Testing metric-affine f(R)-gravity by relic scalar gravitational waves S. Capozziello, R. Cianci, M. Laurentis and S. Vignolo Eur. Phys. J. C, 70 1-2 (2010) 341-349 Published online: 24 August 2010 DOI: 10.1140/epjc/s10052-010-1412-5