Transplanckian Axion Monodromy !?

TL;DR

The work provides a concrete, fully backreacted realization of transplanckian axion monodromy within string theory by embedding axion monodromy in warped KS throats, viewed as 5d flux compactifications on Sasaki–Einstein manifolds. It derives a consistent 5d effective theory for the axion and the breathing mode, analyzes backreaction on the vacuum energy, and shows that the axion can traverse arbitrarily large distances without triggering an infinite tower of light states. The paper also presents a 4d AdS4×X7 analog in M-theory, reinforcing the universality of the mechanism, and discusses holographic duals, duality walls, and potential links to de Sitter embeddings and swampland conjectures. Together, these results demonstrate that transplanckian field excursions can be realized in string-theory vacua with controlled backreaction, providing a concrete counterexample to swampland claims against large-field inflationary scenarios and suggesting new avenues for connecting swampland distance and de Sitter conjectures. The findings have broad implications for the viability of large-field models within quantum gravity and for understanding how backreaction shapes effective field theories in warped geometries.

Abstract

We show that warped throats of the Klebanov-Strassler kind, regarded as 5d flux compactifications on Kähler-Einstein manifolds $\bf{X}_5$ describe fully backreacted solutions of transplanckian axion monodromy. We show that the asymptotic Klebanov-Tseytlin solution features a 5d axion physically rolling through its dependence on an spatial coordinate, and traversing arbitrarily large geodesic distances in field space. The solution includes the backreaction on the breathing mode of the compactification space and on the vacuum energy, which yields a novel form of flattening. We establish the description of the system in terms of an effective 5d theory for the axion, and verify its validity in transplanckian regimes. In this context, rolling axion monodromy configurations with limited field space range would correspond, in the holographic dual field theory, to duality walls, which admit no embedding in string theory so far. We present an identical realization of transplanckian axion monodromy in 4d in fluxed version of AdS$_4\times \bf{X}_7$. We speculate that similar models in which the axion rolls in the time direction naturally correspond to embedding of the same mechanism in de Sitter vacua, thus providing a natural arena for large field inflation, and potentially linking the swampland de Sitter and distance conjectures.