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  • 51.
    Konstandin, Thomas
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    The effective matter potential for highly relativistic neutrinos2006In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 634, no 03-feb, p. 267-271Article in journal (Refereed)
    Abstract [en]

    We investigate matter effects on highly relativistic neutrinos. The self-energy of neutrinos is determined in an electron or neutrino background taking into account resonance and finite width effects of the gauge bosons. We find minor changes compared to the formerly used formula for the propagator function and large deviations of the effective width from the decay width of the gauge bosons considering higher moments of the electron or neutrino distribution function.

  • 52.
    Kuhnel, Florian
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. AlbaNova University Center, Sweden.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. AlbaNova University Center, Sweden; University of Iceland, Iceland.
    Signatures of compact halos of sterile-neutrino dark matter2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 96, no 10, article id 103020Article in journal (Refereed)
    Abstract [en]

    We investigate compact halos of sterile-neutrino dark matter and examine observable signatures with respect to neutrino and photon emission. Primarily, we consider two cases: primordial black-hole halos and ultracompact minihalos. In both cases, we find that there exists a broad range of possible parameter choices such that detection in the near future with x-ray and gamma-ray telescopes might be well possible. In fact, for energies above 10 TeV, the neutrino telescope IceCube would be a splendid detection machine for such macroscopic dark-matter candidates.

  • 53.
    Kühnel, Florian
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Alballova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, Roslagstullsbacken 21, S-10691 Stockholm, Sweden..
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Alballova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, Roslagstullsbacken 21, S-10691 Stockholm, Sweden.;Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Decaying dark matter in halos of primordial black holes2019In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 8, article id 687Article in journal (Refereed)
    Abstract [en]

    We investigate photon signatures of general decaying dark-matter particles in halos of primordial black holes. We derive the halo-profile density and the total decay rate for these combined dark-matter scenarios. For the case of axion-like particles of masses below O(1)keV, we find strong bounds on the decay constant which are several orders of magnitude stronger than the strongest existing bounds, for all halo masses above O(10-5) solar masses. Using future X-ray measurements, it will be possible to push these bounds on such combined dark-matter scenarios even further.

  • 54. Linde, Johan
    et al.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Snellman, Håkan
    KTH, Superseded Departments, Physics.
    Decuplet baryon magnetic moments in the chiral quark model1998In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 57, no 9, p. 5916-5919Article in journal (Refereed)
    Abstract [en]

    We present calculations of the decuplet baryon magnetic moments in the chiral quark model. As input we use parameters obtained in qualitatively accurate fits to the octet baryon magnetic moments studied previously. The values found for the magnetic moments of Delta(++) and Omega(-) are in good agreement with experiments. We finally calculate the total quark spin polarizations of the decuplet baryons and find that they are considerably smaller than what is expected from the non-relativistic quark model.

  • 55. Linde, Johan
    et al.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Snellman, Håkan
    KTH, Superseded Departments, Physics.
    Octet baryon magnetic moments in the chiral quark model with configuration mixing1998In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 57, no 1, p. 452-464Article in journal (Refereed)
    Abstract [en]

    The Coleman-Glashow sum-rule for magnetic moments is always fulfilled in the chiral quark model, independently of SU(3) symmetry breaking. This is due to the structure of the wave functions, coming from the non-relativistic quark model. Experimentally, the Coleman-Glashow sum-rule is violated by about ten standard deviations. To overcome this problem, two models of wave functions with configuration mixing are studied. One of these models violates the Coleman-Glashow sum-rule to the right degree and also reproduces the octet baryon magnetic moments rather accurately.

  • 56. Lindner, Manfred
    et al.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Seidl, Gerhart
    Seesaw mechanisms for Dirac and Majorana neutrino masses2002In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 65, no 5, p. 053014-Article in journal (Refereed)
    Abstract [en]

    We investigate the seesaw mechanism for generally non-fine-tuned n x n mass matrices involving both Dirac and Majorana neutrinos. We specifically show that the number of naturally light neutrinos cannot exceed half of the dimension of the considered mass matrix. Furthermore, we determine a criterion for mass matrix textures leading to light Dirac neutrinos with the seesaw mechanism. In particular, we study 4 x 4 and 6 x 6 mass matrix textures and give some examples in order to highlight these types of texture. Next, we present a model scheme based on non-Abelian and discrete symmetries satisfying the above mentioned criterion for light Dirac neutrinos. Finally, we investigate the connection between symmetries and the invariants of a mass matrix on a formal level.

  • 57. Lindner, Manfred
    et al.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Tomàs, Ricard
    Winter, Walter
    Tomography of the Earth's core using supernova neutrinos2003In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 19, no 6, p. 755-770Article in journal (Refereed)
    Abstract [en]

    We investigate the possibility to use the neutrinos coming from a future galactic supernova explosion to perform neutrino oscillation tomography of the Earth's core. We propose to use existing or planned detectors, resulting in an additional payoff. Provided that all of the discussed uncertainties can be reduced as expected, we find that the average matter densities of the Earth's inner and outer cores could be measured with a precision competitive with geophysics. However, since seismic waves are more sensitive to matter density jumps than average matter densities, neutrino physics would give partly complementary information.

  • 58. Lindner, Manfred
    et al.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Winter, Walter
    A combined treatment of neutrino decay and neutrino oscillations2001In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 607, no 02-jan, p. 326-354Article in journal (Refereed)
    Abstract [en]

    Neutrino decay in vacuum has often been considered as an alternative to neutrino oscillations. Because nonzero neutrino masses imply the possibility of both neutrino decay and neutrino oscillations, we present a model-independent formal treatment of these combined scenarios. For that, we show for the example of Majoron decay that in many cases decay products are observable and may even oscillate. Furthermore, we construct a minimal scenario in which we study the physical implications of neutrino oscillations with intermediate decays.

  • 59. Lindner, Manfred
    et al.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Winter, Walter
    Decays of supernova neutrinos2002In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 622, no 02-jan, p. 429-456Article in journal (Refereed)
    Abstract [en]

    Supernova neutrinos could be well-suited for probing neutrino decay, since decay may be observed even for very small decay rates or coupling constants. We will introduce an effective operator framework for the combined description of neutrino decay and neutrino oscillations for supernova neutrinos, which can especially take into account two properties: one is the radially symmetric neutrino flux, allowing a decay product to be re-directed towards the observer even if the parent neutrino had a different original direction of propagation. The other is decoherence because of the long baselines for coherently produced neutrinos. We will demonstrate how to use this effective theory to calculate the time-dependent fluxes at the detector. In addition, we will show the implications of a Majoron-like decay model. As a result, we will demonstrate that for certain parameter values one may observe some effects which could also mimic signals similar to the ones expected from supernova models, making it in general harder to separate neutrino and supernova properties.

  • 60.
    Malinsky, Michal
    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.
    Xing, Zhi-zhong
    Zhang, He
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Non-unitary neutrino mixing and CP violation in the minimal inverse seesaw model2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 679, no 3, p. 242-248Article in journal (Refereed)
    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.

  • 61.
    Malinsky, Michal
    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.
    Nonstandard neutrino interactions from a triplet seesaw model2009In: Physical Review D, ISSN 1550-7998, Vol. 79, no 1, p. 011301(R)-Article in journal (Refereed)
    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.

  • 62.
    Malinsky, Michal
    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.
    Nonunitarity effects in a realistic low-scale seesaw model2009In: Physical Review D, ISSN 1550-7998, Vol. 79, no 7, p. 073009-Article in journal (Refereed)
    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.

  • 63. Meier, Christoph
    et al.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Analysis of a three flavor neutrino oscillation fit to recent Super-Kamiokande data2000In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 18, no 1, p. 97-106Article in journal (Refereed)
    Abstract [en]

    We have analyzed the most recent available Super-Kamiokande data in a three flavor neutrino oscillation model. We have here neglected possible matter effects and we performed a fit to atmospheric and solar Super-Kamiokande data. We have investigated a large parameter range where the mixing angles were restricted to 0 less than or equal to theta (i) less than or equal to pi /2, i = 1,2,3, and the mass squared differences were taken to be in the intervals 10(-11) eV(2) less than or equal to Deltam(2) less than or equal to 10(-2) eV(2) and 10(-4) eV(2) less than or equal to DeltaM(2) less than or equal to 10 eV(2), i.e., the hierarchy between the mass squared differences is not completely determined. This yielded a best solution characterized by the parameter values theta (1) similar or equal to 45 degrees, theta (2) similar or equal to 10 degrees, theta (3) similar or equal to 45 degrees, Deltam(2) similar or equal to 4.4 x 10(-10) eV(2), and DeltaM(2) similar or equal to 1.01. x 10(-3) eV(2), which shows that the analyzed experimental data speak in favor of a bimaximal mixing scenario with one of the mass squared differences in the just-so domain and the other one in the range capable of providing a solution to the atmospheric neutrino problem.

  • 64.
    Melbéus, Henrik
    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.
    Continuum photon spectrum from Z1Z1 annihilations in universal extra dimensions2012In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 706, no 4-5, p. 329-332Article in journal (Refereed)
    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.

  • 65.
    Melbéus, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Royal Inst Technol KTH, Dept Theoret Phys, Sch Engn Sci, S-10691 Stockholm, Sweden..
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Royal Inst Technol KTH, Dept Theoret Phys, Sch Engn Sci, S-10691 Stockholm, Sweden..
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Royal Inst Technol KTH, Dept Theoret Phys, Sch Engn Sci, S-10691 Stockholm, Sweden..
    Erratum to: Continuum photon spectrum from Z(1)Z(1) annihilations in universal extra dimensions2012In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 713, no 3, p. 350-350Article in journal (Refereed)
  • 66.
    Melbéus, Henrik
    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.
    Higgs dark matter in UEDs: A good WIMP with bad detection prospects2012In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 715, no 1-3, p. 164-169Article in journal (Refereed)
    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.

  • 67.
    Melbéus, Henrik
    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.
    Higgs Kaluza–Klein dark matter in universal extra dimensions2008Manuscript (preprint) (Other academic)
  • 68.
    Melbéus, Henrik
    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.
    Delving into extra dimensions2012In: Physics world, ISSN 0953-8585, Vol. 25, no 9, p. 27-30Article in journal (Refereed)
  • 69.
    Melbéus, Henrik
    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.
    Searches for hyperbolic extra dimensions at the LHC2008In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2008, no 08, p. 077-Article in journal (Refereed)
    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.

  • 70. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Leptonic CP violation at neutrino telescopes2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 86, no 6, p. 067701-Article in journal (Refereed)
    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.

  • 71. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrino flux ratios at neutrino telescopes: The role of uncertainties of neutrino mixing parameters and applications to neutrino decay2007In: Physical Review D, ISSN 1550-7998, Vol. 75, no 12, p. 125017-1-125017-12Article in journal (Refereed)
    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.

  • 72.
    Meloni, Davide
    et al.
    Università di Roma Tre.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Riad, Stella
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) modelManuscript (preprint) (Other academic)
    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.

  • 73. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Riad, Stella
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) model2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 12, p. 052-Article in journal (Refereed)
    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.

  • 74. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Riad, Stella
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Renormalization group running of fermion observables in an extended non-supersymmetric SO(10) model2017In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 3, article id 045Article in journal (Refereed)
    Abstract [en]

    We investigate the renormalization group evolution of fermion masses, mixings and quartic scalar Higgs self-couplings in an extended non-supersymmetric SO(10) model, where the Higgs sector contains the 10(H), 120(H), and 126(H) representations. The group SO(10) is spontaneously broken at the GUT scale to the Pati-Salam group and subsequently to the Standard Model (SM) at an intermediate scale MI. We explicitly take into account the effects of the change of gauge groups in the evolution. In particular, we derive the renormalization group equations for the different Yukawa couplings. We find that the computed physical fermion observables can be successfully matched to the experimental measured values at the electroweak scale. Using the same Yukawa couplings at the GUT scale, the measured values of the fermion observables cannot be reproduced with a SM-like evolution, leading to differences in the numerical values up to around 80%. Furthermore, a similar evolution can be performed for a minimal SO(10) model, where the Higgs sector consists of the 10(H) and 126(H) representations only, showing an equally good potential to describe the low-energy fermion observables. Finally, for both the extended and the minimal SO(10) models, we present predictions for the three Dirac and Majorana CP-violating phases as well as three effective neutrino mass parameters.

  • 75. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Winter, Walter
    Zhang, He
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Non-standard interactions versus non-unitary lepton flavor mixing at a neutrino factory2010In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2010, no 04, p. 041-Article in journal (Refereed)
    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.

  • 76. Meloni, Davide
    et al.
    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.
    Exact and approximate formulas for neutrino mixing and oscillations with non-standard interactions2009In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2009, no 04, p. 033-Article in journal (Refereed)
    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.

  • 77. Merle, Alexander
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Dark matter: Supersymmetry wimps out?2012In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 8, no 8, p. 584-586Article in journal (Other (popular science, discussion, etc.))
    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.

  • 78.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    A brief status of non-standard neutrino interactions2013In: NOW 2012: Proceedings of the Neutrino Oscillation Workshop / [ed] Paolo Bernardini, Gianluigi Fogli, Eligio Lisi, Elsevier, 2013, p. 301-307Conference paper (Refereed)
    Abstract [en]

    In this plenary talk, we review the status of non-standard neutrino interactions (NSIs). First, we give a brief introduction to neutrino flavor transitions with NSIs based on the standard paradigm of neutrino oscillations. Then, we discuss alternative scenarios for neutrino flavor transitions such as neutrino decoherence, neutrino decay, and NSIs. Second, we investigate NSIs with three neutrino flavors. In general, we introduce production and detection NSIs, including the so-called zero-distance effect, and matter NSIs. In addition, we study mappings and approximate formulas for NSIs. Third, we present a brief account of theoretical models for NSIs. Fourth and most important, we investigate in detail the phenomenology of NSIs based on different types of data from neutrino experiments. Fifth, we give some phenomenological bounds on both matter and production/detection NSIs as well as we present sensitivity and discovery reach of NSIs at future experiments. Finally, we present a summary and state our conclusions.

  • 79.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    After Higgs2012In: New scientist (1971), ISSN 0262-4079, Vol. 215, no 2881, p. 29-29Article in journal (Other (popular science, discussion, etc.))
  • 80.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Another collider is not the way forward2013In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 494, no 7435, p. 35-35Article in journal (Other academic)
  • 81.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Bimaximal fermion mixing from the quark and leptonic mixing matrices2005In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 622, no 02-jan, p. 159-164Article in journal (Refereed)
    Abstract [en]

    In this Letter. we show how the mixing angles of the standard parameterization add when multiplying the quark and leptonic mixing matrices. i.e., we derive explicit sum rules for the quark and leptonic mixing angles. In this connection, we also discuss other recently proposed sum rules for the mixing angles assuming bimaximal fermion mixing. In addition, we find that the present experimental and phenomenological data of the mixing angles naturally fulfill our sum rules, and thus, give rise to bilarge or bimaximal fermion mixing.

  • 82.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Cutting with Occam's razor2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 86, no 9, p. 097301-Article in journal (Refereed)
    Abstract [en]

    We comment positively on the recent article "Seesaw mechanism with Occam's razor" [K. Harigaya et al. Phys. Rev. D 86, 013002 (2012).] by Harigaya, Ibe, and Yanagida. In this article, the authors are using the principle of Occam's razor in neutrino physics-a principle that should be applied more often in science in general. At the end, we also discuss the Bayesian method in statistics, in which Occam's razor is naturally built in.

  • 83.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Don't let furore over neutrinos blur results2012In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 485, no 7398, p. 309-309Article in journal (Refereed)
  • 84.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Dynamics of quarks and leptons: theoretical Studies of Baryons and Neutrinos2000Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The Standard Model of Elementary Particle Physics (SM) is the present theoryfor the elementary particles and their interactions and is a well-established theorywithin the physics community. The SM is a combination of Quantum Chromodynamics(QCD) and the Glashow{Weinberg{Salam (GWS) electroweak model. QCDis a theory for the strong force, whereas the GWS electroweak model is a theoryfor the weak and electromagnetic forces. This means that the SM describes allfundamental forces in Nature, except for the gravitational force. However, the SMis not a nal theory and some of its problems will be discussed in this thesis.In the rst part of this thesis, several properties of baryons are studied suchas spin structure, spin polarizations, magnetic moments, weak form factors, andnucleon quark sea isospin asymmetries, using the chiral quark model (QM). TheQM is an eective chiral eld theory developed to describe low energy phenomena of baryons, since perturbative QCD is not applicable at low energies. The resultsof the QM are in good agreement with experimental data.The second part of the thesis is devoted to the concept of quantum mechanicalneutrino oscillations. Neutrino oscillations can, however, not occur within the GWSelectroweak model. Thus, this model has to be extended in some way. All studiesincluding neutrino oscillation are done within three avor neutrino oscillationmodels. Both vacuum and matter neutrino oscillations are considered. Especially,global ts to all data of candidates for neutrino oscillations are presented and alsoan analytical formalism for matter enhanced three avor neutrino oscillations usingtime evolution operators is derived. Furthermore, investigations of matter eectswhen neutrinos traverse the Earth are included.The thesis begins with an introductory review of the QM and neutrino oscillationsand ends with the research results, which are given in the nine accompanyingscientic articles.

  • 85.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Effects and influences on neutrino oscillations due to a thin density layer perturbation added to a matter density profile2001In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 522, no 04-mar, p. 280-286Article in journal (Refereed)
    Abstract [en]

    In this Letter, we show the effects on the transition probabilities for neutrino oscillations due to a thin constant density layer perturbation added to an arbitrary matter density profile, In the case of two neutrino flavors, we calculate the effects both analytically and numerically, whereas in the case of three neutrino flavors, we perform the studies purely numerically. As an realistic example we consider the effects of the Earth's atmosphere when added to the Earth's matter density profile on the neutrino oscillation transition probabilities for atmospheric neutrinos.

  • 86.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Effects of Non-Standard Interactions in the MINOS Experiment2008In: Neutrino Factories, Superbeams And Betabeams / [ed] Osamu Yasuda, Naba Mondal, Chihiro Ohmori, 2008, p. 213-215Conference paper (Refereed)
    Abstract [en]

    In this talk, we investigate the effects of non-standard interactions (NSI) in the MINOS experiment based on a full three-flavor neutrino oscillation framework simulation. The simulation was performed using the GLoBES software. The results indicate that the allowed region in the sin(2)(2 theta(23))-Delta m(31)(2) plane is extended due to NSI effects, that there is a degeneracy between the leptonic mixing angle theta(13) and the NSI parameter epsilon(e tau), and that MINOS can put a lower upper bound on sin(2)(2 theta(13)) than CHOOZ only for small values of vertical bar epsilon(e tau)vertical bar.

  • 87.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Equivalence between Gaussian averaged neutrino oscillations and neutrino decoherence2001In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 502, no 04-jan, p. 159-166Article in journal (Refereed)
    Abstract [en]

    In this Letter, we show that a Gaussian averaged neutrino oscillation model is equivalent to a neutrino decoherence model. Without loss of generality, the analysis is performed with two neutrino flavors. We also estimate the damping (or decoherence) parameter for atmospheric neutrinos and compare it to earlier obtained results.

  • 88.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Extrinsic CPT Violation in Neutrino Oscillations2004In: NEUTRINO FACTORIES AND SUPERBEAMS: 5th International Workshop on Neutrino Factories and Superbeams; NuFact 03 / [ed] Adam Para, Fermi National Accelerator Laboratory, American Institute of Physics , 2004, p. 265-268Conference paper (Refereed)
    Abstract [en]

    In this talk, we investigate extrinsic CPT violation in neutrino oscillations in matter with three flavors. Note that extrinsic CPT violation is different from intrinsic CPT violation. Extrinsic CPT violation is one way of quantifying matter effects, whereas intrinsic CPT violation would mean that the CPT invariance theorem is not valid. We present analytical formulas for the extrinsic CPT probability differences and discuss their implications for long-baseline experiments and neutrino factory setups.

  • 89.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Four's a crowd2013In: New scientist (1971), ISSN 0262-4079, Vol. 219, no 2925, p. 32-32Article in journal (Refereed)
  • 90.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    International Linear Collider: Another collider is not the way forward2013In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 494, no 7435Article in journal (Refereed)
  • 91.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    LHC reality check2012In: New scientist (1971), ISSN 0262-4079, Vol. 216, no 2895, p. 36-36Article in journal (Other academic)
  • 92.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Monte Carlo Simulations of Protein Structure and Aggregation: A Study of Melittin1996Independent thesis Advanced level (professional degree), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The subject of this thesis is Monte Carlo simulations of protein structure and aggregation. Monte Carlo methods for docking α-helices in a protein has been investigated and tested. The protein Melittin was used in all Monte Carlo simulations. Melittin is a toxin and the principal part of the venom of the honey bee Apis mellifera.

    Different energy functions were used in the MC simulations, however electrostatic energy and Lennard - Jones energy were always included in the (total) energy functions.

    Rigid helix docking was simulated, but in some simulations the side chains of the protein were flexible (loose).

    The main task was to investigate how the solvation energy would affect the protein in simulations. So the influence of solvation energy has been investigated and a comparison between simulations with and without solvation energy has been made.

    Two different programs for calculating protein (solvent-accessible) surface area have also been compared.

    The conclusion of this thesis are summarized in the end and future development projects of solvation energy simulations are also discussed.

  • 93.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrino extras2012In: New scientist (1971), ISSN 0262-4079, Vol. 216, no 2885, p. 31-31Article in journal (Other (popular science, discussion, etc.))
  • 94.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Neutrino oscillations in matter and their applications2001In: Physica scripta. T, ISSN 0281-1847, Vol. T93, p. 18-25Article in journal (Refereed)
    Abstract [en]

    In this paper, an introduction to the evolution operator method for three flavor neutrino oscillations in matter based on the Cayley-Hamilton formalism is presented as well as some its theoretical and experimental applications.

  • 95.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrinos and the hunt for the last mixing angle2012In: Europhysics News, ISSN 0531-7479, Vol. 43, no 4, p. 22-25Article in journal (Refereed)
    Abstract [en]

    In summary, the measurement of Ξ 23 by the Super-Kamiokande experiment resulted in one of the first indications of physics beyond Standard Model, the measurement of Ξ 12 was the first precision measurement in neutrino physics, and the hunt for the value of the third and final mixing angle Ξ 13 was the beginning of the end of the measurements of the mixing angles for the neutrinos, but the beginning of the continuation of measurements of the remaining neutrino parameters.

  • 96.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrinos from Kaluza-Klein Dark Matter Annihilations in the Sun2011In: Physics beyond the Standard Models of Particles, Cosmology and Astrophysics: Proceedings of the Fifth International Conference / [ed] H V Klapdor-Kleingrothaus, I V Krivosheina, R Viollier, World Scientific Publishing , 2011, p. 496-502Conference paper (Refereed)
    Abstract [en]

    In this talk, we compute fluxes of neutrinos from Kaluza–Klein dark matter annihilations in the Sun based on cross-sections from both five- and six-dimensional models. For our numerical calculations, we use WimpSim and DarkSUSY. In addition, we compare our results with the ones derived earlier in the literature.

  • 97.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrinos from WIMP Annihilations2008In: Dark Matter in Astroparticle and Particle Physics - Dark 2007: Proceedings of the 6th International Heidelberg Conference / [ed] Hans Volker Klapdor-Kleingrothaus, Geraint F. Lewis, World Scientific Publishing , 2008, p. 51-59Conference paper (Refereed)
    Abstract [en]

    In this talk, we make an improved analysis on the production of neutrinos coming from WIMP annihilations inside the Sun as well as the Earth. We treat both neutrino interaction and oscillation effects in aconsistent three-flavor framework. Our numerical simulations are performed in an event-based setting, which is useful for both theoretical studies and creating neutrino telescope Monte Carlo simulations. We find that the yield of muon-type neutrinos is enhanced or suppressed depending on the dominant WIMP annihilation channel. In addition, we find that oscillations can significantly affect the neutrino yields from WIMP annihilations in the Sun. Effectively, the neutrino flavors are mixed. Finally, for the Earth, the oscillations have no large impact at energies for the new neutrino telescopes such as IceCube, ANTARES, and NESTOR.

  • 98.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Non-Hermitian neutrino oscillations in matter with PT symmetric Hamiltonians2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 113, no 6, article id 61001Article in journal (Refereed)
    Abstract [en]

    We introduce and develop a novel approach to extend the ordinary two-flavor neutrino oscillation formalism in matter using a non-Hermitian PT symmetric effective Hamiltonian. The condition of PT symmetry is weaker and less mathematical than that of hermicity, but more physical, and such an extension of the formalism can give rise to sub-leading effects in neutrino flavor transitions similar to the effects by so-called non-standard neutrino interactions. We derive the necessary conditions for the spectrum of the effective Hamiltonian to be real as well as the mappings between the fundamental and effective parameters. We find that the real spectrum of the effective Hamiltonian will depend on all new fundamental parameters introduced in the non-Hermitian PT symmetric extension of the usual neutrino oscillation formalism and that either i) the spectrum is exact and the effective leptonic mixing must always be maximal or ii) the spectrum is approximate and all new fundamental parameters must be small.

  • 99.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Non-standard neutrino interactions2009In: SIXTH INTERNATIONAL WORKSHOP ON NEUTRINO-NUCLEUS INTERACTIONS IN THE FEW-GEV REGION / [ed] Sanchez F; Sorel M; Alvarez-Ruso L; Cervera A; Vicente-Vacas M, American Institute of Physics , 2009, Vol. 1189, p. 16-23Conference paper (Refereed)
    Abstract [en]

    In this talk, I will review non-standard interactions in neutrino physics, especially I will emphazise the impact of non-standard interactions on neutrino oscillations. First, I will give a brief introduction about non-standard interactions and what they are. Then, I will present what has been performed in the literature, what I have done in the field, and what could be done in the future. Next, I will discuss how important non-standard interactions are for neutrino cross-sections. Finally, I will give a summary of the field.

  • 100.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Preprint servers: Follow arXiv's lead2012In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 489, no 7416, p. 367-Article in journal (Refereed)
123 51 - 100 of 138
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