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  • 51.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Snellman, Håkan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Solar Neutrino Day-Night Effect2005Inngår i: NEUTRINO 2004 / [ed] Jacques Dumarchez, Thomas Patzak, François Vannucci, Elsevier Science B.V. , 2005, s. 578-578Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We summarize the results of Ref. [M. Blennow, T. Ohlsson and H. Snellman, Phys. Rev. D 69 (2004) 073006, hep-ph/0311098] in which we determine the effects of three flavor mixing on the day-night asymmetry in the flux of solar neutrinos. Analytic methods are used to determine the difference in the day and night solar electron neutrino survival probabilites and numerical methods are used to determine the effect of three flavor mixing at detectors.

  • 52.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Winter, Walter
    School of Natural Sciences, Institute for Advanced Study, Princeton, United States.
    Damping signatures in future neutrino oscillation experiments2005Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2005, nr 06, s. 049-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discuss the phenomenology of damping signatures in the neutrino oscillation probabilities, where either the oscillating terms or the probabilities can be damped. This approach is a possibility for tests of damping effects in future neutrino oscillation experiments, where we mainly focus on reactor and long-baseline experiments. We extensively motivate different damping signatures due to small corrections by neutrino decoherence, neutrino decay, oscillations into sterile neutrinos, or other mechanisms, and classify these signatures according to their energy ( spectral) dependencies. We demonstrate, at the example of short baseline reactor experiments, that damping can severely alter the interpretation of results, e. g., it could fake a value of sin(2)(2 theta(13)) smaller than the one provided by Nature. In addition, we demonstrate how a neutrino factory could constrain different damping models with emphasis on how these different models could be distinguished, i.e., how easily the actual type of effect could be identified. We find that the damping models cluster in different categories, which can be much better distinguished from each other than models within the same cluster.

  • 53.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Winter, Walter
    School of Natural Sciences, Institute for Advanced Study, Princeton, United States.
    Non-standard Hamiltonian effects on neutrino oscillations2007Inngår i: The European Physical Journal C, ISSN 1434-6044, Vol. 49, nr 4, s. 1023-1039Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate non-standard Hamiltonian effects on neutrino oscillations, which are effective additional contributions to the vacuum or matter Hamiltonian. Since these effects can enter in either the flavor or mass basis, we develop an understanding of the difference between these bases representing the underlying theoretical model. In particular, the simplest of these effects are classified as "pure" flavor or mass effects, where the appearance of such a "pure" effect can be quite plausible as a leading non-standard contribution from theoretical models. Compared to earlier studies investigating particular effects, we aim for a top-down classification of a possible "new physics" signature at future long-baseline neutrino oscillation precision experiments. We develop a general framework for such effects with two neutrino flavors and discuss the extension to three neutrino flavors, and we demonstrate the challenges for a neutrino factory to distinguish the theoretical origin of these effects with a numerical example as well. We find how the precision measurements of neutrino oscillation parameters can be altered by non-standard effects alone (not including non-standard interactions in the creation and detection processes) and that the non-standard effects on Hamiltonian level can be distinguished from other non-standard effects (such as neutrino decoherence and decay) if we consider the specific imprint of the effects on the energy spectra of several different oscillation channels at a neutrino factory.

  • 54.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Schwetz, T.
    Determination of the neutrino mass ordering by combining PINGU and Daya Bay II2013Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2013, nr 9, s. 089-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The relatively large measured value of θ 13 has opened various possibilities to determine the neutrino mass ordering, among them using PINGU, the low-energy extension of the IceCube neutrino telescope, to observe matter effects in atmospheric neutrinos, or a high statistics measurement of the neutrino energy spectrum at a reactor neutrino experiment with a baseline of around 60 km, such as the Daya Bay II project. In this work we point out a synergy between these two approaches based on the fact that when data are analysed with the wrong neutrino mass ordering the best fit occurs at different values of varDelta m 312 for PINGU and Daya Bay II. Hence, the wrong mass ordering can be excluded by a mismatch of the values inferred for varDelta m 312, thanks to the excellent accuracy for varDelta m 312 of both experiments. We perform numerical studies of PINGU and Daya Bay II sensitivities and show that the synergy effect may lead to a high significance determination of the mass ordering even in situations where the 3individual experiments obtain only poor sensitivity.

  • 55.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Schwetz, Thomas
    Identifying the Neutrino mass Ordering with INO and NOvA2012Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 1208Artikkel i tidsskrift (Fagfellevurdert)
  • 56.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Smirnov, Alexei Yu.
    Neutrino Propagation in Matter2013Inngår i: Advances in High Energy Physics, ISSN 1687-7357, E-ISSN 1687-7365, Vol. 2013, s. 972485-Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    We describe the effects of neutrino propagation in the matter of the Earth relevant to experiments with atmospheric and accelerator neutrinos and aimed at the determination of the neutrino mass hierarchy and CP violation. These include (i) the resonance enhancement of neutrino oscillations in matter with constant or nearly constant density, (ii) adiabatic conversion in matter with slowly changing density, (iii) parametric enhancement of oscillations in a multilayer medium, and (iv) oscillations in thin layers of matter. We present the results of semianalytic descriptions of flavor transitions for the cases of small density perturbations, in the limit of large densities and for small density widths. Neutrino oscillograms of the Earth and their structure after determination of the 1-3 mixing are described. A possibility to identify the neutrino mass hierarchy with the atmospheric neutrinos and multimegaton scale detectors having low energy thresholds is explored. The potential of future accelerator experiments to establish the hierarchy is outlined.

  • 57.
    Bonnevier, Johan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Phenomenology of Dark Matter fromNon-Minimal Universal Extra Dimensions2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    We give a general introduction to particle physics, and in particular to particlephysics in extra dimensions. Furthermore, we introduce the concept of dark matter(DM) and discuss some suggestions for what it originates from. Next, we calculatethe cross-section for DM annihilation in the framework of non-minimal universalextra dimensions. This process gives mono-energetic gamma-ray lines with energyclose to the DM particle mass. The calculations are performed for two different DMcandidates, U(1)Y-gaugebosonen B1 och den laddningsneutrala SU(2)L-gaugebosonen Z1. MM-kandidaten är alltid den lättaste partikeln inom den betraktade teorin. Störst  tvärsnitt får man när Z1 tas som den lättaste partikeln, och alltså som MM-kandidat, trots att den är tyngre än vad B1 är när den är tagen som teorins lättaste partikel. Anledningen till att tvärsnittet blir större för Z1 är att den har icke fösumbara självväxelverkningarr, vilket gör att många fler Feynmandiagram bidrar.

  • 58.
    Bonnevier, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Melbéus, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Monoenergetic gamma rays from nonminimal Kaluza-Klein dark matter annihilations2012Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 85, nr 4, s. 043524-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate monoenergetic gamma-ray signatures from annihilations of dark matter comprised of Z(1), the first Kaluza-Klein (KK) excitation of the Z boson in a nonminimal universal extra dimensions (UED) model. The self interactions of the non-Abelian Z(1) gauge boson give rise to a large number of contributing Feynman diagrams that do not exist for annihilations of the Abelian gauge boson B-1, which is the standard Kaluza-Klein dark matter (KKDM) candidate. We find that the annihilation rate is indeed considerably larger for the Z(1) than for the B-1. Even though relic density calculations indicate that the mass of the Z(1) should be larger than the mass of the B-1, the predicted monoenergetic gamma fluxes are of the same order of magnitude. We compare our results to existing experimental limits, as well as to future sensitivities, for image air Cherenkov telescopes, and we find that the limits are reached already with a moderately large boost factor. The realistic prospects for detection depend on the experimental energy resolution.

  • 59.
    Bouchand, Romain
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Radiative Neutrino Mass Generation and Renormalization Group Running in the Ma-Model2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 60.
    Choubey, Sandhya
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Atmospheric neutrinos: Status and prospects2016Inngår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present an overview of the current status of neutrino oscillation studies at atmospheric neutrino experiments. While the current data gives some tantalising hints regarding the neutrino mass hierarchy, octant of θ23 and δCP, the hints are not statistically significant. We summarise the sensitivity to these sub-dominant three-generation effects from the next-generation proposed atmospheric neutrino experiments. We next present the prospects of new physics searches such as non-standard interactions, sterile neutrinos and CPT violation studies at these experiments.

  • 61.
    Choubey, Sandhya
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Neutrino oscillations2017Inngår i: Current Science, ISSN 0011-3891, Vol. 112, nr 7, s. 1381-1384Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Neutrinos are massless as proposed in the Standard Model of particle physics. However, neutrino experiments in the last few decades have revealed that neutrinos flavour oscillate, a scenario possible only if they have mass and mixing. Existence of neutrino mass was the first conclusive evidence of physics beyond the Standard Model, and explaining the smallness of the neutrino masses and peculiar mixing angles still remains a challenge for model-builders proposing beyond Standard Model scenarios. We give a brief introduction to the phenomenon of neutrino oscillations and showcase some recent work where we look for physics beyond the three-generation neutrino oscillation paradigm and its impact on future experiments.

  • 62.
    Choubey, Sandhya
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik. Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad, India.
    Ghosh, Anushree
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Tiwari, D.
    Neutrino physics with non-standard interactions at INO2015Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2015, nr 12, s. 1-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract: Non-standard neutrino interactions (NSI) involved in neutrino propagation inside Earth matter could potentially alter atmospheric neutrino fluxes. In this work, we look at the impact of these NSI on the signal at the ICAL detector to be built at the India-based Neutrino Observatory (INO). We show how the sensitivity to the neutrino mass hierarchy of ICAL changes in the presence of NSI. The mass hierarchy sensitivity is shown to be rather sensitive to the NSI parameters ϵeμ and ϵeτ , while the dependence on ϵμτ and ϵτ τ is seen to be very mild, once the χ2 is marginalised over oscillation and NSI parameters. If the NSI are large enough, the event spectrum at ICAL is expected to be altered and this can be used to discover new physics. We calculate the lower limit on NSI parameters above which ICAL could discover NSI at a given C.L. from 10 years of data. If NSI were too small, the null signal at ICAL can constrain the NSI parameters. We give upper limits on the NSI parameters at any given C.L. that one is expected to put from 10 years of running of ICAL. Finally, we give C.L. contours in the NSI parameter space that is expected to be still allowed from 10 years of running of the experiment.

  • 63.
    Choubey, Sandhya
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik. Harish-Chandra Research Institute, India .
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Bounds on non-standard neutrino interactions using PINGU2014Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 739, s. 357-364Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the impact of non-standard neutrino interactions (NSIs) on atmospheric neutrinos using the proposed PINGU experiment. In particular, we focus on the matter NSI parameters epsilon(mu tau) and vertical bar epsilon(tau tau)-epsilon(mu mu)vertical bar that have previously been constrained by the Super-Kamiokande experiment. First, we present approximate analytical formulas for the difference of the muon neutrino survival probability with and without the above-mentioned NSI parameters. Second, we calculate the atmospheric neutrino events at PINGU in the energy range (2-100) GeV, which follow the trend outlined on probability level. Finally, we perform a statistical analysis of PINGU. Using three years of data, we obtain bounds from PINGU given by -0.0043 (-0.0048) < epsilon(mu tau) < 0.0047 (0.0046) and -0.03 (-0.016) < epsilon(tau tau) < 0.017 (0.032) at 90% confidence level for normal (inverted) neutrino mass hierarchy, which improve the Super-Kamiokande bounds by one order of magnitude. In addition, we show the expected allowed contour region in the epsilon-ettplane if NSIs exist in Nature and the result suggests that there is basically no correlation between epsilon(mu tau) and epsilon(tau tau).

  • 64.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Establishing analogies between the physics of extra dimensions and carbon nanotubes2012Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 714, nr 1, s. 44-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We point out a conceptual analogy between the physics of extra spatial dimensions and the physics of carbon nanotubes which arises for principle reasons, although the corresponding energy scales are at least ten orders of magnitude apart. For low energies, one can apply the Kaluza-Klein description to both types of systems, leading to two completely different but consistent interpretations of the underlying physics. In particular, we discuss in detail the Kaluza-Klein description of armchair and zig-zag carbon nanotubes. Furthermore, we describe how certain experimental results for carbon nanotubes could be re-interpreted in terms of the Kaluza-Klein description. Finally, we present ideas for new measurements that could allow to probe concepts of models with extra spatial dimensions in table-top experiments, providing further links between condensed matter and particle physics.

  • 65.
    Di Bari, Pasquale
    et al.
    University of Southampton.
    King, Stephen
    University of Southampton.
    Luhn, Christoph
    University of Southampton.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Schmidt-May, Angnis
    Max-Planck-Institut fuer Kernphysik.
    Radiative Inflation and Dark Energy2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a model based on radiative symmetry breaking that combines inflation with dark energy and is consistent with the Wilkinson Microwave Anisotropy Probe 7-year regions. The radiative inflationary potential leads to the prediction of a spectral index 0.955 less than or similar to n(S) less than or similar to 0.967 and a tensor to scalar ratio 0.142 less than or similar to r less than or similar to 0.186, both consistent with current data but testable by the Planck experiment. The radiative symmetry breaking close to the Planck scale gives rise to a pseudo Nambu-Goldstone boson with a gravitationally suppressed mass which can naturally play the role of a quintessence field responsible for dark energy. Finally, we present a possible extra dimensional scenario in which our model could be realized.

  • 66. Duerr, Michael
    et al.
    Lindner, Manfred
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    On the quantitative impact of the Schechter-Valle theorem2011Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 6, s. 091-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We evaluate the Schechter-Valle (Black Box) theorem quantitatively by considering the most general Lorentz invariant Lagrangian consisting of point-like operators for neutrinoless double beta decay. It is well known that the Black Box operators induce Majorana neutrino masses at four-loop level. This warrants the statement that an observation of neutrinoless double beta decay guarantees the Majorana nature of neutrinos. We calculate these radiatively generated masses and find that they are many orders of magnitude smaller than the observed neutrino masses and splittings. Thus, some lepton number violating New Physics (which may at tree-level not be related to neutrino masses) may induce Black Box operators which can explain an observed rate of neutrinoless double beta decay. Although these operators guarantee finite Majorana neutrino masses, the smallness of the Black Box contributions implies that other neutrino mass terms (Dirac or Majorana) must exist. If neutrino masses have a significant Majorana contribution then this will become the dominant part of the Black Box operator. However, neutrinos might also be predominantly Dirac particles, while other lepton number violating New Physics dominates neutrinoless double beta decay. Translating an observed rate of neutrinoless double beta decay into neutrino masses would then be completely misleading. Although the principal statement of the Schechter-Valle theorem remains valid, we conclude that the Black Box diagram itself generates radiatively only mass terms which are many orders of magnitude too small to explain neutrino masses. Therefore, other operators must give the leading contributions to neutrino masses, which could be of Dirac or Majorana nature.

  • 67. Edgecock, T. R.
    et al.
    Caretta, O.
    Davenne, T.
    Densam, C.
    Fitton, M.
    Kelliher, D.
    Loveridge, P.
    Machida, S.
    Prior, C.
    Rogers, C.
    Rooney, M.
    Thomason, J.
    Wilcox, D.
    Wildner, E.
    Efthymiopoulos, I.
    Garoby, R.
    Gilardoni, S.
    Hansen, C.
    Benedetto, E.
    Jensen, E.
    Kosmicki, A.
    Martini, M.
    Osborne, J.
    Prior, G.
    Stora, T.
    Mendonca, T. Melo
    Vlachoudis, V.
    Waaijer, C.
    Cupial, P.
    Chance, A.
    Longhin, A.
    Payet, J.
    Zito, M.
    Baussan, E.
    Bobeth, C.
    Bouquerel, E.
    Dracos, M.
    Gaudiot, G.
    Lepers, B.
    Osswald, F.
    Poussot, P.
    Vassilopoulos, N.
    Wurtz, J.
    Zeter, V.
    Bielski, J.
    Kozien, M.
    Lacny, L.
    Skoczen, B.
    Szybinski, B.
    Ustrycka, A.
    Wroblewski, A.
    Marie-Jeanne, M.
    Balint, P.
    Fourel, C.
    Giraud, J.
    Jacob, J.
    Lamy, T.
    Latrasse, L.
    Sortais, P.
    Thuillier, T.
    Mitrofanov, S.
    Loiselet, M.
    Keutgen, Th
    Delbar, Th
    Debray, F.
    Trophine, C.
    Veys, S.
    Daversin, C.
    Zorin, V.
    Izotov, I.
    Skalyga, V.
    Burt, G.
    Dexter, A. C.
    Kravchuk, V. L.
    Marchi, T.
    Cinausero, M.
    Gramegna, F.
    De Angelis, G.
    Prete, G.
    Collazuol, G.
    Laveder, M.
    Mazzocco, M.
    Mezzetto, M.
    Signorini, C.
    Vardaci, E.
    Di Nitto, A.
    Brondi, A.
    La Rana, G.
    Migliozzi, P.
    Moro, R.
    Palladino, V.
    Gelli, N.
    Berkovits, D.
    Hass, M.
    Hirsh, T. Y.
    Schaumann, M.
    Stahl, A.
    Wehner, J.
    Bross, A.
    Kopp, J.
    Neuffer, D.
    Wands, R.
    Bayes, R.
    Laing, A.
    Soler, P.
    Agarwalla, S. K.
    Cervera Villanueva, A.
    Donini, A.
    Ghosh, T.
    Gomez Cadenas, J. J.
    Hernandez, P.
    Martin-Albo, J.
    Mena, O.
    Burguet-Castell, J.
    Agostino, L.
    Buizza-Avanzini, M.
    Marafini, M.
    Patzak, T.
    Tonazzo, A.
    Duchesneau, D.
    Mosca, L.
    Bogomilov, M.
    Karadzhov, Y.
    Matev, R.
    Tsenov, R.
    Akhmedov, E.
    Blennow, M.
    Lindner, M.
    Schwetz, T.
    Fernandez Martinez, E.
    Maltoni, M.
    Menendez, J.
    Giunti, C.
    Gonzalez Garcia, M. C.
    Salvado, J.
    Coloma, P.
    Huber, P.
    Li, T.
    Pavon, J. Lopez
    Orme, C.
    Pascoli, S.
    Meloni, D.
    Tang, J.
    Winter, W.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Scotto-Lavina, L.
    Terranova, F.
    Bonesini, M.
    Tortora, L.
    Alekou, A.
    Aslaninejad, M.
    Bontoiu, C.
    Kurup, A.
    Jenner, L. J.
    Long, K.
    Pasternak, J.
    Pozimski, J.
    Back, J. J.
    Harrison, P.
    Beard, K.
    Bogacz, A.
    Berg, J. S.
    Stratakis, D.
    Witte, H.
    Snopok, P.
    Bliss, N.
    Cordwell, M.
    Moss, A.
    Pattalwar, S.
    Apollonio, M.
    High intensity neutrino oscillation facilities in Europe2013Inngår i: Physical Review Special Topics. Accelerators and Beams, ISSN 1098-4402, E-ISSN 1098-4402, Vol. 16, nr 2, s. 021002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Frejus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of mu(+) and mu(-) beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular He-6 and Ne-18, also stored in a ring. The far detector is also the MEMPHYS detector in the Frejus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. However, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive.

  • 68. Ghosh, Monojit
    et al.
    Goswami, Srubabati
    Physical Research Laboratory India, Ahmedabad, India .
    Raut, Sushant K.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Implications of delta(CP) =-90 degrees towards determining hierarchy and octant at T2K and T2K-II2017Inngår i: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 32, nr 6, artikkel-id 1750034Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The T2K experiment has provided the first hint for the best-fit value for the leptonic CP phase delta(CP) similar to -90 degrees from neutrino data. This is now corroborated by the NO nu A neutrino runs. We study the implications for neutrino mass hierarchy and octant of theta(23) in the context of this data assuming that the true value of delta(CP) in nature is -90 degrees. Based on simple arguments on degeneracies in the probabilities, we show that a clear signal of delta(CP) = -90 degrees coming from T2K neutrino (antineutrino) data is only possible if the true hierarchy is normal and the true octant is higher (lower). Thus, if the T2K neutrino and antineutrino data are fitted separately and both give the true value of delta(CP) = -90 degrees, this will imply that nature has chosen the true hierarchy to be normal and theta(23) approximate to 45 degrees. However, we find that the combined fit of neutrino and antineutrino data will still point to true hierarchy as normal but the octant of theta(23) will remain undetermined. We do our analysis for both, the current projected exposure (7.8 x 10(21) pot) and planned extended exposure (20 x 10(21) pot). We also present the CP discovery potential of T2K emphasizing on the role of antineutrinos. We find that one of the main contributions of the antineutrino data is to remove the degenerate solutions with the wrong octant. Thus, the antineutrino run plays a more significant role for those hierarchy-octant combinations for which this degeneracy is present. If this degeneracy is absent, then only neutrino run gives a better result for fixed theta(13). However, if we marginalize over theta(13) then, sensitivity corresponding to mixed run can be better than pure neutrino run.

  • 69. Girardi, Ivan
    et al.
    Meloni, Davide
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zhang, He
    Zhou, Shun
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Constraining sterile neutrinos using reactor neutrino experiments2014Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Models of neutrino mixing involving one or more sterile neutrinos have resurrected their importance in the light of recent cosmological data. In this case, reactor antineutrino experiments offer an ideal place to look for signatures of sterile neutrinos due to their impact on neutrino flavor transitions. In this work, we show that the high-precision data of the Daya Bay experiment constrain the 3+1 neutrino scenario imposing upper bounds on the relevant active-sterile mixing angle sin(2) 2 theta(14) less than or similar to 0.06 at 3 sigma confidence level for the mass-squared difference Delta m(41)(2) in the range (10(-3), 10(-1)) eV(2). The latter bound can be improved by six years of running of the JUNO experiment, sin(2) 2 theta(14) less than or similar to 0.016, although in the smaller mass range Delta m(41)(2) is an element of(10(-4), 10(-3)) eV(2). We have also investigated the impact of sterile neutrinos on precision measurements of the standard neutrino oscillation parameters theta(13) and Delta m(31)(2) (at Daya Bay and JUNO), theta(12) and Delta m(21)(2) (at JUNO), and most importantly, the neutrino mass hierarchy (at JUNO). We find that, except for the obvious situation where Delta m(41)(2) similar to Delta m(31)(2), sterile states do not affect these measurements substantially.

  • 70. Hagedorn, Claudia
    et al.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Riad, Stella
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Schmidt, Michael A.
    Unification of gauge couplings in radiative neutrino mass models2016Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 9, artikkel-id 111Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the possibility of gauge coupling uni fi cation in various radiative neutrino mass models, which generate neutrino masses at one-and/or two-loop level. Renormalization group running of gauge couplings is performed analytically and numerically at one-and two-loop order, respectively. We study three representative classes of radiative neutrino mass models: (I) minimal ultraviolet completions of the dimension-7 Delta L = 2 operators which generate neutrino masses at one-and/or two-loop level without and with dark matter candidates, (II) models with dark matter which lead to neutrino masses at one-loop level and (III) models with particles in the adjoint representation of SU(3). In class (I), gauge couplings unify in a few models and adding dark matter amplifies the chances for uni fi cation. In class (II), about a quarter of the models admits gauge coupling uni fi cation. In class (III), none of the models leads to gauge coupling uni fi cation. Regarding the scale of uni fi cation, we find values between 10(14) GeV and 10(16) GeV for models belonging to class (I) without dark matter, whereas models in class (I) with dark matter as well as models of class (II) prefer values in the range 5.10(10) - 5.10(14) GeV.

  • 71.
    Heinze, Martin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Malinsky, Michal
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Flavor structure of supersymmetric SO(10) GUTs with extended matter sector2011Inngår i: PHYSICAL REVIEW D, ISSN 1550-7998, Vol. 83, nr 3, s. 035018-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discuss in detail the flavor structure of the supersymmetric SOd(10) grand unified models with the three traditional 16-dimensional matter spinors mixed with a set of extra ten-dimensional vector multiplets which can provide the desired sensitivity of the standard model matter spectrum to the grand unified theory symmetry breakdown at the renormalizable level. We put the qualitative argument that a successful fit of the quark and lepton data requires an active participation of more than a single vector matter multiplet on a firm, quantitative ground. We find that the strict no-go obtained for the fits of the charged-sector observables in case of a single active matter 10 is relaxed if a second vector multiplet is added to the matter sector and excellent, though nontrivial, fits can be devised. Exploiting the unique calculable part of the neutrino mass matrix governed by the SUd(2)(L) triplet in the 54-dimensional Higgs multiplet, a pair of genuine predictions of the current setting is identified: a nonzero value of the leptonic 1-3 mixing close to the current 90% C.L. limit and a small leptonic Dirac CP phase are strongly preferred by all solutions with the global-fit chi(2) values below 50.

  • 72.
    Hällgren, Tomas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Aspects of Dimensional Deconstruction and Neutrino Physics2007Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The existence of at or curved extra spatial dimensions provides new insights into several of the problems which face the Standard Model of particle physics, including the gauge hierarchy problem, the smallness of neutrino masses, and the dark matter problem. However, higher-dimensional gauge theories are not renormalizable and can only be considered as low-energy effective theories, with limited applicability. Dimensional deconstruction provides a class of manifestly gauge invariant possible ultraviolet completions of higher-dimensional gauge theories, formulated within conventional quantum eld theory. In dimensional deconstruction, the fundamental theory is a four-dimensional quantum eld theory and extra spatial dimensions are generated dynamically at low energies. In this thesis, we study di erent applications of dimensional deconstruction in the contexts of neutrino masses, mixing and oscillations, Kaluza{Klein dark matter, and e ective eld theories for discretized higher-dimensional gravity.

    A different possibility to understand the smallness of neutrino masses is provided by the see-saw mechanism. This is a genuinely four-dimensional mechanism, where the light neutrino masses are induced by the addition of heavy right-handed Majorana neutrinos or by other heavy degrees of freedom, such as scalar SU(2)L triplet elds. It has the attractive feature of simultaneously providing a mechanism for generating the observed baryon asymmetry of the Universe. We study in this context a specific left-right symmetric see-saw model.

  • 73.
    Hällgren, Tomas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Konstandin, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Triplet leptogenesis in left-right symmetric seesaw models2008Inngår i: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2008, nr 01, s. 014-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discuss scalar triplet leptogenesis in a specific left-right symmetric seesaw model. We show that the Majorana phases that are present in the model can be effectively used to saturate the existing upper limit on the CP-asymmetry of the triplets. We solve the relevant Boltzmann equations and analyze the viability of triplet leptogenesis. It is known for this kind of scenario that the efficiency of leptogenesis is maximal if there exists a hierarchy between the branching ratios of the triplet decays into leptons and Higgs particles. We show that triplet leptogenesis typically favors branching ratios with not too strong hierarchies, since maximal efficiency can only be obtained at the expense of suppressed CP-asymmetries.

  • 74.
    Hällgren, Tomas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Seidl, Gerhart
    Department of Physics, Oklahoma State University.
    Neutrino oscillations in deconstructed dimensions2005Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2005, nr 02, s. 049-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a model for neutrino oscillations in the presence of a deconstructed non-gravitational large extra dimension compactified on the boundary of a two-dimensional disk. In the deconstructed phase, sub-mm lattice spacings are generated from the hierarchy of energy scales between similar to 1 TeV and the usual B - L breaking scale similar to 10(15) GeV. Here, short-distance cutoffs down to similar to 1eV are motivated by the strong coupling behavior of gravity in local discrete extra dimensions. This could make it possible to probe the discretization of extra dimensions and non-trivial field configurations in theory spaces which have only a few sites, i.e., for coarse latticizations. Thus, the model has relevance to present and future precision neutrino oscillation experiments.

  • 75. Lindner, Manfred
    et al.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Niro, Viviana
    Soft L-e - L-mu - L-tau flavour symmetry breaking and sterile neutrino keV Dark Matter2011Inngår i: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2011, nr 01, s. 034-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discuss how a L-e - L-mu - L-tau flavour symmetry that is softly broken leads to keV sterile neutrinos, which are a prime candidate for Warm Dark Matter. This is to our knowledge the first model where flavour symmetries are applied simultaneously to active and sterile neutrinos explaining at the same time active neutrino properties and this peculiar Dark Matter scenario. The essential point is that different scales of the symmetry breaking and the symmetry preserving entries in the mass matrix lead to one right- handed neutrino which is nearly massless compared to the other two. Furthermore, we naturally predict vanishing theta(13) and maximal theta(23), while the correct value of theta(12) must come from the mixing of the charged leptons. We can furthermore predict an exact mass spectrum for the light neutrinos, which will be testable in the very near future.

  • 76. Liu, Ji-Yuan
    et al.
    Zhou, Shun
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Hybrid textures of Majorana neutrino mass matrix and current experimental tests2013Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, nr 9, s. 093010-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Motivated by recent measurements of a relatively large theta(13) in the Daya Bay and RENO reactor neutrino experiments, we carry out a systematic analysis of the hybrid textures of Majorana neutrino mass matrix M-v, which contain one texture zero and two equal nonzero matrix elements. We show that three neutrino masses (m(1).m(2).m(3)) and three leptonic CP-violating phases (delta, rho, sigma) can fully be determined from two neutrino mass-squared differences (delta m(2), Delta m(2)) and three flavor mixing angles (theta(12), theta(23), theta(13)). Out of sixty logically possible patterns of M-v, thirty-nine are found to be compatible with current experimental data at the 3 sigma level. We demonstrate that the texture zero of M-v is stable against one-loop quantum corrections, while the equality between two independent elements not. Phenomenological implications of M-v for the neutrinoless double-beta decay and leptonic CP violation are discussed, and a realization of the texture zero and equality by means of discrete flavor symmetries is illustrated.

  • 77.
    Ludkiewicz, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Radiative neutrino models and observational consequences2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    We give a general introduction to physics, in particular the physics of the Standard Model (SM). Next we discuss one of the problems the SM faces, that of accommodating the neutrino masses. We discuss the concept of radiative mechanisms. Then we study three particular such models in depth.

    The first is a model due to Ma which introduces three neutrino singlets and one scalar doublet on top of the SM particle content. We discuss the different neutrino masses that this model can hold. It is found that only case of normal hierarchy among the neutrinos is allowed in this model. We also discuss several observable quantities currently being searched for in experiments, and their relation to this model

    The second model is due to Zee and Babu, and is commonly known as the Zee–Babu model. This model adds two electrically charged scalar particles to the SM. We find that this model can describe both the inverted hierarchy and normal hierarchy. The previously mentioned observable quantities are once again discussed, but with this model in mind.

    Finally we discuss a model which accounts for the neutrino masses by assuming that there exists a fourth generation of leptons. It is found that this framework is insufficient to describe the observed neutrino masses.

  • 78.
    Malinsky, Michal
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Xing, Zhi-zhong
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Non-unitary neutrino mixing and CP violation in the minimal inverse seesaw model2009Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 679, nr 3, s. 242-248Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a simplified version of the inverse seesaw model, in which only two pairs of the gauge-singlet neutrinos are introduced, to interpret the observed neutrino mass hierarchy and lepton flavor mixing at or below the TeV scale. This "minimal" inverse seesaw scenario (MISS) is technically natural and experimentally testable. In particular, we show that the effective parameters describing the non-unitary neutrino mixing matrix are strongly correlated in the MISS, and thus, their upper bounds can be constrained by current experimental data in a more restrictive way. The Jarlskog invariants of non-unitary CP violation are calculated, and the discovery potential of such new CP-violating effects in the near detector of a neutrino factory is discussed.

  • 79.
    Malinsky, Michal
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Nonstandard neutrino interactions from a triplet seesaw model2009Inngår i: Physical Review D, ISSN 1550-7998, Vol. 79, nr 1, s. 011301(R)-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate nonstandard neutrino interactions (NSIs) in the triplet seesaw model featuring nontrivial correlations between NSI parameters and neutrino masses and mixing parameters. We show that sizable NSIs can be generated as a consequence of a nearly degenerate neutrino mass spectrum. Thus, these NSIs could lead to quite significant signals of lepton flavor violating decays such as mu(-) --> e(-) nu(e)(nu) over bar (mu) and mu(+) --> e(+)(nu) over bar (e)nu(mu) at a future neutrino factory, effects adding to the uncertainty in determination of the Earth matter density profile, as well as characteristic patterns of the doubly charged Higgs decays observable at the Large Hadron Collider.

  • 80.
    Malinsky, Michal
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Nonunitarity effects in a realistic low-scale seesaw model2009Inngår i: Physical Review D, ISSN 1550-7998, Vol. 79, nr 7, s. 073009-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We analyze the structure of the nonunitary leptonic mixing matrix in the inverse seesaw model with heavy singlets accessible at the LHC. In this model, unlike in the usual TeV seesaw scenarios, the low-scale right-handed neutrinos do not suffer from naturalness issues. Underlying correlations among various parameters governing the nonunitarity effects are established, which leads to a considerable improvement of the generic nonunitarity bounds. In view of this, we study the discovery potential of the nonunitarity effects at future experiments, focusing on the sensitivity limits at a neutrino factory.

  • 81.
    Malinský, Michal
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Intermediate scales in non-supersymmetric SO(10) grand unified theories2009Inngår i: Proceedings of Science: European Physical Society Europhysics Conference on High Energy Physics, Scuola Internazionale Superiore di Studi Avanzati (S I S S A) , 2009, s. PoS(EPS-HEP 2009)288-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    It is often argued that in the class of non-supersymmetric SO(10) grand unified theories there is barely any room for reconciling the lower bound on the position of the GUT scale emerging from the proton decay searches and the lower limit on the absolute neutrino mass scale derived from the neutrino oscillation experiments with the gauge coupling unification constraints. The recent two-loop reassessment of the gauge running provides the first complete picture of the situation, complementing the existing studies in several aspects. The improved analysis reveals a new room in the parametric space that could support a class of non-supersymmetric SO(10) models potentially compatible with all current physical data, including constraints on the relevant Yukawa sector emerging from the quark and lepton masses and mixings. This, in turn, brings back the question of viability of some of the simplest non-supersymmetric GUT scenarios.

  • 82.
    Malinský, Michal
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Non-unitarity effects in the minimal inverse seesaw model2009Inngår i: Proceedings of Science: European Physical Society Europhysics Conference on High Energy Physics, Scuola Internazionale Superiore di Studi Avanzati (S I S S A) , 2009, s. PoS(EPS-HEP 2009)288-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A minimal version of the inverse seesaw model featuring only two pairs of TeV-scale singlet neutrinos is discussed from the perspective of non-standard neutrino interactions. A particular attention is paid to the non-standard patterns of flavour and CP violation emerging due to the possibly enhanced non-decoupling effects of the heavy sector and the associated non-unitarity of the effective lepton mixing matrix.

  • 83.
    Melbéus, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Astrophysical and Collider Signatures of Extra Dimensions2010Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In recent years, there has been a large interest in the subject of extra dimensions in particle physics. In particular, a number of models have been suggested which provide solutions to some of the problems with the current Standard Model of particle physics, and which could be tested in the next generation of high-energy experiments. Among the most important of these models are the large extra dimensions model by Arkani-Hamed, Dimopoulos, and Dvali, the universal extra dimensions model, and models allowing right-handed neutrinos to propagate in the extra dimensions. In this thesis, we study phenomenological aspects of these three models, or simple modifications of them.

     

    The Arkani-Hamed-Dimopoulos-Dvali model attempts to solve the gauge hierarchy problem through a volume suppression of Newton's gravitational constant, lowering the fundamental Planck scale down to the electroweak scale. However, this solution is unsatisfactory in the sense that it introduces a new scale through the radius of the extra dimensions, which is unnaturally large compared to the electroweak scale. It has been suggested that a similar model, with a hyperbolic internal space, could provide a more satisfactory solution to the problem, and we consider the hadron collider phenomenology of such a model.

     

    One of the main features of the universal extra dimensions model is the existence of a potential dark matter candidate, the lightest Kaluza-Klein particle. In the so-called minimal universal extra dimensions model, the identity of this particle is well defined, but in more general models, it could change. We consider the indirect neutrino detection signals for a number of different such dark matter candidates, in a five- as well as a six-dimensional model.

     

    Finally, right-handed neutrinos propagating in extra dimensions could provide an alternative scenario to the seesaw mechanism for generating small masses for the left-handed neutrinos. Since extra-dimensional models are non-renormalizable, the Kaluza-Klein tower is expected to be cut off at some high-energy scale. We study a model where a Majorana neutrino at this cutoff scale is responsible for the generation of the light neutrino masses, while the lower modes of the tower could possibly be observed in the Large Hadron Collider. We investigate the bounds on the model from non-unitarity effects, as well as collider signatures of the model.

  • 84.
    Melbéus, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Particle Phenomenology of Compact Extra Dimensions2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is an investigation of the subject of extra dimensions in particle physics. In recent years, there has been a large interest in this subject. In particular, a number of models have been suggested that provide solutions to some of the problem with the current Standard Model of particle physics. These models typically give rise to experimental signatures around the TeV energy scale, which means that they could be tested in the next generation of high-energy experiments, such as the LHC. Among the most important of these models are the universal extra dimensions model, the large extra dimensions model by Arkani-Hamed, Dimopolous, and Dvali, and models where right-handed neutrinos propagate in the extra dimensions.

    In the thesis, we study phenomenological aspects of these models, or simple modifications of them. In particular, we focus on Kaluza–Klein dark matter in universal extra dimensions models, different aspects of neutrino physics in higher dimensions, and collider phenomenology of extra dimensions. In addition, we consider consequences of the enhanced renormalization group running of physical parameters in higher-dimensional models.

  • 85.
    Melbéus, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Phenomenology of Hyperbolic Large Extra Dimensions for Hadron Colliders2007Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The subject of extra dimensions has experienced a renewed interest in recent years. Arkani-Hamed, Dimopoulos, and Dvali (ADD) have pointed out that it is possiblethat there exist extra dimensions that are as large as micrometer sized, if theStandard Model fields are restricted to a four-dimensional brane. In the ADD model, only the graviton is able to probe the extra dimensions. The main motivation for this model is that it could solve the hierarchy problem between the electroweak scale and the Planck scale by lowering the Planck scale to 1 TeV. However, in the ADD model, the radius of the extra dimensions is large, giving a new hierarchy problem between this radius and the electroweak scale. In addition, there are significant constraints on the model coming from astrophysics. To improve on the ADD model, it is possible to consider a model with curved extra dimensions. An interesting scenario is provided by extra dimensions of hyperbolic geometry. In this case, it is possible to bring the Planck scale down to 1 TeV without the need of a large radius. Also, the constraints that are important for the ADD model can be completely avoided. The most efficient probe of large extra dimensions is particle physics. In particular, it is possible to study their phenomenology in high-energy particle accelerators such as the Large Hadron Collider, which will be completed in 2008. The phenomenology of the ADD model has been extensively studied. In this thesis, we consider the phenomenology of a model where the internal space is a hyperbolic disc. We obtain the Kaluza-Klein spectrum approximately and study the Kaluza-Klein modes. The results are cross sections for production of a graviton together with a photon or a hadronic jet, which are the most important reactions for LHC physics.

  • 86.
    Melbéus, Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Continuum photon spectrum from Z1Z1 annihilations in universal extra dimensions2012Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 706, nr 4-5, s. 329-332Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We calculate the continuum photon spectrum from the pair annihilation of a Z1 LKP in non-minimal universal extra dimensions. We find that, due to the preferred annihilation into W+ W- pairs, the continuum flux of collinear photons is relatively small compared to the standard case of the B1 as the LKP. This conclusion applies in particular to the spectral endpoint, where also the additional fermionic contributions are not large enough to increase the flux significantly. When searching for the line signal originating from Z1 Z1 annihilations, this is actually a perfect situation, since the continuum signal can be regarded as background to the smoking gun signature of a peak in the photon flux at an energy that is nearly equal to the mass of the dark matter particle. This signal, in combination with (probably) a non-observation of the continuum signal at lower photon energies, constitutes a perfect handle to probe the hypothesis of the Z1 LKP being the dominant component of the dark matter observed in the Universe.

  • 87.
    Melbéus, Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Higgs dark matter in UEDs: A good WIMP with bad detection prospects2012Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 715, nr 1-3, s. 164-169Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the first Kaluza-Klein excitation of the Higgs boson in universal extra dimensions as a dark matter candidate. The first-level Higgs boson could be the lightest Kaluza-Klein particle, which is stable due to the conservation of Kaluza-Klein parity, in non-minimal models where boundary localized terms modify the mass spectrum. We calculate the relic abundance and find that it agrees with the observed dark matter density if the mass of the first-level Higgs boson is slightly above 2 TeV, not considering coannihilations and assuming no relative mass splitting among the first-level Kaluza-Klein modes. In the case of coannihilations and a non-zero mass splitting, the mass of the first-level Higgs boson can range from 1 TeV to 4 TeV. We study also the prospects for detection of this dark matter candidate in direct as well as indirect detection experiments. Although the first-level Higgs boson is a typical weakly interacting massive particle, an observation in any of the conventional experiments is very challenging.

  • 88.
    Melbéus, Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Higgs Kaluza–Klein dark matter in universal extra dimensions2008Manuskript (preprint) (Annet vitenskapelig)
  • 89.
    Melbéus, Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Delving into extra dimensions2012Inngår i: Physics world, ISSN 0953-8585, Vol. 25, nr 9, s. 27-30Artikkel i tidsskrift (Fagfellevurdert)
  • 90.
    Melbéus, Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Searches for hyperbolic extra dimensions at the LHC2008Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2008, nr 08, s. 077-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate a model of large extra dimensions where the internal space has the geometry of a hyperbolic disc. Compared with the ADD model, this model provides a more satisfactory solution to the hierarchy problem between the electroweak scale and the Planck scale, and it also avoids constraints from astrophysics. In general, a novel feature of this model is that the physical results depend on the position of the brane in the internal space, and in particular, the signal almost disappears completely if the brane is positioned at the center of the disc. Since there is no known analytic form of the Kaluza-Klein spectrum for our choice of geometry, we obtain a spectrum based on a combination of approximations and numerical computations. We study the possible signatures of our model for hadron colliders, especially the LHC, where the most important processes are the production of a graviton together with a hadronic jet or a photon. We find that the signals are similar to those of the ADD model, regarding both qualitative behavior and strength. For the case of hadronic jet production, it is possible to obtain relatively strong signals, while for the case of photon production, this is much more difficult.

  • 91. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Leptonic CP violation at neutrino telescopes2012Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 86, nr 6, s. 067701-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With the advent of the recent measurements in neutrino physics, we investigate the role of high-energy neutrino flux ratios at neutrino telescopes for the possibility of determining the leptonic CP-violating phase delta and the underlying pattern of the leptonic mixing matrix. We find that the flux ratios show a dependence of O(10%) on the CP-violating phase, and for optimistic uncertainties on the flux ratios less than 10%, they can be used to distinguish between CP-conserving and CP-violating values of the phase at 2 sigma in a nonvanishing interval around the maximal value vertical bar delta vertical bar = pi/2.

  • 92. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Neutrino flux ratios at neutrino telescopes: The role of uncertainties of neutrino mixing parameters and applications to neutrino decay2007Inngår i: Physical Review D, ISSN 1550-7998, Vol. 75, nr 12, s. 125017-1-125017-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we derive simple and general perturbative formulas for the flavor flux ratios R-alpha beta=phi(nu alpha)/phi(nu beta) that could be measured at neutrino telescopes. We discuss in detail the role of the uncertainties of the neutrino mixing parameters showing that they have to be seriously taken into account in any realistic discussion about flavor measurements at neutrino telescopes. In addition, we analyze the impact of such uncertainties in telling the standard neutrino oscillation framework from scenarios involving, e.g., neutrino decay and we find that the ratio R-e mu is the most sensitive one to new physics effects beyond the standard model. We also compute the more realistic muon-to-shower ratio for a particular configuration of the IceCube experiment, observing that using this experimental quantity a clear separation between standard and nonstandard neutrino physics cannot be obtained.

  • 93.
    Meloni, Davide
    et al.
    Università di Roma Tre.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Riad, Stella
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) modelManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In the context of non-supersymmetric SO(10) models, we analyze the renormalization group equations for the fermions (including neutrinos) from the GUT energy scale down to the electroweak energy scale, explicitly taking into account the effects of an intermediate energy scal induced by a Pati-Salam gauge group. To determine the renomalization group running, we use a numerical minimization procedure based on a nested sampling algoritm that randomly generates the values of 19 model parameters at the GUT scale, evolves them, and finally constructs the values of te physical observables and compares them to the existing experimental data at the electroweak scale. We show that the evolved fermion masses and mixings present sizavle deviations from the values obtained without including the effects of the intermediate scale.

  • 94. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Riad, Stella
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) model2014Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 12, s. 052-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the context of non-supersymmetric SO(10) models, we analyze the renormalization group equations for the fermions (including neutrinos) from the GUT energy scale down to the electroweak energy scale, explicitly taking into account the effects of an intermediate energy scale induced by a Pati-Salam gauge group. To determine the renormalization group running, we use a numerical minimization procedure based on a nested sampling algorithm that randomly generates the values of 19 model parameters at the GUT scale, evolves them, and finally constructs the values of the physical observables and compares them to the existing experimental data at the electroweak scale. We show that the evolved fermion masses and mixings present sizable deviations from the values obtained without including the effects of the intermediate scale.

  • 95. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Winter, Walter
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Non-standard interactions versus non-unitary lepton flavor mixing at a neutrino factory2010Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2010, nr 04, s. 041-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The impact of heavy mediators on neutrino oscillations is typically described by non-standard four-fermion interactions (NSIs) or non-unitarity (NU). We focus on leptonic dimension-six effective operators which do not produce charged lepton flavor violation. These operators lead to particular correlations among neutrino production, propagation, and detection non-standard effects. We point out that these NSIs and NU phenomenologically lead, in fact, to very similar effects for a neutrino factory, for completely different fundamental reasons. We discuss how the parameters and probabilities are related in this case, and compare the sensitivities. We demonstrate that the NSIs and NU can, in principle, be distinguished for large enough effects at the example of non-standard effects in the mu-tau-sector, which basically corresponds to differentiating between scalars and fermions as heavy mediators as leading order effect. However, we find that a near detector at superbeams could provide very synergistic information, since the correlation between source and matter NSIs is broken for hadronic neutrino production, while NU is a fundamental effect present at any experiment.

  • 96. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Exact and approximate formulas for neutrino mixing and oscillations with non-standard interactions2009Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2009, nr 04, s. 033-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present, both exactly and approximately, a complete set of mappings between the vacuum (or fundamental) leptonic mixing parameters and the effective ones in matter with non-standard neutrino interaction (NSI) effects included. Within the three-flavor neutrino framework and a constant matter density profile, a full set of sum rules is established, which enables us to reconstruct the moduli of the effective leptonic mixing matrix elements, in terms of the vacuum mixing parameters in order to reproduce the neutrino oscillation probabilities for future long-baseline experiments. Very compact, but quite accurate, approximate mappings are obtained based on series expansions in the neutrino mass hierarchy parameter eta equivalent to Delta m(21)(2)/Delta m(31)(2), the vacuum leptonic mixing parameter s(13) equivalent to sin theta(13), and the NSI parameters epsilon(alpha beta). A detailed numerical analysis about how the NSIs affect the smallest leptonic mixing angle theta(13), the deviation of the leptonic mixing angle theta(23) from its maximal mixing value, and the transition probabilities useful for future experiments are performed using our analytical results.

  • 97.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    keV sterile Neutrino Dark Matter and Neutrino Model Building2012Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 375, nr Part 2, s. 012047-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A sterile neutrino with a mass around the keV scale could be an interesting candidate for warm dark matter. Although there are several scenarios and production mechanisms known in which such a particle could yield the correct abundance, there are astonishingly few models around that can actually yield an explanation for the appearance of a keV-like scale. We here review three main classes of such mass models for keV sterile neutrino dark matter, based on split seesaw, on L-e - L-mu - L-tau symmetry, and on the Froggatt-Nielsen mechanism, respectively.

  • 98.
    Merle, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Niro, Viviana
    University of Turino.
    Deriving models for keV sterile neutrino Dark Matter with the Froggatt-Nielsen mechanism2011Inngår i: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2011, nr 7, s. 023-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sterile neutrinos with a mass around the keV scale are an attractive particle physics candidate for Warm Dark Matter. Although many frameworks have been presented in which these neutrinos can fulfill all phenomenological constraints, there are hardly any models known that can explain such a peculiar mass pattern, one sterile neutrino at the keV scale and the other two considerably heavier, while at the same time being compatible with low-energy neutrino data. In this paper, we present models based on the Froggatt-Nielsen mechanism, which can give such an explanation. We explain how to assign Froggatt-Nielsen charges in a successful way, and we give a detailed discussion of all conditions to be fulfilled. It turns out that the typical arbitrariness of the charge assignments is greatly reduced when trying to carefully account for all constraints. We furthermore present analytical calculations of a few simplified models, while quasi-perfect models are found numerically.

  • 99. Merle, Alexander
    et al.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Dark matter: Supersymmetry wimps out?2012Inngår i: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 8, nr 8, s. 584-586Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Supersymmetric particles are prime candidates to make up the dark matter of the Universe — yet the lack of evidence for them so far from the Large Hadron Collider could force a rethink.

  • 100. Nath, Pran
    et al.
    Malinsky, Michal
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zurek, K.
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    The Hunt for New Physics at the Large Hadron Collider2010Inngår i: NUCLEAR PHYSICS B: PROCEEDINGS SUPPLEMENTS, 2010, Vol. 200-02, s. 185-+Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed to explain the baryon excess in the universe, the possible existence of extra gauge groups and extra matter, and importantly the path Nature chooses to resolve the hierarchy problem - is it supersymmetry or extra dimensions. Many models of new physics beyond the standard model contain a hidden sector which can be probed at the LHC. Additionally, the LHC will be a. top factory and accurate measurements of the properties of the top and its rare decays will provide a window to new physics. Further, the LHC could shed light on the origin of neutralino masses if the new physics associated with their generation lies in the TeV region. Finally, the LHC is also a laboratory to test the hypothesis of TeV scale strings and D brane models. An overview of these possibilities is presented in the spirit that it will serve as a companion to the Technical Design Reports (TDRs) by the particle detector groups ATLAS and CMS to facilitate the test of the new theoretical ideas at the LHC. Which of these ideas stands the test of the LHC data will govern the course of particle physics in the subsequent decades.

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