Massive galaxy clusters are the youngest and, therefore, most massive objects in the Universe. Their dark matter-dominated gravitational potential wells are filled with gas, heated to 10s of millions of Kelvin by shocks and compression. The SRG/eROSITA X-ray space telescope recently surveyed the sky, hunting for this hot gas in clusters, detecting an unprecedentedly large number. Employing...
Hydrogen "snow clouds" - which are so cold and dense that they contain particles of solid or liquid molecular hydrogen - are a well motivated form of baryonic dark matter. Theoretical models of snow cloud structure prefer cloud masses in the planetary range, but radii as large as planetary orbits. Increasingly there is evidence that such gas plays an important role in our own Galaxy, but the...
Combining Geometric Algebra with tetrads is an excellent tool to describe the geometric character of General Relativity. In this talk, I will briefly introduce the formalism and illustrate its potential by presenting the calculations of an orbital precision around a Schwarzschild black hole. Compared with tensor calculus, **we reduce a system of 4 coupled differential equations to a single,...
There is currently no evidence for a baryon asymmetry in our Universe. Instead, cosmological observations have only demonstrated the existence of a quark-antiquark asymmetry, which does not necessarily imply a baryon asymmetric Universe, since the baryon number of the dark sector particles is unknown. In this paper we discuss a framework where the total baryon number of the Universe is equal...
Minimally modified gravity models are a class of modified gravity theories with only two local degrees of freedom as in General Relativity. I want to discuss the implications on the early Universe.
As long as the non-dynamical scalar field is sub-dominant at the background one recovers the standard results for slow-roll inflation both for the power and biscpectrum. Otherwise, it is possible...
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 talk, I want to present a possible embedding of this scenario within a particle physics framework and discuss its phenomenology. The model is set up of a minimal dark matter decay, where the dark sector contains two...
Can modifications to Hawking evaporation of small black holes be probed by observing gravitational waves from the early Universe? In this talk I will argue that the answer to this tantalizing question may in fact be positive.
It has been recently proposed that Hawking evaporation might slow down significantly after a black hole has lost about half of its mass, considerably extending its...
We apply current analytical knowledge on the characteristic mass and linear evolution of miniclusters down to redshift $z=0$ to the hypothetical minicluster distribution of the Milky Way.
Using the core-halo relation for stable soliton solutions composed of axion-like particles (ALPs), we connect the galactic minicluster mass distribution to that of their ALP star cores.
We consider...
The effective number of neutrinos, $N_{\mathrm{eff}}$, is an important parameter in standard hot big bang cosmology. In this work, we compute the dominant QED correction to the neutrino-electron interaction rate in the vicinity of neutrino decoupling in the early universe, and estimate its impact on $N_{\mathrm{eff}}$. We find that the correction to the interaction rate is at the sub-percent...
Polarisation studies over a significant redshift range are an important tool in understanding the evolution of cosmic magnetic fields and unrevealing their origin. As most depolarisation effects are highly wavelength depended, the combination of different surveys allows us to distinguish between different effects.
We use the synergy of LOFAR and Apertif; starting with sources known to show...
The growth of small-scale structures in dark matter is hard to
access with numerical, observational and conventional analytical methods.
However, information about initial conditions and the properties of dark matter are supposed to leave their footprints in these small scale structures.
I present analytical work, where we show with Kinetic Field Theory (KFT) that the dark matter density...
On the largest scales the Universe appears to be almost perfectly
homogeneous and isotropic, adhering to the cosmological principle. On smaller scales inhomogeneities and anisotropies become increasingly prominent, reflecting the origin, emergence and formation of structure in the Universe and its cosmological impact. Also, a range of tensions between various cosmological observations may...
We study leptogenesis from the decays of sterile (right-handed) neutrinos produced from bubble collisions at a first order phase transition. We explore the new parameter space opened up by this new mechanism, making comparisons with other existing leptogenesis scenarios (in particular involving bubbles), and find that bubble collisions enable leptogenesis with RHNs at the natural mass scale...
The microphysics of dark matter remains a mystery, with current data only setting upper bounds on interaction cross sections, or lower bounds on the mass in the case of a thermal relic. Going to higher redshift and smaller scales will let us improve these bounds, but more importantly, may allow us to distinguish between models with otherwise similar signals. In particular, I will present a...
The dynamics of the early universe is influenced by interesting quantum effects like the formation of scalar and tensor perturbations during inflation. I will discuss how such processes can be investigated more closely with quantum simulation. This uses modern quantum technology like ultracold quantum gases in optical traps with time-dependent scattering length. I will also discuss further...
Discovering primordial parity violation would have profound implications for our understanding of early Universe physics and would greatly inform inflationary models. Tantalizing evidence of cosmic parity violation in the four-point statistics of galaxy clustering is currently inconclusive due to uncertainty in observational systematics and covariance estimation. The covariance is challenging...
The tight constraints on the $\mu$ type distortions in the CMB blackbody spectrum coming from the FIRAS observations can be used to set up the bounds on primordial curvature perturbations and thus on the Primordial Black Holes (PBHs). To do so, the conventional works assume the Gaussian initial conditions. However, it is well known that the enhancement in the primordial power spectrum needed...
In this talk, I will discuss the effect of very low cosmic string tensions on the associated stochastic gravitational wave background. I will show that the gravitational wave spectrum is qualitatively different from the one produced by cosmic strings with larger tensions. In fact, it exhibits a very distinct oscillatory feature with dips in the amplitude at multiples of the frequency of the...
Bayesian parameter inference is one of the key elements for model selection in cosmological research. However, the inference tools require a large number of calls to simulation codes which can lead to high and sometimes even infeasible computational costs. In this work we combine fast and differentiable emulators with active sampling to accelerate MCMC analyses of CMB physics by 1-2 magnitudes...
Structure formation is a central topic for cosmology. The density perturbation power spectrum, i.e., Gaussian information, has already been constrained by data, but not much is known for the density perturbation bispectrum, the first cumulant beyond pure Gauss. For large-scales, conventional analytical methods based on hydrodynamic approximations provide accurate results, but for smaller...
The integrated 3-point correlation function (i3PCF) is a higher-order statistic (beyond traditional 2-point methods) that can be measured directly from weak lensing cosmic shear data by correlating local 1-point aperture mass statistics with local shear 2-point correlation functions (2PCF) measured within well-defined patches across a galaxy survey footprint. We have developed an accurate...
A framework to describe long-distance dynamics of an electroweak phase transition is offered by fluctuating hydrodynamics. In this setup the neutral Higgs component can be modelled to evolve according to a Langevin equation. In this talk we report on recent results for the thermal Higgs interaction rate close to a first order EW phase transition, which appears as a coefficient in a Langevin...
Over a combination of large areas as well as smaller, deep fields observations, the LOFAR Two-metre sky survey (LoTSS, Tasse+ 2021, Sabater+ 2021, Shimwell+ 2022) is producing detailed knowledge of sources at low radio frequencies (144 MHz), across large periods of cosmic time. The combined area of these surveys as well as their depth and ancillary information provides exciting opportunities...
A cosmological first-order phase transition during the evolution of the Universe can give rise to intriguing phenomena like electroweak baryogenesis or the generation of a stochastic background of gravitational waves through bubble nucleation. This study aims at exploring critical aspects of the bubble wall velocity, which significantly impact these phenomena. Recent investigations have...
