Abundance Of Neutralino Research Articles

Muon g−2 and lepton flavor violation in supersymmetric GUTs

We present a class of supersymmetric (SUSY) GUT models that can explain the apparent discrepancy between the SM predictions and experimental values of muon g−2 while providing testable signals for lepton flavor violation in charged lepton decays. Moreover, these models predict LSP neutralino abundance that is compatible with the Planck dark matter bounds. We find that scenarios in the framework of SU(4)c×SU(2)L×SU(2)R unification, with additional symmetries to explain fermion masses and neutrino oscillations, provide interesting benchmarks for the search of SUSY by correlating a possible manifestation of it in dark matter, rare lepton decays, and LHC signals. Published by the American Physical Society 2024

T \u2212 b \u2212 \u03c4 Yukawa unification in non-holomorphic MSSM

We show that in the CMSSM with the non-holomorphic soft SUSY breaking terms, the Yukawa coupling unification of the third family fermions at the GUT scale, called t − b − τ Yukawa unification (YU), is possible under the recent collider and Dark Matter results. The YU parameter can also be found Rtbτ≈ 1, called perfect unification. We find that the squark masses exceed 3 TeV while the stau can be considerably lighter. In the case of YU, the tan β is in the interval [46,55]. We obtain bino-like dark matter (DM) of mass in the range of 0.6 TeV ≲ {m}_{upchi_1^0} ≲ 1.3 TeV where the recent Dark Matter direct detection limits are also satisfied. We also identify A-resonance solutions which reduce the relic abundance of LSP neutralino down to the ranges compatible with the current Planck measurements.

B \u2212 \u03c4 Yukawa unification in SUSY SU(5) with mirage mediation: LHC and dark matter implications

We consider a class of b − τ Yukawa unified Supersymmetric (SUSY) SU(5) GUTs, in which the asymptotic gaugino M1,2,3 masses are generated through the mirage mediated supersymmetry breaking, which is a combination of the gravity and anomaly mediation. Due to the contributions from the anomaly contribution, M3 is always lighter than M1 and M2, and consequently for the range of asymptotic masses considered, the gluino mass {m}_{tilde{g}} at low scale is bounded from above at about 4 TeV. We realize two different regions, in one of which the MSSM μ−term is less than about 3 TeV. This region yields a stop mass up to 5 TeV, and the stop mass is nearly degenerate with the LSP neutralino for mass around 0.8 to 1.7 TeV. A stau mass can be realized up to about 5 TeV, and the stau mass is approximately degenerate with the LSP neutralino for mass around 2 to 3 TeV. In addition, an A-funnel solution with {m}_Aapprox 2{m}_{{tilde{chi}}_1^0} and {m}_{{tilde{chi}}_1^0}sim 700-900 GeV is realized. These three cases yield LSP dark matter abundance in accordance with observations. A second region, on the other hand, arises for {m}_{tilde{g}}lesssim 1.1{m}_{{tilde{chi}}_1^0} . The μ−term is rather large (≳20 TeV), and the LSP neutralino is a bino-wino mixture. The gluino mass (∼ 0.8−1.2 TeV) is nearly degenerate with the LSP neutralino mass and hence, the gluino-neutralino coannihilation processes play a role in reducing the relic abundance of LSP neutralino down to ranges allowed by the current WMAP measurements. The two regions above can be distinguished through the direct detection experiments. The first region with relatively low μ values yields Higgsino-like DM, whose scattering on the nucleus typically has a large cross-section. We find that such solutions are still allowed by the current results from the LUX experiment, and they will be severely tested by the LUX-Zeplin (LZ) experiment. The second region contains bino-wino DM whose scattering cross-section is relatively low. These solutions are harder to rule out in the foreseeable future.

Is natural higgsino-only dark matter excluded?

The requirement of electroweak naturalness in supersymmetric (SUSY) models of particle physics necessitates light higgsinos not too far from the weak scale characterized by m_{weak}sim m_{W,Z,h}sim 100hbox { GeV}. On the other hand, LHC Higgs mass measurements and sparticle mass limits point to a SUSY breaking scale in the multi-TeV regime. Under such conditions, the lightest SUSY particle is expected to be a mainly higgsino-like neutralino with non-negligible gaugino components (required by naturalness). The computed thermal WIMP abundance in natural SUSY models is then found to be typically a factor 5–20 below its measured value. To gain concordance with observations, either an additional DM particle (the axion is a well-motivated possibility) must be present or additional non-thermal mechanisms must augment the neutralino abundance. We compare present direct and indirect WIMP detection limits to three natural SUSY models based on gravity-, anomaly- and mirage-mediation. We show that the case of natural higgsino-only dark matter where non-thermal production mechanisms augment its relic density, is essentially excluded by a combination of direct detection constraints from PandaX-II, LUX and Xenon-1t experiments, and by bounds from Fermi-LAT/MAGIC observations of gamma rays from dwarf spheroidal galaxies.

Least fine-tuned U(1) extended SSM

We consider the Higgs boson mass in a class of the UMSSM models in which the MSSM gauge group is extended by an additional U(1)′ group. Implementing the universal boundary condition at the GUT scale we target phenomenologically interesting regions of UMSSM where the necessary radiative contributions to the lightest CP-even Higgs boson mass are significantly small and LSP is always the lightest neutralino. We find that the smallest amount of radiative contributions to the Higgs boson mass is about 50 GeV in UMSSM, this result is much lower than that obtained in the MSSM framework, which is around 90 GeV. Additionally, we examine the Higgs boson properties in these models in order to check whether if it can behave similar to the SM Higgs boson under the current experimental constraints. We find that enforcement of smaller radiative contribution mostly restricts the U(1)′ breaking scale as vS≲10 TeV. Besides, such low contributions demand hS∼0.2–0.45. Because of the model dependency in realizing these radiative contributions θE6<0 are more favored, if one seeks for the solutions consistent with the current dark matter constraints. As to the mass spectrum, we find that stop and stau can be degenerated with the LSP neutralino in the range from 300 GeV to 700 GeV; however, the dark matter constraints restrict this scale as mt˜,mτ˜≳500 GeV. Such degenerate solutions also predict stop-neutralino and stau-neutralino co-annihilation channels, which are effective to reduce the relic abundance of neutralino down to the ranges consistent with the current dark matter observations. Finally, we discuss the effects of heavy MZ′ in the fine-tuning. Even though the radiative contributions are significantly low, the required fine-tuning can still be large. We comment about reinterpretation of the fine-tuning measure in the UMSSM framework, which can yield efficiently low results for the fine-tuning the electroweak scale.

Quasi-Yukawa unification and fine-tuning in U(1) extended SSM

We consider the low scale implications in the U(1)' extended MSSM (UMSSM). We restrict the parameter space such that the lightest supersymmetric particle (LSP) is always the lightest neutralino. In addition, we impose quasi Yukawa unification (QYU) at the grand unification scale (M_GUT). QYU strictly requires the ratios among the yukawa couplings as y_t/y_b ~ 1.2, y_tau/y_b ~ 1.4, and y_t/y_tau ~ 0.8. We find that the need of fine-tuning over the fundamental parameter space of QYU is in the acceptable range (Delta_EW <= 10^3), even if the universal boundary conditions are imposed at M_ GUT, in contrast to CMSSM and NUHM. UMSSM with the universal boundary conditions yields heavy stops (m_{stop} >~ 2.5 TeV), gluinos (m_gluino >~ 2 TeV), and squarks from the first two families (m_squarks >~ 4 TeV). Similarly the stau mass is bounded from below at about 1.5 TeV. Despite this heavy spectrum, we find Delta_EW >~ 300, which is much lower than that needed for the minimal supersymmetric models. In addition, UMSSM yield relatively small mu-term, and the LSP neutralio is mostly form by the Higgsinos of mass >~ 700 GeV. We obtain also bino-like dark matter (DM) of mass about 400 GeV. Wino is usually found to be heavier than Higgsinos and binos, but there is a small region where mu ~ M_1 ~ M_2 ~ 1 TeV. We also identify chargino-neutralino coannihilation channel and A-resonance solutions which reduce the relic abundance of LSP neutralino down to the ranges compatible with the current WMAP measurements.

MSSM Dark Matter in Light of Higgs and LUX Results

The constraints imposed on the Minimal Supersymmetric Standard Model (MSSM) parameter space by the Large Hadron Collider (LHC) Higgs mass limit and gluino mass lower bound are revisited. We also analyze the thermal relic abundance of lightest neutralino, which is the Lightest Supersymmetric Particle (LSP). We show that the combined LHC and relic abundance constraints rule out most of the MSSM parameter space except a very narrow region with very largetan⁡β (~50). Within this region, we emphasize that the spin-independent scattering cross section of the LSP with a proton is less than the latest Large Underground Xenon (LUX) limit by at least two orders of magnitude. Finally, we argue that nonthermal Dark Matter (DM) scenario may relax the constraints imposed on the MSSM parameter space. Namely, the following regions are obtained:m0≃O(4) TeV andm1/2≃600 GeV for lowtan⁡β (~10);m0~m1/2≃O(1) TeV orm0≃O(4) TeV andm1/2≃700 GeV for largetan⁡β (~50).

Natural SUSY with a bino- or wino-like LSP

In natural SUSY models higgsinos are always light because \mu^2 cannot be much larger than M_Z^2, while squarks and gluinos may be very heavy. Unless gluinos are discovered at LHC13, the commonly assumed unification of gaugino mass parameters will imply correspondingly heavy winos and binos, resulting in a higgsino-like LSP and small inter-higgsino mass splittings. The small visible energy release in higgsino decays makes their pair production difficult to detect at the LHC. Relaxing gaugino mass universality allows for relatively light winos and binos without violating LHC gluino mass bounds and without affecting naturalness. In the case where the bino mass M_1<~ \mu, then one obtains a mixed bino-higgsino LSP with instead sizable w_1-z_1 and z_2-z_1 mass gaps. The thermal neutralino abundance can match the measured dark matter density in contrast to models with a higgsino-like LSP where WIMPs (weakly interacting massive particles) are underproduced by factors of 10-15. If instead M_2<~ \mu, then one obtains a mixed wino-higgsino LSP with large z_2-z_1 but small w_1-z_1 mass gaps with still an under-abundance of thermally-produced WIMPs. Portions of the light wino parameter space may already be excluded by the IceCube upper bound on the spin-dependent neutralino-nucleon cross section. We discuss dark matter detection in other direct and indirect detection experiments and caution that the bounds from these must be interpreted with care. Finally, we show that LHC13 experiments should be able to probe these non-universal mass scenarios via a variety of channels including multi-lepton + etmiss events, WZ+etmiss events, Wh+etmiss events and W^\pm W^\pm +etmiss events from electroweak chargino and neutralino production.

Mixed axion/neutralino dark matter in the SUSY DFSZ axion model

We examine mixed axion/neutralino cold dark matter production in the SUSY DFSZaxion model where an axion superfield couples to Higgs superfields.We calculate a wide array of axino and saxion decay modes along with theirdecay 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 fa≲1012 GeV that the DM abundance is mainly comprised of axions as the saxion/axino decay occurs before the standard neutralino freeze-out and thus itsabundance remains suppressed. For 1012≲fa≲1014 GeV, thesaxion/axino decays occur after neutralino freeze-out so that the neutralino abundance is enhancedby the production via decay and subsequent re-annihilation.For fa≳1014 GeV, both neutralino dark matter and dark radiation aretypically overproduced. For judicious parameter choices, these can be suppressedand the combined neutralino/axion abundance brought into accord with measured values.A SUSY benchmark model with a standard overabundance (SOA) of bino DM is also examined and typically remains excluded due at least to too great a neutralino DM abundance forfa≲1015 GeV. For fa≳1015 GeV and lower saxion masses, large entropyproduction from saxion decay can dilute all relics and the SOA model can beallowed by all constraints.

Implications of a 125 GeV Higgs scalar for the LHC supersymmetry and neutralino dark matter searches

The ATLAS and CMS collaborations have reported an excess of events in the $\ensuremath{\gamma}\ensuremath{\gamma}$, $Z{Z}^{*}\ensuremath{\rightarrow}4\ensuremath{\ell}$ and $W{W}^{*}$ search channels at an invariant mass $m\ensuremath{\simeq}125\text{ }\text{ }\mathrm{GeV}$, which could be the first evidence for the long-awaited Higgs boson. We investigate the consequences of requiring ${m}_{h}\ensuremath{\simeq}125\text{ }\text{ }\mathrm{GeV}$ in both the minimal supergravity and 2-parameter nonuniversal Higgs supersymmetric models. In minimal supergravity, large values of trilinear soft breaking parameter $|{A}_{0}|$ are required, and universal scalar ${m}_{0}\ensuremath{\gtrsim}0.8\text{ }\text{ }\mathrm{TeV}$ is favored so that we expect squark and slepton masses typically in the multi-TeV range. This typically gives rise to an ``effective supersymmetric'' type of sparticle mass spectrum. In this case, we expect gluino pair production as the dominant sparticle creation reaction at LHC. For ${m}_{0}\ensuremath{\lesssim}5\text{ }\text{ }\mathrm{TeV}$, the superpotential parameter $\ensuremath{\mu}\ensuremath{\gtrsim}2\text{ }\text{ }\mathrm{TeV}$ and ${m}_{A}\ensuremath{\gtrsim}0.8\text{ }\text{ }\mathrm{TeV}$, greatly restricting neutralino annihilation mechanisms. These latter conclusions are softened if ${m}_{0}\ensuremath{\sim}10--20\text{ }\text{ }\mathrm{TeV}$ or if one proceeds to the 2-parameter nonuniversal Higgs model. The standard neutralino abundance tends to be far above WMAP-measured values unless the neutralino is Higgsino-like. We remark upon possible nonstandard (but perhaps more attractive) cosmological scenarios which can bring the predicted dark matter abundance into accord with the measured value, and discuss the implications for direct and indirect detection of neutralino cold dark matter.

Mixed axion/neutralino cold dark matter in supersymmetric models

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 (aZ̃1 CDM). The mixed aZ̃1 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 abundance can be greatly enhanced by the decay of thermally-produced axinos (ã) to neutralinos, followed by neutralino re-annihilation at temperatures much lower than freeze-out. In this case, the relic density is usually neutralino dominated, and goes as ∼ (fa/N)/mã3/2. If axino decay occurs before neutralino freeze-out, then instead the neutralino abundance can be augmented by relic axions to match the measured abundance. Entropy production from late-time axino decays can diminish the axion abundance, but ultimately not the neutralino abundance. In aZ̃1 CDM models, it may be possible to detect both a WIMP and an axion as dark matter relics. We also discuss possible modifications of our results due to production and decay of saxions. In the appendices, we present expressions for the Hubble expansion rate and the axion and neutralino relic densities in radiation, matter and decaying-particle dominated universes.

Thermal leptogenesis and the gravitino problem in the Asaka-Yanagida axion/axino dark matter scenario

A successful implementation of thermal leptogenesis requires the re-heat temperature after inflation TR to exceed ∼ 2 × 109 GeV. Such a high TR 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. In this case, sparticle decays bypass the gravitino, and decay more quickly to the axino LSP, thus avoiding the BBN constraints. In addition, thermally produced gravitinos decay inertly to axion+axino, also avoiding BBN constraints. We calculate the relic abundance of mixed axion/axino dark matter in the AY scenario, and investigate under what conditions a value of TR sufficient for thermal leptogenesis can be generated. A high value of PQ breaking scale fa is needed to suppress overproduction of axinos, while a small vacuum misalignment angle θi is needed to suppress overproduction of axions. The large value of fa results in late decaying neutralinos. We show that, to avoid BBN constraints, the AY scenario requires a rather low thermal abundance of neutralinos, while higher values of neutralino mass also help. We combine these constraint calculations along with entropy production from late decaying saxions, and find the saxion needs to be typically at least several times heavier than the gravitino. A successful implementation of the AY scenario suggests that LHC should discover a spectrum of SUSY particles consistent with weak scale supergravity; that the apparent neutralino abundance is low; that an axion direct detection signal (probably with ma in the sub-μeV range) may be possible, but no direct or indirect signals for WIMP dark matter should be observed.

Relic densities including Sommerfeld enhancements in the MSSM

We have developed a general formalism to compute Sommerfeld enhancement (SE) factors for a multi-state system of fermions, in all possible spin configurations and with generic long-range interactions. We show how to include such SE effects in an accurate calculation of the thermal relic density for WIMP dark matter candidates. We apply the method to the MSSM and perform a numerical study of the relic abundance of neutralinos with arbitrary composition and including the SE due to the exchange of the W and Z bosons, photons and Higgses. We find that the relic density can be suppressed by a factor of a few in a seizable region of the parameter space, mostly for Wino-like neutralino with mass of a few TeV, and up to an order of magnitude close to a resonance.

T − b − τ Yukawa unification for μ &lt; 0 with a sub-TeV sparticle spectrum

We show compatibility with all known experimental constraints of t-b-tau Yukawa coupling unification in supersymmetric SU(4)_c x SU(2)_L x SU(2)_R which has non-universal gaugino masses and the MSSM parameter mu < 0. In particular, the relic neutralino abundance satisfies the WMAP bounds and Delta (g-2)_mu is in good agreement with the observations. We identify benchmark points for the sparticle spectra which can be tested at the LHC, including those associated with gluino and stau coannihilation channels, mixed bino-Higgsino state and the A-funnel region. We also briefly discuss prospects for testing Yukawa unification with the ongoing and planned direct detection experiments.

Supersymmetric interpretation of the Egret GeV anomaly, Xenon-10 dark matter search limits, and the CERN LHC

The observation of the Egret experiment of an excess of diffuse gamma rays with energies above ${E}_{\ensuremath{\gamma}}=1\text{ }\text{ }\mathrm{GeV}$ has previously been interpreted in the context of the minimal supergravity model (mSUGRA) as coming from neutralino annihilation into mainly $b$-quarks in the galactic halo, with neutralino mass in the vicinity of 50--70 GeV. We observe that, in order to obtain the correct relic abundance of neutralinos in accord with WMAP measurements, the corresponding neutralino-proton direct detection (DD) rates should be in excess of recent limits from the Xenon-10 collaboration. While it does not appear possible to satisfy the Egret, WMAP, and Xenon-10 constraints simultaneously within the mSUGRA model, we find that it is easily possible in models with nonuniversal Higgs soft masses (NUHM). In either case, gluino pair production from ${m}_{\stackrel{\texttildelow{}}{g}}\ensuremath{\sim}400--500\text{ }\text{ }\mathrm{GeV}$ should occur at large rates at the CERN LHC, and a gluino pair production signal should be visible with just $0.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity. The NUHM interpretation predicts a rather light spectrum of heavy Higgs bosons with ${m}_{A}\ensuremath{\sim}140--200\text{ }\text{ }\mathrm{GeV}$ over the whole parameter space which would interpret Egret data. Spin-independent DD rates are predicted to be just above ${10}^{\ensuremath{-}8}\text{ }\text{ }\mathrm{pb}$, within range of the next round of direct dark matter detection experiments.

Neutralino dark matter in the NMSSM

We analyse the direct detection of neutralino dark matter in the framework of the next-to-minimal supersymmetric standard model. Taking into account all the available constraints from LEPII and Tevatron, including bounds from the muon anomalous magnetic moment and flavour constraint as b → sγ, we compute the neutralino–nucleon cross section and compare the results with the sensitivity of dark matter detectors. We also study the relic abundance of neutralinos, comparing it with WMAP observations. We show that a light singlet-like Higgs can escape accelerator constraints allowing for scenarios with large cross sections and a very interesting phenomenology.

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.

Neutralino dark matter from heavy gravitino decay

We propose a new scenario of nonthermal 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 abundance of the neutralino dark matter is obtained without spoiling the big-bang nucleosynthesis by injection of hadronic showers from gravitino decay. The neutralino abundance obtained in this mechanism is insensitive to the details of the superparticle mass spectrum, unlike the standard thermal abundance. We also briefly mention the testability of the scenario in future experiments.

Mixed Wino Dark Matter: consequences for direct, indirect and collider detection

In supersymmetric models with gravity-mediated SUSY breaking and gaugino mass unification, the predicted relic abundance of neutralinos usually exceeds the strict limits imposed by the WMAP collaboration. One way to obtain the correct relic abundance is to abandon gaugino mass universality and allow a mixed wino-bino lightest SUSY particle (LSP). The enhanced annihilation and scattering cross sections of mixed wino dark matter (MWDM) compared to bino dark matter lead to enhanced rates for direct dark matter detection, as well as for indirect detection at neutrino telescopes and for detection of dark matter annihilation products in the galactic halo. For collider experiments, MWDM leads to a reduced but significant mass gap between the lightest neutralinos so that chi_2^0 two-body decay modes are usually closed. This means that dilepton mass edges-- the starting point for cascade decay reconstruction at the CERN LHC-- should be accessible over almost all of parameter space. Measurement of the m_{\tz_2}-m_{\tz_1} mass gap at LHC plus various sparticle masses and cross sections as a function of beam polarization at the International Linear Collider (ILC) would pinpoint MWDM as the dominant component of dark matter in the universe.

Statistical analysis of supersymmetric dark matter in the minimal supersymmetric standard model after WMAP

We study supersymmetric dark matter in the general flavor diagonal minimal supersymmetric standard model by means of an extensive random scan of its parameter space. We find that, in contrast with the standard minimal supergravity lore, the large majority of viable models features either a Higgsino or a winolike lightest neutralino, and yields a relic abundance well below the Wilkinson Microwave Anisotropy Probe (WMAP) bound. Among the models with neutralino relic density within the WMAP range, Higgsinolike neutralinos are still dominant, though a sizable fraction of binos is also present. In this latter case, coannihilations are shown to be essential in order to obtain the correct neutralino abundance. We then carry out a statistical analysis and a general discussion of neutralino dark matter direct detection and of indirect neutralino detection at neutrino telescopes and at antimatter search experiments. We point out that current data exclude only a marginal portion of the viable parameter space, and that models whose thermal relic abundance lies in the WMAP range will be significantly probed only at future direct detection experiments. Finally, we emphasize the importance of relic density enhancement mechanisms for indirect detection perspectives, in particular, at future antimatter search experiments.