Arch Capital Group ACGL.O will replace Twitter on the S&P 500 from Nov. 1. Amazon.com Inc AMZN.O joined a chorus of Big Tech firms that have disappointed investors this week by forecasting a slowdown in sales growth for the all-important holiday season and warned of a hit to consumers' purchasing power. Tech sector earnings were viewed as a major test of the strength of corporate America in the face of decades-high inflation and the dismal results have fed into fears of a looming recession from aggressive monetary policy tightening by the Federal Reserve.