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  • 301. Girardi, Ivan
    et al.
    Meloni, Davide
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zhang, He
    Zhou, Shun
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Constraining sterile neutrinos using reactor neutrino experiments2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 8Article in journal (Refereed)
    Abstract [en]

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

  • 302. Goulko, Olga
    et al.
    Mishchenko, Andrey S.
    Prokofiev, Nikolay
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Svistunov, Boris
    Dark continuum in the spectral function of the resonant Fermi polaron2016In: PHYSICAL REVIEW A, ISSN 2469-9926, Vol. 94, no 5, article id 051605Article in journal (Refereed)
    Abstract [en]

    We present controlled numerical results for the ground-state spectral function of the resonant Fermi polaron in three dimensions. We establish the existence of a "dark continuum"-a region of anomalously low spectral weight between the narrow polaron peak and the rest of the spectral continuum. The dark continuum develops when the s-wave scattering length is of the order of the inverse Fermi wave vector, a less than or similar to 1/k(F), i.e., in the absence of a small interaction-related parameter when the spectral weight is not expected to feature a near-perfect gap structure after the polaron peak.

  • 303.
    Green-Petersen, Minna
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Diffusion-Limited Aggregation: a Model for Computer Simulation of Fractal Growth2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Diffusion-limited aggregation (DLA) is a model for computer simulation of particle aggregation.

    It is known to generate aggregates with a characteristic appearance with

    many branches spreading in all directions and a specic fractal dimension. The aggregates

    resemble many created by processes in nature such as crystallization,  uid  ow and

    growth of bacteria colonies. In this thesis the DLA model and a few variations of it are

    investigated to illuminate its  exibility. The variations investigated are a noise-reduced

    model, introducing surface tension and increasing the  ux of particles. The fractal dimension

    is calculated in each case and compared to the results of similar experiments,

    both simulated and real.

  • 304.
    Grimvall, Göran
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
    Accuracy of models2008In: SCIENTIFIC MODELING AND SIMULATIONS, ISSN 1874-8554, Vol. 15, no 1-3, p. 41-57Article in journal (Refereed)
    Abstract [en]

    The ability of a mathematical model to accurately describe a phenomenon depends on how well the model incorporates all relevant aspects, how robust the model is with respect to its mathematical form, and with respect to the numerical values of input parameters. Some models are primarily intended to reproduce known data. In other cases the purpose is to make a prediction outside the range of knowledge, or to establish details in a physical mechanism. These aspects of modelling are discussed, with examples mainly taken from the field of materials science.

  • 305.
    Grimvall, Göran
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Accuracy of models2009In: Scientific Modeling and Simulations, Springer Netherlands, 2009, p. 41-57Chapter in book (Refereed)
    Abstract [en]

    The ability of a mathematical model to accurately describe a phenomenon depends on how well the model incorporates all relevant aspects, how robust the model is with respect to its mathematical form, and with respect to the numerical values of input parameters. Some models are primarily intended to reproduce known data. In other cases the purpose is to make a prediction outside the range of knowledge, or to establish details in a physical mechanism. These aspects of modelling are discussed, with examples mainly taken from the field of materials science.

  • 306.
    Grimvall, Göran
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Characteristic quantities and dimensional analysis2009In: Scientific Modeling and Simulations, Springer Netherlands, 2009, p. 21-39Chapter in book (Refereed)
    Abstract [en]

    Phenomena in the physical sciences are described with quantities that have a numerical value and a dimension, i.e., a physical unit. Dimensional analysis is a powerful aspect of modeling and simulation. Characteristic quantities formed by a combination of model parameters can give new insights without detailed analytic or numerical calculations. Dimensional requirements lead to Buckingham's Π theorem - a general mathematical structure of all models in physics. These aspects are illustrated with many examples of modeling, e.g., an elastic beam on supports, wave propagation on a liquid surface, the Lennard-Jones potential for the interaction between atoms, the Lindemann melting rule, and saturation phenomena in electrical and thermal conduction.

  • 307.
    Grimvall, Göran
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
    Characteristic quantities and dimensional analysis2008In: SCIENTIFIC MODELING AND SIMULATIONS, ISSN 1874-8554, Vol. 15, no 1-3, p. 21-39Article in journal (Refereed)
    Abstract [en]

    Phenomena in the physical sciences are described with quantities that have a numerical value and a dimension, i.e., a physical unit. Dimensional analysis is a powerful aspect of modeling and simulation. Characteristic quantities formed by a combination of model parameters can give new insights without detailed analytic or numerical calculations. Dimensional requirements lead to Buckingham's Pi theorem-a general mathematical structure of all models in physics. These aspects are illustrated with many examples of modeling, e. g., an elastic beam on supports, wave propagation on a liquid surface, the Lennard-Jones potential for the interaction between atoms, the Lindemann melting rule, and saturation phenomena in electrical and thermal conduction.

  • 308.
    Grimvall, Göran
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
    Editorial: A Timely Contribution to a Half-Century-Old Topic2014In: Physical Review X, ISSN 2160-3308, E-ISSN 2160-3308, Vol. 4, no 1, p. 010001-Article in journal (Refereed)
  • 309.
    Grimvall, Göran
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
    Extrapolative procedures in modelling and simulations: the role of instabilities2008In: SCIENTIFIC MODELING AND SIMULATIONS, ISSN 1874-8554, Vol. 15, no 1-3, p. 5-20Article in journal (Refereed)
    Abstract [en]

    In modelling and simulations there is a risk that one extrapolates into a region where the model is not valid. In this context instabilities are of particular interest, since they can arise without any precursors. This paper discusses instabilities encountered in the field of materials science, with emphasis on effects related to the vibrations of atoms. Examples deal with, i.a., common lattice structures being either metastable or mechanically unstable, negative elastic constants that imply an instability, unexpected variations in the composition dependence of elastic constants in alloys, and mechanisms governing the ultimate strength of perfect crystals.

  • 310.
    Grimvall, Göran
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Extrapolative procedures in modelling and simulations: The role of instabilities2009In: Scientific Modeling and Simulations, Springer, 2009, p. 5-20Chapter in book (Refereed)
    Abstract [en]

    In modelling and simulations there is a risk that one extrapolates into a region where the model is not valid. In this context instabilities are of particular interest, since they can arise without any precursors. This paper discusses instabilities encountered in the field of materials science, with emphasis on effects related to the vibrations of atoms. Examples deal with, i.a., common lattice structures being either metastable or mechanically unstable, negative elastic constants that imply an instability, unexpected variations in the composition dependence of elastic constants in alloys, and mechanisms governing the ultimate strength of perfect crystals.

  • 311.
    Grimvall, Göran
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
    Variation of elastic shear constants in transition metal alloys2005In: Complex Inorganic Solids: Structural, Stability, and Magnetic Properties of Alloys / [ed] Turchi, PEA; Gonis, A; Rajan, K; Meike, A, 2005, p. 295-305Conference paper (Refereed)
  • 312.
    Grimvall, Göran
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
    Magyari-Köpe, Blanka
    Ozolins, Vidvuds
    Persson, Kristin A.
    Lattice instabilities in metallic elements2012In: Reviews of Modern Physics, ISSN 0034-6861, E-ISSN 1539-0756, Vol. 84, no 2, p. 945-986Article in journal (Refereed)
    Abstract [en]

    Most metallic elements have a crystal structure that is either body-centered cubic (bcc), face-centered close packed, or hexagonal close packed. If the bcc lattice is the thermodynamically most stable structure, the close-packed structures usually are dynamically unstable, i.e., have elastic constants violating the Born stability conditions or, more generally, have phonons with imaginary frequencies. Conversely, the bcc lattice tends to be dynamically unstable if the equilibrium structure is close packed. This striking regularity essentially went unnoticed until ab initio total-energy calculations in the 1990s became accurate enough to model dynamical properties of solids in hypothetical lattice structures. After a review of stability criteria, thermodynamic functions in the vicinity of an instability, Bain paths, and how instabilities may arise or disappear when pressure, temperature, and/or chemical composition is varied are discussed. The role of dynamical instabilities in the ideal strength of solids and in metallurgical phase diagrams is then considered, and comments are made on amorphization, melting, and low-dimensional systems. The review concludes with extensive references to theoretical work on the stability properties of metallic elements.

  • 313.
    Grip, Linnea
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Florin, Naemi
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Self-Organised Criticality in the Drossel-Schwabl Forest Fire Model2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    As self-organised criticality is a relatively new and undiscovered field of study, it is of great interest to further determine the behaviour of self-organised critical systems. In this report, the two-dimensional Drossel-Schwabl forest fire model is introduced and theoretically examined, in order to explain the properties of self-organised criticality. Thereafter, the results of simulations are presented, with critical exponents very close to the derived values of earlier studies. The presence of power laws in the model is discussed, as well as their implications of self-organised behaviour in both theoretical and real forest fires.

  • 314.
    Grishin, Alex M.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Multifunctional oxides on Si2005In: Proc. Electrochem. Soc., 2005, p. 482-497Conference paper (Refereed)
    Abstract [en]

    We review the projects ongoing at the Royal Institute of Technology on engineering and application of novel oxides on Si platform. Colossal magnetoresistance (CMR) in La 1-x(Sr,Ca,Pb) xMnO 3 films grown on Si has been tailored to room temperature to make a prototype of uncooled IR bolometer. Demonstrator of ferroelectric PZT/SiC field effect transistor operates at temperatures up to 300 °C. Ferroelectric niobate (Na,K)NbO 3 films have been sintered and found to be feasible for biomedical, microwave and electro-optical applications.

  • 315. Gronberg, Christina
    et al.
    Sitsel, Oleg
    Lindahl, Erik
    Gourdon, Pontus
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Membrane Anchoring and Ion-Entry Dynamics in P-type ATPase Copper Transport2016In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 111, no 11, p. 2417-2429Article in journal (Refereed)
    Abstract [en]

    Cu+-specific P-type ATPase membrane protein transporters regulate cellular copper levels. The lack of crystal structures in Cu+-binding states has limited our understanding of how ion entry and binding are achieved. Here, we characterize the molecular basis of Cu+ entry using molecular-dynamics simulations, structural modeling, and in vitro and in vivo functional assays. Protein structural rearrangements resulting in the exposure of positive charges to bulk solvent rather than to lipid phosphates indicate a direct molecular role of the putative docking platform in Cu+ delivery. Mutational analyses and simulations in the presence and absence of Cu+ predict that the ion-entry path involves two ion-binding sites: one transient Met148-Cys382 site and one intramembranous site formed by trigonal coordination to Cys384, Asn689, and Met717. The results reconcile earlier biochemical and x-ray absorption data and provide a molecular understanding of ion entry in Cu+-transporting P-type ATPases.

  • 316.
    Gustav, Lindgren
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Modellering av oljedegenerering2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis project was to create a model of engine oil deterioration, suitable for implementation in the engine control unit. To this end, the model has to be sufficiently simple not to unnecessarily waste limited computing power and yet exact enough not to over- or underestimate the oil change interval too much. Too frequent oil changes mean an unnecessary extra cost for new oil and loss of availability while too long oil change intervals may damage the engine, at an even greater cost. The model was divided into four sub-models, one for each of the processes that cause oil deterioration, i.e. dilution by fuel, chemical degradation, soot contamination and dilution by water. The models created were based on publicized scientific studies of the various processes. In order to validate the models they were implemented in Matlab and compared with experiment data. Various modification attempts were made and the resulting models were evaluated based on their correspondence with measurements.

    Dilution by fuel, dilution by water and soot contamination are all processes whose causes and dynamics are relatively well known. Oil degradation on the other hand is a complex process that depends on a large number of factors which makes it very complicated to model. This is especially problematic as oil degradation usually is limiting for oil change intervals.

    Out of the four sub-models that were created, the model for fuel dilution gave the best correspondence with measurements. However data was only available for the part of the model handling evaporation and thus it is unknown how well the model for fuel influx performs. As the model is very simple there is reason to believe that the correspondence between the modelled influx and the actual influx is not very good. The model for oil degradation could not be validated using the available data and further experiments are necessary. However it was concluded from the data available that a model based only on oil temperature, as was first intended, will not be sufficient. The water dilution model was reasonably accurate in predicting average water concentrations, but missed short term variations completely. In order to fully validate the model, further experiments, where the various rates of condensation are measured, will be necessary. The model for oil-soot already available at Scania was considered sufficient and no further work has been done on this model. A short description of the model has been included for completeness.

  • 317. Hagedorn, Claudia
    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.
    Schmidt, Michael A.
    Unification of gauge couplings in radiative neutrino mass models2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 111Article in journal (Refereed)
    Abstract [en]

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

  • 318. Haggkvist, R.
    et al.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Lundow, Per Håkan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Markstrom, K.
    Andren, D.
    Kundrotas, P.
    On the Ising model for the simple cubic lattice2007In: Advances in Physics, ISSN 0001-8732, E-ISSN 1460-6976, Vol. 56, no 5, p. 653-755Article, review/survey (Refereed)
    Abstract [en]

    The Ising model was introduced in 1920 to describe a uniaxial system of magnetic moments, localized on a lattice, interacting via nearest-neighbour exchange interaction. It is the generic model for a continuous phase transition and arguably the most studied model in theoretical physics. Since it was solved for a two-dimensional lattice by Onsager in 1944, thereby representing one of the very few exactly solvable models in dimensions higher than one, it has served as a testing ground for new developments in analytic treatment and numerical algorithms. Only series expansions and numerical approaches, such as Monte Carlo simulations, are available in three dimensions. This review focuses on Monte Carlo simulation. We build upon a data set of unprecedented size. A great number of quantities of the model are estimated near the critical coupling. We present both a conventional analysis and an analysis in terms of a Puiseux series for the critical exponents. The former gives distinct values of the high- and low-temperature exponents; by means of the latter we can get these exponents to be equal at the cost of having true asymptotic behaviour being found only extremely close to the critical point. The consequences of this for simulations of lattice systems are discussed at length.

  • 319. Hallnaes, Martin
    et al.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    A product formula for the eigenfunctions of a quartic oscillator2015In: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, E-ISSN 1096-0813, Vol. 426, no 2, p. 1012-1025Article in journal (Refereed)
    Abstract [en]

    We consider the Schrodinger operator on the real line with an even quartic potential. Our main result is a product formula of the type psi(k)(x)psi(k)(y) = integral(R) psi(k)(z)K(x,y, z)dz for its eigenfunctions psi(k). The kernel function K is given explicitly in terms of the Airy function Ai(x), and it is positive for appropriate parameter values. As an application, we obtain a particular asymptotic expansion of the eigenfunctions psi(k).

  • 320.
    Hallnäs, Martin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    An Explicit Formula for Symmetric Polynomials Related to the Eigenfunctions of Calogero-Sutherland Models2007In: SIGMA. Symmetry, Integrability and Geometry, ISSN 1815-0659, E-ISSN 1815-0659, Vol. 3, no 037Article in journal (Refereed)
    Abstract [en]

    We review a recent construction of an explicit analytic series representation for symmetric polynomials which up to a groundstate factor are eigenfunctions of Calogero Sutherland type models. We also indicate a generalisation of this result to polynomials which give the eigenfunctions of so-called 'deformed' Calogero-Sutherland type models.

  • 321.
    Hallnäs, Martin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Exactly solved quantum many-body systems in one dimension2005Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis is devoted to the study of various examples of exactly solved quantum many-body systems in one-dimension. It is divided into two parts: the first provides background and complementary results to the second, which consists of three scientific papers. The first paper concerns a particu- lar extension, corresponding to the root system CN, of the delta-interaction model. We prove by construction that its exact solution, even in the gen- eral case of distinguishable particles, can be obtained by the coordinate Bethe ansatz. We also elaborate on the physical interpretation of this model. It is well known that the delta-interaction is included in a four parameter family of local interactions. In the second paper we interpret these parameters as cou- pling constants of certain momentum dependent interactions and determine all cases leading to a many-body system of distinguishable particles which can be solved by the coordinate Bethe ansatz. In the third paper we consider the so-called rational Calogero-Sutherland model, describing an arbitrary number of particles on the real line, confined by a harmonic oscillator potential and interacting via a two-body interaction proportional to the inverse square of the inter-particle distance. We construct a novel solution algorithm for this model which enables us to obtain explicit formulas for its eigenfunctions. We also show that our algorithm applies, with minor changes, to all extensions of the rational Calogero-Sutherland model which correspond to a classical root system.

  • 322.
    Hallnäs, Martin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Quantum many-body systems exactly solved by special functions2007Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    This thesis concerns two types of quantum many-body systems in one dimension exactly solved by special functions: firstly, systems with interactions localised at points and solved by the (coordinate) Bethe ansatz; secondly, systems of Calogero-Sutherland type, as well as certain recently introduced deformations thereof, with eigenfunctions given by natural many-variable generalisations of classical (orthogonal) polynomials. The thesis is divided into two parts. The first provides background and a few complementary results, while the second presents the main results of this thesis in five appended scientific papers. In the first paper we consider two complementary quantum many-body systems with local interactions related to the root systems CN, one with delta-interactions, and the other with certain momentum dependent interactions commonly known as delta-prime interactions. We prove, by construction, that the former is exactly solvable by the Bethe ansatz in the general case of distinguishable particles, and that the latter is similarly solvable only in the case of bosons or fermions. We also establish a simple strong/weak coupling duality between the two models and elaborate on their physical interpretations. In the second paper we consider a well-known four-parameter family of local interactions in one dimension. In particular, we determine all such interactions leading to a quantum many-body system of distinguishable particles exactly solvable by the Bethe ansatz. We find that there are two families of such systems: the first is described by a one-parameter deformation of the delta-interaction model, while the second features a particular one-parameter combination of the delta and the delta-prime interactions. In papers 3-5 we construct and study particular series representations for the eigenfunctions of a family of Calogero-Sutherland models naturally associated with the classical (orthogonal) polynomials. In our construction, the eigenfunctions are given by linear combinations of certain symmetric polynomials generalising the so-called Schur polynomials, with explicit and rather simple coefficients. In paper 5 we also generalise certain of these results to the so-called deformed Calogero-Sutherland operators.

  • 323. Hallnäs, Martin
    et al.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    A Unified Construction of Generalized Classical Polynomials Associated with Operators of Calogero-Sutherland Type2010In: Constructive approximation, ISSN 0176-4276, E-ISSN 1432-0940, Vol. 31, no 3, p. 309-342Article in journal (Refereed)
    Abstract [en]

    In this paper we consider a large class of many-variable polynomials which contains generalizations of the classical Hermite, Laguerre, Jacobi and Bessel polynomials as special cases, and which occur as the polynomial part in the eigenfunctions of Calogero-Sutherland type operators and their deformations recently found and studied by Chalykh, Feigin, Sergeev, and Veselov. We present a unified and explicit construction of all these polynomials.

  • 324.
    Hallnäs, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Exact solutions of two complementary one-dimensional quantum many-body systems on the half-line2005In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 46, no 5Article in journal (Refereed)
    Abstract [en]

    We consider two particular one-dimensional quantum many-body systems with local interactions related to the root system C-N. Both models describe identical particles moving on the half-line with nontrivial boundary conditions at the origin, but in the first model the particles interact with the delta interaction while in the second via a particular momentum dependent interaction commonly known as delta-prime interaction. We show that the Bethe ansatz solution of the delta-interaction model is consistent even for the general case where the particles are distinguishable, whereas for the delta-prime interaction it only is consistent and nontrivial in the fermion case. We also establish a duality between the bosonic delta- and the fermionic delta-prime model, and we elaborate on the physical interpretations of these models.

  • 325.
    Hallnäs, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Explicit formulae for the eigenfunctions of the N-body Calogero model2006In: Journal of Physics A: Mathematical and General, ISSN 0305-4470, E-ISSN 1361-6447, Vol. 39, no 14, p. 3511-3533Article in journal (Refereed)
    Abstract [en]

    We consider the quantum Calogero model, which describes N non-distinguishable quantum particles on the real line confined by a harmonic oscillator potential and interacting via two-body interactions proportional to the inverse square of the inter-particle distance. We elaborate a novel solution algorithm which allows us to obtain fully explicit formulae for its eigenfunctions, arbitrary coupling parameter and particle number. We also show that our method applies, with minor changes, to all Calogero models associated with classical root systems.

  • 326.
    Hallnäs, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Quantum Calogero-Sutherland type models and generalised classical polynomials2007Manuscript (preprint) (Other academic)
    Abstract [en]

    In this paper we consider a large class of many-variable polynomials which contains generalisations of the classical Hermite, Laguerre, Jacobi and Bessel polynomials as special cases, and which occur as the polynomial part in the eigenfunctions of Calogero-Sutherland type operators and their deformations recently found and studied by Chalykh, Feigin, Sergeev, and Veselov. We present a unified and explicit construction of all these polynomials.

  • 327.
    Hallnäs, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Paufler, Cornelius
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Generalized local interactions in 1D: solutions of quantum many-body systems describing distinguishable particles2005In: Journal of Physics A: Mathematical and General, ISSN 0305-4470, E-ISSN 1361-6447, Vol. 38, no 22, p. 4957-4974Article in journal (Refereed)
    Abstract [en]

    As is well known, there exists a four-parameter family of local interactions in 1D. We interpret these parameters as coupling constants of delta-type interactions which include different kinds of momentum-dependent terms, and determine all cases leading to many-body systems of distinguishable particles which are exactly solvable by the coordinate Bethe ansatz. We find two such families of systems, one with two independent coupling constants deforming the well-known delta-interaction model to non-identical particles, and the other with a particular one-parameter combination of the delta and (the so-called) delta-prime interaction. We also find that the model of non-identical particles gives rise to a somewhat unusual solution of the Yang-Baxter relations. For the other model we write down explicit formulae for all eigenfunctions.

  • 328.
    Hallström, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Sjösund, Lars Lowe
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Strömsten, David
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Computer Simulation of Actin Polymerization in Cellular Protrusion2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Motility or spontaneous motion of eukaryotic cells, such as white blood cells, has been

    extensively studied in the recent literature. A mechanism has been established based

    on polymerization of actin filaments that pushes the cell wall forwards. However, many

    features of this phenomenon remain incompletely understood and more insights from

    modeling is desirable. We study the problem of understanding the origin and magnitude

    of the velocity achieved by the moving cells, and compare it with existing experimental

    results. We have developed and simulated a simplified model based on the relevant

    features of eukaryotic protrusion, formulating main elements required to describe the

    cellular motility. The main simplification is the isolation of a few actin filaments, whereas

    other similar models have previously been built on more complicated cases of polymer

    ensembles. The strength of the simplified model is that it clarifies the actual e

    ffective

    elements of cellular protrusion. A computer program simulates the growth of an actin

    polymer behind a cellular membrane and delivers the protrusion speed of the eukaryotic.

    We also construct a real time 3D graphical representation of the movement process.

    The results obtained are in reasonable agreement with experimental results for the cell

    velocity. The agreement is actually improved compared to previous studies of more

    complicated models, indicating that our simplified model indeed seems to work very

    well. Moreover, the detailed graphical representation highlights the process in greater

    detail than has previously been achieved.

  • 329.
    Hansen, Fredrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Multidimensional Analysis of Non-Standard Neutrino Interactions Using the Proposed ESSnuSB Experiment2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 330.
    Hansen, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Holmgren, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Neutrinos from Dark Matter Annihilation in the Sun2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Dark Matter (DM) is believed to consist ofWeakly Interactive Massive Particles (WIMPs)

    which interact only through gravity and the weak nuclear force. These particles can become

    trapped in gravitational wells such as the Sun and a theoretical value of the capture

    rate can be calculated. At high particle density the WIMPs annihilating spontaneously

    into Standard Model (SM) particles. Due to particle equilibrium the total annihilation

    rate can be related to the capture rate by a simple expression. This report will focus on

    calculating the capture rate and the related annihilation rate as well as calculating the

    neutrino  ux of the Sun. At rst we will give a brief introduction to cosmology and a

    theoretical argument for the WIMPs as the prime DM candidate. Then we will look at

    the theoretical background and the mechanism through which WIMPs become trapped

    and evaporate or annihilate. Finally we will perform a numerical analysis of the WIMP

    cycle within the Sun and calculate the capture rate for a variety of theoretical WIMP

    masses. We will look at the capture rate due to scattering both by hydrogen nucleii and

    by more massive elements. The Scattering by hydrogen will be the prime contributor to

    the total capture rate and is the only spin dependent contribution.

  • 331. Hariharan, Parameswaran
    et al.
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Jiang, Xiaoxu
    Pardon, Els
    Steyaert, Jan
    Kaback, H. Ronald
    Guan, Lan
    Thermodynamics of Nanobody Binding to Lactose Permease2016In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 55, no 42, p. 5917-5926Article in journal (Refereed)
    Abstract [en]

    Camelid nanobodies (Nbs) raised against the outward-facing conformer of a double-Trp mutant of the lactose permease of Escherichia coli (LacY) stabilize the permease in outward-facing conformations. Isothermal titration calorimetry is applied herein to dissect the binding thermodynamics of two Nbs, one that markedly improves access to the sugar-binding site and another that dramatically increases the affinity for galactoside. The findings presented here show that both enthalpy and entropy contribute favorably to binding of the Nbs to wild-type (WT) LacY and that binding of Nb to double-Trp mutant G46W/G262W is driven by a greater enthalpy at an entropic penalty. Thermodynamic analyses support the interpretation that WT LacY is stabilized in outward-facing conformations like the double-Trp mutant with closure of the cytoplasmic cavity through conformational selection. The LacY conformational transition required for ligand binding is reflected by a favorable entropy increase. Molecular dynamics simulations further suggest that the entropy increase likely stems from release of immobilized water molecules primarily from the cytoplasmic cavity upon closure.

  • 332.
    Hedkvist, Olle
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Finding the Free Energy Proles of Protein Transitions2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 333.
    Heinze, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Malinsky, Michal
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Flavor structure of supersymmetric SO(10) GUTs with extended matter sector2011In: PHYSICAL REVIEW D, ISSN 1550-7998, Vol. 83, no 3, p. 035018-Article in journal (Refereed)
    Abstract [en]

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

  • 334.
    Hekmati, Pedram
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Abelian Extensions, Fractional Loop Group and Quantum Fields2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the theory of Lie group extensions, Lie conformal algebras and twisted K-theory, in the context of quantum physics. These structures allow for a mathematically precise description of certain aspects of interacting quantum field theories. We review three concrete examples, namely symmetry breaking (or anomalies) in gauge theory, classification of D-brane charges in string theory and the formulation of integrable hierarchies in the language of Poisson vertex algebras. The main results are presented in three appended scientific papers.

    In the first paper we establish, by construction, a criterion for when an infinite dimensional abelian Lie algebra extension corresponds to a Lie group extension.

    In the second paper we introduce the fractional loop group LqG, that is the group of maps from a circle to a compact Lie group G, with only a small degree of differentiability q ε R+ in the Sobolev sense. We construct abelian extensions and highest weight modules for the Lie algebra Lqg, and discuss an application to equivariant twisted K-theory on G.

    In the third paper, we construct a structure of calculus algebra on the Lie conformal algebra complex and provide a more detailed description in the special case of the complex of variational calculus.

  • 335.
    Hekmati, Pedram
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Group Extensions, Gerbes and Twisted K-theory2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis reviews the theory of group extensions, gerbes and twisted K-theory. Application to anomalies in gauge theory is briefly discussed. The main results are presented in two appended scientific papers. In the first paper we establish, by construction, a criterion for when an infinite dimensional abelian Lie algebra extension corresponds to a Lie group extension. In the second paper we introduce the fractional loop group L_qG, construct highest weight modules for the Lie algebra and discuss an application to twisted K-theory on G.

  • 336.
    Hekmati, Pedram
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Integrability Criterion for Abelian Extensions of Lie Groups2010In: Proceedings of the American Mathematical Society, ISSN 0002-9939, E-ISSN 1088-6826, Vol. 138, no 11, p. 4137-4148Article in journal (Refereed)
    Abstract [en]

    We establish a criterion for when an abelian extension of infinite-dimensional Lie algebras (g) over cap = g circle plus(omega) a integrates to a corresponding Lie group extension A (sic) (G) over cap (sic) G, where G is connected, simply connected and A congruent to a/Gamma for some discrete subgroup Gamma subset of a. When pi(1) (G) not equal 0, the kernel A is replaced by a central extension (A) over cap of pi(1) (G) by A.

  • 337.
    Hekmati, Pedram
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Mickelsson, Jouko
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Fractional Loop Group and Twisted K-theory2010In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 299, no 3, p. 741-763Article in journal (Refereed)
    Abstract [en]

    We study the structure of abelian extensions of the group L (q) G of q-differentiable loops (in the Sobolev sense), generalizing from the case of the central extension of the smooth loop group. This is motivated by the aim of understanding the problems with current algebras in higher dimensions. Highest weight modules are constructed for the Lie algebra. The construction is extended to the current algebra of the supersymmetric Wess-Zumino-Witten model. An application to the twisted K-theory on G is discussed.

  • 338. Hellgren, M.
    et al.
    Sandberg, L.
    Edholm, Olle
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    A comparison between two prokaryotic potassium channels (KirBac1.1 and KcsA) in a molecular dynamics (MD) simulation study2006In: Biophysical Chemistry, ISSN 0301-4622, E-ISSN 1873-4200, Vol. 120, no 1, p. 1-9Article in journal (Refereed)
    Abstract [en]

    The two potassium ion channels KirBac1.1 and KcsA are compared in a Molecular Dynamics (MD) simulation study. The location and motion of the potassium ions observed in the simulations are compared to those in the X-ray structures and previous simulations. In our simulations several of the crystallography resolved ion sites in KirBac1.1 are occupied by ions. In addition to this, two in KirBac1.1 unresolved sites where occupied by ions at sites that are in close correspondence to sites found in KcsA. There is every reason to believe that the conserved alignment of the selectivity filter in the potassium ion channel family corresponds to a very similar mechanism for ion transport across the filter. The gate residues, Phe146 in KirBac1.1 and Ala111 in KcsA acted in the simulations as effective barriers which never were passed by ions nor water molecules.

  • 339.
    Henelius, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Fishman, R. S.
    Hybrid quantum-classical Monte Carlo study of a molecule-based magnet2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 21Article in journal (Refereed)
    Abstract [en]

    Using a Monte Carlo (MC) method, we study an effective model for the Fe(II)Fe(III) bimetallic oxalates. Within a hybrid quantum-classical MC algorithm, the Heisenberg S=2 and S-'=5/2 spins on the Fe(II) and Fe(III) sites are updated using a quantum MC loop while the Ising-type orbital angular momenta on the Fe(II) sites are updated using a single-spin classical MC flip. The effective field acting on the orbital angular momenta depends on the quantum state of the system. We find that the mean-field phase diagram for the model is surprisingly robust with respect to fluctuations. In particular, the region displaying two compensation points shifts and shrinks but remains finite.

  • 340.
    Henelius, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Lin, T.
    Enjalran, M.
    Hao, Z.
    Rau, J. G.
    Altosaar, J.
    Flicker, F.
    Yavors'kii, T.
    Gingras, M. J. P.
    Refrustration and competing orders in the prototypical Dy2Ti2O7 spin ice material2016In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 93, no 2, article id 024402Article in journal (Refereed)
    Abstract [en]

    Spin ices, frustratedmagnetic materials analogous to common water ice, have emerged over the past 15 years as exemplars of high frustration in three dimensions. Recent experimental developments aimed at interrogating anew the low-temperature properties of these systems, in particular whether the predicted transition to long-range order occurs, behoove researchers to scrutinize our current dipolar spin ice model description of these materials. In this work, we do so by combining extensive Monte Carlo simulations and mean-field theory calculations to analyze data from previous magnetization, diffuse neutron scattering, and specific-heat measurements on the paradigmatic Dy2Ti2O7 spin ice material. In this work, we also reconsider the possible importance of the nuclear specific heat C-nuc in Dy2Ti2O7. We find that C-nuc is not entirely negligible below a temperature similar to 0.5 K and must therefore be taken into account in a quantitative analysis of the calorimetric data of this compound below that temperature. We find that in this material, small effective spin-spin exchange interactions compete with the magnetostatic dipolar interaction responsible for the main spin ice phenomenology. This causes an unexpected " refrustration" of the long-range order that would be expected from the incompletely self-screened dipolar interaction and which positions the material at the boundary between two competing classical long-range-ordered ground states. This allows for the manifestation of new physical low-temperature phenomena in Dy2Ti2O7, as exposed by recent specific-heat measurements. We show that among the four most likely causes for the observed upturn of the specific heat at low temperature [an exchange-induced transition to long-range order, quantum non-Ising (transverse) terms in the effective spin Hamiltonian, the nuclear hyperfine contribution, and random disorder], only the last appears to be reasonably able to explain the calorimetric data.

  • 341. Henrion, Ulrike
    et al.
    Renhorn, Jakob
    Börjesson, Sara I.
    Nelson, Erin M.
    Schwaiger, Christine S.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Bjelkmar, Pär
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Wallner, Björn
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Elinder, Fredrik
    Tracking a complete voltage-sensor cycle with metal-ion bridges2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 22, p. 8552-8557Article in journal (Refereed)
    Abstract [en]

    Voltage-gated ion channels open and close in response to changes in membrane potential, thereby enabling electrical signaling in excitable cells. The voltage sensitivity is conferred through four voltage-sensor domains (VSDs) where positively charged residues in the fourth transmembrane segment (S4) sense the potential. While an open state is known from the Kv1.2/2.1 X-ray structure, the conformational changes underlying voltage sensing have not been resolved. We present 20 additional interactions in one open and four different closed conformations based on metal-ion bridges between all four segments of the VSD in the voltage-gated Shaker K channel. A subset of the experimental constraints was used to generate Rosetta models of the conformations that were subjected to molecular simulation and tested against the remaining constraints. This achieves a detailed model of intermediate conformations during VSD gating. The results provide molecular insight into the transition, suggesting that S4 slides at least 12 angstrom along its axis to open the channel with a 3(10) helix region present that moves in sequence in S4 in order to occupy the same position in space opposite F290 from open through the three first closed states.

  • 342. Herland, Egil V.
    et al.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Bonderson, Parsa
    Gurarie, Victor
    Nayak, Chetan
    Radzihovsky, Leo
    Sudbo, Asle
    Freezing of an unconventional two-dimensional plasma2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 7, p. 075117-Article in journal (Refereed)
    Abstract [en]

    We study an unconventional two-dimensional, two-component classical plasma on a sphere, with emphasis on detecting signatures of melting transitions. This system is relevant to Ising-type quantum Hall states, and is unconventional in the sense that it features particles interacting via two different two-dimensional Coulomb interactions. One species of particle in the plasma carries charge of both types (Q(1), Q(2)), while the other species carries only charge of the second type (0,-Q(2)). We find signatures of a freezing transition at Q(1)(2) similar or equal to 140. This means that the species with charge of both types will form a Wigner crystal, whereas the species with charge of the second type also shows signatures of being a Wigner crystal, due to the attractive intercomponent interaction of the second type. Moreover, there is also a Berezinskii-Kosterlitz-Thouless phase transition at Q(2)(2) similar or equal to 4, at which the two species of particles bind to form molecules that are neutral with respect to the second Coulomb interaction. These two transitions appear to be independent of each other, giving a rectangular phase diagram. As a special case, Q(2) = 0 describes the (conventional) two-dimensional one-component plasma. Our study is consistent with previous studies of this plasma, and sheds new light on the freezing transition of this system.

  • 343. Herland, Egil V.
    et al.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Bonderson, Parsa
    Gurarie, Victor
    Nayak, Chetan
    Sudbo, Asle
    Screening properties and phase transitions in unconventional plasmas for Ising-type quantum Hall states2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 2, p. 024520-Article in journal (Refereed)
    Abstract [en]

    Utilizing large-scale Monte Carlo simulations, we investigate an unconventional two-component classical plasma in two dimensions which controls the behavior of the norms and overlaps of the quantum-mechanical wave functions of Ising-type quantum Hall states. The plasma differs fundamentally from that which is associated with the two-dimensional XY model and Abelian fractional quantum Hall states. We find that this unconventional plasma undergoes a Berezinskii-Kosterlitz-Thouless phase transition from an insulator to a metal. The parameter values corresponding to Ising-type quantum Hall states lie on the metallic side of this transition. This result verifies the required properties of the unconventional plasma used to demonstrate that Ising-type quantum Hall states possess quasiparticles with non-Abelian braiding statistics.

  • 344. Herland, Egil V.
    et al.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Sudbo, Asle
    Phase transitions in a three dimensional U(1)xU(1) lattice London superconductor: Metallic superfluid and charge-4e superconducting states2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 13, p. 134511-Article in journal (Refereed)
    Abstract [en]

    We consider a three dimensional lattice U(1)xU(1) and [U(1)](N) superconductors in the London limit with individually conserved condensates. The U(1)xU(1) problem, generically, has two types of intercomponent interactions of different characters. First, the condensates are interacting via a minimal coupling to the same fluctuating gauge field. A second type of coupling is the direct dissipationless drag represented by a local intercomponent current-current coupling term in the free-energy functional. In this work, we present a study of the phase diagram of a U(1)xU(1) superconductor which includes both of these interactions. We study phase transitions and two types of competing paired phases which occur in this general model: (i) a metallic super-fluid phase (where there is order only in the gauge-invariant phase difference of the order parameters), (ii) a composite superconducting phase where there is order in the phase sum of the order parameters which has many properties of a single-component superconductor but with a doubled value of electric charge. We investigate the phase diagram with particular focus on what we call "preemptive phase transitions." These are phase transitions unique to multicomponent condensates with competing topological objects. A sudden proliferation of one kind of topological defects may come about due to a fluctuating background of topological defects in other sectors of the theory. For U U(1)xU(1) theory with unequal bare stiffnesses where components are coupled by a noncompact gauge field only, we study how this scenario leads to a merger of two U(1) transitions into a single U(1)xU(1) discontinuous phase transition. We also report a general form of vortex-vortex bare interaction potential and possible phase transitions in an N-component London superconductor with individually conserved condensates.

  • 345. Herland, Egil V.
    et al.
    Bojesen, Troels A.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Sudbo, Asle
    Phase structure and phase transitions in a three-dimensional SU(2) superconductor2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 13, p. 134503-Article in journal (Refereed)
    Abstract [en]

    We study the three-dimensional SU(2)-symmetric noncompact CP1 model, with two charged matter fields coupled minimally to a noncompact Abelian gauge field. The phase diagram and the nature of the phase transitions in this model have attracted much interest after it was proposed to describe an unusual continuous transition associated with deconfinement of spinons. Previously, it has been demonstrated for various two-component gauge theories that weakly first-order transitions may appear as continuous ones of a new universality class in simulations of relatively large, but finite systems. We have performed Monte Carlo calculations on substantially larger systems sizes than those in previous works. We find that in some area of the phase diagram where at finite sizes one gets signatures consistent with a single first-order transition; in fact, there is a sequence of two phase transitions with an O(3) paired phase sandwiched in between. We report (i) a new estimate for the location of a bicritical point and (ii) the first resolution of bimodal distributions in energy histograms at relatively low coupling strengths. We perform a flowgram analysis of the direct transition line with rescaling of the linear system size in order to obtain a data collapse. The data collapses up to coupling constants where we find bimodal distributions in energy histograms.

  • 346. Hernandez, Andres
    et al.
    Konstandin, Thomas
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Schmidt, Michael G.
    Effective action in a general chiral model: Next to leading order derivative expansion in the worldline method2008In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 793, no 3, p. 425-450Article in journal (Refereed)
    Abstract [en]

    We present a formalism to determine the imaginary part of a general chiral model in the derivative expansion. Our formalism is based on the worldline path integral for the covariant current that can be given in an explicit chiral and gauge covariant form. The effective action is then obtained by integrating the covariant current, taking account of the anomaly.

  • 347.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. AlbaNova University Center, Sweden.
    Halo-independent tests of dark matter annual modulation signals2015In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 9, article id 012Article in journal (Refereed)
    Abstract [en]

    New halo-independent lower bounds on the product of the dark matter-nucleon scattering cross section and the local dark matter density that are valid for annual modulations of dark matter direct detection signals are derived. They are obtained by making use of halo-independent bounds based on an expansion of the rate on the Earth's velocity that were derived in previous works. In combination with astrophysical measurements of the local energy density, an observed annual modulation implies a lower bound on the cross section that is independent of the velocity distribution and that must be fulfilled by any particle physics model. In order to illustrate the power of the bounds we apply them to DAMA/LIBRA data and obtain quite strong results when compared to the standard halo model predictions. We also extend the bounds to the case of multi-target detectors.

  • 348.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Halo-independent tests of dark matter direct detection signals2015In: Proceedings of Science, Proceedings of Science (PoS) , 2015Conference paper (Refereed)
    Abstract [en]

    We discuss a new halo-independent framework that can be used to relate dark matter direct detection signals with constraints from LHC, indirect detection and the thermal freeze-out paradigm. From an observed direct detection signal we show that a lower bound on the product of the dark matter-nucleon cross section and the energy density, that is independent of the velocity distribution, can be derived. This allows to obtain strong and robust halo-independent constraints on particle physics models. We also extend this framework to the case of annual modulation signals and we illustrate the use of the lower bounds with the DAMA signal. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).

  • 349.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Higgs lepton flavor violation2015In: Proceedings of Science, Proceedings of Science (PoS) , 2015Conference paper (Refereed)
    Abstract [en]

    We study lepton-flavor-violating Higgs decays in the light of the recently observed deviation in the H → τμ channel with respect to the Standard Model, which should be confirmed/excluded in the second run of the LHC. Starting from an EFT approach, we discuss both tree-level and looplevel UV completions. In particular, we find that, in agreement with previous analyses, loop-level realizations are in general too suppressed, while models containing at least two Higgs doublets can explain the enhancement. We also analyze well-motivated neutrino mass models that could in principle accommodate the excess, finding two popular examples: the Zee model and left-right symmetric models. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).

  • 350.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Predicting the capture rate in the Sun from a direct detection signal independently of the astrophysics2016In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 718, no 4, article id 42027Article in journal (Refereed)
    Abstract [en]

    The goal of the works on which this talk is based is to relate a direct detection signal with neutrino limits from the Sun independently of the astrophysics. In order to achieve this we derive a halo-independent lower bound on the dark matter capture rate in the Sun from a direct detection signal, with which one can set upper limits on the branching ratios into different channels from the absence of a high-energy neutrino flux in neutrino observatories. We also extend this bound to the case of inelastic scattering, both endothermic and exothermic. From two inelastic signals we show how the dark matter mass, the mass difference of the states and the couplings to neutrons and protons can be obtained. Furthermore, one can also pin down the exothermic/endothermic nature of the scattering, and therefore a precise lower bound on the solar capture rate is predicted. We also discuss isospin violation and uncertainties due to form factors.

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