Screened axio-dilaton cosmology: novel forms of early dark energy
PMC12460588
· 10.1140/epjc/s10052-025-14735-4
Gap Declaration
To produce the axion-dilaton screening screening mechanism as simply as possibly while automatically being consistent with astrophysical constraints it is sufficient to restrict the axion coupling to electrons, which is what we consider in this paper. More work is required to consider additional couplings, in particular with simulations with a non trivial profile. However, this is beyond the scope of the current paper. Here f is the growth factor and is the variance of the mass fluctuations within a sphere of radius Mpc. We denote dimensionless fields with tilde’s, as in , reserving for the dimensionful version.
Abstract
We study the cosmology of multi-field Dark Energy, using a well-motivated axio-dilaton model that contains the minimal number of fields to have the 2-derivative sigma-model interactions that power-counting arguments show naturally compete with General Relativity at low energies. Our analysis differs from earlier, related, studies by treating the case where the dilaton’s couplings to matter are large enough to require screening to avoid unacceptable dilaton-mediated forces in the solar system. We use a recently proposed screening mechanism that exploits the interplay between stronger-than-gravitational axion-matter couplings with the 2-derivative axion-dilaton interactions to suppress the couplings of the dilaton to bulk matter. The required axion-matter couplings also modify cosmology, wit…
Conclusions / Discussion
Conclusion Dynamical dark energy requires the existence of very light fields since it is only scalars with masses smaller than the Hubble scale H that move over cosmological timescales, as would be required to be responsible for the time-dependence. On the other hand, it is also generic that a dimensionless scalar field that is gravitationally coupled to a scalar potential of size – where is a generic order-unity function – acquires a mass of order . So given the fact that the Dark Energy density is so small, it perhaps might not be a surprse to find very light scalars at play in the recent history of the universe.17 Of theories with light scalar fields those with only one scalar are special because only for these is it impossible to have two-derivative sigma-model interactions. Two-derivative interactions are special because they scale with energy in the same way as do the two-derivative interactions of GR and this allows them to compete with GR without also jeopardizing the low-energy expansion that justifies working within the semiclassical approximation. The axio-dilaton models we study here provide a minimal, well-motivated example of what the dynamics of such fields can loo…
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