small effects - such as neutrino wave packet decoherence, neutrino quantum decoherence, and neutrino decay - can be studied. This framework is based on the introduction of damping factors on the probability level of the neutrino oscillation formulas.

  • 130.
    Blennow, Mattias
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Mass hierarchy sensitivity at future oscillation facilities2015In: NUCLEAR AND PARTICLE PHYSICS PROCEEDINGS, KTH Royal Inst Technol, Dept Theoret Phys, Sch Engn Sci, AlbaNova Univ Ctr, S-10691 Stockholm, Sweden.: Elsevier, 2015, Vol. 265, p. 171-173Conference paper (Refereed)
    Abstract [en]

    Within the neutrino community, there has been a recent discussion on the validity of the chi(2) approximation when evaluating the results of oscillation experiments sensitive to the neutrino mass hierarchy. In this proceeding, we discuss the resolution of this discussion by going back to the basic statistical definitions in the computation of experimental sensitivities.

  • 131.
    Blennow, Mattias
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    On the Bayesian approach to neutrino mass ordering2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, p. 139-Article in journal (Refereed)
    Abstract [en]

    We study the framework of Bayesian statistics for analyzing the capabilities and results of future experiments looking to solve the issue of the neutrino mass ordering. Starting from the general scenario, we then give examples of the procedure for experiments with Gaussian and non-Gaussian distributions for the indicator. We describe in detail what can and cannot be said about the neutrino mass ordering and a future experiment's capabilities to determine it. Finally, we briefly comment on the application to other binary measurements, such as the determination of the octant of theta (23).

  • 132.
    Blennow, Mattias
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Theoretical and Phenomenological Studies of Neutrino Physics2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis is devoted to the theory and phenomenology of neutrino physics. While the standard model of particle physics has been extremely successful, it fails to account for massive neutrinos, which are necessary to describe the observations of neutrino oscillations made by several different experiments. Thus, neutrino physics is a possible window for exploring the physics beyond the standard model, making it both interesting and important for our fundamental understanding of Nature.

    Throughout this thesis, we will discuss different aspects of neutrino physics, ranging from taking all three types of neutrinos into account in neutrino oscillation experiments to exploring the possibilities of neutrino mass models to produce a viable source of the baryon asymmetry of the Universe. The emphasis of the thesis is on neutrino oscillations which, given their implication of neutrino masses, is a phenomenon where other results that are not describable in the standard model could be found, such as new interactions between neutrinos and fermions.

  • 133.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Carrigan, Marcus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Martinez, Enrique Fernandez
    Probing the Dark Matter mass and nature with neutrinos2013In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 6, p. 038-Article in journal (Refereed)
    Abstract [en]

    We study the possible indirect neutrino signal from dark matter annihilations inside the Sun's core for relatively light dark matter masses in the O (10) GeV range. Due to their excellent energy reconstruction capabilities, we focus on the detection of this flux in liquid argon or magnetized iron calorimeter detectors, proposed for the next generation of far detectors of neutrino oscillation experiments and neutrino telescopes. The aim of the study is to probe the ability of these detectors to determine fundamental properties of the dark matter nature such as its mass or its relative annihilation branching fractions to different channels. We find that these detectors will be able to accurately measure the dark matter mass as long as the dark matter annihilations have a significant branching into the neutrino or at least the tau channel. We have also discovered degeneracies between different dark matter masses and annihilation channels, where a hard tau channel spectrum for a lower dark matter mass may mimic that of a softer quark channel spectrum for a larger dark matter mass. Finally, we discuss the sensitivity of the detectors to the different branching ratios and find that it is between one and two orders of magnitude better than the current bounds from those coming from analysis of Super-Kamiokande data.

  • 134.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics. Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad, India.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Raut, Sushant K.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Exploring source and detector non-standard neutrino interactions at ESS nu SB2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 096Article in journal (Refereed)
    Abstract [en]

    We investigate source and detector non-standard neutrino interactions at the proposed ESS nu SB experiment. We analyze the effect of non-standard physics at the probability level, the event-rate level and by a full computation of the ESS nu SB setup. We find that the precision measurement of the leptonic mixing angle theta(23) at ESS nu SB is robust in the presence of non-standard interactions, whereas that of the leptonic CP-violating phase delta is worsened at most by a factor of two. We compute sensitivities to all the relevant source and decector non-standard interaction parameters and find that the sensitivities to the parameters epsilon(s)(mu e) and epsilon(d)(mu e) are comparable to the existing limits in a realistic scenario, while they improve by a factor of two in an optimistic scenario. Finally, we show that the absence of a near detector compromises the sensitivity of ESS nu SB to non-standard interactions.

  • 135.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Clementz, Stefan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Asymmetric capture of Dirac dark matter by the Sun2015In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2015, no 8, article id 036Article in journal (Refereed)
    Abstract [en]

    Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles and anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.

  • 136.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Clementz, Stefan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Pinning down inelastic dark matter in the Sun and in direct detection2016In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2016, no 4, article id 004Article in journal (Refereed)
    Abstract [en]

    We study the solar capture rate of inelastic dark matter with endothermic and/or exothermic interactions. By assuming that an inelastic dark matter signal will be observed in next generation direct detection experiments we can set a lower bound on the capture rate that is independent of the local dark matter density, the velocity distribution, the galactic escape velocity as well as the scattering cross section. In combination with upper limits from neutrino observatories we can place upper bounds on the annihilation channels leading to neutrinos. We find that, while endothermic scattering limits are weak in the isospin-conserving case, strong bounds may be set for exothermic interactions, in particular in the spin-dependent case. Furthermore, we study the implications of observing two direct detection signals, in which case one can halo-independently obtain the dark matter mass and the mass splitting, and disentangle the endothermic/exothermic nature of the scattering. Finally we discuss isospin violation.

  • 137.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Coloma, P.
    Donini, A.
    Fernandez-Martinez, E.
    Gain fractions of future neutrino oscillation facilities over T2K and NOvA2013In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, p. 159-Article in journal (Refereed)
    Abstract [en]

    We evaluate the probability of future neutrino oscillation facilities to discover leptonic CP violation and/or measure the neutrino mass hierarchy. We study how this probability is affected by positive or negative hints for these observables to be found at T2K and NO nu A. We consider the following facilities: LBNE; T2HK; and the 10 GeV Neutrino Factory (NF10), and show how their discovery probabilities change with the running time of T2K and NO nu A conditioned to their results. We find that, if after 15 years T2K and NO nu A have not observed a 90% CL hint of CP violation, then LBNE and T2HK have less than a 10% chance of achieving a 5 sigma discovery, whereas NF10 still has a similar to 40% chance to do so. Conversely, if T2K and NO nu A have an early 90% CL hint in 5 years from now, T2HK has a rather large chance to achieve a 5 sigma CP violation discovery (75% or 55%, depending on whether the mass hierarchy is known or not). This is to be compared with the 90% (30%) probability that NF10 (LBNE) would have to observe the same signal at 5 sigma. A hierarchy measurement at 5 sigma is achievable at both LBNE and NF10 with more than 90% probability, irrespectively of the outcome of T2K and NO nu A. We also find that if LBNE or a similar very long baseline super-beam is the only next generation facility to be built, then it is very useful to continue running T2K and NO nu A (or at least T2K) beyond their original schedule in order to increase the CP violation discovery chances, given their complementarity.

  • 138.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Coloma, P.
    Fernandez-Martinez, E.
    Searching for sterile neutrinos at the ESSνSB2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2014, no 12Article in journal (Refereed)
    Abstract [en]

     The ESSνSB project is a proposed neutrino oscillation experiment based on the European Spallation Source with the search for leptonic CP violation as its main aim. In this letter we show that a near detector at around 1 km distance from the beamline is not only very desirable for keeping the systematic errors affecting the CP search under control, but would also provide a significant sensitivity probe for sterile neutrino oscillations in the region of the parameter space favored by the long-standing LSND anomaly. We find that the effective mixing angle θμe can be probed down to sin2(2θμe) ≃ 2(8) · 10−3 at 5σ assuming 15% bin-to-bin (un)correlated systematics.

  • 139.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Coloma, P.
    Fernández-Martnez, E.
    MacHado, P. A. N.
    Zaldvar, B.
    Global constraints on vector-like WIMP effective interactions2016In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2016, no 4, article id 015Article in journal (Refereed)
    Abstract [en]

    In this work we combine information from relic abundance, direct detection, cosmic microwave background, positron fraction, gamma rays, and colliders to explore the existing constraints on couplings between Dark Matter and Standard Model constituents when no underlying model or correlation is assumed. For definiteness, we include independent vector-like effective interactions for each Standard Model fermion. Our results show that low Dark Matter masses below 20 GeV are disfavoured at the 3 σ level with respect to higher masses, due to the tension between the relic abundance requirement and upper constraints on the Dark Matter couplings. Furthermore, large couplings are typically only allowed in combinations which avoid effective couplings to the nuclei used in direct detection experiments.

  • 140.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Coloma, Pilar
    Fernandez-Martinez, Enrique
    Reassessing the sensitivity to leptonic CP violation2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 3, article id 005Article in journal (Refereed)
    Abstract [en]

    We address the validity of the usual procedure to determine the sensitivity of neutrino oscillation experiments to CP violation. An explicit calibration of the test statistic is performed through Monte Carlo simulations for several experimental setups. We find that significant deviations from a chi(2) distribution with one degree of freedom occur for experimental setups with low sensitivity to ffi. In particular, when the allowed region to which ffi is constrained at a given confidence level is comparable to the whole allowed range, the cyclic nature of the variable manifests and the premises of Wilk's theorem are violated. This leads to values of the test statistic significantly lower than a chi(2) distribution at that confidence level. On the other hand, for facilities which can place better constraints on ffi the cyclic nature of the variable is hidden and, as the potential of the facility improves, the values of the test statistics first become slightly higher than and then approach asymptotically a chi(2) distribution. The role of sign degeneracies is also discussed.

  • 141.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Coloma, Pilar
    Fernandez-Martinez, Enrique
    The MOMENT to search for CP violation2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 3, article id 197Article in journal (Refereed)
    Abstract [en]

    In this letter, we analyze for the first time the physics reach in terms of sensitivity to leptonic CP violation of the proposed MuOn-decay MEdium baseline NeuTrino beam (MOMENT) experiment, a novel neutrino oscillation facility that would operate with neutrinos from muon decay. Apart from obtaining a sufficiently intense flux, the bottlenecks to the physics reach of this experiment will be achieving a high enough suppression of the atmospheric background and, particularly, attaining a sufficient level of charge identification. We thus present our results as a function of these two factors. As for the detector, we consider a very massive Gd-doped Water Cherenkov detector. We find that MOMENT will be competitive with other currently planned future oscillation experiments if a charge identification of at least 80 % can be achieved at the same time that the atmospheric background can be suppressed by at least a factor of ten. We also find a large synergy of MOMENT with the current generation of neutrino oscillation experiments, T2K and NOvA, which significantly enhances its final sensitivity.

  • 142.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Coloma, Pilar
    Huber, Patrick
    Schwetz, Thomas
    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.

  • 143.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Edsjö, Joakim
    Fysikum, Stockholm University.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrinos from WIMP annihilations in the Sun including neutrino oscillations2011In: The Proceedings of the 22nd International Conference on Neutrino Physics and Astrophysics / [ed] Geoffrey Mills, Steve Elliott, Terrence Goldman, and Thomas Bowles, Elsevier, 2011, Vol. 221, p. 37-38Conference paper (Refereed)
    Abstract [en]

    The prospects to detect neutrinos from the Sun arising from dark matter annihilations in the core of the Sun are reviewed. Emphasis is placed on new work investigating the effects of neutrino oscillations on the expected neutrino fluxes.

  • 144.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Edsjö, Joakim
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrinos from WIMP annihilations in the Sun including neutrino oscillations2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T127, p. 19-21Article in journal (Refereed)
    Abstract [en]

    The prospects for detecting neutrinos from the Sun arising from dark matter annihilations in the core of the Sun are reviewed. Emphasis is placed on new work investigating the effects of neutrino oscillations on the expected neutrino fluxes.

  • 145.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Edsjö, Joakim
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrinos from WIMP annihilations obtained using a full three-flavor Monte Carlo approach2008In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2008, no 01, p. 021-Article in journal (Refereed)
    Abstract [en]

    Weakly interacting massive particles (WIMPs) are one of the main candidates for making up the dark matter in the Universe. If these particles make up the dark matter, then they can be captured by the Sun or the Earth, sink to the respective cores, annihilate, and produce neutrinos. Thus, these neutrinos can be a striking dark matter signature at neutrino telescopes looking towards the Sun and/or the Earth. Here, we improve previous analyses on computing the neutrino yields from WIMP annihilations in several respects. We include neutrino oscillations in a full three-flavor framework as well as all effects from neutrino interactions on the way through the Sun (absorption, energy loss, and regeneration from tau decays). In addition, we study the effects of non-zero values of the mixing angle theta(13) as well as the normal and inverted neutrino mass hierarchies. Our study is performed in an event-based setting which makes these results very useful both for theoretical analyses and for building a neutrino telescope Monte Carlo code. All our results for the neutrino yields, as well as our Monte Carlo code, are publicly available. We find that the yield of muontype neutrinos from WIMP annihilations in the Sun is enhanced or suppressed, depending on the dominant WIMP annihilation channel. This effect is due to an effective favor mixing caused by neutrino oscillations. For WIMP annihilations inside the Earth, the distance from source to detector is too small to allow for any significant amount of oscillations at the neutrino energies relevant for neutrino telescopes.

  • 146.
    Blennow, Mattias
    et al.
    Max-Planck-Institut für Physik.
    Edsjö, Joakim
    Department of Physics, Stockholm University.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    WIMP neutrinos from the Sun and the Earth2008In: : idm2008, SISSA , 2008, p. 4p-Conference paper (Refereed)
    Abstract [en]

    We discuss the propagation treatment of the indirect dark matter detection using WIMP annihilations in the Sun and the Earth. In particular, we focus on treating neutrino interactions and oscillations in a consistent framework, including tau neutrino regeneration and a full three-flavor neutrino oscillation framework. We also discuss the equivalence of using a Monte Carlo approach - suited for inclusion in neutrino telescope Monte Carlos - and the density matrix formalism.

  • 147.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Fernandez-Martinez, Enrique
    Zaldivar, Bryan
    Freeze-in through portals2014In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 1, p. 003-Article in journal (Refereed)
    Abstract [en]

    The popular freeze-out paradigm for Dark Matter (DM) production, relies on DM-baryon couplings of the order of the weak interactions. However, different search strategies for DM have failed to provide a conclusive evidence of such (non-gravitational) interactions, while greatly reducing the parameter space of many representative models. This motivates the study of alternative mechanisms for DM genesis. In the freeze-in framework, the DM is slowly populated from the thermal bath while never reaching equilibrium. In this work, we analyse in detail the possibility of producing a frozen-in DM via a mediator particle which acts as a portal. We give analytical estimates of different freeze-in regimes and support them with full numerical analyses, taking into account the proper distribution functions of bath particles. Finally, we constrain the parameter space of generic models by requiring agreement with DM relic abundance observations.

  • 148.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Herrero Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Schwetz, Thomas
    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.

  • 149.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Schwetz, T.
    Vogl, S.
    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, Vol. 2015, 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.

  • 150.
    Blennow, Mattias
    et al.
    Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), München, Germany.
    Melbéus, Henrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrinos from Kaluza-Klein dark matter in the Sun2010In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, Vol. 2010, no 01, p. 018-Article in journal (Refereed)
    Abstract [en]

    We investigate indirect neutrino signals from annihilations of Kaluza-Klein dark matter in the Sun. Especially, we examine a five- as well as a six-dimensional model, and allow for the possibility that boundary localized terms could affect the spectrum to give different lightest Kaluza-Klein particles, which could constitute the dark matter. The dark matter candidates that are interesting for the purpose of indirect detection of neutrinos are the first Kaluza-Klein mode of the U(1) gauge boson and the neutral component of the SU(2) gauge bosons. Using the DarkSUSY and WimpSim packages, we calculate muon fluxes at an Earth-based neutrino telescope, such as IceCube. For the five-dimensional model, the results hat we obtained agree reasonably well with the results that have previously been presented in the literature, whereas for the six-dimensional model, we find that, at tree-level, the results are the same as for the five-dimensional model. Finally, if the first Kaluza-Klein mode of the U(1) gauge boson constitutes the dark matter, IceCube can constrain the parameter space. However, in the case that the neutral component of the SU(2) gauge bosons is the LKP, the signal is too weak to be observed.

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