Suppose the semimetal - the solid material, in which the conducting and valence zones are intersected at isolated points - the so-called Weyl nodes. Near this points, the Hamiltonian of electrons is effectively reduced to the Weyl-like Hamiltonian, $$ H_{W} = \pm v_{F}\sigma \cdot (\mathbf p - \mathbf p_{\pm}) $$ where "$\pm$" is what we called the chirality in solid bodies, and $v_{F} <1$ is the velocity of their propagation.
Suppose $\mathbf p_{\pm} = \pm \mathbf b$, so that there is non-zero distance $2\mathbf b$ between the Weyl nodes for left and right fermions in momentum space. Such semimetal is the particular case of so-called Weyl semimetal.
How to explain qualitatively that non-zero $\mathbf b$ implies the existence of anomalous Hall effect (AHE), namely, the current $$ \mathbf{J}_{\text{AHE}} \simeq \frac{e^{2}}{2\pi}[\mathbf b \times \mathbf E], $$ in presence of electric field?
