First author: Marika Asgari
We present a pedagogical review of the halo model, a flexible framework that can describe the distribution of matter and its tracers on non-linear scales for both conventional and exotic cosmological models. We start with the premise that the complex structure of the cosmic web can be described by the sum of its individual components: dark matter, gas, and galaxies, all distributed within spherical haloes with a range of masses.
First author: Obinna Umeh
There is no source for cosmic vorticity within the cold dark matter cosmology. However, vorticity has been observed in the universe, especially on the scales of clusters, filaments, galaxies, etc. Recent results from high-resolution general relativistic N-body simulation show that the vorticity power spectrum dominates over the power spectrum of the divergence of the peculiar velocity field on scales where the effective field theory of large-scale structure breaks down.
First author: Shahnawaz A. Adil
Hubble constant $H_0$ and weighted amplitude of matter fluctuations $S_8$ determinations are biased to higher and lower values, respectively, in the late Universe with respect to early Universe values inferred by the Planck collaboration within flat $\Lambda$CDM cosmology. If these anomalies are physical, i.e. not due to systematics, they naively suggest that $H_0$ decreases and $S_8$ increases with effective redshift. Here, on the assumption that matter density parameter today $\Omega_{m}$ is a constant, we show that $S_8$ determinations from $f \sigma_8(z)$ constraints increase with effective redshift, thereby providing corroborating support for an $S_8$ discrepancy that is physical in origin.
First author: Mayukh R. Gangopadhyay
We employ a machine learning (ML) algorithm to analyze cosmological background data and the linear red-shift space distortion (RSD) data in a model-independent way, with specific focus on the Hubble expansion rate and the growth of large-scale structure. We find strong evidence that the natural enhancement in the Hubble parameter at low redshifts is due to the underlying phantom nature of dark energy, rather than low matter density.
First author: Amjad Ashoorioon
We study varying forms of viscous dark matter and try to address the intriguing tensions of the standard model of cosmology with the recent cosmological data, including the Hubble and $S_8$ tensions. We note that assuming the dark matter viscosity depends on the Hubble parameter, dark matter density, or both, one can improve the statistics. Although the models tend to aggravate the Hubble tension a bit, they tend to reduce the $S_8$ tension, even in comparison with the constant viscosity case.
First author: Bartolomeo Fiorini
One of the main objectives of stage IV galaxy surveys is to constrain gravity on cosmological scales. To this end, it is crucial to make accurate theoretical predictions in the nonlinear regime of structure formation in order to maximise the scientific return. This is possible at a relatively low computational cost thanks to COLA simulations, an approximate and much faster alternative to full $N$-body simulations. In this thesis, we focus on two modified gravity theories, $f(R)$ and nDGP, and present an analysis of how COLA simulations can be combined with empirical models for the galaxy-halo connection to produce realistic mock galaxy catalogues in modified gravity.
First author: Giovanni Aricò
We present the first analysis of cosmic shear measured in DES Y3 that employs the entire range of angular scales in the data. To achieve this, we build upon recent advances in the theoretical modelling of weak lensing provided by a combination of $N$-body simulations, physical models of baryonic processes, and neural networks. Specifically, we use BACCOemu to model the linear and nonlinear matter power spectrum including baryonic physics, allowing us to robustly exploit scales smaller than those used by the DES Collaboration.
First author: Ashok K. Singal
In recent years, large radio surveys of Active Galactic Nuclei (AGNs), comprising millions of sources, have become available where one could investigate dipole asymmetries, assumedly arising due to a peculiar motion of the Solar system. Investigations of such dipoles have yielded in past much larger amplitudes (a factor of 2 to 20) than that of the CMB dipole, though their inferred directions in sky seem to lie, within statistical uncertainties, close to the CMB dipole.
First author: Yan-Heng Yu
Primordial gravitational waves are one of the most important predictions of inflation theory, and measurements of their imprints on the cosmic microwave background are actively pursued, but not yet succeed until now. Here we point out that measurements of primordial gravitational waves could be conceivable through searching for a signal of second-order tensor perturbations, which were produced due to nonlinear couplings between the linear tensor and scalar perturbations in the early universe.
First author: Hao Yu
In this work, we study the applications of entropy bounds in two toy cosmological models with particle production (annihilation), i.e., radiation-dominated universe and dust-dominated universe. Since entropy bounds are involved in the volume of the thermodynamc system, we need to specify the thermodynamc system in the universe in advance. We consider the co-moving volume and the volume covered by the particle horizon as the target thermodynamic system.
