Planckian axions and the Weak Gravity Conjecture

By Thomas C. Bachlechner, Cody Long, Liam McAllister. 2015

151 citations recorded by the source corpus.

A bstractSeveral recent works [1-3] have claimed that the Weak Gravity Conjecture (WGC) excludes super-Planckian displacements of axion fields, and hence large-field axion inflation, in the absence of monodromy. We argue that in theories with N ≫ 1 axions, super-Planckian axion diameters D$$ \mathcal{D} $$ are readily allowed by the WGC. We clarify the non-trivial relationship between the kinetic matrix K — unambiguously defined by its form in a Minkowski-reduced basis — and the diameter of the axion fundamental domain, emphasizing that in general the diameter is not solely determined by the eigenvalues f12 ≤ ⋅ ⋅ ⋅ ≤ fN2 of K: the orientations of the eigenvectors with respect to the identifications imposed by instantons must be incorporated. In particular, even if one were to impose the condition fN< Mpl, this would imply neither D$$ \mathcal{D} $$< Mpl nor D$$ \mathcal{D} $$<NMpl$$ \sqrt{N}{M}_{\mathrm{pl}} $$. We then estimate the actions of instantons that fulfill the WGC. The leading instanton action is bounded from below by S≥SMpl/fN$$ S\ge \mathcal{S}\;{M}_{\mathrm{pl}}/{f}_N $$, with S$$ \mathcal{S} $$ a fixed constant, but in the universal limit S≳SNMpl/fN$$ S\gtrsim \mathcal{S}\sqrt{N}\ {M}_{\mathrm{pl}}/{f}_N $$. Thus, having fN> Mpl does not immediately imply the existence of unsuppressed higher harmonic contributions to the potential. Finally, we argue that in effective axion-gravity theories, the zero-form version of the WGC can be satisfied by gravitational instantons that make negligible contributions to the potential.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/304d472316d3c01e55e21119263b0f1ac38f70c9

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Eran Palti
2. Gary Shiu
3. Pablo Soler
4. M. Montero
5. Michael J. Reece
6. B. Heidenreich
7. Tom Rudelius
8. T. Weigand

In Nuclear and High Energy Physics

1. Eran Palti
2. Gary Shiu
3. Pablo Soler
4. Michael J. Reece
5. B. Heidenreich
6. Tom Rudelius
7. M. Montero
8. T. Weigand

Citations in the corpus

• Sharpening the weak gravity conjecture with dimensional reduction (2015, background): “In the context of axion inflation, wormhole solutions have previously been studied by [8, 10] and criticized by [9, 12].”
• The Weak Gravity Conjecture in three dimensions (2016, methodology): “In particular, it has been recently applied to large-field inflationary models and relaxions [2–22].”
• The Swampland: Introduction and Review (2019, background): “ means that the decay constants for each axion need to decrease by a factor of p N, so f˘p1 N , which then precisely cancels the enhancement of the total decay constant [105,106,109{111]. However, in [120] it was argued that a similar way out to alignment, with sub-leading instantons, can be impleme”
• Evidence for a sublattice weak gravity conjecture (2016, background): “From a phenomenological perspective, the WGC is especially interesting due to its ability to constrain models of large-field axion inflation [6–25].”
• Backreacted axion field ranges in string theory (2016, unknown): “The complex-structure moduli Kahler potential is the mirror of the P[1,1,1,6,9] CY studied in [61].”