Superstring theoryをめぐって(放談室)

Exact interior and exterior solutions to Einstein's field equations are derived for vacuum strings. The exterior solution for a uniform density vacuum string corresponds to a conical space while the interior solution is that of a spherical cap. For Mu equals 0-1/4 the external metric is ds-squared = -dt-squared + dr-squared + (1-4 Mu)-squared r-squared dphi-squared + dz-squared, where Mu is the mass per unit length in the string in Planck masses per Planck length. A maximum mass per unit length for a string is 6.73 x 10 to the 27th g/cm. It is shown that strings cause temperature fluctuations in the cosmic microwave background and produce equal brightness double QSO images separated by up to several minutes of arc. Formulae for lensing probabilities, image splittings, and time delays are derived for strings in a realistic cosmological setting. String searches using ST, the VLA, and the COBE satellite are discussed.

Gravitational Lensing Effects of Vacuum Strings: Exact Solutions

A spatially homogeneous and anisotropic exact Bianchi type-I string cosmological model is investigated in Brans-Dicke (1961) scalar-tensor theory of gravitation. Some properties of the model are also discussed.

A String cosmological model in Brans-Dicke theory of gravitation

In the spacetime induced by a rotating cosmic string we compute the energy levels of a massive spinless particle coupled covariantly to a homogeneous magnetic field parallel to the string. Afterwards, we consider the addition of a scalar potential with a Coulomb-type and a linear confining term and completely solve the Klein–Gordon equations for each configuration. Finally, assuming rigid-wall boundary conditions, we find the Landau levels when the linear defect is itself magnetized. Remarkably, our analysis reveals that the Landau quantization occurs even in the absence of gauge fields provided the string is endowed with spin.

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Relativistic Landau levels in the rotating cosmic string spacetime

Exact Bianchi type II, VIII and IX String cosmological models are obtained in the Saez-Ballester theory of gravitation. Some physical and geometrical properties of the models are studied.

Exact Bianchi type II, VIII and IX string cosmological models in Saez-Ballester theory of gravitation

The gravitational field of a stationary circular cosmic string loop, externally supported against collapse, is investigated in the context of Brans-Dicke theory in the weak field approximation of the field equations. The solution is quasi-conformally related to the corresponding solution in Einstein's General Relativity(GR) and goes over to the corresponding solution in GR when the Brans-Dicke parameter w becomes infinitely large.

/pdf/circular-cosmic-string-loop-in-brans-dicke-theory-4lqs7ly1fk.pdf

Circular cosmic string loop in Brans-Dicke theory

We consider global properties of gravitomagnetism by investigating the gravitomagnetic field of a rotating cosmic string. We show that although the gravitomagnetic field produced by such a configuration of matter vanishes locally, it can be detected globally. In this context we discuss the gravitational analogue of the Aharonov–Bohm effect.

/pdf/global-aspects-of-gravitomagnetism-besav41o5e.pdf

Global aspects of gravitomagnetism

We discuss the gravitomagnetism in the context of scalar-tensor theories of gravity. We obtain the equation of motion of a particle in terms of gravitoelectric and gravitomagnetic fields. We discuss the gravitomagnetic time delay and the Lense-Thirring effect in the context of scalar-tensor theories of gravity. In the particular case of Brans-Dicke Theory, we compare the results obtained with those predicted by general relativity and show that within the accuracy of experiments designed to measure these effects, both theories predict essentially the same results.

/pdf/on-some-aspects-of-gravitomagnetism-in-scalar-tensor-uwuphw5nyp.pdf

On some aspects of gravitomagnetism in scalar-tensor theories of gravity

We consider global properties of gravitomagnetism by investigating the gravitomagnetic field of a rotating cosmic string. We show that although the gravitomagnetic field produced by such a configuration of matter vanishes locally, it can be detected globally. In this context we discuss the gravitational analogue of the Aharonov-Bohm effect.

The gravitational field of a stationary circular cosmic string loop ,externally supported against collapse, is investigated in the context of Brans-Dicke theory in the weak field approximation of the field equations. The solution is quasi-conformally related to the corresponding solution in Einstein's General Relativity(GR) and goes over to the corresponding solution in GR when the Brans-Dicke parameter $\omega $ becomes infinitely large.

/pdf/circular-cosmic-string-loop-in-brans-dicke-theory-2s6absgpw1.pdf

A. Barros

Papers

Circular cosmic string loop in Brans-Dicke theory

Global aspects of gravitomagnetism

On some aspects of gravitomagnetism in scalar-tensor theories of gravity

Global aspects of gravitomagnetism

Circular Cosmic String Loop in Brans-Dicke Theory