Yellen's dilemma: a downturn with no easy response

By Howard Schneider and Ann Saphir WASHINGTON (Reuters) - The Federal Reserve's carefully scripted decision to raise interest rates last December, and begin a return to "normal" policy, may now become a nightmare for the U.S. central bank if an economic downturn forces a return to unconventional methods. Fed chair Janet Yellen told lawmakers this week she was studying ways to "be prepared" in the event the current slide in world stock markets, concern about financial sector stress, and slowing e