We discuss the possibility to observe the products of dark matter annihilation that was going on in the early Universe. Of all the particles that could be generated by this process we consider only photons, as they are both uncharged and easily detectable. The earlier the Universe was, the higher the dark matter concentration $n$ and the annihilation rate (proportional to $n^2$) were. However, the emission from the very early Universe cannot reach us because of the opacity. The main part of the signal was generated at the moment the Universe had just become transparent for the photons produced by the annihilation. Thus, the dark matter annihilation in the early Universe should have created a sort of relic emission. We obtain its flux and the spectrum.
If weakly interacting massive particles (WIMPs) constitute dark matter, it is shown that we may expect an extragalactic gamma-ray signal in the energy range 0.5 - 20 {MeV} with a maximum near 8 {MeV}. We show that an experimentally observed excess in the gamma-ray background at 0.5 - 20 {MeV} could be created by the relic WIMPs annihilation only if the dark matter structures in the universe had appeared before the universe became transparent for the annihilation products ($z \simeq 300$). We discuss in more detail physical conditions whereby this interpretation could be possible.
We investigate the possibility that ultra-high energy cosmic rays (UHECRs) originate from the annihilation of relic superheavy (SH) dark matter in the Galactic halo. In order to fit the data on UHECRs, a cross section of $<σ_Av>\sim 10^{-26}\textrm{cm}^2 (M_X/10^{12} \textrm{GeV})^{3/2}$ is required if the SH dark matter follows a Navarro--Frenk--White (NFW) density profile. This would require extremely large-$l$ contributions to the annihilation cross section. An interesting finding of our calculation is that the annihilation in sub-galactic clumps of dark matter dominates over the annihilati…
We evaluate the relic density of neutralinos in the minimal supergravity (mSUGRA) model. All 2-->2 neutralino annihilation diagrams, as well as all processes involving sleptons, charginos, neutralinos and third generation squarks are included. Relativistic thermal averaging of the velocity times cross sections is performed. We find that co-annihilation effects are only important on the edges of the model parameter space, where some amount of fine-tuning is necessary to obtain a reasonable relic density. Alternatively, at high tan(beta), annihilation through very broad Higgs resonances gives ri…
The neutralino, the lightest stable supersymmetric particle, is a strong theoretical candidate for the missing astronomical "dark matter". Depending on their annihilation cross section, relic neutralinos from early formation of the Universe trapped in orbits around massive objects may currently be annihilating at measurable rates. The Minimal Supersymmetric extension of the Standard Model predicts that the gamma rays emerging from one of the annihilation modes will give a distinct monochromatic signal with energy between 100GeV and 10TeV, depending on the neutralino mass. An additional "contin…
We discuss the relic abundance of massive long lived colored particles with mass of the order of 1 TeV. We first examine the case where the massive colored particles have the standard color only. Next we consider the "Quirk Model" suggested by M. Luty, in which the colored particles transform under an additional non-abelian gauge group with a scale much smaller than the particles' mass. In both cases, the relic abundance is reduced via a "late" hadronic annihilation stage. In the second case the relic Quirks bind to ordinary quarks forming fractional charged objects and also anomalous heavy is…
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.
Energy injected into the Cosmic Microwave Background at redshifts z<10^6 will distort its spectrum permanently. In this paper we discuss the distortion caused by annihilations of relic particles. We use the observational bounds on deviations from a Planck spectrum to constrain a combination of annihilation cross section, mass, and abundance. For particles with (s-wave) annihilation cross section, <σ|v|>=σ_0, the bound is f[(σ_0/6e-27cm^3/s)(Ω_{X\bar{X}}h^2)^2]/(m_X/MeV)<0.2, where m_X is the particle mass, Ω_{X\bar{X}} is the fraction of the critical density the particle and its antiparticle c…
Annihilation of high energy, $\sim 10^{21}$eV, neutrinos on big bang relic neutrinos of $\sim 1$eV mass, clustered in the Galactic halo or in a nearby galaxy cluster halo, has been suggested to generate, through hadronic Z decay, high energy nucleons and photons which may account for the detected flux of >10^{20}eV cosmic-rays. We show that the flux of high energy nucleons and photons produced by this process is dominated by annihilation on the uniform, non-clustered, neutrino background, and that the energy generation rate of 10^{21}eV neutrinos required to account for the detected flux of >1…
As predicted by quantum chromodynamics(QCD), around $T\sim 190$ MeV in the early universe, the QCD transition occurs during which the quarks are combined into the massive hadrons. This process reduces the effective relativistic degree of freedom, and causes a change in the expansion behavior of the universe. Similarly, the $e^+e^-$ annihilation occurred around $T\sim 0.5$ Mev has the same kind of effect. Besides, the dark energy also drives the present stage accelerating expansion. We study these combined effects on the relic gravitational waves (RGWs). In our treatment, the QCD transition and…
We reexamine the impact of dark matter (DM) annihilation on the intergalactic medium, taking into account the clumping of DM particles. We find that energy injection from the annihilation of the thermal relic DM particles may significantly raise the gas temperature at high redshifts and leave a strong imprint on the cosmological 21-cm signal, provided the particle mass is below ~1 TeV. Further, we find that while the energy injection from DM annihilation could not alone complete the reionization of the Universe, it could make a significant contribution to the electron optical depth.
If neutrinos are a significant contributor to the matter density of the universe, then they should have $\sim$ eV mass and cluster in galactic (super) cluster halos, and possibly in galactic halos as well. It was noted in the early 1980's that cosmic ray neutrinos with energy within $δE/E_R=Γ_Z/M_Z \sim 3%$ of the peak energy $E_R=4 (eV/m_ν)\times 10^{21}$ eV will annihilate on the nonrelativistic relic antineutrinos (and vice versa) to produce the Z-boson with an enhanced, resonant cross section of ${\cal O}(G_F)\sim 10^{-32}{cm}^2$. The result of the resonant neutrino annihilation is a hadro…
We calculate the relic density of dark matter in the MSSM with CP violation. We analyse various scenarios of neutralino annihilation: the cases of a bino, bino-wino and bino-Higgsino LSP, annihilation through Higgs, as well as sfermion coannihilation scenarios. Large phase effects are found, on the one hand due to shifts in the masses, on the other hand due to modifications of the couplings. Taking special care to disentangle the effects in masses and couplings, we demonstrate that the presence of CP phases can have a significant influence on the neutralino relic abundance. Typical variations …
Decays of superheavy relic particles may produce extremely energetic neutrinos. Their annihilations on the relic neutrinos can be the origin of the cosmic rays with energies beyond the Greisen-Zatsepin-Kuzmin cutoff. The red shift acts as a cosmological filter selecting the sources at some particular value z_e, for which the present neutrino energy is close to the Z pole of the annihilation cross section. We predict no directional correlation of the ultrahigh-energy cosmic rays with the galactic halo. At the same time, there can be some directional correlations in the data, reflecting the dist…
We evaluate the antiproton--to--proton flux ratio which can be generated by neutralino--neutralino annihilation in the galactic halo, considering the most general compositions for the relic neutralinos and modelling the neutralino local density according to its relic abundance. We find that in the case of mixed neutralino compositions this $\bar p/p$ ratio is higher than for pure higgsinos or gauginos. It is shown how the expected improvements in sensitivity for the new measurements of the $\bar p/p$ may provide very useful information, complementary to the one obtainable with other experiment…
We point out that if the lightest supersymmetric particle (LSP) is a Higgsino- or Wino-like neutralino, the net effect of coannihilations with sleptons is to increase the relic abundance, rather than producing the usual suppression, which takes place if the LSP is Bino-like. The reason for the enhancement lies in the effective thermally averaged cross section at freeze-out: sleptons annihilate (and co-annihilate) less efficiently than the neutralino(s)-chargino system, therefore slepton coannihilations effectively act as parasite degrees of freedom at freeze-out. Henceforth, the thermal relic …
In a class of low-energy supersymmetry models the photino is a natural dark matter candidate. We investigate the effects of post-freeze-out photino annihilations which can generate electromognetic cascades and lead to photo-destruction of $^4$He and subsequent overproduction of D and $^3$He. We also generalize our analysis to a generic dark matter component whose relic abundance is {\it not} determined by the cross section of the self-annihilations giving rise to electromagnetic showers.
In supersymmetric models with a long-lived stau being the lightest Standard Model superpartner, the stau abundance during primordial nucleosynthesis is tightly constrained. Considering the complete set of stau annihilation channels in the minimal supersymmetric Standard Model (MSSM) with real parameters for scenarios in which sparticle coannihilations are negligible, we calculate the decoupling of the lighter stau from the primordial plasma and identify processes which are capable to deplete the resulting stau abundance significantly. We find particularly efficient stau annihilation at the res…
We review the prospects for discovering supersymmetric dark matter in a recently proposed set of post-LEP supersymmetric benchmark scenarios. We consider direct detection through spin-independent nuclear scattering, as well as indirect detection through relic annihilations to neutrinos, photons, and positrons. We find that several of the benchmark scenarios offer good prospects for direct detection through spin-independent nuclear scattering, as well as indirect detection through muons produced by neutrinos from relic annihilations in the Sun, and photons from annihilations in the galactic cen…
A new set of supersymmetric benchmark scenarios has recently been proposed in the context of the constrained MSSM (CMSSM) with universal soft supersymmetry-breaking masses, taking into account the constraints from LEP, $b \to s γ$ and $g_μ- 2$. These points have previously been used to discuss the physics reaches of different accelerators. In this paper, we discuss the prospects for discovering supersymmetric dark matter in these scenarios. We consider direct detection through spin-independent and spin-dependent nuclear scattering, as well as indirect detection through relic annihilations to n…
Working within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking, we evaluate the cosmological relic density from lightest neutralinos produced in the early universe. Our numerical calculation is distinct in that it involves direct evaluation of neutralino annihilation cross sections using helicity amplitude techniques, and thus avoids the usual expansion as a power series in terms of neutralino velocity. Thus, our calculation includes relativistic Boltzmann averaging, neutralino annihilation threshold effects, and prope…
We carry out a detailed analysis of fluxes of cosmic ray antiprotons, positrons, electrons and photons to be expected from the annihilation of relic heavy neutrinos in the galactic halo. The spectra of particles are evaluated by Monte Carlo simulation. The results of calculations show that the investigation of cosmic ray positron spectra at high energies could provide a distinctive signal for annihilation of very heavy neutrinos in the Galaxy and give an important information on parameters of dark matter particles.
The next-to-leading order (NLO) QCD corrections are calculated for the pair-annihilation of spin-1 dark matter (DM) by dimensionally regularizing both ultraviolet and infrared singularities in non-relativistic limit (v<<1). The complete O(alphas) 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 same mass as the DM particle. The NLO QCD correction could give the sizable shift to the DM mass constrained by relic density measurements.
Recently the possibility was widely discussed that a large fraction of the highest energy cosmic rays may be decay products of Z bosons which were produced in the resonant annihilation of ultrahigh energy cosmic neutrinos on cosmological relic neutrinos. If one takes this so-called Z-burst scenario seriously, one may infer the mass of the heaviest relic neutrino as well as the necessary ultrahigh energy cosmic neutrino flux from a comparison of the predicted Z-burst spectrum with the observed cosmic ray spectrum.
In co-annihilation scenarios, the weakly interacting dark matter particle (WIMP) is close in mass to another particle that can decay into the WIMP. As a result, both particles freeze out at roughly the same time in the early universe, and both contribute to the effective dark matter annihilation cross-section. Since the heavier particle does not need to be weakly interacting, the co-annihilation processes are in general subject to sizeable radiative corrections. Here this is analyzed for the example of neutralino-stop co-annihilation in supersymmetry. The leading QCD corrections are calculated…
Applying the microcanonical definition of entropy to a weakly interacting and self--gravitating neutralino gas, we evaluate the change in the local entropy per particle of this gas between the freeze out era and present day virialized halo structures. An ``entropy consistency'' criterion emerges by comparing theoretical and empirical estimates of this entropy. We apply this criterion to the cases when neutralinos are mostly B-inos and mostly Higgsinos, in conjunction with the usual ``abundance'' criterion requiring that present neutralino relic density complies with $0.2<Ω_{\tildeχ^1_0} < 0.4$…
