arXiv subjects

John Dumancic

Publications and source records attributed to John Dumancic.

3 recordsLinked to original sources

arXiv2025

Multi-axion like description of the dark sector in light of the Hubble and $σ_8$ tensions

Local methods of direct determination of the Hubble constant and $σ_8$ seem to conflict with the predictions made from the cosmic microwave background and $Λ$CDM. We propose a proof-of-concept model that models portions of the dark sector as several coupled axion-like fields, resulting in both early and late time departures from $Λ$CDM. We determine that the model successfully eliminates both the Hubble and $σ_8$ tensions, while remaining consistent with both the DESI survey and the BAO sound horizon.

astro-ph.CO↗

arXiv2024

Dynamics of Inspiraling Dark Energy

We investigate the dynamics of a multifield dark energy model, which arises from certain rapid-turning and inspiraling trajectories in field space. We find the speed of sound $c_s$ of the dark energy perturbations around the background and show that $c_s$ is monotonically decreasing with time. Furthermore, it has a positive-definite lower bound that implies a certain clustering scale. We also extend the previously known background solution for dark energy to an exact solution that includes matter. This allows us to address the implications of our model for two cosmological tensions. More precisely, we argue that the $σ_8$ tension can be alleviated generically, while reducing the Hubble tension requires certain constraints on the parameter space of the model. Notably, a necessary condition for alleviating the Hubble tension is that the transition from matter domination to the dark energy epoch begins earlier than in $Λ$CDM.

hep-th↗

arXiv2022

Dark Energy from Inspiraling in Field Space

We find an exact solution of the equations of motion of a two-field cosmological model, which realizes multi-field dark energy. The latter is characterized by field-space trajectories with turning rates that are always large. We study a class of two-field models and show that it is possible to have such trajectories, giving accelerated space-time expansion, even when the scalar potential preserves the rotational invariance of the field-space metric. For the case of Poincaré-disk field space, we derive the form of the scalar potential compatible with such background solutions and, furthermore, we find the exact solutions analytically. Their field-space trajectories are spirals inward, toward the center of the Poincaré disk. Interestingly, the functional form of the relevant scalar potential is compatible with a certain hidden symmetry, although the latter is broken by the presence of a constant term.

hep-th↗