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 by the axino decay more or less dilutes the gravitinos.
The existence of dark matter provides strong evidence for physics beyond the Standard Model. Extending the Standard Model with the Peccei-Quinn symmetry and/or supersymmetry, compelling dark matter candidates appear. For the axion, the neutralino, the gravitino, and the axino, I review primordial production mechanisms, cosmological and astrophysical constraints, experimental searches, and prospects for experimental identification.
In supersymmetric extensions of the Standard Model, the lightest neutralino, the gravitino, and the axino can appear as the lightest supersymmetric particle and as such provide a compelling explanation of the non-baryonic dark matter in our Universe. For each of these dark matter candidates, I review the present status of primordial production mechanisms, cosmological constraints, and prospects of experimental identification.
Supersymmetric extensions of the Standard Model that incorporate the axion solution to the strong CP problem necessarily contain also the axino, the fermionic partner of the axion. In contrast to the neutralino and the gravitino, the axino mass is generically not of the order of the supersymmetry-breaking scale and can be much smaller. The axino is therefore an intriguing candidate for a stable superpartner. In a previous Letter [1] it was shown that axinos are a natural candidate for cold dark matter in the Universe when they are generated non-thermally through out-of-equilibrium neutralino d…
Supersymmetric extensions of the Standard Model when combined with the Peccei-Quinn solution to the strong CP problem necessarily contain also the axino, the fermionic partner of the axion. In contrast to the neutralino and the gravitino, the axino mass is generically not of the order of the supersymmetry breaking scale and can be much smaller. The axino is therefore an intriguing candidate for a stable superpartner. The axinos are a natural candidate for cold dark matter in the Universe when they are generated non-thermally through out-of-equilibrium neutralino decays or via a competing therm…
The addition of the QCD axion to the Minimal Supersymmetric Standard Model (MSSM) not only solves the strong CP problem but also modifies the dark sector with new dark matter candidates. While SUSY axion phenomenology is usually restricted to searches for the axion itself or searches for the ordinary SUSY particles, this work focuses on scenarios where the axion's superpartner, the axino, may be detectable at the Large Hadron Collider (LHC) in the decays of neutralinos displaced from the primary vertex. In particular, we focus on the KSVZ axino within the hadronic axion window. The decay lengt…
We show that axinos produced in the early Universe in the decay of the lightest neutralinos are a natural candidate for cold dark matter. We argue that axinos may well provide the main component of the missing mass in the Universe because their relic density is often comparable with the critical density.
Over almost all of minimal supergravity (mSUGRA or CMSSM) model parameter space, there is a large overabundance of neutralino cold dark matter (CDM). We find that the allowed regions of mSUGRA parameter space which match the measured abundance of CDM in the universe are highly fine-tuned. If instead we invoke the Peccei-Quinn-Weinberg-Wilczek solution to the strong CP problem, then the SUSY CDM may consist of an axion/axino admixture with an axino mass of order the MeV scale, and where mixed axion/axino or mainly axion CDM seems preferred. In this case, fine-tuning of the relic density is typi…
There exist several well-motivated candidates for non-baryonic cold dark matter, including neutralinos, axions, axinos, gravitinos, Wimpzillas. I review the dark matter properties of the neutralino and the current status of its detection. I also discuss the axino as a new interesting alternative.
We investigate the detectability of axino-like particle, which is defined as a supersymmetric partner of axion-like particle and can be a good candidate for dark matter in our Universe. Especially, we consider the fixed target experiments to search for the light axino-like particle with a neutralino as the next-to-lightest supersymmetric particle. We calculate the production and decay rate of neutralinos and the consequent number of events (such as photons and charged leptons) that are produced when the neutralinos decay to the axino-like particles.
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…
We study the cosmological impact of the supersymmetric DFSZ axion model. Extending recent works, we first provide a comprehensive analysis of thermal production of the DFSZ axino considering all the possible scattering, decay and inverse decay processes depending on various mass parameters and the reheat temperature. Although it is hard for the DFSZ axino to be in thermal equilibrium, its coupling is still large enough to generate huge axino population which can turn into overabundant neutralino density. We examine the neutralino parameter space to identify the dark matter property depending o…
If the axino is the lightest superpartner and satisfies cosmological bounds, including a preferred range of the relic abundance of cold dark matter, then the usual stringent constraints on the parameter space of the CMSSM become greatly relaxed. The lightest superpartner of the usual CMSSM spectrum will appear to be stable in collider experiments but will not necessarily obey relic abundance constraints. It may be either neutral (lightest neutralino) or charged (typically a stau). With the axino as cold dark matter, large regions of the CMSSM, often corresponding to heavy superpartners, become…
We examine some conditions which are needed to allow the Peccei-Quinn scale (f_a) as high as the SUSY GUT scale (M_{GUT} \sim 10^{16} GeV) in the context of the PQMSSM with either an axino or a neutralino LSP. The main problem in non-SUSY models with f_a\sim M_{GUT} is the generation of an overabundance of axion dark matter (\sim f_a^{7/6}) due to vacuum misalignment. We show that once all the components of the axion supermultiplet are included, the upper limit on f_a can be evaded due to large entropy injection from saxion decays. This large entropy injection also dilutes all other quasi-stab…
We calculate the relic abundance of thermally produced neutralino cold dark matter in the general 19 parameter supergravity (SUGRA-19) model. A scan over GUT scale parameters reveals that models with a bino-like neutralino typically give rise to a dark matter density Ω_{\tz_1}h^2\sim 1-1000, i.e. between 1 and 4 orders of magnitude higher than the measured value. Models with higgsino or wino cold dark matter can yield the correct relic density, but mainly for neutralino masses around 700-1300 GeV. Models with mixed bino-wino or bino-higgsino CDM, or models with dominant co-annihilation or A-re…
We calculate the relic abundance of mixed axion/neutralino cold dark matter which arises in R-parity conserving supersymmetric (SUSY) models wherein the strong CP problem is solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/saxion/axino supermultiplet. By numerically solving the coupled Boltzmann equations, we include the combined effects of 1. thermal axino production with cascade decays to a neutralino LSP, 2. thermal saxion production and production via coherent oscillations along with cascade decays and entropy injection, 3. thermal neutralino production and re-annihilati…
The axino dark matter hypothesis in RSII brane model is studied. Within the framework of CMSSM we assume that the lightest neutralino or stau is the NLSP, and that the axino production has a single contribution from the NLSP decay. It is found that the axino can play the role of dark matter in the universe and we determine what the axino mass should be for different values of the five-dimensional Planck mass. An upper bound is obtained for the latter
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 …
Supersymmetric models based on anomaly-mediated SUSY breaking (AMSB) generally give rise to a neutral wino as a WIMP cold dark matter (CDM) candidate, whose thermal abundance is well below measured values. Here, we investigate four scenarios to reconcile AMSB dark matter with the measured abundance: 1. non-thermal wino production due to decays of scalar fields ({\it e.g} moduli), 2. non-thermal wino production due to decays of gravitinos, 3. non-thermal wino production due to heavy axino decays, and 4. the case of an axino LSP, where the bulk of CDM is made up of axions and thermally produced …
We examine mixed axion/neutralino cold dark matter production in the SUSY DFSZ axion model where an axion superfield couples to Higgs superfields. We calculate a wide array of axino and saxion decay modes along with their decay temperatures, and thermal and non-thermal production rates. For a SUSY benchmark model with a standard underabundance (SUA) of Higgsino-like dark matter (DM), we find for the PQ scale f_a< 10^{12} GeV that the DM abundance is mainly comprised of axions as the saxion/axino decay occurs before the standard neutralino freeze-out and thus its abundance remains suppressed. F…
We examine dark matter production rates in supersymmetric axion models typified by the mass hierarchy m_gravitino << m_neutralino << m_axino. In such models, one expects the dark matter to be composed of an axion/gravitino admixture. After presenting motivation for how such a mass hierarchy might arise, we examine dark matter production in the SUSY Kim-Shifman-Vainshtein-Zakharov (KSVZ) model, the SUSY Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) model and a hybrid model containing contributions from both KSVZ and DFSZ. Gravitinos can be produced thermally and also non-thermally from axino, saxio…
SUSY models with a modified dark sector require constraints to be reinterpreted, which may allow for scenarios with low tuning. A modified dark sector can also change the phenomenology greatly. The addition of the QCD axion to the Minimal Supersymmetric Standard Model (MSSM) solves the strong CP problem and also modifies the dark sector with new dark matter candidates. While SUSY axion phenomenology is usually restricted to searches for the axion itself or searches for the ordinary SUSY particles, this work focuses on scenarios where the axion's superpartner, the axino may be detectable at the…
We examine the minimal supergravity (mSUGRA) model under the assumption that the strong CP problem is solved by the Peccei-Quinn mechanism. In this case, the relic dark matter (DM) abundance consists of three components: {\it i}). cold axions, {\it ii}). warm axinos from neutralino decay, and {\it iii}). cold or warm thermally produced axinos. To sustain a high enough re-heat temperature (T_R\agt 10^6 GeV) for many baryogenesis mechanisms to function, we find that the bulk of DM should consist of cold axions, while the admixture of cold and warm axinos should be rather slight, with a very ligh…
Successful implementation of thermal leptogenesis requires re-heat temperatures T_R\agt 2\times 10^9 GeV, in apparent conflict with SUSY models with TeV-scale gravitinos, which require much lower T_R in order to avoid Big Bang Nucleosynthesis (BBN) constraints. We show that mixed axion/axino dark matter can reconcile thermal leptogenesis with the gravitino problem in models with m_{\tG}\agt 30 TeV, a rather high Peccei-Quinn breaking scale and an initial mis-alignment angle θ_i < 1. We calculate axion and axino dark matter production from four sources, and impose BBN constraints on long-lived …
Axion/axino dark matter (DM) is explored in the minimal supergravity (mSUGRA) and Yukawa-unified supersymmetric grand-unified theory (SUSY GUT) models with surprising results. For this type of scenario, relic DM abundance has three components: {\it i}.) cold axions, {\it ii.}) warm axinos from neutralino decay, and {\it iii.}) cold or warm thermally produced axinos. Reheat temperatures $T_R$ exceeding $10^6$ GeV are required in order to solve the gravitino/Big Bang Nucleosynthesis (BBN) problem while also allowing for baryogensis via non-thermal leptogenesis. In order to attain high enough reh…
Gravity-mediated SUSY breaking models with R-parity conservation give rise to dark matter in the universe. I review neutralino dark matter in the minimal supergravity model (mSUGRA), models with non-universal soft SUSY breaking terms (NUSUGRA) which yield a well-tempered neutralino, and models with unified Yukawa couplings at the GUT scale (as may occur in an SO(10) SUSY GUT theory). These latter models have difficulty accommodating neutralino dark matter, but work very well if the dark matter particles are axions and axinos.
Gravitinos and axinos produced in the late decays of other supersymmetric particles are well-motivated dark matter (DM) candidates, whose experimental evidences are very distinctive and different from other standard candidates, as thermal produced neutralinos in similar supersymmetric models. In particular, charged sleptons could appear stable because of the length of its lifetime. The direct production of such particles at both the Large Hadron Collider (LHC) and a future International Linear Collider (ILC) can give not only a clear signature of supersymmetry but also the first non-gravitatio…
The identification of dark matter in our particle physics model is still a very open question. Here we will argue that axinos can be successful dark matter candidates in models with supersymmetry and the axion solution of the strong CP problem. Axinos can be the lightest supersymmetric particle (LSP), or can be heavier than the LSP. Axinos can be produced in the right abundance by thermal scatterings and if they are the LSP also by out of equilibrium decays of the lightest superpartner of SM fields (LSPSMs). On the other hand heavier (not LSP) axinos can generate a part of the neutralino LSP d…
Supersymmetric models with t-b-τYukawa unification at M_{GUT} qualitatively predict a sparticle mass spectrum including first and second generation scalars at the 3--15 TeV scale, third generation scalars at the (few) TeV scale and gluinos in the sub-TeV range. The neutralino relic density in these models typically turns out to lie far above the measured dark matter abundance, prompting the suggestion that instead dark matter is composed of an axion/axino mixture. We explore the axion and thermal and non-thermal axino dark matter abundance in Yukawa-unified SUSY models. We find in this scenari…
A TeV scale decaying dark matter chiral multiplet N is introduced in addition to the minimal supersymmetric standard model(MSSM). For a calculable abundance of N, we introduce heavy axino decaying to N and MSSM particles including the lightest supersymmetric particle(LSP). In the scenario that heavy axino, once dominating the energy density of the universe, decays after the LSP decouples, it is possible to estimate the relative cosmic abundances of N and the LSP. Dimension 6 interactions allow the lifetime of the fermionic or the bosonic superpartner of N in the 10^{27} s range to be compatibl…
An unidentified 3.5 keV line from X-ray observations of galaxy clusters has been reported recently. Although still under scrutiny, decaying dark matter could be responsible for this signal. We investigate whether an axino with a mass of 7 keV could explain the line, keeping the discussion as model independent as possible. We point out several obstacles, which were overlooked in the literature, and which make the axino an unlikely candidate. The only viable scenario predicts a light metastable neutralino, with a mass between 0.1 and 10 GeV and a lifetime between $10^{-3}$ and $10^4$ s.
The Kim-Nilles mechanism relates the $μ$ term with the axion scale $f_a$, leading to the axino-Higgsino-Higgs Yukawa coupling of order $μ/f_a$. This can bring a dangerous thermal production of axinos. If the axino is stable, its mass has to be as small as ${\cal O}$(0.1keV), or the reheat temperature should be lower than ${\cal O}$(10GeV) taking the lower axion scale $10^{10}$ GeV in order not to overclose the Universe. If the axino decays to a neutralino, the overproduced neutralinos can re-annihilate appropriately to saturate the observed dark matter density if the annihilation rate is of or…
Weak scale supersymmetry is a highly motivated extension of the Standard Model that has a strong degree of support from data. It provides several viable dark matter candidates: the lightest neutralino (a WIMP), the gravitino, and the axion/axino supermultiplet. The LHC turn-on is imminent. The discovery of supersymmetry at the LHC will go a long way towards establishing the nature of dark matter. I present arguments why mainly axion cold dark matter is a better fit for supersymmetric models than neutralinos. I also argue that Yukawa-unified SUSY GUT theories based on SO(10) with mixed axion/ax…
We study the neutralino radiative decay into the lightest supersymmetric particle (LSP) in the framework of a minimal anomalous U(1)' extension of the MSSM. It turns out that in a suitable decoupling limit the axino, which is present in the Stückelberg multiplet, is the LSP. We compute the branching ratio (BR) for the decay of a neutralino into an axino and a photon. We find that in a wide region of the parameter space, the BR is higher than 93% in contrast with the typical value (<=1%) in the CMSSM.
We consider axino dark matter in large R-parity violation (RPV). In moduli-dominated universe, axino is produced thermally or non-thermally via saxion decay, then late-decaying moduli dilute axino density, which results in the right abundance to explain the present dark matter. At the same time baryon asymmetry is generated due to moduli-induced baryogenesis via the large RPV. Axino is cosmologically stable in spite of the large RPV since its decay rate is suppressed by the axion decay constant, heavy squark mass or kinematics.
Recent analyses of WMAP9 data show that dark radiation-- parametrized by the apparent number of additional neutrinos ΔN_{eff} contributing to the cosmic expansion-- is consistent with the Standard Model and bounded from above by about ΔN_{eff} ~< 0.5 at 95% CL. We consider the mixed axion/neutralino cold dark matter scenario which arises in R-parity conserving supersymmetric (SUSY) models wherein the strong CP problem is solved by hadronic axions with a concommitant axion(a)/saxion(s)/axino(\ta) supermultiplet. Our new results include improved calculations of thermal axion and saxion productio…
Heavy-neutrino (or neutralino) stars are studied using the general relativistic equations of hydrostatic equilibrium and the relativistic equation of state for degenerate fermionic matter. The Tolman-Oppenheimer-Volkoff equations are then generalized to include a system of degenerate neutrino and neutralino matter that is gravitationally coupled. The properties and implications of such an interacting astrophysical system are discussed in detail.
Salient aspects of the meeting are summarized, including our knowledge of dark matter at different cosmological and astrophysical distance scales, ranging from large-scale structure to the cores of galaxies, and our speculations on particle candidates for dark matter, including neutrinos, neutralinos, axinos, gravitinos and cryptons. Comments are also made on prospects for detecting dark matter particles and on the dark energy problem.
We present an overview of supersymmetry searches, both at collider experiments and via searches for dark matter (DM). We focus on three DM possibilities in the SUSY context: the thermally produced neutralino, a mixture of axion and axino, and the gravitino, and compare and contrast signals that may be expected at colliders, in direct detection (DD) experiments searching of DM relics left over from the Big Bang, and indirect detection (ID) experiments designed to detect the products of DM annihilations within the solar interior or galactic halo. Detection of DM particles using multiple strategi…
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.
The supersymmetrized DFSZ axion model is highly motivated not only because it offers solutions to both the gauge hierarchy and strong CP problems, but also because it provides a solution to the SUSY mu problem which naturally allows for a Little Hierarchy. We compute the expected mixed axion-neutralino dark matter abundance for the SUSY DFSZ axion model in two benchmark cases-- a natural SUSY model with a standard neutralino underabundance (SUA) and an mSUGRA/CMSSM model with a standard overabundance (SOA). Our computation implements coupled Boltzmann equations which track the radiation densit…
We have studied the detection of long-lived staus at the IceCube neutrino telescope, after their production inside the Earth through the inelastic scattering of high energy neutrinos. The theoretical predictions for the stau flux are calculated in two scenarios in which the presence of long-lived staus is naturally associated to viable supersymmetric dark matter. Namely, we consider the cases with superWIMP (gravitino or axino) and neutralino dark matter (along the coannihilation region). In both scenarios the maximum value of the stau flux turns out to be about 1 event/yr in regions with a li…
If one simultaneously invokes the SUSY solution to the gauge hierarchy problem and the PQ solution to the strong CP problem, then one might expect mixed axion/neutralino dark matter (DM), i.e. two dark matter particles. In this case, dark matter production involves oscillation production of axions, thermal and non-thermal neutralino production and thermal and non-thermal production of axinos and saxions. The latter particles may feed additional neutralinos into the cosmic soup, or dilute all relics via additional entropy production, or feed dark radiation into the cosmos. Depending on the SUSY…
Bridging the divide: axion searches and axino phenomenology at colliders
University of Chicago（芝加哥大学）；Enrico Fermi Institute, University of Chicago（恩里科·费米研究所，芝加哥大学）；Kavli Institute for Cosmological Physics, University of Chicago（卡弗里宇宙物理学研究所，芝加哥大学）；Leinweber Institute for Theoretical Physics, University of Chicago（莱因韦伯理论物理研究所，芝加哥大学）；Kavli Institute for Physics and Mathematics of the Universe (WPI)（宇宙物理与数学卡弗里研究所（WPI））；The University of Tokyo Institutes for Advanced Study（东京大学高等研究院）；The University of Tokyo（东京大学）
A new scheme for lightest supersymmetric particle (LSP) dark matter is introduced and studied in theories of TeV supersymmetry with a QCD axion, $a$, and a high reheat temperature after inflation, $T_R$. A large overproduction of axinos ($\tilde{a}$) and gravitinos ($\tilde{G}$) from scattering at $T_R$, and from freeze-in at the TeV scale, is diluted by the late decay of a saxion condensate that arises from inflation. The two lightest superpartners are $\tilde{a}$, with mass of order the TeV scale, and $\tilde{G}$ with mass $m_{3/2}$ anywhere between the keV and TeV scales, depending on the m…
We review the main proposals of particle physics for the composition of the cold dark matter in the universe. Strong axion contribution to cold dark matter is not favored if the Peccei-Quinn field emerges with non-zero value at the end of inflation and the inflationary scale is superheavy since, under these circumstances, it leads to unacceptably large isocurvature perturbations. The lightest neutralino is the most popular candidate constituent of cold dark matter. Its relic abundance in the constrained minimal supersymmetric standard model can be reduced to acceptable values by pole annihilat…
We propose a new scenario of non-thermal production of neutralino cold dark matter, in which the overproduction problem of lightest supersymmetric particles (LSPs) in the standard thermal history is naturally solved. The mechanism requires a heavy modulus field which decays mainly to ordinary particles releasing large entropy to dilute gravitinos produced just after inflation and thermal relics of LSPs. Significant amount of gravitinos are also pair-produced at the decay, which subsequently decay into the neutralinos. We identify the regions of the parameter space in which the requisite abunda…
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 analy…
What is the upper limit of the mass of the neutralino dark matter whose thermal relic is consistent with the observation? If the neutralino dark matter and colored sparticles are extremely degenerated in mass, with a mass difference less than the QCD scale, the dark matter annihilation is significantly increased and enjoys the "second freeze-out" after the QCD phase transition. In this case, the neutralino dark matter with a mass much greater than 100 TeV can realize the correct dark matter abundance. We study the dark matter abundance and its detection in the case of such highly degenerated m…
I present an overview of theoretical expectations for detection of dark matter (DM) at the LHC, concentrating entirely on supersymmetric candidates. En route, I present a unified theory which explains dark matter signals at indirect and direct detection experiments. While direct DM detection is likely impossible at LHC, detection of SUSY matter states is robust, where LHC with \sqrt{s}=7 TeV and 1fb^{-1} can access m(gluino) 1 TeV for m(squark) m(gluino), and m(gluino) 640 GeV for m(squark)>> m(gluino). Models with well-tempered neutralinos will soon be tested by Xenon-100/LUX, and should prov…
We propose a complete R-parity violating supersymmetric model with baryon triality that contains a Dine-Fischler-Srednicki-Zhitnitsky axion chiral superfield. We parametrize supersymmetry breaking with soft terms, and determine under which conditions the model is cosmologically viable. As expected we always find a region of parameter space in which the axion is a cold dark matter candidate. The mass of the axino, the fermionic partner of the axion, is controlled by a Yukawa coupling. When heavy [${\mathcal O}$(TeV)], the axino decays early and poses no cosmological problems. When light [$\math…
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…
The lightest neutralino is a viable dark matter (DM) candidate. In this paper we study indirect detection of the wino-like neutralino DM using positrons and antiprotons from the annihilation in the galactic halo. When the mass is around 2 TeV, which is favored from the thermal relic abundance, the non-perturbation effect significantly enhances the annihilation cross sections into positrons and antiprotons. We find that the positron and antiproton fluxes with energies larger than 100 GeV may become larger than the expected backgrounds. Since the positron flux is less sensitive to the astrophysi…
We present a detailed discussion of Sommerfeld enhancements in neutralino dark matter relic abundance calculations for several popular benchmark scenarios in the general MSSM. Our analysis is focused on models with heavy wino- and higgsino-like neutralino LSP and models interpolating between these two scenarios. This work is the first phenomenological application of effective field theory methods that we have developed in earlier work and that allow for the consistent study of Sommerfeld enhancements in non-relativistic neutralino and chargino co-annihilation reactions within the general MSSM,…
Generic extensions of the Standard Model that respect baryon and lepton numbers have accidentally stable particles. Typical examples are the lightest exotic neutral fermion, or "neutralino", and fields with non-trivial lepton and baryon charges. In this paper we show that an accidentally stable neutralino is a natural dark matter candidate in models with warped extra dimensions. We find that annihilation into other Kaluza-Klein resonances is often allowed and very efficient. The observed dark matter abundance may then be obtained with couplings of order unity and a compactification scale above…
We evaluate the relic density of the lightest neutralino, the lightest supersymmetric particle, in the Minimal Supersymmetric extension of the Standard Model (MSSM). 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 higgsi…
We investigate the correlated predictions of singlet extended MSSM models for direct detection of the lightest neutralino with its cosmological relic density. To illustrate the general effects of the singlet, we take heavy sleptons and squarks. We apply LEP, $(g-2)_μ$ and perturbativity constraints. We find that the WMAP upper bound on the cold dark matter density limits much of the parameter space to regions where the lightest neutralino can be discovered in recoil experiments. The results for the NMSSM and UMSSM are typically similar to the MSSM since their light neutralinos have similar com…
Within the minimal supergravity model (mSUGRA) framework, the expectation for the relic density of neutralinos exceeds the WMAP determination unless neutralinos a) have a significant higgsino component, b) have a mass close to half that of a heavy Higgs boson, or c)can efficiently co-annihilate with a charged or colored particle. Within a 1-parameter extension of the mSUGRA model which includes non-universal Higgs masses, we show that agreement with the WMAP data can be obtained over a wide range of mSUGRA parameters for scenarios a) and b), so that the phenomenological implications may be muc…
