We conjecture an intrinsic UV cutoff for the validity of the effective field theory with a large number of species coupled to gravity. In four dimensions such an UV cutoff takes the form $\Lambda =\sqrt{\lambda /N}{M}_p$ for $N$ scalar fields with the same potential $\lambda {\varphi }_i^4$, $i=1,\dots ,N$. This conjecture implies that the assisted chaotic inflation or $N$-flation might be in the swampland, not in the landscape. Similarly an UV cutoff $\Lambda =g{M}_p/\sqrt{N}$ is conjectured for the U(1) gauge theory with $N$ species.

• Received 30 January 2008

DOI:https://doi.org/10.1103/PhysRevD.77.105029