Ibáñez i Insa, JordiVerdaguer Oms, Enric, 1950-2010-07-052010-07-0519830031-9007https://hdl.handle.net/2445/13299An exact solution of the Einstein equations in vacuum representing two pairs of gravitational solitons propagating on an expanding universe is given and studied. It is suggested that the solitons evolve from quasiparticles to pure gravitational waves. Two of the four solitons collide and the focusing produced on null rays is studied. Although the spacetime following the collision is highly distorted, null rays do not focus to a singularity.3 p.application/pdfeng(c) American Physical Society, 1983Relativitat general (Física)SolitonsPartícules (Física nuclear)Ones gravitacionalsCol·lisions (Física nuclear)General relativity (Physics)SolitonsParticles (Nuclear physics)Gravitational wavesCollisions (Nuclear physics)info:eu-repo/semantics/article79589info:eu-repo/semantics/openAccess