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A bstract I present a model addressing coherently the naturalness problem of the electroweak scale and the observed pattern of deviations from the Standard Model in semileptonic decays of B mesons. The Higgs and the two scalar leptoquarks responsible for the B -physics anomalies, S 1 = 3 ¯ , 1 , 1 / 3 and S 3 = 3 ¯ , 3 , 1 / 3 , arise as pseudo Nambu-Goldstone bosons of a new strongly coupled sector at the multi-TeV scale. I focus on an explicit realization of such a dynamics in terms of a new strongly coupled gauge interaction and extra vectorlike fermions charged under it. The model presents a very rich phenomenology, ranging from flavour observables, Higgs and electroweak precision measurements, and direct searches of new states at the LHC.

A bstract Motivated by additional experimental hints of Lepton Flavour Universality violation in B decays, both in charged- and in neutral-current processes, we analyse the ingredients necessary to provide a combined description of these phenomena. By means of an Effective Field Theory (EFT) approach, based on the hypothesis of New Physics coupled predominantly to the third generation of left-handed quarks and leptons, we show how this is possible. We demonstrate, in particular, how to solve the problems posed by electroweak precision tests and direct searches with a rather natural choice of model parameters, within the context of a U(2) q ×U(2) ℓ flavour symmetry. We further exemplify the general EFT findings by means of simplified models with explicit mediators in the TeV range: coloured scalar or vector leptoquarks and colour-less vectors. Among these, the case of an SU(2) L -singlet vector leptoquark emerges as a particularly simple and successful framework.

A bstract In this paper we present the complete one-loop matching conditions, up to dimension-six operators of the Standard Model effective field theory, resulting by integrating out the two scalar leptoquarks S 1 ∼ 3 1 1 3 and S 3 ∼ 3 3 1 3 . This allows a phenomenological study of low-energy constraints on this model at one-loop accuracy, which will be the focus of a subsequent work. Furthermore, it provides a rich comparison for functional and computational methods for one-loop matching, that are being developed. As a corollary result, we derive a complete set of dimension-six operators independent under integration by parts, but not under equations of motions, called Green’s basis , as well as the complete reduction formulae from this set to the Warsaw basis.

A bstract We perform a complete study of the low-energy phenomenology of S 1 and S 3 leptoquarks, aimed at addressing the observed deviations in B -meson decays and the muon magnetic dipole moment. Leptoquark contributions to observables are computed at one-loop accuracy in an effective field theory approach, using the recently published complete one-loop matching of these leptoquarks to the Standard Model effective field theory. We present several scenarios, discussing in each case the preferred parameter space and the most relevant observables.

A bstract The emission of collinear radiation off an elementary lepton can be factorised from the hard scattering process by introducing Parton Distribution Functions of a Lepton (LePDF), which, contrary to protons, can be derived from first principles. In case of multi-TeV lepton colliders, such as the muon colliders currently being proposed, the complete structure of Standard Model interactions must be taken into account. In this work we solve numerically the corresponding DGLAP equations at the double-log order and provide public files with LePDFs for both muons and electrons, including polarisation effects. We discuss several interesting aspects of the resulting PDFs and compare them with the Effective Vector Approximation, showing that the latter fails to describe well the vector bosons PDFs at small momentum fractions, unless it is extended to higher orders.

A bstract In view of recent experimental indications of violations of Lepton Flavor Universality (LFU) in B decays, we analyze constraints and implications of LFU interactions, both using an effective theory approach, and an explicit dynamical model. We show that a simple dynamical model based on a SU(2) L triplet of massive vector bosons, coupled predominantly to third generation fermions (both quarks and leptons), can significantly improve the description of present data. In particular, the model decreases the tension between data and SM predictions concerning: i) the breaking of τ - μ universality in B → D (*) ℓν decays; ii) the breaking of μ - e universality in B → Kℓ + ℓ − decays. Indirectly, the model might also decrease the discrepancy between exclusive and inclusive determinations of | V cb | and | V ub |. The minimal version of the model is in tension with ATLAS and CMS direct searches for the new massive vectors (decaying into τ + τ − pairs), but this tension can be decreased with additional non-standard degrees of freedom. Further pre-dictions of the model both at low- and high-energies, in view of future high-statistics data, are discussed.

A bstract We study the role of the Z / γ -interference parton distribution function (PDF) in high-energy muon colliders. We review how this PDF emerges when electroweak interactions are applied to the collinear splitting process and show that the leading-order approximation is significantly suppressed due to an accidental cancellation. However, this suppression does not appear in the leading-logarithm resummed numerical result, where the Z / γ PDF is instead comparable to those of other electroweak gauge bosons. By extending the analytical approximation to next-to-leading order, we show the mechanism by which the suppression is lifted and provide a more accurate approximation to the numerical result. Furthermore, we explore the impact of the Z / γ PDF in several processes at future muon colliders. High-energy Compton scattering is identified as a promising process for observing experimentally this peculiar electroweak effect with high precision. We also quantify the impact of the Z / γ PDF on Higgs physics and, as a new physics example, in resonant single-production of axion-like particles (ALP).

A bstract We study the effective field theory sensitivity of an LHC analysis for the τν final state with an associated b -jet. To illustrate the improvement due to the b -tagging, we first recast the recent CMS analysis in the τν channel, using an integrated luminosity of 35.9 fb − 1 at s = 13 TeV, and provide limits on all the dimension-six effective operators which contribute to the process. The expected limits from the b -tagged analysis are then derived and compared. We find an improvement of approximately ∼ 30% in the bounds for operators with a b quark. We also discuss in detail possible angular observables to be used as a discriminator between dimension-six operators with different Lorentz structure. Finally, we study the impact of these limits on some simplified scenarios aimed at addressing the observed deviations from the Standard Model in lepton flavor universality ratios of semileptonic B -meson decays. In particular, we compare the collider limits on those scenarios set by our analysis either with or without the b -tagging, assuming an integrated luminosity of 300 fb − 1 , with relevant low-energy flavor measurements.

A bstract In this work, we reinterpret ATLAS and CMS dijet resonance searches to set robust constraints on all hypothetical tree-level scalar and vector mediators with masses up to 5 TeV, assuming a diquark or a quark-antiquark coupling with an arbitrary flavor composition. To illustrate the application of these general results, we quantify the permissible size of new physics in B ¯ q → D q ∗ + π K consistent with the absence of signal in dijet resonance searches. Along the way, we perform a full SMEFT analysis of the aforementioned non-leptonic B meson decays at leading-order in α s . Our findings uncover a pressing tension between the new physics explanations of recently reported anomalies in these decays and the dijet resonant searches. The high- p T constraints are crucial to drain the parameter space consistent with the low- p T flavor physics data.

A bstract In this paper we provide a combined explanation of charged- and neutral-current B -physics anomalies assuming the presence of a light sterile neutrino N R which contributes to the B → D (*) τν processes. We focus in particular on two simplified models, where the mediator of the flavour anomalies is either a vector leptoquark U 1 μ ∼ ( 3 , 1 , 2/3) or a scalar leptoquark S 1 ∼ ( 3 ¯ , 1 , 1/3). We find that U 1 μ can successfully reproduce the required deviations from the Standard Model while being at the same time compatible with all other flavour and precision observables. The scalar leptoquark instead induces a tension between B s mixing and the neutral-current anomalies. For both states we present the limits and future projections from direct searches at the LHC finding that, while at present both models are perfectly allowed, all the parameter space will be tested with more luminosity. Finally, we study in detail the cosmological constraints on the sterile neutrino N R and the conditions under which it can be a candidate for dark matter.