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F. M. Renard

Publications and source records attributed to F. M. Renard.

At least 55 records · Page 3Linked to original sources
arXiv2006

Associated tW production at LHC: a complete calculation of electroweak supersymmetric effects at one loop

We compute, in the MSSM framework, the total electroweak contributions at one loop for the process pp -> tW+X, initiated by the parton process bg -> tW. The supersymmetric effect is analyzed for various choices of the SUSY benchmark points. Choosing realistic unpolarized and polarized experimental quantities, we show the size of the various effects and discuss their dependence on the MSSM parameters.

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arXiv2005

Complete electroweak one loop contributions to the pair production cross section of MSSM charged and neutral Higgs bosons in e+e- collisions

In this paper, we review the production cross section for charged and neutral Higgs bosons pairs in $e^{+}e^{-}$ collisions beyond the tree level, in the framework of the Minimal Supersymmetric Standard Model (MSSM). A complete list of formulas for all electroweak contributions at the one loop level is given. A numerical code has been developed in order to compute them accurately and, in turn, to compare the MSSM Higgs bosons pair production cross sections at tree level and at the one loop level.

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arXiv2005

Weak Interaction Sum Rules for Polarized top-antitop Production at LHC

We consider two polarization asymmetries in the process of top-antitop production at LHC. We show that the theoretical predictions for these two quantities, at the strong and electroweak partonic one-loop level, are free of QCD and QED effects. At this perturbative level we derive two sum rules, that relate measurable quantities of top-antitop production to genuinely weak inputs. This would allow to perform two independent tests of the candidate theoretical model, with a precision that will be fixed by the future experimental accuracies of the different polarization measurements. A tentative quantitative illustration of this statement for a specific MSSM scenario is enclosed, and a generalization to include two other future realistic measurements is also proposed.

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arXiv2005

Single Neutralino production at CERN LHC

The common belief that the lightest supersymmetric particle (LSP) might be a neutralino, providing also the main Dark Matter (DM) component, calls for maximal detail in the study of the neutralino properties. Motivated by this, we consider the direct production of a single neutralino $\tchi^0_i$ at a high/energy hadron collider, focusing on the $\tchi^0_1$ and $\tchi^0_2$ cases. At Born level, the relevant subprocesses are $q\bar q\to \tchi^0_i \tilde g$, $g q\to \tchi^0_i \tilde q_{L,R}$ and $q\bar q'\to \tchi^0_i\tchi^\pm_j$; while at 1-loop, apart from radiative corrections to these processes, we consider also $gg\to \tchi^0_i\tilde{g}$, for which a numerical code named PLATONgluino is released. The relative importance of these channels turns out to be extremely model dependent. Combining these results with an analogous study of the direct $\tchi^0_i\tchi^0_j$ pair production, should help in testing the SUSY models and the Dark Matter assignment.

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arXiv2005

About helicity conservation in gauge boson scattering at high energy

We remark that the high energy gauge boson scattering processes involving two-body initial and final states, satisfy certain selection rules described as helicity conservation of the \underline{gauge boson} amplitudes (GBHC). These rules are valid at Born level, as well as at the level of the leading and sub-leading 1-loop logarithmic corrections, in both the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). A "fermionic equivalence" theorem is also proved, which suggests that GBHC is valid at all orders in MSSM at sufficiently high energies, where the mass suppressed contributions are neglected.

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arXiv2004

Special Supersymmetric features of large invariant mass unpolarized and polarized top-antitop production at LHC

We consider the top-antitop invariant mass distributions for production of unpolarized and polarized top quark pairs at LHC, in the theoretical framework of the MSSM. Assuming a "moderately" light SUSY scenario, we derive the leading logarithmic electroweak contributions at one loop in a region of large invariant mass, $M_{t\bar t}\simeq1$ TeV, for the unpolarized differential cross section $dσ/dM_{t\bar t}$ and for the differential longitudinal top polarization asymmetry $A_t(M_{t\bar t})$. We perform a realistic evaluation of the expected uncertainties of the two quantities, both from a theoretical and from an experimental point of view, and discuss the possibility of obtaining, from accurate measurements of the two mass distributions, stringent consistency tests of the model, in particular identifications of large $\tanβ$ effects.

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arXiv2004

Split Supersymmetry at the Logarithmic Test of Future Colliders

We consider a large number of pair production processes at future colliders (LHC, ILC) for values of the c.m. energy in the TeV range, where a logarithmic expansion of Sudakov kind would provide a reliable description of Split supersymmetric electroweak effects. We calculate all the leading and next to leading terms of the expansions, that would differ drastically in the considered domain from those of an extreme "light" scenario. We imagine then two possible competitive future situations, at LHC and at ILC, where the determination of the energy dependence of the cross sections of certain processes could reveal a "signal" of the correct supersymmetric scheme.

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arXiv2004

Supersymmetry Tests from a Combined Analysis of Chargino, Neutralino, and Charged Higgs Boson Pair Production at a 1 TeV Linear Collider

We consider the production of chargino, neutralino and charged Higgs boson pairs at future linear colliders for c. m. energies in the one TeV range within the MSSM. We compute the leading (double) and next-to leading (linear) supersymmetric logarithmic terms of the so-called "Sudakov expansion" at one-loop level. We show that a combined analysis of the slopes of the chargino, neutralino, and charged Higgs boson pair production cross sections would offer a simple possibility for determining \tanβfor large (\gsim 10) values, and the parameters M_1, M_2, and μ. This test could provide a strong consistency check of the considered supersymmetric model.

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arXiv2004

Testing soft electroweak SUSY breaking from neutralino, chargino, and charged Higgs boson pairs production at linear colliders

We consider the production of neutralino, chargino, and charged Higgs boson pairs in the MSSM framework at future $e^+e^-$ colliders. We show that, for c.m. energies in the one TeV range and in a ``moderately'' light SUSY scenario, a combined analysis of the slopes of these production cross sections could lead to a strong consistency test involving the soft supersymmetric breaking parameters $M_1$, $M_2$, the Higgsino parameter $μ$, and $\tanβ$.

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arXiv2004

Supersymmetric virtual effects in heavy quark pair production at LHC

We consider the production of heavy ($b,t$) quark pairs at proton colliders in the theoretical framework of the MSSM. Under the assumption of a "moderately" light SUSY scenario, we first compute the leading logarithmic MSSM contributions at one loop for the elementary processes of production from a quark and from a gluon pair in the 1 TeV c.m. energy region. We show that in the initial gluon pair case (dominant in the chosen situation at LHC energies) the electroweak and the strong SUSY contributions concur to produce an enhanced effect whose relative value in the cross sections could reach the twenty percent size for large $\tanβ$ values in the realistic proton-proton LHC process.

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arXiv2004

Special features of heavy quark-antiquark pair production ratios at LHC

We consider the ratio of the cross section of production of heavy bottom-antibottom pairs ($σ_{b\bar b}$) to the cross section of production of top-antitop pairs ($σ_{t\bar t}$) at LHC. We show that in this ratio a major fraction of virtual contributions (including QCD components) disappears, leaving a residual dominant electroweak Yukawa effect that might be strongly enhanced in the presence of supersymmetry. A quantitative numerical analysis of the size of the effect is also performed under the assumption of a relatively light supersymmetric scenario.

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arXiv2004

Supersymmetry Tests from a Combined Analysis of Chargino and Charged Higgs Boson Pair Production at a 1 TeV Linear Collider

We consider the production of chargino and charged Higgs boson pairs at future linear colliders for c.m. energies in the one TeV range. Working in the MSSM under the assumption of a "moderately" light SUSY scenario, we compute the leading (double) and next-to leading (linear) supersymmetric logarithmic terms of the so-called "Sudakov expansion" at one loop. We show that a combined analysis of the slopes of the chargino and of the charged Higgs production cross sections would offer a simple possibility for determining $\tanβ$ for large ($\gtrsim 10$) values and an allowed strip in the ($M_2,μ$) plane. This could provide a strong consistency test of the considered supersymmetric model.

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arXiv2004

Neutralino-neutralino annihilation to photon and gluon pairs in MSSM models

The complete 1-loop computation of the processes $(\tchi^0_i \tchi^0_j \leftrightarrowγγ, ~ gg)$, for any pair of the four MSSM neutralinos, has been performed for an arbitrary c.m energy. As a first application suitable for Dark Matter (DM) searches, the neutralino-neutralino annihilation is studied at relative velocities $v/c\simeq 10^{-3}$ describing the present DM distribution in the galactic halo, and $v/c\simeq 0.5$ determining neutralino relic density contributions. Numerical results are presented for 31 MSSM benchmark models indicating considerable sensitivity to the input parameters. Numerical codes are released, which may be used for the computation of the annihilation of any two neutralinos to two photons or two gluons at the aforementioned $v/c$ values. In the near future, we intend to complement them with codes for the inverse process $γγ\to \tchi^0_i \tchi^0_j$, observable at the future high energy Linear Colliders.

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arXiv2003

Logarithmic Fingerprints of Virtual Supersymmetry

We consider the high energy behaviour of the amplitudes for production of leptons, quarks, Higgs bosons, sleptons, squarks, gauge bosons, charginos, neutralinos. We concentrate our discussion on the universal (process independent) logarithmic terms which factorize the Born amplitude and which are typically of the form [a ln(s/m^2)-ln^2(s/m^2)]. We perform a systematic determination of the coefficient "a" for the various final states and we emphasize the striking features which differentiate the SM and the MSSM cases. We show that a comparison with experiments at future colliders should provide a clean way to test the gauge and Higgs structures of the electroweak interactions owing to the presence of sizeable (visible) virtual logarithmic supersymmetric contributions.

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arXiv2003

A high energy determination of Yukawa couplings in SUSY models

We consider the production, at future lepton colliders, of final fermion, sfermion, scalar pairs in SUSY models. For third family fermions and sfermions and for charged Higgses, the leading Yukawa effect at one loop for large c.m. energies comes from a linear logarithm of Sudakov type, that only depends, in the MSSM, on one SUSY mass scale and on tan(beta). Assuming a relatively light SUSY scenario, we illustrate a possible determination of tan(beta) at c.m. energies of about 1 TeV, working systematically at subleading logarithmic accuracy, at the one-loop level.

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arXiv2002

Charged Higgs Production in the 1 TeV Domain as a Probe of Supersymmetric Models

We consider the production, at future lepton colliders, of charged Higgs pairs in supersymmetric models. Assuming a relatively light SUSY scenario, and working in the MSSM, we show that, for c.m. energies in the one TeV range, a one-loop logarithmic Sudakov expansion that includes an "effective" next-to subleading order term is adequate to the expected level of experimental accuracy. We consider then the coefficient of the linear (subleading) SUSY Sudakov logarithm and the SUSY next to subleading term of the expansion and show that their dependence on the supersymmetric parameters of the model is drastically different. In particular the coefficient of the SUSY logarithm is only dependent on $\tanβ$ while the next to subleading term depends on a larger set of SUSY parameters. This would allow to extract from the data separate informations and tests of the model.

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arXiv2002

The processes $e^-e^+\toγγ, Z γ, ZZ$ in SM and MSSM

We present the results of a complete analysis of the one loop electroweak corrections to $e^-e^+\toγγ, ~Zγ, ~ZZ$ in the Standard (SM) and the Minimal Supersymmetric Standard Model (MSSM). A special emphasis is put on the high energy behaviour of the various helicity amplitudes and the way the logarithmic structure is generated. The large magnitude of these effects, which induce striking differences between the SM and MSSM cases at high energies, offers the possibility of making global tests which could check the consistency of these models, and even decide whether any additional new physics is required.

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