Over the course of my Bachelor’s, Master’s and Ph.D. I have had the opportunity to work on several short and long-term research projects on various topics in Physics through internships, research assistantships or thesis projects (please refer to my CV for details). I have worked mainly on analytical and computational projects in the fields of laser optics, planetary and space science, geosciences, x-ray reflectometry, and of course, astrophysics. Please refer to my Google Scholar profile for a full list of publications that I am involved in.

Here, I present some of my current research projects in weak lensing cosmology and their associated publications:

The integrated 3-point correlation functions

Integrated 3PCFs image

In this series of works we have developed a set of practical higher-order statistics called the integrated 3-point correlation functions which can be easily measured from galaxy imaging data alongside conventional 2-point statistical methods and has the potential to put tighter constraints on cosmological, galaxy bias as well as baryonic feedback parameters (see image above; courtesy: Halder et al. 2023). This statistic measures the position-dependent 2-point correlation functions of a field (e.g. 3 x 2-point galaxy-lensing correlations) inside a local 2D patch and correlates them with the 1-point average shear or galaxy density within the same patch. This correlation admits a very well-defined physical interpretation as the modulation of the small-scale 2PCFs by long-wavelength features of the field and in turn is sensitive to the higher-order squeezed bispectrum configurations (3-point function) of the field. Using semi-analytical methods based on perturbation theory for accurately modelling this statistic along with the inclusion of galaxy bias, intrinsic alignments, baryonic feedback effects as well as other nuisance parameters, we have extensively validated our models against N-body simulations and with state-of-the art machine learning neural networks developed fast inference pipelines for their application to galaxy survey data (which we are currently undertaking). We are also extending this to a simulation based inference framework.

Halder, Friedrich, Seitz, Varga (2021)
The integrated 3-point correlation function of cosmic shear
arXiv:2102.10177   MNRAS

Halder, Barreira (2022)
Response approach to the integrated shear 3-point correlation function: the impact of baryonic effects on small scales
arXiv:2201.05607   MNRAS

Gong, Halder, Barreira, Seitz, Friedrich (2023)
Cosmology from the integrated shear 3-point correlation function: simulated likelihood analyses with machine-learning emulators
arXiv:2304.01187   JCAP

Halder, Gong, Barreira, Friedrich, Seitz, Gruen (2023)
Beyond 3x2-point cosmology: the integrated shear and galaxy 3-point correlation functions
arXiv:2305.17132   JCAP

Gebauer, Halder, Seitz, Anbajagane (2025)
𝚂𝙱𝚒𝟹𝙿𝙲𝙵: Simulation-based inference with the integrated 3PCF
arXiv:2510.13805  

 

The PDF of cosmic density fluctuations

Joint PDF image

Along with my collaborators I have worked on modelling the 1-point PDF of weak lensing convergence as well as the joint PDF of 3D matter and galaxy density fluctuations (see image on the left; courtesy: Friedrich et al. 2022). Conventional 2-point analysis tools would compress this joint PDF into just 3 quantities: the variance of matter density fluctuations, the variance of galaxy density fluctuations, and their cross-covariance. In this work, we developed a model for the full shape of the joint galaxy-matter PDF and extensively validated it using N-body simulations and mock Halo Occupation Distribution (HOD) galaxy catalogs. Studying the full shape of the 1-point PDF is another way to go beyond 2-point analyses and enables further insights into the nature of the cosmic web of structures, especially on cosmological as well as galaxy bias and stochasticity parameters. We are currently extending our modelling to perform a joint-PDF analysis using CMB lensing data from SPT and DESY3 lens galaxies.

Friedrich, Halder, Boyle, Uhlemann, Britt, Codis, Gruen, Hahn (2022)
The PDF perspective on the tracer-matter connection: Lagrangian bias and non-Poissonian shot noise
arXiv:2107.02300   MNRAS

Barthelemy, Halder, Gong, Uhlemann (2024)
Making the leap I: Modelling the reconstructed lensing convergence PDF from cosmic shear with survey masks and systematics
arXiv:2307.09468   JCAP

Friedrich, Castiblanco, Halder, Uhlemann (2025)
Bye binormal: analysing the joint PDF of galaxy density and weak lensing convergence
arXiv:2507.16957   MNRAS