BRUSSELS—New research by two U.S. academics suggests that Google Inc. is harming Internet users and violating competition laws by skewing search results to favor its own services, a potentially significant twist in Europe’s long-running antitrust investigation of the U.S. search company.

The research combines statistical testing with detailed legal and economic analysis to examine the ramifications of Google’s practice of promoting its own specialized search services, such as for local restaurants or doctors, at the expense...