Scheming in the SMEFT

We discuss the constraints on the Standard Model Effective Field Theory inferred from global fits to electroweak data. Special attention is paid to two unconstrained combinations of Wilson coefficients that are present when the analysis is restricted to measurements of $\bar\psi\psi\to\bar\psi\psi$ scatterings. We illustrate how these unconstrained directions arise due to a reparameterization invariance that characterizes $\bar\psi\psi\to\bar\psi\psi$ processes but is not respected in $\bar\psi\psi\to\bar\psi\psi\bar\psi\psi$ scatterings. This invariance is independent of the operator basis adopted and of the choice of the input parameters. This is verified comparing the results obtained in the {$\hat \alpha_{em}, \hat m_Z, \hat G_F$} input scheme with those of a {$\hat m_W, \hat m_Z, \hat G_F$} scheme.Comment: 5 + 1 pages, 2 figures. Contribution to the proceedings of EPS-HEP 2017, European Physical Society conference on High Energy Physics, 5-12 July 2017, Venice, Ital

Higgs physics beyond the SM: the non-linear EFT approach

Depending on whether electroweak physics beyond the Standard Model is based on a linear or on a non-linear implementation of the electroweak symmetry breaking, a linear or a chiral Effective Lagrangian is more appropriate. In this talk, the main low-energy signals that allow to recognize whether the observed Higgs scalar is a dynamical (composite) particle or rather an elementary one are presented, in a model-independent way. The patterns of effective couplings produced upon the assumption of specific composite Higgs models are also discussed.Comment: 8 pages, 1 figure. Proceedings of the talk given at the XXIXth Rencontres de Physique de la Vall\'ee d'Aoste, La Thuile (Italy), March 201

Signatures of dynamical scalars

Effective Lagrangians represent an important, model independent tool for studying physics beyond the Standard Model, via its impact on electroweak scale observables. In particular, two different effective descriptions may be appropriate, depending on how the electroweak symmetry breaking is realized at high energies: a linear effective Lagrangian is best suited in presence of linear dynamics, while a non-linear -chiral- one is more pertinent for scenarios featuring a non-linear realization. In this talk I will present a few examples of low-energy signals that differentiate the phenomenology of the two descriptions, thus providing a powerful insight into the nature of the Higgs boson.Comment: 4 pages; contribution to the Proceedings of the 50th Rencontres de Moriond, Electroweak Session. arXiv admin note: substantial text overlap with arXiv:1505.0063

Scheming in the SMEFT... and a reparameterization invariance!

We explain a reparameterization invariance in the Standard Model Effective Field Theory present when considering $\bar{\psi} \psi \rightarrow \bar{\psi} \psi$ scatterings (with $\psi$ a fermion) and how this leads to unconstrained combinations of Wilson coefficients in global data analyses restricted to these measurements. We develop a $\{\hat{m}_W, \hat{m}_Z,\hat{G}_F\}$ input parameter scheme and compare results to the case when an input parameter set $\{\hat{\alpha}, \hat{m}_Z,\hat{G}_F\}$ is used to constrain this effective theory from the global data set, confirming the input parameter independence of the unconstrained combinations of Wilson coefficients, and supporting the reparameterization invariance explanation. We discuss some conceptual issues related to these degeneracies that are relevant for LHC data reporting and analysis.Comment: 41 pages, 8 tables, 8 figures. addendum in appendix - results obtained allowing two independent flavor contractions for the operator Q_ll in the U(3)^5 flavor symmetric limi

Examining the neutrino option

The neutrino option is a scenario where the electroweak scale, and thereby the Higgs mass, is generated simultaneously with neutrino masses in the seesaw model. This occurs via the leading one loop and tree level diagrams matching the seesaw model onto the Standard Model Effective Field Theory. We advance the study of this scenario by determining one loop corrections to the leading order matching results systematically, performing a detailed numerical analysis of the consistency of this approach with Neutrino data and the Standard Model particle masses, and by examining the embedding of this scenario into a more ultraviolet complete model. We find that the neutrino option remains a viable and intriguing scenario to explain the origin of observed particle masses.Comment: 26 pages, 6 figures v2, typo corrections and refs adde

The SMEFTsim package, theory and tools

We report codes for the Standard Model Effective Field Theory (SMEFT) in FeynRules -- the SMEFTsim package. The codes enable theoretical predictions for dimension six operator corrections to the Standard Model using numerical tools, where predictions can be made based on either the electroweak input parameter set $\{\hat{\alpha}_{ew}, \hat{m}_Z, \hat{G}_F \}$ or $\{\hat{m}_{W}, \hat{m}_Z, \hat{G}_F\}$. All of the baryon and lepton number conserving operators present in the SMEFT dimension six Lagrangian, defined in the Warsaw basis, are included. A flavour symmetric ${\rm U}(3)^5$ version with possible non-SM $\rm CP$ violating phases, a (linear) minimal flavour violating version neglecting such phases, and the fully general flavour case are each implemented. The SMEFTsim package allows global constraints to be determined on the full Wilson coefficient space of the SMEFT. As the number of parameters present is large, it is important to develop global analyses on reduced sets of parameters minimizing any UV assumptions and relying on IR kinematics of scattering events and symmetries. We simultaneously develop the theoretical framework of a "W-Higgs-Z pole parameter" physics program that can be pursued at the LHC using this approach and the SMEFTsim package. We illustrate this methodology with several numerical examples interfacing SMEFTsim with MadGraph5. The SMEFTsim package can be downloaded at https://feynrules.irmp.ucl.ac.be/wiki/SMEFTComment: Corrected numerics of section 10.5.1, references added, minor changes and corrected typos. Version published in JHE

SMEFTsim 3.0 -- a practical guide

The SMEFTsim package is designed to enable automated computations in the Standard Model Effective Field Theory (SMEFT), where the SM Lagrangian is extended with a complete basis of dimension six operators. It contains a set of models written in FeynRules and pre-exported to the UFO format, for usage within Monte Carlo event generators. The models differ in the flavor assumptions and in the input parameters chosen for the electroweak sector. The present document provides a self-contained, pedagogical reference that collects all the theoretical and technical aspects relevant to the use of SMEFTsim and it documents the release of version 3.0. Compared to the previous release, the description of Higgs production via gluon-fusion in the SM has been significantly improved, two flavor assumptions for studies in the top quark sector have been added, and a new feature has been implemented, that allows the treatment of linearized SMEFT corrections to the propagators of unstable particles.Comment: Version published in JHEP. Code available at https://SMEFTsim.github.i

Probing the Charm Yukawa Coupling in Higgs + Charm Production

We propose a new method to determine the coupling of the Higgs boson to charm quarks, via Higgs production in association with a charm-tagged jet: $pp\to hc$. As a first estimate, we find that at the LHC with 3000 fb$^{-1}$ it should be possible to derive a constraint of order one, relative to the SM value of the charm Yukawa coupling. As a byproduct of this analysis, we present an estimate of the exclusive $pp \to hD^{(*)}$ electroweak cross section. Within the SM, the latter turns out to be not accessible at the LHC even in the high-luminosity phase.Comment: 5 pages, 3 figure

SMEFT calculations for the LHC

This talk summarizes the status of calculations in the Standard Model Effective Field Theory and gives an overview of the computational techniques that are most commonly employed in order to make predictions for LHC processes in this framework