By Howard Schneider NEW YORK (Reuters) – Digital money, a curiosity just a few years ago, is emerging as an intense concern among central banks with the potential to erode the power of monetary policy, and even in the best of worlds likely to make control of interest rates more difficult, according to new Federal Reserve and other research. A New York Fed symposium this week laid out the puzzle central bankers face in dealing with emerging digital technologies that range from new ways to process payments to new asset categories like cryptocurrencies and stablecoins. There are benefits seen in …