BOJ considering ways to deepen negative rates at minimal cost - sources

TOKYO (Reuters) - The Bank of Japan is brainstorming ways to deepen negative interest rates at minimal cost, as it considers adopting it as a main policy response to a slowing economy and intensifying global risks, sources familiar with the bank's thinking said.Any such move will likely be combined with measures to prevent the yield curve from flattening too much, as excessive declines in long- and super-long yields will erode profit margins of financial institutions, they said.As global risks..