Can Branes Travel Beyond CTC Horizon in Gödel Universe ? ∗

Gödel universe in M-theory is a supersymmetric and homogeneous background with rotation and four-form magnetic flux. It is known that, as seen in inertial frame of co-moving observer, all geodesics with zero orbital angular momentum orbit inside ‘surface of light velocity’ (CTC horizon). To learn if other probes can travel beyond the CTC horizon, we study dynamics of M-graviton and, in particular, M2-brane, whose motion is affected by Lorentz force exerted by the four-form magnetic flux and by nonzero orbital angular momentum. Classically, we find that both probes gyrate closed orbits, but diameter and center of gyration depends on sign and magnitude of probe’s energy, charge and orbital angular momentum. For M2-brane, orbits in general travel outside the CTC horizon. Quantum-mechanically, we find that wave function and excitation energy levels are all self-similar. We draw analogy of probe’s dynamics with Landau problem for charged particle in magnetic field. Work supported in part by the KOSEF Interdisciplinary Research Grant 98-07-02-07-01-5 and the KOSEF Leading Scientist Grant. • Albert Einstein —– For us believing physicists, the distinction between the past, the present, and the future is only an illusion.