Inflation Assisted by Heterotic Axions

Abstract

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 $m^2{\varphi }^2$-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 $g_s$. For isotropic compactifications leading to of order $\mathcal{O}(10^4)$ axions in the four dimensional spectrum we find that with $(M,g_s)\simeq (M_{GUT},0.5)$ the observed temperature fluctuations in the CMB are correctly reproduced. We assume an initially random distribution for the vevs of the axions. The spectral index, $n_s$, is generically more red than for $m^2{\varphi }^2$-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 $0.946\lesssim n_s\lesssim 0.962$. The tensor-to-scalar ratio, $r$, is more sensitive to the vevs, but typically smaller than in $m^2{\varphi }^2$-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, $n_s\simeq 0.951$ corresponds to $r\simeq 0.036$.

1+21 pages, 2 figures, v2: Typos corrected, v3: Typos, very minor corrections, reference added, to appear in JCAP

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• N-flation from multiple DBI type actions
• Cosmological signatures of ultralight dark matter with an axionlike potential
• Inflation at the Tip
• IR Inflation from Multiple Branes
• Assisted coupled quintessence
• Large Gravitational Waves and Lyth Bound in Multi Brane Inflation
• DBI N-flation
• On Number of Nflation Fields
• Spectrum of Curvature Perturbation of Multi-field Inflation with Small-Field Potential
• Evidence for Inflation in an Axion Landscape
• Trans-Planckian censorship constraints on properties and cosmological applications of axion-like fields
• Phase Diagram for Nflation