  Since the Efimov effect was introduced in 1970, a detailed theoretical
understanding of Efimov physics has been developed in the few-body context.
However, it has proven to be challenging to describe the role Efimov-type
correlations play in many-body systems such as quenched or collapsing
Bose-Einstein condensates (BECs). To study the impact the Efimov effect can
have in such scenarios, we consider a light impurity immersed in a weakly
interacting BEC, forming a Bose polaron. In this case, the higher-order
correlations are localized around the impurity, making it more feasible to
develop a theoretical description. Specifically, we employ a Gaussian state
variational Ansatz in the reference frame of the impurity, capable of both
capturing the Efimov effect and the formation of the polaron cloud. We find
that the Efimov effect leads to a cooperative binding of bosons to the impurity
and the formation of a many-body bound state. As a result, the polaron is not
the ground state, but rendered a metastable excited state which can decay into
these Efimov clusters. While this decay is slow for small interaction
strengths, it becomes more prominent as the attractive scattering length
increases, up to the point where the polaron becomes completely unstable. This
critical scattering length can be interpreted as a many-body shifted Efimov
resonance, where the scattering of two excitations of the bath with the polaron
can lead to bound state formation. Compared to the few-body case, the resonance
is shifted to smaller attractive scattering lengths due to the participation of
the polaron cloud in the cooperative binding process. This corresponds to an
intriguing scenario of polaron-assisted chemistry, where many-body effects lead
to enhanced signal of the chemical recombination process, which can be directly
probed in state-of-the-art experiments.
