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Register a new userCan we discover dual-component thermal WIMP dark matter?
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Stefano Profumo
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We address the question of whether the upcoming generation of dark matter search experiments and colliders will be able to discover if the dark matter in the Universe has two components of weakly interacting massive particles (WIMPs). We outline a model-independent approach, and we study the specific cases of (1) direct detection with low-background 1 ton noble-gas detectors and (2) a 0.5 TeV center of mass energy electron-positron linear collider. We also analyze the case of indirect detection via two gamma-ray lines, which would provide a verification of such a discovery, although multiple gamma-ray lines can in principle originate from the annihilation of a single dark matter particle. For each search channel, we outline a few assumptions to relate the very small set of parameters we consider (defining the masses of the two WIMPs and their relative abundance in the overall dark matter density) with the relevant detection rates. We then draw general conclusions on which corners of a generic dual-component dark matter scenario can be explored with current and next generation experiments. We find that in all channels the ideal setup is one where the relative mass splitting between the two WIMP species is of order 1, and where the two dark matter components contribute in a ratio close to 1:1 to the overall dark matter content of the Universe. Interestingly, in the case of direct detection, future experiments might detect multiple states even if only ~ 10% of the energy-density of dark matter in the Universe is in the subdominant species.
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The paper contains description of the main properties of the galactic dark matter (DM) particles, available approaches for detection of DM, main features of direct DM detection, ways to estimate prospects for the DM detection, the first collider search for a DM candidate within an Effective Field Theory, complete review of ATLAS results of the DM candidate search with LHC RUN I, and less complete review of exotic dark particle searches with other accelerators and not only. From these considerations it follows that one is unable to prove, especially model-independently,a discovery of a DM particle with an accelerator, or collider. One can only obtain evidence on existence of a weakly interacting neutral particle, which could be, or could not be the DM candidate. The current LHC DM search program uses only the missing transverse energy signature. Non-observation of any excess above Standard Model expectations forces the LHC experiments to enter into the same fighting for the best exclusion curve, in which (almost) all direct and indirect DM search experiments permanently take place. But this fighting has very little (almost nothing) to do with a real possibility of discovering a DM particle. The true DM particles possess an exclusive galactic signature --- annual modulation of a signal, which is accessible today only for direct DM detection experiments. There is no way for it with a collider, or accelerator. Therefore to prove the DM nature of a collider-discovered candidate one must find the candidate in a direct DM experiment and demonstrate the galactic signature for the candidate. Furthermore, being observed, the DM particle must be implemented into a modern theoretical framework. The best candidate is the supersymmetry, which looks today inevitable for coherent interpretation of all available DM data.
Multi-component dark matter scenarios constitute natural extensions of standard single-component setups and offer attractive new dynamics that could be adopted to solve various puzzles of dark matter. In this work we present and illustrate properties of a minimal UV-complete vector-fermion dark matter model where two or three dark sector particles are stable. The model we consider is an extension of the Standard Model (SM) by spontaneously broken extra $U(1)_X$ gauge symmetry and a Dirac fermion. All terms in the Lagrangian which are consistent with the assumed symmetry are present, so the model is renormalizable and consistent. To generate mass for the dark-vector $X_mu$ the Higgs mechanism with a complex singlet $S$ is employed in the dark sector. Dark matter candidates are the massive vector boson $X_mu$ and two Majorana fermions $psi_pm$. All the dark sector fields are singlets under the SM gauge group. The set of three coupled Boltzmann equations has been solved numerically and discussed. We have performed scans over the parameter space of the model implementing the total relic abundance and direct detection constraints. The dynamics of the vector-fermion dark matter model is very rich and various interesting phenomena appear, in particular, when the standard annihilations of a given dark matter are suppressed then the semi-annihilations,
We propose a new mechanism where asymmetric dark matter (ADM) and the baryon asymmetry are both generated in the same decay chain of a metastable weakly interacting massive particle (WIMP) after its thermal freeze-out. Dark matter and baryons are connected by a generalized baryon number that is conserved, while the DM asymmetry and baryon asymmetry compensate each other. This unified framework addresses the DM-baryon coincidence while inheriting the merit of the conventional WIMP miracle in predicting relic abundances of matter. Examples of renormalizable models realizing this scenario are presented. These models generically predict ADM with sub-GeV to GeV-scale mass that interacts with Standard Model quarks or leptons, thus rendering potential signatures at direct detection experiments sensitive to low mass DM. Other interesting phenomenological predictions are also discussed, including: LHC signatures of new intermediate particles with color or electroweak charge and DM induced nucleon decay; the long-lived WIMP may be within reach of future high energy collider experiments.
In the next-to minimal supersymmetric standard model (NMSSM) one additional singlet-like Higgs boson with small couplings to standard model (SM) particles is introduced. Although the mass can be well below the discovered 125 GeV Higgs boson mass its small couplings may make a discovery at the LHC difficult. We use a novel scanning technique to efficiently scan the whole parameter space and determine the range of cross sections and branching ratios for the light singlet-like Higgs boson below 125 GeV. This allows to determine the perspectives for the future discovery potential at the LHC. Specific LHC benchmark points are selected representing the salient NMSSM features.
The discovery of dark matter (DM) at XENONnT or LZ would place constraints on DM particle mass and coupling constants. It is interesting to ask when these constraints can be compatible with the DM thermal production mechanism. We address this question within the most general set of renormalisable models that preserve Lorentz and gauge symmetry, and that extend the Standard Model by one DM candidate of mass $m_{rm DM}$ and one particle of mass $M_{med}$ mediating DM-quark interactions. Our analysis divides into two parts. First, we postulate that XENONnT/LZ has detected $mu_Ssimmathcal{O}(100)$ signal events, and use this input to calculate the DM relic density, $Omega_{DM} h^2$. Then, we identify the regions in the $M_{med} - Omega_{DM} h^2$ plane which are compatible with the observed signal and with current CMB data. We find that for most of the models considered here, $mathcal{O}(100)$ signal events at XENONnT/LZ and the DM thermal production are only compatible for resonant DM annihilations, i.e. for $M_{med}simeq2 m_{DM}$. In this case, XENONnT/LZ would be able to simultaneously measure $m_{DM}$ and $M_{med}$. We also discuss the dependence of our results on $m_{DM}$, $mu_S$ and the DM spin, and provide analytic expressions for annihilation cross-sections and mediator decay widths for all models considered in this study.
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