Absence of thermodynamic phase transition in a model glass former

The glass transition can be viewed simply as the point at which the viscosi ty of a structurally disordered liquid reaches a universal threshold value( 1). But this is an operational definition that circumvents fundamental issu es, such as whether the glass transition is a purely dynamical phenomenon(2 ). If so, ergodicity gets broken (the system becomes confined to some part of its phase space), but the thermodynamic properties of the liquid remain unchanged across the transition, provided they are determined as thermodyna mic equilibrium averages over the whole phase space. The opposite view(3-6) claims that an underlying thermodynamic phase transition is responsible fo r the pronounced slow-down in the dynamics at the liquid-glass boundary. Su ch a phase transition would trigger the dynamic standstill, and then he mas ked by it. Here we perform Monte Carlo simulations of a two-dimensional sys tem of polydisperse hard disks far within its glassy phase. The approach(7) allows for non-local moves in a way that preserves micro-reversibility. We find no evidence for a thermodynamic phase transition up to very high dens ities; the glass is thus indistinguishable from the liquid on purely thermo dynamic grounds.