Wave diffraction by a cosmic string

•Gravitational waves could help us to reveal cosmic strings – topological defects of early Universe.•Wave diffraction in conical spacetime of a cosmic string is solved analytically.•The Cornu spiral is shown to appear when the string is on the line of sight.•For a string located within our galaxy, the highest amplification would occur at a frequency range of LIGO detector.

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.