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  • 151.
    Blennow, Mattias
    et al.
    Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), München, Germany.
    Melbéus, Henrik
    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.
    Non-unitary neutrino mixing from an extra-dimensional seesaw model2010Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We study the generation of light neutrino masses in an extra-dimensional model, where right-handed neutrinos are allowed to propagate in the extra dimension, while the Standard model (SM) particles are confined to a brane. Motivated by the fact that extra-dimensional models are non-renormalizable, we truncate the Kaluza–Klein (KK) towers at a maximal KK index. The structure of the bulk Majorana mass term, motivated by the Sherk–Schwarz mechanism, implies that the right-handed KK neutrinos pair to form Dirac neutrinos, except for a number of unpaired Majorana neutrinos at the top of each tower. These heavy Majorana neutrinos are the only sources of lepton number breaking in the model, and similarly to the type-I seesaw mechanism, they naturally generate small masses for the left-handed neutrinos. The lower KK modes mix with the light neutrinos, and the mixing effects are not suppressed with respect to the light neutrino masses. Compared to conventional fermionic seesaw models, the non-unitary effects induced by such mixing are quite significant. We study the signals of this model at the Large Hadron Collider (LHC), and find that the current bounds on the non-unitarity parameters are strong enough to exclude an observation.

  • 152. Blennow, Mattias
    et al.
    Melbéus, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zhang, He
    Renormalization group running of the neutrino mass operator in extra dimensions2011Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2011, nr 04, s. 052-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the renormalization group (RG) running of the neutrino masses and the leptonic mixing parameters in two different extra-dimensional models, namely, the Universal Extra Dimensions (UED) model and a model, where the Standard Model (SM) bosons probe an extra dimension and the SM fermions are confined to a four-dimensional brane. In particular, we derive the beta function for the neutrino mass operator in the UED model. We also rederive the beta function for the charged-lepton Yukawa coupling, and confirm some of the existing results in the literature. The generic features of the RG running of the neutrino parameters within the two models are analyzed and, in particular, we observe a power-law behavior for the running. We note that the running of the leptonic mixing angle theta(12) can be sizable, while the running of theta(23) and theta(13) is always negligible. In addition, we show that the tri-bimaximal and the bimaximal mixing patterns at a high-energy scale are compatible with low-energy experimental data, while a tri-small mixing pattern is not. Finally, we perform a numerical scan over the low-energy parameter space to infer the high-energy distribution of the parameters. Using this scan, we also demonstrate how the high-energy theta(12) is correlated with the smallest neutrino mass and the Majorana phases.

  • 153. Blennow, Mattias
    et al.
    Melbéus, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zhang, He
    RG running in a minimal UED model in light of recent LHC Higgs mass bounds2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 712, nr 4-5, s. 419-424Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study how the recent ATLAS and CMS Higgs mass bounds affect the renormalization group running of the physical parameters in universal extra dimensions. Using the running of the Higgs self-coupling constant, we derive bounds on the cutoff scale of the extra-dimensional theory itself. We show that the running of physical parameters, such as the fermion masses and the CKM mixing matrix, is significantly restricted by these bounds. In particular, we find that the running of the gauge couplings cannot be sufficient to allow gauge unification at the cutoff scale.

  • 154. Blennow, Mattias
    et al.
    Melbéus, Henrik
    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.
    Signatures from an extra-dimensional seesaw model2010Ingår i: Physical Review D, ISSN 1550-7998, Vol. 82, nr 4, s. 045023-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the generation of small neutrino masses in an extra-dimensional model, where singlet fermions are allowed to propagate in the extra dimension, while the standard model particles are confined to a brane. Motivated by the fact that extra-dimensional models are nonrenormalizable, we truncate the Kaluza-Klein towers at a maximal Kaluza-Klein number. This truncation, together with the structure of the bulk Majorana mass term, motivated by the Sherk-Schwarz mechanism, implies that the Kaluza-Klein modes of the singlet fermions pair to form Dirac fermions, except for a number of unpaired Majorana fermions at the top of each tower. These heavy Majorana fermions are the only sources of lepton number breaking in the model, and similarly to the type-I seesaw mechanism, they naturally generate small masses for the left-handed neutrinos. The lower Kaluza-Klein modes mix with the light neutrinos, and the mixing effects are not suppressed with respect to the light-neutrino masses. Compared to conventional fermionic seesaw models, such mixing can be more significant. We study the signals of this model at the Large Hadron Collider, and find that the current low-energy bounds on the nonunitarity of the leptonic mixing matrix are strong enough to exclude an observation.

  • 155.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Meloni, Davide
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Terranova, Francesco
    Westerberg, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Non-standard interactions using the OPERA experiment2008Ingår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 56, nr 4, s. 529-536Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the implications of non-standard interactions on neutrino oscillations in the OPERA experiment. In particular, we study the non-standard interaction parameter epsilon(mu tau) . We show that the OPERA experiment has a unique opportunity to reduce the allowed region for this parameter compared with other experiments such as the MINOS experiment, mostly due to the higher neutrino energies in the CNGS beam compared to the NuMI beam. We find that OPERA is mainly sensitive to a combination of standard and non-standard parameters and that a resulting anti-resonance effect could suppress the expected number of events. Furthermore, we show that running OPERA for five years each with neutrinos and anti-neutrinos would help in resolving the degeneracy between the standard parameters and epsilon(mu tau) . This scenario is significantly better than the scenario with a simple doubling of the statistics by running with neutrinos for ten years.

  • 156. Blennow, Mattias
    et al.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Approximative two-flavor framework for neutrino oscillations with nonstandard interactions2008Ingår i: Physical Review D, ISSN 1550-7998, Vol. 78, nr 9, s. 093002-1-093002-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we develop approximative two-flavor neutrino oscillation formulas including subleading nonstandard interaction effects. Especially, the limit when the small mass-squared difference approaches zero is investigated. The approximate formulas are also tested against numerical simulations in order to determine their accuracy and they will probably be most useful in the GeV energy region, which is the energy region where most upcoming neutrino oscillation experiments will be operating. Naturally, it is important to have analytical formulas in order to interpret the physics behind the degeneracies between standard and nonstandard parameters.

  • 157.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Effective neutrino mixing and oscillations in dense matter2005Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 609, nr 3-4, s. 330-338Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the effective case of two-flavor neutrino oscillations in infinitely dense matter by using a perturbative approach. We begin by briefly summarizing the conditions for the three-flavor neutrino oscillation probabilities to take on the same form as the corresponding two-flavor probabilities. Then, we proceed with the infinitely dense matter calculations. Finally, we study the validity of the approximation of infinitely dense matter when the effective matter potential is large, but not infinite, this is done by using both analytic and numeric methods.

  • 158.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Skrotzki, Julian
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Effects of non-standard interactions in the MINOS experiment2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 660, nr 5, s. 522-528Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the effects of non-standard interactions on the determination of the neutrino oscillation parameters Delta m(31)(2), theta(23), and theta(13) in the MINOS experiment. We show that adding non-standard interactions to the analysis lead to an extension of the allowed parameter space to larger values of Delta m(31)(2) and smaller theta(23), and basically removes all predictability for theta(13). In addition, we discuss the sensitivities to the non-standard interaction parameters of the MINOS experiment alone. In particular, we examine the degeneracy between theta(13) and the non-standard interaction parameter epsilon(e tau). We find that this degeneracy is responsible for the removal of the theta(13) predictability and that the possible bound on vertical bar epsilon(e tau)vertical bar is competitive with direct bounds only if a more stringent external bound on theta(13) is applied.

  • 159.
    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 Effect2005Ingår i: NEUTRINO 2004 / [ed] Jacques Dumarchez, Thomas Patzak, François Vannucci, Elsevier Science B.V. , 2005, s. 578-578Konferensbidrag (Refereegranskat)
    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.

  • 160.
    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 experiments2005Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2005, nr 06, s. 049-Artikel i tidskrift (Refereegranskat)
    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.

  • 161.
    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 oscillations2007Ingår i: The European Physical Journal C, ISSN 1434-6044, Vol. 49, nr 4, s. 1023-1039Artikel i tidskrift (Refereegranskat)
    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.

  • 162.
    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 II2013Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2013, nr 9, s. 089-Artikel i tidskrift (Refereegranskat)
    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.

  • 163.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Schwetz, Thomas
    Identifying the Neutrino mass Ordering with INO and NOvA2012Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 1208Artikel i tidskrift (Refereegranskat)
  • 164.
    Blennow, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Smirnov, Alexei Yu.
    Neutrino Propagation in Matter2013Ingår i: Advances in High Energy Physics, ISSN 1687-7357, E-ISSN 1687-7365, Vol. 2013, s. 972485-Artikel, forskningsöversikt (Refereegranskat)
    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.

  • 165.
    Blomberg, Clas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Fluctuations for good and bad: The role of noise in living systems2006Ingår i: Physics of Life Reviews, ISSN 1571-0645, Vol. 3, nr 3, s. 133-161Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The intention is to provide a broad overview of the role of noise and basic methods to describe noise effects in biological systems. It starts from a brief discussion of the statistical mechanical basis, and Brownian motion which is generalised to calculations of randomly induced transitions over energy barriers, and stochastic resonance. The description of discrete step processes provides another approach, which also is a basis of a stochastic description of chemical reactions. Macromolecular structure changes are considered as triggered by the background fluctuations. A strong emphasis is put on "fluctuation-dissipation" relations, relations between the irregular fluctuations and the dissipative spreading of energy towards a most probable distribution. We also take up some applications to non-linear systems, noise effects together with oscillations and signal transmission as well as models on unidirectional motion of various kinds with Brownian ratchets and active transport as examples.

  • 166.
    Blomberg, Clas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Physics of Life: the physicist's road to biology2007Bok (Refereegranskat)
    Abstract [en]

    The purpose of the book is to give a survey of the physics that is relevant for biological applications, and also to discuss what kind of biology needs physics. The book gives a broad account of basic physics, relevant for the applications and various applications from properties of proteins to processes in the cell to wider themes such as the brain, the origin of life and evolution. It also considers general questions of common interest such as reductionism, determinism and randomness, where the physics view often is misunderstood. The subtle balance between order and disorder is a repeated theme appearing in many contexts. There are descriptive parts which shall be sufficient for the comprehension of general ideas, and more detailed, formalistic parts for those who want to go deeper, and see the ideas expressed in terms of mathematical formulas. - Describes how physics is needed for understanding basic principles of biology - Discusses the delicate balance between order and disorder in living systems - Explores how physics play a role high biological functions, such as learning and thinking.

  • 167.
    Blomquist, Emil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Boman, Trotte
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    The Dirac Equation for a Particle in a Spherical Box Potential with Application in Bag Modeling2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Dirac-ekvationen är en relativistisk vågekvation och var den första ekvationen att inkludera spinn i relativistisk kvantmekanik. I vår rapport kommer Dirac-ekvationen att härledas och lösas för en partikel i en sfärisk lådpotential. Den kommer sedan att jämföras med den icke-relativistiska Schrödinger-ekvationen samt en relativistiskt korrigerad Schrödinger-ekvation. Några av Dirac-ekvationens användningsområden, såsom för Bogoliubovs modell, kommer att undersökas och diskuteras och det faktum att Diracekvationen kan ge oss information om hur elementära partiklar fungerar valideras.

  • 168. Bojesen, Troels Arnfred
    et al.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Sudbø, Asle
    Phase transitions and anomalous normal state in superconductors with broken time-reversal symmetry2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 10, s. 104509-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using Monte Carlo simulations, we explore the phase diagram and the phase transitions in U(1) x Z(2) n-band superconductors with spontaneously broken time-reversal symmetry (also termed s + is superconductors), focusing on the three-band case. In the limit of infinite penetration length, the system under consideration can, for a certain parameter regime, have a single first-order phase transition from a U(1) x Z(2) broken state to a normal state due to a nontrivial interplay between U(1) vortices and Z(2) domain walls. This regime may also apply to multicomponent superfluids. For other parameters, when the free energy of the domain walls is low, the system undergoes a restoration of broken Z(2) time-reversal symmetry at temperatures lower than the temperature of the superconducting phase transition. We show that inclusion of fluctuations can strongly suppress the temperature of the Z(2) transition when frustration is weak. The main result of our paper is that for relatively short magnetic field penetration lengths, the system has a superconducting phase transition at a temperature lower than the temperature of the restoration of the broken Z(2) symmetry. Thus, there appears a new phase that is U(1) symmetric, but breaks Z(2) time-reversal symmetry, an anomalous dissipative (metallic) state.

  • 169. Bojesen, Troels Arnfred
    et al.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Sudbø, Asle
    Time reversal symmetry breakdown in normal and superconducting states in frustrated three-band systems2013Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, nr 22, s. 220511-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We discuss the phase diagram and phase transitions in U(1) x Z(2) three-band superconductors with broken time reversal symmetry. We find that beyond mean-field approximation and for sufficiently strong frustration of interband interactions there appears an unusual metallic state precursory to a superconducting phase transition. In that state, the system is not superconducting. Nonetheless, it features a spontaneously broken Z(2) time reversal symmetry. By contrast, for weak frustration of interband coupling the energy of a domain wall between different Z(2) states is low and thus fluctuations restore broken time reversal symmetry in the superconducting state at low temperatures.

  • 170.
    Bonnevier, Johan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Phenomenology of Dark Matter fromNon-Minimal Universal Extra Dimensions2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    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.

  • 171.
    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 annihilations2012Ingår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 85, nr 4, s. 043524-Artikel i tidskrift (Refereegranskat)
    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.

  • 172. Borah, Debasish
    et al.
    Ghosh, Monojit
    Gupta, Shivani
    Prakash, Suprabh
    Raut, Sushant K.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Analysis of four-zero textures in the 3+1 neutrino framework2016Ingår i: Physical Review D, ISSN 2470-0010, Vol. 94, nr 11, artikel-id 113001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The presence of a zero texture in the neutrino mass matrix can indicate the presence of an underlying symmetry which can generate neutrino mass and mixing. In this paper, for the first time, we study the four-zero textures of the low energy neutrino mass matrix in the presence of an extra light-sterile neutrino, i.e., the 3 + 1 neutrino scheme. In our analysis, we find that out of the 210 possible four-zero textures only 15 textures are allowed. We divide the allowed four-zero textures into two classes-A in which the value of mass matrix element M-ee is zero and class B in which M-ee is nonzero. In this way, we obtain ten possible four-zero textures in class A and five possible four-zero textures in class B. In our analysis, we find that for normal hierarchy the allowed number of textures in class A (B) is nine (three). For the case of inverted hierarchy, we find that two textures in class A are disallowed, and these textures are different from the disallowed textures for normal hierarchy in class A. However, we find that all the five textures in class B are allowed for the inverted hierarchy. Based on analytic expressions for the elements M-alpha beta, we discuss the reasons for certain textures being disallowed. We also discuss the correlations between the different parameters of the allowed textures. Finally, we present the implications of our study on experimental searches for neutrinoless double beta decay.

  • 173.
    Bouchand, Romain
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Radiative Neutrino Mass Generation and Renormalization Group Running in the Ma-Model2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 174.
    Bouchand, Romain
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Running of radiative neutrino masses: the scotogenic model2012Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 7, s. 084-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the renormalization group equations of Ma's scotogenic model, which generates an active neutrino mass at 1-loop level. In addition to other benefits, the main advantage of the mechanism exploited in this model is to lead to a natural loop-suppression of the neutrino mass, and therefore to an explanation for its smallness. However, since the structure of the neutrino mass matrix is altered compared to the ordinary type I seesaw case, the corresponding running is altered as well. We have derived the full set of renormalization group equations for the scotogenic model which, to our knowledge, had not been presented previously in the literature. This set of equations reflects some interesting structural properties of the model, and it is an illustrative example for how the running of neutrino parameters in radiative models is modified compared to models with tree-level mass generation. We also study a simplified numerical example to illustrate some general tendencies of the running. Interestingly, the structure of the RGEs can be exploited such that a bimaximal leptonic mixing pattern at the high-energy scale is translated into a valid mixing pattern at low energies, featuring a large value of theta(13). This suggests very interesting connections to flavour symmetries.

  • 175.
    Brandt, Erik G.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Interactions and dynamics in biophysical model systems2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Computer simulations of simplified model systems provide understanding of how complex biological systems behave. The simulations give detailed information about the systems, with atomistic resolution, that can be used in combination with experimental knowledge to shed light on underlying physical principles. The thesis presents background information about the studies of two important model systems in biological physics.

    First, metal ion-binding to proteins is investigated in a computational study on a zinc-binding synthetic peptide, to elucidate the binding details. The major scientific contributions from the study are the identification and mapping of the detailed contributions to the binding. A novel correction scheme is worked out, where classic free energy calculations are combined with density functional theory to adjust for quantum mechanical effects.  The sensitivity of the zinc-binding to a specific amino acid segment can be explained in terms of the zinc coordination.

    Second, equilibrium density fluctuations in biological membranes are studied using computer simulations of the lipid bilayer. The fluctuations are linked to several processes; pore formation, membrane permeability and transport of small molecules across themembrane. Because the lipid bilayer behaves similar to a 2D fluid the density fluctuations can be described in the framework of generalized hydrodynamics. The major scientific contributions from the study are the direct calculation of the density-density autocorrelation function from raw data and the observation that the diffusive contribution to the power spectrum (the Rayleigh line) is not single-exponential. In addition, the accuracy of the approximate hydrodynamic solutions is questionable for the propagation of sound waves in the membrane.

  • 176.
    Brandt, Erik G.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Molecular Dynamics Simulations of Fluid Lipid Membranes2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Lipid molecules form thin biological membranes that envelop all living cells, and behave as two-dimensional liquid sheets immersed in bulk water. The interactions of such biomembranes with their environment lay the foundation of a plethora of biological processes rooted in the mesoscopic domain - length scales of 1-1000 nm and time scales of 1-1000 ns. Research in this intermediate regime has for a long time been out of reach for conventional experiments, but breakthroughs in computer simulation methods and scattering experimental techniques have made it possible to directly probe static and dynamic properties of biomembranes on these scales.

    Biomembranes are soft, with a relatively low energy cost of bending, and are thereby influenced by random, thermal fluctuations of individual molecules. Molecular dynamics simulations show how in-plane (density fluctuations) and out-of-plane (undulations) motions are intertwined in the bilayer in the mesoscopic domain. By novel methods, the fluctuation spectra of lipid bilayers can be calculated withdirect Fourier analysis. The interpretation of the fluctuation spectra reveals a picture where density fluctuations and undulations are most pronounced on different length scales, but coalesce in the mesoscopic regime. This analysis has significant consequences for comparison of simulation data to experiments. These new methods merge the molecular fluctuations on small wavelengths, with continuum fluctuations of the elastic membrane sheet on large wavelengths, allowing electron density profiles (EDP) and area per lipid to be extracted from simulations with high accuracy.

    Molecular dynamics simulations also provide insight on the small-wavelength dynamics of lipid membranes. Rapidly decaying density fluctuations can be described as propagating sound waves in the framework of linearized hydrodynamics, but there is a slow, dispersive, contribution that needs to be described by a stretched exponential over a broad range of length- and time scales - recent experiments suggest that this behavior can prevail even on micrometer length scales. The origin of this behavior is discussed in the context of fluctuations of the bilayer interface and the molecular structure of the bilayer itself. Connections to recent neutron scattering experiments are highlighted.

  • 177.
    Brandt, Erik G.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Braun, Anthony R.
    Sachs, Jonathan N.
    Nagle, John F.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Interpretation of Fluctuation Spectra in Lipid Bilayer Simulations2011Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 100, nr 9, s. 2104-2111Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Atomic resolution and coarse-grained simulations of dimyristoylphosphatidylcholine lipid bilayers were analyzed for fluctuations perpendicular to the bilayer using a completely Fourier-based method. We find that the fluctuation spectrum of motions perpendicular to the bilayer can be decomposed into just two parts: 1), a pure undulation spectrum proportional to q(-4) that dominates in the small-q regime; and 2), a molecular density structure factor contribution that dominates in the large-q regime. There is no need for a term proportional to q(-2) that has been postulated for protrusion fluctuations and that appeared to have been necessary to fit the spectrum for intermediate q. We suggest that earlier reports of such a term were due to the artifact of binning and smoothing in real space before obtaining the Fourier spectrum. The observability of an intermediate protrusion regime from the fluctuation spectrum is discussed based on measured and calculated material constants.

  • 178.
    Brandt, Erik G.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Dynamic structure factors from lipid membrane molecular dynamics simulations2009Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 96, nr 5, s. 1828-1838Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic structure factors for a lipid bilayer have been calculated from molecular dynamics simulations. From trajectories of a system containing 1024 lipids we obtain wave vectors down to 0.34 nm(-1), which enables us to directly resolve the Rayleigh and Brillouin lines of the spectrum. The results confirm the validity of a model based on generalized hydrodynamics, but also improves the line widths and the position of the Brillouin lines. The improved resolution shows that the Rayleigh line is narrower than in earlier studies, which corresponds to a smaller thermal diffusivity. From a detailed analysis of the power spectrum, we can, in fact, distinguish two dispersive contributions to the elastic scattering. These translate to two exponential relaxation processes in separate time domains. Further, by including a first correction to the wave-vector-dependent position of the Brillouin lines, the results agree favorably to generalized hydrodynamics even up to intermediate wave vectors, and also yields a 20% higher adiabatic sound velocity. The width of the Brillouin lines shows a linear, not quadratic, dependence to low wave vectors.

  • 179.
    Brandt, Erik G.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Molecular Dynamics Simulations of In-Plane Density Fluctuations in Phospholipid Bilayers2010Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 98, nr 3, s. 664A-664AArtikel i tidskrift (Övrigt vetenskapligt)
  • 180.
    Brandt, Erik G.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Stretched exponential dynamics in lipid bilayer simulations2010Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, nr 11, s. 115101-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The decay of fluctuations in fluid biomembranes is strongly stretched and nonexponential on nanometer lengthscales. We report on calculations of structural correlation functions for lipid bilayer membranes from atomistic and coarse-grained molecular dynamics simulations. The time scales extend up to microseconds, whereas the linear size of the largest systems is around 50 nm. Thus, we can cover the equilibrium dynamics of wave vectors over two orders of magnitude (0.2-20 nm(-1)). The time correlations observed in the simulations are best described by stretched exponential functions, with exponents of 0.45 for the atomistic and 0.60 for the coarse-grained model. Area number density fluctuations, thickness fluctuations, and undulations behave dynamically in a similar way and have almost exactly the same dynamics for wavelengths below 3 nm, indicating that in this regime undulations and thickness fluctuations are governed by in-plane density fluctuations. The out-of-plane height fluctuations are apparent only at the longest wavelengths accessible in the simulations (above 6 nm). The effective correlation times of the stretched exponentials vary strongly with the wave vector. The variation fits inverse power-laws that change with wavelength. The exponent is 3 for wavelengths smaller than about 1.25 nm and switches to 1 above this. There are indications for a switch to still another exponent, 2, for wavelengths above 20 nm. Compared to neutron spin-echo (NSE) experiments, the simulation data indicate a faster relaxation in the hydrodynamic limit, although an extrapolation of NSE data, as well as inelastic neutron scattering data, is in agreement with our data at larger wave vectors.

  • 181.
    Brandt, Erik G.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Hellgren, Mikko
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Bergman, Tomas
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Molecular dynamics study of zinc binding to cysteines in a peptide mimic of the alcohol dehydrogenase structural zinc site2009Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, nr 6, s. 975-983Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The binding of zinc (Zn) ions to proteins is important for many cellular events. The theoretical and computational description of this binding (as well as that of other transition metals) is a challenging task. In this paper the binding of the Zn ion to four cysteine residues in the structural site of horse liver alcohol dehydrogenase (HLADH) is studied using a synthetic peptide mimic of this site. The study includes experimental measurements of binding constants, classical free energy calculations from molecular dynamics (MD) simulations and quantum mechanical (QM) electron structure calculations. The classical MD results account for interactions at the molecular level and reproduce the absolute binding energy and the hydration free energy of the Zn ion with an accuracy of about 10%. This is insufficient to obtain correct free energy differences. QM correction terms were calculated from density functional theory (DFT) on small clusters of atoms to include electronic polarisation of the closest waters and covalent contributions to the Zn-S coordination bond. This results in reasonably good agreement with the experimentally measured binding constants and Zn ion hydration free energies in agreement with published experimental values. The study also includes the replacement of one cysteine residue to an alanine. Simulations as well as experiments showed only a small effect of this upon the binding free energy. A detailed analysis indicate that the sulfur is replaced by three water molecules, thereby changing the coordination number of Zn from four (as in the original peptide) to six (as in water).

  • 182. Braun, A R
    et al.
    Brandt, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Edholm, Olof
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Nagle, J F
    Sachs, J N
    Determination of electron density pro les and area-per-lipid from molecular dynamics simulations of large undulating lipid bilayers2011Ingår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 241Artikel i tidskrift (Övrigt vetenskapligt)
  • 183. Braun, Anthony R.
    et al.
    Brandt, Erik G.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Nagle, John F.
    Sachs, Jonathan N.
    Determination of Electron Density Profiles and Area from Simulations of Undulating Membranes2011Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 100, nr 9, s. 2112-2120Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The traditional method for extracting electron density and other transmembrane profiles from molecular dynamics simulations of lipid bilayers fails for large bilayer systems, because it assumes a flat reference surface that does not take into account long wavelength undulations. We have developed what we believe to be a novel set of methods to characterize these undulations and extract the underlying profiles in the large systems. Our approach first obtains an undulation reference surface for each frame in the simulation and subsequently isolates the long-wavelength undulations by filtering out the intrinsic short wavelength modes. We then describe two methods to obtain the appropriate profiles from the undulating reference surface. Most combinations of methods give similar results for the electron density profiles of our simulations of 1024 DMPC lipids. From simulations of smaller systems, we also characterize the finite size effect related to the boundary conditions of the simulation box. In addition, we have developed a set of methods that use the undulation reference surface to determine the true area per lipid which, due to undulations, is larger than the projected area commonly reported from simulations.

  • 184. Bryk, T.
    et al.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Collective excitations in molten iron above the melting point: A generalized collective-mode analysis of simulations with embedded-atom potentials2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 2, s. 024202-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown, that the embedded-atom potential nicely describing structural properties of high pressure Fe can be successfully used for description of collective dynamics of liquid iron. A combination of molecular dynamics simulations and a fit-free analysis based on the approach of generalized collective modes (GCM) is used for calculations of spectra of collective excitations and relaxing modes at 1843 K. The obtained spectrum of acoustic excitations in the long-wavelength region perfectly agrees with the experimental speed of sound and reproduces the dispersion estimated from inelastic X-ray scattering (IXS) experiments. Heat fluctuations in liquid Fe were studied and resulted in calculated ratio of specific heats γ-1.40 being in agreement with the IXS-experiment estimate. We report analysis of the wave-number dependence of relaxation processes and their contributions to dynamic structure factors. This permits estimation of most important relaxation processes contributing to the shape of dynamic structure factors of liquid Fe in different regions of wave numbers.

  • 185.
    Brömstrup, Torben
    et al.
    KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Howard, Rebecca J.
    Trudell, James R.
    Harris, R. Adron
    Lindahl, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik. KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Inhibition versus Potentiation of Ligand-Gated Ion Channels Can Be Altered by a Single Mutation that Moves Ligands between Intra- and Intersubunit Sites2013Ingår i: Structure, ISSN 0969-2126, E-ISSN 1878-4186, Vol. 21, nr 8, s. 1307-1316Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pentameric ligand-gated ion channels (pLGICs) are similar in structure but either inhibited or potentiated by alcohols and anesthetics. This dual modulation has previously not been understood, but the determination of X-ray structures of prokaryotic GLIC provides an ideal model system. Here, we show that a single-site mutation at the F14' site in the GLIC transmembrane domain turns desflurane and chloroform from inhibitors to potentiators, and that this is explained by competing allosteric sites. The F14'A mutation opens an intersubunit site lined by N239 (15'), 1240 (16'), and Y263. Free energy calculations confirm this site is the preferred binding location for desflurane and chloroform in GLIC F14'A. In contrast, both anesthetics prefer an intrasubunit site in wild-type GLIC. Modulation is therefore the net effect of competitive binding between the intersubunit potentiating site and an intrasubunit inhibitory site. This provides direct evidence for a dual-site model of allosteric regulation of pLGICs.

  • 186.
    Brömstrup, Torben
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    Murail, Samuel
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik. Inst Pasteur, Grp Recepteurs Canaux, France.
    Lindahl, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    Single-site mutation changes the location of the most favored Desflurane binding site in the GLIC ligand-gated ion channel2012Ingår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 243Artikel i tidskrift (Övrigt vetenskapligt)
  • 187. Burakovsky, L.
    et al.
    Chen, S. P.
    Preston, D. L.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Mikhaylushkin, A. S.
    Simak, S. I.
    Moriarty, J. A.
    High-Pressure-High-Temperature Polymorphism in Ta: Resolving an Ongoing Experimental Controversy2010Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, nr 25, s. 255702-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phase diagrams of refractory metals remain essentially unknown. Moreover, there is an ongoing controversy over the high-pressure melting temperatures of these metals: results of diamond anvil cell (DAC) and shock wave experiments differ by at least a factor of 2. From an extensive ab initio study on tantalum we discovered that the body-centered cubic phase, its physical phase at ambient conditions, transforms to another solid phase, possibly hexagonal omega phase, at high temperature. Hence the sample motion observed in DAC experiments is very likely not due to melting but internal stresses accompanying a solid-solid transformation, and thermal stresses associated with laser heating.

  • 188.
    Bäcklund, Anna
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Bengtsson, Ingemar
    Four remarks on spin coherent states2014Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T163Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We discuss how to recognize the constellations seen in the Majorana representation of quantum states. Then we give explicit formulae for the metric and symplectic form on SU (2) orbits containing general number states. Their metric and symplectic areas differ unless the states are coherent. Finally we discuss some patterns that arise from the Lieb-Solovej map, and for dimensions up to nine we find the location of those states that maximize the Wehrl-Lieb entropy.

  • 189.
    Bühlmann, Michael
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Gravitational Law in Extra Dimensions2013Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Some recent theories which try to amend shortcomings of current models in physics suggest

    the existence of additional dimensions. Such extra dimensions would modify the inverse

    square law of gravity.

    A short overview over gravitational theory is presented and some of the extensions to

    general relativity and models which use extra dimensions, so-called Kaluza–Klein theories

    are discussed. A derivation of the correction to Newton’s gravitational law due to extra

    dimensions is performed and yields an additional term of Yukawa-type. We determine its

    interaction range and strength and derive the gravitational constant in the extra dimensional

    space. Experiments which probe Newton’s inverse square law are presented and recent

    results and constraints on corrections of Yukawa-type are discussed.

    This report is part of my bachelor degree project in theoretical physics at KTH.

  • 190. Calogero, F.
    et al.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Goldfishing by gauge theory2006Ingår i: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 47, nr 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new solvable many-body problem of goldfish type is identified and used to revisit the connection between two different approaches to solvable dynamical systems. An isochronous variant of this model is identified and investigated. Alternative versions of these models are presented. The behavior of the alternative isochronous model near its equilibrium configurations is investigated, and a remarkable Diophantine result, as well as related Diophantine conjectures, are thereby obtained.

  • 191.
    Camitz, Martin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Liljeros, Fredrik
    The effect of travel restrictions on the spread of a moderately contagious disease2006Ingår i: BMC Medicine, ISSN 1741-7015, E-ISSN 1741-7015, Vol. 4, s. 32-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Much research in epidemiology has been focused on evaluating conventional methods of control strategies in the event of an epidemic or pandemic. Travel restrictions are often suggested as an efficient way to reduce the spread of a contagious disease that threatens public health, but few papers have studied in depth the effects of travel restrictions. In this study, we investigated what effect different levels of travel restrictions might have on the speed and geographical spread of an outbreak of a disease similar to severe acute respiratory syndrome (SARS). Methods: We used a stochastic simulation model incorporating survey data of travel patterns between municipalities in Sweden collected over 3 years. We tested scenarios of travel restrictions in which travel over distances > 50 km and 20 km would be banned, taking into account different levels of compliance. Results: We found that a ban on journeys > 50 km would drastically reduce the speed and geographical spread of outbreaks, even when compliance is < 100%. The result was found to be robust for different rates of intermunicipality transmission intensities. Conclusion: This study supports travel restrictions as an effective way to mitigate the effect of a future disease outbreak.

  • 192. Campbell, I. A.
    et al.
    Lundow, Per Håkan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Extended scaling analysis of the S=1/2 Ising ferromagnet on the simple cubic lattice2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 1, s. 014411-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is often assumed that for treating numerical (or experimental) data on continuous transitions the formal analysis derived from the renormalization-group theory can only be applied over a narrow temperature range, the "critical region"; outside this region correction terms proliferate rendering attempts to apply the formalism hopeless. This pessimistic conclusion follows largely from a choice of scaling variables and scaling expressions, which is traditional but very inefficient for data covering wide temperature ranges. An alternative "extended scaling" approach can be made where the choice of scaling variables and scaling expressions is rationalized in the light of well established high-temperature series expansion developments. We present the extended scaling approach in detail, and outline the numerical technique used to study the three-dimensional (3D) Ising model. After a discussion of the exact expressions for the historic 1D Ising spin chain model as an illustration, an exhaustive analysis of high quality numerical data on the canonical simple cubic lattice 3D Ising model is given. It is shown that in both models, with appropriate scaling variables and scaling expressions (in which leading correction terms are taken into account where necessary), critical behavior extends from T-c up to infinite temperature.

  • 193.
    Cao, Bo
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Supernova Bound on keV Sterile Neutrinos2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 194. Carey, Alan L.
    et al.
    Mickelsson, Jouko
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Wang, Bai-Ling
    Differential twisted K-theory and applications2009Ingår i: Journal of Geometry and Physics, ISSN 0393-0440, E-ISSN 1879-1662, Vol. 59, nr 5, s. 632-653Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we develop differential twisted K-theory and define a twisted Chern character on twisted K-theory which depends on a choice of connection and curving on the twisting gerbe. We also establish the general Riemann-Roch theorem in twisted K-theory and find some applications in the study of twisted K-theory of compact simple Lie groups.

  • 195. Carlstrom, Johan
    et al.
    Prokofiev, Nikolay
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik. University of Massachusetts, United States; Kurchatov Institute, Russian Federation.
    Svistunov, Boris
    Quantum Walk in Degenerate Spin Environments2016Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 116, nr 24, artikel-id 247202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the propagation of a hole in degenerate (paramagnetic) spin environments. This canonical problem has important connections to a number of physical systems, and is perfectly suited for experimental realization with ultracold atoms in an optical lattice. At the short-to-intermediate time scale that we can access using a stochastic-series-type numeric scheme, the propagation turns out to be distinctly nondiffusive with the probability distribution featuring minima in both space and time due to quantum interference, yet the motion is not ballistic, except at the beginning. We discuss possible scenarios for long-term evolution that could be explored with an unprecedented degree of detail in experiments with single-atom resolved imaging.

  • 196.
    Carlström, Johan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Multicomponent superconductivity: Vortex matter and phase transitions2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The topic of this thesis is vortex-physics in multi component Ginzburg- Landau models. These models describe a newly discovered class of super- conductors with multiple superconducting gaps, and possess many properties that set them apart from single component models. The work presented here relies on large scale computer simulations using various numerical techniques, but also on some analytical methods.

    In Paper I, Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors, we show that in multiband supercon- ductors, even an extremely small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vor- tices, by producing long-range intervortex attraction. This type of vortex interaction results in an unusual response to low magnetic fields, leading to phase separation into domains of two-component Meissner states and vortex droplets.

    In paper II, Type-1.5 superconductivity in two-band systems, we discuss the influence of Josephson coupling and show that non-monotonic intervortex interaction can also arise in two-band superconductors where one of the bands is proximity induced by Josephson interband coupling.

    In paper III, Type-1.5 superconductivity in multiband systems: Effects of interband couplings, we investigate the appearance of Type-1.5 superconduc- tivity in the case with two active bands and substantial inter-band couplings such as intrinsic Josephson coupling, mixed gradient coupling, and density- density interactions. We show that in the presence of these interactions, the system supports type-1.5 superconductivity with fundamental length scales being associated with the mass of the gauge field and two masses of normal modes represented by linear combinations of the density fields.

    In paper IV, Semi-Meissner state and nonpairwise intervortex interactions in type-1.5 superconductors, we demonstrate the existence of nonpairwise in- tervortex forces in multicomponent and layered superconducting systems. We also consider the properties of vortex clusters in a semi-Meissner state of type- 1.5 two-component superconductors. We show that under certain conditions nonpairwise forces can contribute to the formation of complex vortex states in type-1.5 regimes.

    In paper V, Length scales, collective modes, and type-1.5 regimes in three- band superconductors, we consider systems where frustration in phase dif- ferences occur due to competing Josephson inter-band coupling terms. We show that gradients of densities and phase differences can be inextricably intertwined in vortex excitations in three-band models. This can lead to long-range attractive intervortex interactions and the appearance of type-1.5 regimes even when the intercomponent Josephson coupling is large. We also show that field-induced vortices can lead to a change of broken symmetry from U (1) to U (1) ⇥ Z2 in the system. In the type-1.5 regime, it results in a semi-Meissner state where the system has a macroscopic phase separation in domainswithbrokenU(1)andU(1)⇥Z2 symmetries.

    In paper VI, Topological Solitons in Three-Band Superconductors with Broken Time Reversal Symmetry, we show that three-band superconductors with broken time reversal symmetry allow magnetic flux-carrying stable topo- logical solitons. They can be induced by fluctuations or quenching the system through a phase transition. It can provide an experimental signature of the time reversal symmetry breakdown.

    In paper VII, Type-1.5 superconductivity in multiband systems: Magnetic response, broken symmetries and microscopic theory – A brief overview, we give an overview of vortex physics and magnetic response in multi component Ginzburg-Landau theory. We also examine Type-1.5 superconductivity in the context of microscopic theory.

    In paper VIII, Chiral CP2 skyrmions in three-band superconductors, we show that under certain conditions, three-component superconductors (and, in particular, three-band systems) allow stable topological defects different from vortices. We demonstrate the existence of these excitations, charac- terised by a CP2 topological invariant, in models for three-component super- conductors with broken time-reversal symmetry. We term these topological defects “chiral GL(3) skyrmions,” where “chiral” refers to the fact that due to broken time-reversal symmetry, these defects come in inequivalent left- and right-handed versions. In certain cases, these objects are energetically cheaper than vortices and should be induced by an applied magnetic field. In other situations, these skyrmions are metastable states, which can be produced by a quench. Observation of these defects can signal broken time-reversal sym- metry in three-band superconductors or in Josephson-coupled bilayers of s± and s-wave superconductors.

    In paper IX, Phase transition in multi-component superconductors, we ex- amine the thermodynamics of frustrated multi-components superconductors and show that their highly complex energy landscape can give rise new types of phase transitions not present in single component superconductors. 

  • 197.
    Carlström, Johan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Vortex-matter in Multi-component Superconductors2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The topic of this thesis is vortex-physics in multi component Ginzburg- Landau models. These models describe a newly discovered class of supercon- ductors with multiple superconducting gaps, and posses many properties that set them apart from single component models. The work presented here relies on large scale computer simulations using various numerical techniques, but also some analytical methods.

    In Paper I, Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors, we show that in multiband supercon- ductors, even an extremely small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vor- tices by producing long-range intervortex attraction. This type of vortex interaction results in an unusual response to low magnetic fields, leading to phase separation into domains of two-component Meissner states and vortex droplets.

    In paper II, Type-1.5 superconductivity in multiband systems: Effects of interband couplings, we investigate the appearance of Type-1.5 superconduc- tivity in the case with two active bands and substantial inter-band couplings. such as intrinsic Josephson coupling, mixed gradient coupling, and density- density interactions. We show that in the presence of these interactions, the system supports type-1.5 superconductivity with fundamental length scales being associated with the mass of the gauge field and two masses of normal modes represented by mixed combinations of the density fields.

    In paper III, Semi-Meissner state and nonpairwise intervortex interactions in type-1.5 superconductors, we demonstrate the existence of nonpairwise in- teraction forces between vortices in multicomponent and layered supercon- ducting systems. Next, we consider the properties of vortex clusters in a semi-Meissner state of type-1.5 two-component superconductors. We show that under certain conditions nonpairwise forces can contribute to the forma- tion of very complex vortex states in type-1.5 regimes.

    In paper IV, Length scales, collective modes, and type-1.5 regimes in three- band superconductors, we consider systems where frustration in phase differ- ences occur due to competing Josephson inter-band coupling terms. We show that gradients of densities and phase differences can be inextricably inter- twined in vortex excitations in three-band models. This can lead to very long-range attractive intervortex interactions and the appearance of type-1.5 regimes even when the intercomponent Josephson coupling is large. We also show that field-induced vortices can lead to a change of broken symmetry from U (1) to U (1) × Z2 in the system. In the type-1.5 regime, it results in a semi-Meissner state where the system has a macroscopic phase separation in domainswithbrokenU(1)andU(1)×Z2 symmetries.

    In paper V, Topological Solitons in Three-Band Superconductors with Bro- ken Time Reversal Symmetry, we show that three-band superconductors with broken time reversal symmetry allow magnetic flux- carrying stable topolog- ical solitons. They can be induced by fluctuations or quenching the system through a phase transition. It can provide an experimental signature of the time reversal symmetry breakdown. 

  • 198.
    Carlström, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik. University of Massachusetts, United States.
    Entropy- and Flow-Induced Superfluid States2014Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 113, nr 5, s. 055301-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Normally the role of phase fluctuations in superfluids and superconductors is to drive a phase transition to the normal state. This happens due to proliferation of topologically nontrivial phase fluctuations in the form of vortices. Here we discuss a class of systems where, by contrast, nontopological phase fluctuations can produce superfluidity. Here we understand superfluidity as a phenomenon that does not necessarily arises from a broken U(1) symmetry, but can be associated with a certain class of (approximate or exact) degeneracies of the system's energy landscape giving raise to a U(1)-like phase.

  • 199.
    Carlström, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Spontaneous breakdown of time-reversal symmetry induced by thermal fluctuations2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 14, artikel-id 140504Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In systems with broken U(1) symmetry, such as superfluids, superconductors, or magnets, the symmetry restoration is driven by the proliferation of topological defects in the form of vortex loops (unless the phase transition is strongly first order). Here we discuss that the proliferation of topological defects can, by contrast, lead to the breakdown of an additional symmetry. We demonstrate that this effect should take place in s + is superconductors, which are widely discussed in connection with iron-based materials (although the mechanism is much more general). In these systems a vortex excitation can create a "bubble" of fluctuating Z(2) order parameter. The thermal excitation of vortices then leads to the breakdown of Z(2) time-reversal symmetry when the temperature is increased.

  • 200.
    Carlström, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Speight, Martin
    Type-1.5 superconductivity in multiband systems: Effects of interband couplings2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 17, s. 174509-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In contrast to single-component superconductors, which are described at the level of Ginzburg-Landau theory by a single parameter kappa and are divided in type-I kappa < 1/root 2 and type-II kappa > 1/root 2 classes, two-component systems in general possess three fundamental length scales and have been shown to possess a separate "type-1.5" superconducting state. In that state, as a consequence of the extra fundamental length scale, vortices attract one another at long range but repel at shorter ranges, and therefore should form clusters in low magnetic fields. In this work we investigate the appearance of type-1.5 superconductivity and the interpretation of the fundamental length scales in the case of two active bands with substantial interband couplings such as intrinsic Josephson coupling, mixed gradient coupling, and density-density interactions. We show that in the presence of substantial intercomponent interactions of the above types the system supports type-1.5 superconductivity with fundamental length scales being associated with the mass of the gauge field and two masses of normal modes represented by mixed combinations of the density fields.

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