On the impact of dimension-eight SMEFT operators on Higgs measurements

Using the production of a Higgs boson in association with a $W$ boson as a test case, we assess the impact of dimension-8 operators within the context of the Standard Model Effective Field Theory. Dimension-8--SM-interference and dimension-6-squared terms appear at the same order in an expansion in $1/\Lambda$, hence dimension-8 effects can be treated as a systematic uncertainty on the new physics inferred from analyses using dimension-6 operators alone. To study the phenomenological consequences of dimension-8 operators, one must first determine the complete set of operators that can contribute to a given process. We accomplish this through a combination of Hilbert series methods, which yield the number of invariants and their field content, and a step-by-step recipe to convert the Hilbert series output into a phenomenologically useful format. The recipe we provide is general and applies to any other process within the dimension $\le 8$ Standard Model Effective Theory. We quantify the effects of dimension-8 by turning on one dimension-6 operator at a time and setting all dimension-8 operator coefficients to the same magnitude. Under this procedure and given the current accuracy on $\sigma(pp \to h\,W^+)$, we find the effect of dimension-8 operators on the inferred new physics scale to be small, $\mathcal O(\text{few}\,\%)$, with some variation depending on the relative signs of the dimension-8 coefficients and on which dimension-6 operator is considered. The impact of the dimension-8 terms grows as $\sigma(pp \to h\,W^+)$ is measured more accurately or (more significantly) in high-mass kinematic regions. We provide a FeynRules implementation of our operator set to be used for further more detailed analyses.Comment: More operator coefficient choices explored, bugs in FeynRules implementation correcte

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

Left-Right Symmetry and the Charged Higgs Bosons at the LHC

The charged Higgs boson sector of the Minimal Manifest Left-Right Symmetric model (MLRSM) is investigated in the context of LHC discovery search for new physics beyond Standard Model. We discuss and summarise the main processes within MLRSM where heavy charged Higgs bosons can be produced at the LHC. We explore the scenarios where the amplified signals due to relatively light charged scalars dominate against heavy neutral $Z_2$ and charged gauge $W_2$ as well as heavy neutral Higgs bosons signals which are dumped due to large vacuum expectation value $v_R$ of the right-handed scalar triplet. In particular, production processes with one and two doubly charged Higgs bosons are considered. We further incorporate the decays of those scalars leading to multi lepton signals at the LHC. Branching ratios for heavy neutrino $N_R$, $W_2$ and $Z_2$ decay into charged Higgs bosons are calculated. These effects are substantial enough and cannot be neglected. The tri- and four-lepton final states for different benchmark points are analysed. Kinematic cuts are chosen in order to strength the leptonic signals and decrease the Standard Model (SM) background. The results are presented using di-lepton invariant mass and lepton-lepton separation distributions for the same sign (SSDL) and opposite sign (OSDL) di-leptons as well as the charge asymmetry are also discussed. We have found that for considered MLRSM processes tri-lepton and four-lepton signals are most important for their detection when compared to the SM background. Both of the signals can be detected at 14 TeV collisions at the LHC with integrated luminosity at the level of $300 fb^{-1}$ with doubly charged Higgs bosons up to approximately 600 GeV. Finally, possible extra contribution of the charged MLRSM scalar particles to the measured Higgs to di-photon ($H_0^0 \to \gamma \gamma$) decay is computed and pointed out.Comment: FCNC analysis is incorporated while fitting the scalar spectrum. Light doubly charged scalars are still compatible with FCNC. Accepted in JHEP. New References and figures are added. The fitted scalar spectrum is given in detail in appendi

NLO electroweak corrections in extended Higgs Sectors with RECOLA2

We present the computer code RECOLA2 along with the first NLO electroweak corrections to Higgs production in vector-boson fusion and updated results for Higgs strahlung in the Two-Higgs-Doublet Model and Higgs-Singlet extension of the Standard Model. A fully automated procedure for the generation of tree-level and one-loop matrix elements in general models, including renormalization, is presented. We discuss the application of the Background-Field Method to the extended models. Numerical results for NLO electroweak cross sections are presented for different renormalization schemes in the Two-Higgs-Doublet Model and the Higgs-Singlet extension of the Standard Model. Finally, we present distributions for the production of a heavy Higgs boson.Comment: 47 pages, 29 figures, pdflatex, version to appear in JHE

THE TOOLS AND MONTE CARLO WORKING GROUP Summary Report from the Les Houches 2009 Workshop on TeV Colliders

This is the summary and introduction to the proceedings contributions for the Les Houches 2009 "Tools and Monte Carlo" working group.Comment: 144 Pages. Workshop site http://wwwlapp.in2p3.fr/conferences/LesHouches/Houches2009/ . Conveners were Butterworth, Maltoni, Moortgat, Richardson, Schumann and Skand

FeynMG:a FeynRules extension for scalar-tensor theories of gravity

The ability to represent perturbative expansions of interacting quantum field theories in terms of simple diagrammatic rules has revolutionized calculations in particle physics (and elsewhere). Moreover, these rules are readily automated, a process that has catalyzed the rise of symbolic algebra packages. However, in the case of extended theories of gravity, such as scalar-tensor theories, it is necessary to precondition the Lagrangian to apply this automation or, at the very least, to take advantage of existing software pipelines. We present a Mathematica code FeynMG, which works in conjunction with the well-known package FeynRules, to do just that: FeynMG takes as inputs the FeynRules model file for a non-gravitational theory and a user-supplied gravitational Lagrangian. FeynMG provides functionality that inserts the minimal gravitational couplings of the degrees of freedom specified in the model file, determines the couplings of the additional tensor and scalar degrees of freedom (the metric and the scalar field from the gravitational sector), and preconditions the resulting Lagrangian so that it can be passed to FeynRules, either directly or by outputting an updated FeynRules model file. The Feynman rules can then be determined and output through FeynRules, using existing universal output formats and interfaces to other analysis packages