Dark Matter Pair Annihilation Research Articles

Higgs portal vector dark matter for GeV scale γ-ray excess from galactic center

We show that the GeV scale γ-ray excess from the direction of the Galactic Center can be naturally explained by the pair annihilation of Abelian vector dark matter (VDM) into a pair of dark Higgs bosons (VV→ ϕ ϕ), followed by the subsequent decay of ϕ into bb̄ or τ τ̄ . All the processes are described by a renormalizable VDM model with the Higgs portal, which is naturally flavor-dependent. Some parameter space of this scenario can be tested at the near future direct dark matter search experiments such as LUX and XENON1T.

Self-interacting scalar dark matter with local Z3 symmetry

We construct a self-interacting scalar dark matter (DM) model with local discrete Z3 symmetry that stabilizes a weak scale scalar dark matter X. The model assumes a hidden sector with a local U(1)X dark gauge symmetry, which is broken spontaneously into Z3 subgroup by nonzero VEV of dark Higgs field ϕX (⟨ϕX⟩≠0). Compared with global Z3 DM models, the local Z3 model has two new extra fields: a dark gauge field Z′ and a dark Higgs field ϕ (a remnant of the U(1)X breaking). After imposing various constraints including the upper bounds on the spin-independent direct detection cross section and thermal relic density, we find that the scalar DM with mass less than 125 GeV is allowed in the local Z3 model, in contrary to the global Z3 model. This is due to new channels in the DM pair annihilations open into Z′ and ϕ in the local Z3 model. Most parts of the newly open DM mass region can be probed by XENON1T and other similar future experiments. Also if ϕ is light enough (a few MeV ≲mϕ≲ O(100) MeV), it can generate a right size of DM self-interaction and explain the astrophysical small scale structure anomalies. This would lead to exotic decays of Higgs boson into a pair of dark Higgs bosons, which could be tested at LHC and ILC.

Antihelium from dark matter

Cosmic-ray antinuclei provide a promising discovery channel for the indirect detection of particle dark matter. Hadron showers produced by the pair annihilation or decay of Galactic dark matter generate antinucleons which can in turn form light antinuclei. Previous studies have only focused on the spectrum and flux of low energy antideuterons which, although very rarely, are occasionally also produced by cosmic-ray spallation. Heavier elements ($A\ensuremath{\ge}3$) have instead entirely negligible astrophysical background and a primary yield from dark matter which could be detectable by future experiments. Using a Monte Carlo event generator and an event-by-event phase space analysis, we compute, for the first time, the production spectrum of $^{3}\overline{\mathrm{He}}$ and $^{3}\overline{\mathrm{H}}$ for dark matter annihilating or decaying to $b\overline{b}$ and ${W}^{+}{W}^{\ensuremath{-}}$ final states. We then employ a semianalytic model of interstellar and heliospheric propagation to calculate the $^{3}\overline{\mathrm{He}}$ flux as well as to provide tools to relate the antihelium spectrum corresponding to an arbitrary antideuteron spectrum. Finally, we discuss prospects for current and future experiments, including GAPS and AMS-02.

Constraining dark matter annihilation with the isotropicγ-ray background: Updated limits and future potential

The nature of the Isotropic $\gamma$-ray Background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi $\gamma$-ray space Telescope ({\it Fermi}) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars, star-forming galaxies or galactic milli-second pulsars. A recent prediction of the diffuse $\gamma$-ray emission from Active Galactic Nuclei (AGN) with a large viewing angle with respect to the line-of-sight (l.o.s.) has demonstrated that this faint but numerous population is also expected to contribute significantly to the total IGRB intensity. A more exotic contribution to the IGRB invokes the pair annihilation of dark matter (DM) weakly interacting massive particles (WIMPs) into $\gamma$-rays. In this work, we evaluate the room left for galactic DM at high latitudes ($>10^\circ$) by including photons from both prompt emission and inverse Compton scattering, emphasizing the impact of the newly discovered contribution from misaligned AGN (MAGN) for such an analysis. Summing up all significant galactic and extragalactic components of the IGRB, we find that an improved understanding of the associated astrophysical uncertainties is still mandatory to put stringent bounds on thermally produced DM. On the other hand, we also demonstrate that the IGRB has the potential to be one of the most competitive {\it future} ways to test the DM WIMP hypothesis, once the present uncertainties are even slightly reduced. In fact, if MAGN contribute even at 90% of the maximal level consistent with our current understanding, thermally produced WIMPs would be severely constrained as DM candidates for masses up to several TeV.

Erratum: Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos I. General framework and S-wave annihilation

We compute analytically the tree-level annihilation rates of a collection of non-relativistic neutralino and chargino two-particle states in the general MSSM, including the previously unknown off-diagonal rates. The results are prerequisites to the calculation of the Sommerfeld enhancement in the MSSM, which will be presented in subsequent work. They can also be used to obtain concise analytic expressions for MSSM dark matter pair annihilation in the present Universe for a large number of exclusive two-particle final states.

Electroweak bremsstrahlung in binolike dark matter annihilations

We investigate the effects of electroweak bremsstrahlung on bino-like neutralino dark matter pair annihilations in the minimal supersymmetric standard model (MSSM). We calculate the nonrelativistic pair annihilation cross sections via $W$-strahlung from leptonic final states, $\chi\chi$ $\to$ $W\ell\bar{\nu}$, and compare them with the contributions of the relevant two-body final states. We explore the case that sleptons lie below the TeV scale, while squarks are extremely heavy. It is found that the electroweak bremsstrahlung can give a dominant contribution to the cross section for some parameter regions which include slepton coannihilation regions with the observed relic abundance. We also evaluate the neutrino spectra at injection in the Sun. It is shown that energetic neutrinos via weak bremsstrahlung processes can be dominant over contributions of the two-body final states.

Search for dark matter in compact hydrogen clouds

Abstract The recently published Galactic Arecibo L-Band Feed Array-H i Compact Cloud Catalogue lists 20 neutral hydrogen clouds that might pinpoint previously undiscovered high-latitude dwarf galaxies. Detection of an associated gamma-ray dark matter signal could provide a route to distinguish unambiguously between truly dark-matter-dominated systems that have accumulated neutral hydrogen but have not successfully ignited star formation and pure gaseous structures devoid of dark matter. We use 4.3 years of Fermi observations to derive gamma-ray flux upper limits in the 1–300 GeV energy range for the sample. Limits on gamma rays from pair annihilation of dark matter are also presented depending on the yet unknown astrophysical factors.

Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos I. General framework and S-wave annihilation

We compute analytically the tree-level annihilation rates of a collection of non- relativistic neutralino and chargino two-particle states in the general MSSM, including the previously unknown off-diagonal rates. The results are prerequisites to the calculation of the Sommerfeld enhancement in the MSSM, which will be presented in subsequent work. They can also be used to obtain concise analytic expressions for MSSM dark matter pair annihilation in the present Universe for a large number of exclusive two-particle final states.

PAMELA and FERMI limits on the neutralino-chargino mass degeneracy

Searches for Dark Matter (DM) particles with indirect detection techniques have reached important milestones with the precise measurements of the anti-proton (p̄) and gamma-ray spectra, notably by the PAMELA and FERMI-LAT experiments. While the γ-ray results have been used to test the thermal Dark Matter hypothesis and constrain the Dark Matter annihilation cross section into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA experiment remains relatively unexploited. Here we show that the latter can be used to set a constraint on the neutralino-chargino mass difference. To illustrate our point we use a Supersymmetric model in which the gauginos are light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP) is the neutralino. In this framework the W+W− production is expected to be significant, thus leading to large p̄ and γ-ray fluxes. After determining a generic limit on the Dark Matter pair annihilation cross section into W+W− from the p̄ data only, we show that one can constrain scenarios in which the neutralino-chargino mass difference is as large as ≃ 20 GeV for a mixed neutralino (and intermediate choices of the p̄ propagation scheme). This result is consistent with the limit obtained by using the FERMI-LAT data. As a result, we can safely rule out the pure wino neutralino hypothesis if it is lighter than 450 GeV and constitutes all the Dark Matter.

Evaluating the gamma-ray evidence for self-annihilating dark matter from the Virgo cluster

Based on three years of Fermi Large Area Telescope (LAT) gamma-ray data of the Virgo cluster, evidence for an extended emission associated with dark matter pair annihilation in the b b-bar channel has been reported by Han et al. [1]. After an in depth spatial and temporal analysis, we argue that the tentative evidence for a gamma-ray excess from the Virgo cluster is mainly due to the appearance of a population of previously unresolved gamma-ray point sources in the region of interest. These point sources are not part of the LAT second source catalogue (2FGL), but are found to be above the standard detection significance threshold when three or more years of LAT data is included.

A model-independent analysis of the Fermi Large Area Telescope gamma-ray data from the Milky Way dwarf galaxies and halo to constrain dark matter scenarios

We implemented a novel technique to perform the collective spectral analysis of sets of multiple gamma-ray point sources using the data collected by the Large Area Telescope onboard the Fermi satellite. The energy spectra of the sources are reconstructed starting from the photon counts and without assuming any spectral model for both the sources and the background. In case of faint sources, upper limits on their fluxes are evaluated with a Bayesian approach. This analysis technique is very useful when several sources with similar spectral features are studied, such as sources of gamma rays from annihilation of dark matter particles. We present the results obtained by applying this analysis to a sample of dwarf spheroidal galaxies and to the Milky Way dark matter halo. The analysis of dwarf spheroidal galaxies yields upper limits on the product of the dark matter pair annihilation cross section and the relative velocity of annihilating particles that are well below those predicted by the canonical thermal relic scenario in a mass range from a few GeV to a few tens of GeV for some annihilation channels.

Gamma-ray lines in the Fermi data: is it a bubble?

Recently, tentative evidence for an excess of gamma rays at energies around 130 GeV has been reported from analyses of data from the Fermi Large Area Telescope (LAT). The excess is potentially of great interest, as it could be associated with the pair-annihilation of Galactic dark matter and the subsequent production of monochromatic or internal bremsstrahlung gamma rays. The 130 GeV excess appears when an optimized selection of the target region of interest is employed, a procedure that depends upon the assumed dark matter density profile. For the profiles producing an appreciable signal, these target regions vastly overlap with the region corresponding to the so-called ``Fermi bubbles''. We argue that the tentative evidence for a line feature is likely due to hard photons in the Fermi bubbles regions, where the gamma-ray spectrum contains a spectral break in the energy range of interest (100–150 GeV). Although the origin of this broken power-law is unclear, it is probably related to standard astrophysical processes and not to dark matter annihilation. A broken power-law provides as good a fit as a line ``excess'', even within small energy windows, and a significantly better fit for large energy windows.

Dark matter after the BESS-Polar II experiment

The BESS-Polar collaboration has recently performed a precise measurement of the local antiproton flux which is consistent with a pure secondary production of antiprotons. We constrain a possible primary component originating from dark matter pair-annihilations. We derive limits on the annihilation cross section which are stronger than or comparable to those from the PAMELA satellite experiment for dark matter masses up to 200 GeV. Especially, we exclude thermal WIMPs with masses in the range 3--20 GeV if they annihilate dominantly into quark pairs unless their cross section is velocity suppressed.

Cosmic ray-dark matter scattering: a new signature of (asymmetric) dark matter in the gamma ray sky

We consider the process of scattering of Galactic cosmic-ray electrons and protons off of dark matter with the radiation of a final-state photon. This process provides a novel way to search for Galactic dark matter with gamma rays. We argue that for a generic weakly interacting massive particle, barring effects such as co-annihilation or a velocity-dependent cross section, the gamma-ray emission from cosmic-ray scattering off of dark matter is typically smaller than that from dark matter pair-annihilation. However, if dark matter particles cannot pair-annihilate, as is the case for example in asymmetric dark matter scenarios, cosmic-ray scattering with final state photon emission provides a unique window to detect a signal from dark matter with gamma rays. We estimate the expected flux level and its spectral features for a generic supersymmetric setup, and we also discuss dipolar and luminous dark matter. We show that in some cases the gamma-ray emission might be large enough to be detectable with the Fermi Large Area Telescope.

Morphology of the Galactic dark matter synchrotron emission with self-consistent cosmic-ray diffusion models

A generic prediction in the paradigm of weakly interacting dark matter is the production of relativistic particles from dark matter pair annihilation in regions of high dark matter density. Ultrarelativistic electrons and positrons produced in the center of the Galaxy by dark matter annihilation should produce a diffuse synchrotron emission. While the spectral shape of the synchrotron dark matter haze depends on the particle model (and secondarily on the Galactic magnetic fields), the morphology of the haze depends primarily on (1) the dark matter density distribution, (2) the Galactic magnetic field morphology, and (3) the diffusion model for high-energy cosmic-ray leptons. Interestingly, an unidentified excess of microwave radiation with characteristics similar to those predicted by dark matter models has been claimed to exist near the Galactic center region in the data reported by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, and is dubbed the ``WMAP haze.'' In this study, we carry out a self-consistent treatment of the variables enumerated above, enforcing constraints from the available data on cosmic rays, radio surveys, and diffuse gamma rays. We outline and make predictions for the general morphology and spectral features of a ``dark matter haze'' and we compare them to the WMAP haze data. We also characterize and study the spectrum and spatial distribution of the inverse-Compton emission resulting from the same population of energetic electrons and positrons. We point out that the spectrum and morphology of the radio emission at different frequencies are powerful diagnostics to test whether a Galactic synchrotron haze indeed originates from dark matter annihilation.

QCD radiative correction to pair annihilation of spin-1 bosonic dark matter

The next-to-leading order QCD corrections are calculated for the pair annihilation of spin-1 dark matter (DM) by dimensionally regularizing both ultraviolet and infrared singularities in the nonrelativistic (v<<1) limit. The complete O({alpha}{sub s}) correction is about 8% due to the massless gluon contribution. An extra 5% will be added if there is a new interaction from a massive gluon of approximately the same mass as the DM particle. The next-to-leading order QCD correction could result in a sizable shift to the DM mass constrained by relic density measurements.

Searching for Dark Matter with X‐Ray Observations of Local Dwarf Galaxies

A generic feature of weakly interacting massive particle (WIMP) dark matter models is the emission of photons over a broad energy band resulting from the stable yields of dark matter pair annihilation. Inverse Compton scattering off cosmic microwave background photons of energetic electrons and positrons produced in dark matter annihilation is expected to produce significant diffuse X-ray emission. Dwarf galaxies are ideal targets for this type of dark matter search technique, being nearby, dark matter dominated systems free of any astrophysical diffuse X-ray background. In this paper, we present the first systematic study of X-ray observations of local dwarf galaxies aimed at the search for WIMP dark matter. We outline the optimal energy and angular ranges for current telescopes and analyze the systematic uncertainties connected to electron/positron diffusion. We do not observe any significant X-ray excess, and we translate this null result into limits on the mass and pair annihilation cross section for particle dark matter. Our results indicate that X-ray observations of dwarf galaxies currently constrain dark matter models at the same level as or even more strongly than gamma-ray observations of the same systems, although at the expenses of introducing additional assumptions and related uncertainties in the modeling of diffusion and energy loss processes. The limits we find constrain portions of the supersymmetric parameter space, particularly if the effect of dark matter substructures is included. Finally, we comment on the role of future X-ray satellites (e.g., Constellation-X, XEUS) and on their complementarity with GLAST and other gamma-ray telescopes in the quest for particle dark matter.

The Dark Matter Annihilation Signal from Galactic Substructure: Predictions forGLAST

We present quantitative predictions for the detectability of individual Galactic dark matter subhalos in gamma-rays from dark matter pair annihilations in their centers. Our method is based on a hybrid approach, employing the highest resolution numerical simulations available (including the recently completed one billion particle Via Lactea II simulation) as well as analytical models for the extrapolation beyond the simulations' resolution limit. We include a self-consistent treatment of subhalo boost factors, motivated by our numerical results, and a realistic treatment of the expected backgrounds that individual subhalos must outshine. We show that for reasonable values of the dark matter particle physics parameters (M_X ~ 50 - 500 GeV and ~ 10^-26 - 10^-25 cm^3/s) GLAST may very well discover a few, even up to several dozen, such subhalos, at 5 sigma significance, and some at more than 20 sigma. We predict that the majority of luminous sources would be resolved with GLAST's expected angular resolution. For most observer locations the angular distribution of detectable subhalos is consistent with a uniform distribution across the sky. The brightest subhalos tend to be massive (median Vmax of 24 km/s) and therefore likely hosts of dwarf galaxies, but many subhalos with Vmax as low as 5 km/s are also visible. Typically detectable subhalos are 20 - 40 kpc from the observer, and only a small fraction are closer than 10 kpc. The total number of observable subhalos has not yet converged in our simulations, and we estimate that we may be missing up to 3/4 of all detectable subhalos.

Nonthermal x rays from the Ophiuchus galaxy cluster and dark matter annihilation

We investigate a scenario where the recently discovered nonthermal hard x-ray emission from the Ophiuchus cluster originates from inverse Compton scattering of energetic electrons and positrons produced in weakly interacting dark matter pair annihilations. We show that this scenario can account for both the x ray and the radio emission, provided the average magnetic field is of the order of $0.1\text{ }\text{ }\ensuremath{\mu}\mathrm{G}$. We demonstrate that Gamma-Ray Large Area Telescope (GLAST) will conclusively test the dark matter annihilation hypothesis. Depending on the particle dark matter model, GLAST might even detect the monochromatic line produced by dark matter pair annihilation into two photons.

Detecting dark matter WIMPs in the Draco dwarf: A multiwavelength perspective

We explore the possible signatures of dark matter pair annihilations in the nearby dwarf spheroidal galaxy Draco. After investigating the mass models for Draco in the light of available observational data, we carefully model the dark matter density profile, taking advantage of numerical simulations of hierarchical structure formation. We then analyze the gamma-ray and electron/positron yield expected for weakly interacting dark matter particle (WIMP) models, including an accurate treatment of the propagation of the charged particle species. We show that unlike in larger dark matter structures—such as galaxy clusters—spatial diffusion plays here an important role. While Draco would appear as a pointlike gamma-ray source, synchrotron emission from electrons and positrons produced by WIMP annihilations features a spatially extended structure. Depending upon the cosmic ray propagation setup and the size of the magnetic fields, the search for a diffuse radio emission from Draco can be a more sensitive indirect dark matter search probe than gamma rays. Finally, we show that available data are consistent with the presence of a black hole at the center of Draco: if this is indeed the case, very significant enhancements of the rates for gamma rays and other emissions related to dark matter annihilations are expected.