ased on the section II A <a class="reference external" href="https://arxiv.org/pdf/2204.11864.pdf">Ng et al. 2022</a> paper.</p></li>
<li><p>the volumetric merger rate density of PBHs has a power-law dependence on the age of the Universe <span class="math notranslate nohighlight">\(t(z)\)</span> extending up to <span class="math notranslate nohighlight">\(z \gtrsim 10^3\)</span>.</p></li>
</ul>
<p><span class="math">\begin{equation}
\dot{n}_{PBH} = n_o \left(\frac{t(z)}{t_o}\right)^{-34/37} \text{Mpc}^{-3}\