  Previously we have studied the Generalized Minimal Massive Gravity (GMMG) in
asymptotically $AdS_3$ background, and have shown that the theory is free of
negative-energy bulk modes. Also we have shown GMMG avoids the aforementioned
bulk-boundary unitarity clash. Here instead of $AdS_3$ space we consider
asymptotically flat space, and study this model in the flat limit. The dual
field theory of GMMG in the flat limit is a $BMS_3$ invariant field theory,
dubbed (BMSFT) and we have BMS algebra asymptotically instead of Virasoro
algebra. In fact here we present an evidence for this claim. Entanglement
entropy of GMMG is calculated in the background in the flat null infinity. Our
evidence for mentioned claim is the result for entanglement entropy in filed
theory side and in the bulk (in the gravity side). At first using Cardy formula
and Rindler transformation, we calculate entanglement entropy of BMSFT in three
different cases. Zero temperature on the plane and on the cylinder, and
non-zero temperature case. Then we obtain the entanglement entropy in the bulk.
Our results in gravity side are exactly in agreement with field theory
calculations.
