The author claims that Hubble drag from the expanding FRW background drives perturbations in a time-crystal phantom dark energy model to decay, but the analysis drops metric perturbations and contains a sign error in the perturbation energy calculation.
Stable Cosmic Time Crystals
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abstract
Cosmological time crystals are created when a scalar field moves periodically through phase space in a spatially flat Friedmann-Robertson-Walker spacetime due to the presence of a limit cycle. All such cosmological time crystals in the literature suffer from gradient instabilities occurring at Null Energy Condition violating phases where the square sound speed for cosmological perturbations becomes negative. Here we present stable cosmological time crystals. Our analysis suggests this new form of scalar matter--cosmic time crystals--may be considered as a physically viable cosmological matter source.
fields
gr-qc 1years
2025 1verdicts
REJECT 1representative citing papers
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A Note on the Stability of the Dark Energy Model from Time Crystals
The author claims that Hubble drag from the expanding FRW background drives perturbations in a time-crystal phantom dark energy model to decay, but the analysis drops metric perturbations and contains a sign error in the perturbation energy calculation.