WASHINGTON (Reuters) -U.S. antitrust regulators published guidelines on Wednesday on the kinds of mergers and acquisitions they object to, reaffirming the skepticism with which President Joe Biden's administration has approached many deals, especially in the technology sector. The U.S. Justice Department and Federal Trade Commission (FTC) have mounted an unprecedented number of legal challenges to mergers since Biden came to office in 2021. Their success in court has been mixed, with two losses recorded just last week in their attempts to scupper Microsoft Corp's $69 billion deal to buy video game maker Activision Blizzard Inc and to undo a merger in the sugar industry.