Disordered bosons: Critical phenomena and evidence for new low energy excitations.

We study the [ital T]=0 critical properties of the superfluid-insulator transition in 2D hard core Bose systems with disorder. Using quantum Monte Carlo simulations and finite size scaling on 64[times]64 lattices we find the dynamical exponent [ital z]=0.5[plus minus]0.1 and the correlation length exponent [nu]=2.2[plus minus]0.2. At the transition, the system is metallic with a conductivity [sigma][sub [ital c]]=(1.2[plus minus]0.2)([ital e][sup *])[sup 2]/[ital h] and a nonzero compressibility [kappa][ne]0. These conclusions differ from the existing scaling theory as well as from simulations on simplified models argued to be in the same universality class. Our results are suggestive of [ital new] low lying collective excitations (modified from usual phonons) in the [ital disordered] system.