FRIGERIO Michele
Organisme : CNRS
Chargé de Recherche
(HDR)
michele.frigerio
umontpellier.fr
Bureau: , Etg: 1, Bât: 13  Site : Campus Triolet
Administration Locale: Membre d'un pool d'experts
 Direction d'équipe

Domaines de Recherche:  Physique/Physique des Hautes Energies  Phénoménologie
 Physique/Physique des Hautes Energies  Théorie
 Physique/Physique des Hautes Energies  Expérience

Dernieres productions scientifiques :


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)
Texte intégral en Openaccess :
Ref HAL: hal03022749_v1
Ref Arxiv: 2011.03003
Ref INSPIRE: 1828484
DOI: 10.1007/JHEP03(2021)182
Ref. & Cit.: NASA ADS
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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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Ref INSPIRE: 1789740
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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.



Effective approach to lepton observables: The seesaw case
Auteur(s): Coy R., Frigerio M.
(Article) Publié:
Physical Review D, vol. 99 p.095040 (2019)
Texte intégral en Openaccess :
Ref HAL: hal01949587_v1
Ref Arxiv: 1812.03165
DOI: 10.1103/PhysRevD.99.095040
WoS: WOS:000470859800009
Ref. & Cit.: NASA ADS
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8 Citations
Résumé: In the absence of direct evidence of new physics, any ultraviolet theory can be reduced to its specific set of lowenergy effective operators. As a case study, we derive the effective field theory for the seesaw extension of the Standard Model, with sterile neutrinos of mass $M>m_W$. We systematically compute all Wilson coefficients generated at one loop. Hence, it becomes straightforward to (i) identify the seesaw parameters compatible with the smallness of neutrino masses; (ii) compute precision lepton observables, which may be sensitive to scales as large as $M\sim 10^3$ TeV; and (iii) establish sharp correlations among those observables. We find that the flavourconserving Wilson coefficients set an upper bound on the flavourviolating ones. The lowenergy limits on $\mu\to e$ and $\tau\to e,\mu$ transitions suppress flavour violation in $Z$ and Higgs decays, as well as electric dipole moments, far beyond the experimental reach. The bounds from the universality of $G_F$ and the invisible $Z$ width are more stringent than present and future limits on $\tau\to e,\mu$ transitions. We also present a general spurion analysis, to compare the seesaw with different models, thus assessing the discriminating potential of the effective approach.



The Bearable Compositeness of Leptons
Auteur(s): Frigerio M., Nardecchia Marco, Serra Javi, Vecchi Luca
(Article) Publié:
Jhep, vol. 10 p.017 (2018)
Texte intégral en Openaccess :
Ref HAL: hal01851263_v1
Ref Arxiv: 1807.04279
Ref INSPIRE: 1681965
DOI: 10.1007/JHEP10(2018)017
WoS: 000446567500001
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7 Citations
Résumé: Partial compositeness as a theory of flavor in the lepton sector is assessed. We begin presenting the first systematic analysis of neutrino mass generation in this context, and identifying the distinctive mass textures. We then update the bounds from charged lepton flavor and CP violating observables. We put forward a U(1)$^{3}$ × CP symmetry of the composite sector, in order to allow the new physics to be not far above the TeV scale. This hypothesis effectively suppresses the new contributions to the electron EDM and μ → eγ, by far the most constraining observables, and results in a novel pattern of flavor violation and neutrino masses. The CP violation in the elementarycomposite mixing is shown to induce a CKM phase of the correct size, as well as orderone phases in the PMNS matrix. We compare with the alternative possibility of introducing multiple scales of compositeness for leptons, that also allow to evade flavor and CP constraints. Finally, we examine violations of lepton flavor universality in Bmeson semileptonic decays. The neutralcurrent anomalies can be accommodated, predicting strong correlations among different lepton flavors, with a few channels close to the experimental sensitivity.

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