Search for a light extra gauge boson in Littlest Higgs model at a linear collider

Littlest Higgs model predicts some extra particles beyond the Standard Model. Among them, an extra neutral gauge boson A_H is lightest and its mass could be a few hundred GeV. We study production and decay of A_H at future e^+ e^- inear collider and compare them with those of Z' bosons in supersymmetric (SUSY) E_6 models. We find that, if the extra gauge boson mass is smaller than \sqrt{s} of the linear collider, the forward-backward asymmetries of b- and c-quarks at the A_H pole differ significantly from those given by the Z' bosons, and are useful to test the littlest Higgs model and SUSY E_6 models.