In the context of supersymmetric models where the gauginos may have both Majorana and Dirac masses we investigate the general constraints from flavour-changing processes on the scalar mass matrices. One finds that the chirality-flip suppression of flavour-changing effects usually invoked in the pure Dirac case holds in the mass insertion approximation but not in the general case, and fails in particular for inverted hierarchy models. We quantify the constraints in several flavour models which correlate fermion and scalar superpartner masses. We also discuss the limit of very large Majorana gaugino masses compared to the chiral adjoint and Dirac masses, where the remaining light eigenstate is the "fake" gaugino, including the consequences of suppressed couplings to quarks beyond flavour constraints.
We consider scenarios with large flavour violating entries in the squark mass matrices focusing on the mixing between second and third generation squarks. These entries govern both, flavour violating low energy observables on the one hand and squark and gluino decays on the other hand. We first discuss the constraints on the parameter space due to the recent data on B mesons from the B factories and Tevatron. We then consider flavour violating squark and gluino decays and show that they can still be typically of order 10% despite the stringent constraints from low energy data. Finally we brief…
We study the effect of squark generation mixing on gluino production and decays at LHC in the Minimal Supersymmetric Standard Model (MSSM) for the case that the gluino is lighter than all squarks and dominantly decays into three particles, $gl -> q qbar neut_k, gl -> q qbar' char_l$. We assume mixing between the second and the third squark generations in the up-type and down-type squark sectors. We show that this mixing can lead to very large branching ratios of the quark-flavour violating gluino three-body decays despite the strong constraints on quark-flavour violation (QFV) from the experim…
We study the flavour changing neutral Higgs boson decays that can be induced from genuine supersymmetric particles at the one-loop level and within the context of the Minimal Supersymmetric Standard Model. We consider all the possible flavour changing decay channels of the three neutral Higgs bosons into second and third generation quarks, and focus on the Supersymmetric-QCD corrections from squark-gluino loops which are expected to provide the dominant contributions. We assume here the more general hypothesis for flavour mixing, where there is misalignment between the quark and squark sectors…
We study the two-body decays of the gluino at full one-loop level in the Minimal Supersymmetric Standard Model with quark-flavour violation (QFV) in the squark sector. The renormalization is done in the $\overline{\rm DR}$ scheme. The gluon and photon radiations are included by adding the corresponding three-body decay widths. We discuss the dependence of the gluino decay widths on the QFV parameters. The main dependence stems from the $\tilde c_R - \tilde t_R$ mixing in the decays to up-type squarks, and from the $\tilde s_R - \tilde b_R$ mixing in the decays to down-type squarks due to the s…
In recent years it has been learned that scalar superpartner masses and trilinear couplings should both generically be larger than about 20 TeV at the short distance string scale if our world is described by a compactified string or M-theory with supersymmetry breaking and stabilized moduli. Here we study implications of this, somewhat generally and also in detail for a particular realization (compactification of M-theory on a G_2 manifold) where there is significant knowledge of the superpotential and gauge kinetic function, and a light gluino. In a certain sense this yields an ultraviolet co…
We study the two-body decays of the gluino at full one-loop level in the Minimal Supersymmetric Standard Model with quark-flavour violation (QFV) in the squark sector. The renormalization is done in the DRbar scheme and hard gluon and photon radiations are included by adding the corresponding three-body decay widths. In the numerics the dependence of the gluino decay widths on the QFV parameters is discussed with special emphasis put on the separation of the electroweak and the SUSY QCD corrections. The main dependence stems from the $\tilde c_R - \tilde t_R$ mixing in the decays to up-type sq…
I present results for the finite renormalization of the Cabibbo-Kobayashi-Maskawa (CKM) matrix induced by gluino--squark diagrams in the MSSM with non-minimal sources of flavour violation. Subsequently I derive bounds on the flavour--off--diagonal elements of the squark mass matrices by requiring that the radiative corrections to the CKM elements do not exceed the experimental values. The constraints on the associated dimensionless quantities $δ^{d LR}_{ij}$, $j>i$, are stronger than the bounds from flavour-changing neutral current (FCNC) processes if gluino and squarks are heavier than 500$ \…
We study quark flavour violation (QFV) in the squark sector of the Minimal Supersymmetric Standard Model (MSSM). We assume mixing between the second and the third squark generations, i.e. sc_R-st_{L,R} mixing mixing. We focus on QFV effects in bosonic squark decays, in particular on the decay into the lightest Higgs boson h0, su_2 -> su_1 h0, where su_{1,2} are the lightest up-type squarks. We show that the branching ratio of this QFV decay can be quite large (up to 50 %) due to large QFV trilinear couplings, and large sc_R-st_{L, R} and st_L-st_R mixing, despite the strong constraints on QFV …
We present results of our study of tan(beta)-enhanced loop corrections in the Minimal Supersymmetric Standard Model (MSSM) with Minimal Flavour Violation (MFV). We demonstrate that these corrections induce flavour changing neutral current (FCNC) gluino couplings which have a large impact on the Wilson coefficient C_8 of the chromomagnetic operator. To illustrate the phenomenological consequences of this gluino-squark contribution to C_8, we briefly discuss its effect on the mixing-induced CP asymmetry in the decay B_d -> phi K_S.
The gluino-induced contribution to the decay $b \to s γ$ is investigated in supersymmetric frameworks with generic sources of flavour violation. It is emphasized that the operator basis of the standard model effective Hamiltonian is enlarged and that a suitable redefinition allows to realize the usual scheme of leading and next-to-leading logarithmic contributions when QCD corrections are included. The effects of the leading order QCD corrections on the inclusive branching ratio for $b \to s γ$ are shown. Constraints on supersymmetric sources of flavour violation are derived.
We study the effects of squark generation mixing on squark and gluino production and decays at LHC in the Minimal Supersymmetric Standard Model (MSSM) with focus on the mixing between second and third generation squarks. Taking into account the constraints from B-physics experiments we show that various regions in parameter space exist where decays of squarks and/or gluinos into quark flavour violating (QFV) final states can have large branching ratios. Here we consider both fermionic and bosonic decays of squarks. Rates of the corresponding QFV signals, e.g. pp -> t t bar{c} bar{c} missing-E_…
The gluino-induced contributions to the decay b-> s gamma are investigated in supersymmetric frameworks with generic sources of flavour violation. It is shown that, when QCD corrections are taken into account, the relevant operator basis of the Standard Model effective Hamiltonian gets enlarged to contain: i) magnetic and chromomagnetic operators with a factor of alpha_s and weighted by a quark mass m_b or m_c; ii) magnetic and chromomagnetic operators of lower dimensionality, also containing alpha_s; iii) four-quark operators weighted by a factor alpha_s^2. Numerical results are given, showin…
We consider supersymmetric extensions of the standard model with general non-universal soft breaking terms. We analyse in a model-independent way the constraints on these terms at the electroweak energy scale coming from gluino mediated flavour (F) changing neutral current and CP-violating processes. We have computed the complete $ΔF=1$ and $ΔF=2$ effective hamiltonian for gluino mediated processes, including for the first time the effect of box diagrams in the evaluation of $ε^{\prime}/ε$. We present numerical results for the constraints on these non-universal soft breaking terms for differen…
Quark flavour conserving (QFC) fermionic squark decays, such as ~t_{1,2} -> t neutralino_i, are usually assumed in squark search analyses. Here we study quark flavour violating (QFV) bosonic squark decays, such as ~u_2 -> ~u_1 h^0/Z^0, where the mass eigenstates ~u_{1,2} are mixtures of scharm and stop quarks. We show that the branching ratios of such QFV decays can be very large due to sizable ~c_R - ~t_{R/L} and ~t_R - ~t_L mixing effects despite the very strong constraints on the QFV parameters from B meson data. This can result in remarkable QFV signatures with significant rates at LHC (14…
We re-assess constraints from flavour-changing neutral currents in the kaon system on supersymmetric scenarios with a light gluino, two heavy generations of squarks and a lighter third generation. We compute for the first time limits in scenarios with three heavy squark families, taking into account QCD corrections at the next-to-leading order. We compare our limits with those in the case of two heavy families. We use the mass insertion approximation and consider contributions from gluino exchange to constrain the mixing between the first and second squark generation. While it is not possible …
We present a detailed and complete calculation of the gluino and scalar quarks contribution to the flavour-changing top quark decay into a charm quark and a photon, gluon, or a Z boson within the minimal supersymmetric standard model including flavour changing gluino-quarks-scalar quarks couplings in the right-handed sector. We compare the results with the ones presented in an earlier paper where we considered flavour changing couplings only in the left-handed sector. We show that these new couplings have important consequences leading to a large enhancement when the mixing of the scalar partn…
The branching fraction for the decays of gluinos to third generation quarks is expected to be enhanced in classes of supersymmetric models where either third generation squarks are lighter than other squarks, or in mixed-higgsino dark matter models constructed to be in concordance with the measured density of cold dark matter. In such scenarios, gluino production events at the CERN Large Hadron Collider should be rich in top and bottom quark jets. Requiring b-jets in addition to missing transverse energy should, therefore, enhance the supersymmetry signal relative to Standard Model backgrounds…
The mSUGRA parameter space corresponding to light sleptons well within the reach of LHC and relatively light squarks and gluinos (mass $\le$ 1 TeV) has three regions consistent with the WMAP data on dark matter relic density and direct mass bounds from LEP 2. Each region can lead to distinct leptonic signatures from squark-gluino events during the early LHC experiments (integrated luminosity $\sim 10 ~fb^{-1}$ or even smaller). In the much studied stau-LSP coannihilation region with a vanishing common trilinear coupling ($A_0$) at the GUT scale a large fraction of the final states contain elec…
We compute the finite renormalisation of the Cabibbo-Kobayashi-Maskawa (CKM) matrix induced by gluino-squark diagrams in the MSSM with non-minimal sources of flavour violation. Subsequently we derive bounds on the flavour-off-diagonal elements of the squark mass matrices by requiring that the radiative corrections to the CKM elements do not exceed the experimental values. Our constraints on the associated dimensionless quantities delta^{d LR}_{ij}, j>i, are stronger than the bounds from flavour-changing neutral current (FCNC) processes if gluino and squarks are heavier than 500 GeV. Our bound …
Heavy flavour tagging provides a broad range of possibilities in testing QCD features at LEP. We present here a study of 4jets events at LEP I where the so-called light gluinos could be directly produced. We show that microvertex techniques offer a unique chance to exploit simple kinematical distributions in order to optimise the signal coming from gluino production with respect to the background of ordinary QCD events. Our results indicate that experimental analyses along the lines suggested here can exclude or reveal the presence of a gluino for masses up to 10 GeV and lifetimes below 10$^{-…
We compare the prospects for observing theories with Majorana or Dirac gauginos at a future 100 TeV proton-proton collider. Calculating the expected discovery and exclusion regions, we find that for heavy gluino masses the squark discovery reach is significantly reduced in Dirac gluino models relative to the Majorana case. However, if the squark and gluino masses are close the reach is similar in both scenarios. We also consider the electroweak fine tuning of theories observable at such a collider, and the impact of existing constraints from flavour and CP violating observables. Models with Ma…
We present the results of the gluino and scalar quarks contribution to the flavour changing top quark decay into a charm quark and a photon, gluon or a $Z^0$\ boson within the minimal supersymmetric standard model. We include the mixing of the scalar partners of the left and right handed top quark. This mixing has several effects, the most important of which are to greatly enhance the c Z decay mode for large values of the soft SUSY breaking scalar mass $m_S$\ and to give rise to a GIM--like suppresion in the c $γ$\ mode for certain combinations of parameters.
We investigate the constraints on the flavour violating parameters from the decay B --> X_s gamma, taking into account the interplay of the various sources of flavour violation in the unconstrained MSSM. We present a systematic leading logarithmic QCD analysis of these model-independent constraints, including contributions from gluinos, neutralinos, charginos, charged Higgs bosons and interferences between them. We show that two simple combinations of elements of the down squark mass matrix are stringently bounded over large parts of the parameter space where only weak assumptions on the hiera…
The current 7 TeV run of the LHC experiment shall be able to probe gluino and squark masses up to values larger than 1 TeV. Assuming that hints for SUSY are found in the jets plus missing energy channel by the end of a 5 fb$^{-1}$ run, we explore the flavour constraints on three models with a CMSSM-like spectrum: the CMSSM itself, a Seesaw extension of the CMSSM, and Flavoured CMSSM. In particular, we focus on decays that might have been measured by the time the run is concluded, such as $B_s\toμμ$ and $μ\to eγ$. We also analyse constraints imposed by neutral meson bounds and electric dipole m…
Flavour changing effects originating from the exchange of scalar particles in the processes e^+ e^- -> H b \bar{s}, H \bar{b} s, with H = h^0, H^0, A^0, are investigated in the Minimal Supersymmetric Standard Model with non-minimal flavour violation at the one-loop level. The dominating SUSY-QCD contributions with squark--gluino loops are calculated and discussed. We consider the SUSY scenario with non-minimal flavour mixing in the down-type squark-mass matrix. The flavour-changing cross sections are derived, and we discuss the dependence on the MSSM parameters and the strength of flavour mixi…
We study the implications of a large nu_mu - nu_tau mixing angle on flavour changing transitions of quarks and leptons in supersymmetric extensions of the standard model. Two patterns of supersymmetry breaking are considered, models with modular invariance and the standard scenario of universal soft breaking terms at the GUT scale. The analysis is performed for two symmetry groups G x U(1)_F, with G=SU(5) and G=SU(3)^3, where U(1)_F is a family symmetry. Models with modular invariance are in agreement with observations only for restricted scalar quark and gaugino masses, (M_squark^2)/(m_gluino…
In this article, we study the two body gluino decays $\tilde{g} \rightarrow \tilde{u}_i \bar{u}_g$, $\tilde{g} \rightarrow \tilde{d}_i \bar{d}_g$ with $i=1,2,...6$ and $g=1,2,3$ in the Minimal Supersymmetric Standard Model (MSSM) with quark flavour violation (QFV). At the outset, constraints on QFV parameters $δ_{ij}^{U/D(LR)}$ and $δ_{ij}^{U/D(RL)}$ with $i,j=1,2,3$ and $(i\neq j) $ are calculated for a specific set of MSSM parameters using charge and color breaking minima (CCB) and unbounded from below minima (UFB) conditions. These constraints are more stringent compared to the constraints …
We study single top production at the LHC in a SUSY-QCD model with a heavy Dirac gluino. The presence of a heavy Dirac gluino allows for notable top-up flavour changing neutral currents. In this scenario, we find that the process ug->tg gives the largest contribution to single top production via FCNCs at the LHC. The key features of this signal are that the top quark is produced very forward and that it is asymmetric to its anti-top counterpart, as the latter lacks a valence quark.
We consider FCNC and CP violating processes mediated by gluino exchange in generalized supersymmetric theories. We present the constraints on flavour (F) changing squark mass terms at the electroweak energy scale, focusing our analysis on $ΔF = 2$ transitions. Results are also given for $ΔF = 1$ CP conserving processes both in the hadronic and leptonic sectors, while we limit ourselves to some remarks on the relevance of box diagrams in the evaluation of $ε^{\prime}/ε$.
It has been claimed that Dirac gaugino masses are necessary for realistic models of low-scale supersymmetry breaking, and yet very little attention has been paid to the phenomenology of a light gravitino when gauginos have Dirac masses. We begin to address this deficit by investigating the couplings and phenomenology of the gravitino in the effective Lagrangian approach. We pay particular attention to the phenomenology of the scalar octets, where new decay channels open up. This leads us to propose a new simplified effective scenario including only light gluinos, sgluons and gravitinos, allowi…
