In this paper, we explore the impact of extra radiation on predictions of $pp \to t\bar{t}X, X = h/W^{\pm}/Z$ processes within the dimension-6 SMEFT framework. While full next-to-leading order calculations are of course preferred, they are not always practical, and so it is useful to be able to capture the impacts of extra radiation using leading-order matrix elements matched to the parton shower. While a matched leading-order calculation for $t\bar{t}X$ is not expected to reproduce the next-to-leading order inclusive cross section precisely, we show that it does capture the relative impact of the EFT effects by considering the ratio of matched SMEFT inclusive cross sections to Standard Model values, $σ_{\rm SMEFT}(t\bar{t}Xj)/σ_{\rm SM}(t\bar{t}Xj) \equiv μ$. Furthermore, we compare leading order calculations with and without extra radiation and find several cases, such as the effect of the operator $(φ^{\dagger}i\!\overleftrightarrow{D}_{\!μ}φ) (\bar{t}γ^μt)$ on $t\bar{t}h$ and $t\bar{t}W$, for which the relative cross section prediction increases by more than $10\%$ -- significantly larger than the uncertainty derived by varying the input scales in the calculation, including the additional scales required for matching. Being leading order at heart, matching has the benefit that it can be applied to all operators and processes relevant to $pp \to t\bar{t}X, X = h/W^{\pm}/Z +$ jet, is computationally fast and not susceptible to negative weights. Therefore, it is a useful approach in $t\bar{t}X+$ jet studies where complete next-to-leading order results are currently unavailable or unwieldy.
Electroweak interactions assign a central role to the gauge group $SU(2)_L \times U(1)_Y$, which is either realized linearly (SMEFT) or nonlinearly (e.g., HEFT) in the effective theory obtained when new physics above the electroweak scale is integrated out. Although the discovery of the Higgs boson has made SMEFT the default assumption, nonlinear realization remains possible. The two can be distinguished through their predictions for the size of certain low-energy dimension-6 four-fermion operators: for these, HEFT predicts $O(1)$ couplings, while in SMEFT they are suppressed by a factor $v^2/…
The modern viewpoint is that the Standard Model is the leading part of an effective field theory that obeys the symmetry $SU(3)_C \times SU(2)_L \times U(1)_Y$. Since the discovery of the Higgs boson, it is generally assumed that this symmetry is realized linearly (SMEFT), but a nonlinear realization (e.g., HEFT) is still possible. The two differ in their predictions for the size of certain low-energy dimension-6 four-fermion operators: for these, HEFT allows $O(1)$ couplings, while in SMEFT they are suppressed by a factor $v^2/Λ_{\rm NP}^2$, where $v$ is the Higgs vev. In this talk, I argue t…
At NLO in QCD, the $tWZ$ production process interferes with resonant LO processes, $t\bar{t}Z$ and $t\bar{t}$, and a method to meaningfully disentangle these overlapping processes needs to be employed. I discuss the diagram-removal procedure needed to obtain an operative definition of $tWZ$ at NLO accuracy. I also show the predictions we obtain in the context of the Standard Model and in the Standard Model Effective Field Theory including the relevant dimension-six SMEFT operators.
We calculate $pp \to \ell^{+}ν, \ell^-\bar ν$ to ${\cal{O}}(1/Λ^4)$ within the Standard Model Effective Field Theory (SMEFT) framework. In particular, we calculate the four-fermion contribution from dimension six and eight operators, which dominates at large center of mass energy. We explore the relative size of the $\mathcal O(1/Λ^4)$ and $\mathcal O(1/Λ^2)$ results for various kinematic regimes and assumptions about the Wilson coefficients. Results for Drell-Yan production $pp \to \ell^+\ell^-$ at ${\cal{O}}(1/Λ^4)$ are also provided. Additionally, we develop the form for four fermion contac…
More accurate $σ(\mathcal{G} \,\mathcal{G}\rightarrow h)$, $Γ(h \rightarrow \mathcal{G} \,\mathcal{G}, \mathcal{A} \mathcal{A}, \barΨ Ψ)$ and Higgs width results via the geoSMEFT
One-loop corrections to $h\to b\bar b$ and $h\to τ\bar τ$ decays in the Standard Model Dimension-6 EFT: four-fermion operators and the large-$m_t$ limit
We study the processes $pp \to t\bar{t}Z$ and $pp \to tZj$ in the framework of Standard Model Effective Field Theory (SMEFT), employing conventional cut-and-count as well as machine learning techniques to take advantage of kinematic information in complex final states involving multiple leptons and $b$ jets. We explore the projected sensitivity for two SMEFT operators, $\mathcal{O}_{tZ}$ and $\mathcal{O}_{tW}$, that induce electroweak dipole moment interactions for top quarks, through direct searches in these electroweak top production processes at the HL-LHC. New physics modifications to domi…
We present the three-body decay of the Higgs boson into two leptons and a photon to dimension-eight in the Standard Model Effective Field Theory (SMEFT). In order to obtain this result we interfere the full one-loop Standard Model result with the tree-level result in the SMEFT. This is the first calculation of the partial width of the Higgs boson into two leptons and a photon in the SMEFT to incorporate the full one-loop dependence for the Standard Model as well as the full tree level dimension-eight dependence in the SMEFT. We find that this channel can aid in distinguishing strongly interact…
We perform global fits within Standard Model Effective Field Theory (SMEFT) combining top-quark pair production processes and decay with $b\rightarrow s$ flavor changing neutral current transitions and $Z \to b \bar b$ in three stages: using existing data from the LHC and $B$-factories, using projections for the HL-LHC and Belle II, and studying the additional new physics impact from a future lepton collider. The latter is ideally suited to directly probe $\ell^+\ell^-\rightarrow t\bar t$ transitions. We observe powerful synergies in combining both top and beauty observables as flat directions…
We explore the impact of Renormalisation Group (RG) effects in the Standard Model Effective Field Theory (SMEFT) interpretations of LHC measurements. We implement the RG running and mixing for the Wilson coefficients as obtained from the one-loop anomalous dimension matrix in the SMEFT into a Monte Carlo generator. This allows to consistently predict and combine in global fits collider observables characterised by different scales. As a showcase, we examine the impact of RG running in the strong coupling on the SMEFT predictions for $t \bar t$ production cross sections and differential distrib…
We present the first analysis of top spin polarizations, $t \bar t$ spin correlations, and $t \bar t$ spin entanglement at the LHC in the context of the Standard Model Effective Field Theory, that goes beyond Leading Order QCD accuracy. The complete set of independent dimension-6 operators entering $t \bar t$ production is identified, and their effects on all top spin observables are extracted at linear and quadratic order in $c/Λ^2$. By comparing results at LO and NLO, we note that the inclusion of higher orders, while not dramatically changing the picture, often amounts to notable numerical …
We study single top quark production in association with a $WZ$ pair at the LHC in the context of the Standard Model (SM) and the Standard Model Effective Field Theory (SMEFT). A significant advantage of $tWZ$ compared to other EW top production processes is its sensitivity to unitarity-violating behaviour induced in its $2\to2$ sub-amplitudes through modified EW interactions. At NLO in QCD, $tWZ$ interferes with $t\bar{t}Z$ and $t\bar{t}$ and a method to meaningfully separate it from these overlapping processes needs to be employed. In order to define $tWZ$ production for total rates and diff…
The use of the SMEFT Lagrangian to quantify possible Beyond the Standard Model (BSM) effects is standard in LHC and future collider studies. One of the usual assumptions is to truncate the expansion with the dimension-$6$ operators. The numerical impact of the next terms in the series, the dimension-$8$ operators, is unknown in general. We consider a specific BSM model containing a charge-${2 3}$ heavy vector-like quark and compute the operators generated at dimension-$8$. The numerical effects of these operators are studied for the $t\bar{t}h$ process, where they contribute at tree level and …
We consider associated $Zh$ production with $Z \to \ell^+ \ell^-$ and $h \to b \bar b$ decays in hadronic collisions. In the framework of the Standard Model effective field theory (SMEFT) we calculate the QCD corrections to this process and achieve next-to-next-to-leading order plus parton shower (NNLO$+$PS) accuracy using the MiNNLO$_{\rm PS}$ method. This precision is obtained for a subset of six SMEFT operators, including the corrections from effective Yukawa- and chromomagnetic dipole-type interactions. Missing higher-order QCD effects associated with the considered dimension-six operators…
We present a model-independent anatomy of the $ΔF=2$ transitions $K^0-\bar K^0$, $B_{s,d}-\bar B_{s,d}$ and $D^0-\bar D^0$ in the context of the Standard Model Effective Field Theory (SMEFT). We present two master formulae for the mixing amplitude $\big[M_{12} \big]_\text{BSM}$. One in terms of the Wilson coefficients (WCs) of the Low-Energy Effective Theory (LEFT) operators evaluated at the electroweak scale $μ_\text{ew}$ and one in terms of the WCs of the SMEFT operators evaluated at the BSM scale $Λ$. The coefficients $P_a^{ij}$ entering these formulae contain all the information below the …
Recently the RBC-UKQCD lattice collaboration presented new results for the hadronic matrix elements relevant for the ratio $\varepsilon'/\varepsilon$ in the Standard Model (SM). With the present knowledge of the Wilson coefficients and isospin breaking effects there is still much room for new physics (NP) contributions to $\varepsilon'/\varepsilon$ which could both enhance or suppress this ratio to agree with the data. The new SM value for the $K^0-\bar K^0$ mass difference $ΔM_K$ from RBC-UKQCD is on the other hand by $2σ$ above the data hinting for NP required to suppress $ΔM_K$. Simultaneou…
SMEFT everywhere: a NLO study of $\boldsymbol{pp \to t\bar{t}H}$ with decaying tops
Institute of Nuclear and Particle Physics, NCSR Demokritos（核粒子物理研究所，德谟克利特国家研究中心）；Institute for Theoretical Particle Physics and Cosmology, RWTH Aachen University（亚琛工业大学理论粒子物理与宇宙学研究所）
In this paper we systematically consider the baryon ($B$) and lepton ($L$) number violating dinucleon to dilepton decays ($pp\to \ell^+\ell^{\prime+}, pn\to \ell^+\barν^\prime, nn\to \barν\barν^\prime$) with $ΔB=ΔL=-2$ in the framework of effective field theory. We start by constructing a basis of dimension-12 (dim-12) operators mediating such processes in the low energy effective field theory (LEFT) below the electroweak scale. Then we consider their standard model effective field theory (SMEFT) completions upwards and their chiral realizations in baryon chiral perturbation theory (B$χ$PT) do…
Impact of dim-6 $ν$SMEFT operators on low-scale leptogenesis
KEK Theory Center, IPNS, KEK（高能加速器研究机构理论中心）；Theoretical Division, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室理论部）；Johannes Gutenberg-Universität Mainz（美因茨约翰内斯古腾堡大学）
