Effects of an induced electric field on \pi^{-}/\pi^{+} ratio in   heavy-ion collisions
  Using an isospin- and momentum-dependent transport model, we examine the effects of an electric field induced by a variable magnetic field on the \pi^{-}/\pi^{+} ratio in central to peripheral heavy-ion collisions at beam energies of 400 and 1500MeV/nucleon. It is shown that while the induced electric field does not affect the total multiplicities of both $\pi^{-}$ and $\pi^{+}$ mesons at both the lower beam energy of 400MeV/nucleon and the higher beam energy of 1500MeV/nucleon, it reduces (enhances) the emission of $\pi^{-}$ ($\pi^{+}$) mesons in midrapidity, but enhances (reduces) the emission of $\pi^{-}$ ($\pi^{+}$) mesons in forward and backward rapidities especially for the more peripheral collisions at the lower beam energy because of the rapidly transient variable magnetic field at more peripheral collisions and longer reaction duration time at the lower beam energy. These findings indicate that the total \pi^{-}/\pi^{+} ratio is still a precisely reliable probe of symmetry energy at both the lower and higher beam energies, but one should consider the induced electric field when using the differential \pi^{-}/\pi^{+} ratio to probe the symmetry energy especially for the lower beam energy and more peripheral collisions. Finally, the relative suppression factor based on the ratio of \pi^{-}/\pi^{+} in different rapidities is proposed to be an effective probe of the induced electric field generated in heavy-ion collisions due to its maximizing effects of induced electric fields on the differential \pi^{-}/\pi^{+} ratio but minimizing effects of some uncertainty factors in heavy-ion collisions. 
Gao-Feng Wei, Shi-Hai Dong, Xin-Wei Cao, and Yun-Liang Zhang
nucl-th