Research by the institute-affiliated UNC Tax Center shows just six publicly traded U.S. companies, including Amazon and Warren Buffett’s Berkshire Hathaway Inc., would have paid half the estimated $32 billion in revenue generated by a 15% corporate minimum tax signed into law last month. “Who actually pays a lot is just not very many firms at all,” said Jeff Hoopes, UNC Kenan-Flagler Business School professor and the center’s research director, who is one of the study’s authors. “My guess is it will not be the same firms every single year.”