模拟时变暗能量的衰变暗物质
Decaying dark matter mimicking time-varying dark energy
摘要：
在$Λ$ CDM模型中，暗物质在比哈勃时间更长的时间尺度上衰变为惰性相对论能量，这将产生一个膨胀历史，这可能被误解为稳定的暗物质具有随时间变化的暗能量。我们计算了相应的伪状态方程参数$\widetilde w_ϕ$，作为红移的函数，并表明$\widetilde w_ϕ$的演化强烈依赖于假设的暗物质密度值，错误地采取了规模为$a^{-3}$。根据后者，可以获得模拟精粹的模型（$\widetilde w_ϕ> -1$）、幻象模型（$\widetilde w_ϕ< -1$）或状态方程参数穿过幻象分界线的模型，从高红移的$\widetilde w_ϕ> -1$发展到低红移的$\widetilde w_ϕ< -1$。目前，所有这些模型一般都向$\widetilde w_ϕ\approx -1$收敛。密度扰动的增长打破了含衰减暗物质的$Λ$ CDM模型和相应的伪精粹模型之间的简并性。
英文摘要：
A $Λ$CDM model with dark matter that decays into inert relativistic energy on a timescale longer than the Hubble time will produce an expansion history that can be misinterpreted as stable dark matter with time-varying dark energy. We calculate the corresponding spurious equation of state parameter, $\widetilde w_ϕ$, as a function of redshift, and show that the evolution of $\widetilde w_ϕ$ depends strongly on the assumed value of the dark matter density, erroneously taken to scale as $a^{-3}$. Depending on the latter, one can obtain models that mimic quintessence ($\widetilde w_ϕ> -1$), phantom models ($\widetilde w_ϕ< -1$) or models in which the equation of state parameter crosses the phantom divide, evolving from $\widetilde w_ϕ> -1$ at high redshift to $\widetilde w_ϕ< -1$ at low redshift. All of these models generically converge toward $\widetilde w_ϕ\approx -1$ at the present. The degeneracy between the $Λ$CDM model with decaying dark matter and the corresponding spurious quintessence model is broken by the growth of density perturbations.
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