Effects of Magnetic Fields on the Diskoseismic Modes of Accreting Black Holes

The origin of the rapid quasi-periodic variabilities observed in a number of accreting black hole X-ray binaries is not understood. It has been suggested that these variabilities are associated with diskoseismic oscillation modes of the black hole accretion disk. In particular, in a disk with no magnetic field, the so-called g-modes (inertial oscillations) can be self-trapped at the inner region of the disk due to general relativistic effects. Real accretion disks, however, are expected to be turbulent and contain appreciable magnetic fields. We show in this paper that even a weak magnetic field (with the magnetic energy much less than the thermal energy) can modify or "destroy" the self-trapping zone of disk g-modes, rendering their existence questionable in realistic black hole accretion disks. The so-called corrugation modes (c-modes) are also strongly affected when the poloidal field approaches equal-partition. On the other hand, acoustic oscillations (p-modes), which do not have vertical structure, are not affected qualitatively by the magnetic field, and therefore may survive in a turbulent, magnetic disk.Comment: 21 pages, 5 figures, accepted for publication in Ap

Nuclear Magnetic Relaxation Rate in the Vortex State of a Chiral p-Wave Superconductor

The site-selective nuclear spin-lattice relaxation rate T1^{-1} is theoretically studied inside a vortex core in a chiral p-wave superconductor within the framework of the quasiclassical theory of superconductivity. It is found that T1^{-1} at the vortex center depends on the sense of the chirality relative to the sense of the magnetic field. Our numerical result shows a characteristic difference in T1^{-1} between the two chiral states, k_x + i k_y and k_x - i k_y under the magnetic field.Comment: 2 pages, 2 figures; To be published in Physica C; Proc. of LT23, Hiroshima (Japan), 20-27 Aug. 200

Corotational Damping of Diskoseismic C-modes in Black Hole Accretion Discs

Diskoseismic c-modes in accretion discs have been invoked to explain low-frequency variabilities observed in black-hole X-ray binaries. These modes are trapped in the inner-most region of the disc and have frequencies much lower than the rotation frequency at the disc inner radius. We show that because the trapped waves can tunnel through the evanescent barrier to the corotational wave zone, the c-modes are damped due to wave absorption at the corotation resonance. We calculate the corotational damping rates of various c-modes using the WKB approximation. The damping rate varies widely depending on the mode frequency, the black hole spin parameter and the disc sound speed, and is generally much less than 10% of the mode frequency. A sufficiently strong excitation mechanism is needed to overcome this corotational damping and make the mode observable.Comment: 10 pages, 5 figures, MNRAS in pres