Speaker
Description
Strongly interacting dark sectors with pseudo–Nambu–Goldstone bosons provide a compelling and versatile framework for sub-GeV dark matter. While the original SIMP paradigm emphasizes number-changing $3\to2$ processes as the primary mechanism for setting the relic abundance, the phenomenology of pionic dark matter is significantly richer. Depending on the mass spectrum and interaction strengths, the relic density may instead be governed by $2\to2$ annihilations (WIMP-like regime), semi-annihilation channels involving vector mesons, as well as higher-order processes such as $\pi\pi\pi\to\rho$. A comprehensive description therefore requires a framework that consistently incorporates pion dynamics, vector resonances, anomalous interactions, and portal couplings.
We study QCD-like dark sectors in which the dark matter candidates are pions stabilized by unbroken dark flavor symmetries. The low-energy effective theory is formulated within the Hidden Local Symmetry (HLS) approach. The resulting HLS Lagrangian, augmented by the gauged Wess–Zumino–Witten term, is constructed in a representation-independent way and applies to complex, real, and pseudo-real fermion theories.
As a minimal benchmark, we consider 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 ensure thermal contact with the visible sector and to evaluate its impact on the relic abundance and the stability of dark matter within the HLS framework.