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A. Djouadi

Publications and source records attributed to A. Djouadi.

At least 73 records · Page 4Linked to original sources
arXiv2000

Three-Body Decays of SUSY Particles

We analyze the decays of charginos, neutralinos, gluinos and the first/second generation squarks in the Minimal Supersymmetric extension of the Standard Model, focusing on the three-body decays in scenarios where the ratio $\tan β$ of vacuum expectation values of the two Higgs doublet fields is large. We show that the three-body decays of the next-to-lightest neutralinos (lightest charginos) into $b\bar{b},τ^+τ^-$ ($τν$) final states, where third generation sfermion and Higgs boson exchange diagrams play an important role, are dominant. Furthermore, we show that decays of gluinos into $b\bar{b}$ final states and squark decays into lighter sbottoms through gluino exchange can also have sizeable branching fractions, especially in scenarios where the soft SUSY breaking gaugino mass parameters are not unified at the GUT scale.

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arXiv2000

Report of the Beyond the Standard Model Working Group of the 1999 UK Phenomenology Workshop on Collider Physics (Durham)

The Beyond the Standard Model Working Group discussed a variety of topics relating to exotic searches at current and future colliders, and the phenomenology of current models beyond the Standard Model. For example, various supersymmetric (SUSY) and extra dimensions search possibilities and constraints are presented. Fine-tuning implications of SUSY searches are derived. The implications of Higgs (non)-discovery are discussed, as well as the program HDECAY. The individual contributions are included seperately. Much of the enclosed work is original, although some is reviewed.

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arXiv2000

The Higgs Working Group: Summary Report

Report of the Higgs working group for the Workshop "Physics at TeV Colliders", Les Houches, France 8-18 June 1999. It contains 6 separate sections: 1. Measuring Higgs boson couplings at the LHC. 2. Higgs boson production at hadron colliders at NLO. 3. Signatures of Heavy Charged Higgs Bosons at the LHC. 4. Light stop effects and Higgs boson searches at the LHC. 5. Double Higgs production at TeV Colliders in the MSSM. 6. Programs and Tools for Higgs Bosons.

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arXiv2000

Reconstructing the Chargino System at $e^+e^-$ Linear Colliders

In most supersymmetric theories charginos, $\tildeχ^\pm_{1,2}$, belong to the class of the lightest supersymmetric particles. The chargino system can be reconstructed completely in $e^+e^-$ collider experiments: $e^+e^-\to\tildeχ_i^+ \tildeχ_j^- [i,j=1,2]$. By measuring the total cross sections and the asymmetries with polarized beams, the chargino masses and the gaugino-higgsino mixing angles of these states can be determined accurately. If only the lightest charginos $\tildeχ_1^\pm$ are kinematically accessible in a first phase of the machine, transverse beam polarization or the measurement of chargino polarization in the final state is needed to determine the mixing angles. From these observables the fundamental SUSY parameters can be derived: the SU(2) gaugino mass $M_2$, the modulus and the cosine of the CP-violating phase of the higgsino mass parameter $μ$, and $\tanβ= v_2/v_1$, the ratio of the vacuum expectation values of the two neutral Higgs doublet fields. The remaining two-fold ambiguity of the phase can be resolved by measuring the normal polarization of the charginos. Sum rules of the cross sections can be exploited to investigate the closure of the two-chargino system.

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arXiv2000

Associated Production of Higgs Bosons with Scalar Quarks at Future Hadron and $e^+e^-$ Colliders

We analyze the production of neutral Higgs particles in association with the supersymmetric scalar partners of the third generation quarks at future high--energy hadron colliders [upgraded Tevatron, LHC] and $e^+e^-$ linear machines [including the $γγ$ option]. In the Minimal Supersymmetric extension of the Standard Model, the cross section for the associated production of the lightest neutral $h$ boson with the lightest top squark pairs can be rather substantial at high energies. This process would open a window for the measurement of the $h \tilde{t} \tilde{t}$ coupling, the potentially largest coupling in the supersymmetric theory.

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arXiv2000

The Reconstruction of Trilinear Higgs Couplings

To establish the Higgs mechanism {\it sui generis} experimentally, the Higgs self-interaction potential must be reconstructed. This task requires the measurement of the trilinear and quadrilinear self-couplings, as predicted in the Standard Model or in supersymmetric theories. The couplings can be probed in multiple Higgs production at high-luminosity e+e- linear colliders. We present the theoretical analysis for the production of neutral Higgs-boson pairs in the relevant channels of double Higgs-strahlung and associated multiple Higgs production.

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arXiv1999

Light Scalar Top Quarks and Supersymmetric Dark Matter

A stable neutralino $χ_1^0$, assumed to be the lightest supersymmetric particle, is a favored particle physics candidate for the cosmological Dark Matter. We study co-annihilation of the lightest neutralino with the lighter scalar top quark $\tilde{t}_1$. We show that for natural values of the neutralino mass, $\lsim 300$ GeV, the $χ_1^0 - \tilde{t}_1$ mass difference has to exceed $\sim 10$ to 30 GeV if $χ_1^0$, is to contribute significantly to the Dark Matter. Scenarios with smaller mass splitting, where $\tilde{t}_1$ is quite difficult to detect at collider experiments, are thus cosmologically disfavored. On the other hand, for small $\tilde{t}_1 - χ_1^0$ mass splitting, we show that co--annihilation allows very large neutralino masses, $m_{χ_1^0} \sim 5$ TeV, without ``overclosing'' the Universe.

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arXiv1999

Stop-Stop-Higgs Production at future Linear Collider

In the Minimal Supersymmetric Standard Model, the cross section for the associated production of the lightest neutral Higgs boson with the lightest top squark pairs can be rather substantial at high energies. We summarize the properties of this production process at a future e^+e^- linear collider, including the $γγ$ mode.

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arXiv1999

Decays of the Lightest Top Squark

We analyze higher order decay modes of the lightest top squark $\tilde{t}_1$ in the Minimal Supersymmetric extension of the Standard Model (MSSM), where the lightest SUSY particle (LSP) is assumed to be the neutralino $χ_1^0$. For small $\tilde{t}_1$ masses accessible at LEP2 and the Tevatron, we show that the four-body decay mode into the LSP, a bottom quark and two massless fermions, $\tilde{t}_1 \ra b χ_1^0 f\bar{f}'$, can dominate in a wide range of the MSSM parameter space over the loop-induced decay into a charm quark and the LSP, $\tilde{t}_1 \ra c χ_1^0$. This result might affect the experimental searches on this particle, since only the later signal has been considered so far.

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arXiv1999

Production of Neutral Higgs-Boson Pairs at LHC

The reconstruction of the Higgs potential in the Standard Model or supersymmetric theories demands the measurement of the trilinear Higgs couplings. These couplings affect the multiple production of Higgs bosons at high energy colliders. We present a systematic overview of the cross sections for the production of pairs of (light) neutral Higgs bosons at the LHC. The analysis is carried out for the Standard Model and its minimal supersymmetric extension.

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arXiv1999

Impact of the SUSY Decays on the Search for the MSSM Higgs bosons at the LHC

In the context of the Minimal Supersymmetric extension of the Standard Model, we discuss the impact of the decays of the neutral Higgs bosons into supersymmetric particles, charginos/neutralinos and sfermions. We show that these decay modes could be dominant, when they are kinematically accessible, thus strongly suppressing the branching ratios for the decay channels which are used to detect the Higgs bosons at hadron colliders. These SUSY decay modes should therefore not be overlooked in the search for the Higgs particles at the LHC.

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arXiv1999

Testing Higgs Self-couplings at e^+e^- Linear Colliders

To establish the Higgs mechanism sui generis experimentally, the self-energy potential of the Higgs field must be reconstructed. This task requires the measurement of the trilinear and quadrilinear self-couplings, as predicted, for instance, in the Standard Model or in supersymmetric theories. The couplings can be probed in multiple Higgs production at high-luminosity e^+e^- linear colliders. Complementing earlier studies to develop a coherent picture of the trilinear couplings, we have analyzed the production of pairs of neutral Higgs bosons in all relevant channels of double Higgs-strahlung, associated multiple Higgs production and WW/ZZ fusion to Higgs pairs.

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arXiv1998

Determining SUSY Parameters in Chargino Pair-Production in $e^+e^-$ Collisions

In most supersymmetric theories, charginos $\tildeχ^\pm_{1,2}$, mixtures of charged color-neutral gauginos and higgsinos, belong to the class of the lightest supersymmetric particles. They are easy to observe at $e^+e^-$ colliders. By measuring the total cross sections and the left-right asymmetries with polarized electron beams in $e^+e^-\to\tildeχ_i^-\tildeχ_j^+ [i,j=1,2]$, the chargino masses and the gaugino-higgsino mixing angles can be determined. From these observables the fundamental SUSY parameters can be derived: the SU(2) gaugino mass $M_2$, the modulus $|μ|$ and $\cos Φ_μ$ of the higgsino mass parameter, and $\tanβ= v_2/v_1$, the ratio of the vacuum expectation values of the two neutral Higgs doublet fields. The solutions are unique; the CP-violating phase $Φ_μ$ can be determined uniquely by analyzing effects due to the normal polarization of the charginos.

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arXiv1998

Chargino Pair Production in $e^+e^-$ Collisions

Charginos $χ_1^\pm$ are expected to be the lightest observable supersymmetric particles in many supersymmetric models. We present a procedure which will allow to determine the chargino mixing angles and, subsequently, the fundamental SUSY parameters $M_2, μ$ and $\tanβ$ by measurements of the total cross section and the spin correlations in $e^+e^-$ annihilation to $χ_1^+ χ_1^-$ chargino pairs.

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arXiv1997

Two-Loop Electroweak Heavy-Fermion Corrections to Higgs-Boson Production and Decay

The dominant electroweak corrections to the production cross sections and partial decay widths of a light Standard-Model Higgs boson, with mass M_H << 2m_t, are due to top-quark loops. By means of a low-energy theorem, we study at the two-loop level the leading shifts in the Higgs-boson couplings to pairs of light fermions and gauge bosons induced by a sequential isodoublet of high-mass fermions. For tree-level and loop-induced Higgs-boson couplings, these corrections are of relative orders O(G_mu^2 m_F^4) and O(G_mu m_F^2), respectively, where m_F represents a generic heavy-fermion mass, with m_F >> M_W, M_H. Except for the Hbb-bar coupling, all results carry over to the case of the top-quark-induced corrections. We discuss possible phenomenological consequences of our results.

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arXiv1997

Higgs Boson Production in Association with Scalar Top Quarks at Proton Colliders

We investigate the production of Higgs particles in association with the supersymmetric scalar partners of the top quark at proton colliders. In the minimal supersymmetric extension of the Standard Model, the cross sections for the production of the lightest neutral Higgs boson in association with top squark pairs can be rather large, substantially exceeding the rate for the associated Higgs boson production with top quarks. If the lightest top squark is not much heavier than the top quark, this process will enhance the potential of the CERN Large Hadron Collider to discover the lightest neutral Higgs boson, and will open a window to the study of the Higgs-stop coupling, the potentially largest electroweak coupling in the supersymmetric theory.

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arXiv1997

The search for the Standard Model Higgs boson at present and future colliders

I briefly review the Higgs sector in the Standard Model. After summarizing the properties of the Higgs boson, I will discuss the prospects for discovering this particle at the present colliders LEP2 and Tevatron and at the next generation colliders LHC and a high-energy $e^+e^-$ linear collider. The possibilities of studying the properties of the Higgs particle will be then summarized. [Contribution to the European Network Workshop "Tests of the Electroweak Symmetry Breaking}, Ouranoupolis, Greece, May 1997.]

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