Planck 2015 results. XX. Constraints on inflation

P.A.R Ade, N. Aghanim, M. Arnaud, F. Arroja, M. Ashdown, J. Aumont, C. Baccigalupi, Rosa Maria Ballardini, A.J. Banday, R.B. Barreiro, Per Rex Christensen, Anne Mette Frejsel, Pavel Nasselski, Igor Dmitrievich Novikov, Hans Ulrik Nørgaard-Nielsen