Wave propagation in axion electrodynamics

In this paper, the axion contribution to the electromagnetic wave propagation is studied. First we show how the axion electrodynamics model can be embedded into a premetric formalism of Maxwell electrodynamics. In this formalism, the axion field is not an arbitrary added Chern-Simon term of the Lagrangian, but emerges in a natural way as an irreducible part of a general constitutive tensor.We show that in order to represent the axion contribution to the wave propagation it is necessary to go beyond the geometric approximation, which is usually used in the premetric formalism. We derive a covariant dispersion relation for the axion modified electrodynamics. The wave propagation in this model is studied for an axion field with timelike, spacelike and null derivative covectors. The birefringence effect emerges in all these classes as a signal of Lorentz violation. This effect is however completely different from the ordinary birefringence appearing in classical optics and in premetric electrodynamics. The axion field does not simple double the ordinary light cone structure. In fact, it modifies the global topological structure of light cones surfaces. In CFJ-electrodynamics, such a modification results in violation of causality. In addition, the optical metrics in axion electrodynamics are not pseudo-Riemannian. In fact, for all types of the axion field, they are even non-Finslerian

Identification of human papillomavirus DNA in cutaneous lesions of Cowden syndrome

Background: Cowden syndrome (CS) or multiple hamartoma syndrome is a cancer-associated genodermatosis inherited in an autosomal dominant pattern. One of the diagnostic criteria is facial papules which are felt to be trichilemmomas, benign hair follicle tumors, which some consider to be induced by human papillomavirus (HPV). Objective: To search for HPV in skin tumors, especially trichilemmomas, from patients with CS. Methods: Skin lesions from patients with CS were classified histologically. Each tumor was then analyzed for HPV DNA by polymerase chain reaction with different primer sets; positive amplicons were typed by direct sequencing. Results: Twenty-nine biopsies from 7 patients with CS were investigated. Only 2 of 29 tumors clinically suspected of being trichilemmomas were confirmed histologically. In addition, 3 sclerotic fibromas, also typical of CS, were found, as well as 1 sebaceous hyperplasia. The other 23 lesions showed histological features of HPV-induced tumors in various stages of development. HPV DNA was found in 19 of 29 cutaneous lesions. Tumors without any histological signs of HPV induction were negative for HPV DNA. Two tumors which were histologically classified as common warts contained HPV types 27 and 28. All the 17 other HPV types belong to the group of epidermodysplasia-verruciformis-associated types. Conclusions: The majority of cutaneous lesions in CS contain HPV DNA. They may have a variety of histological patterns. Trichilemmomas are not clinically distinctive and can be difficult to identify in CS patients. Copyright (C) 2003 S. Karger AG, Basel

Semiclassical Spectrum of Small Bose-Hubbard Chains: A Normal Form Approach

We analyze the spectrum of the 3-site Bose-Hubbard model with periodic boundary conditions using a semiclassical method. The Bohr-Sommerfeld quantization is applied to an effective classical Hamiltonian which we derive using resonance normal form theory. The derivation takes into account the 1:1 resonance between frequencies of a linearized classical system, and brings nonlinear terms into a corresponding normal form. The obtained expressions reproduce the exact low-energy spectrum of the system remarkably well even for a small number of particles N corresponding to fillings of just two particles per site. Such small fillings are often used in current experiments, and it is inspiring to get insight into this quantum regime using essentially classical calculations.Comment: Minor corrections to the coefficients of the effective Hamiltonian in Eqs 14,15,18,19. Figs 1,2 are slightly modified, correspondingl

Stationary wave patterns generated by an impurity moving with supersonic velocity through a Bose-Einstein condensate

Formation of stationary 3D wave patterns generated by a small point-like impurity moving through a Bose-Einstein condensate with supersonic velocity is studied. Asymptotic formulae for a stationary far-field density distribution are obtained. Comparison with three-dimensional numerical simulations demonstrates that these formulae are accurate enough already at distances from the obstacle equal to a few wavelengths.Comment: 7 pages, 3 figure

Matrix theory of gravitation

A new classical theory of gravitation within the framework of general relativity is presented. It is based on a matrix formulation of four-dimensional Riemann-spaces and uses no artificial fields or adjustable parameters. The geometrical stress-energy tensor is derived from a matrix-trace Lagrangian, which is not equivalent to the curvature scalar R. To enable a direct comparison with the Einstein-theory a tetrad formalism is utilized, which shows similarities to teleparallel gravitation theories, but uses complex tetrads. Matrix theory might solve a 27-year-old, fundamental problem of those theories (sec. 4.1). For the standard test cases (PPN scheme, Schwarzschild-solution) no differences to the Einstein-theory are found. However, the matrix theory exhibits novel, interesting vacuum solutions.Comment: 24 page

Intrinsic Photoconductivity of Ultracold Fermions in Optical Lattices

We report on the experimental observation of an analog to a persistent alternating photocurrent in an ultracold gas of fermionic atoms in an optical lattice. The dynamics is induced and sustained by an external harmonic confinement. While particles in the excited band exhibit long-lived oscillations with a momentum dependent frequency a strikingly different behavior is observed for holes in the lowest band. An initial fast collapse is followed by subsequent periodic revivals. Both observations are fully explained by mapping the system onto a nonlinear pendulum.Comment: 5+7 pages, 4+4 figure

Partial reconstitution of cutaneous microvessels in long-term survivors after allogeneic bone marrow transplantation

BACKGROUND: Graft-versus-host disease (GVHD) is a major complication after allogeneic hematopoietic stem cell transplantation (HSCT) and skin is involved in acute and chronic disease. Immune-mediated vessel attack and subsequent microvessel loss have been observed in skin of patients with chronic GVHD. OBJECTIVES: To test whether long-term survivors (LTS) after allogeneic HSCT without cutaneous GVHD show signs of persistent vascular remodeling. METHODS: Microvessels in skin biopsies were investigated in a cohort of 32 LTS with a median follow-up of 17 years (range 11-26). Five were currently classified as having chronic GVHD other than skin involvement. RESULTS: LTS showed no significant difference in median microvessel density and relative vessel size distribution pattern compared to healthy controls. Past experience of GVHD and current status of chronic GVHD other than skin involvement had no impact on vessel density. In contrast, recipients with chronic cutaneous GVHD of sclerotic type and patients with lichen sclerosus have significant microvessel loss in the upper dermis. CONCLUSION: The complex therapy of allogeneic HSCT had no sustained effect on the microvascular architecture of LTS when clinicopathological evidence of cutaneous GVHD is absent. Microvascular remodeling as observed during chronic GVHD recovers completely after resolution of chronic cutaneous GVHD

Universality in nonadiabatic behaviour of classical actions in nonlinear models with separatrix crossings

We discuss dynamics of approximate adiabatic invariants in several nonlinear models being related to physics of Bose-Einstein condensates (BEC). We show that nonadiabatic dynamics in Feshbach resonance passage, nonlinear Landau-Zener (NLZ) tunnelling, and BEC tunnelling oscillations in a double-well can be considered within a unifying approach based on the theory of separatrix crossings. The separatrix crossing theory was applied previously to some problems of classical mechanics, plasma physics and hydrodynamics, but has not been used in the rapidly growing BEC-related field yet. We derive explicit formulas for the change in the action in several models. Extensive numerical calculations support the theory and demonstrate its universal character. We also discovered a qualitatively new nonlinear phenomenon in a NLZ model which we propose to call {\em separated adiabatic tunnelling}Comment: Accepted for publication in Physical Review E; Several misprints are corrected; main results are emphasized in the end of Introduction (including finite conversion efficiency in Feshbach resonance passage due to geometric jump in the action); bibliography is extende

Conservation laws for vacuum tetrad gravity

Ten conservation laws in useful polynomial form are derived from a Cartan form and Exterior Differential System (EDS) for the tetrad equations of vacuum relativity. The Noether construction of conservation laws for well posed EDS is introduced first, and an illustration given, deriving 15 conservation laws of the free field Maxwell Equations from symmetries of its EDS. The Maxwell EDS and tetrad gravity EDS have parallel structures, with their numbers of dependent variables, numbers of generating 2-forms and generating 3-forms, and Cartan character tables all in the ratio of 1 to 4. They have 10 corresponding symmetries with the same Lorentz algebra, and 10 corresponding conservation laws.Comment: Final version with additional reference

Beyond Einstein-Cartan gravity: Quadratic torsion and curvature invariants with even and odd parity including all boundary terms

Recently, gravitational gauge theories with torsion have been discussed by an increasing number of authors from a classical as well as from a quantum field theoretical point of view. The Einstein-Cartan(-Sciama-Kibble) Lagrangian has been enriched by the parity odd pseudoscalar curvature (Hojman, Mukku, and Sayed) and by torsion square and curvature square pieces, likewise of even and odd parity. (i) We show that the inverse of the so-called Barbero-Immirzi parameter multiplying the pseudoscalar curvature, because of the topological Nieh-Yan form, can only be appropriately discussed if torsion square pieces are included. (ii) The quadratic gauge Lagrangian with both parities, proposed by Obukhov et al. and Baekler et al., emerges also in the framework of Diakonov et al.(2011). We establish the exact relations between both approaches by applying the topological Euler and Pontryagin forms in a Riemann-Cartan space expressed for the first time in terms of irreducible pieces of the curvature tensor. (iii) Only in a Riemann-Cartan spacetime, that is, in a spacetime with torsion, parity violating terms can be brought into the gravitational Lagrangian in a straightforward and natural way. Accordingly, Riemann-Cartan spacetime is a natural habitat for chiral fermionic matter fields.Comment: 12 page latex, as version 2 an old file was submitted by mistake, this is now the real corrected fil