%0 Generic %1 smith2019oscillating %A Smith, Tristan L. %A Poulin, Vivian %A Amin, Mustafa A. %D 2019 %K library %T Oscillating scalar fields and the Hubble tension: a resolution with novel signatures %U http://arxiv.org/abs/1908.06995 %X We present a detailed investigation of a sub-dominant oscillating scalar field ('early dark energy', EDE) in the context of resolving the Hubble tension. Consistent with earlier work, but without relying on fluid approximations, we find that a scalar field frozen due to Hubble friction until $log_10(z_c)\sim3.5$, reaching $\rho_EDE(z_c)/\rho_\rm tot\sim10$%, and diluting faster than matter afterwards can bring cosmic microwave background (CMB), baryonic acoustic oscillations, supernovae luminosity distances, and the late-time estimate of the Hubble constant from the SH0ES collaboration into agreement. A scalar field potential which scales as $V(\phi) \phi^2n$ with $2n3.4$ around the minimum is preferred at the 68% confidence level, and the Planck polarization places additional constraints on the dynamics of perturbations in the scalar field. In particular, the data prefers a potential which flattens at large field displacements. An MCMC analysis of mock data shows that the next-generation CMB observations (i.e., CMB-S4) can unambiguously detect the presence of the EDE at very high significance. This projected sensitivity to the EDE dynamics is mainly driven by improved measurements of the $E$-mode polarization. We also explore new observational signatures of EDE scalar field dynamics: (i) We find that depending on the strength of the tensor-to-scalar ratio, the presence of the EDE might imply the existence of isocurvature perturbations in the CMB. (ii) We show that a strikingly rapid, scale-dependent growth of EDE field perturbations can result from parametric resonance driven by the anharmonic oscillating field for $n2$. This instability and ensuing potentially nonlinear, spatially inhomogenoues, dynamics may provide unique signatures of this scenario.

@misc{smith2019oscillating, abstract = {We present a detailed investigation of a sub-dominant oscillating scalar field ('early dark energy', EDE) in the context of resolving the Hubble tension. Consistent with earlier work, but without relying on fluid approximations, we find that a scalar field frozen due to Hubble friction until ${\rm log}_{10}(z_c)\sim3.5$, reaching $\rho_{\rm EDE}(z_c)/\rho_{\rm tot}\sim10$%, and diluting faster than matter afterwards can bring cosmic microwave background (CMB), baryonic acoustic oscillations, supernovae luminosity distances, and the late-time estimate of the Hubble constant from the SH0ES collaboration into agreement. A scalar field potential which scales as $V(\phi) \propto \phi^{2n}$ with $2\lesssim n\lesssim 3.4$ around the minimum is preferred at the 68% confidence level, and the {\em Planck} polarization places additional constraints on the dynamics of perturbations in the scalar field. In particular, the data prefers a potential which flattens at large field displacements. An MCMC analysis of mock data shows that the next-generation CMB observations (i.e., CMB-S4) can unambiguously detect the presence of the EDE at very high significance. This projected sensitivity to the EDE dynamics is mainly driven by improved measurements of the $E$-mode polarization. We also explore new observational signatures of EDE scalar field dynamics: (i) We find that depending on the strength of the tensor-to-scalar ratio, the presence of the EDE might imply the existence of isocurvature perturbations in the CMB. (ii) We show that a strikingly rapid, scale-dependent growth of EDE field perturbations can result from parametric resonance driven by the anharmonic oscillating field for $n\approx 2$. This instability and ensuing potentially nonlinear, spatially inhomogenoues, dynamics may provide unique signatures of this scenario.}, added-at = {2019-08-21T04:58:18.000+0200}, author = {Smith, Tristan L. and Poulin, Vivian and Amin, Mustafa A.}, biburl = {https://www.bibsonomy.org/bibtex/226c473ee641b8230b0ee222ce5af806a/gpkulkarni}, description = {Oscillating scalar fields and the Hubble tension: a resolution with novel signatures}, interhash = {3e8f1ac2a0f9a631c286820de78fa109}, intrahash = {26c473ee641b8230b0ee222ce5af806a}, keywords = {library}, note = {cite arxiv:1908.06995Comment: 26 pages, 22 figures, comments welcome}, timestamp = {2019-08-21T04:58:18.000+0200}, title = {Oscillating scalar fields and the Hubble tension: a resolution with novel signatures}, url = {http://arxiv.org/abs/1908.06995}, year = 2019 }