Backreaction Issues in Axion Monodromy and Minkowski 4-forms
Irene Valenzuela
TL;DR
Valenzuela reformulates axion monodromy in terms of Minkowski 4-forms arising from Type II string compactifications and shows that backreaction from saxions induces a field-dependent 3-form metric, causing the proper inflaton distance to grow at most logarithmically beyond a critical field value. In the closed-string sector, the maximal safe field range before backreaction becomes significant is flux-independent and of order the Planck mass, suggesting a potential universal obstruction to trans-Planckian excursions. Open-string moduli are proposed as a possible counterexample, where appropriate flux choices may decouple φ_c from s_0 and delay backreaction, though global consistency must be checked. Overall, the work provides a cohesive 4-form-based perspective on backreaction in axion monodromy and identifies open-string directions as promising avenues to circumvent universal limits while highlighting potential fundamental constraints arising from closed-string dynamics.
Abstract
We clarify the differences between the usual Kaloper-Sorbo description of axion monodromy and the effective axionic potential in terms of Minkowski 4-forms derived in string compactifications. The fact that the metric of the 3-form fields coming from string theory is field dependent (unlike in Kaloper-Sorbo) leads to the backreaction issues recently studied in axion monodromy models within string theory. We reanalyse these problems in terms of the 4-forms focusing on the case in which the non-periodic scalars backreact on the Kahler metric of the inflaton reducing the physical field range. In the closed string sector of Type II Calabi-Yau compactifications with fluxes the metric becomes field dependent precisely when $Δφ\sim M_p$, independently of the choice of fluxes. We propose, however, some counter-examples to this universal behaviour by including open string fields.