arXiv subjects

Rostom Karsanov

Publications and source records attributed to Rostom Karsanov.

4 recordsLinked to original sources

arXiv2026

Taub-NUT as gravitational dyon with torsion

We show that the Levi-Civita connection for the Taub-NUT metric is singular on Misner strings and generates an Einstein tensor containing the squares of the delta function. This can be improved by introducing torsion, in which case the Einstein tensor may be interpreted as that of a cosmic string with negative variable tension. Komar flows in Misner strings are generated by torsion, which is therefore responsible for the asymptotic Komar charges. The Taub-NUT metric then appears as a soliton supported by two spin-fluid beams.

gr-qc↗

arXiv2026

Gravielectric and gravimagnetic fluxes in nutty black holes

We introduce the gravielectric (GE) and gravimagnetic (GM) fields in stationary spacetime using the Komar two-form and its dual. This opens the way to extend the Komar-Tomimatsu derivation of mass formulas to a more detailed picture in terms of the local lines of force. We show that Misner strings (MS) carry singular GE and GM fluxes connecting the horizon and the asymptotic zone. Moreover, MS are laterally transparent, so field lines can flow in and out of the bulk. This explains why the usual Komar mass integrals around the Misner strings in the Taub-NUT vacuum solution are negative: the pattern of field lines shows that they flow onto the string from the horizon, so it is necessary to calculate the incoming (positive) but not the outgoing Komar fluxes. This incoming flux is then turned back to the horizon through the Misner strings, realizing the closed circuit without sources. So Misner strings are massless empty tubes, but not rigid rods of negative mass. Similarly, GM field lines can connect positively and negatively charged regions of the horizon, generating, for example, the gravimagnetic dipole moment of the Kerr metric.

gr-qc↗

arXiv2026

Charged nutty black holes are hairy

We uncover the physical nature of the electric and magnetic monopoles discovered by McGuire and Ruffini on Misner strings accompanying charged nutty black holes, showing that these strings carry singular, nonuniform flows of electric and magnetic fields. These fields inevitably have nonzero divergence, thereby simulating the effective electric and magnetic charge densities along the strings. The latter create a complex short-range electromagnetic hair zone around the horizon, making the combined Misner-Dirac strings classically observable. Typical features of this new type of hair are presented. We also note that rotation can act as a hair generator even in the absence of NUT.

gr-qc↗

arXiv2025

Gauged supergravities: solutions with Killing tensor

We perform full integration of the stationary axisymmetric Einstein-Maxwell-dilaton-axion (EMDA) theory with and without potential using a recently proposed generalization of Carter's approach to spacetimes beyond type D, allowing the Killing tensor. Crucial to our construction is a new parametrization of the dilaton and axion fields based on the analyticity argument. The general solution in the ungauged case is asymptotically locally flat and contains two more parameters compared to EMDA black holes previously obtained using Harrison transformations. In the gauged case, the general solution is asymptotically AdS and includes flat and hyperbolic topological solutions, as well as generalization of the Kerr-Sen-AdS metric with three additional parameters. Our approach can be applied to more general four-dimensional ungauged and gauged supergravities.

gr-qc↗