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Inspired by our recent paper reshuffled SIMP dark matter, we notice that the reaction rate of the two-loop induced $2 to 2$ process may dominate over or be comparable with that of the $3 to 2$ process at the chemical freezeout of Co-SIMP dark matter [Phys. Rev. Lett. 125, 131301 (2020)], especially when the Co-SIMP mass is close to the standard model particle mass (called the edge case). To check our point, we then derive the Boltzmann equation with all relevant annihilation cross sections in an electrophilic model and numerically solve it to obtain the cosmological evolution of Co-SIMP dark matter. Our result shows that the two-loop induced $2 to 2$ process does modify the parameter space of the coupling for the edge case in the Co-SIMP mechanism and has to be taken into account in UV completion models.
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We consider Dark Matter composed of an oscillating singlet scalar field. On top of the mass term, the scalar is equipped with a potential spontaneously breaking Z_2-symmetry. This potential dominates at early times and leads to the time-dependent expectation value of the scalar, which decreases in the expanding Universe. As it drops below some critical value, the symmetry gets restored, and the Dark Matter field starts to oscillate around zero. We arrange the spontaneous symmetry breaking through the interaction of the scalar with the Ricci curvature. In that way, superheavy Dark Matter can be produced at very early times. Depending on its mass, the production takes place at inflation (very large masses up to the Grand Unification scale), at preheating, or at radiation-dominated stage (masses 10^{6}-10^{7} Gev).
We present models of resonant self-interacting dark matter in a dark sector with QCD, based on analogies to the meson spectra in Standard Model QCD. For dark mesons made of two light quarks, we present a simple model that realizes resonant self-interaction (analogous to the $phi$-K-K system) and thermal freeze-out. We also consider asymmetric dark matter composed of heavy and light dark quarks to realize a resonant self-interaction (analogous to the $Upsilon(4S)$-B-B system) and discuss the experimental probes of both setups. Finally, we comment on the possible resonant self-interactions already built into SIMP and ELDER mechanisms while making use of lattice results to determine feasibility.
We propose a self-interacting boosted dark matter (DM) scenario as a possible origin of the recently reported excess of electron recoil events by the XENON1T experiment. The Standard Model has been extended with two vector-like fermion singlets charged under a dark $U(1)_D$ gauge symmetry to describe the dark sector. While the presence of light vector boson mediator leads to sufficient DM self-interactions to address the small scale issues of cold dark matter, the model with GeV scale DM can explain the XENON1T excess via scattering of boosted DM component with electrons at the detector. The requirement of large annihilation rate of heavier DM into the lighter one for sufficient boosted DM flux leads to suppressed thermal relic abundance. A hybrid setup of thermal and non-thermal contribution from late decay of a scalar can lead to correct relic abundance. All these requirements leave a very tiny parameter space for sub-GeV DM keeping the model very predictive for near future experiments.
Axion is a promising candidate of dark matter. After the Peccei-Quinn symmetry breaking, axion strings are formed and attached by domain walls when the temperature of the universe becomes comparable to the QCD scale. Such objects can cause cosmological disasters if they are long-lived. As a solution for it, the Lazarides-Shafi mechanism is often discussed through introduction of a new non-Abelian (gauge) symmetry. We study this mechanism in detail and show configuration of strings and walls. Even if Abelian axion strings with a domain wall number greater than one are formed in the early universe, each of them is split into multiple Alice axion strings due to a repulsive force between the Alice strings even without domain wall. When domain walls are formed as the universe cools down, a single Alice string can be attached by a single wall because a vacuum is connected by a non-Abelian rotation without changing energy. Even if an Abelian axion string attached by domain walls are created due to the Kibble Zurek mechanism at the chiral phase transition, such strings are also similarly split into multiple Alice strings attached by walls in the presence of the domain wall tension. Such walls do not form stable networks since they collapse by the tension of the walls, emitting axions.
Dark matter may self-interact through a continuum of low-mass states. This happens if dark matter couples to a strongly-coupled nearly-conformal hidden sector. This type of theory is holographically described by brane-localized dark matter interacting with bulk fields in a slice of 5D anti-de Sitter space. The long-range potential in this scenario depends on a non-integer power of the spatial separation, in contrast to the Yukawa potential generated by the exchange of a single 4D mediator. The resulting self-interaction cross section scales like a non-integer power of velocity. We identify the Born, classical and resonant regimes and investigate them using state-of-the-art numerical methods. We demonstrate the viability of our continuum-mediated framework to address the astrophysical small-scale structure anomalies. Investigating the continuum-mediated Sommerfeld enhancement, we demonstrate that a pattern of resonances can occur depending on the non-integer power. We conclude that continuum mediators introduce novel power-law scalings which open new possibilities for dark matter self-interaction phenomenology.
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