Oscillatory dark energy with phantom crossings in Einstein-Gauss-Bonnet gravity
Abstract
Recent baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument (DESI), combined with supernova observations, show a mild preference for an evolving dark-energy equation of state, in which dark energy remains phantom-like at higher redshift while a transition toward the quintessence regime emerges around z≲0.5. Beyond the monotonic evolution of the equation of state, an oscillatory dark-energy scenario provides a potential alternative realization of dynamical dark energy. We study such an oscillatory scenario within the Einstein-scalar-Gauss-Bonnet gravity framework, where a scalar field with a hybrid exponential-quadratic potential couples nonminimally to the Gauss-Bonnet (GB) invariant. We choose a Gaussian GB coupling function localized around the minimum of the potential. During the late-time epoch, the field thereby oscillates around the potential minimum and eventually exits toward a stable de Sitter attractor phase. In the minimally coupled limit, the effective equation of state oscillates in the quintessence regime at low redshift, z∼0, without crossing the phantom divide. The nonminimal coupling amplifies the oscillations and drives the effective equation of state across the phantom divide multiple times. Although a sufficiently strong coupling can induce negative scalar and tensor sound speeds, rendering the perturbation modes unstable. We identify a region of parameter space in which the model undergoes multiple phantom crossings while remaining free of ghost and gradient instabilities and approaching a stable de Sitter attractor in the future.
Related
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BibTeX
@misc{hussain2026oscillatory,
title = {{Oscillatory dark energy with phantom crossings in Einstein-Gauss-Bonnet gravity}},
author = {Saddam Hussain and Sandip Biswas},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.37437},
eprint = {2609.37437},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.37437},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Oscillatory dark energy with phantom crossings in Einstein-Gauss-Bonnet gravity
AU - Saddam Hussain
AU - Sandip Biswas
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.37437
UR - https://arxiv.org/abs/2609.37437
AB - Recent baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument (DESI), combined with supernova observations, show a mild preference for an evolving dark-energy equation of state, in which dark energy remains phantom-like at higher redshift while a transition toward the quintessence regime emerges around z≲0.5. Beyond the monotonic evolution of the equation of state, an oscillatory dark-energy scenario provides a potential alternative realization of dynamical dark energy. We study such an oscillatory scenario within the Einstein-scalar-Gauss-Bonnet gravity framework, where a scalar field with a hybrid exponential-quadratic potential couples nonminimally to the Gauss-Bonnet (GB) invariant. We choose a Gaussian GB coupling function localized around the minimum of the potential. During the late-time epoch, the field thereby oscillates around the potential minimum and eventually exits toward a stable de Sitter attractor phase. In the minimally coupled limit, the effective equation of state oscillates in the quintessence regime at low redshift, z∼0, without crossing the phantom divide. The nonminimal coupling amplifies the oscillations and drives the effective equation of state across the phantom divide multiple times. Although a sufficiently strong coupling can induce negative scalar and tensor sound speeds, rendering the perturbation modes unstable. We identify a region of parameter space in which the model undergoes multiple phantom crossings while remaining free of ghost and gradient instabilities and approaching a stable de Sitter attractor in the future.
ER -