We study a new class of signals where fermionic dark matter is absorbed by bound electron targets. Fermionic absorption signals in direct detection and neutrino experiments are sensitive to dark matter with sub-MeV mass, probing a region of parameter space in which dark matter is otherwise challenging to detect. We calculate the rate and energy deposition spectrum in xenon-based detectors, making projections for current and future experiments. We present two possible models that display fermionic absorption by electrons and study the detection prospects in light of other constraints.
Absorption of fermionic dark matter leads to a range of distinct and novel signatures at dark matter direct detection and neutrino experiments. We study the possible signals from fermionic absorption by nuclear targets, which we divide into two classes of four Fermi operators: neutral and charged current. In the neutral current signal, dark matter is absorbed by a target nucleus and a neutrino is emitted. This results in a characteristically different nuclear recoil energy spectrum from that of elastic scattering. The charged current channel leads to induced $β$ decays in isotopes which are st…
We present a new class of direct detection signals; absorption of fermionic dark matter. We enumerate the operators through dimension six which lead to fermionic absorption, study their direct detection prospects, and summarize additional constraints on their suppression scale. Such dark matter is inherently unstable as there is no symmetry which prevents dark matter decays. Nevertheless, we show that fermionic dark matter absorption can be observed in direct detection and neutrino experiments while ensuring consistency with the observed dark matter abundance and required lifetime. For dark ma…
We perform a systematic study of the fermionic DM absorption interactions on electron target in the context of effective field theory. The fermionic DM absorption is not just sensitive to sub-MeV DM with efficient energy release, but also gives a unique signature with clear peak in the electron recoil spectrum whose shape is largely determined by the atomic effects. Fitting with the Xenon1T and PandaX-II data prefers DM mass at $m_χ= 59$keV and 105keV, respectively, while the cut-off scale is probed up to around 1TeV. The DM overproduction in the early Universe, the invisible decay effect on t…
The CMB observation sets stringent constraints on MeV dark matter (DM) annihilating into charged states/photons in s-wave, and the recent observation of the 21-cm absorption at the cosmic dawn reported by EDGES is also very strict for s-wave annihilations of MeV DM. The millicharged DM with p-wave dominant annihilations during the freeze-out period are considered in literatures to give an explanation about the 21-cm absorption, with photon mediated scattering cooling the hydrogen. In this paper, we focus on the annihilation of millicharged DM being s-wave dominant. To explain the 21-cm absorpt…
The fermionic dark matter (DM) absorption by nucleus or electron targets provides a distinctive signal to search for sub-GeV DM. We consider a Dirac fermion DM charged under a dark gauge group and with the dark magnetic dipole operator. The DM field mixes with right-handed neutrino and interacts with the ordinary electromagnetic charge current via the kinetic mixing term of gauge fields. As a result, the incoming DM is absorbed and converted into neutrino in final state through the dipole-charge interaction. For the DM absorption by nucleus, the recoil energy spectrum exhibit a peak at $m_χ^2/…
Superconducting targets have recently been proposed for the direct detection of dark matter as light as a keV, via elastic scattering off conduction electrons in Cooper pairs. Detecting such light dark matter requires sensitivity to energies as small as the superconducting gap of O(meV). Here we show that these same superconducting devices can detect much lighter DM, of meV to eV mass, via dark matter absorption on a conduction electron, followed by emission of an athermal phonon. We demonstrate the power of this setup for relic kinetically mixed hidden photons, pseudoscalars, and scalars, sho…
Dopant atoms in semiconductors can be ionized with $\sim10$ meV energy depositions, allowing for the design of low-threshold detectors. We propose using doped semiconductor targets to search for sub-MeV dark matter scattering or sub-eV dark matter absorption on electrons. Currently unconstrained cross sections could be tested with a 1 g-day exposure in a doped detector with backgrounds at the level of existing pure semiconductor detectors, but improvements would be needed to probe the freeze-in target. We discuss the corresponding technological requirements and lay out a possible detector desi…
The stronger than expected 21-cm absorption was observed by EDGES recently, and another anomaly of $^8$Be transitions would be signatures of new interactions. These two issues may be related to each other, e.g., pseudoscalar $A$ mediated fermionic millicharged dark matter (DM), and the 21-cm absorption could be induced by photon mediated scattering between MeV millicharged DM and hydrogen. This will be explored in this paper. For fermionic millicharged DM $\barχ χ$ with masses in a range of $2 m_A < 2 m_χ < 3 m_A$, the p-wave annihilation $\barχ χ\to A A$ would be dominant during DM freeze-out…
We consider a class of models in which thermal dark matter is lighter than an MeV. If dark matter thermalizes with the Standard Model below the temperature of neutrino-photon decoupling, equilibration and freeze-out cools and heats the Standard Model bath comparably, alleviating constraints from measurements of the effective number of neutrino species. We demonstrate this mechanism in a model consisting of fermionic dark matter coupled to a light scalar mediator. Thermal dark matter can be as light as a few keV, while remaining compatible with existing cosmological and astrophysical observatio…
Light dark matter($\simeq 1-30~\rm{MeV}$) particles pair produced in electron-positron annihilation $ e^-e^+ \stackrelγ{\longrightarrow} χ\barχ$ inside the supernova core can take away the energy released in the supernova SN1987A explosion. Working within the formalism of $q$-deformed statistics (with the average value of the supernovae core temperature(fluctuating) being $T_{SN} = 30~\rm{MeV}$) and using the Raffelt's criterion on the emissivity for any new channel $\dot{\varepsilon}(e^+ e^- \to χ\overlineχ) \le 10^{19}~{erg~g^{-1}s^{-1}}$, we find that as the deformation parameter $q$ change…
The EDGES Collaboration has reported an anomalously strong 21cm absorption feature corresponding to the era of first star formation, which may indirectly betray the influence of dark matter during this epoch. We demonstrate that, by virtue of the ability to mediate cooling processes whilst in the condensed phase, a small amount of axion dark matter can explain these observations within the context of standard models of axions and axion-like-particles. The EDGES best-fit result favours an axion-like-particles mass in the (10, 450) meV range, which can be compressed for the QCD axion to (100, 45…
Direct detection of right-handed fermionic dark matter: electron-recoil measurements in Xe atoms
Instituto de Astrofísica de La Plata (CONICET-UNLP)（拉普拉塔天体物理研究所）；Facultad de Ciencias Astronómicas y Geofísicas de La Plata (UNLP)（拉普拉塔大学天文与地球物理学院）；ICRANet（国际相对论天体物理中心网络）；Department of Physics, Isfahan University of Technology（伊斯法罕理工大学物理系）；Departamento de Fisica (UNLP) and Instituto de Física de La Plata (CONICET-UNLP)（拉普拉塔大学物理系和拉普拉塔物理研究所）
We present a model in which the dark matter particle is frozen-in at MeV scale. In this model, the mediator between the standard model sector and the dark sector can automatically provide a self-interaction for dark matter. The interaction strength is naturally to be the in the region in favor of the cluster mass deficit anomaly. Due to the self-scattering, the Lyman-$α$ constraint can be relaxed to $m_D \gtrsim 2 $ keV. In this region the self-interaction and the Fermi pressure both play roles on forming a dark matter core at the center of the dwarf galaxies.
We consider the cosmology and phenomenology of a dark photon portal to a simple dark sector consisting of a single, light, fermionic dark matter particle species with mass in the MeV range. We entertain three possible kinetic mixing structures of a new Abelian gauge group U(1)$_{\text{dark}}$ with the visible sector through U(1)$_{\text{e.m.}}$, U(1)$_{\text{Y}}$ and T[SU(2)$_{\text{L}}$]. We assume the dark photon to be massive and around the MeV scale, thus close to the mass scale of the dark matter candidate. We compute the dark matter relic density via freeze-out and freeze-in, entertainin…
In this paper, we present a model for sub-MeV dark matter with strong self interactions which can solve some of the small scale crisis of the $Λ$CDM. The dark matter is a Majorana fermion with only off-diagonal interactions with a hidden $U(1)_D$ gauge boson. The relic density is obtained by freeze-out of Boltzmann suppressed annihilations to a light fermionic species. The self interaction is a one loop process and constrained to be between 0.1 to 1 cm$^2$/g. Severe constraints from the BBN on $N_{eff}$ require that the dark and visible sector are not in thermal equilibrium during freeze-out. …
First search for light fermionic dark matter absorption on electrons using germanium detector in CDEX-10 experiment
Tsinghua University（清华大学）；Institute of Physics, Academia Sinica（中央研究院物理研究所）；NUCTECH Company（同方威视技术股份有限公司）；YaLong River Hydropower Development Company（雅砻江流域水电开发有限公司）
We propose the use of three-dimensional Dirac materials as targets for direct detection of sub-MeV dark matter. Dirac materials are characterized by a linear dispersion for low-energy electronic excitations, with a small band gap of O(meV) if lattice symmetries are broken. Dark matter at the keV scale carrying kinetic energy as small as a few meV can scatter and excite an electron across the gap. Alternatively, bosonic dark matter as light as a few meV can be absorbed by the electrons in the target. We develop the formalism for dark matter scattering and absorption in Dirac materials and calcu…
The possibility of direct detection of light fermionic dark matter in neutrino detectors is explored from a model-independent standpoint. We consider all operators of dimension six or lower which can contribute to the interaction $\bar{f} p \to e^+ n$, where $f$ is a dark Majorana or Dirac fermion. Constraints on these operators are then obtained from the $f$ lifetime and its decays which produce visible $γ$ rays or electrons. We find one operator which would allow $\bar{f} p \to e^+ n$ at interesting rates in neutrino detectors, as long as $m_f \lesssim m_π$. The existing constraints on light…
Because of their tiny band gaps Dirac materials promise to improve the sensitivity for dark matter particles in the sub-MeV mass range by many orders of magnitude. Here we study several candidate materials and calculate the expected rates for dark matter scattering via light and heavy dark photons as well as for dark photon absorption. A particular emphasis is placed on how to distinguish a dark matter signal from background by searching for the characteristic daily modulation of the signal, which arises from the directional sensitivity of anisotropic materials in combination with the rotation…
Dark photons are well motivated hypothetical dark sector particles that could account for observations that cannot be explained by the standard model of particle physics. A search for dark photons that are produced by an electron beam striking a thick tungsten target and subsequently interact in a 3 kiloton-scale neutrino detector in Yemilab, a new underground lab in Korea, is proposed. Dark photons can be produced by "darkstrahlung" or by oscillations from ordinary photons produced in the target and detected by their visible decays, "absorption" or by their oscillation to ordinary photons. By…
Underground Production of Electromagnetic Dark States by MeV-scale Electron Beams and Detection with CCDs
Marietta Blau Institute for Particle Physics, Austrian Academy of Sciences（奥地利科学院玛丽亚·布劳粒子物理研究所）；University of Vienna, Faculty of Physics（维也纳大学物理学院）；University of Vienna, Vienna Doctoral School in Physics（维也纳大学维也纳物理博士学院）
Semiconductors are by now well-established targets for direct detection of MeV to GeV dark matter via scattering off electrons. We show that semiconductor targets can also detect significantly lighter dark matter via an absorption process. When the dark matter mass is above the band gap of the semiconductor (around an eV), absorption proceeds by excitation of an electron into the conduction band. Below the band gap, multi-phonon excitations enable absorption of dark matter in the 0.01 eV to eV mass range. Energetic dark matter particles emitted from the sun can also be probed for masses below …
Dark Matter Detection Using Phonon Sensing in Amorphous Materials
Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；University of California, Berkeley（加州大学伯克利分校）；CERN（欧洲核子研究组织）；Technion – Israel Institute of Technology（以色列理工学院）；Peking University（北京大学）；Kavli Institute for Theoretical Physics（卡弗里理论物理研究所）
The unexpectedly strong 21cm absorption signal detected by the EDGES experiment suggests that the baryonic gas was colder at redshift $z\sim 17$ than predicted in the standard scenario. We discuss a mechanism to lower the baryon temperature after recombination. We introduce a stable, negatively-charged particle with a non-negligible cosmological abundance, such that the universe remains charge-neutral but the electron and proton numbers are no longer equal. The deficit of electrons during recombination results in an earlier decoupling of the baryon gas temperature from that of the CMB. This im…
Light dark matter is a compelling experimental target in light of stringent constraints on heavier WIMPs. However, for a sub-MeV WIMP, the universe is sufficiently well understood at temperatures below 10 MeV that there is no room for it to be a thermal relic. Avoiding thermalization is itself a strong constraint with significant implications for direct detection. In this paper, we explore the space of models of sub-MeV dark matter with viable cosmologies. The parameter space of these models that is also consistent with astrophysical and lab-based limits is highly restricted for couplings to e…
In face of the small-scale structure problems of the collisionless cold dark matter (DM) paradigm, a popular remedy is to introduce a strong DM self-interaction which can be generated nonperturbatively by a MeV-scale light mediator. However, if such the mediator is unstable and decays into SM particles, the model is severely constrained by the DM direct and indirect detection experiments. In the present paper, we study a model of a self-interacting fermionic DM, endowed with a light stable scalar mediator. In this model, the DM relic abundance is dominated by the fermionic DM particle which is…
Recent breakthroughs in cryogenic silicon detector technology allow for the observation of single electron-hole pairs released via particle interactions within the target material. This implies sensitivity to energy depositions as low as the smallest band gap, which is $\sim1.2$ eV for silicon, and therefore sensitivity to eV/$c^2$-scale bosonic dark matter and to thermal dark matter at masses below 100 MeV/$c^2$. Various interaction channels that can probe the lowest currently accessible masses in direct searches are related to standard photoelectric absorption. In any of these respective dar…
We present a description of the originally developed $β$-spectrometer consisting of two Si(Li)-detectors with sensitive area thickness above 8~mm and $4π$-geometry. The full absorption spectrometer allows for direct measurements of $β$-spectra, disregarding the corrections to the response function induced by the electron backscattering from the crystal surface. In case of $β$-spectra of transitions to the excited state of the daughter isotope additional 3" BGO-detector is used in order to detect the $γ$-quanta in coincidence with the pair of Si(Li)-spectrometers.
Fermionic sub-GeV Dark Matter from evaporating Primordial Black Holes at DarkSide-50
INFN Laboratori Nazionali del Gran Sasso（意大利国家核物理研究所大萨索国家实验室）；Gran Sasso Science Institute（大萨索科学研究所）；Instituto de Física, Universidade de São Paulo（圣保罗大学物理研究所）；Pacific Northwest National Laboratory（太平洋西北国家实验室）；Physics Department, Augustana University（奥古斯塔纳大学物理系）；Physics Department, Università degli Studi di Pisa（比萨大学物理系）；INFN Pisa（意大利国家核物理研究所比萨分部）；Fermi National Accelerator Laboratory（费米国家加速器实验室）；INFN Sezione di Roma（意大利国家核物理研究所罗马分部）；INFN Cagliari（意大利国家核物理研究所卡利亚里分部）；Physics Department, Università degli Studi di Genova（热那亚大学物理系）；INFN Genova（意大利国家核物理研究所热那亚分部）；Department of Mathematics and Physics – Roma Tre University（罗马第三大学数学与物理系）；INFN Roma Tre（意大利国家核物理研究所罗马第三分部）；Physics Department, Università degli Studi di Cagliari（卡利亚里大学物理系）；Physics Department, Università degli Studi “Federico II” di Napoli（那不勒斯费德里科二世大学物理系）
Institute for Particle Physics Phenomenology, Department of Physics, Durham University（达勒姆大学粒子物理现象学研究所）；Instituto de Física Corpuscular (CSIC-Universitat de València)（瓦伦西亚大学-CSIC 核物理研究所）
Polarimetric experiments driven by the strong field of a circularly polarized laser wave can become a powerful tool to limit the parameter space of not yet detected hidden-photons and minicharged particles associated with extra U(1) gauge symmetries. We show how the absorption and dispersion of probe electromagnetic waves in the vacuum polarized by such a background are modified due to the coupling between the visible U(1)-gauge sector and these hypothetical degrees of freedom. The results of this analysis reveal that the regime close to the two-photon reaction threshold can be a sensititive p…
