A Cosmic Voyage: From the Early to the Late-Time Universe with N-point Functions

• Applicant: Jiamin Hou, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 554476934

The large-scale structure of the Universe carries information about its origin, evolution, and fundamental symmetries. Galaxy surveys such as Dark Energy Spectroscopic Instrument (DESI), Euclid mission, and Roman Space Telescope will provide datasets with unprecedented precision and volume. In this Emmy Noether project, I aim to maximize the constraining power of the galaxy surveys and gain deeper insights into fundamental cosmological questions using galaxy N-point functions. This project will pursue two main objectives: (A) Testing the ΛCDM model in the late Universe and (B) Probing the early Universe and inflation. In (A.1), my group will constrain ΛCDM model by extending traditional 2-point statistics analyses to include higher-order statistics. We will advance the current perturbation modelling of the 3-point correlation function (3PCF) and the analytic covariance matrix calculation. We will conduct a joint analysis of the 2- and 3PCF and place constraints on cosmological parameters using DESI data. In (A.2), we will develop machine-learning-based methods to extract cosmological insights from the 2-, and 3PCF. We will construct a suite of simulations to create synthetic galaxy catalogs tailored to the DESI survey. We will apply simulation-based inference to the data to infer cosmological parameters. In (B.1), my group will investigate parity violation on cosmological scales. Parity symmetry states that physical laws should remain unchanged under spatial inversion. Violation of parity symmetry could indicate new physics during the early Universe. We will apply a model-independent search of parity violation on the DESI and Euclid data using the 4-point correlation function (4PCF) and the parity-odd power spectra. We will search for imprints of Baryon Acoustic Oscillation feature on the parity-odd 4PCF (BAO), which would strongly indicate an inflationary origin of the parity signal. In addition, we will develop a parametrized approach to quantify parity violation. In (B.2), we will explore primordial non-Gaussianities in the inflationary epoch. Detecting primordial non-Gaussianities can indicate deviations from the simplest inflationary model. We will advance a new, efficient estimator, the galaxy skew spectra by improving its systematic modelling. We will apply a joint constraint of the power spectrum and the skew spectra to the DESI quasar data to constrain the primordial non-Gaussian signal.

• DFG Programme: Emmy Noether Independent Junior Research Groups