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J. -L. Kneur

Publications and source records attributed to J. -L. Kneur.

34 records · Page 2Linked to original sources
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.

hep-ph↗
arXiv1999

A Direct Reconstruction of the Gaugino Parameters with Phases

A simple algebraic algorithm is described to recover the (complex valued) gaugino/Higgsino basic parameters $μ= |μ| e^{i ϕ_μ}$, $M_1 = |M_1| e^{i ϕ_{M_1}}$, $M_2 = |M_2|$, directly in terms of (a minimal set of) neutralino and chargino masses, accurately measurable at future linear collider energies. An ambiguity in the $M_1$ reconstruction can be resolved by measuring the corresponding $e^+e^- \to χ^0_1 χ^0_2$ cross section. This approach should simplify the determination of allowed ranges of the gaugino parameters, in particular if only a partial set of gaugino masses were measured.

hep-ph↗
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.

hep-ph↗
arXiv1999

Phases in the gaugino sector: direct reconstruction of the basic parameters and impact on the neutralino pair production

We consider recovering analytically the (generally complex) parameters $μ$, $M_1$ and $M_2$ of the gaugino and Higgsino Lagrangian, from appropriate physical input in the chargino and neutralino sectors. For given $\tanβ$, we obtain very simple analytic solutions for $M_2$, $| μ|$, $Arg[μ]$ in the chargino sector and a twofold $| M_1 |$, $Arg[M_1]$ analytic solution in the neutralino sector, assuming two chargino, two neutralino masses, and one of the chargino mixing angles as physical input. The twofold ambiguity in the neutralino parameters reconstruction may be essentially resolved by measuring the $e^+e^- \to χ^0_1 χ^0_2$ production cross-section at future linear collider energies, which we study explicitly with the phase dependences. Some salient features and specific properties of this complex case gaugino "spectrum inversion" are illustrated and compared with the similar inversion in the real case. In particular, our algorithms exhibit in a direct and transparent way the non-trivial theoretical correlation among the chargino and neutralino parameters, and the resulting allowed domains when only a subset of the required physical input masses and production cross-sections is known.

hep-ph↗
arXiv1998

Inverting the Supersymmetric Standard Model Spectrum: from Physical to Lagrangian Ino Parameters

We examine the possibility of recovering the supersymmetric (and soft supersymmetry breaking) Lagrangian parameters as direct {\em analytical} expressions of appropriate physical masses, for the unconstrained (but CP and R-parity conserving) minimal supersymmetric standard model. We concentrate mainly on the algebraically non-trivial "inversion" for the ino parameters, and obtain, for given values of $\tanβ$, simple analytical expressions for the $μ$, $M_1$ and $M_2$ parameters in terms of three arbitrary input physical masses, namely either two chargino and one neutralino masses, or alternatively one chargino and two neutralino masses. We illustrate and discuss in detail the possible occurrence of ambiguities in this reconstruction. The dependence of the resulting ino Lagrangian parameters upon physical masses is illustrated, and some simple generic behaviour uncovered in this way. We finally briefly sketch generalizing such an inversion to the full set of MSSM Lagrangian parameters.

hep-ph↗
arXiv1997

Dynamical Chiral Symmetry Breaking from Variationally Improved Perturbative Expansion

We review how a specific resummation of the so-called "delta-expansion", applied to the QCD Lagrangian, transforms the ordinary perturbative expansion in $α_s$ into an expansion in an arbitrary mass parameter, around the basic scale $\barΛ$. When applied to the pole mass, the resulting expression may be interpreted as a dynamical mass ansatz, to be optimized with respect to the new expansion (mass) parameter. The construction is generalized to obtain estimates of the order parameters of the $SU(n_f)_L \times SU(n_f)_R$ ($n_f =2,3$) symmetry breakdown.

hep-ph↗
arXiv1997

Variational Quark Mass Expansion and the Order Parameters of Chiral Symmetry Breaking

We investigate in some detail a "variational mass" expansion approach, generalized from a similar construction developed in the Gross-Neveu model, to evaluate the basic order parameters of the dynamical breaking of the $SU(2)_L \times SU(2)_R$ and $SU(3)_L \times SU(3)_R$ chiral symmetries in QCD. The method starts with a reorganization of the ordinary perturbation theory with the addition of an arbitrary quark mass $m$. The new perturbative series can be summed to all orders thanks to renormalization group properties, with specific boundary conditions, and advocated analytic continuation in $m$ properties. In the approximation where the explicit breakdown of the chiral symmetries due to small current quark masses is neglected, we derive ansatzes for the dynamical contribution to the "constituent" masses $M_q$ of the $u,d,s$ quarks; the pion decay constant $F_π$; and the quark condensate $< \bar q q > $ in terms of the basic QCD scale $Λ_{\bar{MS}} $. Those ansatzes are then optimized, in a sense to be specified, and also explicit symmetry breaking mass terms can be consistently introduced in the framework. The obtained values of $F_π$ and $M_q$ are roughly in agreement with what is expected from other non-perturbative methods. In contrast we obtain quite a small value of $|< \bar q q >|$ within our approach. The possible interpretation of the latter results is briefly discussed.

hep-ph↗
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.

hep-ph↗
arXiv1996

Optimized-Variational Quark Mass Expansion and Dynamical Chiral Symmetry Breakdown

A recently proposed variational mass expansion approach to dynamical chiral symmetry breakdown is reviewed. We briefly explain how a specific integral ansatz over the analytically continued, arbitrary Lagrangian mass parameter, resums the usual variational mass expansion (``delta-expansion".) The construction is then generalized to obtain non-perturbative expressions for the order parameters of the $SU(n_f)_L \times SU(n_f)_R$ breakdown ($n_f =$ 2 or 3), in QCD. Emphasis is put on some general aspects as well as possible limitations of this approach.

hep-ph↗
arXiv1996

Variational Solution of the Gross-Neveu Model: finite $N$ and Renormalization

We show how to perform systematically improvable variational calculations in the $O(2N)$ Gross-Neveu model for generic $N$, in such a way that all infinities usually plaguing such calculations are accounted for in a way compatible with the perturbative renormalization group . The final point is a general framework for the calculation of non-perturbative quantities like condensates, masses etc$\ldots$, in an asymptotically free field theory. For the Gross-Neveu model, the numerical results obtained from a ``2-loop'' down to low values of $N$.

hep-th↗
arXiv1996

Chiral Symmetry Breaking in QCD: A Variational Approach

We develop a "variational mass" expansion approach, recently introduced in the Gross--Neveu model, to evaluate some of the order parameters of chiral symmetry breakdown in QCD. The method relies on a reorganization of the usual perturbation theory with the addition of an "arbitrary quark mass $m$, whose non-perturbative behaviour is inferred partly from renormalization group properties, and from analytic continuation in $m$ properties. The resulting ansatz can be optimized, and in the chiral limit $m \to 0$ we estimate the dynamical contribution to the "constituent" masses of the light quarks $M_{u,d,s}$; the pion decay constant $F_π$ and the quark condensate $< \bar q q >$.

hep-ph↗
arXiv1996

Radiative Contributions to TGC in the MSSM

We give a brief account of recent calculations of radiative contributions to the Triple Gauge Couplings (TGC) from the Minimal Supersymmetric Standard Model (MSSM), at a 500 GeV $e^+e^-$ collider. Our results indicate that, although these MSSM virtual contributions indeed are of the order of the expected accuracy on TGC measurements, the generally neglected box contributions to TGC also are likely to be relevant at such high energies.

hep-ph↗
arXiv1996

Triple Gauge Boson Couplings

We present the results obtained by the "Triple Gauge Couplings" working group during the LEP2 Workshop (1994-1995). The report concentrates on the measurement of $WWγ$ and $WWZ$ couplings in $e^-e^+\to W^-W^+$ or, more generally, four-fermion production at LEP2. In addition the detection of new interactions in the bosonic sector via other production channels is discussed.

hep-ph↗
arXiv1995

MSSM radiative contributions to the WW$γ$ and WWZ form factors

We evaluate one-loop contributions to the C and P conserving $WWγ, WWZ$ form factors in the Minimal Supersymmetric Standard Model (MSSM), and in a more constrained Supergravity Grand Unified Theory (SUGRA-GUT). A systematic search of maximal effects in the available parameter space, shows that at LEP2 energy MSSM contributions can hardly reach the border of the most optimistic accuracy expected on those couplings, even for particles close to their production thresholds. At NLC energies, the effects are more comfortably of the order of the expected sensitivity, and may therefore provide useful information on MSSM parameter values which will not be available from direct particle production. We also discuss briefly some variance with other studies.

hep-ph↗
arXiv1993

The Potential of a New Linear Collider for the Measurement of the Trilinear Couplings among the Electroweak Vector Bosons

We study the accuracy to be obtained in measuring trilinear $Z^0W^+W^-$ and $γW^+W^-$ couplings in the reaction $e^+e^- \to W^+W^-$ at "New Linear Collider" energies of $500GeV$ to $1000GeV$. We derive simple scaling laws for the sensitivity in the measurement of these couplings. For most couplings the sensitivity increases as $\sqrt{L\cdot s}$, where $L$ denotes the integrated luminosity and $\sqrt s$ denotes the $e^+e^-$ center-of-mass energy. Detailed investigations based on various fits confirm these scaling laws and show that an accuracy of the order of the standard radiative corrections can be reached at the NLC for the design values of the luminosity.

hep-ph↗