Anomalous Couplings in Single Higgs Production through $\gamma\gamma$ Collisions

We show that single Higgs production in $\gamma\gamma$ collisions through laser backscattering provides the best way to look for New Physics (NP) effects inducing anomalous Higgs couplings. Our analysis is based on the four $dim=6$ operators $\O_{UB}$, $\O_{UW}$, $\ol{\O}_{UB}$ and $\ol{\O}_{UW}$ which describe New Physics effects in this sector. Using the Higgs production rate we establish observability limits for the couplings of the aforementioned operators at a level of $10^{-3}$, which means establishing lower bounds on the scale of NP of the order 30 to 200 TeV. Higgs branching ratios, especially the ratio $\Gamma(H\to\gamma\gamma)/\Gamma (H\to\gamma Z)$, are shown to provide powerful ways to disentangle the effects of the various operators.