Nonlinear evolution in Galileon EFTs: Regularization and screening
Abstract
In a scalar effective field theory (EFT) with Galileon symmetry, we distinguish the strong-field expansion from the derivative expansion and study spherically symmetric classical nonlinear dynamics. More concretely, we consider two models related via perturbative field redefinitions: one with second-order equations that can also exhibit screening, and one that includes a higher-derivative term that introduces a propagating ghost. The latter term is of the type that can ``regularise'' the equations to render them well-posed as an initial value problem. For initial data that respect the derivative expansion, we find that the first model (ghost-free, unregularised) develops ill-posed regions during evolution only when the derivative expansion breaks down. This result persists in the strong-field regime. We further find that the regularized model reproduces the evolution of the unregularised one when the latter remains well-posed, while it exhibits tachyonic behaviour when the unregularised one becomes ill-posed. We also consider initial data that corresponds to stationary states that exhibit screening in the unregularised, ghost-free theory. In this case, we find that the regularised theory can remain well-posed for initial data that the unregularised one developed ill-posed regions. However, the ghost term naturally dominates over the Galileon term in the screening regime, contrary to common expectation.
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BibTeX
@misc{thaalba2026nonlinear,
title = {{Nonlinear evolution in Galileon EFTs: Regularization and screening}},
author = {Farid Thaalba and Aaron Held and Ramiro Cayuso and Thomas P Sotiriou},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.05407},
eprint = {2609.05407},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05760382v1},
}
RIS
TY - UNPB
TI - Nonlinear evolution in Galileon EFTs: Regularization and screening
AU - Farid Thaalba
AU - Aaron Held
AU - Ramiro Cayuso
AU - Thomas P Sotiriou
PY - 2026
DA - 2026/09/04
PB - HAL
DO - 10.48550/arxiv.2609.05407
UR - https://hal.science/hal-05760382v1
AB - In a scalar effective field theory (EFT) with Galileon symmetry, we distinguish the strong-field expansion from the derivative expansion and study spherically symmetric classical nonlinear dynamics. More concretely, we consider two models related via perturbative field redefinitions: one with second-order equations that can also exhibit screening, and one that includes a higher-derivative term that introduces a propagating ghost. The latter term is of the type that can ``regularise'' the equations to render them well-posed as an initial value problem. For initial data that respect the derivative expansion, we find that the first model (ghost-free, unregularised) develops ill-posed regions during evolution only when the derivative expansion breaks down. This result persists in the strong-field regime. We further find that the regularized model reproduces the evolution of the unregularised one when the latter remains well-posed, while it exhibits tachyonic behaviour when the unregularised one becomes ill-posed. We also consider initial data that corresponds to stationary states that exhibit screening in the unregularised, ghost-free theory. In this case, we find that the regularised theory can remain well-posed for initial data that the unregularised one developed ill-posed regions. However, the ghost term naturally dominates over the Galileon term in the screening regime, contrary to common expectation.
ER -