Light stops, blind spots, and isospin violation in the MSSM
Andreas Crivellin, Martin Hoferichter, Massimiliano Procura, Lewis C. Tunstall
备注：
38 pages, 15 figures. v2: expanded text in Sec. 3 concerning relic density and (g-2)_mu constraints, clarified text on isospin violation. Fig. 1 is new, minor changes to Figs. 3,4,10. References added, journal version
In the framework of the MSSM, we examine several simplified models where only a few superpartners are light. This allows us to study WIMP--nucleus scattering in terms of a handful of MSSM parameters and thereby scrutinize their impact on dark matter direct-detection experiments. Focusing on spin-independent WIMP--nucleon scattering, we derive simplified, analytic expressions for the Wilson coefficients associated with Higgs and squark exchange. We utilize these results to study the complementarity of constraints due to direct-detection, flavor, and collider experiments. We also identify parameter configurations that produce (almost) vanishing cross sections. In the proximity of these so-called blind spots, we find that the amount of isospin violation may be much larger than typically expected in the MSSM. This feature is a generic property of parameter regions where cross sections are suppressed, and highlights the importance of a careful analysis of the nucleon matrix elements and the associated hadronic uncertainties. This becomes especially relevant once the increased sensitivity of future direct-detection experiments corners the MSSM into these regions of parameter space.
We present a program for calculating the isospin symmetry breaking of the B -> K* gamma decay in the MSSM with minimal flavor violation. This program calculates the NLO supersymmetric contributions to the isospin asymmetry, using the effective Hamiltonian approach and within the QCD factorization method. We show that isospin symmetry breaking proves to be a very restrictive observable, in particular in the mSUGRA parameter space. The program also calculates the inclusive branching ratio associated to b -> s gamma transition, as a comparison reference.
Non-minimal supersymmetric models that predict a tree-level Higgs mass above the Minimal Supersymmetric Standard Model (MSSM) bound are well motivated by naturalness considerations. Indirect constraints on the stop sector parameters of such models are significantly relaxed compared to the MSSM; in particular, both stops can have weak-scale masses. We revisit the stop-catalyzed electroweak baryogenesis (EWB) scenario in this context. We find that the LHC measurements of the Higgs boson production and decay rates already rule out the possibility of stop-catalyzed EWB. We also introduce a gauge-i…
We investigate the implications of the Higgs rate measurements from Run 1 of the LHC for the mass of the light scalar top partner (stop) in the Minimal Supersymmetric Standard Model (MSSM). We focus on light stop masses, and we decouple the second, heavy stop and the gluino to the multi-TeV range in order to obtain a Higgs mass of around 125 GeV. We derive lower mass limits for the light stop within various scenarios, taking into account the effects of a possibly light scalar tau partner (stau) or chargino on the Higgs rates, of additional Higgs decays to undetectable new physics, as well as o…
The "top-down" approach to minimal supersymmetric standard model (MSSM) phenomenology provides model-dependent indications for a natural stop mass. The approach is based on specific assumptions about the supersymmetry-breaking energy scale and parameters degeneracies. In order to determine robust predictions we update the stop-mass prediction within the MSSM with 25 parameters (MSSM-25) by including electroweak fine-tuning as "naturalness data" during the Bayesian fits of the parameters to experimental data. The approximately prior-independent results show that imposing naturalness, taken here…
A Standard Model-like Higgs near 125 GeV in the MSSM requires multi-TeV stop masses, or a near-maximal contribution to its mass from stop mixing. We investigate the maximal mixing scenario, and in particular its prospects for being realized it in potentially realistic GUT models. We work out constraints on the possible GUT-scale soft terms, which we compare with what can be obtained from some well-known mechanisms of SUSY breaking mediation. Finally, we analyze two promising scenarios in detail, namely gaugino mediation and gravity mediation with non-universal Higgs masses.
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.
In this article we study the MSSM with stops and Higgs scalars much lighter than gluinos and squarks of the first two generations. In this setup, one should use an effective field theory with partial supersymmetry in which the gluino and heavy squarks are integrated out in order to connect SUSY parameters (given at a high scale) to observables in the stop sector. In the construction of this effective theory, valid below the gluino mass scale, we take into account $O(α_3)$ and $O(Y_{t,b}^2)$ effects and calculate the matching as well as the renormalization group evolution. As a result, the runn…
We review an analysis of a consistent renormalization of the top and bottom quark/squark sector of the MSSM with complex parameters (cMSSM). Various renormalization schemes are defined, analyzed analytically and tested numerically in the decays Stop_2 -> Sbottom_i H^+/W^+ (i = 1,2). No scheme is found that produces numerically acceptable results over all the cMSSM parameter space, where problems occur mostly already for real parameters. Some numerical examples for Gamma(Stop_2 -> Sbottom_1 H^+) in our preferred scheme, "m_b, A_b DRbar" are shown.
The implications of the LEP Higgs bounds on the MSSM stop masses and mixing are compared in two different regions of the Higgs parameter space. The first region is the Higgs decoupling limit, in which the bound on the mass of the lighter Higgs is $m_h \ge 114.4$ GeV, and the second region is near a non-decoupling limit with $m_h \simeq 93$ GeV, in which the masses of all the physical Higgs bosons are required to be light. Additional constraints from the electroweak $S$- and $T$-parameter and the decays $B \to X_s γ$ and $B_s \to μ^+ μ^-$, which also constrain the Higgs and/or stop sector, are …
We propose using the lightest CP-even Higgs boson in the minimal supersymmetric standard model (MSSM) to probe the stop sector. Unlike measuring stop masses in production/decay processes which requires knowledge of masses and mixing angles of other superparticles, the strategy depends little on supersymmetric parameters other than those in the stop sector in a large region of parameter space. We show that measurements of the Higgs mass and the production rate in the gluon fusion channel, the dominant channel at the LHC, allow for determination of two parameters in the stop mass-squared matrix,…
We calculate the finite temperature 2-loop effective potential in the MSSM with stop condensation, using a 3-dimensional effective theory. We find that in a part of the parameter space, a two-stage electroweak phase transition appears possible. The first stage would be the formation of a stop condensate, and the second stage is the transition to the standard electroweak minimum. The two-stage transition could significantly relax the baryon erasure bounds, but the parameter space allowing it (m_H \lsim 100 GeV, m_tR \sim 155-160 GeV) is not very large. We estimate the reliability of our results…
We compute the one-loop radiative corrections to the masses of the top quark, the stop squarks and the gluino in the Minimal Supersymmetric Standard Model. We include the loops controlled by the strong coupling constant and the top Yukawa coupling, neglecting those controlled by the $SU(2) \times U(1)$ gauge couplings and by other Yukawa couplings. We find that the significant scale-dependence of the renormalization-group-improved tree-level expressions is almost completely removed. Even for natural choices of the renormalization scale, corrections can be numerically relevant. Our results shou…
This work investigates the possibility of a long-lived stop squark in supersymmetric models with the neutralino as the lightest supersymmetric particle (LSP). We study the implications of meta-stable stops on the sparticle mass spectra and the dark matter density. We find that in order to obtain a sufficiently long stop lifetime so as to be observable as a stable R-hadron at an LHC experiment, we need to fine tune the mass degeneracy between the stop and the LSP considerably. This increases the stop-neutralino coanihilation cross section, leaving the neutralino relic density lower than what is…
We discuss the phenomenology of the lightest stops in models where R-parity is broken by bilinear terms. In this class of models we consider scenarios where the R-parity breaking two-body decay stop_1 -> tau + b competes with the leading three-body decays stop_1 -> W^+ + b + neutralino_1, H^+ + b + neutralino_1, b slepton^+_i neutrino_l, b sneutrino_l l^+ (l=e, mu, tau). We demonstrate that the R-parity violating decay can be the dominant one. In particular we focus on the implications for a future electron posistion Linear Collider.
We study the decays of top squarks and bottom squarks in the Minimal Supersymmetric Standard Model with complex parameters A_t, A_b and mu. In a large region of the supersymmetric parameter space the branching ratios of stop_1 and sbottom_1 show a pronounced phase dependence. This could have an important impact on the search for stop_1 and sbottom_1 at a future linear collider and on the determination of the supersymmetric parameters.
We consider the viability of the minimal supersymmetric standard model with a light ($m_{\tilde t_1} < $ 45 GeV) stop. In order for its relic abundance to be cosmologically significant, the photino as dark matter must be quite close in mass to the stop, $(m_{\tilde t_1} - m_{\tilde γ}) \simeq 3 - 7 $ GeV. However, as we show, the photino despite its low mass is virtually undetectable by either direct or indirect means. We also discuss the implications of these masses on the top quark branching ratios.
The first chapter serves as an introduction to the MSSM. I briefly review the model and explain why stops and sbottoms provide an interesting playground for exploring and testing this model. In the second chapter I discuss stop and sbottom production at lepton colliders. I give the analytical formulae for the production cross sections at e+e- and mu+mu- colliders including (general) beam polarization. A numerical analysis shows the cross sections that can be expected at LEP2, an e+e- Linear Collider, and a Muon Collider. In particular, I address the topics of what can be gained by using polari…
In this work, we study the implication of Higgs precision measurements at future Higgs factories on the MSSM parameter space, focusing on the dominant stop sector contributions. We perform a multi-variable fit to both the signal strength for various Higgs decay channels at Higgs factories and the Higgs mass. The chi-square fit results show sensitivity to mA, tan beta, stop mass parameter mSUSY as well as the stop left-right mixing parameter Xt. We also study the impact of the Higgs mass prediction on the MSSM and compare the sensitivities of different Higgs factories.
We consider the regions of the MSSM parameter space where the top squarks become light and even may be the LSP. This happens when the triple scalar coupling A becomes very big compared to m_0. We show that in this case the requirement that the LSP is neutral imposes noticeable constraint on the parameter space excluding low m_0 and m_{1/2} similar to constraint from the Higgs mass limit. In some cases these constraints overlap. This picture takes place in a wide region of \tanβ. In a narrow band close to the border line the stops are long-lived particles and decay into quarks and neutralino (c…
So far the squarks have not been detected at the LHC indicating that they are heavier than a few hundred GeVs, if they exist. The lighter stop can be considerably lighter than the other squarks. We study the possibility that a supersymmetric partner of the top quark, stop, is the next-to-lightest supersymmetric particle in the constrained supersymmetric standard model. Various constraints, on top of the mass limits, are taken into an account, and the allowed parameter space for this scenario is determined. Observing stop which is the next-to-lightest supersymmetric particle at the LHC may be d…
The "golden region'' in the MSSM parameter space is the region where the experimental constraints are satisfied and the amount of fine-tuning is minimized. In this region, the stop trilinear soft term is large, leading to a significant mass splitting between the two stop mass eigenstates. As a result, the decay of the heavier stop into the lighter stop and a Z boson is kinematically allowed throughout the golden region. We propose that the experiments at the Large Hadron Collider (LHC) can search for this decay through an inclusive signature, Z+2jb+missing Et+X. We evaluate the Standard Model …
We have been developing a program package called GRACE/SUSY-loop which automatically calculates the MSSM amplitudes in one-loop order. We present numerical results of calculations for pair-production and three-body decay of the lighter stop ($\widetilde{t}_1$) at the International Linear Collider (ILC) using GRACE/SUSY-loop. Since the distributions of missing transverse energy (MET) depend on mass spectrum of SUSY particles, we consider two scenarios on three-body decay of $\widetilde{t}_1$. In these scenarios, both QCD and EW corrections have positive sign for decay widths and cross sections.
Production of the lightest MSSM Higgs boson h is studied at the LHC. Isorate contours for the h -> gamma gamma and h -> tau+tau- decay channels are shown in the m_A,tan(beta) parameter space. Effects of the SUSY parameters, in particular the stop mixing and stop quark mass, are investigated. Search strategies at the LHC are discussed and the discovery potential is calculated for the CMS experiment. The MSSM parameter space for m_A > 150-200 GeV is expected to be covered with at least one decay channel with an integrated luminosity of 60 fb^{-1}. A light stop quark with large stop mixing can af…
We compute the O(alpha_t alpha_s) two-loop corrections to the neutral Higgs boson masses in the Minimal Supersymmetric extension of the Standard Model. An appropriate use of the effective potential allows us to obtain simple analytical formulae, valid for arbitrary values of mA and of the mass parameters in the stop sector. We elucidate some subtleties of the effective potential calculation, and find full agreement with the numerical output of the existing diagrammatic calculation. We discuss in detail the limit of heavy gluino.
We discuss the fine-tuning issue within the MSSM framework. Following the idea that the fine-tuning can measure effects of some missing mechanism, we impose non-universal gaugino masses at the GUT scalem and explore the low scale implications. We realize that the fine-tuning parametrized with Delta_EW can be as low as zero. We consider the stop mass with a special importance and focus on the mass scales as m_stop <=700 GeV, which are excluded by current experiments when the stop decays into a neutralino along with a top quark or a chargino along with a b quark. We find that the stop mass can b…
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 incorporate the effects of mixing arising from the trilinear terms in the MSSM potential to the effective three dimensional theory for the MSSM at high temperature in the limit of large $m_{A}$. There are relevant one-loop effects that modify the 3D parameters of the effective theory. We calculate the two-loop effective potential of the 3D theory for the Higgs and the right handed stop to analyse the possible phase transitions and to determine the precise region in the $m_{h}$-$m_{\tilde{t}_{2}}$ plane for which the sphaleron constraint for preservation of the baryon asymmetry is satisfied.…
We present the calculation of the stop ($\tilde{t}$) lifetime that results from its decay into gravitinos ($\tildeΨ^μ$) in the final state, namely $\tilde{t}\to \tildeΨ^μ + X$, where $X=t, bW, b lν_l$ for the two-, three- and four-body decay modes. The full calculation is obtained using the Feynman rules for massive gravitino, which is compared with the results obtained employing the equivalence theorem, where the longitudinal component of the gravitino is replaced by the goldstino. The stop turns out to be very long-lived in these scenarios, with lifetimes of $\mathcal{O}$($10^8$s, $10^{14}$s…
We examine the sensitivity of recent LHC searches to signatures of supersymmetry with R-parity violation (RPV). Motivated by naturalness of the Higgs potential, which would favor light third-generation squarks, and the stringent LHC bounds on spectra in which the gluino or first and second generation squarks are light, we focus on scenarios dominated by the pair production of light stops. We consider the various possible direct and cascade decays of the stop that involve the trilinear RPV operators. We find that in many cases, the existing searches exclude stops in the natural mass range and b…
We study the processes `gluon gluon -> squark antisquark CP-odd Higgs' within the theoretical framework of the Supergravity (SUGRA) inspired Minimal Supersymmetric Standard Model (MSSM) at the leading order (LO) in perturbative Quantum Chromo-Dynamics (QCD). Other than constituting a novel production mechanism of the neutral, CP-odd Higgs particle, they also allow one to relate the size of the corresponding production rates to the ratio of the vacuum expectation values of the two Higgs fields tan(beta), to the trilinear couplings A_0 and to the sign of the Higgsino mass term sign(mu). This int…
Light stops can give a strong first order electroweak phase transition in the Minimal Supersymmetric Standard Model (MSSM) satisfying one of the necessary conditions for electroweak baryogenesis. I discuss the region of parameter space where this occurs using a perturbative analysis of the Higgs effective potential. Two-loop QCD corrections associated with stop loops are crucial to open this baryogenesis window, which corresponds to 2.25 < tan beta < 3.6, one stop not much heavier than the top quark, m_A > 120 GeV and a light Higgs boson with m_h < 85 GeV. This region will be explored by LEP I…
We study the decays of top squarks (stop_{1,2}) and bottom squarks (sbottom_{1,2}) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters A_t, A_b, mu and M_1. We show that including the corresponding phases substantially affects the branching ratios of stop_{1,2} and sbottom_{1,2} decays in a large domain of the MSSM parameter space. We find that the branching ratios can easily change by a factor of 2 and more when varying the phases. This could have an important impact on the search for stop_{1,2} and sbottom_{1,2} and the determination of the MSSM parameters at future c…
Electroweak baryogenesis (EWBG) in the MSSM can account for the cosmological baryon asymmetry, but only within a restricted region of the parameter space. In particular, MSSM EWBG requires a mostly right-handed stop that is lighter than the top quark and a standard model-like light Higgs boson. In the present work we investigate the effects of the light stop on Higgs boson production and decay. Relative to the standard model Higgs boson, we find a large enhancement of the Higgs production rate through gluon fusion and a suppression of the Higgs branching fraction into photon pairs. These modif…
If the lightest CP-even Higgs boson in the MSSM is discovered at the LHC, two measurements could be made simultaneously: the Higgs mass m_h and the event rate Bs(gg -> h -> gamma gamma). We study to what extent the combination of these two measurements would allow us to extract parameters in the stop mass matrix, including the off-diagonal mixing term, with a focus on the MSSM golden region where the stops are light and the mixing is large. Even though both the production cross-section and the decay amplitude are not sensitive to supersymmetric parameters outside of the stop sector, the branch…
The di-photon decay channel of the lightest Higgs boson is considerd as a probe to explore CP violation in the Minimal Supersymmetric Standard Model (MSSM). The scalar/pseudo-scalar mixing is considered along with CP violation entering through the Higgs-sfermion-sfermion couplings, with and without light sparticles. The impact of a light stop on the decay width and Branching Ratio (BR) is established through a detailed study of the amplitude of the process H1 --> gamma.gamma. The other sparticles have little influence even when they are light. With a suitable combination of other MSSM paramete…
The author considers the effects of the CP-violating phases, e. g. arg(A_t) and arg(mu) on the e^+ e^- --> {tilde t}_1 {tilde t}_1^* (H_1) processes. The third generation squark trilinear terms give significant contributions to the Higgs potential at the one-loop level. This results in the changes of the stop masses and the lighter stop - the lighter anti-stop - the lightest Higgs coupling. The author shows the coupling and the loop effects on the processes. And the author will discuss the determination method of soft parameters.
The discovery of a Higgs boson with a mass of 126 GeV at the LHC when combined with the non-observation of new physics both in direct and indirect searches imposes strong constraints on supersymmetric models and in particular on the top squark sector. The experiments for direct detection of dark matter have provided with yet more constraints on the neutralino LSP mass and its interactions. After imposing limits from the Higgs, flavour and dark matter sectors, we examine the feasibility for a light stop in the context of the pMSSM, in light of current results for stop and other SUSY searches at…
We reanalyze the possibility of CP violation in the Higgs sector of the minimal supersymmetric standard model (MSSM). Contrary to the result of previous analysis, spontaneous CP violation can not occur by only chargino and neutralino radiative corrections since the vacuum does not stable. Top and stop radiative corrections are crucially needed. However even with this correction there is no experimentally allowed region in \tan β\geq 1. This situation is not remedied even if the stop left-right mixing is included. We also analyze explicit CP violation in the Higgs sector of the MSSM and show th…
In supersymmetric scenarios with a light stop particle $\tilde{t}_1$ and a small mass difference to the lightest supersymmetric particle (LSP) assumed to be the lightest neutralino, the flavour changing neutral current decay $\tilde{t}_1 \to c \tildeχ_1^0$ can be the dominant decay channel and can exceed the four-body stop decay for certain parameter values. In the framework of Minimal Flavour Violation (MFV) this decay is CKM-suppressed, thus inducing long stop lifetimes. Stop decay length measurements at the LHC can then be exploited to test models with minimal flavour breaking through Stand…
Recently, the ATLAS and CMS collaborations have announced exciting hints for a Standard Model-like Higgs boson at a mass of approximately 125 GeV. In this paper, we explore the potential consequences for the MSSM and low scale SUSY-breaking. As is well-known, a 125 GeV Higgs implies either extremely heavy stops (>~ 10 TeV), or near-maximal stop mixing. We review and quantify these statements, and investigate the implications for models of low-scale SUSY breaking such as gauge mediation where the A-terms are small at the messenger scale. For such models, we find that either a gaugino must be su…
In the Minimal Supersymmetric Standard Model (MSSM), a Higgs boson mass of 125 GeV can be obtained with moderately heavy scalar top superpartners provided they are highly mixed. The source of this mixing, a soft trilinear stop-stop-Higgs coupling, can result in the appearance of charge- and color-breaking minima in the scalar potential of the theory. If such a vacuum exists and is energetically favorable, the Standard Model-like vacuum can decay to it via quantum tunnelling. In this work we investigate the conditions under which such exotic vacua arise, and we compute the tunnelling rates to t…
In supersymmetric models a large average stop mass $M_S$ is well known to both boost the lightest Higgs boson mass $m_{h}$ and also make radiative electroweak symmetry breaking unnaturally tuned. The case of `maximal mixing', where the stop trilinear mixing term $A_t$ is set to give $A_t^2/M_S^2 = 6$, allows the stops to be as light as possible for a given $m_h$. Here we make the distinction between minimal $M_S$ and optimal naturalness, showing that the latter occurs for less-than-maximal mixing. Lagrange constrained optimisation reveals that the two coincide closely in the Minimal Supersymme…
We consider the possibility of a Standard Model (SM)-like Higgs in the context of the Minimal Supersymmetric Standard Model (MSSM), with a mass of about 125 GeV and with a production times decay rate into two photons which is similar or somewhat larger than the SM one. The relatively large value of the SM-like Higgs mass demands stops in the several hundred GeV mass range with somewhat large mixing, or a large hierarchy between the two stop masses in the case that one of the two stops is light. We find that, in general, if the heaviest stop mass is smaller than a few TeV, the rate of gluon fus…
We attempt to explain the recent ATLAS 3$σ$ excess of dilepton events with an invariant mass near $Z$ peak through the gluino-mediated sbottom production in a simplified scenario inspired by the Minimal Supersymmetric Standard Model (MSSM). The additional $Z$ bosons can be produced through the cascade decay chain $\tilde{g} \to b \tilde{b}^{\dagger}_{1} \to b \bar{b} \tildeχ^{0}_{2,3} \to b \bar{b} \tildeχ^{0}_1 Z$, in which $\tilde b_1$ is the right-handed sbottom, $\tildeχ_1^0$ is the bino-like lightest supersymmetric particle (LSP) and $\tildeχ_{2,3}^0$ are two nearly degenerate higgsino-li…
Taking the MSSM as an effective low-energy theory, with a cut-off scale of a few TeV, can make significant modifications to the predictions concerning the Higgs and stop sectors. We investigate the consequences of such a scenario for electroweak baryogenesis. We find that the window for MSSM baryogenesis is extended and, most important, can be made significantly more natural. Specifically, it is possible to have one stop lighter than the top and the other significantly lighter than TeV simultaneously with the Higgs mass above the LEP bound. In addition, various aspects concerning CP violation …
In order to reproduce the measured mass of the Higgs boson mh = 125GeV in the minimal supersymmetric standard model, one usually has to rely on heavy stops, increasing the fine tuning of the electroweak scale. By introducing a new gauge sector, the Higgs mass gets a tree-level contribution via a non-decoupling D-term, and mh = 125 GeV can be obtained with lighter stops. In this paper, we study the values of the stops masses needed to achieve the correct Higgs mass in a setup where the gauge group is extended by a single U(1)x interaction. We derive the experimental limits on the mass of the Z'…
We study electroweak baryogenesis and electric dipole moments in the presence of the two leading-order, non-renormalizable operators in the Higgs sector of the MSSM. Significant qualitative and quantitative differences from MSSM baryogenesis arise due to the presence of new CP-violating phases and to the relaxation of constraints on the supersymmetric spectrum (in particular, both stops can be light). We find: (1) spontaneous baryogenesis, driven by a change in the phase of the Higgs vevs across the bubble wall, becomes possible; (2) the top and stop CP-violating sources can become effective; …
We study the MSSM finite temperature electroweak phase transition with lattice Monte Carlo simulations, for a large Higgs mass (m_H ~ 95 GeV) and light stop masses (m_tR ~ 150...160 GeV). We employ a 3d effective field theory approach, where the degrees of freedom appearing in the action are the SU(2) and SU(3) gauge fields, the weakly interacting Higgs doublet, and the strongly interacting stop triplet. We determine the phase diagram, the critical temperatures, the scalar field expectation values, the latent heat, the interface tension and the correlation lengths at the phase transition point…
We have explored the possibilities of scenarios with heavy gluinos and light stops in supersymmetric (SUSY) standard models with extra vector-like multiplets. If we assume the hierarchical structure for soft masses of the minimal supersymmetric standard model (MSSM) scalar fields and extra scalars, the light stop and the observed Higgs boson can be realized. While the stau is the lightest SUSY particle (LSP) in broad parameter space, we have found that the neutralino LSP is realized in the case that the non-zero soft parameters for the MSSM Higgs doublets or the non-universal gaugino masses ar…
We perform a detailed study of the decays of the heavier top and bottom squarks (stop_2 and sbottom_2) in the Minimal Supersymmetric Standard Model (MSSM). We show that the decays into Higgs or gauge bosons can be dominant in a wide range of the model parameters due to the large Yukawa couplings and mixings of stops and sbottoms. Compared to the conventional decays into fermions these bosonic decay modes can have significantly different decay structures and distributions. This could have an important impact on the search for stop_2 and sbottom_2 and the determination of the MSSM parameters at …
We present a calculation of the two-loop top-stop-gluino contributions to Higgs production via gluon fusion in the MSSM. By means of an asymptotic expansion in the heavy particle masses, we obtain explicit and compact analytic formulae that are valid when the Higgs and the top quark are lighter than stops and gluino, without assuming a specific hierarchy between the Higgs mass and the top mass. Being applicable to the heaviest Higgs scalar in a significant region of the MSSM parameter space, our results complement earlier ones obtained with a Taylor expansion in the Higgs mass, and can be easi…
Isospin asymmetry in b -> s gamma transitions provides severe constraints on new physics parameters, due to the small values of the experimental measurements. We exploit here this new observable to study different supersymmetric models. For this purpose, we calculate the isospin symmetry breaking in the MSSM with minimal flavor violation, considering NLO contributions. We study three scenarios for supersymmetry breaking, namely mSUGRA, AMSB and GMSB. In most of the explored regions, we find very restrictive constraints on the allowed parameters for these models.
The construction of an effective 3D theory at high temperatures for the MSSM as a model of electroweak baryogenesis is discussed. The analysis for a single light scalar field shows, that given the experimental constraints, there is no value of the Higgs mass for which a sufficiently first-order phase transition is obtained. A precise determination of the 3D parameters of the effective theory for the case of a light right-handed stop allows us to obtain an upper bound on the masses of the lightest Higgs and right-handed stop using the two-loop effective potential. A two-stage phase transition p…
The LHC discovered the Standard Model (SM) like Higgs boson with mass around 125 GeV. However, there exist hints of deviations from Higgs decays. Including the Tevatron data, the deviations can be explained by the extremely mixed stop sector in the sense of best global fit (BGF). We analyze the relations among the competing reduced coupling hGG, Higgs boson mass,and LHC stop mass m_{\wt t_1} lower bound at the tree- and one-loop level. In particular, we point out that we use the light stop running mass in the Higgs boson mass calculation while the light stop pole mass in the Higgs decays. So t…
Electroweak baryogenesis provides an attractive explanation of the origin of the matter-antimatter asymmetry that relies on physics at the weak scale and thus it is testable at present and near future high-energy physics experiments. Although this scenario may not be realized within the Standard Model, it can be accommodated within the MSSM provided there are new CP-violating phases and the lightest stop mass is smaller than the top-quark mass. In this work we provide an evaluation of the values of the stop (m_{\tilde t}) and Higgs (m_H) masses consistent with the requirements of electroweak b…
We study the decays of the charged Higgs boson H^+ within the Minimal Supersymmetric Standard Model. We find that the supersymetric mode 'stop + sbottom-bar' can dominate the H^+ decays in a wide range of the model parameters due to the large Yukawa couplings and mixings of stop and sbottom. Compared to the conventional modes 'tau^+ nu' and 't b-bar', this mode has very distinctive signatures. This could have a decisive impact on H^+ searches at future colliders. We find also that the QCD corrections to the 'stop + sbottom-bar' mode are significant, but that they do not invalidate our tree-lev…
We study the discovery reach of the gluino ($\widetilde{g}$) and the lightest stop squark ($\widetilde{t}_1$) with baryonic R-parity violation (UDD type) in the context of Minimal Supersymmetric Standard Model (MSSM) at the 14 TeV run of the LHC. We consider the gluino pair production process followed by its decay to a top quark and a real or virtual stop squark. The top quark produced from the decay of the gluino can have sufficient transverse momentum to appear as a single fat jet. We apply the jet substructure technique to tag such a hadronically decaying boosted top quark and find that glu…
Electroweak baryogenesis is an attractive scenario for the generation of the baryon asymmetry of the universe as its realization depends on the presence at the weak scale of new particles which may be searched for at high energy colliders. In the MSSM it may only be realized in the presence of light stops, and with moderate or small mixing between the left- and right-handed components. Consistency with the observed Higgs mass around 125 GeV demands the heavier stop mass to be much larger than the weak scale. Moreover the lighter stop leads to an increase of the gluon-gluon fusion Higgs product…
It is shown that MSSM with first two generations of squarks and sleptons much heavier than the third one naturally predicts the maximal stop mixing as a consequence of the RG evolution, with vanishing (or small) trilinear coupling at the high scale. The Higgs boson is generically heavy, in the vicinity of 125 GeV. In this inverted hierarchy scenario, motivated by the supersymmetric FCNC problem and models for fermion masses based on horizontal symmetries, the mass of the lightest stop is O(0.5) TeV and of gluino - O(2-3) TeV. The LSP can be either higgsino or bino or a mixture of both and it c…
