2,159 research outputs found

### Euclidean spinor Green's functions in the spacetime of a straight cosmic string

We determine generally the spinor Green's function and the twisted spinor
Green's function in an Euclidean space with a conical-type line singularity. In
particular, in the neighbourhood of the point source, we expree them as a sum
of the usual Euclidean spinor Green's functin and a regular term. In four
dimensions, we use these determinations to calculate the vacuum energy density
and the twisted one for a massless spinor field in the spacetime of a straight
cosmic string. In the Minkowski spacetime, we determine explicitly the vacuum
energy density for a massive twisted spinor field.Comment: 20 pages, latex, no figure

### Fine Structure Constant in the Spacetime of a Cosmic String

We calculate the fine structure constant in the spacetime of a cosmic string.
In the presence of a cosmic string the value of the fine structure constant
reduces. We also discuss on numerical results.Comment: 5 pages, Published in Phys. Lett.

### Electrostatics in a wormhole geometry

We determine in closed form the electrostatic potential generated by a point
charge at rest in a simple model of static spherically symmetric wormhole. From
this, we deduce the electrostatic self-energy of this point charge.Comment: latex, 5 pages, a slight correctio

### The south-pointing chariot on a surface

We examine closely the motion of the south-pointing chariot on a surface by
taking into account the fact that both wheels have to roll without slipping. We
firstly develop a procedure of successive approximations. In the limit where
the distance between the wheels tends to zero, we find again the result due to
Santander that the pointer is parallel transported. This is longer true
generally within the first-order approximation. We secondly determine in an
exact manner the motion of the south-pointing chariot on the sphere. Then, we
define a pointer and we prove that this one is parallel transported exactly.Comment: Latex, 16 pages with 3 figure

### Bending of a light ray within a dispersive medium in a uniform gravitational field

Recently, Dressel et al determined the vertical deflection of a light ray in
a medium, with a strong frequency-dependent dispersion, at rest in a uniform
gravitational field. We take up this question within the general relativistic
theory of the propagation of light in a dispersive medium, due to Synge.Comment: Latex, 4 page

### Time transfer functions in Schwarzschild-like metrics in the weak-field limit: A unified description of Shapiro and lensing effects

We present a complete analysis of the light rays within the linearized,
weak-field approximation of a Schwarzschild-like metric describing the
gravitational field of an isolated, spherically symmetric body. We prove in
this context the existence of two time transfer functions and we obtain these
functions in an exact closed-form. We are led to distinguish two regimes. In
the first regime, the two time transfer functions correspond to rays which are
confined in regions of spacetime where the weak-field approximation is valid.
Such a regime occurs in gravitational lensing configurations with double images
of a given source. We find the general expressions of the angular separation
and the difference in light travel time between the two images. In the second
regime, there exists only one time transfer function corresponding to a light
ray remaining in a region of weak field. Performing a Taylor expansion of this
function with respect to the gravitational constant, we obtain the Shapiro time
delay completed by a series of so-called "enhanced terms". The enhanced terms
beyond the third order are new.Comment: 12 pages, added one figure in section 3; a paragraph in Introduction
rewritten without changing the argument; corrected typos; one reference added
for section 2; Eq. (84) rewritten in a more elegant form; slightly revised
argument in section 9, results unchange

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