Speaker
Description
Strongly interacting dark sectors with pseudo–Nambu–Goldstone bosons provide a versatile framework for sub-GeV dark matter. While the original SIMP paradigm emphasises number-changing $3\to2$ processes as the origin of the relic abundance, the phenomenology of pionic dark matter is considerably richer. Depending on the spectrum and couplings, the relic density can instead be controlled by $2\to2$ annihilations (WIMP-like regime), semi-annihilation channels involving vector mesons and further processes like $\pi\pi\pi\to\pi\rho$. A consistent treatment therefore requires a framework that simultaneously captures pion dynamics, vector mesons, anomalous interactions, and portal effects.
We consider QCD-like dark sectors in which the dark matter candidates are pions stabilized by unbroken dark flavor symmetries. The effective theory is formulated using the Hidden Local Symmetry (HLS) approach. The HLS Lagrangian, supplemented by the gauged Wess–Zumino–Witten term, is constructed in a representation-independent manner and is applicable to complex, real, and pseudo-real fermion theories.
As a minimal benchmark, we focus on the pseudo-real symmetry-breaking pattern $SU(2N_f)/Sp(2N_f)$ with $N_f=2$. We incorporate lattice results for $Sp(N_c=4)$ to obtain realistic relations between $m_\pi/f_\pi$ and $m_\rho/m_\pi$. A dark photon portal is included to maintain thermal equilibrium with the visible sector and to assess its impact on relic abundance and dark matter stability within the HLS framework.
| Main Contribution topic | Theory / Phenomenology |
|---|---|
| Secondary contribution topic | Cosmology Dark Matter |