Dynamics of magnetized particles around a charged rotating BH in gravity with a background KR field
Abstract
We investigate the dynamics of magnetized particles orbiting a charged, rotating black hole in the presence of a background Kalb–Ramond (KR) field, a string-theory-inspired modification of general relativity. Using the Hamilton–Jacobi formalism, we derive the equations of motion for particles with magnetic dipole moments, incorporating their interaction with the electromagnetic field modified by the KR parameter. The effective potential, innermost stable circular orbits (ISCOs), and orbital stability are analyzed as functions of the black hole charge, spin, and the Lorentz-violating KR parameter. Our results show that the KR field alters both spacetime geometry and electromagnetic coupling, leading to measurable shifts in ISCO radii and orbital energy relative to Kerr–Newman and Schwarzschild cases. As an astrophysical application, we discuss implications for the magnetar PSR J1745–2900 near Sgr A*, highlighting potential observational signatures in synchrotron emission and pulsar timing. These results provide a framework for testing string-motivated gravity models in strong-field environments.