We explore whether multifield inflationary models make unambiguous predictions for fundamental cosmological observables .
Focusing on N -quadratic inflation , we numerically evaluate the full perturbation equations for models with 2 , 3 , and \mathcal { O } ( 100 ) fields , using several distinct methods for specifying the initial values of the background fields .
All scenarios are highly predictive , with the probability distribution functions of the cosmological observables becoming more sharply peaked as N increases .
For N = 100 fields , 95 % of our Monte Carlo samples fall in the ranges n _ { s } \in ( 0.9455 , 0.9534 ) ; \alpha \in ( -9.741 , -7.047 ) \times 10 ^ { -4 } ; r \in ( 0.1445 , 0.1449 ) ; and r _ { \mathrm { iso } } \in ( 0.02137 , 3.510 ) \times 10 ^ { -3 } for the spectral index , running , tensor-to-scalar ratio , and isocurvature-to-adiabatic ratio , respectively .
The expected amplitude of isocurvature perturbations grows with N , raising the possibility that many-field models may be sensitive to post-inflationary physics and suggesting new avenues for testing these scenarios .