Chaos of particle motion near a black hole with quasitopological electromagnetism

We explore the chaotic behavior of particle motion in a black hole with quasitopological electromagnetism. The chaos bound is found to be violated in the higher order expansion of the metric function and the electric potential near the horizon. We draw the Poincaré sections of particle motion corresponding to the chaos bound violated and nonviolated cases, respectively. Then we study the relationship between the "maximal" Lyapunov exponent λs defined by the static equilibrium and the Lyapunov exponent of the particle geodesic motion near the Reissner-Nordström black hole and the black hole with quasitopological electromagnetism. We find an interesting relationship between the Lyapunov exponent λph of photon's radial falling into the black hole and the maximal Lyapunov exponent λs. For the black holes whose metric function increases monotonically with radius outside horizon, this leads to λph ≥ 2λs.