In the framework of the littlest Higgs model with $T$ parity, we study the contributions of the $T$-even and $T$-odd particles to the branching ratio $R_b$. We find that the precision data of $R_b$ can give strong constraints on the masses of $T$-odd fermions.

• Received 23 August 2009

DOI:https://doi.org/10.1103/PhysRevD.80.055027