Abstract: The most common predictions for rare \(K\) and \(B\) decay branching ratios in the Standard Model are based on the CKM elements \(|V_{cb}|\) and \(|V_{ub}|\) resulting from global fits, that are in the ballpark of their inclusive and exclusive determinations, respectively. In the present paper we follow another route. We assume that the future true values of \(|V_{cb}|\) and \(|V_{ub}|\) will be both from exclusive determinations and set them equal to the most recent ones from FLAG. An unusual pattern of SM predictions results from this study with some existing tensions being dwarfed and new tensions being born. In particular using the HPQCD \(B^0_{s,d}-\bar B^0_{s,d}\) hadronic matrix elements a \(3.1\sigma\) tension in \(\Delta M_s\) independently of \(\gamma\) is found. For \(60^\circ\le\gamma\le 75^\circ\) the tension in \(\Delta M_d\) between \(4.0\sigma\) and \(1.1\sigma\) is found and in the case of \(\epsilon_K\) between \(5.2\sigma\) and \(2.1\sigma\). Moreover, the room for new physics in \(K^+\to\pi^+\nu\bar\nu\), \(K_L\to\pi^0\nu\bar\nu\) and \(B\to K(K^*)\nu\bar\nu\) decays is significantly increased. We compare the results in this EXCLUSIVE scenario with the HYBRID one in which \(|V_{cb}|\) in the former scenario is replaced by the most recent inclusive \(|V_{cb}|\) and present the dependence of all observables considered by us in both scenarios as functions of \(\gamma\). We also compare the determination of \(V_{cb}|\) from \(\Delta M_s\), \(\Delta M_d\), \(\epsilon_K\) and \(S_{\psi K_S}\) using \(B^0_{s,d}-\bar B^0_{s,d}\) hadronic matrix elements from LQCD with \(2+1+1\) flavours, \(2+1\) flavours and their average. Only for the \(2+1+1\) case values for \(\beta\) and \(\gamma\) exist for which the same value of \(|V_{cb}|\) is found: \(|V_{cb}|=42.6(7)\times 10^{-3}\). This in turn implies a \(2.7\sigma\) anomaly in \(B_s\to\mu^+\mu^-\).
Abstract: Leptoquarks are prime candidates for explaining the intriguing hints for lepton flavour universality violation. In particular, the \(SU(2)_L\) doublet of scalar leptoquarks \(S_2\) is capable of providing an explanation for the tensions between the measurements and the Standard Model predictions in \((g-2)_\mu\), \(b\to s\ell^+ \ell^-\) and \(b\to c\tau\nu\) processes, as well as in non-resonant di-electron production. However, in the minimal setup with a single leptoquark generation, a common explanation for all these issues is not possible as this would lead to unacceptably large charged lepton flavour violation. We therefore propose a model with three generations of \(S_2\), each coupling exclusively to a single lepton flavour, \textit{i.e.}~a model extending the Standard Model particle content by an electroquark, a muoquark and a tauquark. We show that after taking into account other constraints, such as those originating from electroweak precision observables and \(\Delta F=2\) processes, it is possible to provide a combined explanation for all these hints of lepton flavour universality violation. Moreover, we find that the presence of the tauquark can generate a dimension-six \({\cal O}_9^U\) operator via off-shell photon penguin diagrams, which, together with the muoquark contribution, further improves the global fit to \(b \to s \ell^+ \ell^-\) data.
Abstract: The persistent tensions between inclusive and exclusive determinations of \(|V_{cb}|\) and \(|V_{ub}|\) weaken the power of theoretically clean rare \(K\) and \(B\) decays in the search for new physics (NP). We demonstrate how this uncertainty can be practically removed by considering within the SM suitable ratios of various branching ratios. This includes the branching ratios for \(K^+\to\pi^+\nu\bar\nu\), \(K_{L}\to\pi^0\nu\bar\nu\), \(K_S\to\mu^+\mu^-\), \(B_{s,d}\to\mu^+\mu^-\) and \(B\to K(K^*)\nu\bar\nu\). Also \(\epsilon_K\), \(\Delta M_d\), \(\Delta M_s\) and the mixing induced CP-asymmetry \(S_{\psi K_S}\), all measured already very precisely, play an important role in this analysis. The highlights of our analysis are 16 \(|V_{cb}|\) and \(|V_{ub}|\) independent ratios that often are independent of the CKM arameters or depend only on the angles \(\beta\) and \(\gamma\) in the Unitarity Triangle with \(\beta\) already precisely known and \(\gamma\) to be measured precisely in the coming years by the LHCb and Belle II collaborations. Once \(\gamma\) Once \(\gamma\) is measured precisely these 16 ratios taken together are expected to be a powerful tool in the search for new physics. Assuming no NP in \(|\epsilon_K|\) and \(S_{\psi K_S}\) we determine independently of \(|V_{cb}|\): \(\mathcal{B}(K^+\to\pi^+\nu\bar\nu)_\text{SM}= (8.60\pm0.42)\times 10^{-11}\) and \(\mathcal{B}(K_L\to\pi^0\nu\bar\nu)_\text{SM}=(2.94\pm 0.15)\times 10^{-11}\). This are the most precise determinations to date. Assuming no NP in \(\Delta M_{s,d}\) allows to obtain analogous results for all \(B\) decay branching ratios considered in our paper without any CKM uncertainties.
Admir Greljo, Ajdin Palavrić, Anders Eller Thomsen
Abstract: We study the flavor structure of the lepton and baryon number–conserving dimension-6 operators in the Standard Model effective field theory (SMEFT). Building on the work of [1], we define several well-motivated flavor symmetries and symmetry breaking patterns that serve as competing hypotheses about the ultraviolet (UV) dynamics beyond the SM, not far above the TeV scale. In particular, we consider four different structures in the quark sector and seven in the charged lepton sector. The set of flavor-breaking spurions is (almost) always taken to be the minimal one needed to reproduce the observed charged fermion masses and mixings. For each case, we explicitly construct and count the operators to the first few orders in the spurion expansion, providing ready-for-use setups for phenomenological studies and global fits. We provide a Mathematica package SMEFTflavor to facilitate similar analyses for flavor symmetries not covered in this work.
Abstract: Discrepancies between recent experimental results and their respective Standard Model predictions, known as flavour anomalies, are reported in semileptonic charged and neutral-current \(B\)-decays, the muon magnetic moment \((g-2)_\mu\), and the extraction of the Cabibbo angle. In this proceedings, we review two New Physics models that introduce two scalar mediators at the TeV scale and aim at a combined explanation of the flavour anomalies. The first model features the leptoquarks \(S_1\) and \(S_3\) and provides tree level solutions to both \(B\)-anomalies and one-loop level solution to the anomalous \((g-2)_\mu\). The second features the leptoquark \(S_1\) and the charged singlet \(\phi^+\). While \(S_1\) provides the same solution to the charged-current \(B\)-anomaly and \((g-2)_\mu\) as in the first model, \(\phi^+\) can accommodate the Cabibbo-angle anomaly independently and together with \(S_1\) can resolve the neutral-current \(B\)-anomaly at one-loop.
Abstract: In this white paper for the Snowmass process, we summarize the role flavor model building plays in the quest for new physics. We review approaches to address the non-generic flavor structure of the Standard Model and discuss how new physics models can be made compatible with the stringent constraints from flavor changing processes that indirectly probe very high scales. We also give an overview of the persistent anomalies in B decays and the anomalous magnetic moment of the muon and some of their most popular new physics explanations.
Abstract: I detail an optimistic future vision for the use of SMEFT at high-energy colliders, and describe the use of the studies which could result for interpretation of future models. I also explore some of the potential pitfalls which could significantly degrade the utility of those results and discuss approaches to avoid them and ensure that results are actually accurate when applied to new models.
Abstract: Mapping UV theories onto low energy effective descriptions is a procedure known as matching. The last decade has seen tremendous progress in the development of new tools for efficiently performing matching calculations, by relying on so-called functional methods. This white paper summarizes the status of functional matching. Specifically, matching for relativistic theories is a fully solved problem up to one-loop order in perturbation theory, and to arbitrary order in the effective field theory expansion. A streamlined prescription that has been partially automated facilitates the application of functional matching to phenomenological studies in the Standard Model EFT framework.
Simone Alioli, Radja Boughezal, Weiguang Cao, Gauthier Durieux, Lukáš Gráf, Brian Quinn Henning, Teppei Kitahara, Hao-Lin Li, Xiaochuan Lu, Camila S. Machado, Adam Martin, Tom Melia, Emanuele Mereghetti, Hitoshi Murayama, Christopher W. Murphy, Jasper Roosmale Nepveu, Sridip Pal, Frank Petriello, Yael Shadmi, Jing Shu, Yaniv Weiss, Ming-Lei Xiao, Jiang-Hao Yu
Abstract: In this contribution to the Snowmass 2021 process we review theoretical developments in the Standard Model Effective Field Theory (SMEFT) with a focus on effects at the dimension-8 level and beyond. We review the theoretical advances that led to the complete construction of the operator bases for the dimension-8 and dimension-9 SMEFT Lagrangians. We discuss the possibility of obtaining all-orders results in the \(1/\Lambda\) expansion for certain SMEFT observables, and briefly present the on-shell approach to constructing SMEFT amplitudes. Finally we present several new phenomenological effects that first arise at dimension-8 and discuss the impact of these terms on experimental analyses.
Title:Using Machine Learning techniques in phenomenological studies in flavour physics
Abstract:
In the recent years, a series of measurements in the observables \(R_{K^{(*)}}\) and \(R_{D^{(*)}}\) concerning the semileptonic decays of the (B) mesons have shown hints of violations of Lepton Flavour Universality (LFU). An updated model-independent analysis of New Physics violating LFU, by using the Standard Model Effective Field Theory (SMEFT) Lagrangian with semileptonic dimension six operators at \(\Lambda = 1\,\mathrm{TeV}\) is presented. We perform a global fit, in order to assess the impact of the New Physics in a broad range of observables including \(B\)-physics, electroweak precision test, Higgs physics and nuclear \(\beta\) decays. We discuss the relevance of the mixing in the first generation for the observables with heavier lepton flavours. We use for the first time in this context a Montecarlo analysis of the likelihood function to extract the confidence intervals and correlations between observables. Our results show that a suitable strategy is to use a Gradient Boosting predictor as a proxy of the real likelihood function, and to analyze the SHAP values as a measure of the impact of each parameter of SMEFT Lagrangian in the fit.
The slides will be available at my repo, in their corresponding branch: CPAN22.
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