The process of stop-chargino production at LHC has been calculated in the Minimal Supersymmetric Standard Model at the complete electroweak one-loop level, assuming a mSUGRA symmetry breaking scheme. Several properties of the angular and invariant mass distributions of the basic bottom-gluon to stop-chargino amplitudes have been derived. For a meaningful collection of different benchmark points the overall electroweak one-loop effects are at most of the order of a few percent. At the realistically expected LHC accuracy, the main supersymmetric electroweak features of the process can be therefore essentially derived in this theoretical scheme from the simple Born level expressions.
Top squark (stop) plays a crucial role in the naturalness of supersymmetry (SUSY) models, which has been extensively searched for in the LHC experiments. Due to the parity-violating couplings, top quark and chargino thus produced from stop decay are expected to be polarized. We investigate the polarization of top quark and chargino, from which we find that the mass differences between neutralino and stop/chargino can affect the degree of polarization of top quark/chargino in the stop decay. We then examine the top polarization effects on kinematics of stop decay in natural SUSY (NSUSY) at the …
We consider the process of associated stop-chargino production in the MSSM at LHC and show that, at the simplest Born level, the production rate is dramatically sensitive to the choice of the benchmark points, oscillating from potentially "visible" maxima of the picobarn size to much smaller, hardly "visible", values. Adopting a canonical choice of SM type CKM matrices, we also show that in some "visible" cases the total rate exhibits a possibly relevant dependence on tan(beta).
The electroweak corrections to the partial widths of the $H^+ \to \tildeχ^+_i \tildeχ_j^0 (i=1,j=1,2)$ decays including one-loop diagrams of the third generation quarks and squarks, are investigated within the Supersymmetric Standard Model. The relative corrections can reach the values about 10%, therefore they should be taken into account for the precise experimental measurement at future colliders.
We consider the production of neutralino, chargino, and charged Higgs boson pairs in the MSSM framework at future $e^+e^-$ colliders. We show that, for c.m. energies in the one TeV range and in a ``moderately'' light SUSY scenario, a combined analysis of the slopes of these production cross sections could lead to a strong consistency test involving the soft supersymmetric breaking parameters $M_1$, $M_2$, the Higgsino parameter $μ$, and $\tanβ$.
In the MSSM with complex parameters, loop corrections to the decay of a stop into a bottom quark and a chargino can lead to a CP violating decay rate asymmetry. We calculate this asymmetry at full one-loop level and perform a detailed numerical study, analyzing the dependence on the parameters and complex phases involved. If the stop can decay into a gluino, the self-energy and the vertex correction dominate due to the strong coupling. It is shown that the vertex contribution is always suppressed. We therefore give a simple approximate formula for the asymmetry. We account for the constraints …
We study the process of the association production of chargino and neutralino including the NLO QCD and the complete one-loop electroweak corrections in the framework of the minimal supersymmetric standard model(MSSM) at the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). In both the NLO QCD and one-loop electroweak calculations we apply the algorithm of the phase-space slicing(PSS) method. We find that the NLO QCD corrections generally increase the Born cross sections, while the electroweak relative corrections decrease the Born cross section in most of the chosen parameter space.…
We present the complete electroweak one-loop corrections to the partial widths for two-body decays of a chargino (neutralino) into a W-boson and a neutralino (chargino). We perform the calculation for the minimal and the next-to-minimal supersymmetric standard model using an on-shell renormalization scheme. Particular attention is paid to the question of gauge invariance which is achieved using the so-called pinch technique. Furthermore we show that these corrections show a strong parameter dependence and usually are in the range of 1-10 percent if the neutralino involved is a higgsino or wino…
In the MSSM with complex parameters, loop corrections to the decay of a stop into a bottom quark and a chargino can lead to a CP violating decay rate asymmetry. We calculate this asymmetry at full one-loop level and perform a detailed numerical study, analyzing the dependence on the parameters and complex phases involved. In addition, we take the Yukawa couplings of the top and bottom quark running. We account for the constraints on the parameters coming from several experimental limits. Asymmetries of several percent are obtained. We also comment on the feasibility of measuring this asymmetry…
The Higgs bosons of the MSSM can be produced from the decay of SUSY particles. We review the evalulation of two decay modes in the MSSM with complex parameters (cMSSM). The first type is the decay of the heavy scalar top quark to a lighter scalar quark and a Higgs boson. The second type is the decay of the heavy chargino to a lighter chargino/neutralino and a Higgs boson. The evaluation is based on a full one-loop calculation including hard QED and QCD radiation. We find sizable contributions to many partial decay widths and branching ratios. They are roughly of O(10%) of the tree-level result…
We investigated the electroweak corrections from one-loop diagrams involving the third generation (s)quarks to the decay width of process $\tildeχ_1^+ \to W^+ \tildeχ_1^{0}$ in the framework of the Minimal Supersymmetric Standard Model. Our calculation shows that these corrections are not very sensitive to the mass of the lightest neutralino $\tildeχ_1^{0}$ and the sbottom mixing angle $θ_{b}$, but depend strongly on the top squark mixing angle $θ_{t}$ and tan$β$. With our chosen parameters, we find that these radiative corrections can exceed 10%, therefore they should be taken into account fo…
We investigate the supersymmetric electroweak corrections to the decay widths of the CP-odd and the heavy CP-even Higgs bosons into chargino or neutralino pair in the framework of the Minimal Supersymmetric Standard Model. The corrections involve the contributions of the order $O(α_{ew} m_{t(b)}^3/m_W^3)$, $O(α_{ew} m_{t(b)}^2/m_W^2)$ and $O(α_{ew} m_{t(b)}/m_W)$. The detailed calculations of the electroweak corrections to the following decay processes: $A^0/H^0 \to \tildeχ^+_1 \tildeχ^-_1$ and $A^0/H^0 \to \tildeχ^0_2 \tildeχ^0_2$ are presented in this paper. We find that these relative corre…
Current searches for direct production of scalar top quarks, or stops, in supersymmetry focus on their decays into W boson + b quark + neutralino by way of top + neutralino and bottom + chargino. While the polarization of the top quark depends on the stop mixing, the chargino turns out to be fully polarized when the bottom Yukawa coupling can be neglected relative the top Yukawa coupling. We compute the energy and angular spectra of the charged lepton in the chargino channel, which could serve as the spin-analyzer of the chargino. In addition, we demonstrate the top polarization could have a s…
We correct a numerical error which led to an overestimate of the baryon asymmetry from supersymmetric electroweak baryogenesis in our paper JHEP07(2000)018. Updated dependences of the baryon asymmetry on chargino mass parameters and the bubble wall velocity are shown. We also include LEP-II-constraints on the chargino mass parameters. Combined with our corrected results for the baryon asymmetry these constraints imply that the phase in the chargino mass matrix must violate CP nearly maximally in order to generate a large enough baryon asymmetry. A number of other typographical errors are also …
We study the baryon asymmetry of the universe in the supersymmetric standard model (SSM). At the electroweak phase transition, the fermionic partners of the charged SU(2) gauge bosons and Higgs bosons are reflected from or transmitted to the bubble wallof the broken phase. Owing to a physical complex phase in their mass matrix, these reflections and transmissions have asymmetries between CP conjugate processes. Equilibrium conditions in the symmetric phaseare then shifted to favor a non-vanishing value for the baryon number density, which is realized through electroweak anomaly. We show that t…
In view of the recent measurement of the muon g-2 and finalization of the LEP electroweak data, we re-examine all the new particle contributions to those observables in the MSSM. The SM fits the latest electroweak data excellently with the observed top-quark mass and the Higgs-boson mass of around 100 GeV, and so does the MSSM in the decoupling limit. The MSSM gives a slightly better fit to the data than the SM (Δχ^2_{min} \sim -2) when relatively light left-handed sleptons of mass \sim 200 GeV and a light chargino of mixed higgsino-wino character (μ/M_2 \sim 1) with mass \sim 100 GeV co-exist…
The lack of evidence for the production of colored supersymmetric particles at the LHC has increased interest in searches for superpartners of the electroweak SM gauge bosons, namely the neutralinos and charginos. These are challenging due to the weak nature of the production process, and the existing discovery reach has significant gaps in due to the difficulty of separating the supersymmetric signal from SM diboson events that produce similar final states and kinematics. We apply the Recursive Jigsaw Reconstruction technique to study final states enriched in charged leptons and missing trans…
We present a phenomenological study of Dirac electroweakinos in a $U(1)_R$ extension of the MSSM with a strictly $R$-symmetric Higgs sector (MRSSM) and gauge-mediated supersymmetry breaking. One of the distinguishing features of the MRSSM is that the lightest chargino can be lighter than the lightest neutralino. Decays from the NLSP chargino to the gravitino LSP will produce exotic signals. We apply LHC-13 mass limits from both prompt and long-lived searches to the chargino NLSP regime of the MRSSM. Imposing the additional constraints coming from the 125 GeV Higgs and from the electroweak sect…
We compute corrections to precision electroweak observables in supersymmetry in the limit that scalar superpartners are very massive and decoupled. This leaves charginos and neutralinos and a Standard Model-like Higgs boson as the only states with unknown mass substantially affecting the analysis. We give complete formulas for the chargino and neutralino contributions, derive simple analytic results for the pure gaugino and higgsino cases, and study the general case. We find that in all circumstances, the precision electroweak fit improves when the charginos and neutralinos are near the curren…
The hallmark way to search for electroweakinos in natural supersymmetry at the LHC involves the trilepton plus missing energy final state. This approach assumes an electroweakino mass hierarchy that allows for cascade decays leading to a final state of $W^{\pm}Z^0$ plus missing energy. There are, however, situations when that decay pattern may not exist, such as when a chargino is the lightest electroweakino and the lightest supersymmetric particle is the gravitino. In regions of the parameter space where this ordering occurs, the production of any combination of neutralino/chargino leads to a…
We calculate the full one-loop electroweak (FEW) corrections to $H^-\to\widetildeχ^-_1\widetildeχ^0_i$ in the minimal supersymmetric standard model (MSSM), and compare with the leading order (LO) corrections including the loops of the (s)quarks only in the third generation and the complete leading order (CLO) corrections including the loops of the (s)quarks in all the three generations. We find that the magnitudes of the FEW corrections can be larger than 10% for $\tanβ>30$. Moreover, comparing with the FEW corrections, both of the LO and the CLO corrections are negligible small for the mode 1…
If light--flavor squarks and gluinos are indeed heavy and chargino pair production is plagued with overwhelming backgrounds, pair production and associated production of stops and charginos will become the key signatures in the upcoming LHC runs. We present fully automated next-to-leading order predictions for heavy flavor squark production at the LHC, including stop-chargino associated production, based on MadGolem. We compute the total and differential NLO rates for a variety of MSSM scenarios with a light third generation. We focus on theoretical uncertainties on differential rates, includi…
We argue that the creation of a baryon asymmetry in the early universe is an intriguing case where several aspects of ``Beyond'' physics are needed. We then concentrate on baryogenesis in a strong first-order phase transition and discuss that supersymmetric variants of the electroweak theory (MSSM and some version of NMSSM) rather naturally provide the necessary ingredients. The charginos and the stops play a prominent role. We present CP-violating dispersion relations in the chargino sector and show results of a concrete model calculation for the asymmetry production based on quasi-classical …
We make use of the formalism developed in Ref. [1], and calculate the chargino mediated baryogenesis in the Minimal Supersymmetric Standard Model. The formalism makes use of a gradient expansion of the Kadanoff-Baym equations for mixing fermions. For illustrative purposes, we first discuss the semiclassical transport equations for mixing bosons in a space-time dependent Higgs background. To calculate the baryon asymmetry, we solve a standard set of diffusion equations, according to which the chargino asymmetry is transported to the top sector, where it biases sphaleron transitions. At the end …
The top squark (stop) may dominantly decay to a bottom quark and a chargino if the mass difference between the stop and the lightest neutralino is comparable or less than the top quark mass. Such a moderately compressed spectrum is a challenging scenario for the stop search at the Large Hadron Collider, because it is difficult to separate the signals from the top and anti-top background. In this paper we focus on the di-leptonic decay channel, and consider many kinematic variables as possible discriminators. These include several MT2 variables and new "compatible-masses" variables which fully …
A right-handed stop not much heavier or even lighter than the Z boson has today desirable phenomenological consequences. We study how it can result within the usual radiative scenario of electroweak symmetry breaking. A restriction on the gaugino mass parameters, M_2 < 0.3 m_10, arises if soft terms satisfy relations suggested by unification theories. Moreover, requiring to get a light stop without unnatural fine-tunings below the per-cent level, we obtain another more interesting upper bound on the chargino mass, M_chargino < M_Z, and we derive interesting conclusions about the masses of the …
Supersymmetric (SUSY) explanation of the discrepancy between the measurement of $(g-2)_μ$ and its SM prediction puts strong upper bounds on the chargino and smuon masses. At the same time, lower experimental limits on the chargino and smuon masses, combined with the Higgs mass measurement, lead to an upper bound on the stop masses. The current LHC limits on the chargino and smuon masses (for not too compressed spectrum) set the upper bound on the stop masses of about 10 TeV. The discovery potential of the future lepton and hadron colliders should lead to the discovery of SUSY if it is responsi…
A rather high Higgs mass, m_h = 126 GeV, suggests that at least a part of the supersymmetric spectrum of the MSSM may live beyond O(1TeV) and hence inaccessible to the LHC. However, there are theoretical and phenomenological reasons supporting a possibility that charginos and neutralinos remain much closer to the electroweak scale. In this paper, we explore such a scenario in the light of recent Higgs measurements, mainly its di-photon decay rate, where the data might indicate a slight excess over the SM prediction. That excess could be fitted by the contribution of light charginos provided ta…
Top squark (stop) can be produced via QCD interaction but also the electroweak interaction at the LHC. In this paper, we investigate the observability of the associated production of stop and chargino, $pp \to \tilde{t}_1\tildeχ^-_1$, in compressed electroweakino scenario at the 14 TeV LHC. Due to the small mass-splitting between the lightest neutralino ($\tildeχ^0_1$) and chargino ($\tildeχ^-_1$), such a single stop production can give a mono-top signature through the stop decay $\tilde{t}_1 \to t \tildeχ^0_1$. Focusing on the leptonic mono-top channel, we propose a lab-frame observable $\cos…
We analyze the partial decay widths of sfermions decaying into charginos and neutralinos $Γ(\tilde{f} -> f'χ)$ at the one-loop level, including the electroweak and strong corrections. We present the renormalization framework, and discuss the value of the corrections. Since these corrections show non-decoupling effects, we analyze the radiative effects induced by a heavy squark sector into the lepton-slepton-chargino/neutralino couplings. We conclude that some knowledge of the heavy sector is needed in order to provide a sufficiently precise prediction for slepton observables at an $e^+e^-$ Lin…
Recently Osland and Vereshagin noticed, based on sample calculations of some box diagrams, that in unpolarised e+e- collisions CP-odd effects in the non-diagonal chargino-pair production process are generated at one-loop. Here we perform a full one-loop analysis of these effects and point out that in some cases the neglected vertex and self-energy contributions may play a dominant role. We also show that CP asymmetries in chargino production are sensitive not only to the phase of mu parameter in the chargino sector but also to the phase of stop trilinear coupling A_t.
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.
We show that, for all values of $Tan β$ and the light right-handed stop mass for which the electroweak phase transition is strong enough to avoid washout following electroweak baryogenesis, the electroweak vacuum is stable over the lifetime of the observed Universe. Cosmological stability of the electroweak vacuum is violated only if the light right-handed stop is lighter than 100-115GeV.
We review the extraction of fundamental supersymmetric parameters from experimental observables related to the detection of charginos and selectrons at $e^+e^-$ colliders. We consider supergravity models with universal scalar and gaugino masses and radiatively broken electroweak symmetry. Two scenarios are considered: (a) The lightest chargino is light enough to be produced at LEP2, and (b) the right handed selectron is light enough to be produced at LEP2. We show how the validity of supergravity models can be tested even if experimental errors are large. Interesting differences between the sp…
Very precise measurements of masses and cross sections are expected to be achievable with a future linear collider. With such an accuracy one must incorporate loop corrections in order to make meaningful predictions for the underlying new physics parameters. For the electroweakino sector, this involves fitting one-loop predictions to expected measurements of the cross section and forward-backward asymmetry for chargino pair production and of the accessible chargino and neutralino masses. We consider two scenarios with characteristic features, chosen taking recent LHC SUSY and Higgs searches in…
The simplest interpretation of the global success of the Standard Model is that new physics decouples well above the electroweak scale. Supersymmetric extension of the Standard Model offers the possibility of light chargino and the right-handed stop (with masses below $M_Z$), and still maintaining the successful predictions of the Standard Model. The value of $R_b$ can then be enhanced up to $\sim 0.218$ (the Standard Model value is $\sim 0.216$). Light chargino and stop give important contribution to rare processes such as $b\rightarrow s γ$, $\overline K^0-K^0$ and $\overline B^0-B^0$ mixing…
The $αm_t^2/m_W^2$ order supersymmetric electroweak corrections arising from loops of chargino, neutralino, and squark to top quark pair production by $gg$ fusion at LHC are calculated in the minimal supersymmetric model. We found that the corrections amount about a few percent.
Previously, in the context of the minimal supersymmetric standard model (without {\em a priori} assumptions of parameter unification), we studied the constraints on weak-scale SUSY parameters from chargino production at LEP II, using as observables $\mch$, $\mLSP$, the cross section and the leptonic branching fraction. Here, exploiting the high degree of polarization in chargino production, we add to our earlier work the forward-backward asymmetries of the visible hadrons and leptons in chargino decays. For a chargino that is mostly gaugino, the parameter space can now be restricted to a small…
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 …
We test the impact of the ATLAS and CMS multi-lepton searches performed at the LHC with 8 as well as 13 TeV center-of-mass energy (using only the pre-2018 results) on the chargino and neutralino sector of the NMSSM. Our purpose consists in analyzing the actual reach of these searches for a full model and in emphasizing effects beyond the MSSM that affect the performance of current (MSSM-inspired) electroweakino searches. To this end, we consider several scenarios characterizing specific features of the NMSSM electroweakino sector. We then perform a detailed collider study, generating Monte-Car…
Very precise measurements of masses and cross sections, with errors of <1%, are expected to be achievable with a future linear collider. Such an accuracy gives sensitivity at the level of quantum corrections, which therefore must be incorporated in order to make meaningful predictions for the underlying new physics parameters. For the chargino-neutralino sector, this involves fitting one-loop predictions to expected measurements of the cross sections and forward-backward asymmetries and of the accessible chargino and neutralino masses. Our analysis shows how an accurate determination of the de…
We explore the one-loop electroweak radiative corrections in $SU(5)\times U(1)$ supergravity via explicit calculation of vacuum-polarization and vertex-correction contributions to the $ε_1$ and $ε_b$ parameters. Experimentally, these parameters are obtained from a global fit to the set of observables $Γ_{l}, Γ_{b}, A^{l}_{FB}$, and $M_W/M_Z$. We include $q^2$-dependent effects, which induce a large systematic negative shift on $ε_{1}$ for light chargino masses ($m_{χ^\pm_1}\lsim70\GeV$). The (non-oblique) supersymmetric vertex corrections to $\Zbb$, which define the $ε_b$ parameter, show a sig…
The results of many LHC searches for supersymmetric particles are interpreted using simplified models, in which one fixes the masses and couplings of most sparticles then scans over a few remaining masses of interest. We present a new technique for combining multiple simplified models (that requires no additional simulation) thereby highlighting the utility and limitations of simplified models in general, and demonstrating a simple way of improving LHC search strategies. The technique is used to derive limits on the stop mass that are model independent, modulo some reasonably generic assumptio…
We perform a model independent analysis of the chargino contributions to the CP asymmetry in B -> Phi K(S) process. We use the mass insertion approximation method generalized by including the possibility of a light right-stop. We find that the dominant effect is given by the contributions of the mass insertions deltaU_LL(32) and deltaU_RL(32) to the Wilson coefficient of the chromomagnetic operator. By considering both these contributions simultaneously, the CP asymmetry in B -> Phi K(S) process is significantly reduced and negative values, which are within the 1-sigma experimental range and s…
One loop contributions to the Higgs boson masses and mixings from the chargino sector consisting of the chargino, the W, and the charged Higgs boson ($χ^+-W-H^+$) exchanges and including the effects of large CP violating phases are computed. It is found that the chargino sector makes a large contribution to the mixings of the CP even and the CP odd Higgs sectors through the induced one loop effects and may even dominate the mixing generated by the stop and the sbottom sectors. Effects of the chargino sector contribution to the Higgs boson masses are also computed. It is found that the sum of t…
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\%.
The multi-sector SUSY breaking predicts pseudo-goldstino which can couple to the visible sector more strongly than the ordinary gavitino and thus induce the decays of the lightest neutralino and chargino (collectively called electroweakinos) inside the detector. In this note we study the electroweakino pair productions via vector boson fusion (VBF) processes followed by decays to pseudo-goldstino at the LHC. Our Monte Carlo simulations show that at the 14 TeV LHC with 3000 fb^{-1} luminosity the dominant production channel pp->chargino+neutralino+2 jets can have a statistical significance abov…
We present a Monte-Carlo event generator for simulating chargino pair-production at the International Linear Collider (ILC) at next-to-leading order in the electroweak couplings. By properly resumming photons in the soft and collinear regions, we avoid negative event weights, so the program can simulate physical (unweighted) event samples. Photons are explicitly generated throughout the range where they can be experimentally resolved. Inspecting the dependence on the cutoffs separating the soft and collinear regions, we evaluate the systematic errors due to soft and collinear approximations. I…
We present a set of NLO SUSY-QCD calculations for the pair production of neutralinos and charginos at the LHC, and their matching to parton-shower programs in the framework of the POWHEG-BOX program package. The code we have developed provides a SUSY Les Houches Accord interface for setting supersymmetric input parameters. Decays of the neutralinos and charginos and parton-shower effects can be simulated with PYTHIA. To illustrate the capabilities of our program, we present phenomenological results for a representative SUSY parameter point. We find that NLO-QCD corrections increase the product…
We present the full $\mathcal{O}(α_s)$ supersymmetric QCD corrections for stop-anti-stop annihilation into electroweak final states within the Minimal Supersymmetric Standard Model (MSSM). We also incorporate Coulomb corrections due to gluon exchange between the incoming stops. Numerical results for the annihilation cross sections and the predicted neutralino relic density are presented. We show that the impact of the radiative corrections on the cosmologically preferred region of the parameter space can become larger than the current experimental uncertainty, shifting the relic bands within t…
The possibility of creating baryon asymmetry at the electroweak phase transition in the minimal supersymmetric standard model is considered for the case when right-handed squarks are much lighter than left-handed ones. It is shown that the usual requirement v(T_c)/T_c > 1 for baryogenesis can be satisfied in a range of the parameters of the model, consistent with present experimental bounds.
SUSY events in which a light stop decays to a chargino may manage to pass the cuts designed for top counting experiments at the Tevatron with no significant diminution of signal. Events in which a top decays via stop are detected with fair efficiency compared to SM top events when $\stop\into b\wino$. More importantly, direct pair production of light stops contributes significantly to the cut samples. Many SUSY models with stops lighter than 100 GeV are viable even for $Γ(t\into\stop) \approx Γ(t\into bW)$.
We explore modifications to the loop-induced Higgs couplings hγγ and hγZ from light charginos in the Minimal Supersymmetric Standard Model. When the lightest chargino mass is above the naive LEP bound of order 100 GeV the effects are modest, with deviations in the decay branching ratios typically less than 15% from the Standard Model predictions. However, if the charginos are lighter than 100 GeV, more dramatic alterations to these couplings are possible as a consequence of the rise of the one loop form factor. For example, the diphoton signal strength can be enhanced by as much as 70% compare…
The recent LHC discovery of a Higgs-like boson at 126 GeV has important consequences for SUSY, pushing the spectrum of strong-interacting supersymmetric particles to high energies, very difficult to probe at the LHC. This gives extra motivation to study the direct production of electroweak particles, as charginos and neutralinos, which are presently very poorly constrained. The aim of this work is to improve the analysis of chargino-neutralino pair production at LHC, focusing on the kinematics of the processes. We propose a new method based on the study of the poles of a certain kinematical va…
We study the decays of the lightest top squark in supergravity models with and without R-parity. Using the simplest model with an effective explicit bilinear breaking of R-parity and radiative electroweak symmetry breaking we show that, below the threshold for decays into charginos $\tilde t_1\to cχ^+_1$, the lightest stop decays mainly into third generation fermions, $\tilde t_1\to bτ$ instead of the R-parity conserving mode $\tilde t_1\to cχ^0_1$, even for tiny tau--neutrino mass values. Moreover we show that, even above the threshold for decays into charginos, the decay $\tilde t_1\to bτ$ m…
At a future linear collider, very precise measurements, typically with errors of <1%, are expected to be achievable. Such an accuracy yields sensitivity to quantum corrections, which therefore must be incorporated into theoretical calculations in order to determine the underlying new physics parameters from linear collider measurements. In the context of the chargino--neutralino sector of the minimal supersymmetric standard model, this involves fitting one-loop predictions to prospective measurements of cross sections, forward-backward asymmetries and the accessible chargino and neutralino mas…
We compute the wall velocity in the MSSM. We therefore generalize the SM equations of motion for bubble walls moving through a hot plasma at the electroweak phase transition and calculate the friction terms which describe the viscosity of the plasma. We give the general expressions and apply them to a simple model where stops, tops and W bosons contribute to the friction. In a wide range of parameters including those which fulfil the requirements of baryogenesis we find a wall velocity of order v = 0.05-0.1 much below the SM value.
The light stop pair if produced in hadron colliders and decaying through the likely decay chain stop->chargino + b followed by chargino->neutralino + f f', can mimic closely a top quark event when the mass of the stop is close to that of the top quark. Because of the much lower production rate, the stop event can be buried under the top quark event sample. In order to uncover the stop event, specific selection cuts need to be applied. Through Monte Carlo simulation with suitable kinematic cuts, we found that such stop event can be extracted from the top quark sample and detected by the top qua…
We discuss supersymmetric contributions to the electroweak precision measurements in the Minimal Supersymmetric Standard Model for two cases: the quark-lepton universality violation $δ_{q\ell}$ in charged currents and the ratio $R_b=Γ(Z\rightarrow b\bar{b})/Γ(Z\rightarrow \rm hadrons)$. The recent experimental data suggest deviations from the Standard Model for these observables, at the 1-$σ$ level for the former and at more than 3-$σ$ level for the latter. We analyze the non-oblique corrections from the SUSY particles to explain these discrepancies. The observed non-zero $δ_{q\ell}$ may be ex…
In most supersymmetric theories, charginos $\tildeχ^\pm_{1,2}$ belong to the class of the lightest supersymmetric particles and the couplings of Higgs bosons to charginos are in general complex so that the CP--violating chargino contributions to the loop--induced coupling of the lightest Higgs boson to photon pairs can be sizable even in the decoupling limit of large pseudoscalar mass $m_A$ with only the lightest Higgs boson kinematically accessible at future high energy colliders. We introduce a specific benchmark scenario of CP violation consistent with the electric dipole moment constraints…
