2006 set a record for mergers and acquisitions worldwide. Deals totaled .79 trillion, 38% higher than in 2005, and 55 of the transactions were valued at more than billion each, according to data from Thomson Financial. Europe was one of the big players, registering 39% more deals than in 2005 for a total of .43 trillion. The U.S. came in at .56 trillion, 36% higher than the year before. Private equity firms were major movers in this trend, responsible for 20% of global M&A activity and 27% of activity in the U.S., according to Thomson. How long will this M&A binge continue, and when it does come to an end, what will be the factors behind the retreat? Knowledge at Wharton asked management professor Harbir Singh , an expert on corporate acquisitions and restructuring, to offer his views on the M&A landscape. Knowledge at Wharton: A recent report in The New York Times said that of 790 deals in the U.S.…