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Dark matter from the centre of SU(N)
Auteur(s): Frigerio M., GrimbaumYamamoto Nicolas, Hambye Thomas
(Document sans référence bibliographique) Texte intégral en Openaccess :
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Ref Arxiv: 2212.11918
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Ref. & Cit.: NASA ADS
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Résumé: A dark sector with nonabelian gauge symmetry provides a sound framework to justify stable dark matter (DM) candidates. We consider scalar fields charged under a $SU(N)$ gauge group, and show that the centre of $SU(N)$, the discrete subgroup $Z_N$ also known as $N$ality, can ensure the stability of scalar DM particles. We analyse in some details two minimal DM models of this class, based on $SU(2)$ and $SU(3)$, respectively. These models have nontrivial patterns of spontaneous symmetry breaking, leading to distinctive phenomenological implications. For the $SU(2)$ model these include a specific interplay of two DM states, with the same interactions but different masses, and several complementary DM annihilation regimes, either within the dark sector or through the Higgs portal. The $SU(3)$ model predicts dark radiation made of a pair of dark photons with a unique gauge coupling, as well as regimes where DM semiannihilations become dominant and testable.



EFFECTIVE COMPARISON OF LEPTON MODELS
Auteur(s): Frigerio M.
Conférence invité: 32nd Rencontres de Blois (Blois, FR, 20211017)
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Résumé: We advocate effective field theory to analyse new physics in the lepton sector. When the new states are out of experimental reach, the only parameters relevant for phenomenology are the Wilson coefficients of higher dimensional operators, obtained by decoupling the heavy states. We illustrate the advantages of such effective description for a few representative models of neutrino masses, which may induce a variety of lowenergy leptonic observables.



Holographic models of composite Higgs in the Veneziano limit. Part II. Fermionic sector
Auteur(s): Elander D., Frigerio M., Knecht Marc, Kneur J.L.
(Article) Publié:
Jhep, vol. 05 p.066 (2022)
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Ref Arxiv: 2112.14740
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DOI: 10.1007/JHEP05(2022)066
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Résumé: We continue our study of stronglycoupled, approximately scaleinvariant gauge theories with a large number of flavours, which provide a suitable ultraviolet completion of the compositeHiggs scenario. We identify the requisite operators to realise partial compositeness of the StandardModel fermions. In order to compute the spectrum of composite fermionic states, we extend the bottomup holographic models, which we previously introduced to capture the main features of the nonperturbative dynamics in the Veneziano limit, by adding fermion fields in the bulk. We identify regions in parameter space where some fermionic bound states become light, depending in particular on the number of flavours, the operator scaling dimensions, and the bulk Yukawa couplings. We also observe a dense spectrum of states, when multiscale dynamics is induced by a large backreaction of bulk scalars on the geometry. Adapting the formalism of the holographic Wilsonian renormalisation group, we study the linear coupling between the composite and elementary fermions, as a function of energy scale. We find that, in some circumstances, the associated operators are dangerously irrelevant: the renormalisationgroup flow gives rise to a large linear coupling in the infrared, even when it is irrelevant from the point of view of the ultraviolet fixed point. We finally compute the partially composite spectrum, correlate it with the analysis of the flow, and assess the potential phenomenological implications, e.g. for the topquark partners.



Effective comparison of neutrinomass models
Auteur(s): Coy R., Frigerio M.
(Article) Publié:
Physical Review D, vol. 105 p.115041 (2022)
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Ref Arxiv: 2110.09126
DOI: 10.1103/PhysRevD.105.115041
WoS: WOS:000822568800005
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Résumé: New physics in the lepton sector may account for neutrino masses, affect electroweak precision observables, induce chargedlepton flavour violation, and shift dipole moments. The lowenergy predictions of different models are most conveniently compared within the formalism of effective field theory. To illustrate the benefits of this approach, we derive the Wilson coefficients for a set of representative models: the fermionic seesaw mechanisms (type I and III), the Zee model, and a minimal leptoquark model. In each case, the Weinberg and the dipole operators have qualitatively different origins. In parallel, we present the modelindependent constraints on the Wilson coefficients coming from various lepton observables. We then show that it becomes straightforward to understand the allowed parameter space for each model, and to discriminate between them. The Zee and leptoquark models are suitable to address the muon g − 2 anomaly.We also confront the models with the anomalies in the Wboson mass and semileptonic Bmeson decays.



Holographic models of composite Higgs in the Veneziano limit. Part I. Bosonic sector
Auteur(s): Elander D., Frigerio M., Knecht Marc, Kneur J.L.
(Article) Publié:
Jhep, vol. 03 p.182 (2021)
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Ref Arxiv: 2011.03003
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DOI: 10.1007/JHEP03(2021)182
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Résumé: We study stronglycoupled, approximately scaleinvariant gauge theories, which develop a mass gap in the infrared. We argue that a large number of fermion flavours is most suitable to provide an ultraviolet completion for the composite Higgs scenario. The holographic approach allows to describe the qualitative features of the nonperturbative dynamics in the Veneziano limit. We introduce new bottomup holographic models, which incorporate the backreaction of flavour on the geometry, and show that this can correlate the mass gap to the scale of flavoursymmetry breaking. We compute the mass spectrum for the various composite bosonic states, and study its dependence on the scaling dimension of the symmetrybreaking operators, as well as on the number of flavours. The different regions with a light dilaton are critically surveyed. We carefully assess the domain of validity of the holographic approach, and compare it with lattice simulations and the NambuJonaLasinio model.



On the spectrum of composite resonances
Auteur(s): Frigerio M.
Conference: Strong dynamics for physics within and beyond the Standard Model at LHC and Future Colliders (Trento, IT, 20190909)
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Résumé: I discuss the infrared mass spectrum of stronglycoupled gauge theories, thatinduce the Higgs as a composite pseudoNambuGoldstone boson. The set ofcomposite states accompanying the Higgs is determined by the symmetries of thetheory. Here we estimate their mass spectrum by nonperturbative techniquesinspired by QCD, as well as by exploiting gaugegravity duality. 1 CompositeHiggs: motivations and relevant energy scales As the Large Hadron Collider (LHC)did not find new states significantly coupled to the Standard Model (SM) belowthe TeV scale, any SM extension by such heavy states suffers from a littlehierarchy problem, as the mass of the scalar Higgs boson lies close to the 100GeV scale. Still, some SM extensions have the potential to address the bighierarchy between the TeV scale and the Planck scale. One possibility is toavoid elementary scalar fields, and assume the observed Higgs is a compositeobject, with a compositeness scale f 1 TeV. This scenario requires a stronglycoupled sector, whose spectrum generically includes several additional compositestates besides the Higgs. The mass of the lowestlying states cannot exceed ∼4πf , and some could be significantly lighter and within the LHC reach. Definitepredictions for the mass spectrum require to specify the stronglycoupled theoryin the ultraviolet (UV). Here we will assume it is a gauge theory of fermions,that confines in the infrared. We will estimate its mass spectrum in some welldefined approximations, by employing nonperturbative techniques inspired by QCD1) , as well as gaugegravity duality techniques 2). In models where the Higgsis a pseudoNambuGoldstone boson (pNGB) the electroweak scale, v 246 GeV, isinduced in two steps. The theory has a global (flavour) symmtry G F , that isspontaneously broken to a subgroup H F at the scale f. The electroweak symmetrySU (2) L × U (1) Y is embedded in 91



New physics in $b\to s\ell\ell$ transitions at one loop
Auteur(s): Coy R., Frigerio M., Mescia Federico, Sumensari Olcyr
(Article) Publié:
Eur.phys.j.c, vol. 80 p.52 (2020)
Texte intégral en Openaccess :
Ref HAL: hal02340141_v1
Ref Arxiv: 1909.08567
Ref INSPIRE: 1754713
DOI: 10.1140/epjc/s100520197581y
WoS: WOS:000523449400003
Ref. & Cit.: NASA ADS
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7 Citations
Résumé: We investigate newphysics contributions to $b\rightarrow s \ell \ell $ transitions in the context of an effective field theory extension of the Standard Model, including operator mixing at one loop. We identify the few scenarios where a single Wilson coefficient, $C/\Lambda ^2 \sim 1/\mathrm{TeV}^2$, induces a substantial shift in the lepton flavour universality ratios $R_K$ and $R_{K^*}$ at one loop, while evading Zpole precision tests, collider bounds, and other flavour constraints. Novel fits to the present data are achieved by a lefthanded current operator with quarkflavour indices (2, 2) or (3, 3). Interestingly, the running of the Standard Model Yukawa matrices gives the dominant effect for these scenarios. We match the favoured effectivetheory scenarios to minimal, singlemediator models, which are subject to additional stringent constraints. Notably, we recognise three viable instances of a leptoquark with one coupling to fermions only. If the anomalies were confirmed, it appears that oneloop explanations have good prospects of being directly tested at the LHC.
