Quantum hoop conjecture and a natural cutoff for vacuum energy of a
  scalar field
  We propose here a quantum hoop conjecture which states: the de Broglie
wavelength of a quantum system cannot be arbitrarily small, it must be larger
than the characterized Schwarzschild radius of the quantum system. Based on
this conjecture, we find an upper bound for the wave number (or the momentum)
of a particle, which offers a natural cutoff for the vacuum energy of a scalar
field.
