Enhancing inflationary tensor modes through spectator fields

Matteo Biagetti, Matteo Fasiello, Antonio Riotto
2013 Physical Review D  
We show that a large contribution to tensor modes during inflation can be generated by a spectator scalar field with speed of sound lower than unity.
doi:10.1103/physrevd.88.103518 fatcat:zjxph3gzenhlxeghqmx7ndtfuq