From the University of Texas at Austin Economics Department:

Dr. Coibion on low interests: “One of the defining features of the current economic crisis has been the zero bound on nominal interest rates….

From the St. Louis fed:

Working Paper #2013-007C;  ” Global Dynamics at the Zero Lower Bound“,    by William T. Gavin, Benjamin D. Keen, Alexander Richter and Nathaniel Throckmorton

Abstract: …We also evaluate how monetary policy affects the likelihood of hitting the ZLB. A policy rule based on a dual mandate is more likely to cause ZLB events when the central bank places greater emphasis on output stabilization.