Which new process was added to the nebular theory of solar system formation to account for the existence of Jupiter-mass planets that orbit close to their stars (the "hot Jupiters") ?

Due to their very intense activity and magnetic fields, they are covered with sunspots hundreds of times bigger than those on the Sun. These therefore generate perturbations in the star's spectrum that are much greater than those caused by planets, making them much harder to detect, even when they are hot Jupiters.