On the existence of bound states in SIMP dark sectors
- Author(s)
- Xiaoyong Chu, Josef Pradler, Daris Samart
- Abstract
In strongly interacting massive particle (SIMP) scenarios, dark matter is comprised of stable dark pions whose $3\to 2$ or $4\to 2$ reactions set the dark matter relic abundance. Recent work has shown that shallow two-pion bound states significantly affect the freeze-out, but did not establish whether such states actually form. In this work we demonstrate that a scalar isosinglet bound state does exist in a well-defined region of parameter space by solving an on-shell Lippmann--Schwinger equation in a chiral-unitary framework and analyzing the $S$-wave $ππ$ amplitude in the complex energy plane. We determine the range of $m_π/f_π$ for which a pole appears below the two-pion threshold, extract the corresponding residue, and, in the non-relativistic limit, obtain the bound-state wave function at the origin, $|Ψ(0)|$, which controls bound-state-assisted annihilation and decay rates relevant for catalyzed freeze-out. Comparing this T-matrix based result with variational estimates using simple finite-range potentials, we find agreement within order-one factors for shallow binding. For binding energies of order the freeze-out temperature, $E_B \sim m_π/20$, we obtain $|Ψ(0)|\sim \mathcal{O}(0.1)\,m_π^{3/2}$, thereby supporting the parametric assumptions used in previous phenomenological analyses.
- Organisation(s)
- Particle Physics
- External organisation(s)
- Chinese Academy of Sciences (CAS), Österreichische Akademie der Wissenschaften (ÖAW), Khon Kaen University
- No. of pages
- 28
- Publication date
- 12-2025
- Austrian Fields of Science 2012
- 103034 Particle physics
- Keywords
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/d88e3cb0-1053-454d-8370-279bead24e02