The taste of new physics: Flavour violation from TeV-scale phenomenology to Grand Unification Björn Herrmann To cite this version: Björn Herrmann. The taste of new physics: Flavour violation from TeV-scale phenomenology to Grand Unification. High Energy Physics - Phenomenology [hep-ph]. Communauté Université Grenoble Alpes, 2019. tel-02181811 HAL Id: tel-02181811 https://tel.archives-ouvertes.fr/tel-02181811 Submitted on 12 Jul 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. The taste of new physics: Flavour violation from TeV-scale phenomenology to Grand Unification Habilitation thesis presented by Dr. BJÖRN HERRMANN Laboratoire d’Annecy-le-Vieux de Physique Théorique Communauté Université Grenoble Alpes Université Savoie Mont Blanc – CNRS and publicly defended on JUNE 12, 2019 before the examination committee composed of Dr. GENEVIÈVE BÉLANGER CNRS Annecy President Dr. SACHA DAVIDSON CNRS Montpellier Examiner Prof. ALDO DEANDREA Univ. Lyon Referee Prof. ULRICH ELLWANGER Univ. Paris-Saclay Referee Dr. SABINE KRAML CNRS Grenoble Examiner Prof. FABIO MALTONI Univ. Catholique de Louvain Referee July 12, 2019 ii “We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time.” T. S. Eliot iii Abstract The present manuscript, submitted as Habilitation Thesis in view of the Habilitation à diriger la recherche, presents an important part of my recent and current research work on the possibility of Non-Minimal Flavour Violation within supersymmetric theories. The first part of this manuscript contains an introduction to the concept of flavour and its description, first within the Standard Model of particle physics, then in theories beyond the latter. A dedicated discussion of the Minimal Supersymmetric Standard Model (MSSM) allows to introduce the framework of Non-Minimal Flavour Violation. The second part of this manuscript is composed of a selection of published work to which I have significantly contributed mainly between 2013 and 2018. I review in particuler work on experimental signatures of Non-Minimal Flavour Violation in the squark sector of the MSSM. In addition, I discuss the implementation of Non-Minimal Flavour Violation within Grand Unified frameworks including flavour symmetries. In the third and last part of this manuscript, I briefly discuss ongoing and future projects, to be understood as perspectives stemming from the presented published work. v To all who have contributed – in whatever way – to this manuscript. vii Acknowledgements I would like to start by expressing my gratitude to the members of the examination commit- tee for having accepted to evaluate the present manuscript and to participate to the habilitation defence. I am particularly thankful for the fruitful exchanges that we have had around this manuscript and the associated presentation. Second, I have to thank my collaborators, including the students, for the enriching and fruitful work on our common projects, presented in this manuscript and beyond. Without our numerous discussions and exchange of knowledge, the presented results could not have been achieved and working in research would not be so much fun. Moreover, I am grateful for their kindness together with the relaxed and pleasant working atmosphere within the different collaborations. Moreover, I am grateful to my colleagues at Laboratoire d’Annecy-le-Vieux de Physique Théorique for the inspiring working conditions and the pleasant atmosphere. I particularly acknowledge Fawzi Boudjema and Luc Frappat, successive directors of the institute, for their constant sup- port of my activities and the preparation of my habilitation. Special thanks go to our admis- trative team, Dominique Turc, Véronique Jonnery, and Virginie Malaval, for their availability, support, efficiency, and kindness. Finally, I would like to thank my university colleagues, most of them not working in the same discipline, for their interest in my work, their support, and the numerous discussions about physics and life. Last but not least, I thank my beloved wife Aurélie, who has been at my side during my whole research career, constantly inspiring me with her sympathy, her support, her curiosity, her humour, her zest for life, and, above all, her love. ix Contents Acknowledgements vii 1 Flavour violation in particle physics1 1.1 Flavour in the Standard Model.............................1 1.2 Extending the Standard Model.............................5 1.3 The Minimal Supersymmetric Standard Model....................8 2 Flavour constraints on new physics models 15 2.1 The experimental situation................................ 15 2.2 An MCMC study of squark generation mixing.................... 17 3 Exploring squark generation mixing at the LHC 27 3.1 Recasting of LHC limits on squark and neutralino masses.............. 31 3.2 Prospects for a dedicated search at LHC........................ 35 3.3 Identifying the squark flavour structure in a simplified model........... 39 3.4 Applications to the general MSSM........................... 48 4 A window towards Grand Unification 51 4.1 Fermion and sfermion sectors with SU(5)-like unification.............. 51 4.2 Flavour Violation in A4 × SU(5) Supersymmetry................... 52 5 Outlook and perspectives 65 5.1 Flavoured Grand Unification in Supersymmetry................... 65 5.2 Lepton flavour violation and non-universality.................... 70 5.3 Machine Learning in particle phenomenology.................... 71 5.4 Non-standard signatures of new physics at colliders................. 72 5.5 Precision calculations beyond the Standard Model.................. 73 1 Chapter 1 Flavour violation in particle physics In elementary particle physics, the concept of flavour allows to classify the elementary particles. More precisely, flavour is orthogonal to the arrangement of elementary matter fields into quarks and leptons. There are three generations of matter fields, meaning that there are three flavours of up-type quarks (up, charm, top), down-type quarks (down, strange, bottom), charged leptons (electron, muon, tau), and neutrinos (associated to the three leptons). It is important to note that the physical eigenstates are not necessarily flavour eigenstates of the theory, meaning that a physical particle may carry more than one flavour. This is the central topic of the work presented in this manuscript. This first Chapter is dedicated to a discussion of flavour, first within the Standard Model of particle physics, then within supersymmetric extensions of the latter. Particular attention will be paid to the concepts of Minimal Flavour Violation (MFV) as opposed to Non-Minimal Flavour Violation (NMFV). The latter will be at the centre of the present manuscript. 1.1 Flavour in the Standard Model The Standard Model of particle physics [1,2,3,4,5,6,7] describes the subatomic particles known at present. It is based on the gauge group SU(3)C × SU(2)L × U(1)Y, the three factors being relative to the strong, weak, and electromagnetic interactions, respectively. The associ- ated gauge bosons are the gluon, denoted g, the W- and Z-bosons, denoted W± and Z0, and the photon, denoted g. Matter is encompassed in the fermionic fields ! uL qL = , uR , dR , dL ! (1.1) nL `L = , eR , eL where u(i) = u, c, t contains the three up-type quark flavour eigenstates, d(i) = d, s, b) the three down-type quark flavour eigenstates, e(i) = e, m, t the three lepton flavour eigenstates, (i) and n = ne, nm, nt the three neutrino flavour eigenstates. The indices L and R refer to the chirality of the respective fermions. Moreover, the left-handed fields qL and `L are SU(2) doublets, while the right-handed fields are SU(2) singlets. Note that, although the observation of neutrino oscillations [8,9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22] strongly suggests their existence, right-handed neutrinos are not part of the Standard Model particle content. The fermionic matter fields together with their quantum numbers regarding the strong, weak, and electromagnetic interactions, are summarized in Table 1.1. 2 Chapter 1. Flavour violation in particle physics BL TT3 YQ uL 1/3 0 1/2 +1/2 1/3 2/3 dL 1/3 0 1/2 -1/2 1/3 -1/3 uR 1/3 0 0 0 4/3 2/3 dR 1/3 0 0 0 -2/3 -1/3 nL 0 1 1/2 +1/2 1 0 eL 0 1 1/2 -1/2 1 -1 eR 0 1 0 0 -2 -1 TABLE 1.1: Quantum numbers of the fermions in the Standard Model of particle physics. B and L denote baryon and lepton numbers, T and T3 refer to weak isospin, Y denotes weak hypercharge, and Q = T3 + Y/2 is the electric charge. The theory is completed by the complex scalar Higgs field [23, 24, 25, 26, 27, 28] ! ! H+ G+ H = −! H = , (1.2) H0 p1 v + h0 + iG0 2 where the last part correspondsp to the expansion of the neutral component around the vacuum expectation value hHi = v/ 2 ≈ 174 GeV upon electroweak symmetry breaking. The physical degree of freedom h0, the so-called Higgs-boson1, has been experimentally discovered by the ATLAS and CMS collaborations at the Large Hadron Collider [29, 30]. The matter fields acquire mass through the Yukawa interaction with the Higgs field. In the interaction eigenbasis, the corresponding Lagrangian reads SM v (i) (i) v ¯(i) (i) v ¯(i) (i) L = p u¯ Yuu H + p d Ydd H + p ` Ye` H , (1.3) Yuk 2 L R 2 L R 2 L R where Yu, Yd, and Y` are the Yukawa matrices for up-type quarks, down-type quarks, and leptons, respectively.