The lightest neutralino, assumed to be the lightest supersymmetric particle, is proposed to be a dark matter (DM) candidate for the mass $\cal{O}$(100) GeV. Constraints from various direct dark matter detection experiments and Planck measurements exclude a substantial region of parameter space of the minimal supersymmetric standard model (MSSM). However, a "mild-tempered" neutralino with dominant bino composition and a little admixture of Higgsino is found to be a viable candidate for DM. Within the MSSM framework, we revisit the allowed region of parameter space that is consistent with all existing constraints. Regions of parameters that are not sensitive to direct detection experiments, known as "blind spots," are also revisited. Complimentary to the direct detection of DM particles, a mild-tempered neutralino scenario is explored at the LHC with the center of mass energy $\rm \sqrt{s}$=13 TeV through the top-squark pair production, and its subsequent decays with the standard-model-like Higgs boson in the final state. Our considered channel is found to be very sensitive also to the blind spot scenario. Detectable signal sensitivities are achieved using the cut-based method for the high luminosity options $\rm 300$ and $\rm 3000 ~fb^{-1}$, which are further improved by applying the multi-variate analysis technique.
We have included the effective description of squark interactions with charginos/neutralinos in the MadGraph MSSM model. This effective description includes the effective Yukawa couplings, and another logarithmic term which encodes the supersymmetry-breaking. We have performed an extensive test of our implementation analyzing the results of the partial decay widths of squarks into charginos and neutralinos obtained by using FeynArts/FormCalc programs and the new model file in MadGraph. We present results for the cross-section of top-squark production decaying into charginos and neutralinos.
Within the low-energy effective Minimal Supersymmetric extension of the Standard Model (effMSSM) we calculate the neutralino relic density taking into account slepton-neutralino, squark-neutralino and neutralino/chargino- neutralino coannihilation channels. By including squark (stop and sbottom) coannihilation channels we extend our comparative study to all allowed coannihilations and obtain the general result that all of them give sizable contributions to the reduction of the neutralino relic density. Due to these coannihilation processes some models (mostly with large neutralino masses) ente…
Light electroweakinos, the neutral and charged fermionic supersymmetric partners of the Standard Model $\mathrm{SU}(2)\times\mathrm{U}(1)$ gauge bosons and of the two $\mathrm{SU}(2)$ Higgs doublets, are an important target for searches for new physics with the Large Hadron Collider (LHC). However, if the lightest neutralino is the dark matter, constraints from direct dark matter detection experiments rule out large swaths of the parameter space accessible to the LHC, including in large part the so-called "well-tempered" neutralinos. We focus on the Minimal Supersymmetric Standard Model (MSSM)…
We discuss the possibility of new sources of flavour violation in the squark sector of supersymmetric models in the context of the dark matter relic density. We show that the corresponding non-minimal flavour violation terms in the squark mass matrices can have an important impact on the thermally averaged (co)annihilation cross section of the neutralino, and in consequence can modify its predicted relic density. We discuss in detail the relevant effects and present a numerical study of neutralino annihilation and coannihilation in this context. We also comment on the LHC phenomenology of the …
The dark-matter prediction is usually considered as one of the successes of low-energy supersymmetry. We argue that, after LEP constraints are taken into account, the correct prediction for the dark-matter density, at a quantitative level, is no longer a natural consequence of supersymmetry, but it requires special relations among parameters, highly sensitive to small variations. This is analogous to the problem of electroweak-symmetry breaking, where the correct value of the Z mass is obtained only with a certain degree of fine tuning. In the general parameter space of low-energy supersymmetr…
We compute the cross section for chi chi -> q qbar g at order alpha_s^2/M_{squark}^6 arising from interference between the tree-level and loop-induced processes. This interference term is the same order in alpha_s as chi chi -> gg; for mass degenerate squarks M_{squark_R} = M_{squark_L} = M_{squark} we find v_{rel} sigma_{int} = [-2 m_{chi}^2 / 3 M_{squark}^2] v_{rel} sigma(chi chi -> gg).
We study the effect of the neutralino polarization in a squark cascade decay $\tilde{q} \to q \tildeχ^0_2 \to q l^\pm \tilde{l}^\mp \to q l^\pm \tilde{l}^\mp \to q l^\pm l^\mp \tildeχ^0_1$. Charge asymmetry in the lepton-jet invariant mass distribution appears depending on the chirality structure of the sfermion-fermion-neutralino coupling. With use of the Monte Carlo simulation, we show that the asymmetry is measurable in LHC. We also show that the distribution of the charge asymmetry is sensitive to the (s)lepton flavor.
In a R-parity violating (RPV) model of neutrino mass with three bilinear couplings $μ_i$ and three trilinear couplings $λ'_{i33}$, where $i$ is the lepton index, we find six generic scenarios each with a distinctive pattern of the trilinear couplings consistent with the oscillation data. These patterns may be reflected in direct RPV decays of the lighter top squark or in the RPV decays of the lightest superparticle, assumed to be the lightest neutralino. Typical signal sizes at the Tevatron RUN II and the LHC have been estimated and the results turn out to be encouraging.
The parameters of the Minimal Supersymmetric Standard Model appear to require uncomfortably precise adjustment in order to reconcile the electroweak symmetry breaking scale with the lower mass limits on a neutral Higgs scalar boson. This problem can be significantly ameliorated in models with a running gluino mass parameter that is smaller than the wino mass near the scale of unification of gauge couplings. A "compressed" superpartner mass spectrum results; compared to models with unified gaugino masses, the ratios of the squark and gluino masses to the lightest superpartner mass are reduced. …
The one loop corrected effective Lagrangian for the quark-squark-chargino and quark-squark-neutralino interactions is computed. The effective Lagrangian takes into account the loop corrections arising from the exchange of the gluinos, charginos, neutralinos, W, Z, the charged Higgs, and the neutral Higgs. We further analyze the squark decays into charginos and neutralinos and discuss the effect of the loop corrections on them. The analysis takes into account CP phases in the soft parameters. It is found that the loop corrections to the stop decay widths into chargino and neutralinos can be as …
The production of one hard jet in association with missing transverse energy is a major LHC search channel motivated by many scenarios for physics beyond the Standard Model. In scenarios with a weakly interacting dark matter candidate, like supersymmetry, it arises from the associated production of a quark partner with the dark matter agent. We present the next-to-leading order cross section calculation as the first application of the fully automized MadGolem package. We find moderate corrections to the production rate with a strongly reduced theory uncertainty.
It is pointed out that a bino-dominated well-tempered bino-higgsino in the Minimal Supersymmetric Standard Model (MSSM) with heavy non-SM- like scalars can satisfy the 2016 LUX constraints on the scattering cross-section of dark matter on nuclei only if $\tanβ$ is smaller than about 3. This, together with the Higgs mass constraint, sets a lower bound on the stops masses of about 25 TeV. The LUX constraints can be satisfied for larger $\tanβ$ if the non-SM-like Higgs bosons are light enough. However, this region of parameter space is strongly constrained by recent LHC results of the Higgs boson…
Pair production of light top squarks at the 8-TeV LHC can be used to probe the gaugino-Higgsino sector of the Minimal Supersymmetric Standard Model. The case where the lightest neutralino is a mixture of Bino and Higgsino, satisfying the thermal dark matter relic density, is investigated. In such a scenario, the lightest top squark decays mostly into $(i)$ a top quark plus the second or third lightest neutralino, and $(ii)$ a bottom quark plus the lightest chargino, instead of a decay scenario of the lightest top squark into a top quark and the lightest neutralino. Final states with $\geq 2$ j…
In the post-LEP2 era, and in light of recent measurements of the cosmic abundance of cold dark matter (CDM) in the universe from WMAP, many supersymmetric models tend to predict 1. an overabundance of CDM and 2. pessimistically low rates for direct detection of neutralino dark matter. However, in models with a ``well-tempered neutralino'', where the neutralino composition is adjusted to give the measured abundance of CDM, the neutralino is typically of the mixed bino-wino or mixed bino-higgsino state. Along with the necessary enhancement to neutralino annihilation rates, these models tend to g…
We examine for representative gaugino-higgsino mixing scenarios sneutrino-neutralino and sneutrino-chargino production in deep inelastic ep-scattering at the cm-energy of 1.8 TeV. The cross sections for sneutrino-chargino production are more than one order of magnitude bigger than those for sneutrino-squark production. Also for zino-like neutralinos we find cross sections at least comparable to those for sneutrino-squark production.
The momentum spectrum and the polarization of charginos and neutralinos in squark decays are affected by gluon radiation in the decay process \tilde{q} \to q \tildeχ (g). We determine these corrections and study their impact on the [ql] invariant mass distributions for leptonic \tildeχ decays. The higher-order corrections, though small in general, can be sizeable near pronounced edges of the final-state distributions.
We propose an effective description of squark interactions with charginos/neutralinos. We recompute the strong corrections to squark partial decay widths, and compare the full one-loop computation with the effective description. The effective description includes the effective Yukawa couplings, and another logarithmic term which encodes the supersymmetry-breaking. The proposed effective couplings reproduce correctly the radiative-corrected partial decay widths of the squark decays into charginos and neutralinos in all relevant regions of the parameter space.
We consider a setup where R-parity is violated in the framework of split supersymmetry. The out-of-equilibrium decays of heavy squarks successfully lead to the generation of a baryon asymmetry. We restrict the R-parity violating couplings to the baryon number violating subset to keep the neutralino sufficiently stable to provide the dark matter. The observed baryon asymmetry can be generated for squark masses larger than 10^11 GeV, while neutralino dark matter induces a stronger bound of 10^13 GeV. Some mass splitting between left- and right-handed squarks may be needed to satisfy also constra…
We calculate the supersymmetric QCD corrections in order $α_s$ to the decays $\squark_i \to q' \chargino_j$ (i,j = 1,2) and $\squark_i \to q \neutralino_k$ (k = 1,...4) within the Minimal Supersymmetric Standard Model. In particular we consider the decays of squarks of the third generation, $\stop_i$ and $\sbottom_i$ (i = 1,2), where the left--right mixing must be taken into account. The corrections turn out to be of about 10\%, except for higgsino--like charginos or neutralinos, where they can go up to 40\%.
We discuss the three-body decays stop_1 -> W^+ b neutralino_1, stop_1 -> H^+ b neutralino_1, stop_1 -> b slepton_i neutrino_l, and stop_1 -> b sneutrino_l l^+$ ($l =e,μ,τ$) of the lighter top squark within the minimal supersymmetric standard model. We give the complete analytical formulas for the decay widths and present a numerical study in view of an upgraded Tevatron, the CERN LHC, and a future lepton collider demonstrating the importance of these decay modes.
We examine the stau-neutralino coannihilation (CA) mechanism of the early universe. We use the minimal supergravity (mSUGRA) model and show that from measurements at the Large Hadron Collider one can predict the dark matter relic density with an uncertainty of 6% with 30 fb-1 of data, which is comparable to the direct measurement by Wilkinson Microwave Anisotropy Probe. This is done by measuring four mSUGRA parameters m0, m1/2, A0 and tan(beta) without requiring direct measurements of the top squark and bottom squark masses. We also provide precision measurements of the gaugino, squark, and li…
Under the assumption of gaugino mass unification at a high scale, chargino and neutralino masses depend on the value of the gluino mass, which itself becomes a function of squark masses through self-energy corrections. We demonstrate that this leads to combined bounds on squark and gluino masses from the limits on chargino, neutralino and Higgs boson masses obtained in the CERN LEP-1 and LEP-1.5 runs. These bounds turn out to be comparable to those obtained from direct searches at the Fermilab Tevatron and may be expected to improve as LEP energies go higher.
Within the Minimal Supersymmetric Standard Model we study the three body decay of the lighter top squark into a b-quark, a W-boson and the lightest neutralino and compare this decay with the flavour changing two body decay of the lighter top squark into a c-quark and the lightest neutralino. We do this for scenarios where two body decays at tree level are forbidden for the light top squark. We give the complete analysis for the three body and compare it with the mentioned two body decay. We discuss our numerical results in view of the upgraded Tevatron, the LHC and a 500~GeV $e^+ e^-$ Linear C…
We examine for representative gaugino-higgsino mixing scenarios slepton-neutralino and slepton-chargino production in deep inelastic ep-scattering at $\sqrt{s}=1.8$ TeV. We find sneutrino-chargino production to be the dominant process with cross sections more than one order of magnitude bigger than those for slepton-squark production. Also for associated production of sneutrinos and zino-like neutralinos the cross sections are at least comparable to those for $\tilde l \tilde q$-production, whereas selectron-neutralino/chargino production is with cross sections significantly smaller than those…
The assumption that strongly interacting sparticles will decay directly to the LSP plus jets breaks down in situations where those decays are Yukawa suppressed. That occurs when producing the first two generations of squarks and when, at the same time, there are several electroweakinos lighter than those squarks. In this paper we analyze the signal of pair production of squarks that subsequently decay to an intermediate neutralino ($\tildeχ_3^0$) plus jets. The neutralino will then decay to the LSP (mainly higgsino) and a Higgs. We have simulated the events and designed a discovery strategy ba…
The requirement that the MSSM remain an acceptable effective field theory up to energies beyond the weak scale constrains the sparticle spectrum, and hence the permissible ranges of cold dark matter neutralino-proton cross sections. Specifically, squarks are generally much heavier than sleptons if no tachyons are to appear before the GUT scale ~10^16 GeV, or even before 10 TeV. We display explicitly the allowed ranges of effective squark and slepton masses at the weak scale, and the cross-section ranges allowed if the MSSM is to remain valid without tachyons up to 10 TeV or the GUT scale. The …
Processes of the form $pp\to anything \to X_i X_j \to x\bar{x} + y\bar{y} (+ \slashchar{E})$ are studied via a technique that may be viewed as an adaptation of time-honoured Dalitz plot analyses. $X_i$ and $X_j$ are new heavy states (with $i,j=1...n$), which may be identical or distinct; and $x\bar{x}$ and $y\bar{y}$ are necessarily distinct Standard Model (SM) fermion pairs whose invariant masses can be measured. A Dalitz-like plot of said invariant masses, $M(x\bar{x})$ {\it vs.$$} $M(y\bar{y})$, exhibits a topology connected to the masses and specific decay chains of $X_i$ and $X_j$. Aside …
We examine the case of neutralino dark matter in the focus point region of the MSSM, in which the scalar sparticles are too heavy to be produced at the LHC. Whilst it has been previously asserted that the LHC alone would fail to constrain the properties of the lightest neutralino for such a scenario, we find that one can obtain good predictions of astrophysical quantities such as the relic density, annihilation cross-section and direct search cross-sections by using the shape of the dilepton invariant mass spectrum to constrain neutralino mixing. We demonstrate our technique using a Bayesian a…
We discuss a potential of studying the production and the decay of the lightest top squark (t-tilde_1) in the framework of the supersymmetric standard model at a future e^+e^- collider. In particular, we consider the process t-tilde_1 -> t chi^0_1 (with chi^0_1 being the lightest neutralino) followed by t -> bW. It is shown that, by the study of the angular distribution of the bottom quark (as well as the production cross section of the top squark), properties of chi_1^0 can be extracted. We also discuss that, if chi^0_1 is gaugino-like, the neutralino mixing parameters (i.e., the so-called mu…
We study soft and collinear gluon emission in squark decays to quark--neutralino pair, at next-to-next-to-leading logarithmic (NNLL) accuracy in the end-point region, using Soft Collinear Effective Theory (SCET), and at next-to-leading (NLO) fixed order in the rest of the phase space. As a phenomenological case study we discuss the impact of radiative corrections on the simultaneous measurements of squark and neutralino masses at a linear $e^{+}e^{-}$ collider based on $\sqrt{s} = 3$ TeV Compact Linear Collider (CLIC). Since the majority of mass measurement techniques are based on edges in kin…
This dissertation focuses on phenomenological studies for possible signals for supersymmetric events at the Large Hadron Collider (LHC). We have divided our endeavours into three separate projects. First, we consider SUSY models where the gluino production at the LHC should be rich in top and bottom quark jets. Requiring $b$-jets in addition to missing energy $\eslt$ should, therefore, enhance the supersymmetry signal relative to Standard Model backgrounds. We quantify the increase in the supersymmetry reach of the LHC from $b$-tagging in a variety of well-motivated models of supersymmetry. We…
We provide the next-to-leading order (NLO) predictions for the neutralino pair production via quark-antiquark annihilation and gluon-gluon fusion at the CERN Large Hadron Collider, focusing on the lightest neutralino which is likely to be the lightest supersymmetric particle. The dependence of total LO, NLO cross sections, and $K$ factor on the center-of-mass energy, the $M_2$-$μ$ mass plane, the squark mass, and the factorization and renormalization scales is comprehensively analyzed for three different scenarios in the minimal supersymmetric standard model and the constrained minimal supersy…
In a scenario with heavy supersymmetric sfermions and decoupled supersymmetric Higgs sector, a well tempered neutralino is the remaining candidate for thermal single-component sub-TeV dark matter. Well tempered neutralinos are studied in the context of supersymmetric grand unified theories with third family Yukawa coupling unification. A global chi^2 analysis is performed, including the observables MW, MZ, GF, alpha_em, alpha_s(MZ), Mt, mb(mb), Mtau, b -> s gamma, BR(Bs -> mu^+ mu^-), Mh and Omegah^2. Tensions in simultaneously fitting the Higgs and bottom quark masses while also avoiding glui…
We give explicit expressions for the amplitudes associated with the supersymmetric contributions to the process: b -> s gamma in the context of SUSY extensions of Standard Model with non-universal soft SUSY breaking terms. From experimental data, we deduce the limits on the squark mass insertions obtained from different contributions (gluinos, neutralinos and charginos).
We point out another important production channel of a light pseudoscalar Higgs boson $a_1$ via the decays of neutralinos, including $\widetildeχ_{2,3}^0 \to \widetildeχ_{1}^0 a_1$, in the framework of the NMSSM. We scan the whole parameter space using the most up-to-date version of NMHDECAY and search for regions where $B(\widetildeχ_{2,3}^0 \to \widetildeχ_{1}^0 a_1) > 0.5$. If the gluino and squarks are light enough for copious production of SUSY events at the LHC, there would be numerous number of $\widetildeχ_{2,3}^0$ in subsequent decays of gluinos and squarks. Therefore, the production …
We present a detailed discussion of the elastic scattering of a supersymmetric neutralino off a nucleon or nucleus, with emphasis on the spin--independent interaction. We carefully treat QCD effects on the squark exchange contribution. In particular, we identify a class of terms that survive even in the absence of mixing in both the neutralino and squark sectors; the corresponding quark and gluon operators also appear in analyses of deep--inelastic lepton--nucleon scattering (``twist--2 operators''), so their hadronic matrix elements are well known. We also re--emphasize the importance of mixi…
In this paper we present an analysis at NLO of the contribution from squark-squark production to the experimental signature 2j + 2l + missing E_T (+X) with opposite-sign same flavor leptons, taking into account decays and experimental cuts. We consider the case in which one squark decays directly into the lightest neutralino chi^0_1 and the other one into the second lightest neutralino and subsequently into l^+l^-chi^0_1 via an intermediate slepton. On one hand we study effects of the NLO corrections on invariant mass distributions which can be used for future parameter determination. On the o…
We investigate the prospect of stop squark search at Tevatron RUN-II in mSUGRA motivated as well as unconstrained supersymmetric models, when the lighter stop squark turns out to be the next lightest supersymmetric particle (NLSP). In this case the decay into a 4-body final state consisting of a b quark, the lightest neutralino and two light fermions may compete with the much publicized loop induced two body decay into a charm quark and the lightest neutralino. We systematically study the parameter space in mSUGRA where the lighter stop squark turns out to be the NLSP and calculate the branchi…
We consider the prospects for measuring squark flavor violation through the signal of single top production at the LHC. We study this signal in the context of R-symmetric supersymmetry, which allows for large flavor violation in the squark sector, however the results can also be generalized to the MSSM. The single top signal arises from squark pair production in which one squark decays to a top and gaugino, whereas the other squark decays to a non-top quark and gaugino. We study three decay patterns: (I) squark decay into a quark and neutralino LSP; (II) squark decay into a quark and neutralin…
We study the effect of squark generation mixing on squark production and decays at LHC in the Minimal Supersymmetric Standard Model (MSSM). We show that the effect can be very large despite the very strong constraints on quark flavour violation (QFV) from experimental data on B mesons. We find that the two lightest up-type squarks su_{1,2} can have large branching ratios for the decays into 'c-quark + neutralino_1' and 't-quark + neutralino_1' at the same time due to squark generation mixing, leading to QFV signals 'pp -> c bar{t} (t bar{c}) + missing-E_T + X' with a significant rate. The obse…
We calculate the one-loop supersymmetric electroweak-like and QCD-like corrections to the top-quark pair-production cross section at the Tevatron, including the important effects of non-degenerate top-squarks and left-right top-squark mixing. The largest electroweak effects yield a negative shift in the cross section and are enhanced right below the threshold for top-quark decay into top-squark and higgsino-like neutralino, and can be as large as $-35\%$. The largest QCD effects are positive and are enhanced for light top-squark masses, and can be as large as $20\%$. Such shifts greatly exceed…
We study the effect of squark-generation mixing on production and decays of squarks and gluinos at LHC in the Minimal Supersymmetric Standard Model (MSSM). We show that the mixing effects can be very large in a significant range of the squark-generation mixing parameters despite the very strong constraints on quark-flavour violation (QFV) from experimental data on B mesons. We find that under favourable conditions the QFV decay branching ratio B(gluino -> c bar{t} (t bar{c}) neutralino_1) can be as large as about 50%, which may lead to significant QFV signals at LHC. We also find that the squa…
We present an exploratory study of gaugino-pair production in polarized and unpolarized hadron collisions, focusing on the correlation of beam polarization and gaugino/Higgsino mixing in the general Minimal Supersymmetric Standard Model. Helicity-dependent cross sections induced by neutral and charged electroweak currents and squark exchanges are computed analytically in terms of generalized charges, defined similarly for chargino-pair, neutralino-chargino associated, and neutralino-pair production. Our results confirm and extend those obtained previously for negligible Yukawa couplings and no…
We compute the full O(alpha_s) supersymmetric (SUSY) QCD corrections for neutralino annihilation into massive quarks through gauge or Higgs bosons and squarks in the Minimal Supersymmetric Standard Model (MSSM), including the known resummation of logarithmically enhanced terms. The numerical impact of the corrections on the extraction of SUSY mass parameters from cosmological data is analyzed for gravity-mediated SUSY breaking scenarios and shown to be sizable, so that these corrections must be included in common analysis tools.
We calculate the dominant loop corrections from both standard and supersymmetric QCD to the effective coupling of neutralinos to nucleons. The potentially largest corrections come from gluino-squark loop contributions to the Higgs boson couplings to quarks; these corrections also affect the leading spin-independent squark exchange contribution. Ordinary QCD corrections to the effective coupling of CP-even Higgs bosons to two gluons are also sizable. For large $\tanb$ values, i.e. in the region of parameter space probed by current and near-future direct Dark-Matter search experiments, the total…
In this article we calculate the 1-loop supersymmetric QCD (SQCD) corrections to the decay $\tilde u_1\to c \tildeχ^0_1$ in the MSSM with generic flavour structure. This decay mode is phenomenologically important if the mass difference between the lightest squark $\tilde u_1$ (which is assumed to be mainly stop-like) and the neutralino LSP $\tilde χ^0_1$ is smaller than the top mass. In such a scenario $\tilde u_1\to t \tildeχ^0_1$ is kinematically not allowed and searches for $\tilde u_1\to W b \tildeχ^0_1$ and $\tilde u_1\to c \tildeχ^0_1$ are performed. A large decay rate for $\tilde u_1\to…
We study the monojet and dijet channels at the LHC as a tool for searching for squarks and gluinos. We consider two separate R-parity conserving supersymmetric scenarios. In the first scenario we postulate a large mass hierarchy between squarks ($\tilde q$) and winos ($\widetilde W$), and wino-like neutralino is assumed to be the lightest supersymmetric particle (LSP). The associated squark-wino production, $pp \to \tilde q \widetilde W$, then leads to a monojet-like signature, where the high $p_T$ jet is originated from the squark decay, $\tilde q \to q + \widetilde W$. We demonstrate that th…
We discuss the supersymmetric O(alpha_s) QCD corrections to e+ e- -> squark_i + antisquark_j (i,j = 1,2) and to squark_i -> q' + chargino_j, q + neutralino_k (i,j = 1,2; k = 1...4) within the Minimal Supersymmetric Standard Model. In particular we consider the squarks of the third generation stop_i and sbottom_i including the left-right mixing. In the on-shell scheme also the mixing angle has to be renormalized. We use dimensional reduction (which preserves supersymmetry) and compare it with the conventional dimensional regularization. A detailed numerical analysis is also presented.
If the lighter top squark has no kinematically allowed two-body decays that conserve flavor, then it will form hadronic bound states. This is required in models that are motivated by the supersymmetric little hierarchy problem and obtain the correct thermal relic abundance of dark matter by top-squark-mediated neutralino annihilations, or by top-squark-neutralino co-annihilations. It is also found in models that can accommodate electroweak-scale baryogenesis within minimal supersymmetry. I study the prospects for detecting scalar stoponium from its diphoton decay mode at the Large Hadron Colli…
We study the impact of beam polarization on radiative neutralino production e+e- \to χ^0_1 χ^0_1 photon at the International Linear Collider. We show that longitudinal polarized beams significantly enhance the signal and simultaneously reduce the Standard Model background from radiative neutrino production e+e- \to ν\barνphoton. We point out that the radiative production of neutralinos could be the only accessible SUSY particles, if neutralinos, charginos, sleptons, as well as squarks and gluinos are too heavy to be pair-produced in the first stage of the ILC at sqrt{s} = 500 GeV.
The higgsino Lightest Supersymmetric Particle (LSP) scenario opens up the possibility of decays of strongly produced particles to an intermediate neutralino, due to the Yukawa-suppressed direct decays to the higgsino. Those decays produce multijet signals with a Higgs or a $Z$ boson being produced in the decay of the intermediate neutralino to the LSP. In this paper we study the discovery prospects of squarks that produce $b$-jets and leptons in the final state. Our collider analysis provides signal significances at the 3$σ$ level for luminosities of 1 ab$^{-1}$, and at the 5$σ$ level if we pr…
Supersymmetric monojets may be produced at the Large Hadron Collider by the process qg -> squark neutralino_1 -> q neutralino_1 neutralino_1, leading to a jet recoiling against missing transverse momentum. We discuss the feasibility and utility of the supersymmetric monojet signal. In particular, we examine the possible precision with which one can ascertain the neutralino_1-squark-quark coupling via the rate for monojet events. Such a coupling contains information on the composition of the neutralino_1 and helps bound dark matter direct detection cross-sections and the dark matter relic densi…
We demonstrate the possibility of studying weakly interacting new particles in weak boson fusion, using the example of supersymmetric same-sign charginos. This signal could establish the existence of Majorana neutralinos and give access to their electroweak couplings. It can be observed over (supersymmetric) QCD backgrounds provided the charginos are light and not too close to the squark mass. We finally show how same-sign fermion production can be distinguished from same-sign scalars or vectors arising in other models of new physics.
The spectrum of supersymmetric theories with R-parity violation are much more weakly constrained than that of supersymmetric theories with a stable neutralino. We investigate the signatures of supersymmetry at the LHCb experiment in the region of parameter space where the neutralino decay leaves a displaced vertex. We find sensitivity to squark production up to squark masses of order 1 TeV. We note that if the Higgs decays to neutralinos in this scenario, LHCb should see the lightest Higgs boson before ATLAS and CMS.
We evaluate the relic density of neutralinos in the minimal supergravity (mSUGRA) model. All 2->2 neutralino annihilation diagrams, as well as all initial states involving sleptons, charginos, neutralinos and third generation squarks are included. Relativistic thermal averaging of the velocity times cross sections is performed. We find that co-annihilation effects are only important on the edges of the model parameter space, where some amount of fine-tuning is necessary to obtain a reasonable relic density. Alternatively, at high tan(beta), annihilation through the broad Higgs resonances gives…
We investigate the decays of third generation scalar quarks in the Minimal Supersymmetric extension of the Standard Model, focusing on the three-body modes. We calculate the partial widths of the decays of heavier top and bottom squarks into the lighter ones and a fermion pair [through virtual vector boson, Higgs boson or gaugino exchanges] and the partial widths of the three-body decays of both top squarks into bottom quarks and a pair of fermion and scalar fermion [we consider the case of lighter $\tildeτ$ or $\tilde{b}$ states] and into a bottom quark, the lightest neutralino and a $W$ or a…
We determine the neutralino and chargino masses in the MSSM at one-loop. We perform a Feynman diagram calculation in the on-shell renormalization scheme, including quark/squark and lepton/slepton loops. We find generically the corrections are of order 6%. For a 20 GeV neutralino the corrections can be larger than 20%. The corrections change the region of $μ,\ M_2,\ \tanβ$ parameter space which is ruled out by LEP data. We demonstrate that, e.g., for a given $μ$ and $\tanβ$ the lower limit on the parameter $M_2$ can shift by 20 GeV.
The measurement of sparticle masses in the Minimal Supersymmetric Standard Model at the LHC is analysed, in the scenario where the lightest neutralino decays into three quarks. Such decays, occurring through the baryon-number violating coupling lambda"\_ijk, pose a severe challenge to the capability of the LHC detectors since the final state has no missing energy signature and a high jet multiplicity. We focus on the case of non-zero lambda"\_212 which is the most difficult experimentally. The proposed method is valid over a wide range of SUGRA parameter space with lambda"\_212 between 10^{-5}…
We consider two classes of t-b-tau quasi-Yukawa unification scenarios which can arise from realistic supersymmetric SO(10) and SU(4)_C X SU(2)_L X SU(2)_R models. We show that these scenarios can be successfully implemented in the CMSSM and NUHM1 frameworks, and yields a variety of sparticle spectra with WMAP compatible neutralino dark matter. In NUHM1 we find bino-higgsino dark matter as well as the stau coannihilation and A-funnel solutions. The CMSSM case yields the stau coannihilation and A-funnel solutions. The gluino and squark masses are found to lie in the TeV range.
