Light Weakly Interacting Massive Particles Research Articles

CMB and 21-cm bounds on early structure formation boosted by primordial black hole entropy fluctuations

The dark matter (DM) can consist of the primordial black holes (PBHs) in addition to the conventional weakly interacting massive particles (WIMPs). The Poisson fluctuations of the PBH number density produce the isocurvature perturbations which can dominate the matter power spectrum at small scales and enhance the early structure formation. We study how the WIMP annihilation from those early formed structures can affect the CMB (in particular the E-mode polarization anisotropies and $y$-type spectral distortions) and global 21cm signals. Our studies would be of particular interest for the light (sub-GeV) WIMP scenarios which have been less explored compared with the mixed DM scenarios consisting of PBHs and heavy ($\gtrsim 1$ GeV) WIMPs. For instance, for the self-annihilating DM mass $m_{\chi}=1$ MeV and the thermally averaged annihilation cross section $\langle \sigma v \rangle \sim 10^{-30} \rm cm^3/s$, the latest Planck CMB data requires the PBH fraction with respect to the whole DM to be at most ${\cal O}(10^{-3})$ for the sub-solar mass PBHs and an even tighter bound (by a factor $\sim 5$) can be obtained from the global 21-cm measurements.

Dark matter capture and annihilation in stars: Impact on the red giant branch tip

Context.While stars have often been used as laboratories to study dark matter (DM), red giant branch (RGB) stars and all the rich phenomenology they encompass have frequently been overlooked by such endeavors.Aims.We study the capture, evaporation, and annihilation of weakly interacting massive particle (WIMP) DM in low-mass RGB stars (M = 0.8−1.4 M⊙).Methods.We used a modified stellar evolution code to study the effects of DM self-annihilation on the structure and evolution of low-mass RGB stars.Results.We find that the number of DM particles that accumulate inside low-mass RGB stars is not only constant during this phase of evolution, but also mostly independent of the stellar mass and to some extent stellar metallicity. Moreover, we find that the energy injected into the stellar core due to DM annihilation can promote the conditions necessary for helium burning and thus trigger an early end of the RGB phase. The premature end of the RGB, which is most pronounced for DM particles withmχ ≃ 100 GeV, is thus achieved at a lower helium core mass, which results in a lower luminosity at the tip of the red giant branch (TRGB). Although in the current WIMP paradigm, these effects are only relevant if the number of DM particles inside the star is extremely large, we find that for light WIMPs (mχ ≃ 4 GeV), relevant deviations from the standard TRGB luminosity (∼8%) can be achieved with conditions that can be realistic in the inner parsec of the Milky Way.

Extending light WIMP searches to single scintillation photons in LUX

We present a novel analysis technique for liquid xenon time projection chambers that allows for a lower threshold by relying on events with a prompt scintillation signal consisting of single detected photons. The energy threshold of the LUX dark matter experiment is primarily determined by the smallest scintillation response detectable, which previously required a twofold coincidence signal in its photomultiplier arrays, enforced in data analysis. The technique presented here exploits the double photoelectron emission effect observed in some photomultiplier models at vacuum ultraviolet wavelengths. We demonstrate this analysis using an electron recoil calibration dataset and place new constraints on the spin-independent scattering cross section of weakly interacting massive particles (WIMPs) down to 2.5 GeV/c2 WIMP mass using the 2013 LUX dataset. This new technique is promising to enhance light WIMP and astrophysical neutrino searches in next-generation liquid xenon experiments.2 MoreReceived 23 July 2019Accepted 24 December 2019DOI:https://doi.org/10.1103/PhysRevD.101.042001© 2020 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDark matterParticle dark matterWeakly interacting massive particlesTechniquesDark matter detectorsParticles & FieldsGravitation, Cosmology & Astrophysics

Limits on light WIMPs with a 1 kg-scale germanium detector at 160 eVee physics threshold at the China Jinping Underground Laboratory**Supported by the National Key Research and Development Program of China (2017YFA0402200, 2017YFA0402201), the National Natural Science Foundation of China (11175099, 11275107, 11475117, 11475099, 11475092, 11675088), the National Basic Research Program of China (973 Program) (2010CB833006). We thank the support

We report results of a search for light weakly interacting massive particle (WIMP) dark matter from the CDEX-1 experiment at the China Jinping Underground Laboratory (CJPL). Constraints on WIMP-nucleon spin-independent (SI) and spin-dependent (SD) couplings are derived with a physics threshold of 160 eVee, from an exposure of 737.1 kg-days. The SI and SD limits extend the lower reach of light WIMPs to 2 GeV and improve over our earlier bounds at WIMP mass less than 6 GeV.

Ruling out the light weakly interacting massive particle explanation of the Galactic 511 keV line

Over the past few decades, an anomalous 511 keV gamma-ray line has been observed from the centre of the Milky Way. Dark matter (DM) in the form of light weakly interacting massive particles (WIMPs) annihilating into electron-positron pairs has been one of the leading hypotheses of the observed emission. Given the small required cross section, a further coupling to lighter particles is required to produce the correct relic density. Here, we derive constraints from the Planck satellite on light WIMPs that were in equilibrium with either the neutrino or electron sector in the early universe. For the neutrino sector, we obtain a lower bound on the WIMP mass of 4 MeV for a real scalar and 10 MeV for a Dirac fermion DM particle, at 95% CL. For the electron sector, we find even stronger bounds of 7 and 11 MeV, respectively. Using these results, we show that, in the absence of additional ingredients such as dark radiation, the light thermally produced WIMP explanation of the 511 keV excess is strongly disfavoured by the latest cosmological data. This suggests an unknown astrophysical or more exotic DM source of the signal.

How to calculate dark matter direct detection exclusion limits that are consistent with gamma rays from annihilation in the Milky Way halo

When comparing constraints on the Weakly Interacting Massive Particle (WIMP) properties from direct and indirect detection experiments it is crucial that the assumptions made about the dark matter (DM) distribution are realistic and consistent. For instance, if the Fermi-LAT Galactic centre GeV gamma-ray excess was due to WIMP annihilation, its morphology would be incompatible with the Standard Halo Model that is usually used to interpret data from direct detection experiments. In this article, we calculate exclusion limits from direct detection experiments using self-consistent velocity distributions, derived from mass models of the Milky Way where the DM halo has a generalized NFW profile. We use two different methods to make the mass model compatible with a DM interpretation of the Galactic centre gamma-ray excess. Firstly, we fix the inner slope of the DM density profile to the value that best fits the morphology of the excess. Secondly, we allow the inner slope to vary and include the morphology of the excess in the data sets used to constrain the gravitational potential of the Milky Way. The resulting direct detection limits differ significantly from those derived using the Standard Halo Model, in particular for light WIMPs, due to the differences in both the local DM density and velocity distribution.

Recent status and prospect of CDEX and CJPL

The China Dark Matter Experiment (CDEX) aims at the direct searches of light Weakly Interacting Massive Particles (WIMPs) deploying point-contact germanium detector at the China Jinping Underground Laboratory (CJPL), which has about 2400 m of rock overburdened. Results on light WIMPs from the prototype CDEX-0 with a few gram mass and CDEX-1 with a 994 g mass are reported. The CDEX-10 experiment employed a germanium detector arrays and liquid argon anti-Compton is being constructed and tested. The multi-purpose experiment CDEX-1T and the expansion project of CJPL-II will also be discussed.

BBN and the CMB constrain neutrino coupled light WIMPs

In the presence of a light weakly interacting massive particle (WIMP) with mass ${m}_{\ensuremath{\chi}}\ensuremath{\lesssim}30\text{ }\text{ }\mathrm{MeV}$, there are degeneracies among the nature of the WIMP (fermion or boson), its couplings to the standard model particles (to electrons, positrons, and photons, or only to neutrinos), its mass ${m}_{\ensuremath{\chi}}$, and the number of equivalent (additional) neutrinos, $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}$. These degeneracies cannot be broken by the cosmic microwave background (CMB) constraint on the effective number of neutrinos, ${\mathrm{N}}_{\text{eff}}$. However, since big bang nucleosynthesis (BBN) is also affected by the presence of a light WIMP and equivalent neutrinos, complementary BBN and CMB constraints can help to break some of these degeneracies. In a previous paper [K. M. Nollett and G. Steigman, Phys. Rev. D 89, 083508 (2014)] the combined BBN and Planck [P. A. R. Ade et al. (Planck Collaboration), Astron. Astrophys. 571, A16 (2014)] CMB constraints were used to explore the allowed ranges for ${m}_{\ensuremath{\chi}}$, $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}$, and ${\mathrm{N}}_{\text{eff}}$ in the case where the light WIMPs annihilate electromagnetically (EM) to photons and/or ${e}^{\ifmmode\pm\else\textpm\fi{}}$ pairs. In this paper the BBN predictions for the primordial abundances of deuterium and $^{4}\mathrm{He}$ (along with $^{3}\mathrm{He}$ and $^{7}\mathrm{Li}$) in the presence of a light WIMP that only couples (annihilates) to neutrinos [either standard model (SM) only or both SM and equivalent] are calculated. Recent observational estimates of the relic abundances of D and $^{4}\mathrm{He}$ are used to limit the light WIMP mass, the number of equivalent neutrinos, the effective number of neutrinos, and the present Universe baryon density (${\mathrm{\ensuremath{\Omega}}}_{\mathrm{B}}{h}^{2}$). Allowing for a neutrino coupled light WIMP and $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}$ equivalent neutrinos, the combined BBN and CMB data provide lower limits to the WIMP mass that depend very little on the nature of the WIMP (Majorana or Dirac fermion, real or complex scalar boson), with a best fit ${m}_{\ensuremath{\chi}}\ensuremath{\gtrsim}35\text{ }\text{ }\mathrm{MeV}$, equivalent to no light WIMP at all. The analysis here excludes all neutrino coupled WIMPs with masses below a few MeV, with specific limits varying from 4 to 9 MeV depending on the nature of the WIMP. In the absence of a light WIMP (either EM or neutrino coupled), BBN alone prefers $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}=0.50\ifmmode\pm\else\textpm\fi{}0.23$, favoring neither the absence of equivalent neutrinos ($\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}=0$), nor the presence of a fully thermalized sterile neutrino ($\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}=1$). This result is consistent with the CMB constraint, ${\mathrm{N}}_{\text{eff}}=3.30\ifmmode\pm\else\textpm\fi{}0.27$ [1], constraining ``new physics'' between BBN and recombination. Combining the BBN and CMB constraints gives $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}=0.35\ifmmode\pm\else\textpm\fi{}0.16$ and ${\mathrm{N}}_{\text{eff}}=3.40\ifmmode\pm\else\textpm\fi{}0.16$. As a result, while BBN and the CMB combined require $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}\ensuremath{\ge}0$ at $\ensuremath{\sim}98%$ confidence, they disfavor $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}\ensuremath{\ge}1$ at $>99%$ confidence. Adding the possibility of a neutrino-coupled light WIMP extends the allowed range slightly downward for $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}$ and slightly upward for ${\mathrm{N}}_{\text{eff}}$ simultaneously, while leaving the best-fit values unchanged.

Search for neutrinos from annihilation of captured low-mass dark matter particles in the sun by super-kamiokande.

Super-Kamiokande (SK) can search for weakly interacting massive particles (WIMPs) by detecting neutrinos produced from WIMP annihilations occurring inside the Sun. In this analysis, we include neutrino events with interaction vertices in the detector in addition to upward-going muons produced in the surrounding rock. Compared to the previous result, which used the upward-going muons only, the signal acceptances for light (few-GeV/c^{2}-200-GeV/c^{2}) WIMPs are significantly increased. We fit 3903 days of SK data to search for the contribution of neutrinos from WIMP annihilation in the Sun. We found no significant excess over expected atmospheric-neutrino background and the result is interpreted in terms of upper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about the annihilation channel. We set the current best limits on the spin-dependent WIMP-proton cross section for WIMP masses below 200 GeV/c^{2} (at 10 GeV/c^{2}, 1.49×10^{-39} cm^{2} for χχ→bb[over ¯] and 1.31×10^{-40} cm^{2} for χχ→τ^{+}τ^{-} annihilation channels), also ruling out some fraction of WIMP candidates with spin-independent coupling in the few-GeV/c^{2} mass range.

PandaX-I result sets a stringent limit for low-mass dark matter particles

Astrophysical and cosmological observations show that about 27% of the energy in our universe comes from dark matter (DM). What is DM is an outstanding puzzle in science in the 21st century. The weakly interacting massive particles (WIMPs) have been by far the favored candidate for DM, although they cannot be accommodated in the standard model of strong and electroweak interactions. DM theory asserts that our solar system is bathed in the DM halo of the MilkyWay,withmillions ofWIMPs passing throughour body every second. Interactions of DM with ordinary matter are exceedinglyweak andmay be detected by sensitive equipment through the energy deposited in a detector by elastic scattering of WIMPs with the nuclei of ordinary matter. There are many such directsearch experiments around the world, trying to catch the faint signals released in the form of photons, electrons or heat using different technologies. Several experiments, such as the Dark Matter/Large Sodium Iodide Bulk for Rare Processes experiment in Italy, theCoherentGermanium Neutrino Technology and Cryogenic Dark Matter Search (CDMS) experiments in the USA and the Germanled Cryogenic Rare Event Search with Superconducting Thermometers experiment, have in recent years reported positive signals, which could be interpreted as light WIMPs. The first results published in Sci China Phys Mech Astron this year by the PandaX collaboration, however, downgrade these claims [1]. The PandaX (Particle AND Astrophysical Xenon Detector) collaboration is an international team of about 40 scientists led by Professor Xiangdong Ji from Shanghai Jiao Tong University (also affiliated with the University of Maryland). This is the first large-scale xenon DM search experiment carried out in the newly established China Jinping Underground Laboratory (CJPL) in Sichuan, China. CJPL is among the deepest underground laboratories in the world, and being well shielded from the cosmic ray background. Xenon is a noble gas, which becomes liquid at about 110◦ below zero Celsius. The current experiment uses about 120 kg of liquid xenon as the active target for WIMPs. The detector employs a technology called the dual-phase xenon time-projection chamber (TPC), enabling a 3D reconstruction of the events. This technology was shown to be one of the more promising technologies based on the similar 100 kg XENON DM project (XENON100) and the Large Underground Xenon experiments. It now offers improved detection sensitivity over a wide range of DM mass by two orders of magnitude compared with other experiments. The first stage of PandaX operations, the PandaX-I, intends to examine the curious signals of WIMPs in the low-mass region reported by previous experiments. Its detector is a pancake-shaped TPC designed for high photon-collection efficiency. PandaX-I’s first results are based on the data collected in 17.4 live days, with more than 4 million raw events recorded. After removing the low-quality events and narrowing the energy search window to the regions of interest, 46 events are seen in the central fiducial volume with 37 kg of liquid xenon. These events are consistent with signals from the background radiation, the paper reports. Without candidate WIMP DM events, PandaX-I sets a stringent limit for low-mass DM particles and effectively rules out the interpretation of positive experimental results previously reported. Together with the results reported by the China Dark matter Experiment led by scientists at Tsinghua University (also at CJPL) and the SuperCDMS experiments in the USA, PandaX has set one of the best limits for WIMP DM with low mass, as can be seen from the Fig. 1. PandaX’s first result demonstrates that China has become a competitive player in the search for DM, a Science News article commented. ‘It is very exciting to see that our detector has such a capability’, said Jianglai Liu, who led the data analysis and also contributed significantly to the detector construction. Indeed, the PandaX collaboration has since collected more than 75 days of data, which will have five times better detection sensitivity. The PandaX experiment is also upgrading its detector mass to 500 kg, and will commence operations in 2015. Meanwhile, XENON1T, a similar experiment but with a 1.5-ton detector mass, developed by a US-Europe collaboration

Neutrino and dark matter physics with sub-keV germanium detectors

Germanium detectors with sub-keV sensitivities open a window to study neutrino physics to search for light weakly interacting massive particle (WIMP) dark matter. We summarize the recent results on spin-independent couplings of light WIMPs from the TEXONO experiment at the Kuo-Sheng Reactor Neutrino Laboratory. Highlights of the physics motivation, our R&D programme, as well as the status and plans are presented.

Low-mass right-handed sneutrino dark matter: SuperCDMS and LUX constraints and the Galactic Centre gamma-ray excess

Recent results from direct and indirect searches for dark matter (DM) have motivated the study of particle physics models that can provide weakly interacting massive particles (WIMPs) in the mass range 1–50 GeV. Viable candidates for light WIMP DM must fulfil stringent constraints. On the one hand, the observation at the LHC of a Higgs boson with Standard Model properties set an upper bound on the coupling of light DM particles to the Higgs, thereby making it difficult to reproduce the correct relic abundance. On the other hand, the recent results from direct searches in the CDMSlite, SuperCDMS and LUX experiments have set upper constraints on the DM scattering cross section. In this paper, we investigate the viability of light right-handed sneutrino DM in the Next-to-Minimal Supersymmetric Model (NMSSM) in the light of these constraints. To this aim, we have carried out a scan in the NMSSM parameter space, imposing experimental bounds on the Higgs sector and low-energy observables, such as the muon anomalous magnetic moment and branching ratios of rare decays. We demonstrate that the enlarged Higgs sector of the NMSSM, together with the flexibility provided by the RH sneutrino parameters, make it possible to obtain viable RH sneutrino DM with a mass as light as 2 GeV. We have also considered the upper bounds on the annihilation cross section from Fermi LAT data on dwarf spheroidal galaxies, and extracted specific examples with mass in the range 8–50 GeV that could account for the apparent low-energy excess in the gamma-ray emission at the Galactic Centre. Then, we have computed the theoretical predictions for the elastic scattering cross-section of RH sneutrinos. Finally, after imposing the recent bounds from SuperCDMS and LUX, we have found a wide area of the parameter space that could be probed by future low-threshold direct detection experiments.

Study of light detection and sensitivity for a ton-scale liquid xenon dark matter detector

Ton-scale liquid xenon detectors operated in two-phase mode are proposed and being constructed recently to explore the favored parameter space for the Weakly Interacting Massive Particles (WIMPs) dark matter. To achieve a better light collection efficiency while limiting the number of electronics channels compared to the previous generation detectors, large-size photo-multiplier tubes (PMTs) such as the 3-inch-diameter R11410 from Hamamatsu are suggested to replace the 1-inch-square R8520 PMTs. In a two-phase xenon dark matter detector, two PMT arrays on the top and bottom are usually used. In this study, we compare the performance of two different ton-scale liquid xenon detector configurations with the same number of either R11410 (config.1) or R8520 (config.2) for the top PMT array, while both using R11410 PMTs for the bottom array. The self-shielding of liquid xenon suppresses the background from the PMTs and the dominant background is from the pp solar neutrinos in the central fiducial volume. The light collection efficiency for the primary scintillation light is largely affected by the xenon purity and the reflectivity of the reflectors. In the optimistic situation with a 10 m light absorption length and a 95% reflectivity, the light collection efficiency is 43%(34%) for config.1(config.2). In the conservative situation with a 2.5 m light absorption length and a 85% reflectivity, the value is only 18%(13%) for config.1(config.2). The difference between the two configurations is due to the larger PMT coverage on the top for config.1. The slightly different position resolutions for the two configurations have a negligible effect on the sensitivity. Based on the above considerations, we estimate the sensitivity reach of the two detector configurations. Both configurations can reach a sensitivity of 2 ∼ 3 × 10−47cm2 for spin-independent WIMP-nucleon cross section for 100 GeV/c2 WIMPs after two live-years of operation. The one with R8520 PMTs for the top PMT array is more cost-effective, while the one with R11410 PMTs on the top has a factor of two better sensitivity for light WIMPs at 10 GeV/c2.

Equivalent neutrinos, light WIMPs, and the chimera of dark radiation

According to conventional wisdom, in the standard model (SM) of particle physics and cosmology the ``effective number of neutrinos'' measured in the late Universe is ${N}_{\mathrm{eff}}=3$ (more precisely, 3.046). For extensions of the standard model allowing for the presence of $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}$ ``equivalent neutrinos'' (or ``dark radiation''), it is generally the case that ${N}_{\mathrm{eff}}>3$. These canonical results are reconsidered, demonstrating that a measurement of ${N}_{\mathrm{eff}}>3$ can be consistent with $\ensuremath{\Delta}{N}_{\ensuremath{\nu}}=0$ (``dark radiation without dark radiation''). Conversely, a measurement consistent with ${N}_{\mathrm{eff}}=3$ is not inconsistent with the presence of dark radiation ($\ensuremath{\Delta}{N}_{\ensuremath{\nu}}>0$). In particular, if there is a light weakly interacting massive particle (WIMP) that annihilates to photons after the SM neutrinos have decoupled, the photons are heated beyond their usual heating from ${e}^{\ifmmode\pm\else\textpm\fi{}}$ annihilation, reducing the late time ratio of neutrino and photon temperatures (and number densities), leading to ${N}_{\mathrm{eff}}<3$. This opens the window for one or more equivalent neutrinos, including ``sterile neutrinos,'' to be consistent with ${N}_{\mathrm{eff}}=3$. By reducing the neutrino number density in the present Universe, this also allows for more massive neutrinos, relaxing the current constraints on the sum of the neutrino masses. In contrast, if the light WIMP couples only to the SM neutrinos and not to the photons and ${e}^{\ifmmode\pm\else\textpm\fi{}}$ pairs, its late time annihilation heats the neutrinos but not the photons, resulting in ${N}_{\mathrm{eff}}>3$ even in the absence of equivalent neutrinos or dark radiation. A measurement of ${N}_{\mathrm{eff}}>3$ is no guarantee of the presence of equivalent neutrinos or dark radiation. In the presence of a light WIMP and/or equivalent neutrinos, there are degeneracies among the light WIMP mass and its nature (fermion or boson, as well as its couplings to neutrinos and photons), the number and nature (fermion or boson) of the equivalent neutrinos, and their decoupling temperature (the strength of their interactions with the SM particles). As the analysis here reveals, there's more to a measurement of ${N}_{\mathrm{eff}}$ than meets the eye.

Precise relic WIMP abundance and its impact on searches for dark matter annihilation

If dark matter (DM) is a weakly interacting massive particle (WIMP) that is a thermal relic of the early Universe, then its total self-annihilation cross section is revealed by its present-day mass density. This result for a generic WIMP is usually stated as $⟨\ensuremath{\sigma}v⟩\ensuremath{\approx}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}26}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, with unspecified uncertainty, and taken to be independent of WIMP mass. Recent searches for annihilation products of DM annihilation have just reached the sensitivity to exclude this canonical cross section for 100% branching ratio to certain final states and small WIMP masses. The ultimate goal is to probe all kinematically allowed final states as a function of mass and, if all states are adequately excluded, set a lower limit to the WIMP mass. Probing the low-mass region is further motivated due to recent hints for a light WIMP in direct and indirect searches. We revisit the thermal relic abundance calculation for a generic WIMP and show that the required cross section can be calculated precisely. It varies significantly with mass at masses below 10 GeV, reaching a maximum of $5.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}26}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ at $m\ensuremath{\approx}0.3\text{ }\text{ }\mathrm{GeV}$, and is $2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}26}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ with feeble mass dependence for masses above 10 GeV. These results, which differ significantly from the canonical value and have not been taken into account in searches for annihilation products from generic WIMPs, have a noticeable impact on the interpretation of present limits from Fermi-LAT and $\mathrm{WMAP}+\mathrm{ACT}$.

Daily modulation due to channeling in direct dark matter crystalline detectors

The channeling of the ion recoiling after a collision with a weakly interacting massive particle (WIMP) in direct dark matter crystalline detectors produces a larger scintillation or ionization signal than otherwise expected. Channeling is a directional effect, which depends on the velocity distribution of WIMPs in the dark halo of our Galaxy and could lead to a daily modulation of the signal. Here we compute upper bounds to the expected amplitude of daily modulation due to channeling using channeling fractions that we obtained with analytic models in prior work. After developing the general formalism, we examine the possibility of finding a daily modulation due to channeling in the data already collected by the DAMA/NaI and DAMA/LIBRA experiments. We find that even the largest daily modulation amplitudes (of the order of 10% in some instances) would not be observable for WIMPs in the standard halo in the 13 years of data taken by the DAMA Collaboration. For these to be observable, the DAMA total rate should be $1/40$ of what it is or the total DAMA exposure should be 40 times larger. The daily modulation due to channeling will be difficult to measure in future experiments. We find it could be observed for light WIMPs in solid Ne, assuming no background.

Constraints on light WIMP candidates from the isotropic diffuse gamma-ray emission

Motivated by the measurements reported by direct detection experiments, most notably DAMA, CDMS-II, CoGeNT and Xenon10/100, we study further the constraints that might be set on some light dark matter candidates, MDM ∼ few GeV, using the Fermi-LAT data on the isotropic gamma-ray diffuse emission. In particular, we consider a Dirac fermion singlet interacting through a new Z′ gauge boson, and a scalar singlet S interacting through the Higgs portal. Both candidates are WIMP (Weakly Interacting Massive Particles), i.e. they have an annihilation cross-section in the pbarn range. Also they may both have a spin-independent elastic cross section on nucleons in the range required by direct detection experiments. Although being generic WIMP candidates, because they have different interactions with Standard Model particles, their phenomenology regarding the isotropic diffuse gamma-ray emission is quite distinct. In the case of the scalar singlet, the one-to-one correspondence between its annihilation cross-section and its spin-independent elastic scattering cross-section permits to express the constraints from the Fermi-LAT data in the direct detection exclusion plot, σn0−MDM. Depending on the astrophysics, we argue that it is possible to exclude the singlet scalar dark matter candidate at 95% confidence level. The constraints on the Dirac singlet interacting through a Z′ are comparatively weaker.

Light WIMPs in the Sun: Constraints from helioseismology

We calculate solar models including dark matter (DM) weakly-interacting massive particles (WIMPs) of mass 5-50 GeV and test these models against helioseismic constraints on sound speed, convection zone depth, convection zone helium abundance, and small separations of low-degree p-modes. Our main conclusion is that both direct detection experiments and particle accelerators may be complemented by using the Sun as a probe for WIMP DM particles in the 5-50 GeV mass range. The DM most sensitive to this probe has suppressed annihilations and a large spin-dependent elastic scattering cross section. For the WIMP cross-section parameters explored here, the lightest WIMP masses <10 GeV are ruled out by constraints on core sound speed and low-degree frequency spacings. For WIMP masses 30-50 GeV, the changes to the solar structure are confined to the inner 4% of the solar radius and so do not significantly affect the solar p-modes. Future helioseismology observations, most notably involving g-modes, and future solar neutrino experiments may be able to constrain the allowable DM parameter space in a mass range that is of current interest for direct detection.

First Dark Matter Results from the XENON100 Experiment

The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso in Italy, is designed to search for dark matter weakly interacting massive particles (WIMPs) scattering off 62 kg of liquid xenon in an ultralow background dual-phase time projection chamber. In this Letter, we present first dark matter results from the analysis of 11.17 live days of nonblind data, acquired in October and November 2009. In the selected fiducial target of 40 kg, and within the predefined signal region, we observe no events and hence exclude spin-independent WIMP-nucleon elastic scattering cross sections above 3.4 × 10⁻⁴⁴ cm² for 55 GeV/c² WIMPs at 90% confidence level. Below 20 GeV/c², this result constrains the interpretation of the CoGeNT and DAMA signals as being due to spin-independent, elastic, light mass WIMP interactions.

Using the energy spectrum measured by DAMA/LIBRA to probe light dark matter

A weakly interacting massive particle (WIMP) weighing only a few GeV has been invoked as an explanation for the signal from the DAMA/LIBRA experiment. We show that the data from DAMA/LIBRA are now powerful enough to strongly constrain the properties of any putative WIMP. Accounting for the detailed recoil spectrum, a light WIMP with a Maxwellian velocity distribution and a spin-independent interaction cannot account for the data. Even neglecting the spectrum, significant parameter space is excluded by a limit that can be derived from the DAMA unmodulated signal at low energies. Appreciable modification to the astrophysics or particle physics can open light mass windows.