The zoo plot meets the swampland: mutual (in)consistency of single-field inflation, string conjectures, and cosmological data

We consider single-field inflation in light of string-motivated 'swampland' conjectures suggesting that effective scalar field theories with a consistent UV completion must have field excursion Δ φ ≲ MPl, in combination with a sufficiently steep potential, MPlVφ/V ≳ O(1). Here, we show that the swampland conjectures are inconsistent with existing observational constraints on single-field inflation. Focusing on the observationally favoured class of concave potentials, we map the allowed swampland region onto the nS-r 'zoo plot' of inflationary models, and find that consistency with the Planck satellite and BICEP2/Keck Array requires MPlVφ/V ≲ 0.1 and -0.02 ≲ M2 PlVφφ/V < 0, in strong tension with swampland conjectures. Extension to non-canonical models such as DBI Inflation does not significantly weaken the bound.