arXiv subjects

Andrew J. Janca

Publications and source records attributed to Andrew J. Janca.

3 recordsLinked to original sources

arXiv2007

Spinning straight cosmic strings with flat exterior solutions generically violate the weak energy condition

Any interior solution for a cylindrically symmetric, stationary cosmic string with flat exterior, spinning around its longitudinal axis, and without internal longitudinal currents ($g_{zz}=1$, $g_{tz}=0$), must somewhere violate the weak energy condition of standard general relativity. Existing interior solutions may be readily fixed by adding mass to the string above that generating its angular deficit, but at the cost of introducing an exterior gravitational field.

gr-qc↗

arXiv2007

Bounded, asymptotically flat toroidal exteriors for cylindrically symmetric spacetimes

A transitional layer matching the asymptotically flat exterior of a charged, massive toroidal body to an interior with spatially cylindrical symmetry is described. The changes in the geometry, which by themselves would require an energy tensor violating the energy conditions of classical general relativity, are compensated for by an additional strong electric field. Part of its gradient is consumed, depending on how much the exterior toroid departs from local cylindrical symmetry; what is left over can be used to effect further transitions in the cylindrical interior. An example is given of such a transition creating an angular deficit, allowing an otherwise infinite cosmic string to be captured within a bounded source.

gr-qc↗

arXiv2007

So you want to stop time

A model of a stasis chamber, slowing the passage of time in its interior down to arbitrarily small rates relative to the outside world, is considered within classical general relativity. Since the model is adapted from the Majumdar-Papapetrou spacetime, interior spatial volumes are expanded by the same factor (cubed) as the rate of time is reduced. Real and apparent (gravitational) forces as perceived by an interior observer are altered, but in opposite ways. Comparison with special-relativistic time dilation shows the use of such a static stasis chamber to be economical only when the most drastic slowing of time relative to the outside world is desired (d(tau)/dt < 10^{-20}) or when one wants to avoid spending the time needed to accelerate to relativistic speeds.

gr-qc↗