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Charged elliptic flow at zero charge asymmetry

The difference between the flow ellipticities of oppositely charged pions, Δv_2=v_2[π-]-v_2[π+], measured recently by STAR collaboration at RHIC shows a linear dependence on the event charge asymmetry A_+-={(N_+-N_-)/ (N_++N_-)}: Δv_2(A_+-)= Δv_2(0)+ r A_+- with a slope r>0 and a non-zero intercept Δv_2(0)>0 of order 10^{-4}. We point out two novel mechanisms which could explain the non-zero value of the charged elliptic flow Δv_2 at zero charge asymmetry A_+-=0, i.e., the non-zero positive intercept Δv_2(0). Both effects are due to the electric fields created by the colliding ions. These fields have quadrupole asymmetry of the magnitude and the sign needed to account for the nonzero intercept Δv_2(0) in the RHIC data. One of the mechanisms also involves chiral magnetic effect. This mechanism, although negligible at RHIC energies, may become important at LHC energies.