Interpretation of spacetimes with expanding impulsive gravitational waves generated by snapped cosmic strings

Spacetimes representing expanding impulsive gravitational waves propagating on a flat background are studied. The impulses are generated by various configurations of snapped cosmic strings. Employing the previous results [J. PodolskATIN SMALL LETTER Y WITH ACUTE et al., The global uniqueness and C1-regularity of geodesics in expanding impulsive gravitational waves, Classical Quantum Gravity 33, 195010 (2016)], analyzing the geodesic motion in generic expanding impulses, we investigate geometric properties of more intricate stringlike wave sources than the standard case of a single snapped string. Such solutions representing pairs of snapping strings were technically derived in PodolskATIN SMALL LETTER Y WITH ACUTE and Griffiths [The collision and snapping of cosmic strings generating spherical impulsive gravitational waves, Classical Quantum Gravity 17, 1401 (2000)], however, the corresponding physical analysis requires to introduce their generalizations to point out various subtleties in the construction. As the main tool, we thus use the close connection between the spacetime structure and the motion of free test particles crossing the impulse. Within our contribution, the explicit models of a boosted snapped cosmic string and boosted perpendicular or parallel configurations of string pairs are discussed in detail.