Dr. Sai Chaitanya

The standard cosmological model explains the growth of cosmic structure through tiny primordial fluctuations that grow under gravity. These are typically assumed to be adiabatic, where all components (matter, radiation etc.) of the universe fluctuate together. However, an alternative possibility, isocurvature fluctuations, allows different components to vary relative to one another. Although strongly constrained on large cosmological scales (via CMB) and often treated as a nuisance parameter, isocurvature can act as an additional degree of freedom that affects cosmological inference. In this talk I will present an isocurvature-forward program: we study generation of dark matter isocurvature with scale-dependent (often blue-tilted) spectra, construct data-ready templates, and quantify their impact within standard analyses. As an example, we shall discuss a new generation mechanism motivated by hyperbolic internal geometry. I will then discuss how even a small isocurvature component can modify the interpretation of cosmological data, for example existing bounds on thermal warm dark matter mass can be relaxed by a factor of 10. I will briefly comment on similar implications for ultra-light axion dark matter, early-time JWST observations and measurements of neutrino mass. Overall, this highlights how allowing an additional isocurvature degree of freedom in the early universe can reshape our interpretation of cosmological data.