LONDON—European stock indexes opened slightly higher on Tuesday, while U.S. and European government bond yields rose to new multiyear highs as investors adjusted their expectations for rate hikes following hawkish comments from the U.S. Federal Reserve. Fed Chair Jerome Powell said that the central bank could move “more aggressively” to raise rates to fight inflation, possibly by more than 25 basis points at once. Markets scrambled to recalibrate the higher possibility of a 50 bps hike. On Tuesday morning, money markets were pricing in an 80 percent chance of a 50 bps hike in May. At 0853 GMT, the U.S. 10-year Treasury yield was at 2.3497 percent, its highest since 2019. RBC Capital Markets’ chief U.S. economist, Tom Porcelli, wrote in a note to clients that during the speech “it was easy to wonder if a 75bps hike or even going intra-meeting is possible.” “Both outcomes seem incredibly extreme but …