Pressure Dependence of Excitations of Liquid 4He

Con nement of liquid 4He in porous glasses increases its solidication pres-sure and suppresses the super uid transition temperature T. It has been reported that a suciently high degree of connement suppresses T to zero at high pressure, signifying a 'quantum phase transition'. We evaluate the behaviour of the excitation spectrum at wave vectors Q < 2.3 A1 at pres-sures well above 25 bar by calculating the dynamic structure factor, S(Q;E), using the theory of hybridization of one- and two-particle excitations. The aim is to explore whether well-dened excitations exist at high pressures, and whether there is some critical pressure at which they disappear. We nd that as the pressure increases, the one-particle excitation energy is well-dened if its energy lies below the two-roton energy, and ceases to exist as a well-de ned excitation if its energy lies above the two-roton energy. We relate these ndings to potential inelastic neutron scattering measurements. 1