J. P. Krisch

Two-fluid atmosphere for relativistic stars

We have extended the Vaidya radiating metric to include both a radiation fluid and a string fluid. This paper expands our brief introduction to extensions of the Schwarzschild vacuum which appeared in 1998 Phys. Rev. D 57 R5945. Assuming diffusive transport for the string fluid, we find new analytic solutions of Einsteins field equations.

Adding twist to anisotropic fluids

We present a solution generating technique for anisotropic fluids which preserves specific Killing symmetries. Anisotropic matter distributions that can be used with the one parameter Ehlers–Geroch transform are discussed. Example space–times that support the appropriate anisotropic stress-energy are found and the transformation applied. The 3+1 black string solution is one of the space–times with the appropriate matter distribution. Use of the transform with a black string seed is discussed.

Spinning fluid cosmologies in Einstein-Cartan theory

We consider self-consistent spinning fluid cosmologies in both general relativity in Riemannian spacetimes and Einstein-Cartan theory in Riemann-Cartan spacetimes. First we extend slightly the cosmological calculation of Martin et al for general relativistic self-consistent spinning fluids. The existence of spin-squared terms in the field equations in the Einstein-Cartan theory shows, however, that an expanded class of meaningful cosmologies is possible. Under certain assumptions on the arbitrariness of the cosmological shear and expansion the results for the ad hoc Weyssenhoff spin fluid in a spherically symmetric spacetime can be reproduced.

Fractional boundary for the Gott-Hiscock string

A fractional boundary condition is used to join the Gott-Hiscock string to a Levi-Civita vacuum. The use of a fractional derivative generates Israel boundary layers whose density depends on the order of the fractional derivative. Variable boundary layers for the same two bounding space–times can be studied. The string angular deficit depends on the order of the fractional deficit.

Including spin in the Raychaudhuri equation

The Raychaudhuri equation for a spin fluid matter content is developed. The equation is applied to the behavior of an irrotational, unaccelerated fluid. The development of singularities in the expansion is studied for constant spin densities.

Scale symmetries of spherical string fluids

We consider homothetic maps in a family of spherical relativistic star models. A generalization of Vaidya’s radiating metric provides a fluid atmosphere of radiation and strings. The similarity structure of the string fluid is investigated.

A family of strings with spin

Using an equivalence theorem, we discuss some stationary interiors for a string with spin density in a space with torsion. We show that there is a family of solutions characterized by the spin divergences and compare the solutions to string solutions in general relativistic spacetimes.

Fluids with spin and twist

Fluids with persistent vortices that exhibit shear plus expansion (or contraction) in noninertial frames are common physical phenomena. The concept of intrinsic rotation is commonly referred to as spin; the equivalent concept for shear would be shear momenta, referred to as twist in this work. The motion of the Earth’s atmosphere is a prime example of such motion in which the driving engine is the rotation of the Earth plus solar radiation. The general analytical features of persistent vortices that exhibit shear plus expansion and contraction are introduced using the methods of affine geometry. The same theoretical considerations can also be applied to astrophysical examples.

The Casimir energy of the twisted string loop: Uniform and two segment loops

We calculate the Casimir energy of a two segment loop of string with one normal boundary point and one twisted boundary point. The energy is renormalized relative to the twisted uniform loop. The use of the twisted loop in simplifying untwisted loop calculations is discussed.

Minimal coupling of electromagnetic fields in Riemann–Cartan space‐times for perfect fluids with spin density

The electromagnetic field is minimally coupled to gravity in a Riemann–Cartan space‐time containing a charged magnetized spinning fluid. It is required that the overall Lagrangian of the gravitational field, spinning matter, and the electromagnetic field be invariant under a gauge transformation of the vector potential. The theory preserves both charge conservation and particle number conservation. The electromagnetic field, via the vector potential, now interacts directly with the spin energy momentum. The spin transport equation, in addition to the usual Fermi–Walker transport term, contains a contribution due to the torque of the electromagnetic field acting on a magnetic dipole. In the absence of electromagnetism, the field equations reduce to those of the usual self‐consistent Lagrangian formalism for a perfect fluid with spin density.