Split SIMPs with decays

Abstract

We discuss a minimal realization of the strongly interacting massive particle (SIMP) framework. The model includes a dark copy of QCD with three colors and three light flavors. A massive dark photon, kinetically mixed with the Standard Model hypercharge, maintains kinetic equilibrium between the dark and visible sectors. One of the dark mesons is necessarily unstable but long-lived, with potential impact on CMB observables. We show that an approximate “isospin” symmetry acting on the down-type quarks is an essential ingredient of the model. This symmetry stabilizes the dark matter and allows to split sufficiently the masses of the other states to suppress strongly their relic abundances. We discuss for the first time the SIMP cosmology with sizable mass splittings between all meson multiplets. We demonstrate that the SIMP mechanism remains efficient in setting the dark matter relic density, while CMB constraints on unstable relics can be robustly avoided. We also consider the phenomenological consequences of isospin breaking, including dark matter decay. Cosmological, astrophysical, and terrestrial probes are combined into a global picture of the parameter space. In addition, we outline an ultraviolet completion in the context of neutral naturalness, where confinement at the GeV scale is generic. We emphasize the general applicability of several novel features of the SIMP mechanism that we discuss here.

Exothermic dark mesons in light of electron recoil excess at XENON1T

“…Then, general dark mesons can be described by the chiral perturbation theory with the WZW term in the dark sector [13,14,[17][18][19][20][21].…”

“…Here, ξ is the gauge kinetic mixing, M is the dark quark mass matrix, µ parametrizes the dark QCD condensation scale, and the coefficient of the Z corrections to dark mesons is parametrized as c ∼ 1 20,21]. We also note that L WZW is the Wess-Zumino-Witten term, which contains in the leading order,…”

“…Here, we find that there is no extra Z − Z − π − π coupling coming from the gauged WZW term in our case due to Q 2 = 1. The WZW term is important for determining the relic density with 3 → 2 annihilation processes for SIMP dark mesons with N f ≥ 3 in the strongly coupled regime [14,17,18,20,21].…”

“…Split masses for dark mesons were also discussed in refs [20,21],. but the dark charge operator for Z and the dark quark mass matrix are taken to be diagonalized simultaneously, unlike our case.…”

A multi-component SIMP model with U(1)X → Z2 × Z3

“…The Strongly Interacting Massive Particle (SIMP) paradigm [3,4], where the DM relic density is dominantly determined by 3 → 2 processes in the dark sector, is one of such new paradigms and gained a great attention during the last several years; see refs. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] for studies on various aspects of SIMP scenarios. DM in the SIMP scenarios typically has a strong coupling and small mass scale (typically 10 MeV-1 GeV) [3].…”