arXiv subjects

G. Moreau

Publications and source records attributed to G. Moreau.

35 records · Page 2Linked to original sources

arXiv2006

Flavour physics of the RS model with KK masses reachable at LHC

The version of the higher-dimensional Randall-Sundrum (RS) model with matter in the bulk, which addresses the gauge hierarchy problem, has additional attractive features. In particular, it provides an intrinsic geometrical mechanism that can explain the origin of the large mass hierarchies among the Standard Model fermions. Within this context, a good solution for the gauge hierarchy problem corresponds to low masses for the Kaluza-Klein (KK) excitations of the gauge bosons. Some scenarios have been proposed in order to render these low masses (down to a few TeV) consistent with precision electroweak measurements. Here, we give specific and complete realizations of this RS version with small KK masses, down to 1 TeV, which are consistent with the entire structure of the fermions in flavour space: (1) all the last experimental data on quark/lepton masses and mixing angles (including massive neutrinos of Dirac type) are reproduced, (2) flavour changing neutral current constraints are satisfied and (3) the effective suppression scales of non-renormalizable interactions (in the physical basis) are within the bounds set by low energy flavour phenomenology. Our result, on the possibility of having KK gauge boson modes as light as a few TeV, constitutes one of the first theoretical motivations for experimental searches of direct signatures at the LHC collider, of this interesting version of the RS model which accommodates fermion masses.

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arXiv2005

R-parity violating supersymmetry

Theoretical and phenomenological implications of R-parity violation in supersymmetric theories are discussed in the context of particle physics and cosmology. Fundamental aspects include the relation with continuous and discrete symmetries and the various allowed patterns of R-parity breaking. Recent developments on the generation of neutrino masses and mixings within different scenarios of R-parity violation are discussed. The possible contribution of R-parity-violating Yukawa couplings in processes involving virtual supersymmetric particles and the resulting constraints are reviewed. Finally, direct production of supersymmetric particles and their decays in the presence of R-parity-violating couplings is discussed together with a survey of existing constraints from collider experiments.

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arXiv2005

Neutrinos in Warped Extra Dimensions

Amongst the diverse propositions for extra dimensional scenarios, the model of Randall and Sundrum (RS), which offers a solution for the long standing puzzle of the gauge hierarchy problem, has attracted considerable attention from both the theoretical and experimental points of view. In the context of the RS model with gauge bosons and fermions living in the bulk, a novel type of mechanism has arisen for interpreting the strong mass hierarchy of the Standard Model fermions. This purely geometrical mechanism is based on a type and flavor dependent localization of fermions along a warped extra dimension. Here, we find concrete realizations of this mechanism, reproducing all the present experimental data on masses and mixings of the entire leptonic sector. We consider the case of Dirac neutrino masses (due to an additional right handed neutrino) where the various constraints on RS parameter space are taken into account. The scenarios, elaborated in this paper, generate the entire lepton mass hierarchy and mixing, essentially, via the higher-dimensional mechanism, as the Yukawa coupling dependence is chosen to be minimal. In addition, from the above mechanism, we predict the typical lepton mixing angle 10^-5 < sin(theta_13) < 10^-1, a neutrino mass spectrum with normal hierarchy and the smallest neutrino mass to lie approximately in the range: 10^-11 eV < m_nu_1 < 10^-2 eV. A large part of the sin(theta_13) interval should be testable in future neutrino experiments.

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arXiv2004

Realistic Neutrino Masses from Multi-brane Extensions of the Randall-Sundrum Model?

Scenarios based on the existence of large or warped (Randall-Sundrum model) extra dimensions have been proposed for addressing the long standing puzzle of gauge hierarchy problem. Within the contexts of both those scenarios, a novel and original type of mechanism generating small (Dirac) neutrino masses, which relies on the presence of additional right-handed neutrinos that propagate in the bulk, has arisen. The main objective of the present study is to determine whether this geometrical mechanism can produce reasonable neutrino masses also in the interesting multi-brane extensions of the Randall-Sundrum model. We demonstrate that, in some multi-brane extensions, neutrino masses in agreement with all relevant experimental bounds can indeed be generated but at the price of a constraint (stronger than the existing ones) on the bulk geometry, and that the other multi-brane models even conflict with those experimental bounds.

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arXiv2003

Neutrino Mass Patterns within the See-saw Model from Multi-localization along Extra Dimensions

We study a multi-localization model for charged leptons and neutrinos, including the possibility of a see-saw mechanism. This framework offers the opportunity to allow for realistic solutions in a consistent model without fine-tuning of parameters, even if quarks are also considered. Those solutions predict that the large Majorana mass eigenvalues for right-handed neutrinos are of the same order of magnitude, although this almost common mass can span a large range (bounded from above by $\sim 10^{12}{\rm GeV}$). The model also predicts Majorana masses between $\sim 10^{-2}{\rm eV}$ and $\sim 5 \ 10^{-2}{\rm eV}$ for the left-handed neutrinos, both in the normal and inverted mass hierarchy cases. This mass interval corresponds to sensitivities which are reachable by proposed neutrinoless double $β$ decay experiments. The preferred range for leptonic mixing angle $θ_{13}$ is: $10^{-2} \lesssim \sin θ_{13} \lesssim 10^{-1}$, but smaller values are not totally excluded by the model.

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arXiv2002

Status of a Supersymmetric Flavour Violating Solution to the Solar Neutrino Puzzle with Three Generations

We present a general study of a three neutrino flavour transition model based on the supersymmetric interactions which violate R-parity. These interactions induce flavour violating scattering reactions between solar matter and neutrinos. The model does not contain any vacuum mass or mixing angle for the first generation neutrino. Instead, the effective mixing in the first generation is induced via the new interactions. The model provides a natural interpretation of the atmospheric neutrino anomaly, and is consistent with reactor experiments. We determine all R-parity violating couplings which can contribute to the effective neutrino oscillations, and summarize the present laboratory bounds. Independent of the specific nature of the (supersymmetric) flavour violating model, the experimental data on the solar neutrino rates and the recoil electron energy spectrum are inconsistent with the theoretical predictions. The confidence level of the $χ^2$-analysis ranges between $\sim 10^{-4}$ and $\sim 10^{-3}$. The incompatibility, is due to the new SNO results, and excludes the present model. We conclude that a non-vanishing vacuum mixing angle for the first generation neutrino is necessary in our model. We expect this also to apply to the solutions based on other flavour violating interactions having constraints of the same order of magnitude.

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arXiv2002

The cosmological gravitino problem in the context of R-parity violation

Based on the R-parity violation option of the minimal supersymmetric Standard Model, we examine the scenario where the massive gravitino, relic from the hot big-bang, is the lightest supersymmetric particle and can decay through one or several of the trilinear R-parity violating interactions. We calculate the rates of the gravitino decay via the various three-body decay channels with final states involving three quarks and/or leptons. By taking into account the present constraints on the trilinear R-parity violating coupling constants and assuming the gravitino and scalar superpartner masses do not exceed $\sim 80 TeV$, it turns out that the gravitinos could easily have decayed before the present epoch but not earlier than the big-bang nucleosynthesis one. Therefore, the considered scenario would upset the standard big-bang nucleosynthesis and we conclude that it does not seem to constitute a natural solution for the cosmological gravitino problem.

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arXiv2001

R-parity violation and the cosmological gravitino problem

Based on the R-parity violation option of the minimal supersymmetric Standard Model, we examine the scenario where the massive gravitino, relic from the hot big-bang, is the lightest supersymmetric particle and can decay through one or several of the trilinear R-parity violating interactions. We calculate the rates of the gravitino decay via the various three-body decay channels with final states involving three quarks and/or leptons. By taking into account the present constraints on the trilinear R-parity violating coupling constants and assuming the gravitino and scalar superpartner masses do not exceed ${\cal O}(10TeV)$, it turns out that the gravitinos could easily have decayed before the present epoch but not earlier than the big-bang nucleosynthesis one. Therefore, the considered scenario would upset the standard big-bang nucleosynthesis and we conclude that it does not seem to constitute a natural solution for the cosmological gravitino problem.

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arXiv2000

Phenomenological study of the interactions violating the R-parity symmetry in the supersymmetric theories

The supersymmetric extension of the Standard Model can contain interactions violating the so-called R-parity symmetry. Such couplings would lead to the lepton and/or baryon number violation and modify deeply the phenomenology of supersymmetry at future particle colliders. We have worked out tests of the R-parity violating interactions. First, we have studied clear signals of the single production of supersymmetric partners of the Standard Model particles, which involves the R-parity violating interactions, in the context of physics at next leptonic and hadronic colliders. The results show that strong sensitivities could be obtained on the soft supersymmetry breaking parameters and indicate the possibility of an improvement of one to two order of magnitude concerning the present indirect limits on the values of several R-parity violating coupling constants. Besides, it has been verified that the single superpartner production analysis offers the opportunity to reconstruct in a model independent way some superpartner masses with an high accuracy. Secondly, we have studied CP symmetry violation effects, due to the complex phases of R-parity violating coupling constants, in the pair production of either fermions or sfermions of different flavors at future leptonic colliders. We have seen notably that the single top quark production allows to test the CP violation in the hadronic sector. The main conclusion of these works is that complex phases of certain R-parity violating coupling constants could be observed, and in particular within a scenario where those couplings would exhibit a strong hierarchy in flavor space.

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arXiv2000

Single chargino production at linear colliders

We study the single chargino production $e^+ e^- \to \tilde χ^{\pm} μ^{\mp}$ at linear colliders which occurs through the $ł_{121}$ R-parity violating coupling constant. We focus on the final state containing 4 leptons and some missing energy. The largest background is \susyq and can be reduced using the initial beam polarization and some cuts based on the specific kinematics of the single chargino production. Assuming the highest allowed supersymmetric background, a center of mass energy of $\sqrt s=500GeV$ and a luminosity of ${\cal L}=500fb^{-1}$, the sensitivities on the $ł_{121}$ coupling constant obtained from the single chargino production study improve the low-energy experimental limit over a range of $Δm_{\tilde ν} \approx 500GeV$ around the sneutrino resonance, and reach values of $\sim 10^{-4}$ at the $\tilde ν$ pole. The single chargino production also allows to reconstruct the $\tilde χ_1^{\pm}$, $\tilde χ_2^{\pm}$ and $\tilde ν$ masses. The initial state radiation plays a fundamental role in this study.

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arXiv2000

Single superpartner production at Tevatron Run II

We study the single productions of supersymmetric particles at Tevatron Run II which occur in the $2 \to 2-body$ processes involving R-parity violating couplings of type $ł'_{ijk} L_i Q_j D_k^c$. We focus on the single gaugino productions which receive contributions from the resonant slepton productions. We first calculate the amplitudes of the single gaugino productions. Then we perform analyses of the single gaugino productions based on the three charged leptons and like sign dilepton signatures. These analyses allow to probe supersymmetric particles masses beyond the present experimental limits, and many of the $ł'_{ijk}$ coupling constants down to values smaller than the low-energy bounds. Finally, we show that the studies of the single gaugino productions offer the opportunity to reconstruct the $\tilde χ^0_1$, $\tilde χ^{\pm}_1$, $\tilde ν_L$ and $\tilde l^{\pm}_L$ masses with a good accuracy in a model independent way.

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arXiv2000

Summary of the SUSY Working Group of the 1999 Les Houches Workshop

The results obtained by the Working Group on Supersymmetry at the 1999 Les Houches Workshop on Collider Physics are summarized. Separate chapters treat "general" supersymmetry, R-parity violation, gauge mediated supersymmetry breaking, and anomaly mediated supersymmetry breaking.

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arXiv2000

Resonant sneutrino production in Supersymmetry with R-parity violation at the LHC

The resonant production of sneutrinos at the LHC via the R-parity violating couplings $ł'_{ijk} L_i Q_j D^c_k$ is studied through its three-leptons signature. A detailed particle level study of signal and background is performed using a fast simulation of the ATLAS detector. Through the full reconstruction of the cascade decay, a model-independent and precise measurement of the masses of the involved sparticles can be performed. Besides, this signature can be detected for a broad class of supersymmetric models, and for a wide range of values of several $ł'_{ijk}$ coupling constants. Within the MSSM, the production of a 900 GeV sneutrino for $λ^{\prime}_{211}>0.05$, and of a 350 GeV sneutrino for $λ^{\prime}_{211}>0.01$ can be observed within the first three years of LHC running.

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arXiv2000

The three-leptons signature from resonant sneutrino production at the LHC

The resonant production of sneutrinos at the LHC via the R-parity violating couplings $ł'_{ijk} L_i Q_j D^c_k$ is studied through its three-leptons signature. A detailed particle level study of signal and background is performed using a fast simulation of the ATLAS detector. Through the full reconstruction of the cascade decay, a model-independent and precise measurement of the masses of the involved sparticles can be performed. Besides, this signature can be detected in a large part of the SUSY parameter space and for wide ranges of values of several $ł'_{ijk}$ coupling constants.

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arXiv1999

Resonant sneutrino production at Tevatron Run II

We consider the single chargino production at Tevatron $p \bar p \to \tilde ν_i \to \tilde χ^{\pm}_1 l_i^{\mp}$ as induced by the resonant sneutrino production via a dominant \RPV coupling of type $ł'_{ijk} L_i Q_j D_k^c$. Within a supergravity model, we study the three leptons final state. The comparison with the expected background demonstrate that this signature allows to extend the sensitivity on the \susyq mass spectrum beyond the present LEP limits and to probe the relevant \RPV coupling down to values one order of magnitude smaller than the most stringent low energy indirect bounds. The trilepton signal offers also the opportunity to reconstruct the neutralino mass in a model independent way with good accuracy.

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arXiv1999

Experimental Aspects of Supersymmety with R-Parity Violating Couplings at the $e^+e^-$ Linear Collider

A very short review on phenomenological aspects of supersymmetry with violated R-parity at e+e- colliders is given. We present specific examples of a search for supersymmetric particles with violating R-parity couplings at a 500 GeV~e+e- linear collider. The signal extraction, and the mass measurement in the case of a pair production of the lightest neutralino, are performed with the help of Monte Carlo simulation.

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arXiv1998

Report of the GDR working group on the R-parity violation

This report summarizes the work of the "R-parity violation group" of the French Research Network (GDR) in Supersymmetry, concerning the physics of supersymmetric models without conservation of R-parity at HERA, LEP, Tevatron and LHC and limits on R-parity violating couplings from various processes. The report includes a discussion of the recent searches at the HERA experiment, prospects for new experiments, a review of the existing limits, and also theoretically motivated alternatives to R-parity and a brief discussion on the implications of R-parity violation on the neutrino masses.

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