Astrophysics seminars

Uddipan Banik derives a dynamical account of dark-matter halo density profiles using the Boltzmann–Poisson equations for an expanding Universe populated by subhalos of many masses. A self-similar solution links density slope to halo mass growth; including gravitational scattering and subhalo capture gives gamma = 6/(s + 2). Initial collapse with s = 2 produces a prompt cusp of slope 3/2. Hierarchical growth connects the slope to the primordial power spectrum and recovers the Syer–White relation during matter domination. Stable clustering selects an inner Navarro–Frenk–White cusp of slope one, while stalled accretion approaches the outer slope of three. The framework connects these profiles to successive stages of halo assembly.

Paco Villaescusa examines how simulations and artificial intelligence change the extraction of physical knowledge from precision cosmological surveys. The talk asks how much information lies in large-scale structure beyond power spectra, including nonlinear scales and higher-order statistics, and introduces the Quijote and Backlight simulation programmes. It then addresses the uncertain astrophysical processes that complicate small-scale inference through CAMELS, a framework combining cosmology, galaxy formation and machine learning. DREAMS is presented as a route to predicting dark-matter observables while accounting for baryonic uncertainties. The final part considers coupling simulations with increasingly capable AI: Denario is introduced as an agentic research system that generates hypotheses, designs analyses, writes and executes code, interprets results and refines research directions. The discussion considers what coordinated populations of agents and simulations spanning physical scales could make possible.

Taillte May investigates how unstable black-hole quasinormal-mode spectra affect observed gravitational-wave signals. Small changes in a gravitational potential can substantially shift the frequencies normally used to test astrophysical black holes. A simple time-domain model reveals a delay before those shifts appear, tied to the echo travel time between the perturbation and the main potential. In the perturbative regime, the frequency change after one echo agrees with the conventional frequency-domain prediction. Beyond that regime, the intermediate waveform cannot be represented by a single constant frequency shift.

Arefe Abghari tests whether the reported excess in the quasar number-density dipole challenges the Cosmological Principle. If large-scale homogeneity and isotropy hold, the motion responsible for the cosmic microwave background dipole should also predict the dipole in distant-source counts. The analysis examines quasar selection and dipole-estimation systematics. Higher multipoles in the quasar density map, plausibly caused by survey and selection effects, can explain the apparent discrepancy. The talk argues that these effects need careful control before interpreting the measurements as evidence against the standard cosmological model.

Claudio Manzari connects astrophysical observations and precision flavor measurements to two unresolved aspects of CP symmetry. For the strong CP problem, the talk considers QCD axions produced in a supernova core and converted to gamma rays by surrounding magnetic fields. A Galactic supernova could expose this distinctive transient, motivating the GALAXY network of telescopes monitoring the full sky. The second part examines the origin of flavor-sector CP violation through precise measurements of the CKM unitarity triangle. Possible hints of spontaneous CP violation are discussed alongside their implications for quark flavor and the fundamental symmetries of matter.

Ania Liu examines gravitational-wave lensing as a probe of compact objects, dark matter and cosmic large-scale structure. Propagation over cosmological distances can distort signals, but identifying lensing in observations requires disentangling those distortions from uncertain waveform models and other astrophysical effects. The talk describes this phenomenology and the ambiguities it creates for interpretation, then presents recent methods and results from lensing searches using LIGO–Virgo–KAGRA data.