Joakim Edsjö

DarkSUSY: Computing Supersymmetric Dark Matter Properties Numerically

The question of the nature of the dark matter in the Universe remains one of the most outstanding unsolved problems in basic science. One of the best motivated particle physics candidates is the lightest supersymmetric particle, assumed to be the lightest neutralino—a linear combination of the supersymmetric partners of the photon, the Z boson and neutral scalar Higgs particles. Here we describe DarkSUSY, a publicly available advanced numerical package for neutralino dark matter calculations. In DarkSUSY one can compute the neutralino density in the Universe today using precision methods which include resonances, pair production thresholds and coannihilations. Masses and mixings of supersymmetric particles can be computed within DarkSUSY or with the help of external programs such as FeynHiggs, ISASUGRA and SUSPECT. Accelerator bounds can be checked to identify viable dark matter candidates. DarkSUSY also computes a large variety of astrophysical signals from neutralino dark matter, such as direct detection in low-background counting experiments and indirect detection through antiprotons, antideuterons, gamma-rays and positrons from the galactic halo or high-energy neutrinos from the centre of the Earth or of the Sun. Here we describe the physics behind the package. A detailed manual will be provided with the computer package.

Neutralino relic density including coannihilations

We evaluate the relic density of the lightest neutralino, the lightest supersymmetric particle, in the minimal supersymmetric extension of the standard model. For the first time, we include all coannihilation processes between neutralinos and charginos for any neutralino mass and composition. We use the most sophisticated routines for integrating the cross sections and the Boltzmann equation. We properly treat (sub)threshold and resonant annihilations. We also include one-loop corrections to neutralino masses. We find that coannihilation processes are important not only for light Higgsino-like neutralinos, as pointed out before, but also for heavy Higgsinos and for mixed and gauginolike neutralinos. Indeed, coannihilations should be included whenever {vert_bar}{mu}{vert_bar}{approx_lt}2{vert_bar}M{sub 1}{vert_bar}, independently of the neutralino composition. When {vert_bar}{mu}{vert_bar}{approximately}{vert_bar}M{sub 1}{vert_bar}, coannihilations can increase or decrease the relic density in and out of the cosmologically interesting region. We find that there is still a window of light Higgsino-like neutralinos that are viable dark matter candidates and that coannihilations shift the cosmological upper bound on the neutralino mass from 3 to 7 TeV. {copyright} {ital 1997} {ital The American Physical Society}

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.

Cosmological dark matter annihilations into γ rays: A closer look

We investigate the prospects of detecting weakly interacting massive particle (WIMP) dark matter by measuring the contribution to the extragalactic gamma-ray radiation induced, in any dark matter halo and at all redshifts, by WIMP pair annihilations into high-energy photons. We perform a detailed analysis of the very distinctive spectral features of this signal, recently proposed in a short letter by three of the authors: The gamma-ray flux which arises from the decay of

New positron spectral features from supersymmetric dark matter: A way to explain the PAMELA data?

{\ensuremath{\pi}}^{0}

Pre-launch estimates for GLAST sensitivity to dark matter annihilation signals

mesons produced in the fragmentation of annihilation final states shows a severe cutoff close to the value of the WIMP mass. An even more spectacular signature appears for the monochromatic gamma-ray components, generated by WIMP annihilations into two-body final states containing a photon: the combined effect of cosmological redshift and absorption along the line of sight produces sharp bumps, peaked at the rest frame energy of the lines and asymmetrically smeared to lower energies. The level of the flux depends both on the particle physics scenario for WIMP dark matter (we consider, as our template case, the lightest supersymmetric particle in a few supersymmetry breaking schemes), and on the question of how dark matter clusters. Uncertainties introduced by the latter are thoroughly discussed implementing a realistic model inspired by results of the state-of-the-art N-body simulations and semianalytic modeling in the cold dark matter structure formation theory. We also address the question of the potential gamma-ray background originating from active galaxies, presenting a novel calculation and critically discussing the assumptions involved and the induced uncertainties. Furthermore, we apply a realistic model for the absorption of gamma-rays on the optical and near-IR intergalactic radiation field to derive predictions for both the signal and background. Comparing the two, we find that there are viable configurations, in the combined parameter space defined by the particle physics setup and the structure formation scenario, for which the WIMP induced extragalactic gamma-ray signal will be detectable in the new generation of gamma-ray telescopes such as GLAST.

Significant Gamma Lines from Inert Higgs Dark Matter

Department of Physics, Stockholm University, AlbaNova University Center, SE - 106 91 Stockholm, Sweden(Dated: August 27, 2008)The space-borne antimatter experiment PAMELA has recently reported a surprising rise in thepositron to electron ratio at high energies. It has also recently been found that electromagneticradiative corrections in some cases may boost the gamma-ray yield from supersymmetric darkmatter annihilations in the galactic halo by up to three or four orders of magnitude, providingdistinct spectral signatures for indirect dark matter searches to look for. Here, we investigatewhether the same type of corrections can also lead to sizeable enhancements in the positron yield.We find that this is indeed the case, albeit for a smaller region of parameter space than for gammarays; selecting models with a small mass difference between the neutralino and sleptons, like inthe stau coannihilation region in mSUGRA, the effect becomes more pronounced. The resulting,rather hard positron spectrum with a relatively sharp cutoff may potentially fit the rising positronratio measured by the PAMELA satellite. To do so, however, very large “boost factors” have tobe invoked that are not expected in current models of halo structure. If the predicted cutoff wouldalso be confirmed by later PAMELA data or upcoming experiments, one could either assume non-thermal production in the early universe or non-standard halo formation to explain such a spectralfeature as an effect of dark matter annihilation. At the end of the paper, we briefly comment onthe impact of radiative corrections on other annihilation channels, in particular antiprotons andneutrinos.

Accurate relic densities with neutralino, chargino and sfermion coannihilations in mSUGRA

We investigate the sensitivity of the Gamma-ray Large Area Space Telescope (GLAST) for indirectly detecting weakly interacting massive particles (WIMPs) through the γ-ray signal that their pair ann ...

Dark matter interpretation of recent electron and positron data.

One way to unambiguously confirm the existence of particle dark matter and determine its mass would be to detect its annihilation into monochromatic gamma-rays in upcoming telescopes. One of the most minimal models for dark matter is the inert doublet model, obtained by adding another Higgs doublet with no direct coupling to fermions. For a mass between 40 and 80 GeV, the lightest of the new inert Higgs particles can give the correct cosmic abundance of cold dark matter in agreement with current observations. We show that for this scalar dark matter candidate, the annihilation signal of monochromatic gammagamma and Zgamma final states would be exceptionally strong. The energy range and rates for these gamma-ray line signals make them ideal to search for with the soon upcoming GLAST satellite.

Spectral gamma-ray signatures of cosmological dark matter annihilations.

Neutralinos arise as natural dark matter candidates in many supersymmetric extensions of the Standard Model. We present a novel calculation of the neutralino relic abundance in which we include all so-called coannihilation processes between neutralinos, charginos and sfermions, and, at the same time, we apply the state of the art technique to trace the freeze-out of a species in the early Universe. As a first application, we discuss here results valid in the mSUGRA framework; we describe general trends as well as performing a detailed study of the neutralino relic densities in the mSUGRA parameter space. The emerging picture is fair agreement with previous analyses in the same framework, however we have the power to discuss it in much more detail than previously done. For example, we find that the cosmological bound on the neutralino mass is pushed up to ~565 GeV in the stau coannihilation region and to ~1500 GeV in the chargino coannihilation region.