  Atomic dark matter is usually considered to be produced asymmetrically in the
early Universe. In this work, we first propose that the symmetric atomic dark
matter can be thermally produced through the freeze-out mechanism. The dominant
atom anti-atom annihilation channel is the atomic rearrangement. It has a
geometrical cross section much larger than that of elementary fermions. After
the atomic formation, this annihilation process further depletes dark matter
particles and finally freezes out. To give the observed dark matter relic, the
dark atoms are naturally ultraheavy, ranging from $10^6$ to $10^{10}
\,\mathrm{GeV}$.

High Energy Physics - Phenomenology