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  • 1.
    Akhmedov, Evgeny
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Blennow, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Hällgren, Tomas
    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.
    Stability and leptogenesis in the left-right symmetric seesaw mechanism2007Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 4, s. 022-1-022-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyze the left-right symmetric type I+II seesaw mechanism, where an eight-fold degeneracy among the mass matrices of heavy right-handed neutrinos M-R is known to exist. Using the stability property of the solutions and their ability to lead to successful baryogenesis via leptogenesis as additional criteria, we discriminate among these eight solutions and partially lift their eight-fold degeneracy. In particular, we find that viable leptogenesis is generically possible for four out of the eight solutions.

  • 2.
    Bauer, F.
    et al.
    Physik-Department, Technische Universität München.
    Hällgren, Tomas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Seidl, G.
    Department of Physics, Oklahoma State University.
    Discretized gravity in 6D warped space2007Ingår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 278, nr 1-3, s. 32-63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider discretized gravity in six dimensions. where the two extra dimensions have been compactified on a hyperbolic disk of constant curvature. We analyze different realizations of lattice gravity on the disk at the level of an effective field theory for massive gravitons. It is shown that the observed strong coupling scale of lattice gravity in discretized five-dimensional flat or warped space can be increased if the latticized fifth dimension is wrapped around a hyperbolic disk that has a non-trivial warp factor. As an application, we also study the generation of naturally small Dirac neutrino masses via a discrete volume suppression mechanism and discuss briefly collider implications of our model.

  • 3.
    Hällgren, Tomas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Aspects of Dimensional Deconstruction and Neutrino Physics2007Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 4.
    Hällgren, Tomas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Kaluza-klein dark matter from deconstructed universal extra dimensions2007Ingår i: SUSY06: 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions, American Institute of Physics (AIP), 2007, s. 652-655Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider Kaluza-Klein dark matter from deconstructed or latticized universal extra dimensions and study in this model the positron flux from Kaluza-Klein dark matter annihilation in the galactic halo.

  • 5.
    Hällgren, Tomas
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Phenomenological studies of dimensional deconstruction2005Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis, two applications of dimensional deconstruction are studied. The first application is a model for neutrino oscillations in the presence of a large decon- structed extra dimension. In the second application, Kaluza{Klein dark matter from a latticized universal extra dimension is studied. The goal of these projects have been twofold. First, to see whether it is possible to reproduce the relevant features of the higher-dimensional continuum theory, and second, to examine the effect of the latticization in experiments. In addition, an introduction to the the- ory of dimensional deconstruction as well as to the theory of continuous extra dimensions is given. Furthermore, the various higher-dimensional models, such as Arkani-Hamed{Dvali{Dimopolous (ADD) models and models with universal extra dimensions, that have been intensively studied in recent years, are discussed.

  • 6.
    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 models2008Ingår i: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2008, nr 01, s. 014-Artikel i tidskrift (Refereegranskat)
    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.

  • 7.
    Hällgren, Tomas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Indirect detection of Kaluza-Klein dark matter from latticized universal dimensions2006Ingår i: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2006, nr 06, s. 014-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider Kaluza-Klein dark matter from latticized universal dimensions. We investigate two different lattice models, where the models differ in the choice of boundary conditions. The models reproduce relevant features of the continuum model for Kaluza-Klein dark matter. For the model with simple boundary conditions, this is the case even for a model with only a few lattice sites. We study the effects of the latticization on the differential flux of positrons from annihilation of Kaluza-Klein dark matter in the galactic halo. We find that for different choices of the compactification radius, the differential positron flux rapidly converges to the continuum model results as a function of the number of lattice sites. In addition, we consider the prospects for upcoming space-based experiments such as PAMELA and AMS-02 to probe the latticization effect.

  • 8.
    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 dimensions2005Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2005, nr 02, s. 049-Artikel i tidskrift (Refereegranskat)
    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.

  • 9.
    Ohlsson, Tommy
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Blennow, MattiasKTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.Badelek, BarbaraEdsjö, JoakimHällgren, TomasKonstandin, ThomasPearce, MarkKTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    The 2nd Scandinavian NeutrinO Workshop2006Proceedings (redaktörskap) (Refereegranskat)
    Abstract [en]

    The first Scandinavian NeutrinO Workshop (SNOW) was held in Uppsala, Sweden, in February 2001. About five years passed until the next SNOW took place—this time in Stockholm, Sweden between 2 May 2006 and 6 May 2006. The aim of the workshop was to cover a variety of topics in neutrino physics with leading researchers in the field as speakers. The Royal Swedish Academy of Sciences (KVA) awarded SNOW 2006 a grant for inviting such speakers. The workshop was mainly directed towards phenomenology and theory with connections to experiments and gave an opportunity for theorists and experimentalists to work together, discuss the latest results, and combine the different branches of neutrino physics. The different topics discussed were: solar and atmospheric neutrinos, reactor and accelerator neutrinos, neutrinos in astrophysics and cosmology, phenomenology of neutrino data, neutrino oscillations, theory and model building, fundamental properties of neutrinos, neutrinoless double beta decay, and flavor physics.

    Around 70 scientists (spanning from graduate students to world-leading researchers) in the field of neutrino physics participated in SNOW 2006 and 44 talks were presented in plenary sessions. Out of the 44 talks, 37 have been contributed to these proceedings.

    The talks of SNOW 2006 took place in the Oskar Klein Auditorium at the AlbaNova University Center in Stockholm. The AlbaNova University Center is a joint endeavour between the Royal Institute of Technology (KTH) and Stockholm University. The social program included a welcome reception at KVA, an excursion to the Royal Armoury at the Royal Palace in Stockholm as well as a boat trip in the archipelago of Stockholm, a reception at the City Hall of Stockholm arranged by the city, and finally, a workshop dinner at Häringe Castle south of Stockholm.

1 - 9 av 9
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