Relic Dark Matter Research Articles

Dark matter interpretations of ATLAS searches for the electroweak production of supersymmetric particles in s = 8 $$ \sqrt{s}=8 $$ TeV proton-proton collisions

A selection of searches by the ATLAS experiment at the LHC for the electroweak production of SUSY particles are used to study their impact on the constraints on dark matter candidates. The searches use $20\,{\rm fb}^{-1}$ of proton-proton collision data at $\sqrt{s}=8$ TeV. A likelihood-driven scan of a five-dimensional effective model focusing on the gaugino--higgsino and Higgs sector of the phenomenological minimal supersymmetric Standard Model is performed. This scan uses data from direct dark matter detection experiments, the relic dark matter density and precision flavour physics results. Further constraints from the ATLAS Higgs mass measurement and SUSY searches at LEP are also applied. A subset of models selected from this scan are used to assess the impact of the selected ATLAS searches in this five-dimensional parameter space. These ATLAS searches substantially impact those models for which the mass $m(\tilde{\chi}^0_1)$ of the lightest neutralino is less than 65 GeV, excluding 86% of such models. The searches have limited impact on models with larger $m(\tilde{\chi}^0_1)$ due to either heavy electroweakinos or compressed mass spectra where the mass splittings between the produced particles and the lightest supersymmetric particle is small.

Models of a 750 GeV quarkonium and the LHC excesses

We investigate models involving a vector-like quark X, which forms a 750 GeV bound state and reproduces the observed diphoton signals at the LHC, in connection with other excesses in the LHC data. An exotic hypercharge of -4/3 is required to fit the signal cross section, which indicates that there is additional particle(s) that mediates the decay of X in the full theory. We find that, introducing an SU(2) doublet vector-like quark of mass around 600 GeV in our UV-complete framework can accommodate not only the diphoton but also the on-Z excess (and potentially a slight excess in the monojet events). Our models also include a dark matter candidate. The most useful way to probe the models at the LHC is via monojet searches. The relic dark matter density is largely determined by coannihilation effects, and indirect detection of dark matter annihilation signals is the alternative and complementary probe of our models.

Thermal relic dark matter beyond the unitarity limit

We discuss a simple model of thermal relic dark matter whose mass can be much larger than the so-called unitarity limit on the mass of point-like particle dark matter. The model consists of new strong dynamics with one flavor of fermions in the fundamental representation which is much heavier than the dynamical scale of the new strong dynamics. Dark matter is identified with the lightest baryonic hadron of the new dynamics. The baryonic hadrons annihilate into the mesonic hadrons of the new strong dynamics when they have large radii. Resultantly, thermal relic dark matter with a mass in the PeV range is possible.

Conformal complex singlet extension of the Standard Model: scenario for dark matter and a second Higgs boson

We consider a conformal complex singlet extension of the Standard Model with a Higgs portal interaction. The global $U(1)$ symmetry of the complex singlet can be either broken or unbroken and we study each scenario. In the unbroken case, the global $U(1)$ symmetry protects the complex singlet from decaying, leading to an ideal cold dark matter candidate with approximately 100 GeV mass along with a significant proportion of thermal relic dark matter abundance. In the broken case, we have developed a renormalization-scale optimization technique to significantly narrow the parameter space and in some situations, provide unique predictions for all the model's couplings and masses. We have found there exists a second Higgs boson with a mass of approximately $550\,\rm{GeV}$ that mixes with the known $125\,\rm{GeV}$ Higgs with a large mixing angle $\sin\theta\approx 0.47$ consistent with current experimental limits. The imaginary part of the complex singlet in the broken case could provide axion dark matter for a wide range of models. Upon including interactions of the complex scalar with an additional vector-like fermion, we explore the possibility of a diphoton excess in both the unbroken and the broken cases. In the unbroken case, the model can provide a natural explanation for diphoton excess if extra terms are introduced providing extra contributions to the singlet mass. In the broken case, we find a set of coupling solutions that yield a second Higgs boson of mass $720\,\rm{GeV}$ and an $830\,\rm{GeV}$ extra vector-like fermion $F$, which is able to address the $750\,\rm{GeV}$ LHC diphoton excess. We also provide criteria to determine the symmetry breaking pattern in both the Higgs and hidden sectors.

Inflaton dark matter from incomplete decay

We show that the decay of the inflaton field may be incomplete, while nevertheless successfully reheating the universe and leaving a stable remnant that accounts for the present dark matter abundance. We note, in particular, that since the mass of the inflaton decay products is field-dependent, one can construct models, endowed with an appropriate discrete symmetry, where inflaton decay is kinematically forbidden at late times and only occurs during the initial stages of field oscillations after inflation. We show that this is sufficient to ensure the transition to a radiation-dominated era and that inflaton particles typically thermalize in the process. They eventually decouple and freeze out, yielding a thermal dark matter relic. We discuss possible implementations of this generic mechanism within consistent cosmological and particle physics scenarios, for both single-field and hybrid inflation.

Astrophysical constraints on resonantly produced sterile neutrino dark matter

Resonantly produced sterile neutrinos are considered an attractive dark matter (DM) candidate only requiring a minimal, well motivated extension to the standard model of particle physics. With a particle mass restricted to the keV range, sterile neutrinos are furthermore a prime candidate for warm DM, characterised by suppressed matter perturbations at the smallest observable scales. In this paper we take a critical look at the validity of the resonant scenario in the context of constraints from structure formation. We compare predicted and observed number of Milky-Way satellites and we introduce a new method to generalise existing Lyman-α limits based on thermal relic warm DM to the case of resonant sterile neutrino DM . The tightest limits come from the Lyman-α analysis, excluding the entire parameter space (at 2-σ confidence level) still allowed by X-ray observations. Constraints from Milky-Way satellite counts are less stringent, leaving room for resonant sterile neutrino DM most notably around the suggested line signal at 7.1 keV.

Dark matter production mechanisms with a nonthermal cosmological history: A classification

We perform a comprehensive study of models of dark matter (DM) in a Universe with a non-thermal cosmological history, i.e with a phase of pressure-less matter domination before the onset of big-bang nucleosynethesis (BBN). Such cosmological histories are generically predicted by UV completions that contain gravitationally coupled scalar fields (moduli). We classify the different production mechanisms for DM in this framework, generalizing previous works by considering a wide range of DM masses/couplings and allowing for DM to be in equilibrium with a "dark" sector. We identify four distinct parametric regimes for the production of relic DM, and derive accurate semi-analytic approximations for the DM relic abundance. Our results are particularly relevant for supersymmetric theories, in which the standard non-thermally produced DM candidates are disfavored by indirect detection constraints. We also comment on experimental signals in this framework, focusing on novel effects involving the power spectrum of DM density perturbations. In particular, we identify a class of models where the spectrum of DM density perturbations is sensitive to the pressure-less matter dominated era before BBN, giving rise to interesting astrophysical signatures to be looked for in the future. A worthwhile future direction would be to study well-motivated theoretical models within this framework and carry out detailed studies of the pattern of expected experimental signals.

750 GeV messenger of dark conformal symmetry breaking

The tentative hints for a diphoton resonance at a mass of $\sim 750$ GeV from the ATLAS and CMS experiments at the LHC may be interpreted as first contact with a "dark" sector with a spontaneously broken conformal symmetry. The implied TeV scale of the dark sector may be motivated by the interaction strength required to accommodate a viable thermal relic dark matter (DM) candidate. We model the conformal dynamics using a Randall-Sundrum type 5D geometry whose IR boundary is identified with the dynamics of the composite dark sector, while the Standard Model (SM) matter content resides on the UV boundary, corresponding to "elementary" fields. We allow the gauge fields to reside in the 5D bulk, which can be minimally chosen to be $SU(3)_c\times U(1)_Y$. The "dark" radion is identified as the putative 750 GeV resonance. Heavy vector-like fermions, often invoked to explain the diphoton excess, are not explicitly present in our model and are not predicted to appear in the spectrum of TeV scale states. Our minimal setup favors scalar DM of $\mathcal{O}(\text{TeV})$ mass. A generic expectation in this scenario, suggested by DM considerations, is the appearance of vector bosons at $\sim$ few TeV, corresponding to the gluon and hypercharge Kaluza-Klein (KK) modes that couple to UV boundary states with strengths that are suppressed uniformly compared to their SM values. Our analysis suggests that these KK modes could be within the reach of the LHC in the coming years.

Anomalous X-ray galactic signal from 7.1 keV spin-3/2 dark matter decay

In order to explain the recently reported peak at 3.55 keV in the galactic X-ray spectrum, we propose a simple model. In this model, the Standard Model is extended by including a neutral spin-3/2 vector-like fermion that transforms like a singlet under SM gauge group. This 7.1 keV spin-3/2 fermion is considered to comprise a portion of the observed dark matter. Its decay into a neutrino and a photon with decay life commensurate with the observed data, fits the relic dark matter density and obeys the astrophysical constraints from the supernova cooling.

A two-component dark matter model with real singlet scalars confronting GeV γ-ray excess from galactic centre and Fermi bubble

We propose a two-component dark matter (DM) model, each component of which is a real singlet scalar, to explain results from both direct and indirect detection experiments. We put the constraints on the model parameters from theoretical bounds, PLANCK relic density results and direct DM experiments. The γ-ray flux is computed from DM annihilation in this framework and is then compared with the Fermi-LAT observations from galactic centre region and Fermi bubble.

Reconciling the muong−2, a 125 GeV Higgs boson, and dark matter in gauge mediation models

We present a class of models in the framework of gauge mediation supersymmetry breaking where the standard model is supplemented by additional U(1) symmetry which acts only on the third generation fermions. The messenger fields carry non-trivial U(1) charge and are vector-like particles under this symmetry. This leads to additional contribution to the soft supersymmetry breaking mass terms for the third generation squarks and sleptons. In this framework we show that the muon g-2 anomaly, the observed 125 GeV Higgs boson mass and the detected relic dark matter abundance (gravitino in our case) can be simultaneously accommodated. The resolution of the muon g-2 anomaly, in particular, yields the result that the first two generation squark masses, as well the gluino mass, should be <~ 2.5 TeV, which will be tested at LHC14.

Lattice QCD input for axion cosmology

One intriguing beyond-the-Standard-Model particle is the QCD axion, which could simultaneously provide a solution to the Strong $CP$ Problem and account for some, if not all, of the dark matter density in the Universe. This particle is a pseudo-Nambu--Goldstone boson of the conjectured Peccei--Quinn symmetry of the Standard Model. Its mass and interactions are suppressed by a heavy symmetry-breaking scale, ${f}_{a}$, the value of which is roughly greater than ${10}^{9}\text{ }\text{ }\mathrm{GeV}$ (or, conversely, the axion mass, ${m}_{a}$, is roughly less than ${10}^{4}\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$). The density of axions in the Universe, which cannot exceed the relic dark matter density and is a quantity of great interest in axion experiments like ADMX, is a result of the early Universe interplay between cosmological evolution and the axion mass as a function of temperature. The latter quantity is proportional to the second derivative of the temperature-dependent QCD free energy with respect to the $CP$-violating phase, $\ensuremath{\theta}$. However, this quantity is generically nonperturbative, and previous calculations have only employed instanton models at the high temperatures of interest (roughly 1 GeV). In this and future works, we aim to calculate the temperature-dependent axion mass at small $\ensuremath{\theta}$ from first-principle lattice calculations, with controlled statistical and systematic errors. Once calculated, this temperature-dependent axion mass is input for the classical evolution equations of the axion density of the Universe, which is required to be less than or equal to the dark matter density. Due to a variety of lattice systematic effects at the very high temperatures required, we perform a calculation of the leading small-$\ensuremath{\theta}$ cumulant of the theta vacua on large volume lattices for SU(3) Yang--Mills with high statistics as a first proof of concept, before attempting a full QCD calculation in the future. From these pure glue results, the misalignment mechanism yields the axion mass bound ${m}_{a}\ensuremath{\ge}(14.6\ifmmode\pm\else\textpm\fi{}0.1)\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$ when Peccei--Quinn breaking occurs after inflation.

Asymmetric capture of Dirac dark matter by the Sun

Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles and anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.

Model for Thermal Relic Dark Matter of Strongly Interacting Massive Particles.

A recent proposal is that dark matter could be a thermal relic of 3→2 scatterings in a strongly coupled hidden sector. We present explicit classes of strongly coupled gauge theories that admit this behavior. These are QCD-like theories of dynamical chiral symmetry breaking, where the pions play the role of dark matter. The number-changing 3→2 process, which sets the dark matter relic abundance, arises from the Wess-Zumino-Witten term. The theories give an explicit relationship between the 3→2 annihilation rate and the 2→2 self-scattering rate, which alters predictions for structure formation. This is a simple calculable realization of the strongly interacting massive-particle mechanism.

Pseudoscalar portal dark matter

A fermion dark matter candidate with a relic abundance set by annihilation through a pseudoscalar can evade constraints from direct detection experiments. We present simplified models that realize this fact by coupling a fermion dark sector to a two-Higgs doublet model. These models are generalizations of mixed bino-Higgsino dark matter in the MSSM, with more freedom in the couplings and scalar spectra. Annihilation near a pseudoscalar resonance allows a significant amount of parameter space for thermal relic dark matter compared to singlet-doublet dark matter, in which the fermions couple only to the SM Higgs doublet. In a general two-Higgs doublet model, there is also freedom for the pseudoscalar to be relatively light and it is possible to obtain thermal relic dark matter candidates even below 100 GeV. In particular, we find ample room to obtain dark matter with mass around 50 GeV and fitting the Galactic Center excess in gamma-rays. This region of parameter space can be probed by LHC searches for heavy pseudoscalars or electroweakinos, and possibly by other new collider signals.

Relic neutralino surface at a 100 TeV collider

We map the parameter space for MSSM neutralino dark matter which freezes out to the observed relic abundance, in the limit that all superpartners except the neutralinos and charginos are decoupled. In this space of relic neutralinos, we show the dominant dark matter annihilation modes, the mass splittings among the electroweakinos, direct detection rates, and collider cross-sections. The mass difference between the dark matter and the next-to-lightest neutral and charged states is typically much less than electroweak gauge boson masses. With these small mass differences, the relic neutralino surface is accessible to a future 100 TeV hadron collider, which can discover inter-neutralino mass splittings down to 1 GeV and thermal relic dark matter neutralino masses up to 1.5 TeV with a few inverse attobarns of luminosity. This coverage is a direct consequence of the increased collider energy: the Standard Model events with missing transverse momentum in the TeV range have mostly hard electroweak radiation, distinct from the soft radiation shed in compressed electroweakino decays. We exploit this kinematic feature in final states including photons and leptons, tailored to the 100 TeV collider environment.

Detecting boosted dark matter from the Sun with large volume neutrino detectors

We study novel scenarios where thermal dark matter (DM) can be efficiently captured in the Sun and annihilate into boosted dark matter. In models with semi-annihilating DM, where DM has a non-minimal stabilization symmetry, or in models with a multi-component DM sector, annihilations of DM can give rise to stable dark sector particles with moderate Lorentz boosts. We investigate both of these possibilities, presenting concrete models as proofs of concept. Both scenarios can yield viable thermal relic DM with masses O(1)-O(100) GeV. Taking advantage of the energetic proton recoils that arise when the boosted DM scatters off matter, we propose a detection strategy which uses large volume terrestrial detectors, such as those designed to detect neutrinos or proton decays. In particular, we propose a search for proton tracks pointing towards the Sun. We focus on signals at Cherenkov-radiation-based detectors such as Super-Kamiokande (SK) and its upgrade Hyper-Kamiokande (HK). We find that with spin-dependent scattering as the dominant DM-nucleus interaction at low energies, boosted DM can leave detectable signals at SK or HK, with sensitivity comparable to DM direct detection experiments while being consistent with current constraints. Our study provides a new search path for DM sectors with non-minimal structure.

Searching for Sub-Gev Dark Matter at Fixed Target Neutrino Experiments

Low mass dark matter theories, if produced as a thermal relic in the early universe, must be accompanied by light mediators in order to obtain the dark matter abundance observed in the present day universe. These light mediators in turn provide a channel for the production of dark matter at fixed target neutrino experiments, producing a relativistic dark matter beam, which could then be detected by neutral-current-like interactions in neutrino detectors. We consider the possibility that fixed target neutrino experiments such as MiniBooNE and T2K could serve as a new dark matter search avenue, sensitive to sub-GeV dark matter scenarios that would be otherwise undetectable. These experiments are found to provide sensitivity to light stable states that could serve as viable candidates for particle dark matter.

The double-dark portal

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 $\chi$ with Yukawa couplings to light scalars $\phi_i$. The scalars couple to SM quarks via the operator $\bar q q \phi_i^* \phi_j/\Lambda_{ij}$. This can lead to large direct detection signals via the $2\rightarrow3$ process $\chi N \rightarrow \chi N \phi$ if one of the scalars has mass $ \lesssim 10$ keV. For dark matter Yukawa couplings $y_\chi \sim 10^{-3} - 10^{-2}$, dmDM features a thermal relic dark matter candidate while also implementing the SIDM scenario for ameliorating inconsistencies between dwarf galaxy simulations and observations. We undertake the first systematic survey of constraints on light scalars coupled to the SM via the above operator. The strongest constraints are derived from a detailed examination of the light mediator's effects on stellar astrophysics. LHC experiments and cosmological considerations also yield important bounds. Observations of neutron star cooling exclude the minimal model with one dark mediator, but a scenario with two dark mediators remains viable and can give strong direct detection signals. We explore the direct detection consequences of this scenario and find that a heavy $\mathcal{O}(100)$ GeV dmDM candidate fakes different $\mathcal{O}(10)$ GeV WIMPs at different experiments. Large regions of dmDM parameter space are accessible above the irreducible neutrino background.

Modified holographic Ricci dark energy coupled to interacting relativistic and non-relativistic dark matter in the nonflat universe

The modified holographic Ricci dark energy coupled to interacting relativistic and non-relativistic dark matter is considered in the nonflat Friedmann-Robertson-Walker universe. Through examining the deceleration parameter, one can find that the transition time of the Universe from decelerating to accelerating phase in the interacting holographic Ricci dark energy model is close to that in the $\Lambda$ cold dark matter model. The evolution of modified holographic Ricci dark energy's state parameter and the evolution of dark matter and dark energy's densities shows that the dark energy holds the dominant position from the near past to the future. By studying the statefinder diagnostic and the evolution of the total pressure, one can find that this model could explain the Universe's transition from the radiation to accelerating expansion stage through the dust stage. According to the $Om$ diagnostic, it is easy to find that when the interaction is weak and the proportion of relativistic dark matter in total dark matter is small, this model is phantom-like. Through our studying, we find the interaction and the relativistic dark matter's proportion all have great influence on the evolution of the Universe.