In this work, we review the history and current role of global fits in the search for physics beyond the Standard Model (BSM), including precision tests of the Standard Model (SM). Although BSM global fits were initially focused on minimal supersymmetric models, we describe how fits have evolved in response to new data from the Large Hadron Collider (LHC) and elsewhere, expanding to encompass a broad spectrum of BSM scenarios including non-minimal supersymmetry, axion-like particles, extended Higgs sectors, dark matter models, and effective field theories such as SMEFT. We discuss how the role of global fits has shifted from forecasting possible signals of new physics at the LHC to understanding the impact of null results from LHC run-I and II and the discovery of the Higgs boson, and how interest has shifted from global fits for parameter estimation to comprehensive model comparison. We close by discussing potential trends and future applications, emphasizing the potential for machine learning and artificial intelligence to enhance the efficiency of sampling algorithms and comparison between theory and experiment, as well as collaboration and software development.

The 2HDM+S is a singlet extension of the Two-Higgs-Doublet Model (2HDM), which offers rich collider phenomenology. In this paper, we parametrize the 2HDM+S with the Higgs masses and mixing angles, which provide a model-independent framework to study the collider signature. Under five benchmark scenarios, we obtain the 95% C.L. exclusion regions in the Type-II 2HDM+S parameter space by incorporating the SM-like 125 GeV Higgs precision measurements, beyond the Standard Model Higgs direct searches, Z-pole precision measurements and B-physics observables. We present the results in the Higgs boson masses vs , Higgs boson masses vs mixing angles, vs mixing angles and doublet Higgs boson masses vs singlet Higgs boson mass parameter space. We explore the complementarity between direct and indirect Higgs searches, as well as conventional Higgs search channels and exotic Higgs search channels. Compared to the 2HDM scenarios, we find that exotic channels such as A/H → Z h_S/ZA_S can probe large part of the parameter spaces, especially for moderate 1<<7 region where the conventional channels in the 2HDM cannot contribute much.

Recently, the study of long-lived particles (LLPs) has attracted increasing attention. In this work, we analyze the full parameter space of the Type-I Two-Higgs-Doublet Model (2HDM) that allows for light long-lived scalar (H) and pseudoscalar (A) particles. When involving a light beyongd Standard Model (BSM) Higgs, the ∆S could be the main contribution during the global fit of the oblique parameters, which is different to ∆T being the main factor for heavy BSM Higgs cases. By imposing theoretical constraints such as vacuum stability and perturbative unitarity, together with current experimental bounds, we summarize a complete region for a potential light H with cos(β − α) ≃ 1/tanβ , light A with cos(β − α) ≃ 1/tanβ2m_H^2-m_h^2/m_H^2-m_h^2 , and point out the invisible Higgs decay is the most important constraint. We further identify viable regions for LLPs and propose four benchmark regions that simultaneously accommodate a light long-lived particle and the CDF-II measured W boson mass. For these benchmarks, we present the reaches of FASER and FASER 2, where FASER 2 improves the sensitivity by approximately two orders of magnitude compared to FASER.

The 2HDM+S is the singlet extension of the two-Higgs-doublet model (2HDM). The singlet field and its mixing with the 2HDM Higgs sector lead to new contributions to the electroweak precision observables, in particular, the oblique parameters. In this study, we performed a systematic investigation of the impacts of each mixing angle on the oblique parameters. We adopted the mixing angles and physical Higgs masses as our parameters, which allow a mapping when a specific symmetry structure of the Higgs potential and various theoretical considerations are taken into account. We identified five benchmark cases, where at most one mixing angle was nonzero, and analyzed the 95% C.L. allowed parameter space using the oblique parameters. In the alignment limit of the 2HDM, we find that, other than the usual mass relations of m(H)similar to m(H)(+/-) or m(A)similar to m(H*), electroweak precision measurements also impose an upper limit on the neutral Higgs masses. In the cases with nonzero singlet mixing with the 2HDM Higgses H or A, we find approximate mass relations of c(alpha HS)(2) m(H) + s(alpha HS)(2) m(hs) = m(H)(+/-) or c(alpha AS)(2) m(A) + s(alpha AS)(2) m(As) = m(H)+/-. These relations are universal to the 2HDM+S models, with or without further symmetry assumption. We also studied the non-alignment limit of the 2HDM+S, which typically has tighter constraints on the masses and mixing angles. Finally, we examined the complementarity between the electroweak precision analyses and the Higgs coupling precision measurements.

Abstract Long-lived particle (LLP) is one of the well-motivated targets for current collider experiments searching for the physics beyond the Standard Model. In recent years, many dedicated detectors have been developed for such scenarios which are designed to extend the sensitivity to weakly coupled particles with macroscopic cτ. In this work, we investigate the LLP signatures of the neutral component of the fermiophobic fiveplet H 5 0 $$ {H}_5^0 $$ in the Georgi-Machacek model. Due to its fermiophobic nature at tree level, it possesses suppressed decay widths in the low mass region and can naturally be long-lived over a wide region of parameter space. We show that H 5 0 $$ {H}_5^0 $$ can be produced with an appreciable flux in the forward region from the meson decay through loop-induced couplings leading to observable LLP signatures in forward detectors. We evaluate the sensitivity of representative forward detectors to this scenario and compare the result with existing constraints from terrestrial experiments and astrophysical observations. Our results demonstrate that the forward detectors can probe the s H down to 𝒪(10 −5) for sub-GeV scalar masses, and hence providing a powerful and complementary probe of the extended Higgs sectors that is inaccessible to conventional searches.

We study the CP-conserving flipped (Type-Y) Two-Higgs-Doublet Model (2HDM) in the large- regime (>30), focusing on its implications for electroweak phase transitions (EWPTs) and LHC phenomenology. Viable parameter regions supporting a strong first-order EWPT fall into two heavy-Higgs hierarchies: (A) m_H^±≃ m_H<m_A and (B) m_H<m_H^±≃ m_A, both featuring a heaviest CP-odd Higgs A. Scenario A typically proceeds via one-step transitions with lower nucleation temperatures, while Scenario B allows one-step or two-step transitions, opening the decay A→ H^± W^∓ and yielding richer collider signatures. In all cases, nucleation conditions are satisfied, avoiding false-vacuum trapping. We assess LHC prospects through bottom-associated production with multi-b final states: pp→ bbH→ 4b and pp→ bbA→ bb W^± H^∓→ 4bℓ. The 4b channel offers high-statistics discovery potential, reaching signal significances z≳ 25 at the 13 TeV LHC with 300 fb^-1 and up to z≳ 100 at the 14 TeV HL-LHC with 3 ab^-1. The cascade channel, while experimentally more challenging, directly probes the heavy Higgs spectrum and can discriminate between EWPT scenarios. Using optimized selections with a BDT-based multivariate analysis, significances of z ≃ 6.8 can be achieved in favorable regions of Scenario B at the HL-LHC. These results indicate that the HL-LHC can realistically probe the BSM Higgs sector responsible for a strong first-order EWPT and provide insight into the underlying phase transition dynamics in the flipped 2HDM.

We discuss the landscape of flavor physics at the Circular Electron-Positron Collider (CEPC), based on the nominal luminosity outlined in its Technical Design Report. The CEPC is designed to operate in multiple modes to address a variety of tasks. At the Z pole, the expected production of 4 Tera Z bosons will provide unique and highly precise measurements of Z boson couplings, while the substantial number of boosted heavy-flavored quarks and leptons produced in clean Z decays will facilitate investigations into their flavor physics with unprecedented precision. We investigate the prospects of measuring various physics benchmarks and discuss their implications for particle theories and phenomenological models. Our studies indicate that, with its highlighted advantages and anticipated excellent detector performance, the CEPC can explore beauty and tau physics in ways that are superior to or complementary with the Belle II and Large-Hadron-Collider-beauty experiments, potentially enabling the detection of new physics at energy scales of 10 TeV and above. This potential also extends to the observation of yet-to-be-discovered rare and exotic processes, as well as testing fundamental principles such as lepton flavor universality, lepton and baryon number conservation, etc., making the CEPC a vibrant platform for flavor physics research. The WW threshold scan, Higgs-factory operation and top-pair productions of the CEPC further enhance its merits in this regard, especially for measuring the Cabibbo-Kobayashi-Maskawa matrix elements, and Flavor-Changing-Neutral-Current physics of Higgs boson and top quarks. We outline the requirements for detector performance and considerations for future development to achieve the anticipated scientific goals. The role of machine learning for innovative detector design and advanced reconstruction algorithms is also stressed. The CEPC flavor physics program not only develops new capabilities for exploring flavor physics beyond existing projects but also enriches the physics opportunities of this machine. It should be remarked that, given the richness of the CEPC flavor physics, this manuscript is not meant to be a comprehensive survey, but rather an investigation of representative cases. Uncovering the full potential of flavor physics at the CEPC will require further dedicated explorations in the future.

In the Minimal Supersymmetric Standard Model (MSSM), compressed Higgsinos spectrum (Δm^0 ≲ 1 GeV) occurs when |μ| ≪ |M_1|, |M_2| and sign(M_1· M_2)<0, which leads to a long-lived next-to-lightest neutralino. Such a long-lived neutralino could be copiously produced at the LHC, however escape the detection at the LHC main detectors. We examine the discovery potential at the FASER experiment and find that the FASER 2 could cover the neutral Higgsino mass up to about 130 GeV with mass splitting between 4 to 30 MeV. It is complementary to both the LHC Higgsino search in the Δm^0,±≳ 1 GeV region, and displaced vertex and disappearing track searches of charginos with Δm^±≲ 1 GeV.

The Circular Electron-Positron Collider (CEPC), a proposed next-generation Higgs factory, provides new opportunities to explore physics beyond the Standard Model (SM). With its clean electron-positron collision environment and the ability to collect large samples of Higgs, W, and Z bosons, the CEPC enables precision measurements and searches for new physics. This white paper outlines the CEPC's discovery potential, including studies of exotic decays of the Higgs, Z, and top quarks, dark matter and dark sector phenomena, long-lived particles, supersymmetry, and neutrino-related signatures. Advanced detector technologies and reconstruction techniques, such as one-to-one correspondence reconstruction and jet origin identification, significantly improve sensitivity to rare and weakly interacting processes. The CEPC is particularly well suited to probe the electroweak phase transition and test models of electroweak baryogenesis and dark sector interactions. In addition, global fit analyses highlight the CEPC's complementary role in constraining a wide range of new physics scenarios. These features position the CEPC as a powerful tool for exploring the next frontier in fundamental particle physics in the post-Higgs discovery era.

Muons offer a unique opportunity to build a compact high-energy electroweak collider at the 10 TeV scale. A Muon Collider enables direct access to the underlying simplicity of the Standard Model and unparalleled reach beyond it. It will be a paradigm-shifting tool for particle physics representing the first collider to combine the high-energy reach of a proton collider and the high precision of an electron-positron collider, yielding a physics potential significantly greater than the sum of its individual parts. A high-energy muon collider is the natural next step in the exploration of fundamental physics after the HL-LHC and a natural complement to a future low-energy Higgs factory. Such a facility would significantly broaden the scope of particle colliders, engaging the many frontiers of the high energy community. The last European Strategy for Particle Physics Update and later the Particle Physics Project Prioritisation Panel in the US requested a study of the muon collider, which is being carried on by the International Muon Collider Collaboration. In this comprehensive document we present the physics case, the state of the work on accelerator design and technology, and propose an R&D project that can make the muon collider a reality.

In this paper, we present a comprehensive study of the collider search limits on the charged Higgses in the four types of Two Higgs Double Models (2HDM). In addition to constraints from flavor physics measurements, we include both the LEP charged Higgs search channels, as well as the LHC search results on the light and heavy charged Higgses. We consider both the conventional charged Higgs search channels of H^±→τν, cs, cb, tb, and the latest search results on the exotic decay channels H^±→ A W^± / H W^±. We find that H^±→ A W^± / H W^± are complementary to the conventional fermionic channels for m_H^± < m_t. For heavy H^±, H^±→ A W^± / H W^± extend the reach of tanβ beyond that of H^±→ tb in the Type-L 2HDM. We also present the combined reach of all the neutral and charged Higgs searches.

This document is comprised of a collection of consolidated parameters for the key parts of the muon collider. These consolidated parameters follow on from the October 2024 Preliminary Parameters Report. Attention has been given to a high-level consistent set of baseline parameters throughout all systems of the complex, following a 10 TeV center-of-mass design. Additional details of the designs contributing to this baseline design are featured in the appendix. Likewise, explorative variations from this baseline set can be found in the appendix. The data is collected from a collaborative spreadsheet and transferred to overleaf.

The Circular Electron Positron Collider (CEPC) is a large scientific project initiated and hosted by China, fostered through extensive collaboration with international partners. The complex comprises four accelerators: a 30 GeV Linac, a 1.1 GeV Damping Ring, a Booster capable of achieving energies up to 180 GeV, and a Collider operating at varying energy modes (Z, W, H, and ttbar). The Linac and Damping Ring are situated on the surface, while the Booster and Collider are housed in a 100 km circumference underground tunnel, strategically accommodating future expansion with provisions for a Super Proton Proton Collider (SPPC). The CEPC primarily serves as a Higgs factory. In its baseline design with synchrotron radiation (SR) power of 30 MW per beam, it can achieve a luminosity of 5e34 /cm^2/s^1, resulting in an integrated luminosity of 13 /ab for two interaction points over a decade, producing 2.6 million Higgs bosons. Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons, facilitating precise measurements of Higgs coupling at sub-percent levels, exceeding the precision expected from the HL-LHC by an order of magnitude. This Technical Design Report (TDR) follows the Preliminary Conceptual Design Report (Pre-CDR, 2015) and the Conceptual Design Report (CDR, 2018), comprehensively detailing the machine's layout and performance, physical design and analysis, technical systems design, R&D and prototyping efforts, and associated civil engineering aspects. Additionally, it includes a cost estimate and a preliminary construction timeline, establishing a framework for forthcoming engineering design phase and site selection procedures. Construction is anticipated to begin around 2027-2028, pending government approval, with an estimated duration of 8 years. The commencement of experiments could potentially initiate in the mid-2030s.

This document is comprised of a collection of updated preliminary parameters for the key parts of the muon collider. The updated preliminary parameters follow on from the October 2023 Tentative Parameters Report. Particular attention has been given to regions of the facility that are believed to hold greater technical uncertainty in their design and that have a strong impact on the cost and power consumption of the facility. The data is collected from a collaborative spreadsheet and transferred to overleaf.

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.

Abstract We perform the first convergent Bayesian global fits of 4D Composite Higgs Models with partially-composite third generation quarks and leptons based on the minimal SO(5) → SO(4) symmetry breaking pattern. We consider two models with the τ lepton and its associated neutrino in different representations of SO(5). Fitting each model with a wide array of experimental constraints allows us to analyse the Bayesian evidence and currently-observed fine-tuning of each model by calculating the Kullback-Leibler divergence between their respective priors and posteriors. Notably both models are found to be capable of satisfying all constraints simultaneously at the 3σ level at scales of < 5 TeV. From a Bayesian viewpoint of naturalness the model with leptons in the 14 and 10 representations is preferred over those in the 5 representation due to its lower fine-tuning. Finally, we consider the experimental signatures for the preferred parameters in these models, including lepton partner decay signatures and gluon-fusion produced Higgs signal strengths, and discuss their potential phenomenology at future high-luminosity LHC runs.

The exotic decay modes of non-Standard Model Higgses can serve as powerful search channels to explore the parameter space of extended Higgs sectors. In this Snowmass contribution, we illustrate this using the Two-Higgs Doublet Model (2HDM) as an example. We first review the current experimental constraints on the parameter space of a Type-II 2HDM arising from existing searches for the exotic Higgs decay mode $A/H\rightarrow HZ/AZ$. We then present the sensitivity of future colliders to discover addition Higgs bosons using the exotic decay channels $A\rightarrow HZ$, $A\rightarrow H^\pm W^\mp$ and $H^\pm\rightarrow H W^\pm$. We find that a 100 TeV collider can probe almost the entire region of the Type-II 2HDM parameter space that survives current theoretical and experimental constraints and would therefore be an ideal machine to search for heavier Higgses in hierarchical scalar sectors.

In the path towards a muon collider with center of mass energy of 10 TeV or more, a stage at 3 TeV emerges as an appealing option. Reviewing the physics potential of such muon collider is the main purpose of this document. In order to outline the progression of the physics performances across the stages, a few sensitivity projections for higher energy are also presented. There are many opportunities for probing new physics at a 3 TeV muon collider. Some of them are in common with the extensively documented physics case of the CLIC 3 TeV energy stage, and include measuring the Higgs trilinear coupling and testing the possible composite nature of the Higgs boson and of the top quark at the 20 TeV scale. Other opportunities are unique of a 3 TeV muon collider, and stem from the fact that muons are collided rather than electrons. This is exemplified by studying the potential to explore the microscopic origin of the current g-2 and B-physics anomalies, which are both related with muons.

In this work, we summarize a global fit study of Type-II two Higgs doublet models (2HDM), and explore the impact of future SM-like Higgs and Z-pole precision measurements on the allowed parameter space. The work is based on the study results of a global fit of 2HDMs with the tool GAMBIT, utilising various current constraints including theoretical constraints (unitarity, perturbativity and vacuum stability), Higgs searches at colliders, electroweak physics and flavour constraints. We further investigate the ability of future facilities, such as the HL-LHC, CEPC, ILC and FCC-ee to explore the 2HDM parameter space.