Near the midpoint of the year, stocks and bonds both report good returns. But the global stock market has become highly concentrated, our columnist says. (Peter and Maria Hoey/The New York Times) By JEFF SOMMER Caterpillar is known for its yellow construction machinery, not for artificial intelligence. But it also makes power-generation turbines, and as AI data centers consume increasingly large amounts of electricity for their operations, Caterpillar’s stock has soared. Like scores of other…
