Precise scaling relations for self-interacting bosonic dark matter stars

Abstract

The structural properties of bosonic dark matter stars are systematically investigated, presenting precise scaling relations for the mass, radius, central density, and the properties of dark matter particles. The dark matter equation of state is derived from a complex scalar field theory with a quartic self-interaction potential $V(ϕ) = \fracλ{4} |ϕ|^4$, considering boson masses $m_ϕ$ ranging from $10^{-9}$ to $10^{3}$ GeV and self-coupling constants $λ$ ranging from $0.01π$ to $100π$. The scaling relation for the maximum mass of bosonic dark matter stars, the corresponding critical radius and critical central density are obtained as \[ M_{\text{max}} = 0.1 \frac{\sqrtλ}{m_ϕ^2} M_\odot, \qquad R(M_{\text{max}}) = 0.9 \frac{\sqrtλ}{m_ϕ^2} \ \text{km}, \qquad \varepsilon_{\text{max}} = 2.1 \times 10^5 \frac{m_ϕ^4}λ \ \mathrm{MeV/fm^3}, \] where $m_ϕ$ is in GeV, the relations for $R(M_{\text{max}})$ and $\varepsilon_{\text{max}}$ are first put forward. The fitting relative error is less than $4\%$. Based on these scaling relations, we further provide global analytical fits for the stable branch. The relationships between mass and central density as well as radius and central density can be described by a unified function of the form: \[ \tilde{Y} = \frac{A}{\left[1 + \left(5\tilde{\varepsilon}\right)^h\right]^s}, \] where for $Y=M$, $\tilde{M} \equiv M/M_{\text{max}}$, $A=1$, $h=-2$, $s=0.42$; for $Y=R$, $\tilde{R} \equiv R/R(M_{\text{max}})$, $A=1.634$, $h=1$, $s=0.28$; and $\tilde{\varepsilon} \equiv \varepsilon_0/\varepsilon_{\text{max}}$. The fitting relative error is less than $0.1\%$. Furthermore, we find a simple quadratic polynomial mass-radius relation for bosonic dark matter stars.