Evading direct dark matter detection in Higgs portal models

We systematically study light (< few GeV) Dark Matter (DM) models that thermalize with visible matter through the Higgs portal and identify the remaining gaps in the viable parameter space. Such models require a comparably light scalar mediator that mixes with the Higgs to avoid DM overproduction and can be classified according to whether this mediator decays (in)visibly. In a representative benchmark model with Dirac fermion DM, we find that, even with conservative assumptions about the DM-mediator coupling and mass ratio, the regime in which the mediator is heavier than the DM is fully ruled out by a combination of collider, rare meson decay, and direct detection limits; future and planned experiments including NA62 can further improve sensitivity to scenarios in which the Higgs portal interaction does not determine the DM abundance. The opposite, regime in which the mediator is lighter than the DM and the latter annihilates to pairs of visibly-decaying mediators is still viable, but much of the parameter space is covered by rare meson decay, supernova cooling, beam dump, and direct detection constraints. Nearly all of these conclusions apply broadly to the simplest variations (e.g. scalar or asymmetric DM). Future experiments including SHiP, NEWS, and Super-CDMS SNOLAB can greatly improve coverage to this class of models.

The particle-physics nature of dark matter (DM) remains one of the central open questions in modern physics. A widely used framework to investigate DM properties is provided by s -channel simplified models (), which extend the Standard Model with a DM particle and a mediator that connects the visible and dark sectors. Much of the parameter space is already constrained by direct and indirect detection, collider searches, and the measured DM relic abundance. We show, however, that the regime ( m DM ≃ m med / 2 ) remains viable under current bounds and will be stringently tested by forthcoming experiments. Using a full Boltzmann treatment that allows for departures from kinetic equilibrium near resonance, we demonstrate that this regime can reproduce the observed relic density with couplings compatible with direct-detection limits. We also show that models with s -wave dominated annihilation can explain the -LAT Galactic Center Excess with couplings consistent with relic-density and direct-detection constraints. Finally, we propose two minimal constructions that naturally realize m med ≈ 2 m DM , making the resonant scenario generic rather than fine-tuned.

We construct models of dark matter with suppressed spin-independent\nscattering cross section utilizing the existing simplified model framework.\nEven simple combinations of simplified models can exhibit interference effects\nthat cause the tree level contribution to the scattering cross section to\nvanish, thus demonstrating that direct detection limits on simplified models\nare not robust when embedded in a more complicated and realistic framework. In\ngeneral for fermionic WIMP masses &gt;10 GeV direct detection limits on the\nspin-independent scattering cross section are much stronger than those coming\nfrom the LHC. However these model combinations, which we call less-simplified\nmodels, represent situations where LHC searches become more competitive than\ndirect detection experiments even for moderate dark matter mass. We show that a\ncomplementary use of several searches at the LHC can strongly constrain the\ndirect detection blind spots by setting limits on the coupling constants and\nmediators' mass. We derive the strongest limits for combinations of vector +\nscalar, vector + "squark", and "squark" + scalar mediator, and present the\ncorresponding projections for the LHC 14 TeV for a number of searches:\nmono-jet, jets + missing energy, and searches for heavy vector resonances.\n

We propose a two-component dark matter (DM) scenario by extending the Standard Model with two additional <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>S</a:mi><a:mi>U</a:mi><a:mo stretchy="false">(</a:mo><a:mn>2</a:mn><a:msub><a:mo stretchy="false">)</a:mo><a:mi>L</a:mi></a:msub></a:math> doublets, one scalar, and another fermion. To ensure the stability of the DM components, we impose a global <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mi mathvariant="script">Z</e:mi><e:mn>2</e:mn></e:msub><e:mo>×</e:mo><e:msubsup><e:mi mathvariant="script">Z</e:mi><e:mn>2</e:mn><e:mo>′</e:mo></e:msubsup></e:math> symmetry. The lightest neutral states for both the scalar and fermion, which are non-trivially transformed under the extended symmetry, behave as stable two-component DM candidates. While single components are underabundant due to their gauge interactions, in a mass region between <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>m</i:mi><i:mi>W</i:mi></i:msub></i:math> and 525 GeV for the scalar and a mass below 1200 GeV for the fermion, and the fermion DM conflicts with direct detection limits over the whole parameter space, having two components helps to saturate relic density in the regions with under-abundance. Compliance with direct detection constraints leads to two options, either introducing dim-5 effective operators, or embedding the scenarios into a complete UV theory, which reproduces a type II seesaw model, thus naturally including neutrino masses. We analyze the consequences of this scenario at the LHC.

Probing light inelastic dark matter from direct detection

In this review, I describe a class of dark matter (DM) models where DM is either stable due to unbroken dark gauge symmetries, or long-lived due to accidental global symmetries resulting from the underlying dark gauge symmetries. Within these models, I discuss various topics on DM in the context of particle and astroparticle physics and cosmology: DM thermal relic density and (in)direct detection, Higgs inflation assisted with Higgs portal interaction, dark radiation (DR), DM-DR interaction and suppression of the matter power spectrum at large k, strong first order phase transition and gravitational wave production, etc.. Especially I emphasize the importance of dark gauge symmetries, unitarity and renormalizability, and the limitation of the DM effective field theory (EFT) or simplified models for DM searches at high energy colliders, including the role of dark Higgs boson and dark gauge bosons.

We point out that the lightest Kaluza–Klein particle (LKP) dark matter in universal extra dimension (UED) models efficiently annihilates through the coannihilation process including the first KK Higgs bosons when the Higgs mass is slightly heavy as 200–230 GeV, which gives the large Higgs self-coupling. The large self-coupling naturally leads the mass degeneracy between the LKP and the first KK Higgs bosons and large annihilation cross sections of the KK Higgs bosons. These are essential for the enhancement of the annihilation of the LKP dark matter, which allows large compactification scale ∼1 TeV to be consistent with cosmological observations for the relic abundance of dark matter. We found that the thermal relic abundance of the LKP dark matter could be reconciled with the stringent constraint of electroweak precision measurements in the minimal UED model.

The initial density of dark matter (DM) particles, otherwise secluded from the standard model (SM), may be generated at reheating, with an initial temperature ratio for internal thermalizations, ξi=TDM,i/TSM,i. This scenario necessarily implies inflaton-mediated scatterings between DM and SM after reheating, with a rate fixed by the relic abundance of DM and the reheat temperature. These scatterings can be important for an inflaton mass and reheat temperature as high as O(107 GeV) and O(109 GeV), respectively, since the thermally averaged collision terms become approximately independent of the inflaton mass when the bath temperature is larger than the mass. The impact of these scatterings on DM cosmology is studied modeling the perturbative reheating physics by a gauge-invariant set of inflaton interactions up to dimension 5 with the SM gauge bosons, fermions, and the Higgs fields. It is observed that an initially lower (higher) DM temperature will rapidly increase (decrease), even with very small couplings to the inflaton. There is a sharp lower bound on the DM mass below which the relic abundance cannot be satisfied due to faster backscatterings depleting DM quanta to SM particles. For low DM masses, the cosmic microwave background constraints become stronger due to the collisions for ξi&lt;1, probing values as small as O(10−4), and weaker for ξi&gt;1. The big-bang nucleosynthesis constraints become stronger due to the collisions for lower DM masses, probing ξi as small as O(0.1), and weaker for higher DM mass. Thus inflaton-mediated collisions with predictable rates, relevant even for high-scale inflation models, can significantly impact the cosmology of light DM. Published by the American Physical Society 2024

The coannihilation mechanism is a well-motivated alternative to the simple thermal freeze-out mechanism, where the dark matter relic density can be obtained through the coannihilation with a partner particle of similar mass with dark matter. When the partner particle is neutral, the inelastic nature of dark matter can help it to escape the direct detection limits. In this work, we focus on the coannihilation scenario in which the annihilation cross section is dominated by the partner-partner pair annihilation. We pay special interest on the parameter space where the coannihilation partner is long-lived, which leads to displaced signatures at the collider. In such case, it opens the heavy mass parameter space for the coannihilation dark matter, comparing with those dominated by the partner-dark matter annihilation. Specifically, we study an inelastic scalar dark matter model with a specific parameter space, which realizes the domination of partner-partner pair annihilation. Then, we study two different realizations of the coannihilation partner decay and the existing constraints from the relic abundance, direct and indirect dark matter detection and the collider searches. We focus on the channel that the long-lived coannihilation partner decays to dark matter plus leptons. The high-luminosity LHC can reach good sensitivities for such heavy dark matter and coannihilation partner around 100–700 GeV.

In this paper, we investigate the possibility of testing the weakly interacting massive particle (WIMP) dark matter (DM) models by applying the simplest phenomenological model which introduces an interaction term between dark energy (DE) and WIMP DM, i.e., Q = 3γDMHρDM. In general, the coupling strength γDE is close to 0 as the interaction between DE and WIMP DM is very weak, thus the effect of γDE on the evolution of Y associated with DM energy density can be safely neglected. Meanwhile, our numerical calculation also indicates that xf ≈ 20 is associated with DM freeze-out temperature, which is the same as the vanishing interaction scenario. As for DM relic density, it will be magnified by frac{2-3{upgamma}_{mathrm{DM}}}{2}{left[2pi {g}_{ast }{m}_{mathrm{DM}}^3/left(45{s}_0{x}_f^3right)right]}^{gamma_{mathrm{DM}}} times, which provides a new way to test WIMP DM models. As an example, we analyze the case in which WIMP DM is a scalar DM. (SGL+SNe+Hz) and (CMB+BAO+SNe) cosmological observations will give γDM = {0.134}_{-0.069}^{+0.17} and γDM = −0.0008 ± 0.0016, respectively. After further considering the constraints from DM direct detection experiment, DM indirect detection experiment, and DM relic density, we find that the allowed parameter space of the scalar DM model will be completely excluded for the former cosmological observations, while it will increase for the latter ones. Those two cosmological observations lead to an almost paradoxical conclusion. Therefore, one could expect more stringent constraints on the WMIP DM models, with the accumulation of more accurate cosmological observations in the near future.

We consider extensions of the Standard Model by a hidden sector consisting of a gauge field coupled with a scalar field. In the absence of dimensionful parameters in the tree-level potential, radiative symmetry breaking will induce the electroweak scale of the Standard Model and generate mass for the hidden sector gauge field. We consider both $U(1{)}_{\mathrm{D}}$ and $SU(2{)}_{\mathrm{D}}$ dark sector gauge groups and focus on probing the models with a combination of direct detection experiments and gravitational wave observatories. We find that recent dark matter direct detection results significantly constrain the parameter space of the models where they can account for the observed dark matter relic density via freeze-out. The gravitational wave signals originating from strongly first-order electroweak phase transition in these models can be probed in future gravitational wave observatories such as the Laser Interferometer Space Antenna. We show how the projected results complement direct detection experiments and can help probe parameter space near the neutrino floor of direct detection.

Constraining the interaction strength between dark matter and visible matter: II. Scalar, vector and spin-3/2 dark matter

We propose a Majoron-like extension of the Standard Model with an extra global U(1)X-symmetry where neutrino masses are generated through an inverse seesaw mechanism at the 1-loop level. In contrast to the tree-level inverse seesaw, our framework contains dark matter (DM) candidates stabilized by a residual Z2-symmetry surviving spontaneous breaking of the U(1)X-group. We explore the case in which the DM is a Majorana fermion. Furthermore, we provide parameter space regions allowed by current experimental constraints coming from the dark matter relic abundance, (in)direct detection, and charged lepton flavor violation.

We construct a scalar dark matter model with mathrm{U}{(1)}_{L_{mu }-{L}_{tau }} symmetry in which the dark matter interacts with the quark flavours, allowing lepton non-universal b → sell overline{ell} decays. The model can solve b → sμμ left({R}_{K^{left(ast right)}}right) anomaly and accommodate the relic abundance of dark matter simultaneously while satisfying the constraints from other low energy flavour experiments and direct detection experiments of dark matter. The new fields include vector-like heavy quarks U and D, mathrm{U}{(1)}_{L_{mu }-{L}_{tau }} breaking scalar S, as well as the dark matter candidate XI and its heavy partner XR. To explain both b → sμμ anomaly and the dark matter, i) large mass difference between XR and XI is required, ii) electroweak scale dark matter and heavy quarks are favoured, iii) not only electroweak scale but mathcal{O} (10) TeV dark gauge boson Z′ and XR are allowed.

Non-perturbative effect on thermal relic abundance of dark matter