Arm (NASDAQ:ARM) stock is preparing for a major catalyst later this month that investors in the U.K. semiconductor company will want to keep an eye on!This has Arm joining the Nasdaq 100 index before markets open on June 24. That has it replacing satellite radio company Sirius XM (NASDAQ:SIRI). The exact reason for this change is unknown but there are a few things that could be behind it.First off, Arm does have a much higher market capitalization than Sirius XM. It comes in at more than $160 billion as com ...