Artificial intelligence has been a significant driver of the stock market over the past three years.Concerns about artificial intelligence (AI) stocks and their monster valuations aren't exactly new, but the market is now being less coy about it. Following a big multiyear run for the sector, it appears that some investors are setting a high bar for AI stocks. No longer are announcements about higher capital expenditures for AI infrastructure build-out purely driving stocks higher, as investors start to ques ...