Low Dark Matter Mass Research Articles

Cosmological implications of inflaton-mediated dark and visible matter scatterings after reheating

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

DELight: A Direct search Experiment for Light dark matter with superfluid helium

To reach ultra-low detection thresholds necessary to probe unprecedentedly low Dark Matter masses, target material alternatives and novel detector designs are essential. One such target material is superfluid ^44He which has the potential to probe so far uncharted light Dark Matter parameter space at sub-GeV masses. The new “Direct search Experiment for Light dark matter”, DELight, will be using superfluid helium as active target, instrumented with magnetic micro-calorimeters. It is being designed to reach sensitivity to masses well below 100 MeV in Dark Matter-nucleus scattering interactions.

Dark Sector extensions of the Littlest Seesaw in the presence of Primordial Black Holes

The Littlest Seesaw model is a very well motivated dark matter model. Here we consider an extension of that model with an additional scalar and an additional fermionic particle under the freeze-in scenario. Formation of black hole of a certain mass range at primordial times can act as an alternate production mechanism for the dark matter particles as it evaporates via Hawking radiation. Furthermore, the presence of primordial black holes with substantial energy density gives rise to non-standard cosmology which also modifies the freeze-in production. In this paper, we have investigated the extended Littlest Seesaw model under the freeze-in scenario in the presence of a primordial black hole for various interesting cases and constrained the parameter space accordingly. If the universe is primordial black hole dominated at any point in the evolution of the universe, we find that the final relic in that case is dominated mostly by the evaporation component for a high dark matter mass and by the freeze-in component for a low dark matter mass.

Cosmic-ray upscattered inelastic dark matter

Light non-relativistic components of the galactic dark matter halo elude direct detection constraints because they lack the kinetic energy to create an observable recoil. However, cosmic-rays can upscatter dark matter to significant energies, giving direct detection experiments access to previously unreachable regions of parameter-space at very low dark matter mass. In this work we extend the cosmic-ray dark matter formalism to models of inelastic dark matter and show that previously inaccessible regions of the mass-splitting parameter space can be probed. Conventional direct detection of non-relativistic halo dark matter is limited to mass splittings of $\delta\sim10~\mathrm{keV}$ and is highly mass dependent. We find that including the effect of cosmic-ray upscattering can extend the reach to mass splittings of $\delta\sim100~\mathrm{MeV}$ and maintain that reach at much lower dark matter mass.

Same-Sign Dilepton Signature in the Inert Doublet Model * *Supported by the National Natural Science Foundation of China (11805081), Natural Science Foundation of Shandong Province (ZR2019QA021, ZR2018MA047)

In this study, we perform a detailed analysis on the same-sign dilepton signature in the inert doublet model. Focusing on the low dark matter mass region, we randomly scan the corresponding parameter space. Viable samples allowed by various constraints are obtained, and among them are twenty benchmark points that are selected for further study on collider signature. At hadron colliders, the same-sign dilepton signature is produced via with the leptonic decay mode , where H represents the dark matter candidate. We investigate the testability of this signal at the high-luminosity LHC (HL-LHC) and the proposed 27 TeV high-energy LHC (HE-LHC). According to our simulation, the HL-LHC with can barely probe this signal. Meanwhile, for the HE-LHC with , it is promising to obtain a significance when GeV with dark matter mass or 71 GeV.

Implications of dark sector mixing on leptophilic scalar dark matter

We propose a new viable outlook to the mixing between a singlet and a doublet leptonic dark sector fields. This choice relaxes the dark matter (DM) search constraints on the quintessential scalar singlet DM as well as presents new opportunities for its detection in the lab. The mixing produces an arbitrary mass difference between the two components of the extra doublet in a gauge-invariant way, without introducing any new scale of electroweak symmetry breaking in the theory. It also provides a useful handle to distinguish between the dark sector particles of different isospins, which is a challenging task other-wise. As the dark leptons coannihilate non-trivially, the mixing effectively enhances the viable parameter space for the relic density constraint. In low DM mass regime, our analysis shows that with a non-zero mixing, it is possible to relax the existing indirect search bounds on the upper limit of the DM-Standard Model coupling. From the analysis of the 3tau +{E}_T^{mathrm{miss}} and mathrm{ell}tau +{E}_T^{mathrm{miss}} channels for LHC at sqrt{s} = 13 TeV, we show that one ensures the presence of the mixing parameter between the dark sector particles of the theory by looking at the peak and tail positions of the kinematic distributions. Even with a tweak in the values of other free parameters within the viable parameter region, the distinct peak and tail positions of the kinematic distributions remains a constant feature of the model. While both the channels present us the opportunity to detect the mixing signature at the LHC/HL-LHC, the former gives better results in terms of a larger region of mixing parameter. From the fiducial cross section, the projected statistical significance for the integrated luminosity, mathcal{L} = 3 ab−1, are shown for a combined parameter region obeying all the existing constraints, where there is the best possibility to detect such a signature.

The S3 symmetric model with a dark scalar

We study the S3 symmetric extension of the Standard Model in which all the irreducible representations of the permutation group are occupied by SU(2) scalar doublets, one of which is taken as inert and can lead to dark matter candidates. We perform a scan over parameter space probing points against physical constraints ranging from unitarity tests to experimental Higgs searches limits. We find that the latter constraints severely restrict the parameter space of the model. For acceptable points we compute the value of the relic density of the dark scalar candidates and find that it has a region for low dark matter masses which complies with the Higgs searches bounds and lies within the experimental Planck limit. For masses ≳80 GeV the value of the relic density is below the Planck bound, and it reaches values close to it for very heavy masses ∼5 TeV. In this heavy mass region, this opens the interesting possibility of extending the dark sector of the model with additional particles.

Z-pole test of effective dark matter diboson interactions at the CEPC

We investigate the projected sensitivity to effective dark matter (DM)–diboson interaction during the high luminosity Z-pole and 240 GeV runs at the proposed Circular Electron Positron Collider (CEPC). The proposed runs at the 91.2 GeV e^+e^- center of mass energy offers an interesting opportunity to probe effective dark matter couplings to the Z boson, which can be less stringently tested in non-collider searches. We investigate the prospective sensitivity for dimension 6 and dimension 7 effective diboson operators to scalar and fermion dark matter. These diboson operators can generate semi-visible Z boson decay, and high missing transverse momentum mono-photon signals that can be test efficiently at the CEPC, with a small and controllable Standard Model gamma bar{nu }nu background. Projected sensitivities for the effective gamma Z coupling efficient kappa _{gamma Z}< (1030,hbox {GeV})^{-3}, (1970,hbox {GeV})^{-3} for scalar DM, kappa _{gamma Z}< (360,text {GeV})^{-3}, (540,text {GeV})^{-3} for fermion DM are obtain for 25 hbox {fb}^{-1} and 2.5hbox {ab}^{-1}Z-pole luminosities assuming the optimal low dark matter mass range. We also compare the CEPC sensitivities to current direct and indirect search limits on these effective DM-diboson operators.

Simulated Milky Way analogues: implications for dark matter direct searches

We study the implications of galaxy formation on dark matter direct detection using high resolution hydrodynamic simulations of Milky Way-like galaxies simulated within the EAGLE and APOSTLE projects. We identify Milky Way analogues that satisfy observational constraints on the Milky Way rotation curve and total stellar mass. We then extract the dark matter density and velocity distribution in the Solar neighbourhood for this set of Milky Way analogues, and use them to analyse the results of current direct detection experiments. For most Milky Way analogues, the event rates in direct detection experiments obtained from the best fit Maxwellian distribution (with peak speed of 223–289 km/s) are similar to those obtained directly from the simulations. As a consequence, the allowed regions and exclusion limits set by direct detection experiments in the dark matter mass and spin-independent cross section plane shift by a few GeV compared to the Standard Halo Model, at low dark matter masses. For each dark matter mass, the halo-to-halo variation of the local dark matter density results in an overall shift of the allowed regions and exclusion limits for the cross section. However, the compatibility of the possible hints for a dark matter signal from DAMA and CDMS-Si and null results from LUX and SuperCDMS is not improved.

Status and plan of the PandaX experiment

PandaX is a large scale apparatus for the detection of rare events in particle physics and astrophysics with xenon. It is located in the China Jinping Underground Laboratory, which is the deepest underground laboratory all over the world to date. The first and second stages of the PandaX experiment utilize the dual phase xenon time projection chamber technology for the direct detection of one hypothetic candidate of dark matter, the weakly interacting massive particles (WIMPs), in the Galaxy halo. The technology makes it possible to measure both the scintillations and ionizations generated by the scattering of WIMP with nucleus, and thus backgrounds can be suppressed by the character of the measured signals. The aim of the first stage of PandaX, PandaX-I, is to test the possible signals reported by other experiments in low dark matter mass region with 120 kg of xenon. The first results of the PandaX-I experiment were released in August, 2014. No dark matter candidates were observed. Thus the 90% exclusion upper limits on the spin-independent WIMP-nucleon elastic scattering cross section were set. The results disfavored the WIMP interpretation of those signals and placed stringent limit to the property of dark matter below 10 GeV/ c 2. The final results of PandaX-I were released in 2015 based on 54×80.1 kg d of exposure with significantly improved analysis. The new analysis supported the conclusion of the first results and gave stringent limitation on the WIMP-nucleon cross section for WIMP mass smaller than 10 GeV, demonstrating the detection potential of xenon at low WIMP mass region. The second stage, PandaX-II, with an updated detector capable of containing 500 kg of xenon, is being tested and will start data taking in the end of 2015. The sensitivity of PandaX-II is expected to go far beyond the current limits being set by all the experiments so far. Unattainable parameter space of WIMPs will be explored by it. PandaX-III, the third stage, will be an experiment to detect the neutrinoless double beta decay with enriched high pressure 136Xe (to 90%) gaseous detector, so that the nature of neutrino is studied. The detector is able to measure the track of radiations inside it, helping to suppress the background by inspecting the different topological properties of desired signals and background. PandaX-III plans to build such a detector with 200 kg enriched 136Xe first, then build another 4 identical modules to reach ton scale. The initial design and prototype testing of PandaX-III is carrying out by different groups from the institutions all over the world. The first detector module of PandaX-III is expected to be finished construction and start operation in 2018. The success running of the PandaX experiments may lead to important discoveries in physics.

Global constraints on vector-like WIMP effective interactions

In this work we combine information from relic abundance, direct detection, cosmic microwave background, positron fraction, gamma rays, and colliders to explore the existing constraints on couplings between Dark Matter and Standard Model constituents when no underlying model or correlation is assumed. For definiteness, we include independent vector-like effective interactions for each Standard Model fermion. Our results show that low Dark Matter masses below 20 GeV are disfavoured at the 3 σ level with respect to higher masses, due to the tension between the relic abundance requirement and upper constraints on the Dark Matter couplings. Furthermore, large couplings are typically only allowed in combinations which avoid effective couplings to the nuclei used in direct detection experiments.

Constraining Inert Dark Matter by R γγ and WMAP data

Abstract We discuss the constraints on Dark Matter coming from the LHC Higgs data and WMAP relic density measurements for the Inert Doublet Model, which is one of the simplest extensions of the Standard Model providing a Dark Matter candidate. We found that combining the diphoton rate R γγ and the Ω DM h 2 data one can set strong limits on the parameter space of the Inert Doublet Model, stronger or comparable to the constraints provided by the XENON100 experiment for low and medium Dark Matter mass.

Bayes and present dark matter direct search status

Recently there has been a huge activity in the dark matter direct detection field, with the report of an excess from CoGeNT and CRESST along with the annual modulated signal of DAMA/LIBRA and the strong exclusion bound from XENON100. We analyse these results within the framework of Bayesian inference and evidence. Indeed Bayesian methods are well suited for marginalizing over experimental systematics and background. We present the results for spin-independent interaction on nuclei with particular attention to the low dark matter mass region and the compatibility between experiments. In the same vein we also investigate the impact of astrophysical uncertainties on the WIMP preferred parameter space within the class of isotropic dark matter velocity distributions.

Neutrino probes of the nature of light dark matter

Dark matter particles gravitationally trapped inside the Sun may annihilate into Standard Model particles, producing a flux of neutrinos. The prospects of detecting these neutrinos in future multi-kt neutrino detectors designed for other physics searches are explored here. We study the capabilities of a 34/100 kt liquid argon detector and a 100 kt magnetized iron calorimeter detector. These detectors are expected to determine the energy and the direction of the incoming neutrino with unprecedented precision allowing for tests of the dark matter nature at very low dark matter masses, in the range of 10–25 GeV. By suppressing the atmospheric background with angular cuts, these techniques would be sensitive to dark matter-nucleon spin-dependent cross sections at the fb level, reaching down to a few ab for the most favorable annihilation channels and detector technology.

The imprint of cosmic reionization on galaxy clustering

We consider the effect of reionization on the clustering properties of galaxy samples at intermediate redshifts (z~0.3-5.5). Current models for the reionization of intergalactic hydrogen predict that overdense regions will be reionized early, thus delaying the build up of stellar mass in the progenitors of massive lower-redshift galaxies. As a result, the stellar populations observed in intermediate redshift galaxies are somewhat younger and hence brighter in overdense regions of the Universe. Galaxy surveys would therefore be sensitive to galaxies with a somewhat lower dark matter mass in overdense regions. The corresponding increase in the observed number density of galaxies can be parameterized as a galaxy bias due to reionization. We model this process using merger trees combined with a stellar synthesis code. Our model demonstrates that reionization has a significant effect on the clustering properties of galaxy samples that are selected based on their star-formation properties. The bias correction in Lyman-break galaxies (including those in proposed baryonic oscillation surveys at z<1) is at the level of 10-20% for a halo mass of 10^12 solar masses, leading to corrections factors of 1.5-2 in the halo mass inferred from measurements of clustering length. The reionization of helium could also lead to a sharp increase in the amplitude of the galaxy correlation function at z~3. We find that the reionization bias is approximately independent of scale and halo mass. However since the traditional galaxy bias is mass dependent, the reionization bias becomes relatively more important for lower mass systems. The correction to the bias due to reionization is very small in surveys of luminous red galaxies at z<1.

Temperature and Entropy Fields of Baryonic Gas in the Universe

(Abridged)The temperature (T) and entropy (S) fields of baryonic gas/IGM are analyzed using simulation samples by a cosmological hydro/N-body code. We show that in the nonlinear regime the dynamical similarity between the IGM and dark matter will be broken by strong shocks. The heating and entropy production by the shocks breaks the IGM into multiple phases. The mean entropy, or the cosmological entropy floor, is found to be more than 100 h^(-1/3) keV cm^2 in all regions when z 50 h^(-1/3) keV cm^2) mostly resides in areas on scales larger than 1 h^(-1) Mpc and with density $\rho_{dm}>10^2$. Therefore, gravitational shocks are an effective preheating mechanism of the IGM, and probably enough to provide the entropy excess of clusters and groups if the epoch of the gas falling in cluster cores is not earlier than z ~ 2 - 3. On the other hand, at redshifts z < 4, there is always a more than 90% volume of the low dark matter mass density regions filled by the IGM with T < 10^4.5 K. Therefore, the multiphased character and non-Gaussianity of the IGM field would explain the high-temperature and high-entropy gas observed in groups and clusters.