Search

We study CP-conserving non-minimal flavour violation in $A_4 \times SU(5)$ inspired Supersymmetric Grand Unified Theories (GUTs), focussing on the regions of parameter space where dark matter is successfully accommodated due to a light right-handed smuon a few GeV heavier than the lightest neutralino. In this region of parameter space we find that some of the flavour-violating parameters are constrained by the requirement of the dark matter relic density, due to the delicate interplay between the smuon and neutralino masses. By scanning over GUT scale flavour violating parameters, constrained by low-energy quark and lepton flavour violating observables, we find a striking difference in the results in which individual parameters are varied to those where multiple parameters are varied simultaneously, where the latter relaxes the constraints on flavour violating parameters due to cancellations and/or correlations. Since charged lepton-flavour violation provides the strongest constraints within a GUT framework, due to relations between quark and lepton flavour violation, we examine in detail a prominent correlation between some of the flavour violating parameters at the GUT scale consistent with the stringent lepton flavour violating process $\mu \rightarrow e \gamma$. We also examine the relation between GUT scale and low scale flavour violating parameters, for both quarks and leptons, and show how the usual expectations may be violated due to the correlations when multiple parameters are varied simultaneously., Comment: 31 pages, 13 figures. Matches published version

The latest Planck data allow one to determine the dark matter relic density with previously unparalleled precision. In order to achieve a comparable precision on the theory side, we have calculated the full $\mathcal{O}(\alpha_s)$ corrections to the most relevant annihilation and coannihilation processes for relic density calculations within the Minimal Supersymmetric Standard Model (MSSM). The interplay of these processes is discussed. The impact of the radiative corrections on the resulting relic density is found to be larger than the experimental uncertainty of the Planck data., Comment: 7 pages, 2 figures, 18th International Conference From the Planck Scale to the Electroweak Scale, 25-29 May 2015. Ioannina, Greece

We elaborate on a recently found SU(5) relation confined to the up-(s)quark flavour space, that remains immune to large quantum corrections up to the TeV scale. We investigate the possibilities opened by this new window on the GUT scale in order to find TeV-scale SU(5) tests realizable at the LHC. These SU(5) tests appear as relations among observables involving either flavour violation or chirality flip in the up-(s)quark sector. The power of these tests is systematically evaluated using a frequentist, p-value based criterion. SU(5) tests in the Heavy supersymmetry (SUSY), Natural supersymmetry and Top-charm supersymmetry spectra are investigated. The latter scenario features light stops and scharms and is well-motivated from various five-dimensional constructions. A variety of SU(5) tests is obtained, involving techniques of top polarimetry, charm-tagging, or Higgs detection from SUSY cascade decays. We find that O(10) to O(100) events are needed to obtain 50% of relative precision at 3-sigma significance for all of these tests. In addition, we propose a set of precision measurements in ultraperipheral collisions in order to search for the flavour-changing dipole operators of Heavy supersymmetry., 46 pages, 10 figures, v3: final version to appear in JHEP

We study quark flavour violation (QFV) in the squark sector of the Minimal Supersymmetric Standard Model (MSSM). We assume mixing between the second and the third squark generations, i.e. sc_R-st_{L,R} mixing mixing. We focus on QFV effects in bosonic squark decays, in particular on the decay into the lightest Higgs boson h0, su_2 -> su_1 h0, where su_{1,2} are the lightest up-type squarks. We show that the branching ratio of this QFV decay can be quite large (up to 50 %) due to large QFV trilinear couplings, and large sc_R-st_{L, R} and st_L-st_R mixing, despite the strong constraints on QFV from B meson data. This can result in characteristic QFV final states with significant rates at LHC (14 TeV), such as pp -> gluino gluino X -> t + h0 + 3jets + Etmiss + X and pp -> gluino gluino X -> t t (or tbar tbar) + h0 + 2jets + Etmiss + X. The QFV bosonic squark decays can have an influence on the squark and gluino searches at LHC., Figure 3 replaced, Section 4 revised

We study the effects of squark generation mixing on squark and gluino production and decays at LHC in the Minimal Supersymmetric Standard Model (MSSM) with focus on the mixing between second and third generation squarks. Taking into account the constraints from B-physics experiments we show that various regions in parameter space exist where decays of squarks and/or gluinos into quark flavour violating (QFV) final states can have large branching ratios. Here we consider both fermionic and bosonic decays of squarks. Rates of the corresponding QFV signals, e.g. pp -> t t bar{c} bar{c} missing-E_T X, can be significant at LHC(14 TeV). We find that the inclusion of flavour mixing effects can be important for the search of squarks and gluinos and the determination of the underlying model parameters of the MSSM at LHC., 7 pages, 4 figures, a reference updated, Proceedings of The 36th International Conference on High Energy Physics (ICHEP2012), Melbourne, Australia, July 4-11, 2012

We present an extensive analysis of squark and gaugino hadroproduction and decays in non-minimal flavour violating supersymmetry. We employ the so-called super-CKM basis to define the possible misalignment of quark and squark rotations, and we use generalized (possibly complex) charges to define the mutual couplings of (s)quarks and gauge bosons/gauginos. The cross sections for all squark-(anti-)squark/gaugino pair and squark-gaugino associated production processes as well as their decay widths are then given in compact analytic form. For four different constrained supersymmetry breaking models with non-minimal flavour violation in the second/third generation squark sector only, we establish the parameter space regions allowed/favoured by low-energy, electroweak precision, and cosmological constraints and display the chirality and flavour decomposition of all up- and down-type squark mass eigenstates. Finally, we compute numerically the dependence of a representative sample of production cross sections at the LHC on the off-diagonal mass matrix elements in the experimentally allowed/favoured ranges., Comment: 35 pages, 29 (partly colour) figures. Some typos corrected, wording of several paragraphs improved, version accepted by Nucl. Phys. B

Despite the lack of experimental evidence, Supersymmetry remains an attractive candidate for physics beyond the standard model of particle physics. Simple and viable supersymmetric extensions, such as the Minimal Supersymmetric Standard Model, cure, among other shortcomings of the standard model, the electroweak hierarchy problem, the gauge coupling unification and provide attractive dark matter candidates.One of the general characteristics of such extensions is that they may present a non-trivial flavour structure, which can lead to sizable contributions to flavour violating processes which are precisely measured and can be used to constrain the parameter space of new physics. The purpose of this manuscript is to discuss aspects of the extended flavour structure within supersymmetric models.The manuscript will first introduce the Standard Model of particle physics and its supersymmetric extensions before exposing three research projects.The first one will treat the problematic of the reconstruction of the squark flavour structure. Here, we have employed different strategies relying on inference statistical methods together with machine learning algorithms and assuming that a squark-like state is to be observed at colliders. Being a first step in this direction, improvement and complementary study will need to be proposed in case of the actual observation of a squark-like state but the obtained results are appealing.As a second step, we shall discuss constraints and experimental signatures of SU(5) Grand Unified Theories including flavour symmetries. In this framework, we will focus on A4 family symmetry inspired models. This analysis is based on a numerical scan of the parameter space, including experimental flavour constraints as well as dark matter relic density. The results show, as it has already been pointed out before, that the lepton sector is much more constraining that the hadronic one. Additionally, interesting features arise in case of a simultaneous scan over the flavour violating parameters, and suggest that the allowed ranges for these parameters are larger than in the case of a single parameter study because of correlation effects.Finally, the last chapter will be dedicated to leptoquark extensions of the standard model. These models, not necessary supersymmetric, have received considerable attention over the past few years, mainly due to the potential observation of lepton non universality at the Large Hadron Collider. We will discuss such extensions in the context of discrete flavour symmetries, useful tool for constraining the leptoquark patterns to a very predictive form. Finally, a model independent scan will be exposed, where we have obtained a list of potential symmetry candidates able to reproduce very specific leptoquark patterns alongside to the standard model fermionic mixing; Malgré l'absence de signatures expérimentales, les extensions supersymétriques du modèle standard de la physique des particules sont encore considérées parmi les plus attractives. La supersymétrie permet entre autres de résoudre le problème de la hiérarchie électrofaible, favorise l'unification des couplages de jauge nécessaire à une construction réaliste d'une théorie de grande unification, et propose des candidats viable à la matière noire.Une des caractéristiques générale des extensions supersymétriques est de présenter une structure de saveur nouvelle, pouvant entraîner de larges contributions dans les observables de violation de la saveur. L'étude de certaines de ces structures et de leurs conséquences expérimentales est l'objet de ce manuscrit.Ce manuscrit débutera avec une introduction générale au modèle standard de la physique des particules et de ses extensions supersymétriques avant de présenter trois projets de recherche.Dans le premier travail exposé, nous aborderons des approches permettant d'identifier la structure de saveur dans le secteur des squarks (partenaire supersymétrique des quarks). Ces méthodes, pionnières pour la problématique, reposent sur l'observation hypothétique d'un squark et utilisent des méthodes d'inférence statistique et de "machine learning". Bien qu'il ne s'agisse que d'une première approche, les résultats sont encourageants et la méthode pourrait être développée en cas d'observation réelle d'un état semblable à un squark aux collisionneurs.Nous discuterons ensuite de contraintes et conséquences expérimentales présentes dans des modèles de grande unification du type SU(5) avec symétrie de saveur. Dans ce contexte, nous discuterons de modèles inspirés par le groupe A_4. Cette analyse propose une exploration de l'espace des paramètres de ce type de modèles en incluant les contraintes expérimentales de saveur ainsi que la densité relique de matière noire. Les résultats confirment que le secteur leptonique est bien plus contraignant que le secteur hadronique. En addition, plusieurs particularités émergent lors d'une exploration simultanée de l'ensemble des paramètres conduisant à un espace autorisé par les contraintes plus important que dans le cas d'étude ne variant qu'un paramètre à la fois.Finalement, le dernier chapitre de ce manuscrit sera dédié à la discussion d'extensions du modèle standard incluant des leptoquarks. Ces extensions, non nécessairement supersymétriques, ont reçu un regain d'attention ces dernières années, en particulier suite à des mesures qui suggéreraient l'existence de structure non universelle de saveur leptonique. Nous discuterons de ces extensions dans le contexte des symétries discrètes de saveur qui peuvent conduire à des structures de couplages très prédictifs. Enfin, une méthode indépendante de modèles sera proposée pour obtenir une liste de groupes candidats à la reproduction de ces structures de couplages et de mélange fermionique du modèle standard de façon simultanée.

The Minimal Supersymmetric Standard Model (MSSM) is probably the best studied of all new physics theories. In most phenomenological studies, one assumes the hypothesis of minimal flavour violation, where all flavour-violating interactions are related to the CKM-matrix (as it is the case in the standard model). However, if supersymmetry is embedded in larger frameworks such as grand unified theories (GUT), new sources of flavour violation can appear. The corresponding terms in the Lagrangian are directly related to the mechanism of supersymmetry breaking, for which at present no theoretical consensus exists. Several processes have recently been evoked (among others by the co-director of the proposed thesis), which might lead to promising signatures at the LHC if non-minimal flavour violation is realized. These studies, however, included flavour-violating terms directly at the electroweak scale without taking into account their possible origin at some high scale. The main goal of the project is to extend the previous work in order to take into account the link between the electroweak and the GUT scale. This will allow to put constraints on parameters describing supersymmetry breaking using constraints imposed at the electroweak scale. A second goal is the analysis of relevant processes with the help of current Monte-Carlo simulation tools in order to study the background and thus clarify the observability at LHC for different scenarios and regions of parameters space. So, the project is ideally situated at the frontier between model building and more phenomenological aspects. For this reason the project naturally includes interactions with the local particle physics phenomenology group at LAPTh as well as with the the neighbouring experimental groups (e.g. ATLAS, LHCb) at LAPP. Moreover, collaborations on the national, in particular with the LPSC Grenoble, and international level, e.g. with the University of Würzburg (Germany), the University of Münster (Germany) and the newly created International Institute of Physics in Natal (Brasil) are envisaged.; Le modèle standard supersymétrique minimal (MSSM) est probablement une des théories de nouvelle physique les plus étudiées. Dans la plupart des études phénoménologiques, on fait l'hypothèse de la violation minimale de la saveur dans laquelle toutes les interactions violant la saveur sont directement liées à la matrice CKM du modèle Standard. Cependant, si la supersymétrie est plongée dans des cadres plus larges tels que les théories dites de Grande Unification, de nouvelles sources de violation de la saveur peuvent apparaitre. Les termes correspondant dans le lagrangien sont directement liés au choix du mécanisme de brisure de la supersymétrie. Or, à l'heure actuelle, aucun consensus n’existe quant au choix exact du mécanisme de brisure de la SUSY. Plusieurs mécanismes ont été évoqués récemment (entre autre, par le co-directeur de la thèse), qui pourraient conduire à des signatures prometteuses au LHC pour différents scénarios et domaines de paramètre. Le projet est donc idéalement situé à la frontière entre le 'model building' et des aspects plus phénoménologiques. Pour cette raison, le thésard sera naturellement amené à interagir de manière active avec le groupe de phénoménologie de physique des particules du LAPTh ainsi qu'avec les groupes de physique des particules du LAPP (ATLAS, LHCb..), laboratoire expérimental partageant le même bâtiment que le LAPTh. De plus, des collaborations sur le plan national, en particulier avec le LPSC de Grenoble, ainsi que sur le plan international, avec les universités de Würzburg et Münster (Allemagne) et le nouvel institut de physique de NATAL (Brésil) sont également envisagées.