Neutralino Annihilation Research Articles

Relic density of neutralino dark matter in the MSSM withCPviolation

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 in \Omega h^2 solely from modifications in the couplings are O(10%-100%), but can reach an order of magnitude in some cases.

Heavy Higgs resonances for the neutralino relic density in the Higgs decoupling limit of the CP-noninvariant minimal supersymmetric standard model

The lightest neutralino is a compelling candidate to account for cold dark matter in the universe in supersymmetric theories with $R$--parity. In the CP-invariant theory, the neutralino relic density can be found in accord with recent WMAP data if neutralino annihilation in the early universe occurs via the s-channel $A$ funnel. In contrast, in the CP-noninvariant theory two heavy neutral Higgs bosons can contribute to the Higgs funnel mechanism significantly due to a CP-violating {\it complex} mixing between two heavy states, in particular, when they are almost degenerate. With a simple analytic and numerical analysis, we demonstrate that the CP-violating Higgs mixing can modify the profile of the neutralino relic density {\it considerably} in the heavy Higgs funnel with the neutralino mass close to half of the heavy Higgs masses.

Accelerator testing of the general antiparticle spectrometer; a novel approach to indirectdark matter detection

We report on recent accelerator testing of a prototype general antiparticle spectrometer(GAPS). GAPS uses a novel approach for indirect dark matter searches that exploits theantideuterons produced in neutralino–neutralino annihilations. GAPS captures theseantideuterons into a target with the subsequent formation of exotic atoms. These exoticatoms decay with the emission of x-rays of precisely defined energy and a correlated pionsignature from nuclear annihilation. This signature uniquely characterizes theantideuterons. Preliminary analysis of data from a prototype GAPS in an antiproton beamat the KEK accelerator in Japan has confirmed the multiple x-ray/pion star topology andindicated x-ray yields consistent with prior expectations. Moreover, our success in utilizingsolid rather than gas targets represents a significant simplification over our originalapproach and offers potential gains in sensitivity through reduced dead mass in the targetarea.

Adiabatic compression and indirect detection of supersymmetric dark matter

Recent developments in the modelling of the dark matter distribution in our Galaxy pointout the necessity to consider some physical processes to satisfy observational data. Inparticular, models with adiabatic compression, which include the effect of the baryonic gasin the halo, increase significantly the dark matter density in the central region of the MilkyWay. On the other hand, the non-universality in the scalar and gaugino sectors ofsupergravity models can also increase significantly the neutralino annihilation cross section.We show that the combination of both effects gives rise to a gamma-ray flux arising fromthe galactic centre largely reachable by future experiments like GLAST. We also analyse inthis framework the EGRET excess data above 1 GeV, as well as the recent data fromCANGAROO and HESS. The analysis has been carried out imposing the most recentexperimental constraints, such as the lower bound on the Higgs mass, the b → sγ branching ratio, and the muong − 2. In addition, the recently improved upper bound on B(Bs → μ+μ-) has also been taken into account. The astrophysical (WMAP) bounds on the dark matterdensity have also been imposed on the theoretical computation of the relic neutralinodensity through thermal production.

Neutralino annihilation beyond leading order

High-precision measurements of the relic dark matter density and the calculation of dark matter annihilation branching fractions in the sun or the galactic halo today motivate the computation of the neutralino annihilation cross section beyond leading order. We consider neutralino annihilation via squark exchange and parameterize the effective annihilation vertex as a dimension-six operator suppressed by two powers of the squark mass and related to the divergence of the axial vector current of the final-state quarks. Since the axial vector current is conserved at tree level in the limit of massless quarks, this dimension-six operator contains a suppression by the quark mass. The quark mass suppression can be lifted in two ways: (1) by corrections to the dimension-six operator involving the anomalous triangle diagram, and (2) by going to dimension-eight. We address the first of these possibilities by evaluating the anomalous triangle diagram, which contributes to neutralino annihilation to gluon pairs. We relate the triangle diagram via the anomaly equation to the decay of a pseudoscalar into two gluons and use the Adler–Bardeen theorem to extract the next-to-leading order (NLO) QCD corrections to χχ→gg from the known corrections to pseudoscalar decay. The strong dependence of the dominant χχ→qq¯ cross section on the relative velocity of the neutralinos makes these NLO corrections unimportant at χ decoupling but significant today.

Limits to the muon flux from neutralino annihilations in the Sun with the AMANDA detector

A search for an excess of muon–neutrinos from neutralino annihilations in the Sun has been performed with the AMANDA-II neutrino detector using data collected in 143.7 days of live-time in 2001. No excess over the expected atmospheric neutrino background has been observed. An upper limit at 90% confidence level has been obtained on the annihilation rate of captured neutralinos in the Sun, as well as the corresponding muon flux limit at the Earth, both as functions of the neutralino mass in the range 100–5000 GeV.

Gamma-Ray Background from Neutralino Annihilation in the First Cosmological Objects

The paradigm of the neutralino dark matter predicts that the first gravitationally bound objects are earth-mass sized microhaloes, which would emit annihilation gamma-rays. Here we show that, though the flux from individual nearest microhaloes is extremely difficult to detect, meaningful constraints on their survival probability and internal density profile can be set by requiring that the galactic and extragalactic gamma-ray background flux from the microhaloes does not exceed the existing EGRET background data. Possible disruption of microhaloes by stellar encounters does not significantly reduce the background flux. If the probability for microhaloes to survive the hierarchical clustering process of dark matter is as large as indicated by a recent simulation, they could be a significant component of the observed background flux in some photon energy range, even with the standard annihilation cross section and conservative internal density profile of microhaloes. The integrated gamma-ray flux from microhaloes in the halo of the Andromeda galaxy may also be detectable by observations in the near future.

Relic density of dark matter in the next-to-minimal supersymmetric standardmodel

We present a code for computing the relic density of dark matter in the next-to-minimalsupersymmetric standard model (NMSSM). Dominant corrections to the Higgs masses arecalculated with NMHDECAY as well as theoretical and collider constraints. All neutralinoannihilation and coannihilation processes are then computed with an extended version ofmicrOMEGAs, taking into account higher order corrections to Higgs vertices. We explorethe parameter space of the NMSSM and consider in particular the case of a bino LSP, of amixed bino–higgsino LSP and of a singlino LSP. As compared to the case for theMSSM, neutralino annihilation is often more efficient, as it can take place via(additional) Higgs resonances as well as annihilation into light Higgs states. Modelswith a large singlino component can be compatible with WMAP constraints.

Gamma-ray detection from neutralino annihilation in non-universal SUGRA scenarios

We analyze the indirect detection of neutralino dark matter in supergravity scenarios with non-universal soft scalar and gaugino masses. In particular, the gamma-ray flux arising from the galactic center due to neutralino annihilation is computed. In important regions of the parameter space it can be increased significantly (about two orders of magnitude) with respect to the universal scenario. This result is compared with the sensitivity of current and planned experiments, such as the satellite-based detectors EGRET and GLAST and the ground-based atmospheric telescope HESS. For example, for tan β < 35 the sensitivity region of GLAST and HESS can only be reached in non-universal scenarios.

Dark Minihalos with Intermediate Mass Black Holes

We argue that the Milky Way (MW) contains 10(3)-10(4) intermediate mass black holes (IMBHs) of mass approximately 10(2-3)M. Some IMBHs are naked, and some are enshrouded by dense dark minispikes and by minihalos of (10(6)-10(7))M circle. The IMBH is formed off-center by gas accretion in a minihalo. These dense minihalos (the nearest at about 2 kpc) survive mostly without tidal stripping by the MW, and are largely invisible except that their pointlike neutralino annihilation signals (with bolometric luminosities of 10(3-5)L circle 50 GeV / mChi within 0.01-0.1 pc of their centers) stand out well above the MW background and are more luminous than outer dwarf satellite galaxies.

Supersymmetric Dark Matter and the Extragalactic Gamma Ray Background

We trace the origin of the newly determined extragalactic gamma-ray background from EGRET data to an unresolved population of blazars and neutralino annihilation in cold dark matter halos. Using results of high-resolution simulations of cosmic structure formation, we calculate composite spectra and compare with the EGRET data. The resulting best-fit value for the neutralino mass is m(chi) = 515(+110)(-75) GeV (systematic errors approximately 30%).

SUSY dark matter: implications for collider searches and direct and indirect DM detection

The minimal supergravity model (mSUGRA) has become severely constrained by the WMAP determination of Ω CDM h 2, BF(b → sγ) and (g − 2) μ. We determine the favored remaining regions of model parameter space, and their consequences for future searches for SUSY dark matter (DM) at colliders. We also exhibit regions of parameter space where direct detection of SUSY DM can occur. Finally, we note which regions are open to indirect searches for SUSY DM via neutrino telescope searches, or via observation of γs, e +s or p ¯ s from neutralino annihilation in the galactic core or halo.

Solving the cooling flow problem of galaxy clusters by dark matter neutralino annihilation

Recent X-ray observations revealed that strong cooling flow of intracluster gas is not present in galaxy clusters, even though predicted theoretically if there is no additional heating source. I show that relativistic particles produced by dark matter neutralino annihilation in cluster cores provide a sufficient heating source to suppress the cooling flow, under reasonable astrophysical circumstances including adiabatic growth of central density profile, with appropriate particle physics parameters for dark matter neutralinos. In contrast to other astrophysical heat sources such as AGNs, this process is a steady and stable feedback over cosmological time scales after turned on.

Astrophysical sources of high-energy neutrinos

Neutrino telescopes of the cubic-kilometer scale will be able to discover the diffuse, isotropic flux of ∼ (5 10 −8 – 5 10 −7 ) GeV cm −2 s −1 st −1 due to unresolved extragalactic sources of relativistic protons at energies above ∼ 100 TeV above which the atmospheric background practically vanishes. For the brightest point sources with an expected flux in the range ∼ (10 −9 – 10 −10 ) GeV cm −2 s −1 , a detection is possible in long-term exposures. The galactic disk and the extragalactic isotropic background are expected to be the strongest diffuse sources. As judged from their much stronger contribution to the extragalactic gamma ray background, blazars seem to be more important as high energy neutrino sources than GRBs by more than an order of magnitude. Flavor mixing due to oscillations could render an extragalactic flux of neutrinos from neutralino annihilations detectable with cubic-kilometer neutrino telescopes, if flavor discrimination at energies in the 10-100 GeV regime will be achieved.

Detectability of weakly interacting dark matter candidates

We have examined the detectability of weakly interacting dark matter candidates that constitute not all, but only a subdominant component of galactic cold dark matter. We find that neutralinos may remain detectable in direct dark matter searches even if they constitute only 1% of the halo dark matter. Regarding indirect detection, we find that upward-going muon fluxes in underground detectors from neutralino annihilations in the Sun and in the Earth can remain above the threshold of detectability of 10 muons/km 2/yr for neutralinos composing 1% or more of the halo dark matter. Thus if a signal is seen in any of the current dark matter searches it is possible we are only detecting the subdominant component of the total cold dark matter.

MAGIC and the search for signatures of supersymmetric dark matter

The 17 m Imaging Air shower Cherenkov Telescope MAGIC (Roque de los Muchachos Observatory, La Palma, Canary Islands) has recently entered its commissioning phase. One of the main goals of the MAGIC telescope project is to provide an unprecedented sensitivity for the detection of gamma rays with energies as low as 30 GeV. A dedicated search for the gamma rays expected to be produced by WIMP annihilations is a prime object of the MAGIC physics program. We consider annihilating supersymmetric dark matter in M 87 and discuss a possible observation strategy. New calculations concerning the extragalactic gamma ray and neutrino backgrounds owing to cosmological neutralino annihilation are also briefly discussed.

WMAP constraints on SUGRA models with non-universal gaugino masses and prospects for direct detection

We discuss constraints on supersymmetric models arising from the relic density measurements of WMAP as well as from direct and precision measurements, LEP, b → s γ , ( g − 2 ) μ , B s → μ + μ − . We consider mSUGRA models and their extensions with non-universal gaugino masses. We find, as commonly known, that the relic density pinpoints towards very specific regions of the mSUGRA models: coannihilation, focus and heavy Higgs annihilation. The allowed regions widen significantly when varying the top quark mass. Introducing some non-universality in the gaugino masses significantly changes this conclusion as in specific non-universal models the relic density upper limit can be easily satisfied. This occurs with models where M 1 > M 2 at the GUT scale when the LSP has a high wino component. Models where M 3 < M 2 favours the Higgs annihilation channel in large regions of parameter space and at large tan β also favours the annihilation of neutralinos in gauge bosons pairs. We discuss also the potential of direct detection experiments to probe supersymmetric models and point out at the main consequences for colliders based on the mass spectrum. Our calculation of the relic density of neutralinos is based on micrOMEGAs and the SUSY spectrum is generated with SOFTSUSY.

Dark matter search after DAMA withG73e

The Weakly Interacting Massive Particle (WIMP) is one of the main candidates for the relic dark matter (DM). In the effective low-energy minimal supersymmetric standard model (effMSSM) the neutralino nucleon spin and scalar cross sections in the low-mass regime were calculated. The calculated cross sections are compared with almost all experimental currently available exclusion curves for spin-dependent WIMP-proton and WIMP-neutron cross sections. It is demonstrated that in general about 2 orders of magnitude improvement of the current DM experiment sensitivities is needed to reach the (effMSSM) supersymmetric (SUSY) predictions. At the current level of accuracy it looks reasonable to safely neglect subdominant spin WIMP nucleon contributions analyzing the data from spin-nonzero targets. To avoid misleading discrepancies between data and SUSY calculations it is, however, preferable to use a mixed spin-scalar coupling approach. This approach is applied to estimate future prospects of experiments with the odd-neutron high-spin isotope $^{\mathrm{73}}\mathrm{G}\mathrm{e}$. It is noticed that the DAMA evidence favors the light Higgs sector in the effMSSM, a high event rate in a $^{\mathrm{73}}\mathrm{G}\mathrm{e}$ detector and relatively high up-going muon fluxes from relic neutralino annihilations in the Earth and the Sun.

The Status of the ANTARES experiment

ANTARES is a neutrino telescope designed to search for high-energy neutrinos from astrophysical sources such as quasars, gamma-ray bursters, microquasars, supernova remnants and AGN. The objectives also include the indirect search for WIMPs, primary candidates for non-baryonic dark matter, by looking for neutrinos from neutralino annihilations in the centres of the Sun, Earth and Galaxy. The array of 12 lines with 900 photomultiplier tubes will be deployed by 2007 at a depth of about 2500 m in the Mediterranean sea near Toulon (France), 40 km off the coast. It will detect the Cherenkov light emitted in sea water by muons produced via charged-current interactions of neutrinos with surrounding matter. A prototype line and an instrumentation line for monitoring environmental parameters have been successfully deployed and connected to the electro-optical cable, which transmitted the data to the shore station. The current status of the project is presented.

Reconciling Neutralino relic Density with Yukawa Unified Supersymmetric Models

Supersymmetric grand unified models based on the gauge group SO(10) are especially attractive in light of recent data on neutrino masses. The simplest SO(10) SUSY GUT models predict unification of third generation Yukawa couplings in addition to the usual gauge coupling unification. Recent surveys of Yukawa unified SUSY GUT models predict an inverted scalar mass hierarchy in the spectrum of sparticle masses if the superpotential mu term is positive. In general, such models tend to predict an overabundance of dark matter in the universe. We survey several solutions to the dark matter problem in Yukawa unified supersymmetric models. One solution-- lowering the GUT scale mass value of first and second generation scalars-- leads to u_R and c_R squark masses in the 90-120 GeV regime, which should be accessible to Fermilab Tevatron experiments. We also examine relaxing gaugino mass universality which may solve the relic density problem by having neutralino annihilations via the Z or h resonances, or by having a wino-like LSP.