WIMP Annihilation Research Articles

Highlights from Super-Kamiokande

Recent results from Super-Kamiokande experiment are reviewed in this paper; Neutrino mass hierarchy and CP violation in the lepton sector are investigated via νμ → νe oscillation of the atmospheric neutrinos. The event rate, correlation with solar activity, energy spectrum of the solar neutrinos are measured via electron elastic scattering interactions. Neutrino emission from the WIMP annihilation at the center of the Sun are searched in the GeV energy regions. New project, SK-Gd project, to enhance anti-neutrino identification capability, has been approved inside the collaboration group.

Ultimate target for dark matter searches

The combination of S-matrix unitarity and the dynamics of thermal freeze-out for massive relic particles (denoted here simply by WIMPs) implies a lower limit on the density of such particles, that provide a (potentially sub-dominant) contribution to dark matter. This then translates to lower limits to the signal rates for a variety of techniques for direct and indirect detection of dark matter. For illustration, we focus on models where annihilation is s-wave dominated. We derive lower limits to the flux of gamma-rays from WIMP annihilation at the Galactic center; direct detection of WIMPs; energetic neutrinos from WIMP annihilation in the Sun; and the effects of WIMPs on the angular power spectrum and frequency spectrum of the cosmic microwave background radiation. The results suggest that a variety of dark-matter-search techniques may provide interesting avenues to seek new physics, even if WIMPs do not constitute all the dark matter. While the limits are quantitatively some distance from the reach of current measurements, they may be interesting for long-range planning exercises.

SUSY implications from WIMP annihilation into scalars at the Galactic Center

An excess in gamma-rays emanating from the galactic centre has recently been observed in the Fermi-LAT data. This signal can be interpreted as resulting from WIMP annihilation, with the spectrum well-fit by dark matter annihilating dominantly into either bottom-quark or Higgs pairs. Supersymmetric models provide a well-motivated framework to study the implications of this signal in these channels. With a neutralino dark matter candidate, the gamma-ray excess cannot be easily accommodated in the minimal supersymmetric model, which in any case requires tuning below the percent level to explain the observed Higgs mass. Instead we are naturally led to consider the next-to-minimal model with a singlet superfield. This not only allows for the annihilation channel into bottom-quark pairs to be implemented, but also provides new possibilities for annihilation into Higgs-pseudoscalar pairs. We show that the fit to the gamma-ray excess for the Higgs-pseudoscalar channel can be just as good as for annihilation into bottom-quark pairs. Moreover, in the parameter range of interest, the next-to-minimal supersymmetric model solves the mu-problem and can explain the 125 GeV Higgs mass with improved naturalness. We also consider an extension by adding a right-handed neutrino superfield with the right-handed sneutrino acting as a dark matter candidate. Interestingly, this allows for the annihilation into pseudoscalar pairs which also provide a good fit to the gamma-ray excess. Furthermore, in the case of a neutralino LSP, the late decay of a sneutrino NLSP can non-thermally produce the observed relic abundance. Finally, the WIMP annihilation into scalar pairs allows for the possibility of detecting the Higgs or pseudoscalar decay into two photons, providing a smoking-gun signal of the model.

The cosmic cocktail: three parts dark matter

Preface ix 1 The Golden Era of Particle Cosmology, or How I Joined the Chicago Mafia 1 New York City Fermilab: The Atom Smasher in the Prairie Chicago: A New Zeitgeist in Cosmology Dunkle Materie: The Dark Enigma WIMPs at Harvard 2 How Do Cosmologists Know Dark Matter Exists? The Beginning of the Dark Matter Story 9 What Do Galaxies Look Like? Observational Evidence for Dark Matter Formation of Galaxies and Clusters Dark Matter Dominates 3 The Big Picture of the Universe: Einstein and the Big Bang 35 Geometry of the Universe Cosmic Microwave Background Outer Space and the Queen of Sweden Pie Picture of the Universe 4 Big Bang Nucleosynthesis Proves That Atomic Matter Constitutes Only 5% of the Universe 67 A Story about Big Bang Nucleosynthesis Particles in the Early Universe: A Primordial Soup Origins of the Elements Atoms Make Up Only 5% of the Universe 5 What Is Dark Matter? 83 Rocks or Dust Matter and Antimatter Neutrinos MACHOs Black Holes The Particle Zoo The WIMP Miracle WIMPs in the Human Body and a Tennis Match 6 The Discovery of the Higgs Boson 108 Atom Smashers: The Large Hadron Collider CERN Discovery of the Higgs 7 The Experimental Hunt for Dark Matter Particles 123 The Three Prongs of the Hunt for Dark Matter Dark Matter at the Atom Smasher at CERN: Missing Energy plus Jets What Has CERN Done for Society? Will the LHC Bring Doomsday? Direct Detection: Abandoned Mines, Alpine Tunnels, and Nightclubs in Jerusalem Indirect Detection: Annihilations in Space and at the South Pole 8 Claims of Detection: Are They Real? 147 Direct Detection in Underground Laboratories Indirect Detection of WIMP Annihilation: Positrons, Neutrinos, and Gamma Rays The Future of Dark Matter Experiments 9 Dark Energy and the Fate of the Universe 183 Rounding Out the Universe: Type IA Supernovae and Dark Energy The Future of the Universe Epicycles Epilogue Afterword: Dark Stars 215 Acknowledgments 219 Notes 221 Suggestions for Further Reading 233 Index 235

Bounds on dark matter properties from radio observations of Ursa Major II using the Green Bank Telescope

Radio observations of the Ursa Major II dwarf spheroidal galaxy obtained using the Green Bank Telescope are used to place bounds on WIMP dark matter properties. Dark matter annihilation releases energy in the form of charged particles which emit synchrotron radiation in the magnetic field of the dwarf galaxy. We compute the expected synchrotron radiation intensity from WIMP annihilation to various primary channels. The predicted synchrotron radiation is sensitive to the distribution of dark matter in the halo, the diffusion coefficient D_0, the magnetic field strength B, the particle mass m_\chi, the annihilation rate <\sigma v>, and the annihilation channel. Limits on <\sigma v>, m_\chi, B, and D_0 are obtained for the e^+ e^-, \mu^+ \mu^-, \tau^+ \tau^-, and b \bar b channels. Constraints on these parameters are sensitive to uncertainties in the measurement of the dark matter density profile. For the best fit halo parameters derived from stellar kinematics, we exclude 10 GeV WIMPs annihilating directly to e^+ e^- at the thermal rate <\sigma v> = 2.18 x 10^{-26} cm^3/s at the 2\sigma level, for B > 0.6 microGauss (1.6 microGauss) and D_0 = 0.1 (1.0) x the Milky Way diffusion value.

TeV observations of the Galactic center and starburst galaxies

AbstractThe vicinity of the Galactic center harbors many potential accelerators of cosmic rays (CR) that could shine in very-high-energy (VHE) γ-rays, such as pulsar wind nebulae, supernova remnants, binary systems and the central black hole Sgr A*, and is characterized by high gas density, large magnetic fields and a high rate of starburst activity similar to that observed in the core of starburst galaxies. In addition to these astrophysical sources, annihilation of putative WIMPs concentrated in the gravitational well could lead to significant high-energy emission at the Galactic center. The Galactic center region has been observed by atmospheric Cherenkov telescopes, and in particular by the H. E. S. S. array in Namibia for the last ten years above 150 GeV. This large data set, comprising more than 200 hours of observations, led to the discovery of a point-like source spatially compatible with the supermassive black hole Sgr A*, and to an extended diffuse emission, correlated with molecular clouds and attributed to the interaction of cosmic rays with the interstellar medium. Over the same time period, two starburst galaxies, namely M 82 and NGC 253, were detected at TeV energies after very deep exposures. Results from these ten years of observations of the Galactic center region and starburst galaxies at TeV energies are presented, and implications for the various very-high-energy emission mechanisms are discussed.

Radio constraints on Galactic WIMP dark matter

Synchrotron emission from electron cosmic ray populations can be used to study both cosmic rays physics and WIMP dark matter imprints on radio skymaps. We used available radio data – from MHz to GHz – to analyze the contribution from galactic WIMP annihilations and impose constraints on WIMP observables: annihilation cross-section, channel and mass. Depending on the annihilation channel we obtain as competitive bounds as those obtained in FERMI-LAT gamma ray analyses.

W-WIMP annihilation as a source of the Fermi bubbles

The Fermi Gamma-ray Space Telescope discovered two \gamma-ray emitting bubble-shaped structures that extend nearly symmetrically on either side of our Galaxy and appear morphologically connected to the Galactic center. The origin of the emission is still not entirely clear. It was recently shown that the spectral shape of the emission from the Fermi bubbles is well described by an approximately 50 GeV dark matter particle annihilating to b \bar b, with a normalization corresponding to a velocity average annihilation cross section of < \sigma_b v > ~ 8 \times 10^{-27} cm^3/s. We study the minimal hidden sector recently introduced by Weinberg and examine to what extent its weakly-interacting massive particles (W-WIMPs) are capable of accommodating both the desired effective annihilation rate into quarks and the observed relic density.

WIMP-induced gamma ray spectrum of active Galactic nuclei

As direct and indirect dark matter detection experiments continue to place stringent constraints on WIMP masses and couplings, it becomes imperative to expand the scope of the search for particle dark matter by looking in new and exotic places. One such place may be the core of active Galactic nuclei (AGN) where the density of dark matter is expected to be extremely high. Recently, several groups have explored the possibility of observing signals of dark matter from its interactions with the high-energy jets emanating from these galaxies. In this work, we build upon these analyses by including the other components of the WIMP-induced gamma ray spectrum of active Galactic nuclei; namely, (i) the continuum from WIMP annihilation into light standard model states which subsequently radiate and/or decay into photons and (ii) the direct (loop-induced) decay into photons. We work in the context of models of universal extra dimensions (in particular, a model with two extra dimensions) and compute all three components of the gamma ray spectrum and compare with current data. We find that the model with two extra dimensions exhibits several interesting features which may be observable with the Fermi gamma ray telescope. We also show that, in conjunction with other measurements, the gamma ray spectrum from AGN can be an invaluable tool for restricting WIMP parameter space.

Two-photon annihilation of singlet cold dark matter due to noncommutative space-time

Detecting the cosmic rays, in particular gamma-ray, coming from the dark matter annihilation or decay is an indirect way to survey the nature of the dark matter. In the commutative space-time, the annihilation of the dark matter candidates (WIMPs) to photons proceeds through loop corrections. However, it is possible for WIMPs as well as the other standard model singlet particles to couple with photons directly in the noncommutative space-time. In this paper, we study two-photon annihilation of singlet WIMPs in the noncommutative space-time. If the noncommutative interactions are relevant to the relic abundance, one can exclude some dark matter masses using Fermi-Lat data.

Neutrino signals from electroweak bremsstrahlung in solar WIMP annihilation

Bremsstrahlung of W and Z gauge bosons, or photons, can be an important dark matter annihilation channel. In many popular models in which the annihilation to a pair of light fermions is helicity suppressed, these bremsstrahlung processes can lift the suppression and thus become the dominant annihilation channels. The resulting dark matter annihilation products contain a large, energetic, neutrino component. We consider solar WIMP annihilation in the case where electroweak bremsstrahlung dominates, and calculate the resulting neutrino spectra. The flux consists of primary neutrinos produced in processes such as χχ→ν̄νZ and χχ→ν̄ℓW, and secondary neutrinos produced via the decays of gauge bosons and charged leptons. After dealing with the neutrino propagation and flavour evolution in the Sun, we consider the prospects for detection in neutrino experiments on Earth. We compare our signal with that for annihilation to W+W−, and show that, for a given annihilation rate, the bremsstrahlung annihilation channel produces a larger signal by a factor of a few.

Neutrinos from WIMP annihilation in the Sun: Implications of a self-consistent model of the Milky Way’s dark matter halo

Upper limits on the spin-independent (SI) as well as spin-dependent (SD) elastic scattering cross sections of WIMPs with protons, imposed by the Super-Kamiokande (S-K) upper limit on the neutrino flux from WIMP annihilation in the Sun, and their compatibility with the "DAMA-compatible" regions of the WIMP parameter space within which the annual modulation signal observed by the DAMA/LIBRA experiment is compatible with the null results of other direct detection experiments, are studied within the frame work of a self-consistent model of the finite-size dark matter (DM) halo of the Galaxy, the parameters of which are determined by a fit to the rotation curve data of the Galaxy. We find that the S-K implied upper limits on the WIMP-proton elastic cross section as a function of WIMP mass impose stringent restrictions on the branching fractions of the various WIMP annihilation channels. For SI interaction, while the S-K upper limits are consistent with the DAMA-compatible region of the WIMP parameter space if the WIMPs annihilate dominantly to $\bbarb$\ and/or $\cbarc$, portions of the DAMA-compatible region can be excluded if WIMP annihilations to $\tautau$ and $\nu\anu$ occur at larger than ~ 10% and 0.1% levels, respectively. For SD interaction, the restrictions on the possible annihilation channels are much more stringent, essentially ruling out the DAMA-compatible region of the WIMP parameter space if the relatively low-mass ($\sim$ 2 -- 20 GeV) WIMPs under consideration annihilate predominantly to any mixture of $\bbarb$, \ $\cbarc$, \ $\tautau$, \ and $\nu\anu$ final states.

Gamma-ray constraints on the first stars from annihilation of light WIMPs

We calculate the limits on the fraction of viable dark matter minihalos in the early universe to host Population III.1 stars, surviving today as dark matter spikes in our Milky Way halo. Motivated by potential hints of light dark matter from the DAMA and CoGeNT direct dark matter searches, we consider thermal relic WIMP dark matter with masses of 5, 10, and 20 GeV, and annihilation to ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$, and $q\overline{q}$. From this brief study we conclude that, if dark matter is light, either the typical black hole size is $\ensuremath{\lesssim}100{M}_{\ensuremath{\bigodot}}$ (i.e. there is no significant Dark Star phase), and/or dark matter annihilates primarily to ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ or other final states that result in low gamma-ray luminosity, and/or that an extremely small fraction of minihalos in the early universe that seem suitable to host the formation of the first stars actually did.

Possibility of a Dark Matter Interpretation for the Excess in Isotropic Radio Emission Reported by ARCADE

The ARCADE 2 Collaboration has recently measured an isotropic radio emission which is significantly brighter than the expected contributions from known extra-galactic sources. The simplest explanation of such excess involves a "new" population of unresolved sources which become the most numerous at very low (observationally unreached) brightness. We investigate this scenario in terms of synchrotron radiation induced by weakly interacting massive particle (WIMP) annihilations or decays in extra-galactic halos. Intriguingly, for light-mass WIMPs with a thermal annihilation cross section, the level of expected radio emission matches the ARCADE observations.

Dark matter search with the ANTARES neutrino telescope

The ANTARES neutrino telescope was completed in 2008 with the installation of its 12th line. Its scientific scope is very broad, but the two main goals are the observation of astrophysical sources and the indirect detection of dark matter. The latter is possible through neutrinos produced after the annihilation of WIMPs, which would accumulate in sources like the Sun, the Earth or the Galactic Centre. The neutralino, which arises in Supersymmetry models, is one of the most popular WIMP candidates. KK particles, which appear in Universal Extra Dimension models, are another one. Though in most models these annihilations would not directly produce neutrinos, they are expected from the decay of secondary particles. An important advantage of neutrino telescopes with respect to other indirect searches (like gamma rays or cosmic rays) is that a potential signal (for instance from the Sun) would be very clean, since no other astrophysical explanations could mimic it (like pulsars for the case of the positron excess seen by PAMELA). Moreover, the Galactic Centre is accessible for ANTARES, being in the Northern Hemisphere. In this talk I will present the results of the ANTARES telescope for dark matter searches, which include neutralino and KK particles.

Neutrinos from WIMP annihilations in the Sun including neutrino oscillations

The prospects to detect neutrinos from the Sun arising from dark matter annihilations in the core of the Sun are reviewed. Emphasis is placed on new work investigating the effects of neutrino oscillations on the expected neutrino fluxes.

AN INDIRECT SEARCH FOR WEAKLY INTERACTING MASSIVE PARTICLES IN THE SUN USING 3109.6 DAYS OF UPWARD-GOING MUONS IN SUPER-KAMIOKANDE

We present the result of an indirect search for high energy neutrinos from WIMP annihilation in the Sun using upward-going muon (upmu) events at Super-Kamiokande. Datasets from SKI-SKIII (3109.6 days) were used for the analysis. We looked for an excess of neutrino signal from the Sun as compared with the expected atmospheric neutrino background in three upmu categories: stopping, non-showering, and showering. No significant excess was observed. The 90% C.L. upper limits of upward-going muon flux induced by WIMPs of 100 GeV/c$^2$ were 6.4$\times10^{-15}$ cm$^{-2}$ sec$^{-1}$ and 4.0$\times10^{-15}$ cm$^{-2}$ sec$^{-1}$ for the soft and hard annihilation channels, respectively. These limits correspond to upper limits of 4.5$\times10^{-39}$ cm$^{-2}$ and 2.7$\times10^{-40}$ cm$^{-2}$ for spin-dependent WIMP-nucleon scattering cross sections in the soft and hard annihilation channels, respectively.

Fitting formulae for photon spectra from WIMP annihilation

Annihilation of different dark matter (DM) candidates into Standard Model (SM) particles could be detected through their contribution to the gamma ray fluxes that are measured on the Earth. The magnitude of such contributions depends on the particular DM candidate, but certain imprints of produced photon spectra may be analyzed in a model-independent fashion. In this work we provide the fitting formulae for the photon spectra generated by WIMP annihilation into quarks, leptons and gauge bosons channels in a wide range of WIMP masses.

Relic abundance of asymmetric Dark Matter

We investigate the relic abundance of asymmetric Dark Matter particles that were in thermal equilibrium in the early universe. The standard analytic calculation of the symmetric Dark Matter is generalized to the asymmetric case. We calculate the asymmetry required to explain the observed Dark Matter relic abundance as a function of the annihilation cross section. We show that introducing an asymmetry always reduces the indirect detection signal from WIMP annihilation, although it has a larger annihilation cross section than symmetric Dark Matter. This opens new possibilities for the construction of realistic models of MeV Dark Matter.

Two-singlet model for light cold dark matter

We extend the standard model by adding two gauge-singlet ${\mathbb{Z}}_{2}$-symmetric scalar fields that interact with visible matter only through the Higgs particle. One is a stable dark matter WIMP, and the other one undergoes a spontaneous breaking of the symmetry that opens new channels for the dark matter annihilation, hence lowering the mass of the WIMP. We study the effects of the observed dark matter relic abundance on the WIMP annihilation cross section and find that in most regions of the parameters' space, light dark matter is viable. We also compare the elastic-scattering cross section of our dark matter candidate off a nucleus with existing (CDMSII and XENON100) and projected (SuperCDMS and XENON1T) experimental exclusion bounds. We find that most of the allowed mass range for light dark matter will be probed by the projected sensitivity of the XENON1T experiment.