It might take longer to recoup investments in fiber infrastructure than investors like Goldman Sachs and KKR hope. : Get the DealBook newsletter to make sense of major business and policy headlines — and the power-brokers who shape them.__________ Buyout groups are building broadband networks across Europe, attracted by stable, healthy returns — but the numbers get tricky if bigger operators choose to compete. The British fiber infrastructure provider CityFibre is the latest broadband company to receive backing from a big financial sponsor.