It is shown that a decaying neutralino in a supergravity unified framework is a viable candidate for dark matter. Such a situation arises in the presence of a hidden sector with ultraweak couplings to the visible sector where the neutralino can decay into the hidden sector's lightest supersymmetric particle (LSP) with a lifetime larger than the lifetime of the universe. We present a concrete model where the MSSM/SUGRA is extended to include a hidden sector comprised of $U(1)_{X_1} \times U(1)_{X_2}$ gauge sector and the LSP of the hidden sector is a neutralino which is lighter than the LSP neutralino of the visible sector. We compute the loop suppressed radiative decay of the visible sector neutralino into the neutralino of the hidden sector and show that the decay can occur with a lifetime larger than the age of the universe. The decaying neutralino can be probed by indirect detection experiments, specifically by its signature decay into the hidden sector neutralino and an energetic gamma ray photon. Such a gamma ray can be searched for with improved sensitivity at Fermi-LAT and by future experiments such as the Square Kilometer Array (SKA) and the Cherenkov Telescope Array (CTA). We present several benchmarks which have a natural suppression of the hadronic channels from dark matter annihilation and decays and consistent with measurements of the antiproton background.
In supersymmetric models extended with an anomalous $U(1)_H$ different R-parity violating couplings can yield an unstable neutralino. We show that in this context astrophysical and cosmological constraints on neutralino decaying dark matter forbid bilinear R-parity breaking neutralino decays and lead to a class of purely trilinear R-parity violating scenarios in which the neutralino is stable on cosmological scales. We have found that among the resulting models some of them become suitable to explain the observed anomalies in cosmic-ray electron/positron fluxes.
If the energy density of the Universe before nucleosynthesis is dominated by a scalar field phi that decays and reheats the plasma to a temperature T_{RH} smaller than the standard neutralino freeze out temperature, the neutralino relic density differs from its standard value. In this case, the relic density depends on two additional parameters: T_{RH}, and the number of neutralinos produced per phi decay per unit mass of the phi field. In this paper, we numerically study the neutralino relic density as a function of these reheating parameters within minimal supersymmetric standard models and …
Considering the supersymmetric models with light neutralino and R-parity violation, we perform estimates of the signal rate expected at the recently proposed fixed target SHiP experiment exploiting CERN SPS beam of 400 GeV protons. We extend the existing studies by introducing new production channels (in particular through the beauty mesons) and decay modes. We also constrain model parameter space from analysis of negative results of the CHARM experiment.
We have investigated charged Higgs boson production via the gluon-bottom quark mode, gb -> tH+, followed by its decay into a chargino and a neutralino. The calculations are based on masses and couplings given by the Minimal Supersymmetric Standard Model (MSSM) for a specific choice of MSSM parameters. The signature of the signal is characterized by three hard leptons, a substantial missing transverse energy due to the decay of the neutralino and the chargino and three hard jets from the hadronic decay of the top quark. The possibility of detecting the signal over the Standard Model (SM) and no…
Motivated by recent claims of lines in the Fermi gamma-ray spectrum, we critically examine means of enhancing neutralino annihilation into neutral gauge bosons. The signal can be boosted while remaining consistent with continuum photon constraints if a new singlet-like pseudoscalar is present. We consider singlet extensions of the MSSM, focusing on the NMSSM, where a `well-tempered' neutralino can explain the lines while remaining consistent with current constraints. We adopt a complementary numerical and analytic approach throughout in order to gain intuition for the underlying physics. The s…
With the process $e^-γ\to \tildeχ_1^0 \tilde{e}_{L/R}^- \to e^- \tildeχ_1^0 \tildeχ_1^0$ it is possible to constrain selectron masses above the kinematical limit of the pair production process in $e^+e^-$ colliders. We investigate these mass ranges and discuss the possibility to test the renormalization group equations for the selectron masses.
Rare astrophysical events - cosmological gamma-ray bursts with energies over GeV - are considered as an origin of information about some SUSY parameters. The model of generation of the powerful gamma-ray bursts is proposed. According to this model the gamma-ray burst represents as a result of the collapse and the total annihilation of the neutralino clump. About 80 % of the clump mass radiates during about 100 second at the final stage of annihilation. The annihilation spectrum and its characteristic energies are calculated in the framework of Split Higgsino model.
We study the different linear collider modes with regard to the determination of the gaugino mass parameter M_1. In a specific mSUGRA inspired scenario we compare four processes with polarized beams: (a) e+ e- --> neutralino_1 neutralino_2 --> neutralino_1 neutralino_1 e+ e-, (b) e- gamma --> neutralino_1 selectron_{L/R} --> neutralino_1 neutralino_1 e-, (c) gamma gamma --> chargino_1^+ chargino_1^- --> neutralino_1 neutralino_1 e+ e- neutrino_e anti-neutrino_e, (d) e- e- --> selectron_{L/R} selectron_{L/R} --> neutralino_1 neutralino_1 e- e-.
We consider extensions of the standard model based on open strings ending on D-branes, in which gauge bosons and their associated gauginos exist as strings attached to stacks of D-branes, and chiral matter exists as strings stretching between intersecting D-branes. Under the assumptions that the fundamental string scale is in the TeV range and the theory is weakly coupled, we study models of supersymmetry for which signals of annihilating neutralino dark matter are observable. In particular, we construct a model with a supersymmetric R-symmetry violating (but R-parity conserving) effective Lag…
The region of the supersymmetry parameter space, in which charginos decay predominantly into sneutrinos and leptons: chi+ -> \tildeν + l+, is not excluded experimentally for small mass differences between charginos and sneutrinos. The decay sneutrinos are invisible in R-parity conserving theories since they are either the lightest supersymmetric particles or they decay primarily into the channel: neutrino + lightest neutralino. If the energy of the decay leptons is so small that they escape detection, chargino events e+e- -> chi+chi- in e+e- collisions remain invisible, eroding the excluded ch…
We analyze the direct detection rate of minimal supersymmetric neutralino dark matter in germanium, sapphire and sodium iodide detectors, imposing cosmological and accelerator bounds including those from \bsg\ decay. In contrast with several other recent analyses we find models with light charged higgsinos and large stop mixing in which the counting rate in solid state detectors exceeds 10 events/kg/day.
We consider the gamma-ray spectrum from neutralino dark matter annihilations and show that internal bremsstrahlung of W pair final states gives a previously neglected source of photons at energies near the mass of the neutralino. For masses larger than about 1 TeV, and for present day detector resolutions, this results in a characteristic signal that may dominate not only over the continuous spectrum from W fragmentation, but also over the γ-γand γ-Z line signals which are known to give large rates for heavy neutralinos. Observational prospects thus seem promising.
If the sneutrino mass is below the chargino mass, the dominant decay mode of the lightest chargino is via a two-body decay channel $χ^{\pm}_1 \ra \tildeν + l^{\pm}$. Sneutrinos are invisible in $R$-parity conserving supersymmetric models and, if the mass gap $m(χ^{\pm}_1)-m(\tildeν)$ is sufficiently small, the soft decay lepton may escape detection leading to invisible chargino decays. This ``blind spot'' of the supersymmetry parameter space would jeopardize the chargino search at LEP2. We point out that such a scenario can be tested by searching for single $W$ events in $e^+e^- \ra W^+W^-$, w…
The possibility is discussed to observe the sparticle decay modes of the heavy MSSM Higgs bosons at the Large Hadron Collider. We focus on the heavy neutral Higgses, and argue that their decay into neutralinos may access an interesting region in the MSSM parameter space up to masses around 450 GeV for low and intermediate values of tan beta. If neutralinos and sleptons are light enough, this channel - leading to a four lepton final state topology - can complement the reach of the SM channels.
We study the NGS (Non--dissipative Gravitational Singularity) model, which successfully describes the non--linear stage of evolution of perturbations (see [1], [2] and references therein). This model predicts DM density distribution $ρ(r) \sim r^{-α}$ with $α\simeq 1.8$ which holds from very small distances $r_{\rm min} \simeq 0.01~{\rm pc}$ up to very large distances $r_{\rm max} \simeq 5~{\rm Mpc}$. Assuming the neutralino to be a CDM particle, we calculate the annihilation of neutralinos in the vicinity of the singularity (Galactic Center). If neutralinos are the dominant component of DM in…
We study the indirect detection of neutralino dark matter using positrons and gamma rays from its annihilation in the galactic halo. Considering the HESS data as the spectrum constituting the gamma--ray background, we compare the prospects for the experiments GLAST and PAMELA in a general supergravity framework with non--universal scalar and gaugino masses. We show that with a boost factor of about 10, PAMELA will be competitive with GLAST for typical NFW cuspy profiles.
We consider decaying dark matter with masses $10^{7} \lesssim M \lesssim 10^{16}$ GeV, as a source of ultra-high energy (UHE) gamma rays. Using recent limits on UHE gamma-ray flux for energies $E_γ> 2 \cdot 10^{14}$ eV, provided by extensive air shower observatories, we put limits on masses and lifetimes of the dark matter. We also discuss possible dark matter decay origin of tentative 100 PeV photon flux detected with EAS-MSU experiment.
Recently there has been much interest in the use of single-jet mass and jet substructure to identify boosted particles decaying hadronically at the LHC. We develop these ideas to address the challenging case of a neutralino decaying to three quarks in models with baryonic violation of R-parity. These decays have previously been found to be swamped by QCD backgrounds. We demonstrate for the first time that such a decay might be observed directly at the LHC with high significance, by exploiting characteristics of the scales at which its composite jet breaks up into subjets.
We calculate the flux of cosmic gamma rays expected {}from the annihilation of neutralinos in the Galactic halo. Our calculation of the annihilation cross section to two photons improves the existing calculations by inclusion of exact one-loop diagrams for the amplitudes involving Higgs boson and chargino states as well as those involving fermion and sfermion states. A survey of supersymmetric parameter space shows that numerous models would be observable at the $3σ$ level with an air Cerenkov telescope with an exposure of $10^4 \meter^2 \yr$.
We consider a model for neutralino dark matter candidates arising in anomaly-mediated supersymmetry breaking schemes, and examine its testability through the search for exotic cosmic rays produced by neutralino pair annihilations in the dark halo of the Galaxy. We find that the model is already constrained by available antiprotons and positrons measurements and may be further tested in upcoming measurements of these cosmic ray species. We show also that the monochromatic gamma-ray flux from neutralino annihilations is enhanced in this model up to two orders of magnitude with respect to alterna…
We compute the cosmological background radiation of gamma rays and neutrinos due to neutralino annihilation in evolving dark matter halos, assuming the observed dark matter is comprised of thermally excited neutralinos in the MSSM. The spectrum of this gamma-ray background radiation does not show strong annihilation line features, but could amount to a significant fraction of the extragalactic gamma ray continuum flux observed by EGRET above a few GeV. The corresponding cosmological neutrino background is weak compared to the atmospheric foreground. Assuming full mixing, however, the cosmologi…
We discuss how the mass of new physics particles involved in a pair of short decay chains leading to two invisible particles, for example slepton pair production, followed by the decay into two leptons and two neutralinos, may be measured in central exclusive production (CEP) with forward proton tagging. We show how the existing mass measurement strategies in CEP may be improved by making full use of the mass-shell constraints, and demonstrate that, with around 30 signal events, the masses of the slepton and neutralino can be measured with an accuracy of a few GeV.
We consider supersymmetric (SUSY) models wherein the strong CP problem is solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/axino supermultiplet. We examine R-parity conserving models where the neutralino is the lightest SUSY particle, so that a mixture of neutralinos and axions serve as cold dark matter. The mixed axion/neutralino CDM scenario can match the measured dark matter abundance for SUSY models which typically give too low a value of the usual thermal neutralino abundance, such as models with wino-like or higgsino-like dark matter. The usual thermal neutralino abund…
Recently, the Fermi-LAT collaboration reported upper limits on the GeV gamma-ray flux from nearby clusters of galaxies. Motivated by these limits, we study corresponding constraints on gamma-ray emissions from two specific decaying dark matter models, one via grand unification scale suppressed operators and the other via R-parity violating operators. Both can account for the PAMELA and Fermi-LAT excesses of e^\pm. For GUT decaying dark matter, the gamma-rays from the M49 and Fornax clusters, with energy in the range of 1 to 10 GeV, lead to the most stringent constraints to date. As a result, t…
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 $…
A multitude of searches have already been performed by the ATLAS and CMS collaborations at the LHC to probe the heavy Higgses of the Minimal Supersymmetric Standard Model (MSSM) through their decay to the Standard Model particles. In this paper, we study the decay of the MSSM heavy Higgses into neutralino and chargino pairs and estimate the maximum possible branching ratios for these `ino' modes being consistent with the present LHC data. After performing a random scan of the relevant electroweakino parameters, we impose the SM 125 GeV Higgs constraints, low energy flavour data as well as curr…
We analyze the rate of detection of minimal supersymmetric neutralino dark matter in germanium, sapphire and sodium iodide detectors, imposing cosmological and recent accelerator bounds including those from \bsg\ decay. We find, in contrast with several other recent analyses, that although the \bsg\ constraint reduces the number of viable models, models still remain where the counting rate in solid state detectors exceeds 10 kg$^{-1}$ day$^{-1}$.
We discuss on the possibility that colliding dark matter particles in the form of neutralinos may be gravitationally boosted near the super-massive black hole at the galactic center so that they can have enough collision energy to annihilate into a stau pair. Since in some phenomenologically favored supersymmetric models the mass splitting between the neutralino and the lightest stau, one of the two scalar superpartners of the tau lepton, is a few GeVs, this channel may be allowed. In addition, staus can only decay into a tau lepton and another neutralino. We calculate the gamma-ray spectrum a…
The viability of neutralino dark matter as an explanation of the 130 GeV gamma ray signal from the Galactic Center recently observed by the Fermi Large Area Telescope is examined. It is found that the signal can be compatible with a sharp feature from internal bremsstrahlung from a mostly bino dark matter particle of mass around 145 GeV, augmented by a contribution from annihilation into gamma+Z via a small wino admixture. This scenario circumvents the problematic overproduction of lower energy continuum photons that plague line interpretations of this signal. Sleptons approximately degenerate…
Motivated by the interpretation of the recent results on the TeV gamma radiation from the Galactic center, including the new 2004 HESS data, as a by-product of dark matter particles annihilations, we address the question of the largest possible neutralino masses and pair annihilation cross sections in supersymmetric models. Extending the parameter space of minimal models, such as the mSUGRA and the mAMSB scenarios, to general soft SUSY breaking Higgs masses gives access to the largest possible pair annihilation rates, corresponding to resonantly annihilating neutralinos with maximal gaugino-hi…
In light of the recent observation of the Fermi-LAT 130 GeV gamma-ray line, we suggest a model of scalar dark matter in hidden sector, which can decay into two (hidden) photons. The process is radiatively induced by a GUT scale fermion in the loop, which is charged under a hidden sector U(1), and the kinetic mixing ($\sim εF^{μν}F'_{μν}$) enables us to fit the required decay width for the Fermi-LAT peak. The model does not allow any dangerous decay channels into light standard model particles.
A long-lived decaying dark matter as a resolution to Fermi, PAMELA and ATIC anomalies is investigated in the framework of split supersymmetry (SUSY) without R-parity, where the neutralino is regarded as the dark matter and the extreme fine-tuned couplings for the long-lived neutralino are naturally evaded in the usual approach.
Recently reported tentative evidence for a gamma-ray line in the Fermi-LAT data is of great potential interest for identifying the nature of dark matter. We compare the implications for decaying and annihilating dark matter taking the constraints from continuum gamma-rays, antiproton flux and morphology of the excess into account. We find that higgsino and wino dark matter are excluded, also for nonthermal production. Generically, the continuum gamma-ray flux severely constrains annihilating dark matter. Consistency of decaying dark matter with the spatial distribution of the Fermi-LAT excess …
We analyze the recently published Fermi-LAT diffuse gamma-ray measurements in the context of leptonically annihilating or decaying dark matter (DM) with the aim to explain simultaneously the isotropic diffuse gamma-ray and the PAMELA, Fermi and HESS (PFH) anomalous $e^\pm$ data. Five different DM annihilation/decay channels $2e$, $2μ$, $2τ$, $4e$, or $4μ$ (the latter two via an intermediate light particle $ϕ$) are generated with PYTHIA. We calculate both the Galactic and extragalactic prompt and inverse Compton (IC) contributions to the resulting gamma-ray spectra. To find the Galactic IC spec…
We study the inclusive production of the next-to-lightest neutralino chi2, decaying directly, or via slepton, into two leptons and the lightest neutralino. The dilepton invariant mass spectrum in these decays has a characteristic sharp edge near the kinematical upper limit. We propose to exploit this feature as a search strategy for the chi2, and thereby for SUSY. The possibilities to determine neutralinos and slepton masses are also discussed.
High resolution simulations reveal that in the cold dark matter scenario the structures form hierarchically and a large number of substructures survive in the galactic halos. The substructures can be probed if they emit gamma rays via dark matter annihilation. We calculated the gamma ray fluxes from the dark matter annihilations in the substructures of our Galaxy within the frame of the minimal supersymmetric extension of the standard model. The uncertainties of the prediction from both the low energy supersymmetry and especially from the density profiles of dark matter in the substructures ar…
From the relic density measurement by WMAP the WIMP annihilation cross section can be determined in a model independent way. If the WIMPS are postulated to be the neutralinos of Supersymmetry, then only a limited region of the supersymmetric parameter space matches this annihilation cross section. It is shown that the resulting positrons, antiprotons and gamma rays from the neutralino annihilation (mainly into b-bbar quark pairs) provide the correct shape and order of magnitude for the missing gamma and hard positron fluxes in the Galactic Models and are consistent with antiproton production.
We investigate the collider signatures of heavy, long-lived, neutral particles that decay to charged particles plus missing energy. Specifically, we focus on the case of a neutralino NLSP decaying to Z and gravitino within the context of General Gauge Mediation. We show that a combination of searches using the inner detector and the muon spectrometer yields a wide range of potential early LHC discoveries for NLSP lifetimes ranging from 10^(-1)-10^5 mm. We further show that events from Z(l+l-) can be used for detailed kinematic reconstruction, leading to accurate determinations of the neutralin…
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 r…
Recently PAMELA released their first results on the positron and antiproton ratios. Stimulated by the new data, we studied the cosmic ray propagation models and calculated the secondary positron and antiproton spectra. The low energy positron ratio can be consistent with data in the convection propagation model. Above $\sim 10$ GeV PAMELA data shows a clear excess on the positron ratio. However, the secondary antiproton is roughly consistent with data. The positron excess may be a direct evidence of dark matter annihilation or decay. We compare the positron and anti-proton spectra with data by…
Higgs bosons can have a substantial ``invisible'' branching ratio in many extensions of the Standard Model, such as models where the Higgs bosons decay predominantly into light or massless weakly interacting Goldstone bosons. In this work, we examine the production mechanisms and backgrounds for invisibly decaying Higgs bosons at the Next Linear $e^+e^-$ Collider operating in the modes $e^+e^-$, $eγ$, and $γγ$. We demonstrate that such machine is much more efficient to survey for invisibly decaying Higgs bosons than the Large Hadron Collider at CERN.
It is widely believed that dark matter exists within galaxies and clusters of galaxies. Under the assumption that this dark matter is composed of the lightest, stable supersymmetric particle, assumed to be the neutralino, the feasibility of its indirect detection via observations of a diffuse gamma-ray signal due to neutralino annihilations within M31 is examined. To this end, first the dark matter halo of the close spiral galaxy M31 is modeled from observations, then the resultant gamma-ray flux is estimated within supersymmetric model configurations. We conclude that under favorable conditio…
We present a detailed study of the effect of internal bremsstrahlung photons in the context of the minimal supersymmetric standard models and their impact on gamma-ray dark matter annihilation searches. We find that although this effect has to be included for the correct evaluation of fluxes of high energy photons from neutralino annihilation, its contribution is relevant only in models and at energies where the lines contribution is dominant over the secondary photons. Therefore, we find that the most optimistic supersymmetric scenarios for dark matter detection do not change significantly wh…
We investigate the possibility to detect neutralino dark matter in a scenario in which the galactic dark halo is clumpy. We find that under customary assumptions on various astrophysical parameters, the antiproton and continuum gamma-ray signals from neutralino annihilation in the halo put the strongest limits on the clumpiness of a neutralino halo. We argue that indirect detection through neutrinos from the Earth and the Sun should not be much affected by clumpiness. We identify situations in parameter space where the gamma-ray line, positron and diffuse neutrino signals from annihilations in…
We consider the potential benefits of searching for supersymmetric dark-matter through its inelastic excitation, via the "scalar current", of low-lying collective nuclear states in a detector. If such states live long enough so that the gamma radiation from their decay can be separated from the signal due to nuclear recoil, then background can be dramatically reduced. We show how the kinematics of neutralino-nucleus scattering is modified when the nucleus is excited and derive expressions for the form factors associated with exciting collective states. We apply these results to two specific ca…
The lightest neutralino in supersymmetry is the most studied dark matter candidate. This writeup reviews the status of neutralino dark matter in minimal and nonminimal supersymmetric models in light of recent null results at the XENON100 experiment and the observation of a 130 GeV gamma ray signal from the Galactic Center by the Fermi LAT.
We study the complementarity between the indirect detection of dark matter with gamma-rays in H.E.S.S. and the supersymmetry searches with ATLAS at the Large Hadron Collider in the Focus Point region within the mSUGRA framework. The sensitivity of the central telescope of the H.E.S.S. II experiment with an energy threshold of ~ 20 GeV is investigated. We show that the detection of gamma-ray fluxes of O(10^-12) cm-2s-1 with H.E.S.S. II covers a substantial part of the Focus Point region which may be more difficult for LHC experiments. Despite the presence of multi-TeV scalars, we show that LHC …
Decaying axion-like particles (ALP) with masses in the eV range which might occupy dark matter halos of the Milky Way and other galaxies produce a characteristic "bump" feature in the spectrum of extragalactic background light (EBL). This feature leaves an imprint on the gamma-ray spectra of distant extragalactic sources. We derive constraints on the ALP coupling to photons based on analysis of spectra of very-high-energy gamma-ray loud blazars. We combine gamma-ray spectral measurements by Fermi/LAT and Cherenkov telescopes and fit a model in which the intrinsic source spectrum is modified by…
Prospects are examined for the detection of a slow decay of the lightest neutralino (or any other longlived particles) at the CERN LHC and at Very Large Hadron Collider (VLHC). We first point out that such hadron colliders will become the ``neutralino factory'' producing 10^6--10^9 neutralinos/yr, if gluinos and/or squarks actually exist below O(1) TeV. The lightest neutralino (\neu), usually assumed to be stable, will be unstable if lighter superparticles such as the gravitino (\gra) or axino (\axi) exist, or R-parity is not conserved. The decay signal would, however, be missed in usual colli…
A successful implementation of thermal leptogenesis requires the re-heat temperature after inflation T_R to exceed ~2\times 10^9 GeV. Such a high T_R value typically leads to an overproduction of gravitinos in the early universe, which will cause conflicts, mainly with BBN constraints. Asaka and Yanagida (AY) have proposed that these two issues can be reconciled in the context of the Peccei-Quinn augmented MSSM (PQMSSM) if one adopts a mass hierarchy m(sparticle)>m(gravitino)>m(axino), with m(axino) keV. We calculate the relic abundance of mixed axion/axino dark matter in the AY scenario, and …
While the excess in cosmic-ray electrons and positrons reported by PAMELA and Fermi may be explained by dark matter decaying primarily into charged leptons, this does not necessarily mean that dark matter should not have any hadronic decay modes. In order to quantify the allowed hadronic activities, we derive constraints on the decay rates of dark matter into WW, ZZ, hh, qqbar and gg using the Fermi and HESS gamma-ray data. We also derive gamma-ray constraints on the leptonic e+e-, mu+mu- and tau+tau- final states. We find that dark matter must decay primarily into mu+mu- or tau+tau- in order …
If interpreted in terms of decaying dark matter, the steep rise in the positron fraction of cosmic rays above 10 GeV, as observed by the PAMELA experiment, suggests an underlying production mechanism that favors leptonic channels. We consider a scenario where a portion of the dark matter is made of the gauginos of an unbroken hidden-sector U(1), which interact with the visible sector only through a tiny kinetic mixing. The second component of the dark matter is made of neutralinos, and depending on the mass spectrum, the lightest neutralino or the hidden gaugino becomes unstable and subject to…
We examine the neutralino dark matter phenomenology in supersymmetric scenarios with nonuniversal Higgs masses at the gauge coupling unification scale that can acommodate a light Higgs boson, where the correct relic density is obtained mostly through the annihilation into a pseudoscalar A. Our analysis shows that most part of the A pole region can produce detectable gamma-ray and antiproton signals. We further focus on uncertainties influencing the results in indirect and mainly direct detection.
We use high resolution numerical simulations of the formation of cold dark matter halos to simulate the background of decay products from neutralino annihilation, such as gamma-rays or neutrinos. Halos are non-spherical, have steep singular density profiles and contain many thousands of surviving dark matter substructure clumps. This leads to several unique signatures in the gamma-ray background that may be confirmed or rejected by the next generation of gamma-ray experiments. Most importantly, the diffuse background is enhanced by over two orders of magnitude due to annihilation within substr…
We explore and contrast the single-photon and diphoton signals expected at LEP 2, that arise from neutralino-gravitino (e^+ e^- -> chi + gravitino -> gamma + E_miss) and neutralino-neutralino (e^+ e^- -> chi + chi -> gamma + gamma + E_miss) production in supersymmetric models with a light gravitino. LEP 1 limits imply that one may observe either one, but not both, of these signals at LEP 2, depending on the values of the neutralino and gravitino masses: single-photons for m_chi > Mz and m_gravitino < 3 x 10^-5 eV; diphotons for m_chi < Mz and all allowed values of m_gravitino.
Recent advances in N-body simulations of cold dark matter halos point to a substantial density enhancement near the center. This means that, e.g., the $γ$ ray signals from neutralino dark matter annihilations would be significantly enhanced compared to old estimates based on an isothermal sphere model with large core radius. Another important development concerns new detectors, both space- and ground-based, which will cover the window between 50 and 300 GeV where presently no cosmic $γ$-ray data are available. Thirdly, new calculations of the $γ$-ray line signal (a sharp spike of $10^{-3}$ rel…
Recent theoretical developments have shown that gauge mediation has a much larger parameter space of possible spectra and mixings than previously considered. Motivated by this, we explore the collider phenomenology of gauge mediation models where a general neutralino is the lightest MSSM superpartner (the NLSP), focusing on the potential reach from existing and future Tevatron searches. Promptly decaying general neutralino NLSPs can give rise to final states involving missing energy plus photons, Zs, Ws and/or Higgses. We survey the final states and determine those where the Tevatron should ha…
We consider cosmological consequences of a heavy axino, decaying to the neutralino in R-parity conserving models. The importance and influence of the axino decay on the resultant abundance of neutralino dark matter depends on the lifetime and the energy density of axino. For a high reheating temperature after inflation, copiously produced axinos dominate the energy density of the universe and its decay produces a large amount of entropy. As a bonus, we obtain that the upper bound on the reheating temperature after inflation via gravitino decay can be moderated, because the entropy production b…
