Showing papers in "Annalen der Physik in 2006"
TL;DR: In this article, the main approaches in quantizing general relativity: Covariant approaches (perturbation theory, effective theory, and path integrals) and canonical approaches (quantum geometrodynamics, loop quantum gravity).
Abstract: I briefly review the current status of quantum gravity. After giving some general motivations for the need of such a theory, I discuss the main approaches in quantizing general relativity: Covariant approaches (perturbation theory, effective theory, and path integrals) and canonical approaches (quantum geometrodynamics, loop quantum gravity). I then address quantum gravitational aspects of string theory. This is followed by a discussion of black holes and quantum cosmology. I end with some remarks on the observational status of quantum gravity.
130 citations
TL;DR: In this paper, an ansatz for the state-change which is essentially identical to the reduction of the wave function is proposed, which permits a deepening of the concept of compatibility of measurements.
Abstract: The statistical transformation theory contains procedures for the computation of measurement probabilities, but requires for its completion a statement about the state-change due to the measurement process. We discuss and reject an ansatz suggested for this by J. von Neumann. We submit an ansatz for the state-change which is essentially identical to the ‘reduction of the wave function’. It permits a deepening of the concept of compatibility of measurements. Finally, measurements of states subject to con straints are considered.
82 citations
TL;DR: In this paper, the authors present direct and independent measurements of both real and imaginary parts of the metallic conductivity in a large range of frequency around the scattering rate, showing that the key prediction of the Drude model, the frequency dependence of the complex conductivity with its pronounced roll-off was directly observed in an experiment only very recently.
Abstract: By now more than 100 years passed since Paul Drude suggested his highly acclaimed model of electronic transport. In the form advanced by A. Sommerfeld, the Drude model is still heavily utilized to describe, for instance, the optical properties of metals. Surprisingly, the key prediction of the Drude model, the frequency dependence of the complex conductivity with its pronounced roll-off was directly observed in an experiment only very recently. Here we present direct and independent measurements of both the real and imaginary parts of the metallic conductivity in a large range of frequency around the scattering rate.
81 citations
TL;DR: In this article, the authors review selected applications in solid-state materials physics and engineering addressing state-of-the-art ellipsometry concepts, focusing on the generalized ellipsometrical framework.
Abstract: In commemoration of the inventor – Paul Karl Ludwig Drude – examples of contemporary interest in the vivid field of ellipsometry are presented. More than 100 years after his provision of the general concept and the first experimental application, ellipsometry has matured as tool-of-excellence in almost all materials research areas. This contribution reviews selected applications in solid-state materials physics and engineering addressing state-of-the-art ellipsometry concepts. Particular emphasis is placed on the generalized ellipsometry framework. Infrared ellipsometry and magnetooptic infrared ellipsometry provide access to yet another important achievement of Paul Drude in optical physics: The free electron model in conductors, but also clearly reveal deviations from thereof within charge-correlated systems, exemplified here by the observation of Landau level splitting in two-dimensional electron gases using synchrotron light source ellipsometry at terahertz frequencies.
73 citations
TL;DR: In this paper, the authors report on recent advances in this area focusing on common patterns in correlated electron systems including transition metal oxides, intermetallics and organic conductors, which can be attributed to the formation of spin and/or charge ordered states, zero temperature phase transitions and strong coupling to bosonic modes.
Abstract: Infrared spectroscopy has emerged as a premier experimental technique to probe enigmatic effects arising from strong correlations in solids. Here we report on recent advances in this area focusing on common patterns in correlated electron systems including transition metal oxides, intermetallics and organic conductors. All these materials are highly conducting substances but their electrodynamic response is profoundly different from the canonical Drude behavior observed in simple metals. These unconventional properties can be attributed in several cases to the formation of spin and/or charge ordered states, zero temperature phase transitions and strong coupling to bosonic modes.
45 citations
TL;DR: In this article, the authors give a detailed treatment of cosmological perturbation theory and show how these initial perturbations evolve and produce the temperature anisotropies of the cosmic microwave background radiation.
Abstract: These lecture notes cover mainly three connected topics. In the first part we give a detailed treatment of cosmological perturbation theory. The second part is devoted to cosmological inflation and the generation of primordial fluctuations. In part three it will be shown how these initial perturbation evolve and produce the temperature anisotropies of the cosmic microwave background radiation. Comparing the theoretical prediction for the angular power spectrum with the increasingly accurate observations provides important cosmological information (cosmological parameters, initial conditions).
40 citations
TL;DR: In this paper, an algebraic frame for the simultaneous treatment of actual and possible properties of quantum systems is developed, in spite of the fact that the language is enriched with the addition of a modal operator to the orthomodular structure.
Abstract: We develop an algebraic frame for the simultaneous treatment of actual and possible properties of quantum systems. We show that, in spite of the fact that the language is enriched with the addition of a modal operator to the orthomodular structure, contextuality remains a central feature of quantum systems.
34 citations
TL;DR: Despite the presence of closed timelike curves and structures with noneuclidean topology in the space of solutions to the vacuum Einstein equations, neither appears common in the macroscopic universe as mentioned in this paper.
Abstract: Despite the presence of closed timelike curves and of structures with noneuclidean topology in the space of solutions to the vacuum Einstein equations, neither appears common in the macroscopic universe. Several recent results on topological censorship and chronology protection seek to explain why the macroscopic topology and causal structure of spacetime are ordinary.
32 citations
TL;DR: In this article, it is shown that at (c-2) this effect has a simple analogue in the electromagnetic case, and in view of a possible measurement of the clock effect in the gravitational field of the Earth, the influence of some classical perturbing forces of the terrestrial space environment on the orbital motion of test bodies along opposite trajectories is investigated.
Abstract: The general relativistic gravitomagnetic clock effect involves a coupling between the orbital motion of a test particle and the rotation of the central mass and results in a difference in the proper periods of two counter–revolving satellites. It is shown that at (c-2) this effect has a simple analogue in the electromagnetic case. Moreover, in view of a possible measurement of the clock effect in the gravitational field of the Earth, we investigate the influence of some classical perturbing forces of the terrestrial space environment on the orbital motion of test bodies along opposite trajectories.
29 citations
TL;DR: The content of the theory of gravitation is encoded in the properties of the solutions to his field equations as mentioned in this paper, which led to the prediction and the observation of physical phenomena which confirm the important role of general relativity in physics.
Abstract: The content of Einstein’s theory of gravitation is encoded in the properties of the solutions to his field equations. There has been obtained a wealth of information about these solutions in the ninety years the theory has been around. It led to the prediction and the observation of physical phenomena which confirm the important role of general relativity in physics. The understanding of the domain of highly dynamical, strong field configurations is, however, still quite limited. The gravitational wave experiments are likely to provide soon observational data on phenomena which are not accessible by other means. Further theoretical progress will require, however, new methods for the analysis and the numerical calculation of the solutions to Einstein’s field equations on large scales and under general assumptions. We discuss some of the problems involved, describe the status of the field and recent results, and point out some open problems.
28 citations
TL;DR: In this article, the frequency-dependent conductivity σ(o) of a gas of point charges was derived, showing that the width of the spectrum was related to the scattering rate of carriers.
Abstract: More than one hundred years ago Paul Drude derived the frequency-dependent conductivity σ(o) of a gas of point charges, showing that the width of the spectrum was related to the scattering rate of carriers. Seventy five years later, in the late 1970's and early 1980's, it was recognized that σ(o) of a two-dimensional superconductor above it's transition temperature Tc could be described by the Drude response of interpenetrating gases of electrons and vortices. Here we describe measurements of σ(o) in the high-Tc superconductor system Bi2Sr2Ca1-xDyxCu2O8+δ (BSCCO) using time-domain THz spectroscopy that provide evidence for vortices above Tc. We compare this evidence with results obtained by other probes of fluctuations in cuprate superconductors.
TL;DR: In this article, the anomalous Hall effect in disordered band ferromagnets is considered in the framework of quantum transport theory and the effect of strong impurity scattering is analyzed and it is found to affect the ratio of the non-diagonal and diagonal components of the conductivity as well as the relative importance of different mechanisms.
Abstract: The anomalous Hall effect in disordered band ferromagnets is considered in the framework of quantum transport theory. A microscopic model of electrons in a random potential of identical impurities including spin-orbit coupling is used. The Hall conductivity is calculated from the Kubo formula for both, the skew scattering and the side-jump mechanisms. The recently discussed Berry phase induced Hall current is also evaluated within the model. The effect of strong impurity scattering is analyzed and it is found to affect the ratio of the non-diagonal (Hall) and diagonal components of the conductivity as well as the relative importance of different mechanisms.
TL;DR: In this article, the authors briefly review some basic aspects of transport in clean metals focusing on the role of electron-electron interactions and neglecting the effects of impurities, phonons and interband transitions.
Abstract: We briefly review some basic aspects of transport in clean metals focusing on the role of electron-electron interactions and neglecting the effects of impurities, phonons and interband transitions. Both for small Fermi surfaces of two and three-dimensional metals and open Fermi surfaces of quasi one-dimensional metals the dc conductivity σ is largely dominated by momentum and pseudo-momentum conservation, respectively. In general, the frequency and temperature dependencies of σ(o,T) have very little in common. For small Fermi surfaces in three dimensions we find for example that the scattering rate is quadratic in frequency, Γ ∝ o2, even in the absence of a T2 contribution.
TL;DR: The first double-pulsar system was discovered in 2003, consisting of two visible pulsars which orbit the common centre of mass in a slightly eccentric orbit in only 24 hours as mentioned in this paper.
Abstract: This first-ever double-pulsar system was discovered in 2003, consisting of two visible pulsars which orbit the common centre of mass in a slightly eccentric orbit in only 24 hours One of the pulsars appears to be old and recycled with a spin period of only 22 ms Its companion is younger and rotating slower with a period of 28 s, confirming the long-proposed recycling theory for millisecond pulsars The system provides an exciting opportunity to study the workings of pulsar magnetospheres and represents a truly unique laboratory for relativistic gravitational physics Both aspects are greatly facilitated by the very fortunate fact that the orbit is seen nearly perfectly edge on This alignment allows the detection of the Shapiro delay in the pulse arrival times of the 22-ms pulsar when its pulses propagate through the curved space-time near the slowly rotating pulsar In addition to updating on the continuing observations, this contribution introduces a new timing model that represents a variation of Damour-Deruelle (1986) for highly inclined orbits (c) 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim
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TL;DR: In this paper, the authors considered the extension of the standard model with an arbitrary number of U(1) gauge fields coupled to baryon-minus-lepton number and/or hypercharge.
Abstract: We consider the extension of the standard model with an arbitrary number of U(1) gauge fields coupled to baryon-minus-lepton number and/or hypercharge. Under the assumption that Afb from the LEP1 experiment is an unlucky fluctuation, we find moderate evidence for the presence of such fields in the precision electroweak data. A relatively large range of the Higgs boson mass is allowed. We discuss the phenomenology of the extra U(1) fields.
TL;DR: In this paper, the evolution of charged particle production in collisions of heavy ions at relativistic energies is investigated as function of centrality in a nonequilibrium-statistical framework.
Abstract: The evolution of charged-particle production in collisions of heavy ions at relativistic energies is investigated as function of centrality in a nonequilibrium-statistical framework. Precise agreement with recent d + Au and Au + Au data at = 200 GeV is found in a Relativistic Diffusion Model with three sources for particle production. Only the midrapidity source comes very close to local equilibrium, whereas the analyses of the overall pseudorapidity distributions show that the systems remain far from statistical equilibrium.
TL;DR: In this article, the authors review alternative scenarios of the universe's future evolution, including Big-Rip (due to a phantom matter) and sudden future singularities, and reveal the reality of these singularities which comes from the relation to observational characteristics of universe expansion.
Abstract: Following the observational evidence for cosmic acceleration which may exclude a possibility for the universe to recollapse to a second singularity, we review alternative scenarios of its future evolution. Although the de Sitter asymptotic state is still an option, some other asymptotic states which allow new types of singularities such as Big-Rip (due to a phantom matter) and sudden future singularities are also admissible and are reviewed in detail. The reality of these singularities which comes from the relation to observational characteristics of the universe expansion are also revealed and widely discussed.
TL;DR: In this article, the authors present some Dark Energy models in the context of General Relativity and review the properties of dark energy models in scalar-tensor gravity, emphasizing that observations probing both the background and the perturbations will constrain the proposed model most effectively.
Abstract: The observed recent accelerated expansion of the Universe constitutes a dramatic departure from traditional views. The mechanism behind this accelerated expansion is still mysterious and is a major challenge to present-day cosmology. Though it can be due to a new perfect fluid with negative pressure coined Dark Energy, it could also originate from modifications of gravity. We present some Dark Energy models in the context of General Relativity and review in some details the properties of Dark Energy models in scalar-tensor gravity. We emphasize that observations probing both the background and the perturbations will constrain the proposed model most effectively.
TL;DR: In this paper, the Koopman-von Neumann (KvN) formulation of classical non-Abelian gauge field theories is studied and the classical path integral counterpart of the KvN formalism is explored.
Abstract: In this paper we present the Koopman-von Neumann (KvN) formulation of classical non-Abelian gauge field theories. In particular we shall explore the functional (or classical path integral) counterpart of the KvN method. In the quantum path integral quantization of Yang-Mills theories concepts like gauge-fixing and Faddeev-Popov determinant appear in a quite natural way. We will prove that these same objects are needed also in this classical path integral formulation for Yang-Mills theories. We shall also explore the classical path integral counterpart of the BFV formalism and build all the associated universal and gauge charges. These last are quite different from the analog quantum ones and we shall show the relation between the two. This paper lays the foundation of this formalism which, due to the many auxiliary fields present, is rather heavy. Applications to specific topics outlined in the paper will appear in later publications.
TL;DR: Cosmic strings are one-dimensional topological defects which could have been formed in the early stages of our universe as discussed by the authors, and they triggered a lot of interest, mainly for their cosmological implications: they could offer an alternative to inflation for the generation of density perturbations.
Abstract: Cosmic strings are one-dimensional topological defects which could have been formed in the early stages of our Universe. They triggered a lot of interest, mainly for their cosmological implications: they could offer an alternative to inflation for the generation of density perturbations. It was shown however that cosmic strings lead to inconsistencies with the measurements of the cosmic microwave background temperature anisotropies. The picture has changed recently. It was shown that, on the one hand, cosmic strings can be generically formed in the framework of supersymmetric grand unified theories and that, on the other hand, cosmic superstrings could play the role of cosmic strings. There is also some possible observational support. All this led to a revival of cosmic strings research and this is the topic of my lecture.
TL;DR: In this article, a low-energy effective string theory with higher-order string corrections to a tree-level action and with a modulus scalar field (dilaton or compactification modulus) is studied.
Abstract: We study cosmologies based on low-energy effective string theory with higher-order string corrections to a tree-level action and with a modulus scalar field (dilaton or compactification modulus). In the presence of such corrections it is possible to construct nonsingular cosmological solutions in the context of Pre-Big-Bang and Ekpyrotic universes. We review the construction of nonsingular bouncing solutions and resulting density perturbations in Pre-Big-Bang and Ekpyrotic models. We also discuss the effect of higher-order string corrections on a dark energy universe and show several interesting possibilities of the avoidance of future singularities.
TL;DR: Optical frequency combs from mode-locked femtosecond lasers have link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks as discussed by the authors.
Abstract: Optical frequency combs from mode-locked femtosecond lasers have link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks. By extending the limits of time and frequency metrology, they enable new tests of fundamental physics laws. Precise comparisons of optical resonance frequencies of atomic hydrogen and other atoms with the microwave frequency of a cesium atomic clock are establishing sensitive limits for possible slow variations of fundamental constants. Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy. Frequency comb techniques are also providing a key to attosecond science by offering control of the electric field of ultrafast laser pulses. In our laboratories at Stanford and Garching, the development of new instruments and techniques for precision laser spectroscopy has long been motivated by the goal of ever higher resolution and measurement accuracy in optical spectroscopy of the simple hydrogen atom which permits unique confrontations between experiment and fundamental theory. This lecture recounts these adventures and the evolution of laser frequency comb techniques from my personal perspective.
TL;DR: In this paper, the status of quantum cosmology is reviewed, including boundary conditions, singularity avoidance, the quantum-to-classical transition and the origin of irreversibility, and structure formation.
Abstract: I critically review the status of quantum cosmology. The expectations on such a theory are compared with the obtained results. The issues being discussed include the role of boundary conditions, singularity avoidance, the quantum-to-classical transition and the origin of irreversibility, and structure formation.
TL;DR: In this paper, the transition from point mechanics to wave mechanics is discussed in the context of complex projective geometry, and it is shown that the geometrical issues are more general than electromagnetism, namely, they pertain to the transition between point mechanics and wave mechanics.
Abstract: Some concepts of real and complex projective geometry are applied to the fundamental physical notions that relate to Minkowski space and the Lorentz group. In particular, it is shown that the transition from an infinite speed of propagation for light waves to a finite one entails the replacement of a hyperplane at infinity with a light cone and the replacement of an affine hyperplane – or rest space – with a proper time hyperboloid. The transition from the metric theory of electromagnetism to the pre-metric theory is discussed in the context of complex projective geometry, and ultimately, it is proposed that the geometrical issues are more general than electromagnetism, namely, they pertain to the transition from point mechanics to wave mechanics.
TL;DR: In the 25 years since the discovery of the first double quasar Q0957+561, gravitational lensing has established itself as a valuable tool in many branches of astronomy as mentioned in this paper.
Abstract: In the 25 years since the discovery of the first double quasar Q0957+561, gravitational lensing has established itself as a valuable tool in many branches of astronomy. Fields as different as galactic structure, cosmology, or extrasolar planets benefit from the gravitational lensing effect. This article starts with a brief historic reflection, then the basics of light deflection are reviewed. Observable lensing effects and a few examples of strong lensing phenomena are shown. In the main part four applications of ''strong'' lensing will be presented and discussed:
The determination of the Hubble constant from time delay measurements in multiple quasars; it is argued that this method of determining H0 is competitive with other methods by now. The lensing-derived values of H0 are on the low side.
Microlensing of quasars– the effects of compact stellar-mass objects on the apparent brightness – allows us to constrain the quasar size and the occurrence of dark matter objects.
The frequency of giant luminous arcs strongly depends on the high mass end of the galaxy cluster distribution. Recent investigations show that arc statistics is in agreement with the concordance cosmological model. Searching for extrasolar planets is one of the most recent applications of gravitational lensing. The first detection shows that the method works well. This planet-search method is complementary to other programs and has the potential to detect exo-planets with lower masses than other ground-based techniques.
An outlook is provided on the prospects of gravitational lensing in the next few years. In particular the magnification effect on faint high-redshift sources will be used for the investigation of the early universe, and the detection of low-mass extrasolar planets will provide a valuable sample for statistical evaluations of the frequency of exoplanets.
TL;DR: In this article, the authors focus on those aspects of dark matter that are relevant for understanding galaxy formation, and describe the outlook for detecting the most elusive component, non-baryonic dark matter.
Abstract: Dark matter presents a challenge for gravitational theory. It is best attacked in two ways; by studying the confrontation of structure formation with observation and by direct and indirect searches. In this review, I will focus on those aspects of dark matter that are relevant for understanding galaxy formation, and describe the outlook for detecting the most elusive component, non-baryonic dark matter.
TL;DR: A brief summary of a talk on rings surrounding Black Holes that was given at the spring meeting 2005 of the German physical society (DPG) can be found in [1].
Abstract: This paper provides a brief summary of a talk on rings surrounding Black Holes that was given at the spring meeting 2005 of the German physical society (DPG). A detailed discussion of the topics covered in the talk can be found in [1].