On the Origin of the Outgoing Black Hole Modes

The question of how to account for the outgoing black hole modes without drawing upon a transplanckian reservoir at the horizon is addressed. It is argued that the outgoing modes must arise via conversion from ingoing modes. It is further argued that the back-reaction must be included to avoid the conclusion that particle creation cannot occur in a strictly stationary background. The process of ``mode conversion" is known in plasma physics by this name and in condensed matter physics as ``Andreev reflection" or ``branch conversion". It is illustrated here in a linear Lorentz non-invariant model introduced by Unruh. The role of interactions and a physical short distance cutoff is then examined in the sonic black hole formed with Helium-II.Comment: 12 pages, plain latex, 2 figures included using psfig; Analogy to ``Andreev reflection" in superfluid systems noted, references and acknowledgment added, format changed to shorten tex

Structural and dynamical properties of superfluid helium: a density functional approach

We present a novel density functional for liquid 4He, properly accounting for the static response function and the phonon-roton dispersion in the uniform liquid. The functional is used to study both structural and dynamical properties of superfluid helium in various geometries. The equilibrium properties of the free surface, droplets and films at zero temperature are calculated. Our predictions agree closely to the results of ab initio Monte Carlo calculations, when available. The introduction of a phenomenological velocity dependent interaction, which accounts for backflow effects, is discussed. The spectrum of the elementary excitations of the free surface and films is studied.Comment: 37 pages, REVTeX 3.0, figures on request at [email protected]

TEMPERATURE DEPENDENCE OF PHONONS IN LIQUID 4He

On a mesuré la diffusion de neutrons par 4He liquide aux vecteurs d'onde de 0.80 ; 1,13 ; 1,30 et 1,40 Å-1 et aux temperatures de 1,00 ; 1,38 ; 1,77 ; 1,97 ; 2,07 ; 2,12 ; 2,15 ; 2,26 et 4,21 K. On peut voir un pic "uniphonon" dans toutes les distributions lorsque T Tλ.The neutron scattering by liquid 4He for wave vectors of 0.80, 1.13, 1.30 and 1.40 Å-1 has been measured at 1.00, 1.38, 1.77, 1.97, 2.07, 2.12, 2.15, 2.26 and 4.21 K. A "one-phonon" peak is evident in all distributions for T Tλ