高频引力波与现代宇宙学

文章简要综述了由典型现代宇宙学模型和膜振荡模型预期的微波频带的高频引力波的特性和可能的观测方案,以及研究这一课题的重要科学意义和所面临的挑战和机遇.     

The Einstein-Rosen gravitational waves and cosmology

This paper reviews recent applications of the Einstein-Rosen type space-times to some problems of modern cosmology. An extensive overview of inhomogeneous universes filled with gravitational waves, classical fields, and relativistic fluids is given. The dynamics of primordial inhomogeneities, such as gravitational and matter waves and shocks, their interactions, and the global evolution of the models considered, is presented in detail.This paper is dedicated to the 75th birthday of Professor Nathan Rosen, who pioneered the topics considered here and founded the school of relativists to which the authors belong.     

Linear gravitational waves

The equations for a weak gravitational field are investigated without the usual simplifications; attention is paid to the difference between gravitational and electromagnetic waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 98–101, February, 1982.     

引力、引力波和引力波的探测

简要地回顾了引力和引力波概念的由来,以及人们为探测引力波所作的各种努力．     

A Newman-Penrose formalism for gravitational instantons

A Euclidean version of the Newman-Penrose formalism is developed for the study of gravitational instantons. The formalism is explicitly based on theSU(2)×SU(2) spin structure of positive definite metrics. A Geroch-Held-Penrose formulation is also presented. The Euclidean analogues of several fundamental results in relativity are proved, including the Petrov classification and the Ehlers-Sachs, Goldberg-Sachs, and Mariot-Robinson theorems. In addition, the connection between Petrov type and the admissibility of complex structures is elucidated.     

New gravitational tests of early universe cosmology

Gravitational waves and lenses were among the earliest predictions of general relativity. I demonstrate here how both these phenomena can, in conjunction with newly discovered astrophysical objects, be used to test fundamental aspects of early universe cosmology, including (a) scenarios for galaxy formation, and (b) nonadiabatic expansion before and after nucleosynthesis.Research supported in part by the N.S.F. under Grant No. PHY-82-15249.     

Imploding-exploding gravitational waves

A solution of Einstein's vacuum field equations is constructed describing an imploding spherical impulsive gravitational wave followed by an exploding similar wave. The two waves propagate in Minkowskian spacetime and the history of the process is the past and future sheets of the null-cone of an event (taken as origin) in the spacetime. The solution is a superposition of two of Penrose's impulsive wave solutions and is described in a single coordinate system in which the metric tensor components are continuous across the histories of the wave fronts.     

Linear coasting in cosmology and SNe Ia

A strictly linear evolution of the cosmological expansion scale factor is a characteristic feature in several classes of alternative gravity theories as also in the standard (Big-bang) model with specially chosen equations of state of matter. Such an evolution has no free parameters as far as the classical cosmological tests are concerned and should therefore be easily falsifiable. In this Letter we demonstrate how such models present very good fits to the current supernovae Ia data. We discuss the overall viability of such models.     

Probing the formalism through gravitational wave polarizations

The direct observation of gravitational waves (GW) in the near future, and the corresponding determination of the number of independent polarizations, is a powerful tool to test general relativity and alternative theories of gravity. In the present work we use the Newman–Penrose formalism to characterize GWs in quadratic gravity and in a particular class of f(R) Lagrangians. We find that both quadratic gravity and the f(R) theory belong to the most general invariant class of GWs, i.e., they can present up to six independent polarizations of GWs. For a particular combination of the parameters, we find that quadratic gravity can present up to five polarizations states. On the other hand, if we use the Palatini approach for f(R) theories, GWs present only the usual two transverse-traceless polarizations such as in general relativity. Thus, we conclude that the observation of GWs can strongly constrain the suitable formalism for these theories.     

On quadrupole and octupole gravitational radiation in the ANK formalism

Following the approach of Adamo–Newman–Kozameh (ANK) we derive the equations of motion for the center of mass and intrinsic angular moment for isolated sources of gravitational waves in axially symmetric spacetimes. The original ANK formulation is generalized so that the angular momentum coincides with the Komar integral for a rotational Killing symmetry. This is done using the Winicour–Tamburino Linkages which yields the mass dipole-angular momentum tensor for the isolated sources. The ANK formalism then provides a complex worldline in a fiducial flat space to define the notions of center of mass and spin. The equations of motion are derived and then used to analyse a very simple astrophysical process where only quadrupole and octupole contributions are included. The results are then compared with those coming from the post newtonian approximation.     

Using gravitational lenses to detect gravitational waves

Gravitational lenses could be used to detect gravitational waves, because a gravitational wave affects the travel-time of a light ray. In a gravitational lens, this effect produces time-delays between the different images. Thus the bending of light, which was the first experimental confirmation of Einstein's theory, can be used to search for gravitational waves, which are the most poorly confirmed aspect of that same theory. Applying this method to the gravitational lens 0957+561 gives new upper bounds on the amplitude of low-frequency gravitational waves in the universe, and new limits on the energy-density during an early inflationary phase.This Essay received the First Award from the Gravity Research Foundation, 1990-Ed.     

Nonlinear gravitational waves in plasma

An exact solution is obtained for the relativistic collisionless kinetic equations describing a test plasma in the field of a strong plane gravitational wave. The gravitational wave induces in the plasma a longitudinal electric current whose amplitude is maximum at temperatures Te ip m_ec². The interaction of gravitational waves with a system consisting of Boltzmann ions and degenerate electrons is also considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 20–24, July 1981.The authors thank G. G. Ivanov for a number of valuable comments.