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Search Results: 1 - 10 of 208615 matches for " L. Bergamin "
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Negative index of refraction, spacetime folding and perfect imaging in transformation optics
L. Bergamin
Physics , 2009,
Abstract: Negative index of refraction has become an accepted part of transformation optics, which is encountered in transformations that change the orientation of the manifold. Based on this concept, various designs of perfect lenses have been proposed, which all rely on a folding of space or spacetime, where the maps from electromagnetic space to laboratory space are multi-valued. Recently, a new concept for perfect imaging has been proposed by Leonhardt and Philbin, which also uses multi-valued maps, but does neither include negative index of refraction nor an amplification of evanescent modes. In this context it was speculated that multi-valued maps should be seen as the basis of perfect imaging rather than amplification of evanescent modes. It might be useful to review the standard lens based on negative index of refraction from this point of view. In this paper we show that a negative index of refraction is not an inherent characteristic of transformation optics, but rather appears as a specific choice of a sign ambiguity. Furthermore, we point out that the transformation designed lens does not amplify evanescent modes, in contrast to the Pendry-Veselago lens. Instead, evanescent modes at the image point are produced by a duplicated source and thus no imaging of the near field takes place.
Generalized transformation optics from triple spacetime metamaterials
L. Bergamin
Physics , 2008, DOI: 10.1103/PhysRevA.78.043825
Abstract: In this paper various extensions of the design strategy of transformation media are proposed. We show that it is possible to assign different transformed spaces to the field strength tensor (electric field and magnetic induction) and to the excitation tensor (displacement field and magnetic field), resp. In this way, several limitations of standard transformation media can be overcome. In particular it is possible to provide a geometric interpretation of non-reciprocal as well as indefinite materials. We show that these transformations can be complemented by a continuous version of electric-magnetic duality and comment on the relation to the complementary approach of field-transforming metamaterials.
Electromagnetic fields and boundary conditions at the interface of generalized transformation media
L. Bergamin
Physics , 2009, DOI: 10.1103/PhysRevA.80.063835
Abstract: In this paper the interface between two transformation media or between a transformation medium and vacuum is studied. Strictly from the transformation optics point of view the consequences of the boundary conditions at such interfaces are addressed in two different ways. First, we analyze a restricted class of reflectionless interfaces, for which the tools of transformation optics allow to describe the electromagnetic fields on both sides of the interface by means of the same vacuum solution of the Maxwell equations. In a second step, we examine interfaces between two arbitrary transformation media. This analysis is extended to the recently suggested generalization of transformation optics by the author. As a basic application it is shown how the standard law of reflection and refraction at an interface between vacuum and a homogeneous and isotropic medium with arbitrary and independent permittivity and permeability can be understood in a completely geometric way by the use of generalized transformation optics.
Dynamical Symmetry Breaking in SYM Theories as a Non-Semiclassical Effect
L. Bergamin
Physics , 2001, DOI: 10.1140/epjc/s2002-01034-1
Abstract: We study supersymmetry breaking effects in N=1 SYM from the point of view of quantum effective actions. Restrictions on the geometry of the effective potential from superspace are known to be problematic in quantum effective actions, where explicit supersymmetry breaking can and must be studied. On the other hand the true ground state can be determined from this effective action, only. We study whether some parts of superspace geometry are still relevant for the effective potential and discuss whether the ground states found this way justify a low energy approximation based on this geometry. The answer to both questions is negative: Essentially non-semiclassical effects change the behavior of the auxiliary fields completely and demand for a new interpretation of superspace geometry. These non-semiclassical effects can break supersymmetry.
Black holes as boundaries in 2D dilaton supergravity
L. Bergamin,D. Grumiller
Physics , 2007,
Abstract: We discuss 2D dilaton supergravity in the presence of boundaries. Generic ones lead to results different from black hole horizon boundaries. In particular, the respective numbers of physical degrees of freedom differ, thus generalizing the bosonic results of hep-th/0512230.
Dynamical Symmetry Breaking and Static Limits of Extended Super-Yang-Mills Theories: A non-Seiberg-Wittian Approach
L. Bergamin,P. Minkowski
Physics , 2000,
Abstract: From a supersymmetry covariant source extension of N=2 SYM we study non-trivial thermodynamical limits thereof. Using an argument by one of us about the solution of the strong CP problem and the uniqueness of the QCD ground state we find that the dependence of the effective potential on the defining field operators is severely restricted. In contrast to the solution by Seiberg and Witten an acceptable infrared behavior only exists for broken supersymmetry while the gauge symmetry remains unbroken.
SUSY Glue-Balls, Dynamical Symmetry Breaking and Non-Holomorphic Potentials
L. Bergamin,P. Minkowski
Physics , 2003,
Abstract: We discuss the instability of the Veneziano-Yankielowicz effective action (or its supersymmetric ground-state) with respect to higher order derivative terms. As such terms must be present in an effective action, the V-Y action alone cannot describe the dynamics of SYM consistently. We introduce an extension of this action, where all instabilities are removed by means of a much richer structure of the Kaehler potential. We demonstrate that the dominant contributions to the effective potential are determined by the non-holomorphic part of the action and we prove that the non-perturbative ground-state can be equipped with stable dynamics. Making an expansion near the resulting ground-state to second order in the derivatives never leads back to the result by Veneziano and Yankielowicz. As a consequence new dynamical effects arise, which are interpreted as the formation of massive states in the boson sector (glueballs) and are accompanied by dynamical supersymmetry breaking. As this regime of the dynamics is not captured by standard semi-classical analysis (instantons etc.), our results do not contradict these calculations but investigate the physics of the system beyond these approximations.
Graded Poisson-Sigma Models and Dilaton-Deformed 2D Supergravity Algebra
L. Bergamin,W. Kummer
Physics , 2002, DOI: 10.1088/1126-6708/2003/05/074
Abstract: Fermionic extensions of generic 2d gravity theories obtained from the graded Poisson-Sigma model (gPSM) approach show a large degree of ambiguity. In addition, obstructions may reduce the allowed range of fields as given by the bosonic theory, or even prohibit any extension in certain cases. In our present work we relate the finite W-algebras inherent in the gPSM algebra of constraints to algebras which can be interpreted as supergravities in the usual sense (Neuveu-Schwarz or Ramond algebras resp.), deformed by the presence of the dilaton field. With very straightforward and natural assumptions on them --like demanding rigid supersymmetry in a certain flat limit, or linking the anti-commutator of certain fermionic charges to the Hamiltonian constraint-- in the ``genuine'' supergravity obtained in this way the ambiguities disappear, as well as the obstructions referred to above. Thus all especially interesting bosonic models (spherically reduced gravity, the Jackiw-Teitelboim model etc.)\ under these conditions possess a unique fermionic extension and are free from new singularities. The superspace supergravity model of Howe is found as a special case of this supergravity action. For this class of models the relation between bosonic potential and prepotential does not introduce obstructions as well.
Killing horizons kill horizon degrees
L. Bergamin,D. Grumiller
Physics , 2006, DOI: 10.1142/S0218271806009571
Abstract: Frequently it is argued that the microstates responsible for the Bekenstein-Hawking entropy should arise from some physical degrees of freedom located near or on the black hole horizon. In this Essay we elucidate that instead entropy may emerge from the conversion of physical degrees of freedom, attached to a generic boundary, into unobservable gauge degrees of freedom attached to the horizon. By constructing the reduced phase space it can be demonstrated that such a transmutation indeed takes place for a large class of black holes, including Schwarzschild.
On the Effective Description of Dynamically Broken SUSY-Theories
L. Bergamin,P. Minkowski
Physics , 2002,
Abstract: We introduce a new class of effective actions describing dynamically broken supersymmetric theories in an essentially non-perturbative region. Our approach is a generalization of the known supersymmetric non-linear sigma models, but allows in contrast to the latter the description of dynamical supersymmetry breaking by non-perturbative non-semiclassical effects. This non-perturbative breaking mechanism takes place in confined theories, where the effective fields are composite operators. It is necessary within the context of quantum effective actions and the associated concept of symmetry breaking as a hysteresis effect. In this paper we provide a mathematical definition and description of the actions, its application to specific supersymmetic gauge theories is presented elsewhere.
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