A flux of ultra-high-energy (UHE) neutrinos, produced by astrophysical sources at cosmological distances, is anticipated to exist and reach Earth. In this paper, we investigate the impact on the total flux, energy spectrum, and arrival directions of UHE neutrinos of neutrino-dark matter (DM) scatterings. We study scatterings both in the intergalactic medium and in the Milky Way. We emphasize the complementarity among neutrino detectors at different latitudes, that can probe anisotropies induced by neutrinos scattering with the Milky Way DM halo. We also discuss that, with mild astrophysical assumptions, limits on the DM-nu scattering cross section can be placed even if the neutrino sources are unknown. Finally, we explore all this phenomenology with the recent UHE neutrino event KM3230213A, and place the corresponding limits on the DM-nu scattering cross section.

We calculate the one-loop renormalization group equations of the neutrino mass matrix when the Standard Model particle content is extended with a massive gauge boson which has family-dependent couplings to the left-handed leptons. We show that quantum effects induced by the extra gauge boson increase the rank of the neutrino mass matrix at the one-loop level, in contrast to the well-known result that Standard Model fields can only increase the rank at the two-loop level. We also discuss the possibility of generating dynamically the measured mass differences and mixing angles between the active neutrinos in scenarios with normal and inverted mass ordering.

We explore the possibility that the underlying flavour structure of the Standard Model could be determined by mass chains on a fractal geometry. We consider, as an example, the theory space on a Sierpinski-like geometry. The fermion mass chains on a Sierpinski-like geometry with three decorations (iterations) lead to three zero modes, which can be identified with the three generations of the Standard Model. This framework also reproduces the measured charged and neutral lepton masses and mixing angles with very few parameters. We also briefly discuss the possible extension to the quark sector.

The Migdal effect has been used along with nuclear direct detection experiments to constrain dark matter models in the sub-GeV region. By utilizing the Migdal effect with data from the XENON1T and DarkSide-50 experiments, we constrained the dipolar interactions of dark matter with visible matter. We find that the Migdal limit sets the strongest constraints on dark matter at the Sub-GeV scale. The complementarity of the Migdal effect with dark matter-electron scattering processes is observed.

Dark matter decays into invisible particles can leave an imprint in large-scale structure surveys due to a characteristic redshift-dependent suppression of the power spectrum. We present a model with two quasi-degenerate singlet fermions, chi 1 and chi 2, in which the heavier state decays as chi 2 -> chi & strns;1 nu nu on cosmological time-scales, and that also integrates non-zero neutrino masses. Remarkably, for parameters that yield the correct dark matter abundance via freeze-in and reproduce the observed neutrino masses, dark matter decay can accommodate detectable signals in forthcoming large-scale structure surveys, a diffuse anti-neutrino flux accessible to JUNO, and a gamma-ray line within the energy range probed by COST. Both the cosmological lifetime of chi 2 as well as the small (radiatively induced) mass splitting among chi 1,2 are a natural consequence of the mechanism of neutrino mass generation within this model. This highlights the potential role of large-scale structure surveys in probing some classes of neutrino mass models.

In some scenarios, the dark matter relic abundance is set by the semi-annihilation of two dark matter particles into one dark matter particle and one Standard Model particle. These semi-annihilations might still be occurring today in the Galactic Center at a significant rate, generating a flux of boosted dark matter particles. We investigate the possible signals of this flux component in direct detection and neutrino experiments for sub-GeV dark matter masses. We show that for typical values of the semi-annihilation cross-section, the sensitivity of current experiments to the spin-independent dark matter-proton scattering cross-section can be several orders of magnitude larger than current constraints from cosmic-ray boosted dark matter. We also argue that the upcoming DARWIN and DUNE experiments may probe scattering cross-sections as low as 10^-37 cm^2 for masses between 30 MeV and 1 GeV.

This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers unique opportunities to address some of the most fundamental questions in physics. This motivates a vigorous experimental programme which the theory community fully supports. A strong effort in theoretical neutrino physics is paramount to optimally take advantage of upcoming neutrino experiments and to explore the synergies with other areas of particle, astroparticle, and nuclear physics, as well as cosmology. Progress on the theory side has the potential to significantly boost the physics reach of experiments, as well as go well beyond their original scope. Strong collaboration between theory and experiment is essential in the precision era. To foster such collaboration, we propose to establish a CERN Neutrino Physics Centre. Taking inspiration from the highly successful LHC Physics Center at Fermilab, the CERN Neutrino Physics Centre would be the European hub of the neutrino community, covering experimental and theoretical activities.

We study the decay of a heavy CP-even neutral Higgs into an on-shell Standard Model-like Higgs boson and two photons, H → hγγ, in the two-Higgs doublet model. We argue that the decay channel H → hγγ, followed by the decay of the Standard Model Higgs $$ h\to b\overline{b} $$ h → b b ¯ , could be observed at the 5σ level at the High-Luminosity LHC for masses of the heavy Higgs up to 950 GeV for the type-II, 650 GeV for the Lepton Specific and the Flipped 2HDMs, and 350 GeV for the type-I. We also discuss the possible role of the decay H → hγγ in discriminating among different types of 2HDMs and in enhancing the total number of events in the final state $$ H\to b\overline{b}\gamma \gamma $$ H → b b ¯ γγ compared to the cascade decay H → hh followed by h → γγ h → $$ b\overline{b} $$ b b ¯ with identical final state (although with different kinematical distributions).

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.

We study the decay of a heavy CP-even neutral Higgs into an on-shell Standard Model-like Higgs boson and two photons, H → hγγ, in the two-Higgs doublet model. We argue that the decay channel H → hγγ, followed by the decay of the Standard Model Higgs h→ bb , could be observed at the 5σ level at the High-Luminosity LHC for masses of the heavy Higgs up to 950 GeV for the type-II, 650 GeV for the Lepton Specific and the Flipped 2HDMs, and 350 GeV for the type-I. We also discuss the possible role of the decay H → hγγ in discriminating among different types of 2HDMs and in enhancing the total number of events in the final state H→ bbγγ compared to the cascade decay H → hh followed by h → γγ h → bb with identical final state (although with different kinematical distributions).

An unavoidable prediction of scenarios with Dark Matter (DM) self-interactions is the existence of number changing processes that convert $n$ initial DM particles into $m$ final ones ($n\to m$ processes), possibly accompanied by Standard Model particles. We argue that the $n\rightarrow m$ processes could be probed in DM spikes at the center of galaxies, where the high density may allow sizable rates. We systematically study the implications of the $n \to m$ processes in DM spikes, including other possible interactions involving DM, such as annihilation and self-scattering. We find that for $n\geq3$, the spike is significantly depleted for $n\to m$ cross-sections favored by DM production via thermal freeze-out. On the other hand, the semi-annihilation of two DM particles into one DM particle and one Standard Model particle preserves in general the structure of the spike. Such density modifications significantly affect phenomenological studies of both astrophysics and particle DM processes around DM spikes.

We investigate the possibility that the high-energy neutrino flux observed from the Seyfert galaxy NGC 1068 originates from dark matter annihilations within the density spike surrounding the supermassive black hole at its center. The comparatively lower gamma-ray flux is attributed to a dark sector that couples predominantly to Standard Model neutrinos. To explain the absence of a corresponding neutrino signal from the center of the Milky Way, we propose two scenarios: (i) the disruption of the dark matter spike at the Milky Way center due to stellar heating, or (ii) the annihilation into a dark scalar that decays exclusively into neutrinos, with a decay length longer than the size of the Milky Way but shorter than the distance from Earth to NGC 1068.

The invisible decay of cold dark matter into a slightly lighter dark sector particle on cosmological time-scales has been proposed as a solution to the S_8 tension. In this work we discuss the possible embedding of this scenario within a particle physics framework, and we investigate its phenomenology. We identify a minimal dark matter decay setup that addresses the S_8 tension, while avoiding the stringent constraints from indirect dark matter searches. In our scenario, the dark sector contains two singlet fermions N_1,2, quasi-degenerate in mass, and carrying lepton number so that the heaviest state (N_2) decays into the lightest (N_1) and two neutrinos via a higher-dimensional operator N_2→N̅_1νν. The conservation of lepton number, and the small phase-space available for the decay, forbids the decay channels into hadrons and strongly suppresses the decays into photons or charged leptons. We derive complementary constraints on the model parameters from neutrino detectors, freeze-in dark matter production via νν→ N_1N_2, collider experiments and blazar observations, and we show that the upcoming JUNO neutrino observatory could detect signals of dark matter decay for model parameters addressing the S_8 tension if the dark matter mass is below ≃ 1 GeV.

We calculate the renormalization group equation (RGE) of the lepton-number-violating Weinberg operator with the particle content of the Standard Model (SM), thus completing the set of two-loop RGEs of the SM effective field theory up to dimension 5. We identify new diagrams that could increase the rank of the Wilson coefficient of the Weinberg operator, and we calculate the complete two-loop RGE for the neutrino mass eigenvalues and leptonic mixing matrix. We also briefly discuss some phenomenological implications of the RGEs.

A strongly self-interacting component of asymmetric dark matter particles can form compact dark stars. The high dark matter density in these objects may allow significant dark matter annihilation into Standard Model particles, even when the portals to the visible sector are extremely weak. In this paper we argue that compact dark stars could constitute an important source of energy injection during the cosmic dawn era in addition to that of the baryonic stars. Therefore, if dark stars annihilate into photons, the luminosity of dark stars may significantly raise the gas temperature of the Universe at small redshifts. This modification to the standard thermal history of standard Cosmology would have implications for the observed 21-cm signal and the process of reionization, thus providing a new probe for particle dark matter.

Astronomical and cosmological observations indicate that dark matter should interact very weakly with the electromagnetic radiation. Nevertheless, the existence of such interactions is not precluded by observations nor by theoretical considerations. A promising approach to probe the dark matter electromagnetic properties is through the search of photon-mediated dark matter-nucleus interactions in direct detection experiments. In this paper we present a simple methodology to calculate the scattering rate in a direct detection experiment for given values of the dark matter electric charge, charge radius, electric- and magnetic- dipole moments and anapole moment. In our work we include contributions to the scattering from nuclear recoils and from the Migdal effect. We finally apply this formalism to determine exclusion limits on the five electromagnetic interactions using data from XENON1T, LZ, PICO-60 and DS50 experiments, and we discuss the implications for a simplified dark matter model with t-channel mediators.

The International Fusion Materials Irradiation Facility- DEMO Oriented Neutron Source (IFMIF-DONES) is a scientific infrastructure aimed to provide an intense neutron source for the qualification of materials to be used in future fusion power reactors. Its implementation is critical for the construction of the fusion DEMOnstration Power Plant (DEMO).IFMIF-DONES is a unique facility requiring a broad set of technologies. Although most of the necessary technologies have already been validated, there are still some aspects that introduce risks in the evolution of the project.In order to mitigate these risks, a consortium of companies, with the support of research centres and the funding of the CDTI (Centre for the Development of Industrial Technology and Innovation), has launched the DONES EVO Programme, which comprises six lines of research:•Improvement of signal transmission and integrity (planning and integration risks)•Optimisation of RF conditioning processes (planning and reliability risks)•Development of a reliable beam extraction device (reliability risks)•Development of technologies for the production of medical isotopes (reliability risks)•Improvement of critical parts of the lithium purification system (safety and reliability risks)•Validation of the manufacture of critical components with special materials (reliability risk).DONES EVO will focus on developing the appropriate response to the risks identified in the IFMIF-DONES project through research and prototyping around the associated technologies.This contribution will present a discussion of the risks, the proposed response to them and the evolution of the technologies involved, following selected experiments carried out throughout the project.