WCxf: An exchange format for Wilson coefficients beyond the Standard Model

We perform an updated fit to LHC Higgs data and LEP electroweak precision tests in the framework of the Standard Model Effective Field Theory (SMEFT). We assume a generic structure of the SMEFT operators without imposing any flavour symmetries. The implementation is released as part of the public global SMEFT likelihood. This allows one to fit parameters of a broad class of new physics models to combined Higgs, electroweak, quark flavour, and lepton flavour observables. I. INTRODUCTIONAfter the discovery of the 125 GeV boson [1,2], the Higgs searches at the LHC have turned into precision tests of the Standard Model (SM). The SM predicts the coupling strength between each fundamental particle and the Higgs in terms of that particle's mass, without any adjustable parameters. Beyond the SM (BSM), however, these couplings can be modified, therefore measurements of Higgs production cross sections and decay rates may reveal the fundamental theory underlying the SM. It is beneficial to describe Higgs coupling modifications in the model-independent language of effective field theory (EFT) [3][4][5]. Assuming new physics decouples, that is to say the masses of non-SM particles are parametrically larger than the weak scale, the relevant effective theory at energies E ∼ m h ≈ 125 GeV is the so-called SMEFT. That theory has the same particle content and local symmetry as the SM, but it admits interaction terms (operators) in the Lagrangian with canonical dimensions larger than four. The Higgs data can be interpreted as constraints on Wilson coefficients of the higher-dimensional operators.Advantages of the SMEFT are not restricted to LHC Higgs physics. The theory offers a universal framework to describe a vast spectrum of precision measurements performed in weak scale colliders such as the LHC, Tevatron, or LEP. In particular, it is a perfect language to describe the so-called electroweak precision tests, that is accurate measurements of Z and W boson properties. A straightforward observation is that SMEFT operators may simultaneously affect both Higgs and electroweak observables. Therefore it makes sense to combine the two sets in order to increase the constraining power of data [6][7][8][9][10][11][12][13][14][15][16]. This work represents another step forward in this direction.In this paper we construct a likelihood for Wilson coefficients of dimension-6 SMEFT operators using a large set of Higgs and electroweak observables. Compared to previous analyses, the main novelties are:1. We do not impose any simplifying assumptions about the flavour structure of dimension-6 operators. This makes the analysis considerably more difficult, but the advantage is that our results are more general. The likelihood we provide can thus be used to constrain a variety of BSM models [17] beyond the U (3) 5 or minimal flavour violation paradigm. In particular, it can be applied to models addressing the so-called b → s anomalies [18,19], which must always involve a highly non-trivial flavour structure.2. All code employed for our analysis is o...

“…when new data becomes available. We follow the standard Wilson coefficient exchange format (WCxf) [20], such that our results can be easily imported by other analysis codes.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Flavourful SMEFT likelihood for Higgs and electroweak data

Falkowski

Straub

2020

“…and consider the l.h.s of (13). Using (28) and considering that the -independent terms amount to the contribution of the hypercharge and therefore give zero, we have…”

Section: A Simple Model For Gauge Anomaly Cancellation 31 Cancellatimentioning

confidence: 99%

Quark-lepton connections in Z′ mediated FCNC processes: gauge anomaly cancellations at work

Aebischer

Buras

Cerdà-Sevilla

et al. 2020

Self Cite

We consider scenarios with a heavy Z gauge boson with flavour non-universal quark and lepton couplings with the goal to illustrate how the cancellation of gauge anomalies generated by the presence of an additional U(1) gauge symmetry would imply correlations between FCNC processes within the quark sector, within the lepton sector and most interestingly between quark flavour and lepton flavour violating processes. To this end we present simple scenarios with only left-handed flavour-violating Z couplings and those in which also right-handed flavour-violating couplings are present. The considered scenarios are characterized by a small number of free parameters but in contrast to gauge anomaly cancellation in the Standard Model, in which it takes place separately within each generation, in our scenarios anomaly cancellation involves simultaneously quarks and leptons of all three generations. Our models involve, beyond the ordinary quarks and leptons, three heavy right-handed neutrinos. The models with only left-handed FCNCs of Z involve beyond g Z and M Z two real parameters characterizing the charges of all fermions under the U(1) gauge symmetry and the CKM and PMNS ones in the quark and lepton sectors, respectively. The models with the right-handed FCNCs of Z involve few additional parameters. Imposing constraints from well measured ∆F = 2 observables we identify a number of interesting correlations that involve e.g. ε /ε, B s,d → µ + µ − , B → K(K * ) + − , K + → π + νν, K L → π 0 νν and purely lepton flavour violating decays like µ → eγ, µ → 3e, τ → 3µ and µ − e conversion among others. Also (g − 2) µ,e are considered. The impact of the experimental µ → eγ, µ → 3e and in particular µ − e conversion bounds on rare K and B decays is emphasized.

“…There are a number of commonly used EFT bases, so we will be careful to specify the basis of interest and coefficient normalisation as we proceed with our discussion of constraints. Where these are relevant for application in computational procedures, they will be referenced in accordance with the Wilson Coefficient exchange format (WCxf) [87].…”

Section: Ameliorating Anomaliesmentioning

confidence: 99%

A near-minimal leptoquark model for reconciling flavour anomalies and generating radiative neutrino masses

Bigaran

Gargalionis

Volkas

2019

We introduce two scalar leptoquarks, the SU(2) L isosinglet denoted φ ∼ (3, 1, −1/3) and the isotriplet ϕ ∼ (3, 3, −1/3), to explain observed deviations from the standard model in semi-leptonic B-meson decays. We explore the regions of parameter space in which this model accommodates the persistent tensions in the decay observables R D ( * ) , R K ( * ) , and angular observables in b → sµµ transitions. Additionally, we exploit the role of these exotics in existing models for one-loop neutrino mass generation derived from ∆L = 2 effective operators. Introducing the vector-like quark χ ∼ (3, 2, −5/6) necessary for lepton-number violation, we consider the contribution of both leptoquarks to the generation of radiative neutrino mass. We find that constraints permit simultaneously accommodating the flavour anomalies while also explaining the relative smallness of neutrino mass without the need for cancellation between leptoquark contributions. A characteristic prediction of our model is a rate of muon-electron conversion in nuclei fixed by the anomalies in b → sµµ and neutrino mass; the COMET experiment will thus test and potentially falsify our scenario. The model also predicts signatures that will be tested at the LHC and Belle II.