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Norbert Straumann

Publications and source records attributed to Norbert Straumann.

At least 37 records · Page 2Linked to original sources
arXiv2004

Cosmological Phase Transitions

In this lecture at a school for condensed matter physicists, I begin with basic concepts and tools for investigating phase transitions in quantum field theory. The very different roles of global and gauge symmetries in phase transitions will be elucidated. Among the important applications of the basic theory the thermodynamics of the electroweak transition is treated in detail, and the implications for baryogenesis will be discussed. The status of lattice simulations of the transition from a high temperature quark-gluon plasma to confined hadronic matter with spontaneously broken chiral symmetry is also briefly reviewed. The various changes of the free energy density in cosmological phase transitions reinforce the cosmological constant problem. In the last part of the lecture I shall address this profound mystery of present day physics.

astro-ph↗
arXiv2004

The Role of the Exclusion Principle for Atoms to Stars: A Historical Account

In a first historical part I shall give a detailed description of how Pauli discovered --before the advent of the new quantum mechanics -- his exclusion principle. The second part is devoted to the insight and results that have been obtained in more recent times in our understanding of the stability of matter in bulk, both for ordinary matter (like stones) and self-gravitating bodies.

quant-ph↗
arXiv2003

Dark Energy

After some remarks about the history and the mystery of the vacuum energy I shall review the current evidence for a cosmologically significant nearly homogeneous exotic energy density with negative pressure (`Dark Energy'). Special emphasis will be put on the recent polarization measurements by WMAP and their implications. I shall conclude by addressing the question: Do the current observations really imply the existence of a dominant dark energy component?

gr-qc↗
arXiv2002

The history of the cosmological constant problem

The interesting early history of the cosmological term is reviewed, beginning with its introduction by Einstein in 1917 and ending with two papers of Zel'dovich, shortly before the advent of spontaneously broken gauge theories. Beside classical aspects, I shall also mention some unpublished early remarks by Pauli on possible contributions of vacuum energies in quantum field theory.

gr-qc↗
arXiv2002

On the Cosmological Constant Problems and the Astronomical Evidence for a Homogeneous Energy Density with Negative Pressure

In this article the cosmological constant problems, as well as the astronomical evidence for a cosmologically significant homogeneous exotic energy density with negative pressure (quintessence), are reviewed for a broad audience of physicists and mathematicians. After a short history of the cosmological term it is explained why the (effective) cosmological constant is expected to obtain contributions from short-distance physics corresponding to an energy scale at least as large as the Fermi scale. The actual tiny value of the cosmological constant by particle physics standards represents, therefore, one of the deepest mysteries of present-day fundamental physics. In a second part I shall discuss recent astronomical evidence for a cosmologically significant vacuum energy density or an effective equivalent, called quintessence. Cosmological models, which attempt to avoid the disturbing cosmic coincidence problem, are also briefly reviewed.

astro-ph↗
arXiv2001

Schroedinger discovery of wave mechanics

Schroedinger's great discovery of wave mechanics in 1926 - his annus mirabilis - is discussed in detail. Beside the six most important papers that appeared during the first half of 1926, letters between Schroedinger and leading physicists at this time are main sources of this account.

quant-ph↗
arXiv2001

Weak and Strong Lensing Statistics

After a brief introduction to gravitational lensing theory, a rough overview of the types of gravitational lensing statistics that have been performed so far will be given. I shall then concentrate on recent results of galaxy-galaxy lensing, which indicate that galactic halos extend much further than can be probed via rotation of stars and gas.

astro-ph↗
arXiv2000

On Wolfgang Pauli's most important contributions to physics

After some brief biographical notes, Wolfgang Pauli's main contributions to general relativity, quantum theory, quantum field theory, and elementary particle physics are reviewed. A detailed description is given how Pauli descovered - before the advent of the new quantum mechanics - his exclusion principle.

physics.hist-ph↗
arXiv2000

".. I didn't reflect much on what I was doing.." How Planck discovered his radiation formula

On December 14. 1900, Max Planck communicated his derivation of his radiation formula, which he later called ``an act of desperation''. This date is widely recognized as birthday of quantum theory. For Planck it meant the end of his carefully planned and ambitious research project, in which he wanted to establish the second law of thermodynamics as strictly deterministic law for systems of matter and electromagnetic radiation in interaction. He knew he could not succeed within classical mechanics, but had the somewhat strange hope that the inclusion of Maxwell's electrodynamics would change the situation. Later he always disagreed with Einstein's light-quantum hypothesis, because it implied a renunciation from Maxwell's theory, which in Germany gained full recognition and acceptance as late as the 1890's, mainly through the theoretical and experimental work of Heinrich Hertz.

quant-ph↗
arXiv2000

On the mystery of the cosmic vacuum energy density

After a short history of the $Λ$-term it is explained why the (effective) cosmological constant is expected to obtain contributions from short-distance physics, corresponding to an energy at least as large as the Fermi scale. The actual tiny value of the cosmological constant by particle physics standards represents, therefore, one of the deepest mysteries of present-day fundamental physics. Recent proposals of an approach to the cosmological constant problem which make use of (large) extra dimensions are briefly discussed. Cosmological models with a dynamical $Λ$, which attempt to avoid the disturbing cosmic coincidence problem, are also reviewed.

astro-ph↗
arXiv2000

The mystery of cosmological vacuum energy density and the accelerated expansion of the universe

The principles of General Relativity allow for a non-vanishing cosmological constant, which can possibly be interpreted at least partially in terms of quantum-fluctuations of matter fields. Depending on sign and magnitude it can cause accelerated or decelerated expansion at certain stages of cosmic evolution. Recent observations in cosmology seem to indicate that we presently live in an accelerated phase. We recall the history and fundamental issues connected with the cosmological constant and then discuss present evidences for a positive value, which causes the accelerated expansion.

astro-ph↗
arXiv2000

Reflections on Gravity

A pedagogical description of a simple ungeometrical approach to General Relativity is given, which follows the pattern of well understood field theories, such as electrodynamics. This leads quickly to most of the important weak field predictions, as well as to the radiation damping of binary pulsars. Moreover, certain consistency arguments imply that the theory has to be generally invariant, and therefore one is bound to end up with Einstein's field equations. Although this field theoretic approach, which has been advocated repeatedly by a number of authors, starts with a spin-2 theory on Minkowski spacetime, it turns out in the end that the flat metric is actually unobservable, and that the physical metric is curved and dynamical. Short sections are devoted to tensor-scalar generalizations, the mystery of the vacuum energy density, and quintessence.

astro-ph↗
arXiv1999

Early History of Gauge Theories and Kaluza-Klein Theories, with a Glance at Recent Developments

One of the major developments of twentieth century physics has been the gradual recognition that a common feature of the known fundamental interactions is their gauge structure. In this article the authors review the early history of gauge theory, from Einstein's theory of gravitation to the appearance of non-abelian gauge theories in the fifties. The authors also review the early history of dimensional reduction, which played an important role in the developement of gauge-theory. A description is given how, in recent times, the ideas of gauge-theory and dimensional reduction have emerged naturally in the context of string theory and non-commutative geometry.

hep-ph↗
arXiv1998

Historical and other Remarks on Hidden Symmetries

Apart from a few remarks on lattice systems with global or gauge symmetries, most of this talk is devoted to some interesting ancient examples of symmetries and their breakdowns in elasticity theory and hydrodynamics. Since Galois Theory is in many ways the origin of group theory as a tool to analyse (hidden) symmetries, a brief review of this profound mathematical theory is also given.

hep-ph↗
arXiv1997

The Membrane Model of Black Holes and Applications

These lectures provide a detailed introduction to the electro- dynamics of black holes. A simplified derivation of the basic membrane equations for stationary, axisymmetric black holes is given. The general theory is applied to idealized current generators involving rotating black holes, and we also analyse the Blandford-Znajek process for magnetic energy extraction from rotating black holes.

astro-ph↗
arXiv1997

Slowly Rotating Non-Abelian Black Holes

It is shown that the well-known non-Abelian static SU(2) black hole solutions have rotating generalizations, provided that the hypothesis of linearization stability is accepted. Surprisingly, this rotating branch has an asymptotically Abelian gauge field with an electric charge that cannot vanish, although the non-rotating limit is uncharged. We argue that this may be related to our second finding, namely that there are no globally regular slowly rotating excitations of the particle-like Bartnik-McKinnon solutions.

hep-th↗
arXiv1997

Complex Formulation of Lensing Theory and Applications

The elegance and usefulness of a complex formulation of the basic lensing equations is demonstrated with a number of applications. Using standard tools of complex function theory, we present, for instance, a new proof of the fact that the number of images produced by a regular lens is always odd, provided that the source is not located on a caustic. Several differential and integral relations between the mean curvature and the (reduced) shear are also derived. These emerge almost automatically from complex differentiations of the differential of the lens map, together with Stokes' theorem for complex valued 1-forms.

astro-ph↗