One university’s effort to poach a star faculty member at another Southern California university has devolved into a legal battle that some fear may impede Alzheimer’s disease research. The University of California, San Diego, has filed a lawsuit over last month’s defection of Alzheimer’s disease expert Paul Aisen and other employees to the University of Southern California, which has worked to bolster its reputation in medicine and sciences and has offered lucrative compensation packages to public university faculty.