Carp, a first baseman/outfielder, was a key reserve for the Red Sox during their World Series-championship season in 2013, hitting .296 with 18 doubles, two triples, nine home runs, 43 RBIs and 22 walks in a career-high 86 games.
Tazawa was Boston's primary setup man for most of the 2013 season and had a terrific postseason. In 71 regular-season games, Tazawa was 5-4 with a 3.16 ERA, striking out 72 in 68 1/3 innings pitched. In 13 postseason games, Tazawa was 1-0 with a 1.13 ERA over 7 1/3 innings, including five scoreless outings in the World Series.
Herrera, a utility infielder, was acquired from the Colorado Rockies in a trade for Franklin Morales last month. The 29-year-old switch-hitter has played in 375 games over five big league seasons, hitting .265.