FRANKFURT (Reuters) – European Central Bank policymaker Joachim Nagel raised the bar for an ECB intervention on the bond market on Tuesday, saying he assumed differences in yields to be “fundamentally justified” until proven otherwise. The ECB is working on a new bond-buying scheme to curb borrowing costs for Italy and other indebted countries in the euro zone’s south, which have been rising faster than Germany’s since the central bank stopped purchases and announced plans to raise interest rates. “The financial markets are now making a greater differentiation between different risks due to th…