Search

Direct dark matter detection experiments based on a liquid xenon target are leading the search for dark matter particles with masses above ∼5 GeV/c2, but have limited sensitivity to lighter masses because of the small momentum transfer in dark matter-nucleus elastic scattering. However, there is an irreducible contribution from inelastic processes accompanying the elastic scattering, which leads to the excitation and ionization of the recoiling atom (the Migdal effect) or the emission of a bremsstrahlung photon. In this Letter, we report on a probe of low-mass dark matter with masses down to about 85 MeV/c2 by looking for electronic recoils induced by the Migdal effect and bremsstrahlung using data from the XENON1T experiment. Besides the approach of detecting both scintillation and ionization signals, we exploit an approach that uses ionization signals only, which allows for a lower detection threshold. This analysis significantly enhances the sensitivity of XENON1T to light dark matter previously beyond its reach.

Several extensions to the Standard Model of particle physics, including light dark matter candidates and unification theories, predict deviations from Newton's law of gravitation. For macroscopic distances, the inverse-square law of gravitation is well confirmed by astrophysical observations and laboratory experiments. At micrometer and shorter length scales, however, even the state-of-the-art constraints on deviations from gravitational interaction, whether provided by neutron scattering or precise measurements of forces between macroscopic bodies, are currently many orders of magnitude larger than gravity itself. Here we show that precision spectroscopy of weakly bound molecules can be used to constrain non-Newtonian interactions between atoms. A proof-of-principle demonstration using recent data from photoassociation spectroscopy of weakly bound Yb$_2$ molecules yields constraints on these new interactions that are already close to state-of-the-art neutron scattering experiments. At the same time, with the development of the recently proposed optical molecular clocks, the neutron scattering constraints could be surpassed by at least two orders of magnitude., Comment: 5 pages, 3 figures, 1 table

We explore the challenging but phenomenologically interesting hierarchical mass spectrum of the Inert Doublet Model where relatively light dark matter along with much heavier scalar states can fully satisfy the constraints on the relic abundance and also fulfill other theoretical as well as collider and astrophysical bounds. To probe this region of parameter space at the LHC, we propose a signal process that combines up to two large radius boosted jets along with substantial missing transverse momentum. Aided by our intuitive signal selection, we capture a hybrid process where the di-fatjet signal is significantly enhanced by the mono-fatjet contribution with minimal effects on the SM di-fatjet background. Substantiated by the sizable mass difference between the scalars, these boosted jets, originally produced from the hadronic decay of massive vector bosons, still carry the inherent footprint of their root. These features implanted inside the jet substructure can provide additional handles to deal with a large background involving QCD jets. We adopt a multivariate analysis using boosted decision tree to provide a robust mechanism to explore the hierarchical scenario, which would bring almost the entire available parameter space well within reach of the 14 TeV LHC runs with high luminosity., 21 pages, 11 figures, Text updated, Figure added, matches published PRD version

The New Experiments With Spheres-Gas (NEWS-G) Collaboration aims to shed light on the dark matter sector using the Spherical Proportional Counter. NEWS-G uses light noble gases as targets, to search for light dark matter in the $0.1$ - $10$ GeV range. SEDINE, a $60$ cm in diameter spherical proportional counter, already operates in the Underground Laboratory of Modane, while the full-scale detector - $140$ cm in diameter - is currently under construction. The first results from NEWS-G, based on 9.7 kg$\cdot$days of exposure, are presented, obtaining a 90% confidence level upper limit of $4.4\cdot 10^{37}$ cm$^{2}$ on the nucleon-dark matter interaction cross-section for a candidate with a mass $0.5$ GeV. Recent developments in various aspects of the detector are discussed, along with the status of the project and future prospects.

We discuss prospects of searching for a dark photon ($A'$) which serves as mediator between Standard model (SM) particles and light dark matter (LDM) by using the combined results from the NA64 experiment at the CERN SPS running in high-energy electron (NA64e) and muon (NA64$\mu$) modes. We discuss the most natural values and upper bounds on the $A'$ coupling constant to LDM and show they are lying in the range accessible at NA64. While for the projected $ 5\times10^{12}$ electrons on target (EOT) NA64e is able to probe the scalar and Majorana LDM scenarios, the combined NA64e and NA64$\mu$ results with $\simeq 10^{13}$ EOT and a few $10^{13}$ MOT, respectively, will allow covering significant region in the parameter space of the most interesting LDM models. This makes NA64e and NA64$\mu$ extremely complementary to each other and increases significantly the discovery potential of sub-GeV DM., Comment: 16 pages, 4 figures, revised manuscript, matches to PLB version

We construct a theory in which the solution to the strong CP problem is an emergent property of the background of the dark matter in the Universe. The role of the axion degree of freedom is played by multi-body collective excitations similar to spin-waves in the medium of the dark matter of the Galactic halo. The dark matter is a vector particle whose low energy interactions with the Standard Model take the form of its spin density coupled to $G \widetilde{G}$, which induces a potential on the average spin density inducing it to compensate $\overline{\theta}$, effectively removing CP violation in the strong sector in regions of the Universe with sufficient dark matter density. We discuss the viable parameter space, finding that light dark matter masses within a few orders of magnitude of the fuzzy limit are preferred, and discuss the associated signals with this type of solution to the strong CP problem., Comment: 5 pages, 2 figures. Version published in PRL

Assisted annihilation is a mechanism to generate light dark matter through novel annihilation where two DM and one or more no assister(s) are there in the initial state and two SM or SM-like states are in the final state. We showed that depending on the mass hierarchy between assister and dark matter we can have either a suppression or a boost from a Boltzmann factor in the effective cross-section. This boost helps to achieve the required relic density for a MeV scale dark matter mass.

The Light Dark Matter eXperiment (LDMX) proposes a high-statistics search for low-mass dark matter in fixed-target electron-nucleus collisions. Ultimately, LDMX will explore thermal relic dark matter over most of the viable sub-GeV mass range to a decisive level of sensitivity. To achieve this goal, LDMX employs the missing momentum technique, where electrons scattering in a thin target can produce dark matter via "dark bremsstrahlung" giving rise to significant missing momentum and energy in the detector. To identify these rare signal events, LDMX individually tags incoming beam-energy electrons, unambiguously associates them with low energy, moderate transverse-momentum recoils of the incoming electron, and establishes the absence of any additional forward-recoiling charged particles or neutral hadrons. LDMX will employ low mass tracking to tag incoming beam-energy electrons with high purity and cleanly reconstruct recoils. A high-speed, granular calorimeter with MIP sensitivity is used to reject the high rate of bremsstrahlung background at trigger level while working in tandem with a hadronic calorimeter to veto rare photo-nuclear reactions.

These lectures provide an introduction to models and direct detection of dark matter. We summarize the general features and motivations for candidates in the full dark matter mass range, and then restrict to the keV-TeV mass window. Candidates in this window can be produced by thermal mechanisms in the standard cosmology, and are an important target for experimental searches. We then turn to sub-GeV dark matter (light dark matter) and dark sectors, an area where many new models and experiments are currently being proposed. We discuss the cosmology of dark sectors, specific portal realizations, and some of the prospects for detection. The final parts of these lectures focus on the theory for direct detection, both reviewing the fundamentals for nuclear recoils of WIMPs and describing new directions for sub-GeV candidates.

In the present work we examine the implications on dark matter searches of the possibility of a partial decay of a neutron into a dark matter particle, slightly lighter than itself. Such a scenario recently proposed is required to bridge the discrepancy between the results of two different experiments measuring the life time of the neutron. It was subsequently suggested that this light dark matter candidate could make up the whole of dark matter in the universe. We thus first compute the nucleon cross section based on such models. Then we proceed explore the various signatures appearing in dark matter searches involving nuclear targets, in the case of such a light dark matter candidate., Comment: 10 pages, 5 figures, 1 table. J. Phys. G: Nucl. Part. Phys (2020). arXiv admin note: substantial text overlap with arXiv:1812.08015

The density profiles of dwarf galaxies are a highly varied set. If the dark matter is an ultra-light particle such as axions, then simulations predict a distinctive and unique profile. If the axion mass is large enough to fit the ultra-faint dwarf (UFD) satellites($m\gtrapprox 10^{-21}$ eV), then the models do not fit the density profile of Fornax and Sculptor and are ruled out by more than $3-\sigma$ confidence. If the axion mass is in the mass range that can fit mass profiles of Fornax and Sculptor dwarf spheroidals, then its extended profile implies enormous masses ($\approx10^{11}-10^{12}M_{\odot}$) for the UFDs. These large masses for the UFDS are ruled out by more than $3-\sigma$ confidence by dynamical friction arguments. The tension would increase further considering star formation histories and stellar masses of the UFDs. Unless future ultra-light dark matter (ULDM) simulations with baryonic feedback show a significant change in the density structure of the halos, the current data is incompatible with the ULDM scenario. Relaxing the slope constraint from classical dwarf galaxies would lead to excluding ULDM with mass less than $6\times10^{-22}$ eV., Comment: Accepted for publication in ApJ main journal

The Beam Dump eXperiment (BDX) is a an electron-beam thick-target experiment aimed to investigate the existence of light Dark Matter particles in the MeV-GeV mass region at Jefferson Lab. The experiment will make use of a 10.6 GeV high-intensity electron-beam impinging on the Hall-A beam-dump to produce the Dark Matter particles ( &chi, ) through the Dark Photon portal. The BDX detector located at &sim, 20 m from the dump consists of two main components: an electromagnetic calorimeter to detect the signals produced by the &chi, electron scattering and a veto system to reject background. The expected signature of the DM (Dark Matter) interaction in the Ecal (Electromagnetic calorimeter) is a &sim, GeV electromagnetic shower paired with a null activity in the surrounding active veto counters. Collecting 10 22 electrons on target in 285 days of parasitic run at 65 &mu, A of beam current, and with an expected background of O(5) counts, in the case of a null discovery, BDX will be able to lower the exclusion limits by one to two orders of magnitude in the parameter space of dark-matter coupling versus mass. This paper describes the experiment and presents a summary of the most significant results achieved thus far, which led to the recent approval of the experiment by JLab-PAC46.

Sub-GeV Dark Matter particles upscattered by cosmic rays gain enough kinetic energy to pass the thresholds of large volume detectors on Earth. We then use public Super-Kamiokande and MiniBooNE data to derive a novel limit on the scattering cross section of Dark Matter with electrons that extends down to sub-keV masses, closing a previously allowed wide region of parameter space. We finally discuss search strategies and prospects at existing and planned neutrino facilities., 7 pages, 6 figures. v2: limits extended to larger cross sections, references and clarifications added. v3: Numerical glitch corrected, conclusions unchanged, clarifications and appendix added. Accepted for publication on PRL

Majorons are the Goldstone bosons of spontaneously broken lepton number and hence intimately connected to Majorana neutrino masses. Since all majoron couplings are heavily suppressed by the seesaw scale they are interesting candidates for long-lived dark matter. The signature decay into two mono-energetic neutrinos is potentially detectable with neutrino detectors for majoron masses above MeV and complementary to the loop-induced decays into visible particles. The mass range between keV and MeV can only be probed indirectly with the majoron decay into two photons; keV-scale majorons can be warm or cold dark matter depending on the underlying freeze-in mechanism., 4 pages, contribution to the proceedings of the Neutrino Oscillation Workshop (NOW2018), 9-16 September 2018, Rosa Marina (Ostuni, Brindisi, Italy)

Cryogenic detectors are excellent devices for rare event searches. Thanks to their low energy thresholds, these detectors are at the cutting edge for the investigations of light dark matter (DM). The CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) experiment explores with high sensitivity the parameter space of low mass DM candidates, being the pathfinder in the sub-GeV/c$^2$ mass range. CRESST employs scintillating CaWO$_4$ crystals as target material operated at mK temperature. Thanks to the simultaneous read-out of heat, in the main absorber, and light, with an auxiliary cryogenic light detector, the background in the region of interest is strongly suppressed. In 2018, the first stage of CRESST-III data taking was successfully completed, achieving an unprecedented energy threshold for nuclear recoils, lower than 100 eV. New results of CRESST-III will be presented accompanied by a status update on the ongoing activities.

We consider models of light dark matter coupled to quarks through a vector current interaction. For low energies, these models must be treated through the effective couplings to mesons, which are implemented here through the chiral Lagrangian. We find the rates of dark matter annihilation and decay to the light mesons, and find the expected photon spectrum from the decay of the hadrons. We compare to current and future observations, and show that there is a significant discovery reach for these models., 14 pages

Light dark matter in the context of dark sector theories is an attractive candidate to make up the bulk of the mass of our Universe. We explore here the possibility of using a low-pressure, negative-ion, time-projection-chamber detector to search for light dark matter behind the beam dump of an electron accelerator. The sensitivity of a 10-m long detector is several orders of magnitude better than existing limits. This sensitivity includes regions of parameter space where light dark matter is predicted to have a required relic density consistent with measured dark matter density. Backgrounds at shallow depth will need to be considered carefully. However, several signatures exist, including a powerful directional signature, which will allow a detection even in the presence of backgrounds.

Sub-GeV dark matter candidates are of increasing interest, because long-favored candidates such as GeV-scale WIMPs have not been detected. For low-mass dark matter, model-independent constraints are weak or nonexistent. We show that for such candidates, because the number density is high, cosmic ray propagation can be affected by elastic scattering with dark matter. We call this type of search `reverse direct detection,' because dark matter is the target and Standard Model particles are the beam. Using a simple propagation model for galactic cosmic rays, we calculate how dark matter affects cosmic ray spectra at Earth, and set new limits on the dark matter-proton and dark matter-electron cross sections. For protons, our limit is competitive with cosmological constraints, but is independent. For electrons, our limit covers masses not yet probed, and improves on cosmological constraints by one to two orders of magnitude. We comment on how future work can significantly improve the sensitivity of cosmic-ray probes of dark matter interactions., Main text: 11 pages, 5 figures Appendix: 2 pages, 2 figures. References updated and minor edits made to match version that appears in PRD

As experimental null results increase the pressure on heavy weakly interacting massive particles (WIMPs) as an explanation of thermal dark matter (DM), it seems timely to explore previously overlooked regions of the WIMP parameter space. In this work we extend the minimal gauged $U(1{)}_{{L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}}$ model studied in [M. Bauer, P. Foldenauer, and J. Jaeckel, J. High Energy Phys. 07 (2018) 094.] by a light (MeV-scale) vectorlike fermion $\ensuremath{\chi}$. Taking into account constraints from cosmology, direct and indirect detection we find that the standard benchmark of ${M}_{V}=3{m}_{\ensuremath{\chi}}$ for DM coupled to a vector mediator is firmly ruled out for unit DM charges. However, exploring the near-resonance region ${M}_{V}\ensuremath{\gtrsim}2{m}_{\ensuremath{\chi}}$ we find that this model can simultaneously explain the DM relic abundance $\mathrm{\ensuremath{\Omega}}{h}^{2}=0.12$ and the $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ anomaly. Allowing for small charge hierarchies of $\ensuremath{\lesssim}\mathcal{O}(10)$, we identify a second window of parameter space in the few-GeV region, where $\ensuremath{\chi}$ can account for the full DM relic density.

We investigate the properties of a Bose gas with a conserved charge as a dark matter candidate, taking into account the restrictions imposed by relic abundance, direct and indirect detection limits, big-bang nucleosynthesis and large scale structure formation constraints. We consider both the WIMP-like scenario of dark matter masses ≳1 GeV, and the small mass scenario, with masses ≲10−11 eV. We determine the conditions for the presence of a Bose-Einstein condensate at early times, and at the present epoch.

We point out that the LDMX (Light Dark Matter eXperiment) detector design, conceived to search for sub-GeV dark matter, will also have very advantageous characteristics to pursue electron-nucleus scattering measurements of direct relevance to the neutrino program at DUNE and elsewhere. These characteristics include a 4-GeV electron beam, a precision tracker, electromagnetic and hadronic calorimeters with near 2$\pi$ azimuthal acceptance from the forward beam axis out to $\sim$40$^\circ$ angle, and low reconstruction energy threshold. LDMX thus could provide (semi)exclusive cross section measurements, with detailed information about final-state electrons, pions, protons, and neutrons. We compare the predictions of two widely used neutrino generators (GENIE, GiBUU) in the LDMX region of acceptance to illustrate the large modeling discrepancies in electron-nucleus interactions at DUNE-like kinematics. We argue that discriminating between these predictions is well within the capabilities of the LDMX detector., Comment: 16 pages, 10 figures; updated to match the published version

Very light dark matter is usually taken to consist of uncharged bosons such as axion-like particles or dark photons. Here, we consider the prospect of very light, possibly even sub-eV dark matter carrying a net charge that is (approximately) conserved. By making use of the Affleck-Dine mechanism for its production, we show that a sizable fraction of the energy density can be stored in the asymmetric component. We furthermore argue that there exist regions of parameter space where the energy density contained in symmetric particle-antiparticle pairs without net charge can to some degree be depleted by considering couplings to additional fields. Finally, we make an initial foray into the phenomenology of this scenario by considering the possibility that dark matter is coupled to the visible sector via the Higgs portal., 25 pages + appendices, 4 figures. v2: minor modifications and updated figures

So far, dark matter has only been discovered gravitationally, while its particle identity remains unknown. It is possible that dark matter is so weakly coupled to the visible sector that a direct nongravitational interaction lies well beyond our experimental reach. It is then interesting to ask to what extent indirect probes of dark matter can point to a specific particle physics description. In this note, we discuss two such examples: The first is via 21 cm cosmology and the second is via the study of AGN and black hole growth rate.

In Sect. 2.2, we discussed the effects of the \(b\rightarrow s\bar{q}q\) electroweak penguin interfering with the strong penguin and tree amplitudes. The quintessential electroweak penguin would be \(b\rightarrow s\ell ^+\ell ^-\) decay, or \(b\rightarrow s\nu \nu \) that has no photonic contribution. We now discuss how the study of these processes, present already in SM, could help us probe New Physics. Besides presenting some background development, we begin with the forward-backward asymmetry \(A_\mathrm{FB}(B\rightarrow K^*\ell ^+\ell ^-)\) as a probe of the bsZ vertex, and the subsequent unfolding of the \(P_5^\prime \) and \(R_{K^{(*)}}\) anomalies. We comment briefly on a possible \(Z^\prime \) boson as a source for generating effective \([\bar{s}b][\bar{\ell }\ell ]\) (and \([\bar{s}b][\bar{\nu }\nu ]\)) four-fermi interactions. The \(b\rightarrow s\nu \nu \) process has the same signature as \(b\rightarrow s+\) nothing. A later chapter extends the signature as a probe of light Dark Matter

Accelerator-based experiments are playing an increasingly essential role in exploring the nature of dark matter. Several approaches have been proposed to search for light dark matter at collider and beam-dump experiments, providing unique sensitivity to several well-motivated scenarios. In this contribution, we review the current experimental situation and future efforts in that domain, emphasizing the advantages and challenges of each technique. A new proposal offering unprecedented sensitivity to directly annihilating thermal dark matter, the LDMX experiment, is also presented.

Some of the motivations for considering light dark matter in the sub-GeV mass regime are reviewed, and I discuss work on specific direct detection signatures of MeV and sub-MeV mass dark matter candidates that can be studied using current experiments such as XENON1T, PANDA-X, SuperCDMS, and others.

International audience; Spherical proportional counters (SPCs) are a novel gaseous detector technology employed by the NEWS-G low-mass dark matter search experiment for their high sensitivity to single electrons from ionization. In this paper, we report on the first characterization of the single electron response of SPCs with unprecedented precision, using a UV-laser calibration system. The experimental approach and analysis methodology are presented along with various direct applications for the upcoming next phase of the experiment at SNOLAB. These include the continuous monitoring of the detector response and electron drift properties during dark matter search runs, as well as the experimental measurement of the trigger threshold efficiency. We measure a mean ionization energy of W=27.6±0.2 eV in Ne+CH4 (2%) for 2.8 keV x-rays, and demonstrate the feasibility of performing similar precision measurements at sub-keV energies for future gas mixtures to be used for dark matter searches at SNOLAB.

We present a detailed analysis of the effect of light Dark Matter (DM) on atomic clocks, for the case where DM mass and density are such that occupation numbers are low and DM must be considered as particles scattering off the atoms, rather than a classical field. We show that the resulting atomic clock frequency shifts are first order in the scattering amplitudes, and particularly suited to constrain DM models in the regime where the DM mass $m_\chi \ll$ GeV. We provide some rough order of magnitude estimates of sensitivity that can be confronted to any DM model that allows for non zero differential scattering amplitudes of the two atomic states involved in the clock., Comment: 10 pages, 1 figure, 1 table

It was proposed recently that different chiralities of the dark matter (DM) fermion under a broken dark U(1) gauge group can lead to distinguishable signatures at the LHC through shower patterns, which may reveal the mass origin of the dark sector. We study this subject further by examining the dark shower of two simplified models, the dubbed Chiral Model and the Vector Model. We derive a more complete set of collinear splitting functions with power corrections, specifying the helicities of the initial DM fermion and including the contribution from an extra degree of freedom, the dark Higgs boson. The dark shower is then implemented with these splitting functions, and the new features resulting from its correct modelling are emphasized. It is shown that the DM fermion chirality can be differentiated by measuring dark shower patterns, especially the DM jet energy profile, which is almost independent of the DM energy., Comment: 18 pages, 6 figures

Pseudo-Goldstone dark matter coupled to the Standard Model via the Higgs portal offers an attractive framework for phenomenologically viable pseudo-scalar dark matter. It enjoys natural suppression of the direct detection rate due to the vanishing of the relevant (tree level) Goldstone boson vertex at zero momentum transfer, which makes light WIMP-like dark matter consistent with the strong current bounds. In this work, we explore prospects of detecting pseudo-Goldstone dark matter at the LHC, focusing on the vector boson fusion (VBF) channel with missing energy. We find that, in substantial regions of parameter space, relatively light dark matter ($m_��< 100$ GeV) can be discovered in the high luminosity run as long as it is produced in decays of the Higgs-like bosons., 15 pages

We present the cosmological constraints on the cross section of baryon-dark matter interactions for the dark matter mass below the MeV scale from the Planck CMB (cosmic microwave background) and SDSS (Sloan Digital Sky Survey) Lyman-$\alpha$ forest data. To explore the dark matter mass $m_{\chi}\lesssim 1$ MeV for which the dark matter's free-streaming effect can suppress the observable small scale density fluctuations, in addition to the acoustic oscillation damping in existence of the baryon-dark matter coupling, we apply the approximated treatment of dark matter free-streaming analogous to that of the conventional warm dark matter. We also demonstrate the mass dependence of the baryon-dark matter cross section bounds (for the dark matter mass down to $m_{\chi} \sim 5~{\rm keV}$), in contrast to the dark matter mass independence of the cross section constraints for the light dark matter below the MeV scale claimed in the previous literature., Comment: 8 pages, 13 figures, 2 tables

The Search for Hidden Particles experiment (SHiP) is a new general purpose fixed target facility, whose Technical Proposal has been recently reviewed by the CERN SPS Committee and by the CERN Research Board. The two boards recommended that the experiment proceeds further to a Comprehensive Design phase in the context of the new CERN Working group "Physics Beyond Colliders", aiming at presenting a CERN strategy for the European Strategy meeting of 2019. In its initial phase, the 400GeV proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrating $2\cdot10^{20}$ pot in 5 years. A dedicated detector, based on a long vacuum tank followed by a spectrometer and particle identification detectors, will allow probing a variety of models with light long-lived exotic particles and masses below O(10) GeV /c$^2$. The main focus will be the physics of the so-called hidden portals, i.e. search for dark photons, light scalars, pseudo-scalars, and heavy neutrinos. The sensitivity to heavy neutrinos will allow for the first time to probe, the mass range between the kaon and the charm meson mass, a coupling range for which baryogenesis and active neutrino masses could also be explained. Another dedicated emulsion-based detector will allow detection of light dark matter from dark photon decay in an unexplored parameter range.

We consider the Big Bang Nucleosynthesis (BBN) bounds on light dark matter whose cross section off nucleons is sufficiently large to enable acceleration by scattering off of cosmic rays in the local galaxy. Such accelerated DM could then deposit energy in terrestrial detectors. Since this signal involves DM of mass ~ keV - 100 MeV and requires large cross sections > 10^-31 cm^2 in a relativistic kinematic regime, we find that the DM population in this scenario is generically equilibrated with Standard Model particles in the early universe. For sufficiently low DM masses < 10 MeV, corresponding to the bulk of the favored region of many cosmic-ray upscattering studies, this equilibrated DM population adds an additional component to the relativistic energy density around T ~ few MeV and thereby spoils the successful predictions of BBN. In the remaining ~ 10-100 MeV mass range, the large couplings required in this scenario are either currently excluded or within reach of current or future accelerator-based searches., 6ish pages, 1 figure

We show how the relativistic effective field theory for the superfluid phase of helium-4 can replace the standard methods used to compute the production rates of low momentum excitations due to the interaction with an external probe. This is done by studying the scattering problem of a light dark matter particle in the superfluid, and comparing to some existing results. We show that the rate of emission of two phonons, the Goldstone modes of the effective theory, gets strongly suppressed for sub-MeV dark matter particles due to a fine cancellation between two different tree-level diagrams in the limit of small exchanged momenta. This phenomenon is found to be a consequence of the particular choice of the potential felt by the dark matter particle in helium. The predicted rates can vary by orders of magnitude if this potential is changed. We prove that the dominant contribution to the total emission rate is provided by the phonons. Finally, we analyze the angular distributions for the emissions of one and two phonons, and discuss how they can be used to measure the mass of the hypothetical dark matter particle hitting the helium target., Comment: 5 pages, 3 figures; v2: references updated and typos corrected

In the present contribution, we present preliminary ideas on the advantage of using positron beams on fixed target in searching for the \(A'\). In particular, we will discuss \(A'\) production mechanisms, accessible only at positron machines, which might offer enhanced cross sections compared to the commonly used \(A'\)-strahlung. Recent studies show that the inclusion of such processes in the reinterpretation of old beam dump experiments results in significantly more stringent exclusion limits. Finally, we will discuss the peculiar case of searches for candidates with defined mass, using as a benchmark case the \(^8Be\) 16.7 MeV X-Boson.

We consider the direct detection of dark matter (DM) with polar materials, where single production of optical or acoustic phonons gives excellent reach to scattering of sub-MeV DM for both scalar and vector mediators. Using Density Functional Theory (DFT), we calculate the material-specific matrix elements, focusing on GaAs and sapphire, and show that DM scattering in an anisotropic crystal such as sapphire features a strong directional dependence. For example, for a DM candidate with mass 40 keV and relic abundance set by freeze-in, the daily modulation in the interaction rate can be established at 90\% C.L. with a gram-year of exposure. Non-thermal dark photon DM in the meV - eV mass range can also be effectively absorbed in polar materials., 48 pages, 17 figures. Has animated content which requires Adobe Acrobat reader

The NEWS-G (New Experiment with Spheres - Gas) collaboration searches for dark matter in the form of low-mass Weakly Interacting Massive Particles (WIMPs) using Spherical Proportional Counters (SPCs) filled with gases with low atomic masses. The operation of SEDINE, a 60-cm diameter prototype SPC filled with a mixture of neon and methane and installed at the Laboratoire Souterrain de Modane (LSM) in France, recently set new constraints on the spin-independent WIMP-nucleon scattering cross-section in the sub-GeV/c2 mass region. The collaboration is currently planning the installation a 140-cm ultra-low background SPC in a compact shielding at SNOLAB in Canada. Recent advances in radioactive background control, detector monitoring and sensor development, will provide for this next experimental phase of NEWS-G unprecedented sensitivity to low-mass WIMPs.

We investigate the thermal cosmology and terrestrial and astrophysical phenomenology of a sub-GeV hadrophilic dark sector. The specific construction explored in this work features a Dirac fermion dark matter candidate interacting with a light scalar mediator that dominantly couples to the up-quark. The correct freeze-out relic abundance may be achieved via dark matter annihilation directly to hadrons or through secluded annihilation to scalar mediators. A rich and distinctive phenomenology is present in this scenario, with probes arising from precision meson decays, proton beam dump experiments, colliders, direct detection experiments, supernovae, and nucleosynthesis. In the future, experiments such as NA62, REDTOP, SHiP, SBND, and NEWS-G will be able to explore a significant portion of the cosmologically motivated parameter space., 36 pages, 2 figures

We study the possibility that light dark matter can be produced with right relic density by the decay of other dark sector particles. We study this possibility in a model with right-handed neutrinos, a dark sector singlet scalar and a dark sector singlet fermion. The decay of the heavier dark sector singlet scalar gives rise to the lighter dark sector singlet fermion which serves as the dark matter candidate. We show that the right dark matter relic density can be produced by the decay of the dark sector singlet scalar. We find that the mass of the dark sector singlet fermion can be GeV scale or MeV scale and the interaction of the dark sector singlet fermion is very weak. The dark sector singlet scalar can have a mass of GeV-TeV scale and can have weak scale interactions with the Standard Model(SM) particles. So, in this scenario, dark matter has an interaction with the SM much weaker than the weak interaction, but the dark sector still has weak scale interaction with the SM., Comment: 18 pages, 7 figures, version published in PLB

We study a simplest viable dark matter model with a real singlet scalar, vector-like singlet and a doublet lepton. We find a considerable enhancement in the allowed region of the scalar dark matter parameter spaces under the influence of the new Yukawa coupling. The Yukawa coupling associate with the fermion sector heavily dominant the dark matter parameter spaces satisfying the current relic density of the Universe. Dilepton$+\slashed{E}_T$ signature arising from the new fermionic sector can observe at Large Hadron Collider (LHC). We perform such analysis in the context of 14 TeV LHC experiments with a future integrated luminosity of 3000 ${\rm fb^{-1}}$. We found that a large region of the parameter spaces can be probed by the LHC experiments. The projected exclusion/discovery reach of direct heavy charged fermion searches in this channels is analyzed by performing a detailed cut based collider analysis. The projected exclusion contour reaches up to $1050-1380~{\rm GeV}$ for 3000 ${\rm fb^{-1}}$ for a light dark matter $\mathcal{O}(10)$ GeV from searches in the $ pp \rightarrow E_1^\pm E_1^\mp, E_1^\pm\rightarrow l^\pm S \rightarrow ll + \slashed{E}_T$ channel., 34 pages and 16 Figures: Modifications added, Accepted in Nuclear Physics B

Currently, the standard cosmological model faces some tensions and discrepancies between observations at early and late cosmological time. One of them concerns the well-known H0-tension problem, i.e., a ∼4.4σ-difference between the early-time estimate and late-time measurements of the Hubble constant, H0. Another puzzling question rests in the cosmological lithium abundance, where again local measurements differ from the one predicted by Big Bang Nucleosynthesis (BBN). In this work, we show that a mechanism of light dark matter production might hold the answer for these questions. If dark matter particles are sufficiently light and a fraction of them were produced non-thermally in association with photons, this mechanism has precisely what is needed to destroy Lithium without spoiling other BBN predictions. Besides, it produces enough radiation that leads to a larger H0 value, reconciling early and late-time measurements of the Hubble expansion rate without leaving sizable spectral distortions in the Cosmic Microwave Background spectrum.

Next-generation experiments allow for the possibility to testing the neutrino flavor oscillation model to very high levels of accuracy. Here, we explore the possibility that the dark matter in the current universe is made of two particles, a sterile neutrino and a very light dark matter particle. By using a 3+1 neutrino flavor oscillation model, we study how such a type of dark matter imprints the solar neutrino fluxes, spectra, and survival probabilities of electron neutrinos. The current solar neutrino measurements allow us to define an upper limit for the ratio of the mass of a light dark matter particle $m_\phi$ and the Fermi constant $G_\phi$, such that $G_\phi/m_\phi $ must be smaller than $10^{30}\; G_{\rm F}\; eV^{-1}$ to be in agreement with current solar neutrino data from the Borexino, Sudbury Neutrino Observatory, and Super-Kamiokande detectors. Moreover, for models with a very small Fermi constant, the amplitude of the time variability must be lower than $3\%$ to be consistent with current solar neutrino data. We also found that solar neutrino detectors like Darwin, able to measure neutrino fluxes in the low energy-range with high accuracy, will provide additional constraints to this class of models that complement the ones obtained from the current solar neutrino detectors., Comment: 10 pages, 6 figures

I consider the impact of recent measurements of positron and antiproton spectra in cosmic rays on our understanding of the origins and propagation of cosmic rays, as well as on the annihilation and decay characteristics of particles of Galactic dark matter, from the perspective of current models postulating energy-dependent leakage of cosmic rays from the Galaxy and of the nested leaky-box model, in which the leakage from the Galaxy is independent of energy. The nested leaky-box model provides a straightforward and consistent explanation of the observed spectral intensities, and finds no compelling need for a contribution from the annihilation or decay of Galactic dark matter. Improved observations and modeling efforts are needed to probe the properties of dark matter deeply enough to be significant to particle physics and cosmology.

In this letter, we consider a class of scenarios in which the dark matter is part of a heavy hidden sector that is thermally decoupled from the Standard Model in the early universe. The dark matter freezes-out by annihilating to a lighter, metastable state, whose subsequent abundance can naturally come to dominate the energy density of the universe. When this state decays, it reheats the visible sector and dilutes all relic abundances, thereby allowing the dark matter to be orders of magnitude heavier than the weak scale. For concreteness, we consider a simple realization with a Dirac fermion dark matter candidate coupled to a massive gauge boson that decays to the Standard Model through its kinetic mixing with hypercharge. We identify viable parameter space in which the dark matter can be as heavy as ~1-100 PeV without being overproduced in the early universe., Comment: 4 pages + appendices, 2 figures

General considerations in general relativity and quantum mechanics are known to potentially rule out continuous global symmetries in the context of any consistent theory of quantum gravity. Assuming the validity of such considerations, we derive stringent bounds from gamma-ray, X-ray, cosmic-ray, neutrino, and CMB data on models that invoke global symmetries to stabilize the dark matter particle. We compute up-to-date, robust model-independent limits on the dark matter lifetime for a variety of Planck-scale suppressed dimension-five effective operators. We then specialize our analysis and apply our bounds to specific models including the Two-Higgs-Doublet, Left-Right, Singlet Fermionic, Zee-Babu, 3-3-1 and Radiative See-Saw models. {Assuming that (i) global symmetries are broken at the Planck scale, that (ii) the non-renormalizable operators mediating dark matter decay have $O(1)$ couplings, that (iii) the dark matter is a singlet field, and that (iv) the dark matter density distribution is well described by a NFW profile}, we are able to rule out fermionic, vector, and scalar dark matter candidates across a broad mass range (keV-TeV), including the WIMP regime., Matches Published version in Phys.Lett. B760 (2016) 807-815

A search for dark matter was conducted by looking for an annual modulation signal due to the Earth's rotation around the Sun using XMASS, a single phase liquid xenon detector. The data used for this analysis was 359.2 live days times 832 kg of exposure accumulated between November 2013 and March 2015. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the target nuclei, the exclusion upper limit of the WIMP–nucleon cross section 4.3×10−41 cm2 at 8 GeV/c$^{2}$ was obtained and we exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c$^{2}$ range at ∼10$^{−40}$ cm$^{2}$. The result of a simple modulation analysis, without assuming any specific dark matter model but including electron/γ events, showed a slight negative amplitude. The p-values obtained with two independent analyses are 0.014 and 0.068 for null hypothesis, respectively. We obtained 90% C.L. upper bounds that can be used to test various models. This is the first extensive annual modulation search probing this region with an exposure comparable to DAMA/LIBRA.

Spare a thought for the dark-matter hunters. Every time they're on the verge of trapping the elusive stuff thought to make up the bulk of the universe's matter, it slips away. They don't see the expected signals, or they spot something exciting only to watch it fade into background noise. Each time it's the same: put on a brave face, go back to the drawing board and begin the hunt again. Perhaps it's time for a change of tack. Instead of going after a single species of dark matter particle, maybe people should be looking for a menagerie of dark particles and forces--a whole new "dark sector." After all, there is no reason to think dark matter will be any less intricate than the visible stuff they consider ordinary, with its panoply of particles from electrons to quarks. Here, Clark discusses the entire shadow world in which invisible particles influence one another through forces unfelt by the familiar stuff of stars and planets and people.

We reanalyze the dataset collected during the years 1998--2003 by the deep underwater neutrino telescope NT200 in the lake Baikal with the low energy threshold (10 GeV) in searches for neutrino signal from dark matter annihilations near the center of the Milky Way. Two different approaches are used in the present analysis: counting events in the cones around the direction towards the Galactic Center and the maximum likelihood method. We assume that the dark matter particles annihilate dominantly over one of the annihilation channels $b\bar{b}$, $W^+W^-$, $\tau^+\tau^-$, $\mu^+\mu^-$ or $\nu\bar{\nu}$. No significant excess of events towards the Galactic Center over expected neutrino background of atmospheric origin is found and we derive 90% CL upper limits on the annihilation cross section of dark matter., Comment: 15 pages, 14 figures, published version