The dark matter and baryon asymmetry problems remain two of the most pressing questions in fundamental physics. Considering lepton-flavored dark matter, it has recently been shown that the cogenesis of dark matter and the baryon asymmetry can be economically achieved via conversion-driven freeze-out. This mechanism leverages semi-efficient conversions to drive a departure from equilibrium while preserving independence from initial conditions through early thermalization of the dark sector. In this work, we develop this mechanism further, providing a detailed analysis of the chemical-equilibrium conditions and demonstrating that the framework can be extended to quark-philic scenarios, where the matter-antimatter asymmetry is generated resonantly through baryon-number-conserving CP-violating conversions of a mediator field into Standard Model quarks and dark matter. The strong QCD interactions of the colored mediator, including bound-state formation effects during freeze-out, substantially enlarge the viable parameter space and allow dark matter masses from a few hundred GeV up to the TeV scale. We furthermore assess the impact of thermal effects by comparing a minimal treatment with a setup that approximately accounts for thermal masses and their kinematic consequences. The resulting scenario predicts striking long-lived particle signatures with soft displaced decay products that remain only partially explored at the LHC and motivate dedicated searches at the HL-LHC.

The recently announced NA62 measurement of the K^+^+ν branching ratio, based on 2016–2024 data, is fully consistent with its very accurate Standard Model (SM) prediction. While it is not excluded that the final result based on 2016–2026 data will deviate from the SM prediction, the question arises whether a similar fate awaits the K_L^0ν decay. This decay is currently being searched for by the KOTO experiment, with the present upper bound roughly two orders of magnitude above its very precise SM prediction. The proposed KOTO II experiment aims to provide the first discovery of the K_L^0ν decay and measure its branching ratio. Building on the findings of several previous papers we demonstrate that in the presence of suitably chosen large new complex phases and of a small amount of new right-handed s̅ d couplings, in addition to the left-handed ones, the K_L^0ν branching ratio can still be enhanced by one order of magnitude with respect to the SM prediction while keeping both K^+^+ν and ε_K SM-like. Simultaneously the decays K_S^+μ^-, studied by LHCb, and K_L^0ℓ^+ℓ^-, searched for by KOTO II, can be strongly enhanced and the anomaly in the ratio ε^'/ε, as claimed by Dual QCD, removed. We illustrate this with an example of a specific Z^' scenario.

We present a comprehensive framework for the study of flavored dark matter models, combining relic density calculations with direct and indirect detection limits, collider constraints, and a global analysis of flavor observables based on SMEFT matching and renormalization-group evolution. The framework applies to scalar or fermionic dark matter, including both self-conjugate and non-self-conjugate cases. As a proof of principle, we analyze two scenarios with Majorana dark matter coupling to right-handed charged leptons and to right-handed down-type quarks, assuming a thermal freeze-out. In the leptophilic case, flavor-violating decays such as μ→ e γ dominate the constraints, while LHC searches still leave sizable parameter space. For quark couplings, direct detection bounds and meson mixing severely restrict the allowed couplings, favoring hierarchical flavor structures. The toolchain presented in this paper is publicly available on GitHub .

The kaon physics programme, long heralded as a cutting-edge frontier by the European Strategy for Particle Physics, continues to stand at the intersection of discovery and innovation in high-energy physics (HEP). With its unparalleled capacity to explore new physics at the multi-TeV scale, kaon research is poised to unveil phenomena that could reshape our understanding of the Universe. This document highlights the compelling physics case, with emphasis on exciting new opportunities for advancing kaon physics not only in Europe but also on a global stage. As an important player in the future of HEP, the kaon programme promises to drive transformative breakthroughs, inviting exploration at the forefront of scientific discovery.

This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of t-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In addition, we explore scenarios with either promptly decaying or long-lived particles, as well as featuring diverse dark matter production mechanisms in the early universe. By providing a unified analysis framework, numerical tools and guidelines, this work aims to support future experimental and theoretical efforts in exploring t-channel dark matter models at colliders and in cosmology.

This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $t$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In addition, we explore scenarios with either promptly decaying or long-lived particles, as well as featuring diverse dark matter production mechanisms in the early universe. By providing a unified analysis framework, numerical tools and guidelines, this work aims to support future experimental and theoretical efforts in exploring $t$-channel dark matter models at colliders and in cosmology.

Abstract We study a simplified Dark Matter model in the Dark Minimal Flavour Violation framework. Our model complements the Standard Model with a flavoured Dark Matter Majorana triplet and a coloured scalar mediator that share a Yukawa coupling with the right-handed up-type quarks with the coupling matrix λ. We extend previous work on this topic by exploring a large range of cosmologically viable parameter space, including the coannihilation region and, in particular, the region of conversion-driven freeze-out, while considering constraints from $$ {D}^0\hbox{--} {\overline{D}}^0 $$ D 0 – D ¯ 0 mixing as well as constraints from direct and indirect Dark Matter searches. We find various realisations of conversion-driven freeze-out within the model, that open up allowed windows of parameter space towards small mass splittings and very weak Dark Matter couplings. Finally, we probe the model by reinterpreting current LHC searches for missing energy and long-lived particles. We point out gaps in the coverage of current constraints as well as new opportunities to search for the model at the LHC, in particular, the charge asymmetry in single-top production associated with jets and missing energy.

These proceedings provide a brief overview of the status of B meson physics, putting particular emphasis on precision tests of the Standard Model with meson mixing data, and on the anomalies in charged- and neutral-current semileptonic B decays. In addition to summarising the current status, some promising directions to be pursued at future collider experiments are highlighted.

Form factors are crucial theory input in order to extract $|V_{cb}|$ from $B \to D^{(*)}\ell\nu$ decays, to calculate the Standard Model prediction for ${\cal R}(D^{(*)})$ and to assess the impact of New Physics. In this context, the Dispersive Matrix approach, a first-principle calculation of the form factors, using no experimental data but rather only lattice QCD results as input, was recently applied to $B \to D^{(*)}\ell\nu$. It predicts (within the Standard Model) a much milder tension with the ${\cal R}(D^*)$ measurements than the other form factor approaches, while at the same time giving a value of $|V_{cb}|$ compatible with the inclusive value. However, this comes at the expense of creating tensions with differential $B\to D^*\ell\nu$ distributions (with light leptons). In this article, we explore the implications of using the Dispersive Matrix method form factors, in light of the recent Belle (II) measurements of the longitudinal polarization fraction of the $D^*$ in $B\to D^*\ell\nu$ with light leptons, $F_L^{\ell}$, and the forward-backward asymmetry, $A_{\rm FB}^{\ell}$. We find that the Dispersive Matrix approach predicts a Standard Model value of $F_L^{\ell}$ that is in significant tension with these measurements, while mild deviations in $A_{\rm FB}^{\ell}$ appear. Furthermore, $F_L^{\ell}$ is very insensitive to New Physics such that the latter cannot account for the tension between Dispersive Matrix predictions and its measurement. While this tension can be resolved by deforming the original Dispersive Matrix form factor shapes within a global fit, a tension in ${\cal R}(D^*)$ reemerges. As this tension is milder than for the other form factors, it can be explained by New Physics not only in the tau lepton channel but also in the light lepton modes.

Abstract We study a simplified model of lepton-flavoured complex scalar dark matter set up in the Dark Minimal Flavour Violation framework. In this model the Standard Model is extended by a scalar dark matter flavour triplet and a charged fermionic mediator, through which dark matter couples to the right-handed charged leptons of the Standard Model. This interaction is parameterized by a new 3 × 3 coupling matrix λ. Consistent with the field content of the model, also the Standard Model’s approximate flavour symmetry is extended to include an additional global U(3) associated with the dark matter flavour triplet. In addition to the Standard Model Yukawa couplings, the new coupling matrix λ is assumed to constitute the only source that violates this extended symmetry. We analyse the parameter space of this model by investigating constraints from collider searches, lepton flavour violating decays, the observed dark matter relic density, and direct as well as indirect dark matter detection experiments. By performing a combined analysis of all constraints we find that restrictions from lepton flavour violating decays, the observed relic density and dark matter nucleon scattering are dominant. The combination of the latter two renders limits from collider searches irrelevant while indirect detection constraints are weak due to a p-wave suppression of the annihilation rate. We conclude that lepton-flavoured scalar dark matter has a rich phenomenology and is a viable dark matter candidate.

Abstract We study a simplified model of lepton-flavoured complex scalar dark matter coupling to right-handed leptons and the Higgs boson. The model is set up in the Dark Minimal Flavour Violation framework. In contrast to previous studies of similar models we consider the most general case and do not a priori constrain the hierarchy of dark matter masses and couplings in any way aside from the chosen parameter ranges. In the first part of the analysis we discuss the impact of Higgs portal interactions and the generalised mass hierarchy on the model’s phenomenology. We find that they render new physics masses around the electroweak scale viable, thus qualifying this model to address the (g − 2) μ puzzle. After reviewing the current situation of the latter, we perform two combined analyses — one in which (g − 2) μ allows for significant new physics effects and one in which it does not. We find that while the latter scenario allows for a larger range of new physics scales, both scenarios are equally viable.

As a joint explanation for the dark matter (DM) problem and the muon (g-2) (g−2) anomaly, we propose a simplified model of lepton-flavoured complex scalar DM with couplings to both the left- and right-handed leptons of the Standard Model (SM). Both interactions are governed by the same new flavour-violating coupling matrix \lambda λ , however we allow for a relative scaling of the coupling strength. The SM is further extended by two fermion representations, transforming as an SU(2)_L SU(2)L doublet and singlet, respectively, and mediating these interactions. The fermions additionally couple to the SM Higgs doublet via a new Yukawa coupling. To study the model’s phenomenology we first investigate constraints from collider searches, flavour experiments, precision tests of the SM, the DM relic density, and direct as well as indirect detection experiments individually. We then perform a combined analysis by demanding that all mentioned constraints are satisfied simultaneously. We use the results of this combined analysis and examine if the model is capable of accommodating the (g-2)_\mu (g−2)μ anomaly within its viable parameter space without introducing fine-tuned lepton masses. For all benchmark scenarios we consider, we find that the central value of \Delta a_\mu^\text{exp} Δaμexp can be reached without generating too large corrections to the lepton masses. We hence conclude that this model qualifies as a viable and attractive lepton-flavoured DM model that at the same time solves the (g-2)_\mu (g−2)μ anomaly.

We review the Spring 2022 status of the current $B$ anomalies and their possible interpretation in terms of New Phsyics. We also discuss the discovery potential of targeted LHC and future collider searches for the underlying new particles and their complementarity with low-energy flavour observables.

Measurements of the branching ratios of B -> D-(*)iota(nu) over bar vertical bar B -> D((*))l (nu) over bar B-c -> J vertical bar psi iota(nu) over bar vertical bar B-c -> J vertical bar psi l (nu) over bar the BABAR, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio Lambda(b) -> Lambda(c)iota(nu)over bar / Lambda(b) -> Lambda(c)l(nu)over bar shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within 2 sigma or 1.5 sigma, depending on the R(Lambda(c)) normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results.

Measurements of the branching ratios of $B \to D^{(*)}\tau\bar\nu/B \to D^{(*)}\ell\bar\nu$ and $B_c\to J/\psi\, \tau\bar\nu/B_c\to J/\psi\, \ell\bar\nu$ by the BaBar, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio $\Lambda_b \to\Lambda_c \tau\bar\nu/\Lambda_b \to\Lambda_c \ell\bar\nu$ shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within $2\sigma$ or $1.5\sigma$, depending on the ${\cal R}(\Lambda_c)$ normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results.

We study the Large Hadron Collider (LHC) search potential of a $\mathbb{Z}_4$-based two Higgs doublet model which can simultaneously explain the muon $g-2$ anomaly and the observed dark matter. The neutral scalars in the second Higgs doublet couple to $\mu$ and $\tau$ and largely contribute to the muon anomalous magnetic moment through the one-loop diagram involving $\tau$ and scalars. An additional singlet scalar which is charged under the discrete symmetry can be a dark matter candidate. An upper limit on the scalar mass originates from the unitarity constraint, and the $\mu\tau$ flavor-violating nature of the scalars predicts non-standard signatures at the LHC. However, the previously proposed $\mu^\pm\mu^\pm\tau^\mp\tau^\mp$ signal via the electroweak heavy neutral scalar pair production at the LHC loses sensitivity for increasing scalar mass. We revisit this model and investigate the LHC prospects for the single production of the $\mu\tau$ flavor-violating neutral scalar. It is shown that the single scalar process helps to extend the LHC reach to the 1$\,$TeV mass regime of the scenario. The search potential at the high energy LHC is also discussed.

Motivated by the notorious anomaly in the lepton flavor universality ratios RD(∗) , we study the sensitivity of the Large Hadron Collider (LHC) to a low-mass charged Higgs boson H− lighter than 400GeV in a generic two Higgs doublet model. A combination of current constraints from the Bc→ τν decay, Bs meson mixing data, tau sleptons and di-jet searches at the LHC allows to explain the RD(∗) anomaly at the 1σ level by a lowmass charged Higgs. In this context, we estimate the reach of an LHC search for resonant H− production, where the final state contains an energetic τ lepton decaying hadronically, a neutrino with large transverse momentum, and an additional b-jet (pp→ b+ τh + ν). Requiring the additional b-tagged jet in the τν resonance search profits from the suppression of the Standard Model background, and therefore it allows us to judge the low-mass H− interpretation of the RD(∗) anomaly. To demonstrate this, we perform a fast collider simulation for the τν resonance search with an additional b-tagged jet, and find that most of the interesting parameter region of the whole mass range can already be probed with the current integrated luminosity of 139 fb−1.

A bstract We consider the phenomenological signatures of Simplified Models of Flavourful Leptoquarks, whose Beyond-the-Standard Model (SM) couplings to fermion generations occur via textures that are well motivated from a broad class of ultraviolet flavour models (which we briefly review). We place particular emphasis on the study of the vector leptoquark ∆ μ with assignments ( 3 , 1 , 2 / 3) under the SM’s gauge symmetry, SU(3) C × SU(2) L × U(1) Y , which has the tantalising possibility of explaining both $$ {\mathcal{R}}_{K^{\left(\ast \right)}} $$ R K ∗ and $$ {\mathcal{R}}_{D^{\left(\ast \right)}} $$ R D ∗ anomalies. Upon performing global likelihood scans of the leptoquark’s coupling parameter space, focusing in particular on models with tree-level couplings to a single charged lepton species, we then provide confidence intervals and benchmark points preferred by low (er)-energy flavour data. Finally, we use these constraints to further evaluate the (promising) Large Hadron Collider (LHC) detection prospects of pairs of τ -flavoured ∆ μ , through their distinct (a)symmetric decay channels. Namely, we consider direct third-generation leptoquark and jets plus missing-energy searches at the LHC, which we find to be complementary. Depending on the simplified model under consideration, the direct searches constrain the ∆ μ mass up to 1500-1770 GeV when the branching fraction of ∆ μ is entirely to third-generation quarks (but are significantly reduced with decreased branching ratios to the third generation), whereas the missing-energy searches constrain the mass up to 1150-1700 GeV while being largely insensitive to the third-generation branching fraction.

Measurements of the branching ratios of B → D^(*)τν̅/B → D^(*)ℓν̅ and B_c→ J/ψ τν̅/B_c→ J/ψ ℓν̅ by the BaBar, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio Λ_b →Λ_c τν̅/Λ_b →Λ_c ℓν̅ shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within 2σ or 1.5σ, depending on the R(Λ_c) normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results.