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  • 501.
    Meier, Hannes
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Superfluid Phase Transitions in Disordered Systems2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents results from large scale Monte Carlo simulations of systems subject to a superfluid phase transition in the presence of disorder. The simulations are performed by state-of-the-art, collective Monte Carlo algorithms treating phase degrees of freedom in effective models with amplitude fluctuations integrated out.

    In Paper I a model system for the possible solid to supersolid transition in 4He is presented.The Wolff cluster algorithm is used to study how the presence of linearly correlated random defects is able to alter the universality class of the 3-dimensional XY-model. In the pure case the superfluid density and heat capacity have singular onsets, which are not seen in the supersolid experiments where instead a smooth onset is obtained. Using finite size scaling of Monte Carlo data, we find a similar smooth onset in our simulations, governed by exponents  ν=1 for the superfluid density and α=-1 for the heat capacity. These results are in qualitative agreement with experiments for the observed transition in solid 4He.

    In Paper II a systematic investigation of the scaling result z=d for the dynamic critical exponentat the Bose glass to superfluid quantum phase transition is performed. The result z=d has been believed to be exact for about 20 years, but although it has been questioned lately no accurate estimate of z has been available. An effective link current model of quantum bosons at T=0 with disorder in 2D is simulated using highly effective worm Monte Carlo simulations.The data analysis is based on a finite size scaling approach todetermine the quantum correlation time from simulationdata for boson world lines without any a priori assumption on the critical parameters. The resulting critical exponents are z=1.8 \pm 0.05, ν=1.15 \pm 0.03, and η=-0.3 \pm 0.1. This suggests that z=d is not satisfied.

          

  • 502.
    Meier, Hannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Wallin, Mats
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Fluctuation-induced first order phase transitions in type-1.5 superconductors in zero external field2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 9, article id 094508Article in journal (Refereed)
    Abstract [en]

    In a single-component Ginzburg-Landau model that possesses thermodynamically stable vortex excitations, the zero-field superconducting phase transition is second order even when fluctuations are included. Beyond the mean-field approximation the transition is described in terms of proliferation of vortex loops. Here we determine the order of the superconducting transition in an effective 3D vortex-loop model for the recently proposed multi-band type-1.5 superconductors where the vortex interaction is non-monotonic, i.e., intermediate-range attractive and short-range repulsive. We find that the details of the vortex interaction, despite its short-range nature, can play an important role for the properties of the transition. In the type-1.5 regime with non-monotonic intervortex interaction, in contrast to the single-band case we find a first-order vortex-driven phase transition.

  • 503.
    Meier, Hannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Wallin, Mats
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Phase transitions in systems with critical cluster defectsManuscript (preprint) (Other academic)
  • 504.
    Meier, Hannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Wallin, Mats
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Phase transitions with critical loop disorderManuscript (preprint) (Other academic)
  • 505.
    Meier, Hannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Wallin, Mats
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Quantum Critical Dynamics Simulation of Dirty Boson Systems2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 5Article in journal (Refereed)
    Abstract [en]

    Recently, the scaling result z = d for the dynamic critical exponent at the Bose glass to superfluid quantum phase transition has been questioned both on theoretical and numerical grounds. This motivates a careful evaluation of the critical exponents in order to determine the actual value of z. We study a model of quantum bosons at T = 0 with disorder in 2D using highly effective worm Monte Carlo simulations. Our data analysis is based on a finite-size scaling approach to determine the scaling of the quantum correlation time from simulation data for boson world lines. The resulting critical exponents are z = 1.8 +/- 0.05, nu = 1.15 +/- 0.03, and eta = -0.3 +/- 0.1, hence suggesting that z = 2 is not satisfied.

  • 506.
    Meier, Hannes
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Wallin, Mats
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Teitel, S.
    University of Rochester, Rochester, United States .
    Superfluid transition in a correlated defect network2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 21, p. 214520-Article in journal (Refereed)
    Abstract [en]

    Motivated by recent experiments on the possible supersolid behavior of He-4 solids at low temperature, we consider a model of superfluidity in a defected solid containing a system spanning network of correlated linear dislocations, or planar grain boundaries. Using arguments based on the Harris criterion, as well as numerical simulations, we find that such correlated quenched disorder shifts the familiar superfluid lambda transition to a new disordered universality class in which the correlation length exponent nu >= 1. This results in the temperature derivatives for the superfluid density d rho(s)/dT and for the heat capacity dc/dT remaining finite at the transition T-c, and thus a less singular transition, profoundly different from the usual lambda transition.

  • 507.
    Melbéus, Henrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Astrophysical and Collider Signatures of Extra Dimensions2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

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

     

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

     

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

     

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

  • 508.
    Melbéus, Henrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Particle Phenomenology of Compact Extra Dimensions2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

  • 509.
    Melbéus, Henrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Phenomenology of Hyperbolic Large Extra Dimensions for Hadron Colliders2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

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

  • 510.
    Melbéus, Henrik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Searches for hyperbolic extra dimensions at the LHC2008In: Proc. Sci., 2008Conference paper (Refereed)
    Abstract [en]

    In this poster, we present a model of large extra dimensions where the internal space has the geometry of a hyperbolic disc. Compared with the ADD model, this model provides a more satisfactory solution to the hierarchy problem between the electroweak scale and the Planck scale, and it also avoids constraints from astrophysics. Since there is no known analytic form of the Kaluza-Klein spectrum for our choice of geometry, we obtain a spectrum based on a combination of approximations and numerical computations. We study the possible signatures of our model for hadron colliders, especially the LHC, where the most important processes are the production of a graviton together with a hadronic jet or a photon. We find that for the case of hadronic jet production, it is possible to obtain relatively strong signals, while for the case of photon production, this is much more difficult.

  • 511.
    Melbéus, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Continuum photon spectrum from Z1Z1 annihilations in universal extra dimensions2012In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 706, no 4-5, p. 329-332Article in journal (Refereed)
    Abstract [en]

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

  • 512.
    Melbéus, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Royal Inst Technol KTH, Dept Theoret Phys, Sch Engn Sci, S-10691 Stockholm, Sweden..
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Royal Inst Technol KTH, Dept Theoret Phys, Sch Engn Sci, S-10691 Stockholm, Sweden..
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Royal Inst Technol KTH, Dept Theoret Phys, Sch Engn Sci, S-10691 Stockholm, Sweden..
    Erratum to: Continuum photon spectrum from Z(1)Z(1) annihilations in universal extra dimensions2012In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 713, no 3, p. 350-350Article in journal (Refereed)
  • 513.
    Melbéus, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Higgs dark matter in UEDs: A good WIMP with bad detection prospects2012In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 715, no 1-3, p. 164-169Article in journal (Refereed)
    Abstract [en]

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

  • 514.
    Melbéus, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Higgs Kaluza–Klein dark matter in universal extra dimensions2008Manuscript (preprint) (Other academic)
  • 515.
    Melbéus, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Delving into extra dimensions2012In: Physics world, ISSN 0953-8585, Vol. 25, no 9, p. 27-30Article in journal (Refereed)
  • 516.
    Melbéus, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Searches for hyperbolic extra dimensions at the LHC2008In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2008, no 08, p. 077-Article in journal (Refereed)
    Abstract [en]

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

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

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

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

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

  • 519.
    Meloni, Davide
    et al.
    Università di Roma Tre.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Riad, Stella
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) modelManuscript (preprint) (Other academic)
    Abstract [en]

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

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

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

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

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

  • 522. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zhang, He
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Exact and approximate formulas for neutrino mixing and oscillations with non-standard interactions2009In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2009, no 04, p. 033-Article in journal (Refereed)
    Abstract [en]

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

  • 523. Meng, Qingyou
    et al.
    Varney, Christopher N.
    Fangohr, Hans
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Honeycomb, square, and kagome vortex lattices in superconducting systems with multiscale intervortex interactions2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 2, p. 020509-Article in journal (Refereed)
    Abstract [en]

    The recent proposal of Romero-Isart et al. [Phys. Rev. Lett. 111, 145304 (2013)] to utilize the vortex lattice phases of superconducting materials to prepare a lattice for ultracold-atom-based quantum emulators raises the need to create and control vortex lattices of different symmetries. Here we propose a mechanism by which honeycomb, hexagonal, square, and kagome vortex lattices could be created in superconducting systems with multiscale intervortex interactions. Multiple scales of the intervortex interaction can be created and controlled in layered systems made of different superconducting materials or with differing interlayer spacings.

  • 524.
    Merle, Alexander
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    keV sterile Neutrino Dark Matter and Neutrino Model Building2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 375, no Part 2, p. 012047-Article in journal (Refereed)
    Abstract [en]

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

  • 525.
    Merle, Alexander
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Niro, Viviana
    University of Turino.
    Deriving models for keV sterile neutrino Dark Matter with the Froggatt-Nielsen mechanism2011In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2011, no 7, p. 023-Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 527.
    Merle, Alexander
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Zwicky, Roman
    Explicit and spontaneous breaking of SU(3) into its finite subgroups2012In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, p. 128-Article in journal (Refereed)
    Abstract [en]

    We investigate the breaking of SU(3) into its subgroups from the viewpoints of explicit and spontaneous breaking. A one-to-one link between these two approaches is given by the complex spherical harmonics, which form a complete set of SU(3)-representation functions. An invariant of degrees p and q in complex conjugate variables corresponds to a singlet, or vacuum expectation value, in a (p; q)-representation of SU(3). We review the formalism of the Molien function, which contains information on primary and secondary invariants. Generalizations of the Molien function to the tensor generating functions are discussed. The latter allows all branching rules to be deduced. We have computed all primary and secondary invariants for all proper finite subgroups of order smaller than 512, for the entire series of groups Delta(3n(2)), Delta(6n(2)), and for all crystallographic groups. Examples of sufficient conditions for breaking into a subgroup are worked out for the entire Tn[a]-, Delta(3n(2))-, Delta(6n(2))-series and for all crystallographic groups Sigma(X). The corresponding invariants provide an alternative definition of these groups. A Mathematica package, SUtree, is provided which allows the extraction of the invariants, Molien and generating functions, syzygies, VEVs, branching rules, character tables, matrix (p; q)(SU(3))-representations, Kronecker products, etc. for the groups discussed above.

  • 528.
    Mickelsson, Jouko
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    FAMILIES OF DIRAC OPERATORS AND QUANTUM AFFINE GROUPS2011In: Journal of the Australian Mathematical Society, ISSN 1446-7887, E-ISSN 1446-8107, Vol. 90, no 2, p. 213-220Article in journal (Refereed)
    Abstract [en]

    Twisted K-theory classes over compact Lie groups can be realized as families of Fredholm operators using the representation theory of loop groups. In this paper we show how to deform the Fredholm family in the sense of quantum groups. The family of Dirac-type operators is parametrized by vectors in the adjoint module for a quantum affine algebra and transforms covariantly under a central extension of the algebra.

  • 529.
    Mickelsson, Jouko
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    From gauge anomalies to gerbes and gerbal actions2010In: Motives, quantum field theory, and pseudodifferential operators, Boston: Clay mathematical institute , 2010, p. 211-220Conference paper (Refereed)
  • 530.
    Mickelsson, Jouko
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    From Gauge Anomalies to Gerbes and Gerbal Representations: Group Cocycles in Quantum Theory2010In: Acta Polytechnica: journal of advanced engineering, ISSN 1210-2709, Vol. 50, no 3, p. 42-47Article in journal (Refereed)
  • 531.
    Mickelsson, Jouko
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Star products and central extensions2006In: Analysis, geometry and topology of elliptic operators / [ed] Bernhelm Booss-Bavnbek, Hackensack, NJ: World Scientific Publ. , 2006, p. 401-410Conference paper (Refereed)
  • 532.
    Mickelsson, Jouko
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Twisted K theory invariants2005In: Letters in Mathematical Physics, ISSN 0377-9017, E-ISSN 1573-0530, Vol. 71, no 2, p. 109-121Article in journal (Refereed)
    Abstract [en]

    An invariant for twisted K theory classes on a 3-manifold is introduced. The invariant is then applied to the twisted equivariant classes arising from the supersymmetric Wess-Zumino-Witten model based on the group SU(2). It is shown that the classes defined by different highest weight representations of the loop group LSU(2) are inequivalent. The results are compatible with Freed-Hopkins-Teleman identification of twisted equivariant K theory as the Verlinde algebra.

  • 533.
    Mickelsson, Jouko
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Paycha, Sylvie
    Renormalised Chern-Weil forms associated with families of Dirac operators2007In: Journal of Geometry and Physics, ISSN 0393-0440, E-ISSN 1879-1662, Vol. 57, no 9, p. 1789-1814Article in journal (Refereed)
    Abstract [en]

    We provide local expressions for Chern-Weil type forms built from superconnections associated with families of Dirac operators previously investigated in [S. Scott, Zeta-Chern forms and the local family index theorem, Trans. Amer. Math. Soc. (in press). arXiv: math.DG/0406294] and later in [S. Paycha, S. Scott, Chern-Weil forms associated with superconnections, in: B. Booss-Bavnbeck, S. Klimek, M. Lesch, W. Zhang (Eds.), Analysis, Geometry and Topology of Elliptic Operators, World Scientific, 2006]. When the underlying fibration of manifolds is trivial, the even degree forms can be interpreted as renormalised Chern-Weil forms in as far as they coincide with regularised Chern-Weil forms up to residue correction terms. Similarly, a new formula for the curvature of the local fermionic vacuum line bundles is derived using a residue correction term added to the naive curvature formula. We interpret the odd degree Chern-Weil type forms built from superconnections as Wodzicki residues and establish a transgression formula along the lines of known transgression formulae for eta-forms.

  • 534.
    Mickelsson, Jouko
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Paycha, Sylvie
    THE LOGARITHMIC RESIDUE DENSITY OF A GENERALIZED LAPLACIAN2011In: Journal of the Australian Mathematical Society, ISSN 1446-7887, E-ISSN 1446-8107, Vol. 90, no 1, p. 53-80Article in journal (Refereed)
    Abstract [en]

    We show that the residue density of the logarithm of a generalized Laplacian on a closed manifold defines an invariant polynomial-valued differential form. We express it in terms of a finite sum of residues of classical pseudodifferential symbols. In the case of the square of a Dirac operator, these formulas provide a pedestrian proof of the Atiyah-Singer formula for a pure Dirac operator in four dimensions and for a twisted Dirac operator on a flat space of any dimension. These correspond to special cases of a more general formula by Scott and Zagier. In our approach, which is of perturbative nature, we use either a Campbell-Hausdorff formula derived by Okikiolu or a noncommutative Taylor-type formula.

  • 535.
    Mickelsson, Jouko
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Pellonpää, Juha-Pekka
    Families index theorem in supersymmetric WZW model and twisted K-theory: The SU(2) case2007In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 271, no 3, p. 775-789Article in journal (Refereed)
    Abstract [en]

    The construction of twisted K-theory classes on a compact Lie group is reviewed using the supersymmetric Wess-Zumino-Wittenmodel on a cylinder. The Quillen superconnection is introduced for a family of supercharges parametrized by a compact Lie group and the Chern character is explicitly computed in the case of SU( 2). For large euclidean time, the character form is localized on a D-brane.

  • 536. Moore, R. G.
    et al.
    Nascimento, V. B.
    Zhang, Jiandi
    Rundgren, John
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Jin, R.
    Mandrus, D.
    Plummer, E. W.
    Manifestations of broken symmetry: The surface phases of Ca2-xSrxRuO42008In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 100, no 6, p. 066102-Article in journal (Refereed)
    Abstract [en]

    The surface structural phases of Ca2-xSrxRuO4 are investigated using quantitative low energy electron diffraction. The broken symmetry at the surface enhances the structural instability against the RuO6 rotational distortion while diminishing the instability against the RuO6 tilt distortion occurring within the bulk crystal. As a result, suppressed structural and electronic surface phase transition temperatures are observed, including the appearance of an inherent Mott metal-to-insulator transition for x=0.1 and possible modifications of the surface quantum critical point near x(c)similar to 0.5.

  • 537.
    Moosavi, Per
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    An Exactly Solvable Gauge Theory Model for Correlated Fermions in 3+1 Dimensions2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 538.
    Moosavi, Per
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Interacting fermions and non-equilibrium properties of one-dimensional many-body systems2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Recent experimental progress on ultracold atomic gases have opened up the possibility to simulate many-body systems out of equilibrium. We consider such a system described by the Luttinger model, which is a model of interacting fermions in one spatial dimension.

    It is well known that the Luttinger model is exactly solvable using bosonization. This also remains true for certain extensions of the model, e.g., where, in addition, the fermions are coupled to phonons. We give a self-contained account of bosonization, together with complete proofs, and show how this can be used to solve the Luttinger model and the above fermion-phonon model rigorously.

    The main focus is on non-equilibrium properties of the Luttinger model. We use the exact solution of the Luttinger model, with non-local interactions, to study the evolution starting from a non-uniform initial state with a position-dependent chemical potential. The system is shown to reach a current-carrying final steady state, in which the universal value of the electrical conductance, known from near-to-equilibrium settings, is recovered. We also study the effects of suddenly changing the interactions and show that the final state has memory of the initial state, which is, e.g., manifested by non- equilibrium exponents in its fermion two-point correlation functions.

  • 539.
    Mubashar, Salmana
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Higher loop renormalization in large N-limit2010Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
  • 540.
    Murail, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Broemstrup, Torben
    Howard, Rebecca
    Trudell, James
    Bertaccini, Edward J.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Molecular mechanism of the dual anesthetic modulation effect on Cys-loop receptors2012In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 243Article in journal (Other academic)
  • 541.
    Murail, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Howard, R. J.
    Broemstrup, Torben
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Bertaccini, E. J.
    Harris, R. A.
    Trudell, J. R.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Molecular Mechanism for the Dual Alcohol Modulation of Cys-loop Receptors2012In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 8, no 10, p. e1002710-Article in journal (Refereed)
    Abstract [en]

    Cys-loop receptors constitute a superfamily of pentameric ligand-gated ion channels (pLGICs), including receptors for acetylcholine, serotonin, glycine and γ-aminobutyric acid. Several bacterial homologues have been identified that are excellent models for understanding allosteric binding of alcohols and anesthetics in human Cys-loop receptors. Recently, we showed that a single point mutation on a prokaryotic homologue (GLIC) could transform it from a channel weakly potentiated by ethanol into a highly ethanol-sensitive channel. Here, we have employed molecular simulations to study ethanol binding to GLIC, and to elucidate the role of the ethanol-enhancing mutation in GLIC modulation. By performing 1-μs simulations with and without ethanol on wild-type and mutated GLIC, we observed spontaneous binding in both intra-subunit and inter-subunit transmembrane cavities. In contrast to the glycine receptor GlyR, in which we previously observed ethanol binding primarily in an inter-subunit cavity, ethanol primarily occupied an intra-subunit cavity in wild-type GLIC. However, the highly ethanol-sensitive GLIC mutation significantly enhanced ethanol binding in the inter-subunit cavity. These results demonstrate dramatic effects of the F(14′)A mutation on the distribution of ligands, and are consistent with a two-site model of pLGIC inhibition and potentiation.

  • 542.
    Murail, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Howard, Rebecca J.
    Trudell, James R.
    Bertaccini, Edward
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Tracing the Closing of a Ligand-Gated Ion Channel in Atomic Detail: An Unconstrained Four-Microsecond Simulation of GLIC Leads to a Closed State Remarkably Similar to ELIC2012In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 102, no 3, p. 113A-114AArticle in journal (Other academic)
  • 543.
    Murail, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Wallner, Björn
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Trudell, James R.
    Bertaccini, Edward
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Microsecond Simulations Indicate that Ethanol Binds between Subunits and Could Stabilize an Open-State Model of a Glycine Receptor2011In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 100, no 7, p. 1642-1650Article in journal (Refereed)
    Abstract [en]

    Cys-loop receptors constitute a superfamily of ion channels gated by ligands such as acetylcholine, serotonin, glycine, and gamma-aminobutyric acid. All of these receptors are thought to share structural characteristics, but due to high sequence variation and limited structure availability, our knowledge about allosteric binding sites is still limited. These sites are frequent targets of anesthetic and alcohol molecules, and are of high pharmacological importance. We used molecular simulations to study ethanol binding and equilibrium exchange for the homomeric alpha 1 glycine receptor (GlyR alpha 1), modeled on the structure of the Gloeobacter violaceus pentameric ligand-gated channel. Ethanol has a well-known potentiating effect and can be used in high concentrations. By performing two microsecond-scale simulations of GlyR with/without ethanol, we were able to observe spontaneous binding in cavities and equilibrium ligand exchange. Of interest, it appears that there are ethanol-binding sites both between and within the GlyR transmembrane subunits, with the intersubunit site having the highest occupancy and slowest exchange (similar to 200 ns). This model site involves several residues that were previously identified via mutations as being crucial for potentiation. Finally, ethanol appears to stabilize the GlyR model built on a presumably open form of the ligand-gated channel. This stabilization could help explain the effects of allosteric ligand binding in Cys-loop receptors.

  • 544.
    Månsson, Teresia
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    The Liegh-Strassler deformation and the quest for integrability2007In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479Article in journal (Refereed)
    Abstract [en]

    In this paper we study the one-loop dilatation operator of the full scalar field sector of Leigh-Strassler deformed =4 SYM theory. In particular we map it onto a spin chain and find the parameter values for which the Reshetikhin integrability criteria are fulfilled. Some years ago Roiban found an integrable subsector, consisting of two holomorphic scalar fields, corresponding to the XXZ model. He was pondering about the existence of a subsector which would form generalisation of that model to an integrable q(3) model. Later Berenstein and Cherkis added one more holomorphic field and showed that the subsector obtained this way cannot be integrable except for the case when q = eiβ, β. In this work we show if we add an anti-holomorphic field to the two holomorphic ones, we get indeed an integrable q(3) subsector. We find it plausible that a direct generalisation to a q(2|3) one-loop sector will exist, and possibly beyond one-loop.

  • 545.
    Månsson, Teresia
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Mathematical Physics.
    Lahtinen, Ville
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Suorsa, Juha
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Ardonne, Eddy
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Condensate-induced transitions and critical spin chains2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 4, p. 041403-Article in journal (Refereed)
    Abstract [en]

    We show that condensate-induced transitions between two-dimensional topological phases provide a general framework to relate one-dimensional spin models at their critical points. We demonstrate this using two examples. First, we show that two well-known spin chains, namely, the XY chain and the transverse field Ising chain with only next-nearest-neighbor interactions, differ at their critical points only by a nonlocal boundary term and can be related via an exact mapping. The boundary term constrains the set of possible boundary conditions of the transverse field Ising chain, reducing the number of primary fields in the conformal field theory that describes its critical behavior. We argue that the reduction of the field content is equivalent to the confinement of a set of primary fields, in precise analogy to the confinement of quasiparticles resulting from a condensation of a boson in a topological phase. As the second example we show that when a similar confining boundary term is applied to the XY chain with only next-nearest-neighbor interactions, the resulting system can be mapped to a local spin chain with the u(1)(2) x u(1)(2) critical behavior predicted by the condensation framework.

  • 546. Nascimento, V. B.
    et al.
    Freeland, J. W.
    Saniz, R.
    Moore, R. G.
    Mazur, D.
    Liu, H.
    Pan, M. H.
    Rundgren, John
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
    Gray, K. E.
    Rosenberg, R. A.
    Zheng, H.
    Mitchell, J. F.
    Freeman, A. J.
    Veltruska, K.
    Plummer, E. W.
    Surface-Stabilized Nonferromagnetic Ordering of a Layered Ferromagnetic Manganite2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 22, p. 227201-Article in journal (Refereed)
    Abstract [en]

    An outstanding question regarding the probing or possible device applications of correlated electronic materials (CEMs) with layered structure is the extent to which their bulk and surface properties differ or not. The broken translational symmetry at the surface can lead to distinct functionality due to the charge, lattice, orbital, and spin coupling. Here we report on the case of bilayered manganites with hole doping levels corresponding to bulk ferromagnetic order. We find that, although the hole doping level is measured to be the same as in the bulk, the surface layer is not ferromagnetic. Further, our low-energy electron diffraction and x-ray measurements show that there is a c-axis collapse in the outermost layer. Bulk theoretical calculations reveal that, even at fixed doping level, the relaxation of the Jahn-Teller distortion at the surface is consistent with the stabilization of an A-type antiferromagnetic state.

  • 547. Nascimento, V. B.
    et al.
    Moore, R. G.
    Rundgren, John
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Zhang, Jiandi
    Cai, Lei
    Jin, R.
    Mandrus, D. G.
    Plummer, E. W.
    Procedure for LEED I-V structural analysis of metal oxide surfaces: Ca1.5Sr0.5RuO4(001)2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 3, p. 035408-Article in journal (Refereed)
    Abstract [en]

    Transition metal oxides (TMOs) are famous for the intimate coupling between the lattice, electrons, and spin, creating exotic functionality. Creating a surface, breaking the symmetry, should result in lattice distortions that due to the close coupling could create different "surface phases." Historically it has been very difficult to use low energy electron diffraction I-V to quantitatively determine the surface structure of TMOs. A signature of this problem is the large values commonly reported in the literature of the Pendry reliability factor (R-P), which is used to quantify the agreement between experimental data and calculated diffraction. In this paper we describe a consistent procedure for determining the phase shifts using an optimized muffin-tin potential approach combined with an energy-dependent real and imaginary inner potential. This procedure is used to determine the surface structure of the layered TMO Ca1.5Sr0.5RuO4. An acceptable Pendry reliability factor is achieved (R-P=0.28).

  • 548.
    Natarajan Arul, Murugan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Apostolov, Rossen Pavlov
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Kongsted, Jacob
    epartment of Physics, Chemistry and Pharmacy, University of Southern Denmark.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Association dynamics and linear and nonlinear optical properties of an N-acetylaladanamide probe in a POPC membrane2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 36, p. 13590-13597Article in journal (Refereed)
    Abstract [en]

    Along with the growing evidence that relates membrane abnormalities to various diseases, biological membranes have been acknowledged as targets for therapy. Any such abnormality in the membrane structure alters the membrane potential which in principle can be captured by measuring properties of specific optical probes. There exists by now many molecular probes with absorption and fluorescence properties that are sensitive to local membrane structure and to the membrane potential. To suggest new high-performance optical probes for membrane-potential imaging it is important to understand in detail the membrane-induced structural changes in the probe, the membrane association dynamics of the probe, and its membrane-specific optical properties. To contribute to this effort, we here study an optical probe, N-acetylaladanamide (NAAA), in the presence of a POPC lipid bilayer using a multiscale integrated approach to assess the probe structure, dynamics, and optical properties in its membrane-bound status and in water solvent. We find that the probe eventually assimilates into the membrane with a specific orientation where the hydrophobic part of the probe is buried inside the lipid bilayer, while the hydrophilic part is exposed to the water solvent. The computed absorption maximum is red-shifted when compared to the gas phase. The computations of the two-photon absorption and second harmonic generation cross sections of the NAAA probe in its membrane-bound state which is of its first kind in the literature suggest that this probe can be used for imaging the membrane potential using nonlinear optical microscopy.

  • 549. Nath, Pran
    et al.
    Malinsky, Michal
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zurek, K.
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    The Hunt for New Physics at the Large Hadron Collider2010In: NUCLEAR PHYSICS B: PROCEEDINGS SUPPLEMENTS, 2010, Vol. 200-02, p. 185-+Conference paper (Refereed)
    Abstract [en]

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

  • 550.
    Nikolaou, Marios
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    A Matter of Disorder: Monte Carlo Simulations of Phase Transitions in Strongly Disordered Systems2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Phase transitions and their critical scaling properties, especially in systems with disorder, are important both for our theoretical understanding of our environment, but also for their practical use in applications and materials in our everyday life. This thesis presents results from finite size scaling analysis of critical phenomena in systems with disorder, using high-precision Monte Carlo simulations and state of the art numerical methods. Specifically, theoretical models suitable for simulations in the presence of uncorrelated or correlated disorder are studied.

    Uncorrelated strong disorder, as present in the two dimensional gauge glass model to study the vortex glass phase of high temperature superconductors in an applied magnetic field is shown to lack a finite temperature phase transition. Further, results from dynamic quantities, such as resistance and autocorrelation functions, indicate the existence of two distinct diverging correlation times, one associated with local relaxation and one associated with vortex phase slips.

    Correlated disorder is studied both in the superfluid transition of helium-4 and in the anisotropic critical scaling of a transverse Meissner-like transition in an experimental setup of a high temperature superconductor. For the superfluid helium transition, it is shown that the presence of fractally correlated disorder presumably alters the universality class of the pure model. Also, a comparison with experimental data suggests that the critical scaling theory describing the heat capacity of helium-4 may need to be modified in the presence of the disorder. In the case of superconductors, analyzing experimental data from resistance measurements in a system with columnar defects together with an anisotropy in the applied magnetic field, reveals a fully anisotropic scaling regime.

    Finally, a data analysis is presented from simulations of a charged particle gas system in three dimensions, where the normal Coulomb interaction between charges is changed into a logarithmic interaction. Previous work indicates the possibility of a transition similar to the Kosterlitz-Thouless transition in certain two dimensional systems. On the contrary, our simulations seem to favor a system whose critical scaling behavior is consistent with a transition occurring only at zero critical temperature.

    Overall, disorder in the model systems studied leads to important modifications of the critical scaling properties of pure systems, and thereby also to possible changes of the corresponding universality classes. This results in interesting predictions with experimentally relevant consequences.

891011121314 501 - 550 of 764
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