Annihilation Of Dark Matter Particles Research Articles

Search for dark matter in space

The detection of gamma-rays, antiprotons and positrons due to pair annihilation of dark matter particles in the Milky Way halo is a viable tecniques to search for supersymmetric dark matter candidates if there is the possibility to separate the signal from the backgroung generated by standard production mechanisms. Here we discuss the status of this indirect search and the prospective for the future experiments GLAST and PAMELA.

Hypernovae and light dark matter as possible Galactic positron sources

The electron–positron annihilation source in the Galactic center region has recently been observed with INTEGRAL/SPI, which shows that this 511 keV source is strong and its extension is consistent with the Galactic bulge geometry. The positron production rate, estimated to more than 10 43 per second, is very high and raises a challenging question about the nature of the Galactic positron source. Commonly considered astrophysical positron injectors, namely type Ia supernovae are rare events and fall short to explain the observed positron production rate. In this paper, we study the possibility of Galactic positron production by hypernovae events, exemplified by the recently observed SN2003dh/GRB030329, an asymmetric explosion of a Wolf-Rayet star associated with a γ-ray burst. In these kinds of events, the ejected material becomes quickly transparent to positrons, which spread out in the interstellar medium. Non-radioactive processes, such as decays of heavy dark matter particles (neutralinos) predicted by most extensions of the standard model of particle physics, could also produce positrons as byproducts. However, they are expected to be accompanied by a large flux of high-energy γ-rays, which were not observed by EGRET and ground-based Tcherenkov experiments. In this context, we explore the possibility of direct positron production by annihilation of light dark matter particles.

Gravitational cooling and density profile near caustics in collisionless dark matter haloes

Cold dark matter haloes are populated by high-density structures with sharply-peaked profiles known as caustics which have not yet been resolved by 3-dimensional numerical simulations. Here, we derive semi-analytic expressions for the density profiles near caustics in haloes which form by self-similar accretions of dark matter with infinitesimal velocity dispersion. A simple rescaling shows that similarly to the case of absolutely cold medium these profiles are universal: they are valid for all caustics and irrespective of physical parameters of the halo. We derive the maximum density of the caustics and show that it depends on the velocity dispersion and the caustic location. We show that both the absolute and relative thickness of the caustic monotonically decrease toward the center of the halo while the maximum density grows. This indicates that the radial component of the thermal velocities decreases in the inner streams, i.e. the collisionless medium cools down in the radial direction descending to the center of the halo. Finally, we demonstrate that there can be a significant contribution to the emission measure from dark matter particle annihilation in the caustics.

Spectra of neutrinos from dark matter annihilations

We study the fluxes of neutrinos from annihilations of dark matter particles in the Sun and the Earth. We give the spectra of all neutrino flavors for the main known annihilation channels: ν ν ¯ , b b ¯ , τ τ ¯ , c c ¯ , light quarks, ZZ, W + W − . We present the appropriate formalism for computing the combined effect of oscillations, absorptions, ν τ -regeneration. Total rates are modified by an O ( 0.1 – 10 ) factor, comparable to astrophysical uncertainties, that instead negligibly affect the spectra. We then calculate different signal topologies in neutrino telescopes: through-going muons, contained muons, showers, and study their capabilities to discriminate a dark matter signal from backgrounds. We finally discuss how measuring the neutrino spectra can allow to reconstruct the fundamental properties of the dark matter: its mass and its annihilation branching ratios.

A BRIEF NOTE ON MEV DARK MATTER

Recently, Boehm and co-workers have analyzed the newly detected 511 keV gamma rays from the galactic bulge based on data obtained from INTEGRAL. They conclude that these gamma rays are a consequence of low mass (~ MeV ) particle dark matter annihilations. Their conclusions are consistent with the halo profile favored by the observations, the annihilation cross-sections required for the radiation and also other astro particle physics constraints.1,2 It may be pointed out that exactly such a production of gamma rays from MeV particles was predicted by the author3 some years ago. This was based on a consideration of extremal black holes. We would like to point out that there is a spectrum of possible candidates.

Cosmological lower bound on dark matter masses from the soft gamma-ray background

Motivated by a recent detection of 511 keV photons from the center of our Galaxy, we calculate the spectrum of the soft {gamma}-ray background of the redshifted 511 keV photons from cosmological halos. Annihilation of dark matter particles into electron-positron pairs makes a substantial contribution to the {gamma}-ray background. Mass of such dark matter particles must be or approx. 20 MeV. We include the contribution from the active galactic nuclei and supernovae. The halo substructures may increase the lower bound to > or approx. 60 MeV.

Neutralinos, big bang nucleosynthesis, andL6iin low-metallicity stars

The synthesis of $^{6}\mathrm{L}\mathrm{i}$ during the epoch of big bang nucleosynthesis due to residual annihilation of dark matter particles is considered. By comparing the predicted $^{6}\mathrm{L}\mathrm{i}$ to observations of this isotope in low-metallicity stars, generic constraints on s-wave dark matter annihilation rates into quarks, gauge bosons, and Higgs bosons are derived. It may be shown that, for example, wino dark matter in anomaly-mediated SUSY breaking scenarios with masses ${m}_{\ensuremath{\chi}}\ensuremath{\lesssim}250\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$ or light neutralinos with ${m}_{\ensuremath{\chi}}\ensuremath{\lesssim}20\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$ annihilating into light quarks are, taking face value, ruled out. These constraints may only be circumvented if significant $^{6}\mathrm{L}\mathrm{i}$ depletion has occurred in all three low-metallicity stars in which this isotope has been observed to date. In general, scenarios invoking nonthermally generated neutralinos with enhanced annihilation rates for a putative explanation of cosmic ray positron or galactic center as well as diffuse background gamma-ray signals by present-day neutralino annihilation will have to face a stringent $^{6}\mathrm{L}\mathrm{i}$ overproduction problem. On the other hand, it is possible that $^{6}\mathrm{L}\mathrm{i}$ as observed in low-metallicity stars is entirely due to residual dark matter annihilation during big bang nucleosynthesis, even for neutralinos undergoing a standard thermal freeze-out.

Light and heavy dark matter particles

It has recently been pointed out that the 511 keV emission line detected by Integral/SPI from the bulge of our galaxy could be explained by annihilations of light Dark Matter particles into e^+ e^-. If such a signature is confirmed, then one might expect a conflict with the interpretation of very high energy gamma rays if they also turn out to be due to Dark Matter annihilations. Here, we propose a way to accomodate the existence of both signals being produced by Dark Matter annihilations through the existence of two stable (neutral) Dark Matter particles, as is possible in theories inspired from N=2 supersymmetry.

MeV dark matter: has it been detected?

We discuss the possibility that the recent detection of 511 keV gamma rays from the galactic bulge, as observed by INTEGRAL, is a consequence of low mass (1-100 MeV) particle dark matter annihilations. We discuss the type of halo profile favored by the observations as well as the size of the annihilation cross section needed to account for the signal. We find that such a scenario is consistent with the observed dark matter relic density and other constraints from astrophysics and particle physics.

Search for supersymmetric dark matter with GLAST

The detection of exotic cosmic rays due to pair annihilation of dark matter particles in the Milky Way halo is a viable tecniques to search for supersymmetric dark matter candidates. The study of the spectrum of gamma-rays, antiprotons and positrons offers good possibilities to perform this search in a significant portion of the Minimal Supersymmetric Standard Model parameter space. In particular, the EGRET team has seen a convincing signal for a strong excess of emission from the Galactic center that has no simple explanation with standard processes. We will review the limits achievable with the experiment GLAST taking into accounts the LEP results and we will compare this method with the antiproton and positrons experiments, and direct detection underground experiments. PACS: 95.55.Ka Gamma-ray telescopes – 95.35.+d Dark matter

Can annihilating dark matter be lighter than a few GeVs?

We estimate the gamma-ray fluxes from the residual annihilations of dark matter (DM) particles having a mass mdm ϵ [MeV, O(10) GeV] (a possible solution to the DM issue provided they have a new kind of interactions and no significant coupling to the Z) and compare them to observations. We find that particles lighter than O(100 MeV) can be viable DM candidates provided their dominant annihilation cross section is S-wave suppressed so as to satisfy the gamma-ray constraints. A similar conclusion is obtained for particles lighter than O(10) GeV from the study of radio fluxes, assuming a NFW profile and that they mainly annihilate into electrons.

Small-scale clumps in the galactic halo and dark matter annihilation

Production of small-scale dark matter (DM) clumps is studied in the standard cosmological scenario with an inflation-produced primeval fluctuation spectrum. Special attention is given to the three following problems. (i) The mass spectrum of small-scale clumps with $M\ensuremath{\lesssim}{10}^{3}{M}_{\ensuremath{\bigodot}}$ is calculated with the tidal destruction of the clumps taken into account within a hierarchical model of clump structure. Only 0.1--0.5 % of small clumps survive the stage of tidal destruction in each logarithmic mass interval $\ensuremath{\Delta}\mathrm{ln}M\ensuremath{\sim}1.$ (ii) The mass distribution of clumps has a cutoff at ${M}_{\mathrm{min}}$ due to the diffusion of DM particles out of fluctuation and free streaming at later stages. ${M}_{\mathrm{min}}$ is a model-dependent quantity. In the case that the neutralino, considered as a pure B-ino, is a DM particle, ${M}_{\mathrm{min}}\ensuremath{\sim}{10}^{\ensuremath{-}8}{M}_{\ensuremath{\bigodot}}.$ (iii) The evolution of the density profile in a DM clump does not result in a singularity because of the formation of the core under the influence of tidal interaction. The radius of the core is ${R}_{c}\ensuremath{\sim}0.1R,$ where R is the radius of the clump. The applications for annihilation of DM particles in the Galactic halo are studied. The number density of clumps as a function of their mass, radius, and distance to the Galactic center is presented. The enhancement of the annihilation signal due to clumpiness, valid for arbitrary DM particles, is calculated. In spite of a small survival probability, the global annihilation signal in most cases is dominated by clumps. For the observationally preferable value of the index of the primeval fluctuation spectrum ${n}_{p}\ensuremath{\approx}1,$ the enhancement of the annihilation signal is described by a factor of 2 to 5 for different density profiles in a clump.

Search for supersymmetric dark matter with GLAST

The detection of exotic cosmic rays due to pair annihilation of dark matter particles in the Milky Way halo is a viable techniques to search for supersymmetric dark matter candidates. The study of the spectrum of gamma-rays, antiprotons and positrons offers goof possibilities to perform this search in a significant portion of the Minimal Supersymmetric Standard Model parameter space. In particular the EGRET team have seen a convincing signal for a strong excess of emission from the Galactic center that has no simple explanation with standard processes. We will review the limits achievable with the experiment GLAST taking into account the LEP results and we will compare this method with the antiproton and positrons experiments, and direct detection underground experiments.

Neutrinos from the annihilation or decay of superheavy relic dark matter particles

In light of the mounting evidence that the highest energy cosmic rays are dominated by protons and not gamma-rays, we discuss the prospect that these cosmic rays are generated in the decay or annihilation of superheavy relic particles. We calculate the high energy neutrino spectrum which results and normalize our results to the ultra-high energy cosmic ray spectrum. We show that most scenerios are already constrained by present limits placed by the AMANDA experiment.

Search for dark matter with GLAST

The detection of exotic cosmic rays due to pair annihilation of dark matter particles in the Milky Way halo is a viable techniques to search for supersymmetric dark matter candidates. The study of the spectrum of gamma-rays, antiprotons and positrons offers good possibilities to perform this search in a significant portion of the Minimal Supersymmetric Standard Model parameter space. In particular the EGRET team have seen a convincing signal for a strong excess of emission from the Galactic center that has no simple explanation with standard processes. We will review the limits achievable with the experiment GLAST taking into accounts the LEP results and we will compare this method with the antiproton and positrons experiments.

Cosmic-ray positrons: are there primary sources?

Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.

Dark Matter Annihilation at the Galactic Center

Cold dark matter near the galactic center is accreted by the central black hole into a dense spike. Particle dark matter annihilation makes the spike a compact source of photons, electrons, positrons, protons, antiprotons, and neutrinos. The spike luminosity depends on the halo density profile: halos with finite cores have unnoticeable spikes; halos with inner cusps may have spikes so bright that the absence of a neutrino signal from the galactic center already places upper limits on the density slope of the inner halo. Future neutrino telescopes observing the galactic center could probe the inner structure of the dark halo or indirectly find the nature of dark matter.

Positrons from particle dark-matter annihilation in the Galactic halo: Propagation Green’s functions

We calculate the propagation of positrons from dark-matter particle annihilation in the Galactic halo in different models of the dark matter halo distribution using our three-dimensional code, and present fits to our numerical propagation Green's functions. We show that the Green's functions are not very sensitive to the dark matter distribution for the same local dark matter energy density. We compare our predictions with the computed cosmic ray positron spectra (``background'') for the ``conventional'' cosmic ray nucleon spectrum which matches the local measurements, and a modified spectrum which respects the limits imposed by measurements of diffuse Galactic $\ensuremath{\gamma}$ rays, antiprotons, and positrons. We conclude that significant detection of a dark matter signal requires favorable conditions and precise measurements unless the dark matter is clumpy which would produce a stronger signal. Although our conclusion qualitatively agrees with those of previous authors, it is based on a more realistic model of particle propagation and thus reduces the scope for future speculations. A reliable background evaluation requires new accurate positron measurements and further developments in modeling production and propagation of cosmic ray species in the Galaxy.

Volcanogenic dark matter and mass extinctions

The passage of the Earth through dense clumps of dark matter, the presence of which are predicted by certain cosmologies, would produce large quantities of heat in the interior of this planet through the capture and subsequent annihilation of dark matter particles. This heat can cause large-scale volcanism which could in turn have caused the extinction of the dinosaurs and other mass extinctions. The periodicity of such volcanic outbursts agrees with the frequency of palaeontological mass extinctions as well as the observed periodicity in the occurrence of the largest flood basalt provinces on the globe.

Gamma-rays and neutrinos from dark matter

High energy astrophysical γ-rays and neutrinos can be produced both by the annihilation and possible slow decay of dark matter particles. We discuss the fluxes and spectra of such secondaries produced by dark matter particles in the universe and their observability in competition with other astrophysical γ-ray signals and with atmospheric neutrinos. To do this, we work within the assumption that the dark matter particles are neutralinos with are the lightest supersymmetric particles (LSPs) predicted by supersymmetry theories.