We study a scenario in which the only light new particles are a Majorana fermion dark matter candidate and one or more QCD-charged scalars, which couple to light quarks. This scenario has several interesting phenomenological features if the new particles are nearly degenerate in mass. In particular, LHC searches for the light scalars have reduced sensitivity, since the visible and invisible products tend to be softer. Moreover, dark matter-scalar co-annihilation can allow even relatively heavy dark matter candidates to be consistent thermal relics. Finally, the dark matter nucleon scattering cross section is enhanced in the quasi-degenerate limit, allowing direct detection experiments to use both spin-independent and spin-dependent scattering to probe regions of parameter space beyond those probed by the LHC. Although this scenario has broad application, we phrase this study in terms of the MSSM, in the limit where the only light sparticles are a bino-like dark matter candidate and light-flavored squarks.
We review simplified models in which a singlet Majorana dark matter candidate couples to Standard Model (SM) fermions through interactions mediated by scalar fermion partners. We summarize the two primary production mechanisms in these scenarios: dark matter annihilation mediated by first or second generation scalar fermion partners with significant left-right chiral mixing and co-annihilation with scalar fermion partners nearly degenerate in mass with the dark matter. We then highlight the most interesting phenomenological aspects of charged mediator models relevant for current and future sea…
We consider a scenario, within the framework of the MSSM, in which dark matter is bino-like and dark matter-nucleon spin-independent scattering occurs via the exchange of light squarks which exhibit left-right mixing. We show that direct detection experiments such as LUX and SuperCDMS will be sensitive to a wide class of such models through spin-independent scattering. Moreover, these models exhibit properties, such as isospin violation, that are not typically observed for the MSSM LSP if scattering occurs primarily through Higgs exchange. The dominant nuclear physics uncertainty is the quark …
We consider direct detection prospects for a class of simplified models of fermionic dark matter (DM) coupled to left and right-handed Standard Model fermions via two charged scalar mediators with arbitrary mixing angle $α$. DM interactions with the nucleus are mediated by higher electromagnetic moments, which, for Majorana DM, is the anapole moment. After giving a full analytic calculation of the anapole moment, including its $α$ dependence, and matching with limits in the literature, we compute the DM-nucleon scattering cross-section and show the LUX and future LZ constraints on the paramete…
In the context of a simplified leptophilic Dark Matter (DM) scenario where the mediator is a new charged fermion carrying leptonic quantum number and the DM candidate is either scalar or vector, the complementarity of different bounds is analysed. In this framework, the extra lepton and DM are odd under a $\mathbb Z_2$ symmetry, hence the leptonic mediator can only interact with the DM state and Standard Model (SM) leptons of various flavours. We show that there is the possibility to characterise the DM spin (scalar or vector), as well as the nature of the mediator, through a combined analysis…
We consider a simplified model in which Majorana fermion dark matter annihilates to charged fermions through exchange of charged mediators. We consider the gamma-ray signals arising from the processes $XX \rightarrow \bar f f γ$, $γγ$, and $γZ$ in the most general case, including non-trivial fermion mass and non-trivial left-right mixing and $CP$-violating phase for the charged mediators. In particular, we find the most general spectrum for internal bremsstrahlung, which interpolates between the regimes dominated by virtual internal bremsstrahlung and by final state radiation. We also examine …
Dark matter that was once in thermal equilibrium with the Standard Model is generally prohibited from obtaining all of its mass from the electroweak or QCD phase transitions. This implies a new scale of physics and mediator particles needed to facilitate dark matter annihilations. In this work, we consider scenarios where thermal dark matter annihilates via scalar mediators that are colored and/or electrically charged. We show how partial wave unitarity places upper bounds on the masses and couplings on both the dark matter and mediators. To do this, we employ effective field theories with dar…
We analyze the direct detection signals of a toy model consisting of a Dirac dark matter particle which couples to one Standard Model fermion via a scalar mediator. For all scenarios, the dark matter particle scatters off nucleons via one loop-induced electromagnetic and electroweak moments, as well as via the one-loop exchange of a Higgs boson. Besides, and depending on the details of the model, the scattering can also be mediated at tree level via the exchange of the scalar mediator or at one loop via gluon-gluon interactions. We show that, for thermally produced dark matter particles, the c…
Analysis of $B\to KM_X$ and $B\to K^* M_X$ decays in scalar- and vector-mediator dark-matter scenarios
D. V. Skobeltsyn Institute of Nuclear Physics, M. V. Lomonosov Moscow State University（莫斯科国立大学德·V·斯科别尔钦核物理研究所）；Institute of High Energy Physics, Austrian Academy of Sciences（奥地利科学院高能物理研究所）；Joint Institute for Nuclear Research（联合核研究所）；Faculty of Physics, University of Vienna（维也纳大学物理学院）
We present a new (supersymmetric) framework for obtaining an excellent description of quark, charged lepton and neutrino masses and mixings from a Delta(6n^2) family symmetry with multiplet assignments consistent with an underlying SO(10) Grand Unification. It employs a Higgs mediator sector in place of the usual Froggatt-Nielsen messengers, with quark and lepton messengers, and provides significant improvements over existing models of this type having unsuppressed Yukawa couplings to the third generation and a simplified vacuum alignment mechanism. The neutrino mass differences are naturally …
Sommerfeld Effect and Bound State Formation for Dark Matter Models with Colored Mediators with SE+BSF4DM
Università degli Studi di Padova（帕多瓦大学）；INFN, Sezione di Padova（意大利国家核物理研究所帕多瓦分部）；Johannes Gutenberg-Universität Mainz（约翰内斯·古腾堡美因茨大学）；Technical University of Munich（慕尼黑工业大学）
The relic abundance of the dark matter (DM) particle $d$ is studied in a secluded DM scenario, in which the $d$ number decreasing process dominantly occurs not through the pair annihilation of $d$ into the standard model particles, but via the $dd \to mm$ scattering process with a subsequently decaying mediator particle $m$. It is pointed out that the cosmologically observed relic abundance of DM can be accomplished even with a massive mediator having a mass $m_m$ non-negligibly heavy compared with the DM particle mass $m_d$. In the degenerated $d$-$m$ case ($m_d=m_m$), the DM relic abundance …
We study a model with a vector dark matter (DM) candidate interacting with the SM charged leptons through a scalar portal. The dark matter candidate acquires mass when the complex scalar breaks an abelian gauge symmetry spontaneously. The scalar interacts with the SM charged leptons through a dimension-6 operator. The scalar mediator induces elastic scattering of dark matter with electrons at tree level and also DM-nucleon interaction when the effects from scalar-Higgs mixing are also taken into account. Given the recent results from Xenon1T upper bounds on DM-electron elastic scattering cross…
We examine in greater detail the recent proposal of using superconductors for detecting dark matter as light as the warm dark matter limit of O(keV). Detection of such light dark matter is possible if the entire kinetic energy of the dark matter is extracted in the scattering, and if the experiment is sensitive to O(meV) energy depositions. This is the case for Fermi-degenerate materials in which the Fermi velocity exceeds the dark matter velocity dispersion in the Milky Way of ~10^-3. We focus on a concrete experimental proposal using a superconducting target with a transition edge sensor in …
The connection between Standard Model (SM) particles and dark matter (DM) can be introduced via hidden spin-2 massive mediator. In the present paper we consider the simplified benchmark link between charged lepton sector of SM and DM particles which are considered to be a hidden Dirac fermions from the dark sector. The regarding couplings are established through the dimension-5 operators involving spin-2 mediator field and the energy-momentum tensors of both SM and DM sectors. We study in detail the implication of this scenario for the lepton fixed-target facilities, such as NA64$e$, LDMX, NA6…
A general analysis is performed on the dimension-six operators mixing an almost hidden Z' to the Standard Model (SM), when the Z' communicates with the SM via heavy mediators. These are fermions charged under both Z' and the SM, while all SM fermions are neutral under Z'. We classify the operators as a function of the gauge anomalies behaviour of mediators and explicitly compute the dimension-six operators coupling Z' to gluons, generated at one-loop by chiral but anomaly-free, sets of fermion mediators. We prove that only one operator contribute to the couplings between Z' charged matter and …
The sensitivity of the LHC experiments to the associated production of dark matter with a single top is studied in the framework of an extension of the standard model featuring two Higgs doublets and an additional pseudoscalar mediator. It is found that the experimental sensitivity is dominated by the on-shell production of a charged Higgs boson, when this assumes a mass below 1 TeV. Dedicated selections considering one and two lepton final states are developed to assess the coverage in parameter space for this signature at a centre-of-mass energy of 14 TeV assuming an integrated luminosity of…
In most models of the dark sector, dark matter is charged under some new symmetry to make it stable. We explore the possibility that not just dark matter, but also the force carrier connecting it to the visible sector is charged under this symmetry. This dark mediator then acts as a Double-Dark Portal. We realize this setup in the \emph{dark mediator Dark matter} model (dmDM), featuring a fermionic DM candidate $χ$ with Yukawa couplings to light scalars $ϕ_i$. The scalars couple to SM quarks via the operator $\bar q q ϕ_i^* ϕ_j/Λ_{ij}$. This can lead to large direct detection signals via the $…
In this paper we study a leptophilic dark matter scenario involving feeble dark matter coupling to the Standard Model (SM) and compressed dark matter-mediator mass spectrum. We consider a simplified model where the SM is extended with one Majorana fermion, the dark matter, and one charged scalar, the mediator, coupling to the SM leptons through a Yukawa interaction. We first discuss the dependence of the dark matter relic abundance on the Yukawa coupling going continuously from freeze-in to freeze-out with an intermediate stage of conversion driven freeze-out. Focusing on the latter, we then e…
We present a comprehensive study of a model where the dark matter is composed of a singlet real scalar that couples to the Standard Model predominantly via a Yukawa interaction with a light quark and a colored vector-like fermion. A distinctive feature of this scenario is that thermal freeze-out in the early universe may be driven by annihilation both into gluon pairs at one-loop ($gg$) and by virtual internal Bremsstrahlung of a gluon ($q \bar{q} g$). Such a dark matter candidate may also be tested through direct and indirect detection and at the LHC; viable candidates have either a mass near…
Dark matter and neutrinos provide the two most compelling pieces of evidence for new physics beyond the Standard Model of Particle Physics but they are often treated as two different sectors. The aim of this paper is to determine whether there are viable particle physics frameworks in which dark matter can be coupled to active neutrinos. We use a simplified model approach to determine all possible renormalizable scenarios where there is such a coupling, and study their astrophysical and cosmological signatures. We find that dark matter-neutrino interactions have an impact on structure formatio…
Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to $37~\mathrm{fb}^{-1}$ $\sqrt s = 13$ 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…
We explore the sensitivity to new physics of the recently proposed vIOLETA experiment: a 10 kg Skipper Charged Coupled Device detector deployed 12 meters away from a commercial nuclear reactor core. We investigate two broad classes of models which benefit from the very low energy recoil threshold of these detectors, namely neutrino magnetic moments and light mediators coupled to neutrinos and quarks or electrons. We find that this experimental setup is very sensitive to light, weakly coupled new physics, and in particular that it could probe potential explanations of the event excess observed …
We present a model of vector dark matter that interacts through a low-mass vector mediator based on the Higgsing of an SU(2) dark sector. The dark matter is charged under a U(1) gauge symmetry. Even though this symmetry is broken, the residual global symmetries of the theory prevent dark matter decay. We present the behavior of the model subject to the assumption that the dark matter abundance is due to thermal freeze out, including self-interaction targets for small scale structure anomalies and the possibility of interacting with the Standard Model through the vector mediator.
Secluded dark matter models, in which WIMPs annihilate first into metastable mediators, can present novel indirect detection signatures in the form of gamma rays and fluxes of charged particles arriving from directions correlated with the centers of large astrophysical bodies within the solar system, such as the Sun and larger planets. This naturally occurs if the mean free path of the mediator is in excess of the solar (or planetary) radius. We show that existing constraints from water Cerenkov detectors already provide a novel probe of the parameter space of these models, complementary to ot…
We propose a radiative origin of the two mass splittings of three degenerate Majorana neutrinos. It can be achieved by extending the standard model to have the usual effective dimension 5 operators generating SO(3)-invariant tree-level masses, and a charged scalar singlet coupling with the leptons preserving the U(1) subgroup of SO(3). The mass splittings for the atmospheric and solar neutrino oscillations then arise from one-loop corrections due to the charged scalar singlet coupling and the usual tau Yukawa coupling, respectively.
We investigate a dark sector containing a pair of light non-degenerate scalar particles, with masses in the MeV-GeV range, coupled to the visible sector through heavier mediators. The heaviest dark state is long-lived, and its decays offer new testable signals. We analyze the prospects for detection with the proposed beam-dump facility SHiP, and the proposed LHC experiments FASER and MATHUSLA. Moreover, we consider bounds from the beam-dump experiment CHARM and from colliders (LEP, LHC and BaBar). We present our results both in terms of an effective field theory, where the heavy mediators have…
We investigate a scenario where dark matter (DM) particles can be captured and accumulate in the Sun, and subsequently annihilate into a pair of long-lived mediators. These mediators can decay further out in the Sun or outside of the Sun. Compared to the standard scenario where DM particles annihilate directly into Standard Model particles close to the solar core, here we also obtain fluxes of gamma rays and charged cosmic rays. We simulate this scenario using a full three-dimensional model of the Sun, and include interactions and neutrino oscillations. In particular, we perform a model-indepe…
We describe the implementation of four models for production of dark matter or as- sociated particles at the LHC based on the simplest extensions of the Standard Model. The first kind of models include dark matter production via s-channel mediators. This includes production in association with a jet for a vector boson (Z') or scalar (S) mediator as well as mono-higgs production via associated hZ' production. We implement the simplest t-channel mediator in the form of a scalar with leptonic quantum numbers and completely generic Yukawa couplings to the dark matter fermion and a right-handed SM …
We study charged lepton flavor violation (CLFV) associated with heavy quark pair production in lepton-nucleon deep-inelastic scattering $\ell_i N \to \ell_j q\bar{q} X$. Here $\ell_i$ and $\ell_j$ denote the initial and final leptons; $N$ and $X$ are respectively the initial nucleon and arbitrary final hadronic system. We employ a model Lagrangian in which a scalar and pseudoscalar mediator generates the CLFV. We derive heavy quark structure functions for scalar and pseudoscalar currents and compute momentum distributions of the final lepton for the process. Our focus is on the heavy quark mas…
An analysis is given of the Belle II sensitivities and NA64 constraints on the sub-GeV Dirac dark matter that interacts with charged leptons. We consider two different types of interactions between sub-GeV Dirac dark matter and the charged leptons: the EFT operators and the light vector mediators. We compute the Belle II mono-photon sensitivities on sub-GeV dark matter with 50 ab$^{-1}$ data which are expected to be accumulated in the full Belle II runs. Although the Belle II mono-photon sensitivities on the EFT operators are of similar size as the LEP constraints, Belle II can probe new param…
We consider a spin-3/2 fermionic dark matter (DM) particle interacting with the Standard Model quarks through the exchange of a charged and coloured scalar or vector mediator in a simple $t$-channel model. It is found that for the vector mediator case, almost the entire parameter space allowed by the observed relic density is already ruled out by the direct detection LUX data. No such bounds exist on the interaction mediated by scalar particles. Monojet + missing energy searches at the Large Hadron Collider provide the most stringent bounds on the parameters of the model for this case. The col…
We propose a quasi-degenerate dark matter scenario to simultaneously explain the $1.4\,\textrm{TeV}$ peak in the high-energy cosmic-ray electron-positron spectrum reported by the DAMPE collaboration very recently and the $3.5\,\textrm{keV}$ X-ray line observed in galaxies clusters and from the Galactic centre and confirmed by the Chandra and NuSTAR satellites. We consider a dark $SU(2)'\times U(1)'$ gauge symmetry under which the dark matter is a Dirac fermion doublet composed of two $SU(2)'$ doublets with non-trivial $U(1)'$ charges. At one-loop level the two dark fermion components can have …
We explore a new mechanism for reproducing the Dark Matter (DM) abundance: scatterings of one DM particle on light Standard Model particles. Strong bounds on its decays can be satisfied if DM undergoes freeze-in and has a mass around or below the pion mass. This happens, for example, in theories with a right-handed neutrino interacting with charged fermions through a leptoquark exchange. These leptoquarks can be linked to the ones motivated by the B-physics anomalies if assumptions about the flavour structure are made. DM signals are unusual, with interesting possibilities for direct and indir…
We analyze the indirect astrophysical signatures of secluded models of WIMP dark matter, characterized by a weak-scale rate for annihilation into light MeV-scale mediators which are metastable to decay into Standard Model states. Such scenarios allow a significant enhancement of the annihilation cross section in the galactic halo relative to its value at freeze-out, particularly when the mediator is light enough for this process to proceed through radiative capture to a metastable `WIMP-onium' bound state. For MeV-scale vector mediators charged under a hidden U(1)' gauge group, the enhanced an…
We examine theoretical features of $U(1)_X$ extensions of the Standard Model whose quantum anomalies are canceled per generation. Similarly to other versions, the theory consists of a Two-Higgs-Doublet Model plus a scalar singlet embedded into the $SM \otimes U(1)_X$ gauge group, and introduces small modifications to the $Z$-boson interactions. These changes can be minimized by exclusively charging right-handed fermions under the new Abelian symmetry, and are compensated by the neutral $X$-boson exchange. Non-universality of fermion couplings can also be achieved by requiring one single $X$-ch…
In Higgs portal models of fermion dark matter, scalar couplings are unavoidably suppressed by strong bounds from direct detection experiments. As a consequence, thermal dark matter relics must coexist with mediators in a compressed spectrum of dark particles. Small couplings and small mass splittings lead to slow mediator decays, leaving signatures with displaced vertices or disappearing tracks at colliders. We perform a comprehensive analysis of long-lived mediators at the LHC in the context of a minimal dark matter model with a naturally small Higgs portal, also known as the wino-bino scenar…
We consider constraints on simplified models in which scalar dark matter annihilates to light charged leptons through the exchange of charged mediators. We find that loop diagrams will contribute corrections to the magnetic and electric dipole moments of the light charged leptons, and experimental constraints on these corrections place significant bounds on the dark matter annihilation cross section. In particular, annihilation to electrons with an observable cross section would be ruled out, while annihilation to muons is only permitted if the dominant contributions arise from CP-violating in…
CMS and ATLAS have searched for a doubly-charged boson $H^{\pm\pm}$ which may arise from type II seesaw in the 7 TeV run at the LHC by considering pair or associated production of doubly-charged bosons under the assumption of degenerate triplet scalars. In this work, we consider non-degenerate triplet components with the mass gap $ΔM \sim 1 - 40$ GeV which leads to enhanced pair-production cross-sections of $H^{\pm\pm}$ added by the gauge decays of the heavier neutral and singly-charged bosons. We reevaluate the constraints in the $ΔM-M_{H^{++}}$ plane depending on the triplet vacuum expectati…
Theories with non-Abelian flavour symmetries lead at zeroth order to neutrino degeneracy and massless charged fermions. The flavour symmetry is spontaneously broken sequentially to give hierarchies $Δm_{atm}^2 \gg Δm_{\odot}^2$ and $m_τ\gg m_μ\gg m_e$, and a misalignment of the vacuum between neutrino and charged sectors gives large $θ_{atm}$. Explicit models are given which determine $θ_{atm} = 45^\circ$. A similar construction gives vacuum misalignment for the lighter generations and gives a vanishing $ββ_{0 ν}$ rate, so that there is no laboratory constraint on the amount of neutrino hot da…
Constraints on couplings of several Beyond Standard Model Physics scenarios, mediated by massive intermediate particles including (1) Extra Z-prime, (2) New Light Spin-1 Boson, and (3) Charged Higgs Boson, are placed via neutrino-electron scattering channel to test Standard Model at low energy-momentum transfer regime. Data on $\barν_{e}-e$ and $ν_{e}-e$ scattering from the TEXONO and LSND Experiments, respectively, are used. Upper bounds to coupling constants of Flavor Conserving and Flavor Violating New Light Spin-1 Boson and Charged Higgs Boson with respect to different mediator masses are …
Confining hidden sectors at the GeV scale are well motivated by asymmetric dark matter and naturalness considerations and can also give interesting collider signatures. Here we study such sectors connected to the Standard Model by a TeV scale mediator charged under both QCD and the dark force. Such a mediator admits a Yukawa coupling between quarks and dark quarks which is generically flavour and $CP$ violating. We show that in contrast to expectation, electric dipole moments do not place a strong constraint on this scenario even with $O(1)$ $CP$-violating phases. We also quantitatively explor…
We have considered a model of Dark Minimal Flavour Violation (DMFV), in which a triplet of dark matter particles couple to right-handed up-type quarks via a heavy colour-charged scalar mediator. By studying a large spectrum of possible constraints, and assessing the entire parameter space using a Markov Chain Monte Carlo (MCMC), we can place strong restrictions on the allowed parameter space for dark matter models of this type.
We consider an inelastic dark matter model, where a fermion is charged under a broken U(1) gauge symmetry, and introduce a tiny Majorana mass term to split the fermion into two states with the light one being a dark matter candidate. If the gauge boson is light, it can mediate both elastic and inelastic dark matter self-interactions in dark halos, leading to observational consequences. Using a numerical technique based on partial wave analysis, we accurately calculate the elastic and inelastic self-scattering cross sections. We assume a thermal freeze-out scenario and fix the gauge coupling co…
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 …
Many new physics scenarios contain ultralight scalars, states which are either exactly massless or much lighter than any other massive particle in the model. Axions and majorons constitute well-motivated examples of this type of particle. In this work, we explore the phenomenology of these states in low-energy leptonic observables. After adopting a model independent approach that includes both scalar and pseudoscalar interactions, we briefly discuss the current limits on the diagonal couplings to charged leptons and consider processes in which the ultralight scalar $ϕ$ is directly produced, su…
We analyse dark matter (DM) produced somehow in space-time is charged under the hidden $U^{\prime} (1)$ gauge symmetry and interacting with Standard Model (SM) through the scale invariance breaking sector containing dilatons and dark photons (DP). We find the solutions for DM and DP in terms of observables. The DM observable is under DP field shape influence. DP is the natural mediator between DM and the SM sectors. The phenomenology of DP physics and the registration of dark photons are discussed.
