Stocks stay on rollercoaster despite strong Nvidia earnings

By Lewis Krauskopf and Dhara RanasingheNEW YORK/LONDON (Reuters) -Nvidia Corp's strong earnings report offered only a brief reprieve from worries that have plagued stocks about the return on relentless artificial intelligence investment and lofty valuations on Wall Street.AI darling Nvidia on Wednesday surprised Wall Street with accelerating growth after several quarters of slowing sales and a fourth-quarter forecast that exceeded expectations.Initial relief across world stocks, however, turned sour on Thur ...