NEW YORK (Dow Jones)--The government sold five-year Treasury inflation protected securities Monday at a negative yield for the first time ever, a sign of investors' strong conviction that the Federal Reserve will buy more bonds, which could stoke inflation. The government sold $10 billion in previously sold five-year TIPS for negative 0.55% yield after selling them at a 0.550% yield when they were originally sold in April. Because the market expects inflation will be positive over the next five years though, the expected return for the five-year TIPS is still positive. Investors have been buying TIPS, which provide protection against...