Invisible Higgs boson decay in the littlest Higgs model with T-parity

We study the invisible decay of the Higgs boson into a pair of stable, heavy photons, H→AHAH, in the littlest Higgs model with T-parity. For a symmetry breaking scale of f=450GeV, the branching ratio H→AHAH can be as high as 93% for Higgs masses below 150GeV. For f=500GeV, the invisible branching ratio is about 75% in the Higgs mass range 135-150GeV and 10(5.5)% for mH=200(600)GeV. It drops to a few percent for f larger than 600GeV. We have found regions in parameter space, allowed by the electroweak precision data, with such low values of f for 115GeV