We investigate the impact of momentum-dependent particle widths and propagators on gauge and Higgs bosons and the top quark within the Standard Model (SM) and its effective field theory (SMEFT) extensions near thresholds. By incorporating self-energy corrections via Dyson resummation, we quantify deviations from the fixed-width approximation and assess their implications for collider observables. While effects on the Higgs boson are negligible and the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>W</mi></math> boson shows percent-level deviations in reconstructed transverse mass distributions, the top quark exhibits significant sensitivity near its mass threshold. Future lepton colliders, e.g., electron-positron machines or muon colliders, can offer sensitivity to these effects, enabling constraints on SMEFT Wilson coefficients. We perform a representative case study for the precision frontier available with a staged future muon collider. Our results highlight that momentum dependencies can provide additional sensitivity at precision-era experiments, enhancing the potential for discovering new physics there.

United Kingdom

Christoph Englert

Wrishik Naskar

Michael Spannowsky

Impact of new physics on momentum-dependent particle widths and propagators

Motivated by recently observed anomalies in the flavour sector, we analyse the potential of measurements of top quarks at the Large Hadron Collider (LHC) to provide complementary constraints on interactions that shape low-energy precision investigations in the sector. The measurement of top quark properties, such as the top width and the abundant top pair production channels, are already reaching the percent level at this relatively early stage of the LHC phenomenology program. A focused analysis of four-fermion interactions, employing effective field theory without flavour structure assumptions and incorporating renormalization group evolution effects, bridges meson scale phenomena with key top quark measurements. We demonstrate that the LHC is increasingly competitive with, and complementary to, flavour physics constraints. Our results, which include a first comprehensive analysis of non-leptonic decays in this context, suggest that the LHC’s top physics program could serve as a valuable, complementary tool in the search for physics beyond the Standard Model within the flavour sector.

Oliver Atkinson

Matthew Kirk

Germany

France

Gilberto Tetlalmatzi-Xolocotzi

Collider-flavour complementarity from the bottom to the top

Multi-Higgs boson interactions with massive gauge bosons are known to be tell-tale probes of the vacuum manifold of electroweak symmetry breaking. Phenomenologically, a precise determination of these parameters is hampered through increasingly rare processes at the presently available energy frontier provided by the Large Hadron Collider. Contact interactions of three Higgs bosons with the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>W</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> bosons seem currently well out of experimental reach due to an irrelevant standard model (SM) production cross section. From a theoretical perspective, in perturbative extensions of the SM such interactions are suppressed by weak loops and further diluted in a priori sensitive processes like weak boson fusion (WBF) when they admit a dimension-six Standard Model effective field theory description. In this work, we identify scenarios that can indeed lead to large, and perhaps even observable modifications of WBF triple Higgs production most directly parametrized by Higgs effective field theory. We critically analyse these enhancements at the LHC and future colliders from the perspective of unitarity and demonstrate the radiative stability of such analyses under QCD corrections at hadron colliders. Taking into account the restrictions from unitarity, we finally study the expected sensitivity to the electroweak triple Higgs production within HEFT, considering <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>H</mi><mi>V</mi><mi>V</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>H</mi><mi>H</mi><mi>V</mi><mi>V</mi></math> effective couplings, at both future hadron and lepton colliders. Particularly, we present numerical predictions for LHC, FCC, CLIC, and muon colliders.

 Anisha

Spain

Daniel Domenech

Maria J. Herrero

Argentina

Roberto A. Morales

Higgs effective field theory’s appraisal of triple versus double Higgs weak boson fusion

Effective field theory-based searches for new physics at colliders are relatively insensitive to interactions involving only right-handed down-type quarks. These interactions can hide amongst jet backgrounds at the LHC, and their indirect effects in electroweak and Higgs processes are small. Identifying scenarios in which these interactions dominate, we can naturally pick out just two tree-level mediators, both scalar diquarks. Over the full parameter space of these states, we analyse exotics searches at current and future hadron colliders, Higgs signal strength constraints, and indirect constraints from flavour physics, finding genuine complementarity between the data sets. In particular, while flavour constraints can exclude diquarks in the hundreds of TeV mass range, these can be evaded once a flavour structure is imposed on the couplings, as we illustrate by embedding the diquarks within a composite Higgs model. In combination, however, we show that flavour and collider constraints exclude down-type diquarks to multi-TeV scales, thus narrowing the remaining hiding places for new interactions amongst LHC data.

Switzerland

Christiane Mayer

Sophie Renner

Doubling down on down-type diquarks

We investigate the impact of preheating on baryogenesis in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>R</mi><mn>2</mn></msup></math>-Higgs inflation. In this scenario, the inclusion of a dimension-six operator <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mi>R</mi><mo>/</mo><msup><mi mathvariant="normal">Λ</mi><mn>2</mn></msup><mo stretchy="false">)</mo></mrow><msub><mi>B</mi><mrow><mi>μ</mi><mi>ν</mi></mrow></msub><msup><mover accent="true"><mi>B</mi><mo stretchy="false">˜</mo></mover><mrow><mi>μ</mi><mi>ν</mi></mrow></msup></math> abundantly generates helical hypermagnetic fields during inflation, leading to a baryon asymmetric Universe at the electroweak crossover. Focusing on the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>R</mi><mn>2</mn></msup></math>-like regime, we first derive the relevant dynamics of preheating using a doubly covariant formalism. We find that preheating can happen for the Higgs, transverse gauge, and Goldstone bosons, however, it is dependent on the value of the nonminimal coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ξ</mi><mi>H</mi></msub></math> between the Standard Model Higgs field and the Ricci scalar. We identify the preheating temperature to determine the appropriate scale <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi></math> for driving baryogenesis, which is around <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">Λ</mi><mo>∼</mo><mn>2.2</mn><mo stretchy="false">(</mo><mn>2.6</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup><msub><mrow><mi>M</mi></mrow><mrow><mi mathvariant="normal">P</mi></mrow></msub></mrow></math> for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ξ</mi><mi>H</mi></msub><mo>∼</mo><mn>1</mn><mo stretchy="false">(</mo><mn>10</mn><mo stretchy="false">)</mo></math>. Our results represent the most accurate estimation of the scale of gravity induced baryogenesis in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>R</mi><mn>2</mn></msup></math>-Higgs inflation to date. Areas for further improvement are identified.

Yann Cado

India

Tanmoy Modak

Mariano Quirós

Implication of preheating on gravity assisted baryogenesis in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>R</mi><mn>2</mn></msup></math>-Higgs inflation

We consider a class of singlet scalar extensions of the Standard Model of particle physics in which the scalar couples only to off-shell states. As a result, low-order tree-level processes involving the singlet scalar vanish, providing a unique phenomenology that may allow to evade existing constraints on new singlet scalar fields. We describe search strategies for such states at the Large Hadron Collider and identify the parameter space that can be explored in the future.

Andrei Lazanu

Peter Millington

Scalar radiation zeros at the LHC

A critical element of the LHC physics program is the search for an additional source of <math><mi>C</mi><mi>P</mi></math> violation. This is largely unexplored in the context of nonlinear Higgs physics, which is naturally described in Higgs effective field theory (HEFT). Relevant new higher-dimensional operators modify the production rate and branching ratios of the Higgs boson, decorrelating different Higgs multiplicities. In this work, we consider single Higgs and Higgs pair production via weak boson fusion from the perspective of gauge-Higgs <math><mi>C</mi><mi>P</mi></math> violation through the lens of Higgs nonlinearity. This generalizes existing rate-based searches and analyses by the ATLAS and CMS experiments. Particular focus is given to the phenomenological differences in the expected beyond Standard Model (BSM) sensitivity pattern when comparing HEFT constraints with Standard Model effective field theory (SMEFT) limits.

United States

Akanksha Bhardwaj

Dorival Gonçalves

Alberto Navarro

Nonlinear gauge-Higgs <math><mi>C</mi><mi>P</mi></math> violation

The production of multiple Higgs bosons at the LHC and beyond is a strong test of the mechanism of electroweak symmetry breaking. Taking inspiration from recent experimental efforts to move toward limits on triple-Higgs production at the Large Hadron Collider, we consider generic bosonic deviations of <math><mi>H</mi><mi>H</mi></math> and <math><mi>H</mi><mi>H</mi><mi>H</mi></math> production from the Standard Model in the guise of Higgs effective field theory (HEFT). Including one-loop radiative corrections within the HEFT and going up to <math><mi>O</mi><mo>(</mo><msup><mi>p</mi><mn>4</mn></msup><mo>)</mo></math> in the momentum expansion, we provide a detailed motivation of the parameter range that the LHC (and future hadron colliders) can explore, through accessing nonstandard coupling modifications and momentum dependencies that probe Higgs boson nonlinearities. In particular, we find that radiative corrections can enhance the sensitivity to Higgs self-coupling modifiers and HEFT-specific momentum dependencies can vastly increase triple-Higgs production, thus providing further motivation to consider these processes during the LHC’s high-luminosity phase.

Bosonic multi-Higgs correlations beyond leading order

The production of three Higgs bosons could be a stretch goal for the LHC and a strategic case for future colliders. In this work, we analyse the phenomenological prospects of (neutral) triple Higgs compared to di-Higgs boson production, for a range of Higgs-sector extensions from a strong first-order electroweak phase transition perspective. In parallel, we include constraints from existing exotics and Higgs boson measurements that further limit the parameter space of such models. Resonance contributions offer large modifications in particular for triple Higgs production, albeit starting from a small SM expectation. With enhancements of order 40 over the SM, however, experimental efforts to obtain limits at the HL-LHC are well motivated and well placed. This is further highlighted by the potential of these processes to inform the investigation of the thermal history of our Universe.

Lisa Biermann

Christoph Borschensky

Margarete Mühlleitner

Double and triple Higgs boson production to probe the electroweak phase transition

The juxtaposition of the precision of lepton flavor measurements and the limited energy range of the Large Hadron Collider (LHC) to discover dynamical degrees of freedom linked to the generation of the observed lepton mass patterns naively suggests only a limited relevance of the LHC’s high luminosity phase. This, potentially, extends to future colliders. Using the concrete example of the type-II seesaw model and its effective field theory extension, we show that blind directions create a rich phenomenological interplay of muon precision measurements and electroweak resonance searches at present and future colliders, with testable implications for the HL-LHC phase.

Upalaparna Banerjee

Resurrecting the LHC discovery potential in the extended type-II seesaw model