Dark Matter Coupling Research Articles

Dark matter bound state formation via emission of a charged scalar

The formation of stable or meta-stable bound states can dramatically affect the phenomenology of dark matter (DM). Although the capture into bound states via emission of a vector is known to be significant, the capture via scalar emission suffers from cancellations that render it important only within narrow parameter space. While this is true for neutral scalar mediators, here we show that bound-state formation via emission of a charged scalar can be extremely significant. To this end, we consider DM charged under a dark U(1) force and coupled also to a light complex scalar that is charged under the same gauge symmetry. We compute the cross-sections for bound-state formation via emission of the charged scalar, and show that they can exceed those for capture via vector emission, as well as annihilation, by orders of magnitude. This holds even for very small values of the DM coupling to the charged scalar, and remains true in the limit of global symmetry. We then compute the DM thermal freeze-out, and find that the capture into meta-stable bound states via emission of a charged scalar can cause a late period of significant DM depletion. Our results include analytical expressions in the Coulomb limit, and are readily generalisable to non-Abelian interactions. We expect them to have implications for Higgs-portal scenarios of multi-TeV WIMP DM, as well as scenarios that feature dark Higgses or (darkly-)charged inert scalars, including models of self-interacting DM.

Global analysis of dark matter simplified models with leptophobic spin-one mediators using MasterCode

We report the results of a global analysis of dark matter simplified models (DMSMs) with leptophobic mediator particles of spin one, considering the cases of both vector and axial-vector interactions with dark matter (DM) particles and quarks. We require the DMSMs to provide all the cosmological DM density indicated by Planck and other observations, and we impose the upper limits on spin-independent and -dependent scattering from direct DM search experiments. We also impose all relevant LHC constraints from searches for monojet events and measurements of the dijet mass spectrum. We model the likelihood functions for all the constraints and combine them within the MasterCode framework, and probe the full DMSM parameter spaces by scanning over the mediator and DM masses and couplings, not fixing any of the model parameters. We find, in general, two allowed regions of the parameter spaces: one in which the mediator couplings to Standard Model (SM) and DM particles may be comparable to those in the SM and the cosmological DM density is reached via resonant annihilation, and one in which the mediator couplings to quarks are lesssim , 10^{-3} and DM annihilation is non-resonant. We find that the DM and mediator masses may well lie within the ranges accessible to LHC experiments. We also present predictions for spin-independent and -dependent DM scattering, and present specific results for ranges of the DM couplings that may be favoured in ultraviolet completions of the DMSMs.

MeV neutrino dark matter: relic density, lepton flavour violation and electron recoil

Right-handed neutrinos with MeV to GeV mass are very promising candidates for dark matter (DM). Not only can they solve the missing satellite puzzle, the cusp-core problem of inner DM density profiles, and the too-big-to fail problem, i.e. that the unobserved satellites are too big to not have visible stars, but they can also account for the Standard Model (SM) neutrino masses at one loop. We perform a comprehensive study of the right-handed neutrino parameter space and impose the correct observed relic density and SM neutrino mass differences and mixings. We find that the DM masses are in agreement with bounds from big-bang nucleosynthesis, but that these constraints induce sizeable DM couplings to the charged SM leptons. We then point out that previously overlooked limits from current and future lepton flavour violation experiments such as MEG and SINDRUM heavily constrain the allowed parameter space. Since the DM is leptophilic, we also investigate electron recoil as a possible direct detection signal, in particular in the XENON1T experiment. We find that despite the large coupling and low backgrounds, the energy thresholds are still too high and the predicted cross sections too low due to the heavy charged mediator, whose mass is constrained by LEP limits.

Ultra-compact spherically symmetric dark matter charged star objects

We study the properties of ultra-compact spherically symmetric dark matter sector star objects, being the solution of Einstein equations with two U(1)-gauge fields. One of them is the ordinary Maxwell field, while the auxiliary gauge field pertains to the hidden sector, and mimics the properties of dark matter. The visible and hidden sectors are coupled by a kinetic mixing term with a coupling constant α. We also investigate the possibility of condensation of charged scalar field around the reflecting dark matter star object. It happens that dark matter sector, both dark matter charge and coupling constant, cause shrinking of the star radius for which the condensation may occur.

Searching for Ultralight Dark Matter with Optical Cavities.

We discuss the use of optical cavities as tools to search for dark matter (DM) composed of virialized ultralight fields (VULFs). Such fields could lead to oscillating fundamental constants, resulting in oscillations of the length of rigid bodies. We propose searching for these effects via differential strain measurement of rigid and suspended-mirror cavities. We estimate that more than 2 orders of magnitude of unexplored phase space for VULF DM couplings can be probed at VULF Compton frequencies in the audible range of 0.1-10kHz.

Dark energy, the swampland, and the equivalence principle

It has recently been argued that string theory does not admit de Sitter vacua. This would imply that the current accelerated expansion of the universe is not driven by a cosmological constant (or vacuum energy) but by other means such as a quintessential scalar field. Such a scalar field is in general expected to couple to at least some matter species, such as dark matter. Cosmological observations already constrain such dark matter couplings strongly. We argue that there are a number of interesting scenarios to be explored, such as coupling functions which possess a minimum at finite field values. In these theories, the effective gravitational coupling between dark matter particles grows with time and are consistent with observations of the anisotropies in the cosmic microwave background radiation and large scale structures. We argue that such couplings might also help to alleviate the tension between the swampland conjectures and the properties of the quintessential potential. Observational signatures of violations of the equivalence principle in the dark sector are expected in the non-linear regime on intermediate or small scales.

Neutrino portals to dark matter

We explore the possibility that dark matter interactions with Standard Model particles are dominated by interactions with neutrinos. We examine whether it is possible to construct such a scenario in a gauge invariant manner. We first study the coupling of dark matter to the full lepton doublet and confirm that this generally leads to the dark matter phenomenology being dominated by interactions with charged leptons. We then explore two different implementations of the neutrino portal in which neutrinos mix with a Standard Model singlet fermion that interacts directly with dark matter through either a scalar or vector mediator. In the latter cases we find that the neutrino interactions can dominate the dark matter phenomenology. Present neutrino detectors can probe dark matter annihilations into neutrinos and already set the strongest constraints on these realisations. Future experiments such as Hyper-Kamiokande, MEMPHYS, DUNE, or DARWIN could allow to probe dark matter-neutrino cross sections down to the value required to obtain the correct thermal relic abundance.

A feeble window on leptophilic dark matter

In this paper we study a leptophilic dark matter scenario involving feeble dark matter coupling to the Standard Model (SM) and compressed dark matter-mediator mass spectrum. We consider a simplified model where the SM is extended with one Majorana fermion, the dark matter, and one charged scalar, the mediator, coupling to the SM leptons through a Yukawa interaction. We first discuss the dependence of the dark matter relic abundance on the Yukawa coupling going continuously from freeze-in to freeze-out with an intermediate stage of conversion driven freeze-out. Focusing on the latter, we then exploit the macroscopic decay length of the charged scalar to study the resulting long-lived-particle signatures at collider and to explore the experimental reach on the viable portion of the parameter space.

Production and Detection of Light Dark Matter at Jefferson Lab: The BDX Experiment

The Beam Dump eXperiment (BDX) is a an electron-beam thick-target experiment aimed to investigate the existence of light Dark Matter particles in the MeV-GeV mass region at Jefferson Lab. The experiment will make use of a 10.6 GeV high-intensity electron-beam impinging on the Hall-A beam-dump to produce the Dark Matter particles ( χ ) through the Dark Photon portal. The BDX detector located at ∼20 m from the dump consists of two main components: an electromagnetic calorimeter to detect the signals produced by the χ -electron scattering and a veto system to reject background. The expected signature of the DM (Dark Matter) interaction in the Ecal (Electromagnetic calorimeter) is a ∼GeV electromagnetic shower paired with a null activity in the surrounding active veto counters. Collecting 10 22 electrons on target in 285 days of parasitic run at 65 μ A of beam current, and with an expected background of O(5) counts, in the case of a null discovery, BDX will be able to lower the exclusion limits by one to two orders of magnitude in the parameter space of dark-matter coupling versus mass. This paper describes the experiment and presents a summary of the most significant results achieved thus far, which led to the recent approval of the experiment by JLab-PAC46.

Monochromatic dark neutrinos and boosted dark matter in noble liquid direct detection

If dark matter self-annihilates into neutrinos or a second component of ("boosted") dark matter that is nucleophilic, the annihilation products may be detected with high rates via coherent nuclear scattering. A future multi-ten-tonne liquid xenon detector such as DARWIN, and a multi-hundred-tonne liquid argon detector, ARGO, would be sensitive to the flux of these particles in complementary ranges of $10-1000$ MeV dark matter masses. We derive these sensitivities after accounting for atmospheric and diffuse supernova neutrino backgrounds, and realistic nuclear recoil acceptances. We find that their constraints on the dark neutrino flux may surpass neutrino detectors such as Super-Kamiokande, and that they would extensively probe parametric regions that explain the missing satellites problem in neutrino portal models. The XENON1T and Borexino experiments currently restrict the effective baryonic coupling of thermal boosted dark matter to $\lesssim 10-100 \ \times$ the weak interaction, but DARWIN and ARGO would probe down to couplings 10 times smaller. Detection of boosted dark matter with baryonic couplings $\sim 10^{-3}-10^{-2} \ \times$ the weak coupling could indicate that the dark matter density profile in the centers of galactic halos become cored, rather than cuspy, through annihilations. This work demonstrates that, alongside liquid xenon, liquid argon direct detection technology would emerge a major player in dark matter searches within and beyond the WIMP paradigm.

Dark matter blind spots at one-loop

We evaluate the impact of one-loop electroweak corrections to the spin-independent dark matter (DM) scattering cross-section with nucleons (σSI), in models with a so-called blind spot for direct detection, where the leading-order prediction for the relevant DM coupling to the Higgs boson, and therefore σSI, are vanishingly small. Adopting a simple illustrative scenario in which the DM state results from the mixing of electroweak singlet and doublet fermions, we compute the relevant higher order corrections to the scalar effective operator contributions to σSI, stemming from both triangle and box diagrams involving the SM and dark sector fields. It is observed that in a significant region of the singlet-doublet model-space, the one-loop corrections “unblind” the tree-level blind spots and lead to detectable SI scattering rates at future multi-ton scale liquid Xenon experiments, with σSI reaching values up to a few times 10−47 cm2, for a weak scale DM with mathcal{O}(1) Yukawa couplings. Furthermore, we find that there always exists a new SI blind spot at the next-to-leading order, which is perturbatively shifted from the leading order one in the singlet-doublet mass parameters. For comparison, we also present the tree-level spin-dependent scattering cross-sections near the SI blind-spot region, that could lead to a larger signal. Our results can be mapped to the blind-spot scenario for bino-Higgsino DM in the MSSM, with other sfermions, the heavier Higgs boson, and the wino decoupled.

Gravitational waves and electroweak baryogenesis in a global study of the extended scalar singlet model

We perform a global fit of the extended scalar singlet model with a fermionic dark matter (DM) candidate. Using the most up-to-date results from the Planck measured DM relic density, direct detection limits from the XENON1T (2018) experiment, electroweak precision observables and Higgs searches at colliders, we constrain the 7-dimensional model parameter space. We also find regions in the model parameter space where a successful electroweak baryogenesis (EWBG) can be viable. This allows us to compute the gravitational wave (GW) signals arising from the phase transition, and discuss the potential discovery prospects of the model at current and future GW experiments. Our global fit places a strong upper and lower limit on the second scalar mass, the fermion DM mass and the scalar-fermion DM coupling. In agreement with previous studies, we find that our model can simultaneously yield a strong first-order phase transition and saturate the observed DM abundance. More importantly, the GW spectra of viable points can often be within reach of future GW experiments such as LISA, DECIGO and BBO.

UV complete framework of freeze-in massive particle dark matter

We propose a way to generate tiny couplings of freeze-in massive particle dark matter with the Standard Model particles dynamically by considering an extension of the electroweak gauge symmetry. The dark matter is considered to be a singlet under this extended gauge symmetry which we have assumed to be the one in a very widely studied scenario called left-right symmetric model. Several heavy particles, that can be thermally inaccessible in the early Universe due to their masses being greater than the reheat temperature after inflation, can play the role of portals between dark matter and Standard Model particles through one loop couplings. Due to the loop suppression, one can generate the required non-thermal dark matter couplings without any need of highly fine tuned Yukawa couplings beyond that of electron Yukawa with the Standard Model like Higgs boson. We show that generic values of Yukawa couplings as large as $\mathcal{O}(0.01)$ to $\mathcal{O}(1)$ can keep the dark matter out of thermal equilibrium in the early Universe and produce the correct relic abundance later through the freeze-in mechanism. Though the radiative couplings of dark matter are tiny as required by the freeze-in scenario, the associated rich particle sector of the model can be probed at ongoing and near future experiments. The allowed values of dark matter mass can remain in a wide range from keV to TeV order keeping the possibilities of warm and cold dark matter equally possible.

Indirect detection of sub-GeV dark matter coupling to quarks

We consider photon signals arising from the annihilation or decay of low-mass (sub-GeV) dark matter which couples dominantly to quarks. In this scenario, the branching fractions to the various kinematically accessible hadronic final states can largely be determined from chiral perturbation theory. Several of these final states yield striking spectral features in the sub-GeV photon spectrum. New experiments, such as e-ASTROGAM and AMEGO, are in development to improve sensitivity in this energy range, and we discuss their potential sensitivity to this class of models.

New bounds on dark matter coupling from a global network of optical atomic clocks.

We report on the first Earth-scale quantum sensor network based on optical atomic clocks aimed at dark matter (DM) detection. Exploiting differences in the susceptibilities to the fine-structure constant of essential parts of an optical atomic clock, i.e., the cold atoms and the optical reference cavity, we can perform sensitive searches for DM signatures without the need for real-time comparisons of the clocks. We report a two orders of magnitude improvement in constraints on transient variations of the fine-structure constant, which considerably improves the detection limit for the standard model (SM)-DM coupling. We use Yb and Sr optical atomic clocks at four laboratories on three continents to search for both topological defect and massive scalar field candidates. No signal consistent with a DM coupling is identified, leading to considerably improved constraints on the DM-SM couplings.

Anomaly-free dark matter with harmless direct detection constraints

Dark matter (DM) interacting with the SM fields via a Z′-boson (‘Z′-portal’) remains one of the most attractive WIMP scenarios, both from the theoretical and the phenomenological points of view. In order to avoid the strong constraints from direct detection and dilepton production, it is highly convenient that the Z′ has axial coupling to DM and leptophobic couplings to the SM particles, respectively. The latter implies that the associated U(1) coincides with baryon number in the SM sector. In this paper we completely classify the possible anomaly-free leptophobic Z′ with minimal dark sector, including the cases where the coupling to DM is axial. The resulting scenario is very predictive and perfectly viable from the present constraints from DM detection, EW observables and LHC data (di-lepton, di-jet and mono-jet production). We analyze all these constraints, obtaining the allowed areas in the parameter space, which generically prefer {m}_{Z^{prime }} ≲ 500 GeV, apart from resonant regions. The best chances to test these viable areas come from future LHC measurements.

Opening the energy window on direct dark matter detection

In this article we investigate the benefits of increasing the maximum nuclear recoil energy analysed in dark matter (DM) direct detection experiments. We focus on elastic DM-nucleus interactions, and work within the framework of effective field theory (EFT) to describe the scattering cross section. In agreement with previous literature, we show that an increased maximum energy leads to more stringent upper bounds on the DM-nucleus cross section for the EFT operators, especially those with an explicit momentum dependence. In this article we extend the energy region of interest (ROI) to show that the optimal values of the maximum energy for xenon and argon are of the order of 500 keV and 300 keV, respectively. We then show how, if a signal compatible with DM is observed, an enlarged energy ROI leads to a better measurement of the DM mass and couplings. In particular, for a xenon detector, DM masses of the order of 200 GeV (2 TeV) or lower can be reconstructed for momentum-independent (-dependent) operators. We also investigate three-dimensional parameter reconstruction and apply it to the specific case of scalar DM and anapole DM. We find that opening the energy ROI is an excellent way to identify the linear combination of momentum-dependent and momentum-independent operators, and it is crucial to correctly distinguish these models. Finally, we show how an enlarged energy ROI also allows us to test astrophysical parameters of the DM halo, such as the DM escape speed.

Collider Searches for Dark Matter (ATLAS + CMS)

Several searches for dark matter have been performed by the CMS and ATLAS collaborations, using proton-proton collisions with a center-of-mass energy of 13 TeV produced by the Large Hadron Collider. Different signatures may highlight the presence of dark matter: the imbalance in the transverse momentum in an event due to the presence of undetectable dark matter particles, produced together with one Standard Model particle, a bump in the di-jet or di-lepton invariant mass distributions, or an excess of events in the di-jet angular distribution, produced by a dark matter mediator. No significant discrepancies with respect to the Standard Model predictions have been found in data, so that limits on the dark matter couplings to ordinary matter, or limits on the dark matter particles and mediators masses have been set. The results are also re-interpreted as limits on the dark matter interaction cross-section with baryonic matter, so that a comparison with direct detection experiments is allowed.

Searches for electron interactions induced by new physics in the EDELWEISS-III germanium bolometers

We make use of the EDELWEISS-III array of germanium bolometers to search for electron interactions at the keV scale induced by phenomena beyond the Standard Model. A 90% C.L. lower limit is set on the electron lifetime decaying to invisibles, $\tau > 1.2\times 10^{24}$ years. We investigate the emission of axions or axionlike particles (ALPs) by the Sun, constraining the coupling parameters $g_{ae}<1.1\times 10^{-11}$ and $g_{ae}\times g_{aN}^{\rm eff} < 3.5\times 10^{-17}$ at 90% C.L. in the massless limit. We also directly search for the absorption of bosonic dark matter particles that would constitute our local galactic halo. Limits are placed on the couplings of ALPs or hidden photon dark matter in the mass range $0.8 - 500$ keV/c$^2$. Prospects for searching for dark matter particles with masses down to 150 eV/c$^2$ using improved detectors are presented.

Enhanced photon coupling of ALP dark matter adiabatically converted from the QCD axion

We revisit the adiabatic conversion between the QCD axion and axion-like particle (ALP) at level crossing, which can occur in the early universe as a result of the existence of a hypothetical mass mixing. This is similar to the Mikheyev-Smirnov-Wolfenstein effect in neutrino oscillations. After refining the conditions for the adiabatic conversion to occur, we focus on a scenario where the ALP produced by the adiabatic conversion of the QCD axion explains the observed dark matter abundance. Interestingly, we find that the ALP decay constant can be much smaller than the ordinary case in which the ALP is produced by the realignment mechanism. As a consequence, the ALP-photon coupling is enhanced by a few orders of magnitude, which is advantageous for the future ALP and axion-search experiments using the ALP-photon coupling.