The heat surrounding so-called activist investors — hedge funds that buy up big chunks of a company’s stock, then leverage their position to mount proxy campaigns or otherwise force boards to change the way the company is managed — could hardly be more intense than it is now. Well, okay, maybe there would be even more controversy if Michael Lewis wrote a book about a genius upstart who defied accepted deal conventions and revolutionized corporate takeover battles. But putting aside the Wall Street tizzy inspired by this week’s publication of Lewis’s new book about high-frequency trading, the deal world’s favorite topic remains activist investors like Carl Icahn, Paul Singer, William Ackman and Dan Loeb.