Inflation assisted by heterotic axions

We explore the possibility of obtaining inflation in weakly coupled heterotic string theory, where the model dependent axions are responsible for driving inflation. This model can be considered as a certain extrapolation of m(2)phi(2)-inflation, and is an attempt to explicitly realize the so called N-flation proposal in string theory. The instanton generated potential for the axions essentially has two parameters; a natural mass scale M and the string coupling gs. For isotropic compactifications leading to O(10(4)) axions in the four-dimensional spectrum we find that with (M, gs) similar or equal to (M-GUT, 0.5) the observed temperature fluctuations in the CMB are correctly reproduced. We assume an initially random distribution for the vacuum expectation values (vevs) of the axions. The spectral index, ns, is generically more red than for m(2)phi(2)-inflation. The greater the vevs, the more red the spectral index becomes. Allowing for a wide range of vevs 55 e-foldings from the end of inflation, we find 0.946 less than or similar to n(s) less than or similar to 0.962. The tensortoscalar ratio, r, is more sensitive to the vevs, but typically smaller than in m(2)phi(2)-inflation. Furthermore, in the regime where the leading order theory is valid, r is bounded by r < 0.10. The spectral index and the tensor-to-scalar ratio are correlated. For example, ns similar or equal to 0.951 corresponds to r similar or equal to 0.036.