9th General Meeting of the LHC EFT Working Group

1 Dec 2025, 09:00 → 3 Dec 2025, 12:40 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

General meeting of the LHC EFT Working Group 

The meeting will start at 13:55 on Dec 1st and end at 12:40 on Dec 3th.
To subscribe to the WG mailing list, please click here.

Joint-session with the LHC Higgs WG

There will be a joint session with LHC Higgs WG on Wednesday morning, please access the LHC Higgs WG Meeting Indico (and associated Zoom room) for this.

CERN access

During registration you have the possibility to request an access card. We will then grant access which will generate an Access Card which you should print out and bring with you to show to the staff at the front gate.

If you are unable to print your pass, you can use the provided access code on a small machine at the front gate to print your pass on the day.

CERN accommodation

A number of rooms at the CERN hostel have been pre-booked for the meeting. For information on how to access the room booking, please see the Accommodation section.  If you prefer to stay outside CERN a list of suggestions can be found on the same page.

 

Monday 1 December

13:55 → 15:45 Experimental summaries

Convener: Carmen Diez Pardos (Universitaet Siegen (DE))

13:55 Welcome

14:00 LHCb summary

Speaker: Bo Fang (University of Chinese Academy of Sciences (CN))

14:35 ATLAS SMP+TOP summary

Speaker: Leo Boudet (Centre National de la Recherche Scientifique (FR))

15:10 CMS SMP+TOP summary

Speaker: Saptaparna Bhattacharya (Southern Methodist University (US))

15:45 → 16:15 Coffee

16:15 → 18:00 EFT formalism

Convener: Ken Mimasu (University of Southampton)

16:15 Renormalization of general Effective Field Theories

We present the latest results in the renormalization of general Effective Field Theories. After describing the most general local, Lorentz-invariant, effective field theory of scalars, fermions and gauge bosons (up to mass dimension 6), we obtain a Green’s and a physical basis, the reduction of the former to the latter, and the renormalization group equations at one-loop order.

Speaker: Pablo Olgoso Ruiz (University of Padova)

16:40 Positivity in EFT Renormalization

Positivity bounds constrain the parameter space of effective field theories (EFTs) at low energies, relying only on basic principles of the underlying high-energy dynamics. To complement experimental studies with these bounds, it is important to understand their robustness under loop corrections and across different energy scales. In this talk, I will present a general result that determines the sign of the one-loop renormalization group flow for a class of EFT parameters. This criterion clarifies when renormalization effects preserve positivity bounds, or when they may lead to apparent violations, offering insight into the interplay between positivity bounds and renormalization.

Based on ArXiv: 2505.02910

Speaker: Jasper Roosmale Nepveu (National Taiwan University)

17:05 Emergent Curvature from Flat-Space QFTs: A Computational Search for Gravity

General Relativity (GR) continues to provide an exceptionally accurate description of gravitational phenomena at macroscopic scales. Yet its reconciliation with quantum mechanics remains elusive [1]. A compelling strategy treats GR as a low-energy Effective Field Theory (EFT), seeking its high-energy extension.

Progress in this direction would require matching candidate UV theories to the EFT of gravity by integrating out heavy degrees of freedom. However, such a matching procedure is notoriously difficult, typically done on a case-by-case basis [2], and often considered infeasible for large models.

In this work, we present the first computer-assisted framework for EFT matching of theories involving spin-2 particles. By extending modern EFT toolkits to incorporate gravitational degrees of freedom, we enable systematic exploration of high-energy extensions of gravity within a quantum field theory setting. As a proof-of-concept, we scan a broad class of models featuring a hidden heavy scalar coupled to a spin-2 field. We compute the one-loop contributions to the low-energy gravitational EFT, finding that they can create the leading-order self-interactions of GR, responsible for inducing curvature.

The extended toolkits employ competing methods for matching. The first – Matchmakereft [3] – uses a diagrammatic method, while the second – Matchete [4] – uses a functional method. The results of the two methods are compared and are found to be identical, with each method offering different insights regarding the origin of the contributions to each term in the EFT.

Our computational approach reveals new patterns in quantum corrections to GR and identifies several viable UV scenarios whose low-energy limits reproduce GR-like dynamics. These results suggest that the geometric structure of GR may arise from a fundamentally flat-space quantum field theory (QFT) involving interactions among several fields. More broadly, our approach demonstrates how automated computational tools can overcome long-standing barriers in probing the quantum landscape beyond GR.

References

[1]

S. Carlip, “Quantum Gravity: a Progress Report,” Rep. Prog. Phys., vol. 64, no. 8, pp. 885–942, Aug. 2001, doi: 10.1088/0034-4885/64/8/301.

[2]

G. Isidori, F. Wilsch, and D. Wyler, “The Standard Model effective field theory at work,” Rev. Mod. Phys., vol. 96, no. 1, p. 015006, Mar. 2024, doi: 10.1103/RevModPhys.96.015006.

[3]

A. Carmona, A. Lazopoulos, P. Olgoso, and J. Santiago, “Matchmakereft: automated tree-level and one-loop matching,” Dec. 20, 2021, arXiv: arXiv:2112.10787. doi: 10.48550/arXiv.2112.10787.

[4]

J. Fuentes-Martín, M. König, J. Pagès, A. E. Thomsen, and F. Wilsch, “A Proof of Concept for Matchete: An Automated Tool for Matching Effective Theories,” Eur. Phys. J. C, vol. 83, no. 7, p. 662, Jul. 2023, doi: 10.1140/epjc/s10052-023-11726-1.

Speakers: Alon Lifshits, Gil Arad

17:30 EFT meets Conformal Field Theory

In EFT, the computation of anomalous dimensions of composite operators in $4-\epsilon$ dimensions is central. Precisely this computation has a completely different application, namely to the $\epsilon$-expansion of conformal field theories (CFTs), where instead of taking $\epsilon\to0$ one is interested in results for 3d theories at $\epsilon=1$. Anomalous dimensions of composite operators correspond to directly observable quantities in these 3d CFTs, and multiloop results can be compared with non-perturbative methods such as MC simulations and the conformal bootstrap. I will explain this new synergy between techniques developed for EFT and applications to CFT, focussing on the use of multiloop anomalous dimensions within the conformal bootstrap.

Based on 2507.12518 and work in progress.

Speaker: Johan Henriksson (CERN)

Tuesday 2 December

09:00 → 10:40 HEFT & two-loop SMEFT

Convener: Alejo Nahuel Rossia (University of Padua and INFN Sezione di Padova)

09:00 The Art of Counting: where to cut-off SMEFT and HEFT in Higgs Pair Production

In searches for beyond the Standard Model (BSM) Physics, bottom-up effective field theories (EFTs) such as the Standard Model EFT (SMEFT) and Higgs EFT (HEFT) have become crucial theoretical tools. Besides specifying their particle content and the respective symmetries on which the higher-dimensional operators are built, the choice of a power counting in a small parameter is the third necessary ingredient. The latter dictates how the operators are organized and enables us to perform a truncation on Lagrangian and amplitude level, which is essential when computing physical observables. In this work, we discuss the power counting approaches to SMEFT and HEFT and study their application in the context of the Higgs pair production process.

Speakers: Konstantin Schmid, Konstantin Schmid (University and INFN Padova)

09:25 (Remote) The Potential of HEFT and the scale of New Physics

We consider a scalar theory with an $(N_{GB} + 1)$-plet undergoing spontaneous symmetry breaking $SO(N_{GB} + 1) \to SO(N_{GB})$, with interactions governed by a general potential $V$. Using geometric methods, we compute the high-energy leading term of all scattering amplitudes involving arbitrary numbers of Higgs-like and Goldstone bosons. This infinite set of amplitudes allows us to derive an explicit unitarity bound, expressed as an infinite Taylor series in the center-of-mass energy. We apply these results to the Standard Model scalar sector via the equivalence theorem in the limit of small curvature, providing insight into the distinction between HEFT and SMEFT. Through the study of representative potentials—most notably the Dilaton—we explore, both analytically and numerically, the connection between field-space singularities and the cutoff scale, shedding light on the avenues, backdoors, and obstacles one may encounter in attempting to decouple new physics.

Speaker: Susobhan Chattopadhyay (Tata Institute of Fundamental Research (TIFR), Mumbai)

09:50 Two-loop running in the SMEFT at dimension-six

The Standard Model Effective Field Theory (SMEFT) provides a powerful framework for parameterizing potential new physics in a model-independent way. To analyze data from experiments across different energy scales and to reliably extrapolate ultraviolet (UV) physics effects, it is crucial to know the renormalization group evolution (RGE) of SMEFT operators.

In this talk, I will present the complete set of two-loop SMEFT $\beta$-functions up to dimension-six in the baryon number-conserving sector, calculated with an anti-commuting $\gamma_{5}$, and discuss the methods used to compute them as well as the challenges encountered in this process. In particular, $\gamma_5$-odd traces involving six or more ordinary $\gamma$-matrices require special care, since cyclicity is lost. This subtlety can lead to potentially inconsistent results, which I will discuss in detail.

Our results provide the first complete two-loop SMEFT running up to dimension-six in the baryon number-conserving sector, representing a key ingredient for next-to-leading order (NLO) SMEFT analyses. They enable precision studies of new physics across energy scales and thus significantly extend the SMEFT toolkit available for phenomenological applications.

Speaker: Lukas Born

10:15 Two loop running effects in the Higgs gluon coupling

In this work we extend the existing literature on two-loop renormalisation group equations (RGEs) for the dimension-six Standard Model Effective Field Theory operator involving two gluons and two Higgs bosons. This operator generates an effective coupling between the Higgs boson and gluons. In particular, we extend and complete the contributions that enter the RGEs proportionally to $g_s^2 y^2_{t,b}$.

We then examine the phenomenological impact of including two-loop running effects in Higgs physics fits at the LHC. To better probe this effect, we perform two kinds of fit. Firstly, using a bottom-up approach, we perform fits in terms of the Wilson Coefficients of the included operators to test how their bounds are modified when the running effects are included. Secondly, we specify UV models involving pairs of Vector-like Quarks (VLQs) coupled to the third-generation Standard Model quarks and we perform the Higgs Physics fits in terms of the VLQ couplings.

Speaker: Barbara Anna Erdelyi (Università degli Studi di Padova and INFN Sezione di Padova)

10:40 → 11:10 Coffee

11:10 → 12:25 Fits & two-loop LEFT

Convener: Jonathon Mark Langford (Imperial College (GB))

11:10 (Remote) Updates from the SMEFiT collaboration

We present projections for the New Physics reach of future high-energy colliders in the SMEFiT framework. Our analysis focuses on near-term electron–positron colliders (FCC-ee, LEP3, CEPC, LCF), complemented in some cases by projections for the FCC-hh, LHeC, and MuCol. Results are presented in terms of coupling modifiers (kappa-formalism), effective couplings, and global SMEFT fits, the latter including RGE effects and NLO corrections to EFT cross sections. We also quantify the sensitivity of future colliders to several benchmark scenarios such as composite Higgs models, Two-Higgs-Doublet models and single particle extensions via UV matching.

Speaker: Jaco ter Hoeve (University of Edinburgh)

11:35 A fast and differentiable SMEFT likelihood

The Standard Model Effective Field Theory (SMEFT) has proven to be a valuable framework for studying a broad class of models beyond the SM containing heavy degrees of freedom. The phenomenology of SMEFT can be developed systematically, incorporating essential effects such as Renormalization Group (RG) evolution and matching onto subsequent low-energy Weak Effective Field Theories (WET), enabling predictions for a wide range of observables. A likelihood function for the SMEFT that compares theory predictions to experimental data can be employed to identify patterns of deviation from SM predictions, but also to study the phenomenology of any specific model that can be matched onto SMEFT. In this talk, we present a new major version of the Python package smelli - a SMEFT likelihood, which incorporates a large number of observables, ranging from quark and lepton flavor physics, to Higgs physics, electroweak precision observables, beta decays, and high-mass Drell-Yan tails. It provides a fast and analytically differentiable global flavorful likelihood function for the SMEFT, WET, and for new physics models, with no assumptions on the flavor structure.

Speaker: Aleks Smolkovic (Jozef Stefan Institute)

12:00 Two-loop ADMs in the LEFT and related issues

We derive the complete set of two-loop anomalous dimensions describing the mixing of four-fermion operators in the Low Energy Effective Field Theory (LEFT). The calculation is performed in Naive Dimensional Regularization with anticommuting $\gamma_5$ (the NDR scheme), and the results are given in the "JMS basis" of dimension-six operators. The derivation relies on known results for UV poles in two-loop diagrams in QCD, which are then used to derive the two-loop Anomalous Dimension Matrix (ADM) for the full set of four-fermion operators including O($\alpha_s^2$), O($\alpha_s\alpha$) and O($\alpha^2$) corrections. The method employed is an extension of a common approach to deal with traces containing $\gamma_5$ in NDR. Our results have been implemented in the public code DsixTools. We also discuss and provide the results in the LEFT with 5, 4 and 3 active quark flavors.

Speaker: Marko Pesut (University of Zürich)

14:30 → 15:45 Tools & amplitudes

Convener: Anke Biekoetter (KIT Karlsruhe)

14:30 Multi-Higgs Amplitudes Bootstrapped: Dissecting SMEFT and HEFT

The precise measurement of the Higgs boson properties requires a robust framework to parametrize possible deviations from Standard Model (SM) predictions in the most model-independent way possible. The Effective Field Theory (EFT) framework has become the most widely used since it offers a broad scope and a consistent path to increase the precision of the computations. Two prominent EFTs are the Standard Model Effective Field Theory (SMEFT) and the Higgs Effective Field Theory (HEFT). While similar in many aspects, their phenomenological differences are nowhere more pronounced than in multi-Higgs production. To precisely chart the separation between both EFTs, we study gluon-fusion double and triple Higgs production using bootstrapped on-shell amplitudes. This allows us to get the kinematic dependence of the gauge-invariant amplitude without field-redefinition ambiguities. As part of our study, we develop a technique that allows to build tree-level five-point on-shell amplitudes from lower-point on-shell amplitudes and bootstrapped contact terms. We then match the bootstrapped on-shell scattering amplitudes to the amplitudes computed in SMEFT (up to order $1/\Lambda^4$) and HEFT (at NNLO) and analyze the EFT order at which each kinematic structure appears. We also show how certain structures in $gg\to hhh$ appear only at dimension-12 in SMEFT or N$^3$LO in HEFT.

Speakers: Alejo Nahuel Rossia (University of Padua and INFN Sezione di Padova), Michal Jakub Ryczkowski (Università di Padova and INFN, Sezione di Padova)

14:55 Sherpa implementation of h decaying to b b at NLO (QCD+EW)

In the SMEFT framework, we calculated QCD and EW corrections at NLO to the Higgs decay to a $b \bar b $ pair. To accurately simulate this process for the LHC, we implemented the matrix element into Sherpa. This allows us to study how the parton shower affects those hard matrix elements.

Speaker: Mr shakeel ur rahaman

15:20 Automated operator basis changes for general Effective Field Theories

In this talk, we shall discuss the automation of operator basis changes for effective field theories with arbitrary gauge symmetries and matter content. In particular, we shall describe the workflow, where we start with performing basis changes at the tree level using IBP, completeness relations, and Fierz identities, with the eventual aim of performing completely general basis changes at the one-loop level.

Speaker: Sudeepan Datta (Paul Scherrer Institute (CH))

15:45 → 16:15 Coffee

16:15 → 17:15 Truncation

Convener: David William Sutherland (University of Glasgow (GB))

16:15 Discussion on truncation

This will start with a summary of the problem of truncation and EFT validity, and a summary of proposed solutions and the current treatment in experimental searches. The aim is to stimulate discussion on what the EFT WG can usefully do next on this issue.

Speakers: David William Sutherland (University of Glasgow (GB)), William Shepherd

18:00 → 19:00 Drinks (joint with LHC Higgs WG)

Wednesday 3 December

09:00 → 12:40 Joint session with LHC Higgs WG

See Higgs WG indico: https://indico.cern.ch/event/1597152/timetable/