Effective-Lagrangian approach to gamma gamma -->WW; II: Results and comparison with e+e- -->WW

We present a study of anomalous electroweak gauge-boson couplings which can be measured in e + e − and γγ collisions at a future linear collider like ILC. We consider the gauge-boson sector of a locally SU (2) × U (1) invari-ant effective Lagrangian with ten dimension-six operators added to the Lagrangian of the Standard Model. These operators induce anomalous three-and four-gauge-boson couplings and an anomalous γγH coupling. We calculate the reachable sensitivity for the measurement of the anomalous couplings in γγ → W W . We compare these results with the reachable precision in the reaction e + e − → W W on the one hand and with the bounds that one can get from high-precision observables in Z decays on the other hand. We show that one needs both the e + e − and the γγ modes at an ILC to constrain the largest possible number of anomalous couplings and that the Giga- Z mode offers the best sensitivity for certain anomalous couplings.