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N. Straumann

Publications and source records attributed to N. Straumann.

14 recordsLinked to original sources
arXiv2023

Post-Newtonian Generation of Gravitational Waves in a Theory of Gravity with Torsion

We adapt the post-Newtonian gravitational-radiation methods developed within general relativity by Epstein and Wagoner to the gravitation theory with torsion, recently proposed by Hehl et al., and show that the two theories predict in this approximation the same gravitational radiation losses. Since they agree also on the first post-Newtonian level, they are at the present time - observationally - indistinguishable.

gr-qc↗
arXiv2023

Aharonov-Bohm effect in Presence of Superconductors

The analysis of a previous paper, in which it was shown that the energy for the Aharonov-Bohm effect could be traced to the interaction energy between the magnetic field of the electron and the background magnetic field, is extended to cover the case in which the magnetic field of the electron is shielded from the background magnetic field by superconducting material. The paradox that arises from the fact that such a shielding would apparently preclude the possibility of an interaction energy is resolved and, within the limits of the ideal situation considered, the observed experimental result is derived.

quant-ph↗
arXiv2000

On Pauli's invention of non-abelian Kaluza-Klein Theory in 1953

There are documents which show that Wolfgang Pauli developed in 1953 the first consistent generalization of the five-dimensional theory of Kaluza, Klein, Fock and others to a higher dimensional internal space. Because he saw no way to give masses to the gauge bosons, he refrained from publishing his results formally.

gr-qc↗
arXiv1999

Giant Arc Statistics and Cosmological Parameters

We study with semi-analytical methods the statistics of pronounced arcs caused by lensing of galaxies by foreground galaxy clusters. For the number density and redshift distribution of rich clusters we use Press-Schechter theory, normalized on the basis of empirical data. For the background sources we make use of observational results in the Hubble Deep Field. We present results for three different lens models, in particular for the universal profile suggested by Navarro, Frenk and White. Our primary concern is the dependence of the expected statistics on the cosmological parameters, $Ω_M$, $Ω_Λ$. The theoretical estimates are compared with the cluster arcs survey EMSS, and the resulting constraints in the $Ω$-plane are presented. In spite of considerable theoretical an observational uncertainties a low-density universe is favored. Degeneracy curves for the optical depth and likelihood regions for the arc statistics in the $Ω$-plane depend only weakly on the cosmological constant.

astro-ph↗
arXiv1999

The mystery of the cosmic vacuum energy density and the accelerated expansion of the Universe

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 scale of at least 100 GeV. The actual tiny value of the cosmological constant in any natural scale of units represents, therefore, one of the deepest mysteries of present day fundamental physics. We also briefly discuss recent astronomical evidence for a cosmologically significant vacuum energy density causing an accelerating expansion of the universe. This arises mainly from the Hubble diagram of type Ia supernovae and from the observed temperature fluctuations of the cosmic microwave background radiation. If this should become an established fact, we are also confronted with a disturbing {\it cosmic coincidence} problem.

astro-ph↗
arXiv1998

On rotational excitations and axial deformations of BPS monopoles and Julia-Zee dyons

It is shown that Julia-Zee dyons do not admit slowly rotating excitations. This is achieved by investigating the complete set of stationary excitations which can give rise to non-vanishing angular momentum. The relevant zero modes are parametrized in a gauge invariant way and analyzed by means of a harmonic decomposition. Since general arguments show that the solutions to the linearized Bogomol'nyi equations cannot contribute to the angular momentum, the relevant modes are governed by a set of electric and a set of non self-dual magnetic perturbation equations. The absence of axial dipole deformations is also established.

gr-qc↗
arXiv1997

Internal structure of Einstein-Yang-Mills-Dilaton black holes

We study the interior structure of the Einstein-Yang-Mills-Dilaton black holes as a function of the dilaton coupling constant $γ\in [0,1]$. For $γ\neq 0$ the solutions have no internal Cauchy horizons and the field amplitudes follow a power law behavior near the singularity. As $γ$ decreases, the solutions develop more and more oscillation cycles in the interior region, whose number becomes infinite in the limit $γ\to 0$.

gr-qc↗
arXiv1997

Rotating solitons and non-rotating, non-static black holes

It is shown that the non-Abelian black hole solutions have stationary generalizations which are parameterized by their angular momentum and electric Yang-Mills charge. In particular, there exists a non-static class of stationary black holes with vanishing angular momentum. It is also argued that the particle-like Bartnik-McKinnon solutions admit slowly rotating, globally regular excitations. In agreement with the non-Abelian version of the staticity theorem, these non-static soliton excitations carry electric charge, although their non-rotating limit is neutral.

gr-qc↗
arXiv1996

Cosmological Analogues of the Bartnik--McKinnon Solutions

We present a numerical classification of the spherically symmetric, static solutions to the Einstein--Yang--Mills equations with cosmological constant $Λ$. We find three qualitatively different classes of configurations, where the solutions in each class are characterized by the value of $Λ$ and the number of nodes, $n$, of the Yang--Mills amplitude. For sufficiently small, positive values of the cosmological constant, $Λ< \Llow(n)$, the solutions generalize the Bartnik--McKinnon solitons, which are now surrounded by a cosmological horizon and approach the deSitter geometry in the asymptotic region. For a discrete set of values $Λ_{\rm reg}(n) > Λ_{\rm crit}(n)$, the solutions are topologically $3$--spheres, the ground state $(n=1)$ being the Einstein Universe. In the intermediate region, that is for $\Llow(n) < Λ< \Lhig(n)$, there exists a discrete family of global solutions with horizon and ``finite size''.

hep-th↗
arXiv1995

Pulsation of Spherically Symmetric Systems in General Relativity

The pulsation equations for spherically symmetric black hole and soliton solutions are brought into a standard form. The formulae apply to a large class of field theoretical matter models and can easily be worked out for specific examples. The close relation to the energy principle in terms of the second variation of the Schwarzschild mass is also established. The use of the general expressions is illustrated for the Einstein-Yang-Mills and the Einstein-Skyrme system.

gr-qc↗
arXiv1994

Instability of Gravitating Sphalerons

We prove the instability of the gravitating regular sphaleron solutions of the $SU(2)$ Einstein-Yang-Mills-Higgs system with a Higgs doublet, by studying the frequency spectrum of a class of radial perturbations. With the help of a variational principle we show that there exist always unstable modes. Our method has the advantage that no detailed knowledge of the equilibrium solution is required. It does, however, not directly apply to black holes.

gr-qc↗
arXiv1994

Instability of Einstein-Yang-Mills Solitons for Arbitrary Gauge Groups

We prove that static, spherically symmetric, asymptotically flat, regular solutions of the Einstein-Yang-Mills equations are unstable for arbitrary gauge groups. The proof involves the following main steps. First, we show that the frequency spectrum of a class of radial perturbations is determined by a coupled system of radial "Schroedinger equations". Eigenstates with negative eigenvalues correspond to exponentially growing modes. Using the variational principle for the ground state it is then proven that there always exist unstable modes (at least for "generic" solitons). This conclusion is reached without explicit knowledge of the possible equilibrium solutions.

gr-qc↗
arXiv1993

Selfgravitating Yang-Mills solitons and their Chern-Simons numbers

We present a classification of the possible regular, spherically symmetric solutions of the Einstein-Yang-Mills system which is based on a bundle theoretical analysis for arbitrary gauge groups. It is shown that such solitons must be of magnetic type, at least if the magnetic Yang-Mills charge vanishes. Explicit expressions for the Chern-Simons numbers of these selfgravitating Yang-Mills solitons are derived, which involve only properties of irreducible root systems and some information about the asymptotics of the solutions. It turns out, as an example, that the Chern-Simons numbers are always half-integers or integers for the gauge groups $SU(n)$. Possible physical implications of these results, which are based on analogies with the unstable sphaleron solution of the electroweak theory, are briefly indicated.

gr-qc↗