Is Lumpy Investment Really Irrelevant for the Business Cycle?

Smoothness in aggregate capital accumulation is a necessary condition for New-Keynesian (NK) models to imply a quantitatively relevant monetary transmission mechanism (see, e.g., Woodford 2005). Can that aggregate smoothness be entertained in the context of an NK model featuring lumpy plant-level investment? Our answer is yes. Imperfect competition in goods markets and/or sticky prices are identified as economic mechanisms which render lumpy investment relevant in general equilibrium.