We define a gradient Ricci
soliton to be rigid if it is a flat bundle N ×Γℝk where N is Einstein. It is
known that not all gradient solitons are rigid. Here we offer several natural
conditions on the curvature that characterize rigid gradient solitons. Other
related results on rigidity of Ricci solitons are also explained in the last
section.
Keywords
complete manifold, constant scalar curvature, Ricci
soliton, Einstein manifold