Can Dark Matter be a Scalar Field?

TL;DR

This study investigates a real scalar field as a dark matter candidate, deriving lower mass limits from observational data and confirming its viability without an upper mass constraint.

Contribution

It provides new lower bounds on scalar field dark matter mass using SN Ia and Planck data, expanding the understanding of scalar fields as dark matter candidates.

Findings

Lower mass limit: m ≥ 0.12H_0^{-1} eV

Mass estimate for H_0=73 km/s/Mpc: m ≥ 1.56×10^{-33} eV

No evidence for an upper mass limit from SN Ia data

Abstract

In this paper we study a real scalar field as a possible candidate to explain the dark matter in the universe. In the context of a free scalar field with quadratic potential, we have used Union 2.1 SN Ia observational data jointly with a Planck prior over the dark matter density parameter to set a lower limit on the dark matter mass as $m\geq0.12H_0^{-1}$ eV ($c=\hbar=1$). For the recent value of the Hubble constant indicated by the Hubble Space Telescope, namely $H_0=73\pm1.8$ km s$^{-1}$Mpc$^{-1}$, this leads to $m\geq1.56\times10^{-33}$ eV at 99.7\% c.l. Such value is much smaller than $m\sim 10^{-22}$ eV previously estimated for some models. Nevertheless, it is still in agreement with them once we have not found evidences for a upper limit on the scalar field dark matter mass from SN Ia analysis. In practice, it confirms free real scalar field as a viable candidate for dark matter in agreement with previous studies in the context of density perturbations, which include scalar field self interaction.