Wave diffraction by a cosmic string
  We show that if a cosmic string exists, it may be identified through
characteristic diffraction pattern in the energy spectrum of the observed
signal. In particular, if the string is on the line of sight, the wave field is
shown to fit the Cornu spiral. We suggest a simple procedure, based on Keller's
geometrical theory of diffraction, which allows to explain wave effects in
conical spacetime of a cosmic string in terms of interference of four
characteristic rays. Our results are supposed to be valid for scalar massless
waves, including gravitational waves, electromagnetic waves, or even sound in
case of condensed matter systems with analogous topological defects.
