Neutralino Relic Abundance Research Articles

Supersymmetric explanation of the muon g – 2 anomaly with and without stable neutralino

In this paper we explore the possibility of explaining the muon g − 2 anomaly in various types of supersymmetric extensions of the Standard Model. In particular, we investigate and compare the phenomenological constraints in the MSSM with stable neutralino and the other types of scenarios where the neutralino is unstable. For the latter case we study the Gauge Mediated SUSY Breaking (GMSB) scenario with very light gravitino and the UDD-type R-Parity Violating (RPV) scenario. In the MSSM with stable neutralino, the parameter region favoured by the (g − 2)μ is strongly constrained by the neutralino relic abundance and the dark matter direct detection experiments, as well as by the LHC searches in the lepton plus missing transverse energy channel. On the other hand, the scenarios without stable neutralino are free from the dark matter constraints, while the LHC constraints depends strongly on the decay of the neutralino. We find that in GMSB the entire parameter region favoured by the muon g − 2 is already excluded if the Next Lightest SUSY Particle (NLSP) is the neutralino. In the GMSB scenario with a stau NSLP and in the RPV scenario, LHC constraints are weaker than the stable neutralino case and a larger region of parameter space is available to fit the (g − 2)μ anomaly.

Detecting underabundant neutralinos

The electroweak sector may play a crucial role in discovering supersymmetry. We systematically investigate the patterns of the MSSM-like electroweakinos, when the neutralino relic abundance $\Omega_\chi h^2\leq 0.12$, that is, also admitting for multi-component Dark Matter, in a broad range of the parameter space. We find that for a very large range of parameters the Direct Detection experiments are/will be sensitive to underabundant neutralinos, in spite of the strong rescaling of the flux factor. The second general conclusion is that the bound $\Omega_\chi h^2\leq 0.12$ together with the LUX (XENON1T) limits for the neutralino spin independent scattering cross sections constrain the electroweakino spectrum so that the mass differences between the NLSP and the LSP are smaller than 40 (10) GeV, respectively, with important implications for the collider searches. The future Direct Detection experiments and the high luminosity LHC run will probe almost the entire range of the LSP and NLSP mass spectrum that is consistent with the bound $\Omega_\chi h^2\leq 0.12$.

Heavy neutralino relic abundance with Sommerfeld enhancements — a study of pMSSM scenarios

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, away from the pure-wino and pure-higgsino limits.

Constrained minimal supersymmetric standard model with generalized Yukawa quasiunification

We analyze the constrained minimal supersymmetric standard model with mu>0 supplemented by a generalized `asymptotic' Yukawa coupling quasi-unification condition, which allows an acceptable b-quark mass. We impose constraints from the cold dark matter abundance in the universe, B physics, and the mass of the lightest neutral CP-even Higgs boson. We find that, in contrast to previous results obtained for a more restrictive Yukawa quasi-unification condition, the lightest neutralino can act as a cold dark matter candidate in a relatively wide parameter range. In this range, the lightest neutralino relic abundance is drastically reduced mainly by stau-antistau coannihilations and, thus, the upper bound on this abundance from cold dark matter considerations becomes compatible with the recent data on the branching ratio of B_s --> mu^+mu^-. Also, masses for the lightest neutral CP-even Higgs boson about (125-126) GeV, favored by LHC, can be easily accommodated. The mass of the lightest neutralino, though, comes out large (~1 TeV).

Dark Matter and Higgs Mass in the CMSSM with Yukawa Quasi-Unification

We present an updated analysis of the constrained minimal supersymmetric standard model with μ > 0 supplemented by an 'asymptotic' Yukawa coupling quasi-unification condition, which allows an acceptable b-quark mass. Imposing constraints from the cold dark matter abundance in the universe, B physics, the muon anomalous magnetic moment, and the mass mh of the lightest neutral CP-even Higgs boson, we find that the lightest neutralino cannot act as a cold dark matter candidate. This is mainly because the upper bound on the lightest neutralino relic abundance from cold dark matter considerations, despite the fact that this abundance is drastically reduced by neutralino-stau coannihilations, is incompatible with the recent data on the branching ratio of Bs → μ+μ−. Allowing for a different particle, such as the axino or the gravitino, to be the lightest supersymmetric particle and, thus, constitute the cold dark matter in the universe, we find that the predicted mh's in our model favor the range (119 – 126) GeV.

Hidden SUSY at the LHC: the light higgsino-world scenario and the role of a lepton collider

While the SUSY flavor, CP and gravitino problems seem to favor a very heavy spectrum of matter scalars, fine-tuning in the electroweak sector prefers low values of superpotential mass \mu. In the limit of low \mu, the two lightest neutralinos and light chargino are higgsino-like. The light charginos and neutralinos may have large production cross sections at LHC, but since they are nearly mass degenerate, there is only small energy release in three-body sparticle decays. Possible dilepton and trilepton signatures are difficult to observe after mild cuts due to the very soft p_T spectrum of the final state isolated leptons. Thus, the higgsino-world scenario can easily elude standard SUSY searches at the LHC. It should motivate experimental searches to focus on dimuon and trimuon production at the very lowest p_T(\mu) values possible. If the neutralino relic abundance is enhanced via non-standard cosmological dark matter production, then there exist excellent prospects for direct or indirect detection of higgsino-like WIMPs. While the higgsino-world scenario may easily hide from LHC SUSY searches, a linear e^+e^- collider or a muon collider operating in the \sqrt{s}\sim 0.5-1 TeV range would be able to easily access the chargino and neutralino pair production reactions.

Muons from neutralino annihilations in the Sun: Flipped SU(5)

We consider two classes of supersymmetric flipped SU(5) models with gravity mediated supersymmetry breaking such that the thermal neutralino relic abundance provides the observed dark matter density in the universe. We estimate the muon flux induced by neutrinos that arise from neutralino annihilations in the Sun and discuss prospects for detecting this flux in the IceCube/Deep Core experiment. We also provide comparisons with the corresponding fluxes in the constrained minimal supersymmetric and nonuniversal Higgs models. Regions in the parameter space that can be explored by the IceCube/DeepCore experiment are identified.

Reconciling thermal leptogenesis with the gravitino problem in SUSY models with mixed axion/axino dark matter

Successful implementation of thermal leptogenesis requires re-heattemperatures TR≳2 × 109 GeV, in apparent conflict with SUSY models with TeV-scale gravitinos, which require much lower TR 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 mG̃≳30 TeV, a rather high Peccei-Quinn breaking scaleand an initial mis-alignment angle θi < 1.We calculate axion and axino dark matter production from four sources, and impose BBN constraints on long-lived gravitinos and neutralinos.Moreover, we discuss several SUSY models which naturally have gravitino masses of the order of tens of TeV.We find a reconciliation difficult in Yukawa-unified SUSY and in AMSB with a wino-like lightest neutralino. However, TR ∼ 1010−1012 GeV can easily be achieved in effective SUSY and in models based on mixed moduli-anomaly mediation. Consequences of this scenario include: 1. an LHC SUSY discovery should be consistentwith SUSY models with a large gravitino mass,2. an apparent neutralino relic abundance ΩZ̃1h2≲1,3. no WIMP direct or indirect detection signals should be found, and 4. the axion mass should be less than ∼ 10−6 eV, somewhat below the conventional range which is explored by microwave cavity axion detection experiments.

Impact of a strongly first-order phase transition on the abundance of thermal relics

We study the impact of a strongly first-order electroweak phase transition on the thermal relic abundance of particle species that could constitute the dark matter and that decoupled before the phase transition occurred. We define a dilution factor induced by generic first-order phase transitions, and we explore the parameter space of the minimal supersymmetric extension to the standard model to determine which phase transition temperatures and dilution factors are relevant for the lightest neutralino as a dark matter candidate. We then focus on a specific toy-model setup that could give rise to a strongly first-order electroweak phase transition, and proceed to a detailed calculation of dilution factors and transition temperatures, comparing our findings to actual neutralino dark matter models. Typical models that would produce an excessive thermal relic density and that can be salvaged postulating a strongly first-order electroweak phase transition include massive (multi-TeV) wino or Higgsino-like neutralinos, as well as binolike neutralinos in a wider mass range, with masses as low as 400 GeV. If LHC data indicate an inferred thermal neutralino relic abundance larger than the cold dark matter density, the mismatch could thus potentially be explained by electroweak-scale physics that will also be thoroughly explored with collider experiments in the near future.

Yukawa unification and neutralino dark matter inSU(4)c×SU(2)L×SU(2)R

We consider a left-right symmetric SU(4){sub c}xSU(2){sub L}xSU(2){sub R} (4-2-2) model with gravity mediated supersymmetry breaking. We find that with 4-2-2 compatible nonuniversal gaugino masses, t-b-{tau} Yukawa coupling unification is consistent with neutralino dark matter abundance and with constraints from collider experiments (except (g-2){sub {mu}}). The gluino mass lies close to that of the lightest neutralino, so that the gluino coannihilation channel plays an important role in determining the neutralino relic abundance. By relaxing the Yukawa unification constraint we find stau and stop masses as low as 200-220 GeV. We highlight some benchmark points for these cases with 40{<=}tan{beta}{<=}58.

Neutralino dark matter and trilepton searches in the MSSM

Searches for supersymmetry are among the most exciting physics goals at run II of the Tevatron. In particular, in supersymmetric models with light charginos, neutralinos, and sleptons, associated chargino-neutralino production can potentially be observed as multilepton events with missing energy. We discuss how, in the generic TeV-scale minimal supersymmetric standard model (MSSM), the prospects for these chargino-neutralino searches are impacted by cosmological considerations, namely, the neutralino relic abundance and direct detection limits. We also discuss what an observation of chargino-neutralino production at the Tevatron would imply for the prospects of future direct dark-matter searches without assuming specific patterns of supersymmetry breaking.

Increasing the neutralino relic abundance with slepton coannihilations: consequences forindirect dark matter detection

We point out that if the lightest supersymmetric particle (LSP) is a higgsino- or wino-likeneutralino, the net effect of coannihilations with sleptons is to increase the relic abundance,rather than producing the usual suppression, which takes place if the LSP is bino-like.The reason for the enhancement lies in the effective thermally averaged crosssection at freeze-out: sleptons annihilate (and coannihilate) less efficiently than theneutralino(s)–chargino system, and therefore slepton coannihilations effectively act asparasite degrees of freedom at freeze-out. Henceforth, the thermal relic abundance ofLSPs corresponds to the cold dark matter abundance for smaller values of theLSP mass, and larger values of the neutralino pair annihilation cross section. Inturn, at a given thermal neutralino relic abundance, this implies larger indirectdetection rates, as a result of an increase in the fluxes of antimatter, gammarays and neutrinos from the Sun originating from neutralino pair annihilations.

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.

WMAP dark matter constraints and Yukawa unification in supergravity models withCPphases

The compatibility of producing the observed amount of dark matter, as indicated by the Wilkinson Microwave Anisotropy Probe (WMAP) data, through the relic abundance of neutralinos with Yukawa unification and with the measured rate of $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$ is analyzed in mSUGRA and extended SUGRA unified models with the inclusion of $CP$ phases. The $CP$ phases affect the analysis in several ways, e.g., through the threshold corrections to the $b$-quark mass, via their effects on the neutralino relic density and through the supersymmetry (SUSY) contribution to the $\mathrm{BR}(b\ensuremath{\rightarrow}s\ensuremath{\gamma})$ which is sensitive to the $CP$ phases. We present some specific models with large SUSY phases, which can accommodate the fermion electric dipole moment constraints and give a neutralino relic density in agreement with observations as well as with the $b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unification constraint. The possibility of achieving WMAP relic density constraints with full Yukawa unification is also explored.

Supersymmetric origin of matter

The minimal supersymmetric extension of the standard model (MSSM) can provide the correct neutralino relic abundance and baryon number asymmetry of the universe. Both may be efficiently generated in the presence of $CP$ violating phases, light charginos and neutralinos, and a light top squark. Because of the coannihilation of the neutralino with the light stop, we find a large region of parameter space in which the neutralino relic density is consistent with WMAP and SDSS data. We perform a detailed study of the additional constraints induced when $CP$ violating phases, consistent with the ones required for baryogenesis, are included. We explore the possible tests of this scenario from present and future electron electric dipole moment (EDM) measurements, direct neutralino detection experiments, collider searches and the $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$ decay rate. We find that the EDM constraints are quite severe and that electron EDM experiments, together with stop searches at the Tevatron and Higgs searches at the LHC, will provide a definite test of our scenario of electroweak baryogenesis in the next few years.

Sensitivity of supersymmetric dark matter to thebquark mass

An analysis of the sensitivity of supersymmetric dark matter to variations in the b quark mass is given. Specifically we study the effects on the neutralino relic abundance from supersymmetric loop corrections to the mass of the b quark. It is known that these loop corrections can become significant for large $\mathrm{tan}\ensuremath{\beta}.$ The analysis is carried out in the framework of MSUGRA and we focus on the region where the relic density constraints are satisfied by resonant annihilation through the s-channel Higgs poles. We extend the analysis to include CP phases taking into account the mixing of the CP-even and CP-odd Higgs boson states which play an important role in determining the relic density. Implications of the analysis for the neutralino relic density consistent with the recent WMAP relic density constraints are discussed.

Gluino annihilations and neutralino dark matter

We consider supersymmetric (SUSY) scenarios, compatible with all cosmological and phenomenological requirements, where the lightest SUSY particles (LSPs) are the neutralino and a quasidegenerate gluino. We study the neutralino relic abundance, focusing on gluino (co)annihilation effects. In case the neutralino is B-ino-like, in a wide mass window the relic abundance is naturally driven in the correct range for the LSP to be the main cold dark matter constituent. We show that the gluino is the strongest possible coannihilating partner of a B-ino-like neutralino in the general minimal supersymmetric standard model. Moreover, contrary to other coannihilation scenarios, gluino pair annihilations always dominate over coannihilation processes, even at relatively large gluino-neutralino mass splittings. Finally, we present prospects for neutralino dark matter detection in the outlined framework.

Quintessence and the relic density of neutralinos

The archetypal model for the recently discovered dark energy component of the universe is based on the existence of a scalar field whose dynamical evolution comes down today to a non-vanishing cosmological constant. In the past—before big-bang nucleosynthesis for that matter—that scalar field could have gone through a period of kination during which the universe has expanded at a much higher pace than what is currently postulated in the standard radiation dominated cosmology. I examine here the consequences of such a period of kination on the relic abundance of neutralinos and find that the latter could be much higher—by three orders of magnitude—than what is estimated in the canonical derivation. I shortly discuss the implications of this scenario for the dark matter candidates and their astrophysical signatures.

Cold dark matter and neutralinos

Neutralinos are natural candidates for cold dark matter in many realizations of supersymmetry. We briefly review our recent results in the evaluation of neutralino relic abundance and direct detection rates in a class of supergravity models.

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

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 theneutralino 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 detailthan 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.