Summit Partners, a Boston-based growth equity firm, has promoted three senior staff members to principal on the firm's credit team. Adam Britt and Jack Le Roy, prior to joining Summit, worked for Guggenheim Investment Management as members of the leveraged finance group. Robert Hassell also previously worked for Guggenheim as a member of the leveraged finance group in the U.S. and Ireland. All three joined the firm's Boston office in 2010.