A herd of VCs
According to the university's press release:
Van den Berg uses three models to describe how acquisitions seem to prompt each other. The announcement of a takeover and the initial bid awake the interest of a second party, and this already can drive the price up to a point that stops this second party from taking part in a bidding war. An investment in a buyout can also unveil information that other financiers use in their own investment decisions. This attentiveness to the behaviour of others can lead to a wave of private equity investments. Finally in the consolidation of a branch of business the value of every successive takeover candidate increases, to the extent that more companies have been bought up. This too leads to a new wave of investments.
In short, VCs see other investors chasing a new technology or market opportunity, look harder for companies in the same area, and valuations spiral. That certainly seems to fit some observed behaviour - arguably, we've been seeing something similar in the clean energy sector in the past couple of years.
There's more information on van den Berg's work at his university site.