New Gamma-Ray Contributions to Supersymmetric Dark Matter Annihilation

We compute the electromagnetic radiative corrections to all leading annihilation processes which may occur in the Galactic dark matter halo, for dark matter in the framework of supersymmetric extensions of the Standard Model (MSSM and mSUGRA), and present the results of scans over the parameter space that is consistent with present observational bounds on the dark matter density of the Universe. Although these processes have previously been considered in some special cases by various authors, our new general analysis shows novel interesting results with large corrections that may be of importance, e.g., for searches at the soon to be launched GLAST gamma-ray space telescope. In particular, it is pointed out that regions of parameter space where there is a near degeneracy between the dark matter neutralino and the tau sleptons, radiative corrections may boost the gamma-ray yield by up to three or four orders of magnitude, even for neutralino masses considerably below the TeV scale, and will enhance the very characteristic signature of dark matter annihilations, namely a sharp step at the mass of the dark matter particle. Since this is a particularly interesting region for more constrained mSUGRA models of supersymmetry, we use an extensive scan over this parameter space to verify the significance of our findings. We also re-visit the direct annihilation of neutralinos into photons and point out that, for a considerable part of the parameter space, internal bremsstrahlung is more important for indirect dark matter searches than line signals.Comment: Replaced Fig. 2c which by mistake displayed the same spectrum as Fig. 2d; the radiative corrections reported here are now implemented in DarkSUSY which is available at http://www.physto.se/~edsjo/darksusy

Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites

Annihilating dark matter particles produce roughly as much power in electrons and positrons as in gamma ray photons. The charged particles lose essentially all of their energy to inverse Compton and synchrotron processes in the galactic environment. We discuss the diffuse signature of dark matter annihilations in satellites of the Milky Way (which may be optically dark with few or no stars), providing a tail of emission trailing the satellite in its orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron emission at radio wavelengths might be seen. We discuss the possibility of detecting these signals with current and future observations, in particular EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure

Dark matter annihilation at the galactic center

If cold dark matter is present at the galactic center, as in current models of the dark halo, it is accreted by the central black hole into a dense spike. Particle dark matter then annihilates strongly inside the spike, making it a compact source of photons, electrons, positrons, protons, antiprotons, and neutrinos. The spike luminosity depends on the density profile of the inner halo: halos with finite cores have unnoticeable spikes, while halos with inner cusps may have spikes so bright that the absence of a detected neutrino signal from the galactic center already places interesting 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.Comment: 4 pages, 5 figure

Considerations on rescattering effects for threshold photo- and electro-production of π0\pi^0 on deuteron

We show that for the S-state $\pi^0$-production in processes $\gamma+d\to d+\pi^0$ and $e^-+d\to e^-+d+\pi^0$ the rescattering effects due to the transition: $\gamma+d\to p+p+\pi^-$ (or $n+n+\pi^+)\to d+\pi^0$ are cancelled out due to the Pauli principle. The large values for these effects predicted in the past may result from the fact that the spin structure of the corresponding matrix element and the necessary antisymmetrization induced by the presence of identical protons (or neutrons) in the intermediate state was not taken into account accurately. One of the important consequences of these considerations is that $\pi^0$ photo- and electro-production on deuteron near threshold can bring direct information about elementary neutron amplitudes.Comment: Add a new sectio

Interference of Conversion and Bremsstrahlung Amplitudes in the Decay K_L -> mu^+ mu^- gamma

In the region of large mu^+ mu^- invariant mass, the decay spectrum of K_L -> mu^+ mu^- gamma deviates from the Dalitz pair spectrum, as a result of interference between conversion (K_L -> gamma^* gamma -> mu^+ mu^- gamma) and bremsstrahlung amplitudes. The latter is proportional to the K_L -> mu^+ mu^- matrix element, whose 2 gamma-absorptive part appears to dominate the observed K_L -> mu^+ mu^- decay rate. We examine the extent to which a scrutiny of the K_L -> mu^+ mu^- gamma spectrum in the end-point region could provide evidence on the real part of the K_L -> mu^+ mu^- amplitude. As a by-product, we obtain the absorptive part of the K_L -> gamma^* gamma form factor, using data on the K_L -> pi^+ pi^- gamma spectrum.Comment: 7 pages, 4 figure

Two photon annihilation of Kaluza-Klein dark matter

We investigate the fermionic one-loop cross section for the two photon annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray line with energy equal to the KK dark matter particle mass. We find that the cross section is large enough that if a continuum signature is detected, the energy distribution of gamma-rays should end at the particle mass with a peak that is visible for an energy resolution of the detector at the percent level. This would give an unmistakable signature of a dark matter origin of the gamma-rays, and a unique determination of the dark matter particle mass, which in the case studied should be around 800 GeV. Unlike the situation for supersymmetric models where the two-gamma peak may or may not be visible depending on parameters, this feature seems to be quite robust in UED models, and should be similar in other models where annihilation into fermions is not helicity suppressed. The observability of the signal still depends on largely unknown astrophysical parameters related to the structure of the dark matter halo. If the dark matter near the galactic center is adiabatically contracted by the central star cluster, or if the dark matter halo has substructure surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio

Running mass of the rho0 meson's implication for the dilepton mass spectrum and the mu+mu-/e+e- branching ratio in the K+ --> pi+l+l- decays

We make an attempt to resolve the discrepancy of the observed e+e- mass spectrum in the K+ --> pi+e+e- decay with that predicted by meson dominance. To this end we investigate the properties of the rho0 propagator. We use dispersion relations to evaluate the running mass squared m_rho^2(t) of the rho0 resonance without adjustable parameters. To improve the convergence of the dispersion integral, the momentum dependence of strong vertices is taken from the flux-tube-breaking model of Kokoski and Isgur. The obtained behavior of m_rho^2(t) at small momentum squared t makes the K+ --> pi+e+e- form factor rise faster with increasing $t$ than in the original meson-dominance calculation and more in agreement with the published data. As a consequence, the meson-dominance prediction of the mu+mu-/e+e- branching ratio changes slightly, from 0.224 to 0.236. We do not see any possibility to accommodate into the meson-dominance approach an even steeper e+e- spectrum, indicated by the preliminary data of the E865 collaboration at BNL AGS.Comment: 13 pages, RevTeX, epsf.sty, 4 embedded figure

A New Model-Independent Method for Extracting Spin-Dependent Cross Section Limits from Dark Matter Searches

A new method is proposed for extracting limits on spin-dependent WIMP-nucleon interaction cross sections from direct detection dark matter experiments. The new method has the advantage that the limits on individual WIMP-proton and WIMP-neutron cross sections for a given WIMP mass can be combined in a simple way to give a model-independent limit on the properties of WIMPs scattering from both protons and neutrons in the target nucleus. Extension of the technique to the case of a target material consisting of several different species of nuclei is discussed.Comment: 15 pages, 6 Encapsulated Postscript figure

Cross-correlations in scaling analyses of phase transitions

Thermal or finite-size scaling analyses of importance sampling Monte Carlo time series in the vicinity of phase transition points often combine different estimates for the same quantity, such as a critical exponent, with the intent to reduce statistical fluctuations. We point out that the origin of such estimates in the same time series results in often pronounced cross-correlations which are usually ignored even in high-precision studies, generically leading to significant underestimation of statistical fluctuations. We suggest to use a simple extension of the conventional analysis taking correlation effects into account, which leads to improved estimators with often substantially reduced statistical fluctuations at almost no extra cost in terms of computation time.Comment: 4 pages, RevTEX4, 3 tables, 1 figur

Non-Baryonic Dark Matter - Observational Evidence and Detection Methods

The evidence for the existence of dark matter in the universe is reviewed. A general picture emerges, where both baryonic and non-baryonic dark matter is needed to explain current observations. In particular, a wealth of observational information points to the existence of a non-baryonic component, contributing between around 20 and 40 percent of the critical mass density needed to make the universe geometrically flat on large scales. In addition, an even larger contribution from vacuum energy (or cosmological constant) is indicated by recent observations. To the theoretically favoured particle candidates for non-baryonic dark matter belong axions, supersymmetric particles, and of less importance, massive neutrinos. The theoretical foundation and experimental situation for each of these is reviewed. Direct and indirect methods for detection of supersymmetric dark matter are described in some detail. Present experiments are just reaching the required sensitivity to discover or rule out some of these candidates, and major improvements are planned over the coming years.Comment: Submitted to Reports on Progress in Physics, 59 pages, LaTeX, iopart macro, 14 embedded postscript figure