New constraints on primordial minihalo abundance using cosmic microwave background observations

It was proposed that the massive compact halo objects (MCHOs) would be produced during an earlier epoch of cosmology if the density perturbations are between $3\times {10}^{-4}$ and 0.3. Then these objects can accrete dark matter particles onto them due to their high density. If the dark matter is in the form of the weakly interacting massive particles, the MCHOs can have a significant effect on the evolution of cosmology due to the dark matter annihilation within them. Using the WMAP-7 years data, we investigated the constraints on the current abundance of MCHOs ($f_{\mathrm{MCHOs}}$) formed during the $e^{+}{e}^{-}$ annihilation phase transition. We have found that the $2\sigma$ constraint is $f_{\mathrm{MCHOs}}\lesssim {10}^{-4}$ for dark matter masses in the range between 1 GeV and 1 TeV.

Figure 1

The change of the ionization fraction $x_e$ as a function of the redshift $z$. Upper panel: We fixed the mass of dark matter $m_{\chi }=100\mathrm{GeV}$ and changed the current fraction of MCHOs $f_{\mathrm{MCHOs}}={10}^{-7}$, ${10}^{-6}$, and ${10}^{-5}$, from top to bottom. Lower panel: We fixed the current fraction of MCHOs $f_{\mathrm{MCHOS}}={10}^{-6}$ and changed the dark matter mass $m_{\chi }=10$, 100, and 1000 from top to bottom. Here we fixed the value $⟨\sigma v⟩=3\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$.

Figure 2

The marginalized probability distribution function of parameters $\tau$, $f_{\mathrm{MCHOs}}$, $m_{\chi }$, and $z_{re}$ (solid curves) and the relative mean likelihood (dotted curves).

Figure 3

The 2D contours of the distribution of $f_{\mathrm{MCHOs}}$ and the parameters $\tau$, $m_{\chi }$, and $z_{re}$.