Abstract
Thermal freeze-out is a prominent example of dark matter (DM) production mechanism in the early Universe that can yield the correct relic density of stable weakly interacting massive particles (WIMPs). At the other end of the mass scale, many popular extensions of the Standard Model predict the existence of ultralight scalar fields. These can be coupled to matter, preferentially in a universal and shift-symmetry-preserving way. We study the impact of such conformal and disformal couplings on the relic density of WIMPs, without introducing modifications to the thermal history of the Universe. This can either result in an additional thermal contribution to the DM relic density or suppress otherwise too large abundances compared to the observed levels. In this work, we assume that the WIMPs only interact with the standard model via the light scalar portal. We use simple models of fermionic or scalar DM, although a similar discussion holds for more sophisticated scenarios, and predict that their masses should be between $\ensuremath{\sim}100\text{ }\text{ }\mathrm{GeV}$ and several TeV to comply both with the DM abundance and current bounds on the couplings of the light scalars to matter at the LHC. Future searches will tighten these bounds.
Highlights
There is an overwhelming amount of evidence in favor of the gravitational existence of dark matter (DM) and its impact on baryons
III, we study weakly interacting massive particles (WIMPs) DM relic density emerging from the φ portal to the Standard Model (SM), while in Sec
By taking into account the lower bounds on MSM from the Large Hadron Collider (LHC), as shown with horizontal lines in Fig. 2, and the upper bound mψ=χ ≲ MDM dictated by the effective field theory (EFT) validity, one can obtain the correct value of DM relic density assuming universal coupling, MSM 1⁄4 MDM, for the following mass ranges: 100 GeV ≲ mψ ≲ 1 TeV ðconformal; fermionic ψÞ; ð21Þ
Summary
There is an overwhelming amount of evidence in favor of the gravitational existence of dark matter (DM) and its impact on baryons. It is natural to assume that at least some of such ultralight scalars will couple to both gravity and matter and even possibly drive the accelerating expansion of the Universe [16] Such couplings are expected to be universal to all matter species, including the SM and DM, as dictated by the weak equivalence principle, a violation of this rule is allowed to some extent by current observations that constrain more strongly interactions with baryons [17]. To this end, we employ simple conformal and disformal shift-symmetry-preserving operators. Appendix E is devoted to discussion about a difference between gravitational and electromagnetic waves propagation in a disformally modified metric
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