  We study the effect of Efimov physics (in the few-body sector) to the
spectral response of Bose polaron, a many-body system consisting of an impurity
immersed in a bath of bosonic atoms. We find that the Efimov correlation can be
greatly enhanced by increasing the mass ratio between the bosons and the
impurity, which results in visible signatures in the rf spectrum of the
polaron. Using a diagrammatic approach up to the third-order virial expansion,
we show how the mass imbalance and the enhanced three-body effect modify the
line shape and the width of the polaron spectrum. Moreover, we study the effect
of a finite boson-boson interaction to the spectrum. Taking the realistic
system of Li impurities immersed in Cs bosons with a positive Cs-Cs scattering
length, we find a visible Efimov branch, which is associated with the second
lowest Efimov trimer, in the polaron spectrum. In particular, by adjusting the
boson density the Efimov branch can greatly hybridize with the attractive
polaron branch leading to the spectrum broadening near their avoided level
crossing. Our results can be directly probed in the cold atoms experiments of
Li-Cs and Li-Rb Bose polarons.
