The Cherenkov Telescope Array Observatory

• Garret Cotter (University of Oxford)

The Cherenkov Telescope Array Observatory (CTAO) is the next-generation facility for ground-based very-high-energy gamma-ray astronomy, with construction and early operations underway at sites in La Palma and Chile. Covering roughly 20 GeV to 300 TeV, CTAO will deliver unprecedented sensitivity and angular resolution across both hemispheres. This general talk will introduce CTAO’s observational technique, planned capabilities, and scientific motivation, highlighting its potential to study cosmic particle acceleration, extreme astrophysical environments, dark matter, and fundamental physics. I will also discuss the UK’s role in CTAO, including major instrumentation contributions to the Small-Sized Telescope cameras, and CTAO’s wider relevance for astroparticle phenomenology.

Primordial high energy neutrinos

• Nicolas Grimbaum Yamamoto (Université Libre de Bruxelles)

Among the few ways to probe the early Universe, high energy neutrinos offer a unique window on phenomena occurring before recombination. We discuss primordial high energy neutrinos (PHENUs): neutrinos produced from the decay or annihilation of long-lived relics in the early Universe, arriving at detectors today with energies in the GeV-PeV range. We summarise the results of a general study of this scenario, covering the sharp spectral features such fluxes would display, the theoretical (BBN and CMB) and experimental constraints on the source particle parameter space, and the regions that could realistically be probed by current and future neutrino telescopes. We then present a dedicated Monte Carlo code for computing the distortion of the PHENU spectrum by final state radiation and interactions with the cosmic neutrino background during propagation, and apply it to assess whether the ultrahigh energy neutrino event detected by KM3NeT could be of primordial origin.

An Exciting Dark Matter Solution to the MeV Galactic Anomalies

• Shyam Balaji

In this talk, I will present recent work using MeV Galactic observations to search for dark matter. I will discuss how the long standing 511 keV gamma-ray line, recent 2 MeV in-flight annihilation excess, and anomalous Central Molecular Zone (CMZ) ionisation can be addressed within one model paradigm, "Excited Dark Matter". A brief overview for future experimental prospects will also be covered.

Update on STFC funding

Cosmological gravitational particle production: Scalars and fermions

• Duarte Feiteira

In this talk, I will discuss the gravitational production of scalars and fermions during inflation. For scalars, I will compare Bogolyubov coefficient and Starobinsky stochastic approaches, showing that they only agree in the limit of infinitely long inflation. High-scale inflation is very efficient in particle production, leading to constraints on the existence of free, light, and stable scalars: such particles are viable only if their masses are below the eV scale or if the reheating temperature is in the GeV range. This motivates freeze-in at stronger coupling, which I will explore in the framework of warm dark matter production. For fermions, I will show how the production efficiency depends on the particle mass, which is generated via the Yukawa coupling and sensitive to the corresponding scalar field value. Scalar fields can experience large quantum fluctuations during inflation, driving the average field to the Hubble scale and above. Thus, fermions can be very heavy during inflation, enhancing particle production. Based on 2503.14652, 2509.01673, and 2602.20242.

The cosmology of long range Yukawa interactions in general backgrounds

• Panagiotis Giannadakis (King's College London)

We develop a fully relativistic formulation for the evolution of a dark sector containing fermions coupled to a light scalar field in an arbitrary cosmological background characterised by equation of state parameter w. Treating the fermions as a degenerate Fermi gas decoupled from the background cosmic fluid, and assuming a Yukawa-type coupling with the scalar we show that the scalar dynamics select branches that minimise the effective fermion mass. We identify two broad regimes: a scaling regime, in which the scalar oscillates around a value which minimises fermions effective mass, and the coupled sector redshifts approximately as radiation, and an asymptotic regime, in which the field evolves towards configurations where the fermions recover their bare mass.

Strongly coupled gauge theories in the early universe

• Gaurang Kane

Another Brick in the Wall: Domain Wall Networks Beyond Z₂

• DHRUV PASARI (Durham University)

Domain walls beyond the textbook Z₂ kink have been studied analytically and through effective models, but seldom simulated directly on the lattice. We close that gap, evolving Z₃ and Z₄ wall networks with CosmoLattice. These networks are qualitatively richer than Z₂: walls come in distinct species, meet along junctions, and can transmute into one another rather than simply annihilating. To capture this we develop a wall-counting algorithm for multi-component fields that separates each species, and use it to measure the late-time scaling area of each. In Z₄ the simulations directly exhibit a stability transition, where "opposite" walls split into pairs of "adjacent" walls, confirming our analytic prediction. Finally, we extend the velocity-dependent one-scale model from Z₂ to general Zₙ, encoding the reduced annihilation efficiency and junction friction so that the measured scaling plateaus feed directly into the network dynamics, and ultimately the gravitational-wave signal.

Atom Interferometry for Fundamental Physics: The Signal and the Noise

• George Parish (Kings College London)

In this talk, I will discuss the applications of atom interferometry to searches for fundamental physics signals such as ultralight dark matter and gravitational waves, and how these are being put into practice in projects such as AION. I will also discuss some of the signal analysis techniques being developed to deal with gravity gradient noise and reach the required sensitivities for frontier physics searches.

JUNO

• Xianguo Lu (University of Warwick)