arXiv subjects
Publications and source records attributed to Jaume Guasch.
We present an update of neutral Higgs boson decays into bottom quark pairs in the minimal supersymmetric extension of the Standard Model. In particular the resummation of potentially large higher-order corrections due to the soft SUSY breaking parameters A_b and mu is extended. The remaining theoretical uncertainties due to unknown higher-order SUSY-QCD corrections are analyzed quantitatively.
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 $e^+e^-$ Linear Collider.
We present results on the analysis of the ratio of branching ratios $R=BR(H->b\bar{b})/BR(H->τ^+τ^-)$ of Higgs boson decays as a discriminant quantity between supersymmetric and non-supersymmetric models. A detailed analysis in the effective Lagrangian approach shows how one could discriminate between models at the Large Hadron Collider and the $e^+e^-$ Linear Collider at 500 GeV center of mass energy.
We present a definition of an on-shell renormalization scheme for the sfermion and chargino-neutralino sector of the Minimal Supersymmetric Standard Model (MSSM). Then, apply this renormalization framework to the interaction between charginos/neutralinos and sfermions. A kind of universal corrections is identified, which allow to define effective chargino/neutralino coupling matrices. In turn, these interactions generate (universal) non-decoupling terms that grow as the logarithm of the heavy mass. Therefore the full MSSM spectrum must be taken into account in the computation of radiative corrections to observables involving these interactions. As an application we analyze the full one-loop electroweak radiative corrections to the partial decay widths Γ(\tilde{f} -> f\neut) and Γ(\tilde{f} -> f'\cplus) for all sfermion flavours and generations. These are combined with the QCD corrections to compute the corrected branching ratios of sfermions. It turns out that the electroweak corrections can have an important impact on the partial decay widths, as well as the branching ratios, in wide regions of the parameter space. The precise value of the corrections is strongly dependent on the correlation between the different particle masses.
The production of a heavy supersymmetric charged Higgs boson (M_{H^{\pm}}> 200 GeV) at the Tevatron and at the LHC is studied. We include the leading one-loop quantum effects within the MSSM in the relevant high \tanβregion. Whereas the chances for the Tevatron are limited, and critically depend on the size of the unknown NLO QCD effects, at the LHC the discovery range is more comfortable and may extend the reach above M_{H^{\pm}}= 1 TeV.
We analyze the partial decay widths of sfermions decaying into charginos and neutralinos Γ(\sfermion -> f'χ) at the one-loop level. We present the renormalization framework, and discuss the value of the corrections for top- and bottom-squark decays.
We present a full one-loop calculation of the electroweak corrections to the partial decay widths of the fermionic modes of sfermions Γ(\sfermion \to f'χ). The main technical points of the renormalization are presented, and the main features of the results are discussed.
We investigate the production of a heavy charged Higgs boson at hadron colliders within the context of the MSSM. A detailed study is performed for all important production modes and basic background processes for the t\bar{t}b\bar{b} signature. In our analysis we include effects of initial and final state showering, hadronization, and principal detector effects. For the signal production rate we include the leading SUSY quantum effects at high \tanβ>~ mt/mb. Based on the obtained efficiencies for the signal and background we estimate the discovery and exclusion mass limits of the charged Higgs boson at high values of \tanβ. At the upgraded Tevatron the discovery of a heavy charged Higgs boson (MH^+ >~ 200 GeV) is impossible for the tree-level cross-section values. However, if QCD and SUSY effects happen to reinforce mutually, there are indeed regions of the MSSM parameter space which could provide 3σevidence and, at best, 5σcharged Higgs boson discovery at the Tevatron for masses M_H^+<~ 300 GeV and M_H^+<~ 250 GeV, respectively, even assuming squark and gluino masses in the (500-1000) GeV range. On the other hand, at the LHC one can discover a H^+ as heavy as 1 TeV at the canonical confidence level of 5σ; or else exclude its existence at 95% C.L. up to masses ~ 1.5 TeV. Again the presence of SUSY quantum effects can be very important here as they may shift the LHC limits by a few hundred GeV.
We analyze the ratio of branching ratios R=BR(H->b b-bar)/BR(H->tau^+ tau^-) of Higgs boson decays as a discriminant quantity between supersymmetric and non-supersymmetric models. This ratio receives large renormalization-scheme independent radiative corrections in supersymmetric models at large \tanβ, which are absent in the Standard Model or Two-Higgs-doublet models. These corrections are insensitive to the supersymmetric mass scale. A detailed analysis in the effective Lagrangian approach shows that, with a measurement of +-21% accuracy, the Large Hadron Collider can discriminate between models if the CP-odd Higgs boson mass is below 900 GeV. An e+e- Linear Collider at 500 GeV center of mass energy can discriminate supersymmetric models up to a CP-odd Higgs mass of ~ 1.8 TeV.
We investigate the prospects for heavy charged Higgs boson production through the mechanisms pp-bar(pp)->tbH+ +X at the upgraded Fermilab Tevatron and at the upcoming LHC collider at CERN respectively. We focus on the MSSM case at high values of tan[beta]> m_top/m_bot and include the leading SUSY quantum corrections. A detailed study is performed for all important production modes and basic background processes for the "ttbb" signature. At the upgraded Tevatron a charged Higgs signal is potentially viable in the 220-250 GeV range or excluded at 95%CL up to 300 GeV. At the LHC, a H+ of mass up to 800 GeV can be discovered at 5 sigma or else be excluded up to a mass of ~ 1.5 TeV. The presence ofSUSY quantum effects may highly influence the discovery potential in both machines and can typically shift these limits by 200 GeV at the LHC.
Decays of the top quark induced by flavor changing neutral currents (FCNC) are known to be extremely rare events within the Standard Model. This is so not only for the decay modes into gauge bosons, but most notably in the case of the Higgs channels, e.g. t-> H_{SM}+c, with a branching fraction of 10^{-13} at most. Therefore, detection of FCNC top quark decays in a future high-energy, and high-luminosity, machine like the LHC or the LC would be an indisputable signal of new physics. In this paper we show that within the simplest extension of the SM, namely the general two-Higgs-doublet model, the FCNC top quark decays into Higgs bosons, t->(h^{0},H^{0},A^{0})+c, can be the most favored FCNC modes -- comparable or even more efficient than the gluon channel t-> g+c. In both cases the optimal results are obtained for Type II models. However, only the Higgs channels can have rates reaching the detectable level (10^{-5}), with a maximum of order 10^{-4} which is compatible with the charged Higgs bounds from radiative B-meson decays. We compare with the previous results obtained in the Higgs sector of the MSSM.
Flavor Changing Neutral Current decays of the top quark within the strict context of the Standard Model are known to be extremely rare. In fact, they are hopelessly undetectable at the Tevatron, LHC and LC in any of their scheduled upgradings. Therefore, if a few of these events eventually show up in the future we will have certainly discovered new physics. We argue that this could well be the case for the LHC and the LC both within the Minimal Supersymmetric Standard Model (MSSM) and in a general two-Higgs-doublet model (2HDM), especially if we look for FCNC top quark decays into Higgs bosons.
We present results on the full one-loop electroweak radiative corrections to the squark decay partial widths into charginos and neutralinos. We show the renormalization framework, and present numerical results for the third squark family. The corrections can reach values of ~ 10%, which are comparable to the radiative corrections from the strong sector of the model. Therefore they should be taken into account for the precise extraction of the SUSY parameters at future colliders.
We review the one-loop corrections to the partial decay width of sbottom-quark into a top quark and a chargino for the parameter space relevant to the TESLA e+e- linear collider. We present the results available in the literature for the QCD and the Yukawa coupling corrections in a unified framework. In this way a direct comparison of the size of the various corrections is possible.
Charged Higgs particles are a common feature of many extensions of the Standard Model. While its existence with masses up to the TeV scale can be probed at the Tevatron Run II and LHC hadron colliders, a precise determination of its properties would have to wait for a high energy e+e- linear collider. We have computed the complete one-loop electroweak corrections to the cross-section for charged Higgs bosons pair production in e+e- collisions, in the framework of general Two Higgs Doublet Models, as well as the Minimal Supersymmetric Standard Model. A study is presented for typical values of the model parameters, showing the general behaviour of the corrections.
Flavour changing neutral decays of the top quark are know to be extremely suppressed in the SM. This is especially so for the top quark decay into the SM Higgs boson, whose rate is less than 10^-13. However, it turns out that the decay modes t->c h, with h= h^0,H^0,A^0 any of the MSSM neutral Higgs bosons, can be much more gifted. In particular, the rate into the lightest CP-even Higgs boson h^0 -- which is an accessible decay mode across the whole MSSM parameter space -- is generally higher than the decay into glue, t->c g, even though the latter can also be considerably augmented in the MSSM. Our general conclusion is that the Higgs channel t->c h^0 can be the ``gold-plated'' top quark FCNC decay mode in the MSSM with rates that can reach 10^-4, i.e. already at the visible level for both LHC and LC.
We shortly review the top quark decay into charged Higgs, and present new results on its production at the upgraded Tevatron. We have computed the MSSM cross-section for single charged Higgs in association with the top quark beyond the regime of on-shell t t-bar production followed by the decay t -> H+ b. Our results are higher than recent results in the literature. In the case where H+ belongs to the Higgs sector of the MSSM, we show that the leading supersymmetric radiative corrections may substantially increase the cross-section. Overall we find that the charged Higgs production process can be complementary to the neutral Higgs production processes WΦand b b-barΦ, which have been studied under similar circumstances. Since the neutral and charged Higgs channels are enhanced in the same region of the parameter space, the simultaneous detection of all these processes could be essential for an effective experimental underpinning of the nature of these Higgs particles at the Tevatron-Run II.
In this Thesis we have investigated some effects appearing in top quark observables in the framework of the Minimal Supersymmetric Standard Model (MSSM). We have computed the radiative corrections to some top quark observables, using the on-shell renormalization scheme, and with a physically motivated definition of the tan(beta) parameter. Introductory chapters deal with the MSSM, its renormalization, and the on-shell prescription. In the next chapters we have computed the SUSY-EW corrections (and some SUSY-QCD corrections) to: the non-standard top quark decay partial width Γ(t->H+ b); the FCNC top quark decay width Γ(t-> c h) (h=h^0,H^0,A^0); and the non-standard top quark production through sbottom decays Γ(sbottom -> t χ^-). We have investigated the consequences of the corrections to Γ(t->H^+ b) in the interpretation of the present Tevatron data. Our general conclusion is that the supersymmetric strong and electroweak radiative corrections can be very important in the top/bottom-Higgs super-sector of the MSSM. Therefore, it is necessary to account for these corrections in the theoretical computation of the high energy physics observables, otherwise highly significant information on the potentially underlying SUSY dynamics could be missed. This is true, not only for the future experiments at the LHC and the LC, but also for the present Run I data (and the Run II data around the corner) at the Fermilab Tevatron collider.