The Invisible Higgs Decay Width in the Add Model at the LHC

Assuming flat universal extra dimensions, we demonstrate that for a light Higgs boson the process $pp\to W^*W^* +X \to Higgs,graviscalars +X \to invisible+X$ will be observable at the $5 \sigma$ level at the LHC for the portion of the Higgs-graviscalar mixing ($\xi$) and effective Planck mass ($M_D$) parameter space where channels relying on visible Higgs decays fail to achieve a $5 \sigma$ signal. Further, we show that even for very modest values of $\xi$ the invisible decay signal probes to higher $M_D$ than does the ($\xi$-independent) jets/$\gam$ + missing energy signal from graviton radiation. We also discuss various effects, such as Higgs decay to two graviscalars, that could become important when $m_h/M_D$ is of order 1.