We analyze horizontal mergers when the acquirer holds a passive partial ownership stake (PPO) in the target firm prior to the merger. We show that a PPO reduces the minimal synergy level necessary to make a merger beneficial for consumers. It follows that an antitrust authority ignoring existing...

It is commonly perceived that firms do not want to be outsiders to a merger between competitor firms. We instead argue that it is beneficial to be a non-merging rival firm to a large horizontal merger. Using a sample of mergers with expert-identification of relevant rivals and the event-study...