Tumbling oil prices could provide a massive tailwind for global stock markets by prompting a broader equity rally and clearing a path for central banks to cut interest rates, Karen Ward, the Chief Market Strategist for EMEA at JPMorgan Asset Management, said on Monday, as a tentative U.S.-Iran peace deal is digested by markets. Investors are currently treating higher oil prices as a threat to stocks because of inflation and growth concerns. Oil prices plummeted on Monday following the announcement of a peace deal between the U.S. and Iran to halt…