We investigate the neutrino sector in the framework of flavor deconstruction with an inverse-seesaw realization. This setup naturally links the hierarchical charged-fermion masses to the anarchic pattern of light-neutrino mixing. We determine the viable parameter space consistent with oscillation data and study the phenomenology of heavy neutral leptons (HNL) and lepton-flavor-violating (LFV) processes. Current bounds from direct HNL searches and LFV decays constrain the right-handed neutrino scale to a few TeV, while future μ → e experiments will probe most of the region with Λ ≲ 10 TeV. Among possible realizations, models deconstructing SU(2)L × U(1)B−L or SU(2)L × U(1)R × U(1)B−L are those allowing the lowest deconstruction scale.

The future circular e+e- collider (FCC-ee or CEPC) will provide unprecedented sensitivity to indirect new physics signals emerging as small deviations from the Standard Model predictions in electroweak precision tests. Assuming new physics scenarios containing a dark matter candidate and a t-channel mediator, we analyse the synergy and interplay of future Tera-Z factories and non-collider tests conducted through direct and indirect searches of dark matter. Our results highlight the excellent prospect for a Tera-Z run to indirectly probe the presence and nature of dark matter.

We investigate the low-energy phenomenology of a minimal flavor-deconstructed framework in the lepton sector within an effective field theory approach, focusing on the interplay between flavor and CP violation. Starting from the ultraviolet completion of the model, we derive the effective Yukawa structure through a systematic spurion expansion beyond leading order and identify the dominant sources of flavor and CP violation. We show that, while leading-order effects to dipole operators are approximately aligned with the Yukawa matrices, next-to-leading order contributions generically induce physical CP-violating phases and flavor misalignment, leading to potentially observable low-energy signals. After constructing the corresponding low-energy effective theory, we analyze the phenomenological implications for charged lepton flavor violating observables, lepton flavor universality tests, and electric dipole moments (EDMs). We find that future searches for μ-e conversion and the electron EDM can probe scales in the multi-10 TeV range under natural assumptions on the flavor structure and CP phases. Our results highlight the complementarity between flavor-violating and CP-violating observables and demonstrate that precision measurements in the lepton sector provide a powerful probe of flavor-deconstructed scenarios beyond the direct reach of collider experiments.

We derive the complete set of partial wave unitarity bounds on the most general Axion-Like Particle (ALP) effective interactions up to dimension 8 in the limit of large center-of-mass energy. Exploiting a recently developed formalism based on spinor-helicity techniques, we discuss the unitarity bounds for N → M (with N, M ≥ 2) scattering amplitudes that can be relevant for ALP searches at colliders or in a variety of rare processes. Moreover, we compute positivity bounds on ALP interactions, emphasizing their complementarity with partial wave unitarity bounds. As a byproduct, we show that our results can be used to infer new positivity constraints in the Standard Model Effective Field Theory.

The electric and magnetic dipole moments of the electron and of the muon provide stringent tests of the Standard Model and sensitive probes of new physics. By contrast, the corresponding dipole moments of the τ lepton remain weakly constrained. This study explores the potential of future lepton colliders, focusing on the e^+e^- Future Circular Collider and a multi-TeV muon collider, to probe τ dipole moments. We consider multiple channels, including ℓ^+ℓ^- → τ^+τ^- (ℓ=e,μ), associated Higgs production μ^+μ^- → τ^+τ^- H, radiative Higgs decays H → τ^+τ^-γ, and vector-boson scattering ℓ^+ℓ^- →ℓ^+ℓ^-τ^+τ^- and μ^+μ^- →^+τ^-. Our results show that these facilities are highly complementary and can extend existing bounds by several orders of magnitude.

We develop a formalism, based on spinor-helicity techniques, to generalize the formulation of partial wave unitarity bounds. We discuss unitarity bounds for N -* M (with N; M >= 2) scattering processes- relevant for high-energy future colliders-and spin-2 or higher-spin theories-relevant for effective field theories of gravity-that are not approachable by standard methods. Moreover, we emphasize the power and complementarity of positivity and partial wave unitarity bounds to constrain the parameter space of effective field theories.

We present a concise review of the new physics sensitivity of leptonic dipole moments and their interrelationship. In particular, focusing on the current muon g-2 anomaly, we analyse both high-energy and low-energy tests to confirm or to falsify it.

Beyond Standard Model scenarios addressing the flavor puzzle and the hierarchy problem generally predict dominant new physics couplings with fermions of the third generation. In this Letter, we explore the collider and astrophysical signatures of new light scalar and pseudoscalar particles dominantly coupled to the τ-lepton. The best experimental prospects are expected at Belle II through the e+e− → τ+τ−γγ, τ+τ−γ, 3γ, mono–γ processes, and the τ anomalous magnetic moment. The correlated effects in these searches can unambiguously point toward the underlying new physics dynamics. Moreover, we study astrophysics bounds — especially from core-collapse supernovae and neutron star mergers — finding them particularly effective and complementary to collider bounds. We carry out this program in the well-motivated context of axion-like particles as well as generic CP-even and CP-odd particles, highlighting possible ways to discriminate among them.

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.

The hadronic vacuum polarization (HVP) contributions to the muon g-2 are the crucial quantity to resolve whether new physics is present or not in the comparison between the standard model (SM) prediction and experimental measurements at Fermilab. They are commonly and historically determined via dispersion relations using a vast catalogue of experimentally measured, low-energy e^{+}e^{-}→hadrons cross section data as input. These dispersive estimates result in a SM prediction that exhibits a muon g-2 discrepancy of more than 5σ when compared to experiment. However, recent lattice QCD evaluations of the HVP and a new hadronic cross section measurement from the CMD-3 experiment favor a no-new-physics scenario and, therefore, exhibit a common tension with the previous e^{+}e^{-}→hadrons data. This study explores the current and future implications of these two scenarios on other observables that are also sensitive to the HVP contributions in the hope that they may provide independent tests of the current tensions observed in the muon g-2.

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.

We discuss a set of precision observables that can probe the existence of a light particle X coupled to electrons in the mass range of 1–100 MeV. As a case study, we consider the recent excess of e+e− final-state events at s=16.9 MeV reported by the PADME collaboration. Interestingly, this mass is tantalizingly close to the invariant mass at which anomalous e+e− pair production has previously been observed in nuclear transitions from excited to ground states by the ATOMKI collaboration. For the scenario in which the new particle has a vector coupling to electrons, we show that the PADME excess is already in tension with constraints from the anomalous magnetic moment of the electron. Further improvements in the measurement of the electron g-2, together with upcoming results from PIONEER (searching for π+→e+νX) and Mu3e (searching for μ+→e+ν‾μνeX), are expected to definitively probe this scenario in the near future. We also explore alternative possibilities where the new particle has scalar, pseudoscalar, or axial-vector couplings.

We consider the most general axion-like particle effective field theory, including both CP-odd and CP-even types of interactions, and evaluate the corresponding renormalization group equations, improving and extending previous results in the literature. Our calculations exploit on-shell and unitarity-based methods. The relevant phase-space cut-integrals are carried out using different integration methods, among which the double-cut integration via Stokes’ theorem proves to be technically simpler. A close comparison between the standard Feynman diagrammatic approach and the unitarity-based method enables us to explicitly verify the reduction of complexity in the latter case, along with a more direct and elegant way to establish a connection among anomalous dimensions of operators that are dual under the CP symmetry.

We consider the renormalization group equations of axion-like particle effective field theories and determine the corresponding anomalous dimensions at one loop via on-shell and unitarity-based methods. The calculation of the phase-space cut-integrals is carried out using different integration methods, among which the double-cut integration via Stokes' theorem proves to be technically simpler. A close comparison between the standard Feynman diagrammatic approach and the unitarity-based method enables us to explicitly verify the reduction of complexity in the latter case, along with a more direct and elegant way to establish a connection among anomalous dimensions of operators that are dual under the CP symmetry.

We discuss the construction of the most general CP-violating chiral Lagrangian for an axion-like particle (ALP). Starting with an effective Lagrangian containing light quarks and gluons, we provide its matching onto a chiral effective Lagrangian at 𝒪 (p2) described in terms of mesons and baryons, identifying the correspondence between the Jarlskog invariants of the two theories. After deriving the ALP interactions with mesons and baryons, we analyse a few relevant phenomenological implications such as the permanent electric dipole moments of nucleons and the CP-violating ALP and kaon decays. This work provides the necessary tools for further phenomenological analyses connecting low-energy observables with the couplings of the underlying ultraviolet complete theory.

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.

We elaborate on the application of on-shell and unitarity-based methods for evaluating renormalization group coefficients, and generalize this framework to account for the mixing of operators with different dimensions and leading mass effects. We derive a master formula for anomalous dimensions stemming from the general structure of operator mixings, up to two-loop order, and show how the Higgs low-energy theorem can be exploited to include leading mass effects. A few applications on the renormalization properties of popular effective field theories showcase the strength of the proposed approach, which drastically reduces the complexity of standard loop calculations. Our results provide a powerful tool to interpret experimental measurements of low-energy observables, such as flavor violating processes or electric and magnetic dipole moments, as induced by new physics emerging above the electroweak scale.

The authors of the paper (Vitali et al 2022 J. Phys. A: Math. Theor. 55 224012) analyzed a simple CTRW model with a waiting time distribution defined as the weighted sum of two exponential distributions. They showed that their model meets many paradigmatic features that belong to the anomalous diffusion as it is observed in living systems. This comment point out the previous paper that considers a similar model and improves on the authors' result regarding the time dependence of the mean-square displacement.

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.