The Nasdaq-100 is trading lower, primarily driven by negative investor sentiment towards mega-cap technology stocks following recent earnings reports. Companies like Alphabet and Tesla have seen their stock prices decline after revealing significant increases in capital expenditures related to artificial intelligence. This has sparked broader concerns across the sector about the near-term profitability and return on these substantial AI investments. The sell-off in these key index components is the main catalyst for the QQQ ETF's downward move.