Gauged M-flation, its UV sensitivity and Spectator Species

TL;DR

The paper addresses the UV sensitivity of multi-field inflation by examining gauged M-flation, a D3-brane–motivated matrix inflation model. By computing the spectrum of spectator (isocurvature) modes and applying the FRW species bound, it shows that only a subset of modes are light enough to contribute to the gravitational cutoff, yielding a lowered Λ of a few percent of the Planck scale and a spectator count N_s of order 10^2–10^3 for viable parameters. The results demonstrate that the background field excursions remain below the reduced cutoff and that string-scale corrections are negligible (m_s > Λ), establishing gauged M-flation as UV-safe. This contrasts with naive N-flation expectations and supports the viability of string-theory–inspired large-field inflation without uncontrolled quantum gravity corrections.

Abstract

In this paper we study gauged M-flation, an inflationary model in which inflation is driven by three NxN scalar field matrices in the adjoint representation of U(N) gauge group. We focus our study on the gauged M-flation model which could be derived from the dynamics of a stack of D3-branes in appropriate background flux. The background inflationary dynamics is unaltered compared to the ungauged case of [arXiv:0903.1481[hep-th]], while the spectrum of "spectator species", the isocurvature modes, differs from the ungauged case. Presence of a large number of spectators, although irrelevant to the slow-roll inflationary dynamics has been argued to lower the effective UV cutoff $Λ$ of the theory from the Planck mass, invalidating the main advantage of M-flation in not having super-Planckian field values and unnaturally small couplings. Through a careful analysis of the spectrum of the spectators we argue that, contrary to what happens in N-flation models, M-flation is still UV safe with the modified (reduced) effective UV cutoff $Λ$, which we show to be of order (0.5-1)x10^{-1} M_{pl}. Moreover, we argue that the string scale in our gauged M-flation model is larger than $Λ$ by a factor of 10 and hence one can also neglect stringy effects. We also comment on the stability of classical inflationary paths in the gauged M-flation.