Simplified Dark Matter Models Research Articles

Extended dark matter EFT

Conventional approaches to describe dark matter phenomenology at collider and (in)direct detection experiments in the form of dark matter effective field theory or simplified models suffer in general from drawbacks regarding validity at high energies and/or generality, limiting their applicability. In order to avoid these shortcomings, we propose a hybrid framework in the form of an effective theory, including, however, both the dark matter states and a mediator connecting the former to the Standard Model fields. Since the mediation can be realized through rather light new dynamical fields allowing for non-negligible collider signals in missing energy searches, the framework remains valid for the phenomenologically interesting parameter region, while retaining correlations dictated by gauge symmetry. Moreover, a richer new-physics sector can be consistently included via higher-dimensional operators. Interestingly, for fermionic and scalar dark matter with a (pseudo-)scalar mediator, the leading effects originate from dimension-five operators, allowing to capture them with a rather small set of new couplings. We finally examine the correlations between constraints from reproducing the correct relic density, direct-detection experiments, and mono-jet and Higgs + missing energy signatures at the LHC and point out new cancellation patterns in direct-detection, emerging non-trivially in the effective theory.

Constraints on new scalar and vector mediators from LHC dijet searches

We present a reanalysis of the latest results from CMS dijet searches for an integrated luminosity of together with preliminary results for in the framework of simplified models for dark matter interacting with quarks through the exchange of a scalar, pseudoscalar, vector or pseudovector mediator particle. Within the same framework, we also project the sensitivity of dijet searches in future LHC runs and study how well the parameters of a simplified model could be reconstructed in case of a future discovery at the high luminosity (HL) LHC. Finally, we explore the possibility of discriminating different mediator scenarios by extending the sensitivity of dijet searches for simplified models through the use of angular information. It is the first time that these studies are performed systematically for the case of spin 0 mediators. Among other results we find: (1) no evidence for a dijet signal in the simplified model framework; (2) improvements due to an increased luminosity at the HL-LHC are significant, but mostly for heavy mediators, where dijet searches are limited by statistical, rather than systematical uncertainties; (3) Information on the angular separation of dijets could be used at the HL-LHC to discriminate different mediator scenarios.

Interference effects in dilepton resonance searches for Z\u2032 bosons and dark matter mediators

New Z′ gauge bosons arise in many extensions of the Standard Model and predict resonances in the dilepton invariant mass spectrum. Searches for such resonances therefore provide important constraints on many models of new physics, but the resulting bounds are often calculated without interference effects. In this work we show that the effect of interference is significant and cannot be neglected whenever the Z′ width is large (for example because of an invisible contribution). To illustrate this point, we implement and validate the most recent 139 fb−1 dilepton search from ATLAS and obtain exclusion limits on general Z′ models as well as on simplified dark matter models with spin-1 mediators. We find that interference can substantially strengthen the bound on the Z′ couplings and push exclusion limits for dark matter simplified models to higher values of the Z′ mass. Together with this study we release the open-source code ZPEED, which provides fast likelihoods and exclusion bounds for general Z′ models.

Search for production of four top quarks in final states with same-sign or multiple leptons in proton\u2013proton collisions at sqrt{s}=13,text {TeV}

The standard model (SM) production of four top quarks (text {t} {}{overline{text {t}}} text {t} {}{overline{text {t}}} ) in proton–proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016–2018 data taking of the LHC, corresponds to an integrated luminosity of 137,text {fb}^{-1} at a center-of-mass energy of 13,text {TeV}. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the text {t} {}{overline{text {t}}} text {t} {}{overline{text {t}}} signal are respectively 2.6 and 2.7 standard deviations, and the text {t} {}{overline{text {t}}} text {t} {}{overline{text {t}}} cross section is measured to be 12.6^{+5.8}_{-5.2},text {fb} . The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, y_{text {t}}, yielding a limit of |y_{text {t}}/y_{text {t}}^{mathrm {SM}} | < 1.7 at 95% confidence level, where y_{text {t}}^{mathrm {SM}} is the SM value of y_{text {t}}. They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework, hat{H}<0.12. Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350–470,text {GeV} and 350–550,text {GeV} for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.

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.

Dark matter in the Randall-Sundrum model with non-universal coupling

We consider simplified dark matter models (DM) interacting gravitationally with the standard model (SM) particles in a Randall-Sundrum (RS) framework. In this framework, the DM particles interact through the exchange of spin-2 Kaluza-Klein (KK) gravitons in the s-channel with the SM particles. The parameter space of the RS model with universal couplings to SM particles is known to be strongly constrained from the LHC data. We are thus led to consider models with non-universal couplings. The first model we consider in this study is a top-philic graviton model in which only the right-handed top quarks are taken to interact strongly with the gravitons. In the second, the lepto-philic model, we assume that only the right-handed charged leptons interact strongly with the gravitons. We extend the study to include not only the scalar, vector and spin-1/2 fermions but also spin-3/2 fermionic dark matter. We find that there is a large parameter space in these benchmark models where it is possible to achieve the observed relic density consistent with the direct and indirect searches and yet not to be constrained from the LHC data.

Simplified dark matter models with loop effects in direct detection and the constraints from indirect detection and collider search * * The work of T. L. is supported by the Fundamental Research Funds for the Central Universities, Nankai University (63196013, 63191522)

We reexamine the simplified dark matter (DM) models with fermionic DM particle and spin-0 mediator. The DM-nucleon scattering cross sections in these models are low-momentum suppressed at tree-level, but receive sizable loop-induced spin-independent contribution. We perform one-loop calculations for scalar-type and twist-2 DM-quark operators, and complete two-loop calculations for scalar-type DM-gluon operator. Analyzing the loop-level contribution from new operators, we find that future direct detection experiments could be sensitive to a fraction of the parameter space. The indirect detection and collider search also provide complementary constraints on these models.

BSM constraints from model-independent measurements: A Contur Update

Particle-level measurements, especially of differential cross-sections, made in fiducial regions of phase-space have a high degree of model-independence and can therefore be used to give information about a wide variety of Beyond the Standard Model (BSM) physics implemented in Monte Carlo generators, using a broad range of final states. The Contur package is used to make such comparisons. We summarise a snapshot of current results for a number of BSM scenarios; a UV complete model in which the global Baryon-number minus Lepton-number symmetry is gauged; several Dark Matter simplified models, and two generic light scalar models.

Dark matter pair production in the MSSM and in simplified dark matter models at the LHC

We study the quantitative features of dark matter pair production at the LHC in simplified dark matter models and in the MSSM taking next-to-leading order QCD corrections and parton-shower effects fully into account. Among the large space of dark matter models, we focus on two particular models where a fermionic dark matter candidate interacts with the Standard Model via the exchange of either a vector mediator in the s-channel or coloured scalar mediators in the t-channel. We find that the simplified models are capable of reproducing the predictions of the MSSM to some extent in simplified supersymmetric scenarios, but lack the complexity to describe the complete theory over the full supersymmetric parameter space.

Constraints on mediator-based dark matter and scalar dark energy models using sqrt{s} = 13 TeV pp collision data collected by the ATLAS detector

Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb−1 sqrt{s} = 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015-2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. In this case, also sqrt{s} = 8 TeV pp collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy).

Searching for production of dark matter in association with top quarks at the LHC

In the framework of spin-0 s-channel dark matter (DM) simplified models, we reassess the sensitivity of future LHC runs to the production of DM in association with top quarks. We consider two different missing transverse energy (ETmiss) signatures, namely production of DM in association with either a toverline{t} pair or a top quark and a W boson, where the latter channel has not been the focus of a dedicated analysis prior to this work. Final states with two leptons are studied and a realistic analysis strategy is developed that simultaneously takes into account both channels. Compared to other existing search strategies the proposed combination of toverline{t}+{E}_T^{mathrm{miss}} and tW + ETmiss production provides a significantly improved coverage of the parameter space of spin-0 s-channel DM simplified models.

Searching for dark matter in final states with two jets and missing transverse energy

We reemphasise the usefulness of angular correlations in LHC searches for missing transverse energy (ETmiss) signatures that involve jet (j) pairs with large invariant mass. For the case of mono-jet production via gluon-fusion, we develop a realistic analysis strategy that allows to split the dark matter (DM) signal into distinct one jet-like and two jet-like event samples. By performing state-of-the-art Monte Carlo simulations of both the mono-jet signature and the standard model background, it is shown that the dijet azimuthal angle difference Delta {phi}_{j_1{j}_2} in 2j + ETmiss production provides a powerful discriminant in realistic searches. Employing a shape fit to Delta {phi}_{j_1{j}_2} , we then determine the LHC reach of the mono-jet channel in the context of spin-0 s-channel DM simplified models. The constraints obtained by the proposed Delta {phi}_{j_1{j}_2} shape fit turn out to be significantly more stringent than those that derive from standard ETmiss shape analyses.

Graviton Spectrum in Simplified Dark Matter Models with Graviton Mediators in the de Sitter Space

This is the second in a series of papers investigating the formulation of the simplified Dark Matter models with graviton mediators in cosmological backgrounds. We address here the crucial problem of the fundamental observable of interest, namely the graviton spectrum in an Friedmann–Lemaître–Robertson–Walker (FLRW) cosmological background with an arbitrary Dark Matter background component. We calculate the correction to the free graviton two-point function up to the second order in the coupling constant between the Dark Matter and the graviton in the simplified Dark Matter model with graviton mediators approach in the de Sitter space. Our result is model independent in the sense that it does not depend on the particular form of the Dark Matter fields. In addition, due to the universality of the interaction between the Dark Matter and the graviton, the result obtained here applies to the interaction between the baryonic matter and the gravitons. As an application, we discuss in detail the massive scalar Dark Matter model and calculate the first order correction to the two-point function due to two Dark Matter modes in the adiabatic regime.

LHC Dark Matter Working Group: Next-generation spin-0 dark matter models

Dark matter (DM) simplified models are by now commonly used by the ATLAS and CMS Collaborations to interpret searches for missing transverse energy ($E_T^\mathrm{miss}$). The coherent use of these models sharpened the LHC DM search program, especially in the presentation of its results and their comparison to DM direct-detection (DD) and indirect-detection (ID) experiments. However, the community has been aware of the limitations of the DM simplified models, in particular the lack of theoretical consistency of some of them and their restricted phenomenology leading to the relevance of only a small subset of $E_T^\mathrm{miss}$ signatures. This document from the LHC Dark Matter Working Group identifies an example of a next-generation DM model, called $\textrm{2HDM+a}$, that provides the simplest theoretically consistent extension of the DM pseudoscalar simplified model. A comprehensive study of the phenomenology of the $\textrm{2HDM+a}$ model is presented, including a discussion of the rich and intricate pattern of mono-$X$ signatures and the relevance of other DM as well as non-DM experiments. Based on our discussions, a set of recommended scans are proposed to explore the parameter space of the $\textrm{2HDM+a}$ model through LHC searches. The exclusion limits obtained from the proposed scans can be consistently compared to the constraints on the $\textrm{2HDM+a}$ model that derive from DD, ID and the DM relic density.

Cornering colored coannihilation

In thermal dark matter models, allowing the dark matter candidate to coannihilate with another particle can considerably loosen the relic density constraints on the dark matter mass. In particular, introducing a single strongly interacting coannihilation partner in a dark matter model can bring the upper bound on the dark sector energy scale from a few TeV up to about 10 TeV. While these energies are outside the LHC reach, a large part of the parameter space for such coannihilating models can be explored by future hadron colliders. In this context, it is essential to determine whether the current bounds on dark matter simplified models also hold in non-minimal scenarios. In this paper, we study extended models that include multiple coannihilation partners. We show that the relic density bounds on the dark matter mass in these scenarios are stronger than for the minimal models in most of the parameter space and that weakening these bounds requires sizable interactions between the different species of coannihilation partners. Furthermore, we discuss how these new interactions as well as the additional particles in the models can lead to stronger collider bounds, notably in jets plus missing transverse energy searches. This study serves as a vital ingredient towards the determination of the highest possible energy scale for thermal dark matter models.

Impact of Cosmological and Astrophysical Constraints on Dark Matter Simplified Models

Studies of dark matter models lie at the interface of astrophysics, cosmology, nuclear physics and collider physics. Constraining such models entails the capability to compare their predictions to a wide range of observations. In this review, we present the impact of global constraints to a specific class of models, called dark matter simplified models. These models have been adopted in the context of collider studies to classify the possible signatures due to dark matter production, with a reduced number of free parameters. We classify the models that have been analysed so far and for each of them we review in detail the complementarity of relic density, direct and indirect searches with respect to the LHC searches. We also discuss the capabilities of each type of search to identify regions where individual approaches to dark matter detection are the most relevant to constrain the model parameter space. Finally we provide a critical overview on the validity of the dark matter simplified models and discuss the caveats for the interpretation of the experimental results extracted for these models.

Gravity-mediated Dark Matter models in the de Sitter space

In this paper, we generalize the simplified Dark Matter models with graviton mediator to the curved space-time, in particular to the de Sitter space. We obtain the generating functional of the Green's functions in the Euclidean de Sitter space for the covariant free gravitons. We determine the generating functional of the interacting theory between Dark Matter particles and the covariant gravitons. Also, we calculate explicitly the 2-point and 3-point interacting Green's functions for the symmetric traceless divergence-less covariant graviton. The results derived here are general in the sense that they do not depend on a particular model for the Dark Matter component and they show that the quantum effects of the interaction between the Dark Matter and the gravitons in the de Sitter space are computable by the methods of the standard Quantum Field Theory techniques.

Surrogate models for direct dark matter detection

In this work we introduce RAPIDD, a surrogate model that speeds up the computation of the expected spectrum of dark matter particles in direct detection experiments. RAPIDD replaces the exact calculation of the dark matter differential rate (which in general involves up to three nested integrals) with a much faster parametrization in terms of ordinary polynomials of the dark matter mass and couplings, obtained in an initial training phase. In this article, we validate our surrogate model on the multi-dimensional parameter space resulting from the effective field theory description of dark matter interactions with nuclei, including also astrophysical uncertainties in the description of the dark matter halo. As a concrete example, we use this tool to study the complementarity of different targets to discriminate simplified dark matter models. We demonstrate that RAPIDD is fast and accurate, and particularly well-suited to explore a multi-dimensional parameter space, such as the one in effective field theory approach, and scans with a large number of evaluations.

Revisiting the direct detection of dark matter in simplified models

In this work we numerically re-examine the loop-induced WIMP-nucleon scattering cross section for the simplified dark matter models and the constraint set by the latest direct detection experiment. We consider a fermion, scalar or vector dark matter component from five simplified models with leptophobic spin-0 mediators coupled only to Standard Model quarks and dark matter particles. The tree-level WIMP-nucleon cross sections in these models are all momentum-suppressed. We calculate the non-suppressed spin-independent WIMP-nucleon cross sections from loop diagrams and investigate the constrained space of dark matter mass and mediator mass by Xenon1T. The constraints from indirect detection and collider search are also discussed.

Revisiting simplified dark matter models in terms of AMS-02 and Fermi-LAT

We perform an analysis of the simplified dark matter models in the light of cosmic ray observables by AMS-02 and Fermi-LAT. We assume fermion, scalar or vector dark matter particle with a leptophobic spin-0 mediator that couples only to Standard Model quarks and dark matter via scalar and/or pseudo-scalar bilinear. The propagation and injection parameters of cosmic rays are determined by the observed fluxes of nuclei from AMS-02. We find that the AMS-02 observations are consistent with the dark matter framework within the uncertainties. The AMS-02 antiproton data prefer 30 (50) GeV - 5 TeV dark matter mass and require an effective annihilation cross section in the region of 4 × 10−27 (7 × 10−27) - 4 × 10−24 cm3/s for the simplified fermion (scalar and vector) dark matter models. The cross sections below 2 × 10−26 cm3/s can evade the constraint from Fermi-LAT dwarf galaxies for about 100 GeV dark matter mass.