Resonance enhancement of dark matter interactions: the case for early kinetic decoupling and velocity dependent resonance width

Abstract

Motivated by the possibility of enhancing dark matter (DM) self-interaction cross-section σ self , we have revisited the issue of DM annihilation through a Breit-Wigner resonance. In this case thermally averaged annihilation cross-section has strong temperature dependence, whereas elastic scattering of DM on the thermal bath particles is suppressed. This leads to the early kinetic decoupling of DM and an interesting interplay in the evolution of DM density and temperature that can be described by a set of coupled Boltzmann equations. The standard Breit-Wigner parametrization of a resonance propagator is also corrected by including momentum dependence of the resonance width. It has been shown that this effects may change predictions of DM relic density by more than order of magnitude in some regions of the parameter space. Model independent discussion is illustrated within a theory of Abelian vector dark matter. The model assumes extra U (1) symmetry group factor and an additional complex Higgs field needed to generate a mass for the dark vector boson, which provides an extra neutral Higgs boson h 2 . We discuss the resonance amplification of σ self . It turns out that if DM abundance is properly reproduced, the Fermi-LAT data favor heavy DM and constraint the enhancement of σ self to the range, which cannot provide a solution to the small-scale structure problems.The dark matter (DM) constitutes 84.5% of total Universe matter [1], nevertheless its origin is still unknown in spite of unprecedented effort made both by experimentalists and theoreticians. Even more, the standard WIMP (weakly interacting massive particles) paradigm seems to suffer from various difficulties when confronted with observations on small cosmological scales. For instance "too-big-to-fail" [2, 3] and the "cusp-core" [4][5][6][7] problems are widely discussed in the literature. In particular, the DM densities inferred in central regions of DM dominated galaxies are usually smaller than expected from WIMP simulations [8,9]. It turns out that an appealing alternative is to assume that dark matter may self-interact strongly [10]. The assumption of self-interacting dark matter (SIDM) implies that central (largest) DM density could be reduced. The numerical simulations have shown that SIDM halos are consistent with observations if DM particles have a nuclear-scale self-interaction cross-section 0.1 cm 2 /g < σ self /M DM < 10 cm 2 /g within halos [8,[11][12][13][14][15][16][17][18][19]. The largest values of σ self /M DM are in contradiction with the cluster limit, σ self /M DM < 1.25 cm 2 g −1 [20], therefore scenarios with velocity-dependent σ self /M DM are preffered [21].The aforementioned problems directly encouraged us to study the possibility for the Breit-Wigner resonant enhancement of dark matter annihilation and self-scattering [22][23][24][25][26][27][28][29][30][31][32]. However, it turns out that physics relevant in the vicinity of a resonance is interesting on its own and worth studying in details regardless of any phenomenological a...

Improved bounds on ℤ3 singlet dark matter

“…The requirement that the thermal relic density be equal to the observed value Ω c h 2 = 0.120 ± 0.001 [98] provides a very strong constraint on the model. For an accurate determination of the theoretical prediction matching the precision of measurements, we use the treatment first introduced in [99] and extended to the early kinetic decoupling regime in [76,77], based on solving the coupled system of Boltzmann equations (cBE) for the number density and the second moment of the phase space distribution. 2 Whenever the kinetic decoupling happens significantly later than chemical one we use the micrOMEGAs 5.0 [86] to calculate relic density.…”

“…However, if the latter are enhanced (e.g., by a resonance), or in general when scattering processes are unrelated to the number changing ones (as is the case of semi-annihilation) there is no reason to expect that this standard assumption is satisfied. Indeed, it has been shown recently [76] (see also [77]) that kinetic decoupling can get under way as early as the chemical one and the subsequent change of the shape of the DM phase space distribution can modify the relic abundance by even more than an order of magnitude. In fact, the concrete example that is given in [76] is the case of Z 2 scalar singlet dark matter around the Higgs resonance, which finds its clear analogue in the Higgs resonance region of the Z 3 singlet DM.…”

Gauge-independent approach to resonant dark matter annihilation

“…A popular DM scenario [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] is based on the working hypothesis that there exists a mediator with couplings to both DM and SM particles, and whose mass happens to be approximately twice that of the DM. In such scenarios, one has to consider DM annihilation processes at energies where the tree-level propagator of the mediator becomes singular.…”

Gravitational wave signals of pseudo-Goldstone dark matter in the Z3 complex singlet model

“…Note that the BR inv can exclude points with m χ > m h /2, because the Higgs boson can decay invisibly also to two h 2 if it is light enough. Early kinetic decoupling [92,93] may additionally enhance BR inv several times [31], but in practice this would not change the parameter space of GW signals. In particular, all our points with a potentially measurable GW signal have m χ , m 2 > m h /2.…”