@article{ganjoo_delos_2024, title={Simulations of gravitational heating due to early matter domination}, ISSN={["1475-7516"]}, DOI={10.1088/1475-7516/2024/04/015}, abstractNote={Abstract In cosmologies with an early matter-dominated era (EMDE) prior to Big Bang nucleosynthesis, the boosted growth of small-scale matter perturbations during the EMDE leads to microhalo formation long before halos would otherwise begin to form. For a range of models, halos can even form during the EMDE itself. These halos would dissipate at the end of the EMDE, releasing their gravitationally heated dark matter and thereby imprinting a free-streaming cut-off on the matter power spectrum. We conduct the first cosmological N-body simulations of the formation and evaporation of halos during and after an EMDE. We show that in these scenarios, the free-streaming cut-off after the EMDE can be predicted accurately from the linear matter power spectrum. Although the free streaming can erase much of the EMDE-driven boost to density perturbations, we use our findings to show that the (re-)formation of halos after the EMDE nevertheless proceeds before redshift ∼ 1000. Early-forming microhalos are a key observational signature of an EMDE, and our prescription for the impact of gravitational heating will allow studies of the observational status and prospects of EMDE scenarios to cover a much wider range of parameters.}, number={4}, journal={JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS}, author={Ganjoo, Himanish and Delos, M. Sten}, year={2024}, month={Apr} }
 @article{ganjoo_erickcek_lin_mack_2023, title={The effects of relativistic hidden sector particles on the matter power spectrum}, ISSN={["1475-7516"]}, DOI={10.1088/1475-7516/2023/01/004}, abstractNote={Abstract
               If dark matter resides in a hidden sector minimally coupled to the Standard Model, another particle within the hidden sector might dominate the energy density of the early universe temporarily, causing an early matter-dominated era (EMDE). During an EMDE, matter perturbations grow more rapidly than they would in a period of radiation domination, which leads to the formation of microhalos much earlier than they would form in standard cosmological scenarios. These microhalos boost the dark matter annihilation signal, but this boost is highly sensitive to the small-scale cut-off in the matter power spectrum. If the dark matter is sufficiently cold, this cut-off is set by the relativistic pressure of the particle that dominates the hidden sector. We determine the evolution of dark matter density perturbations in this scenario, obtaining the power spectrum at the end of the EMDE. We analyze the suppression of perturbations due to the relativistic pressure of the dominant hidden sector particle and express the cut-off scale and peak scale for which the matter power spectrum is maximized in terms of the properties of this particle. We also supply transfer functions to relate the matter power spectrum with a small-scale cut-off resulting from the pressure of the dominant hidden sector particle to the matter power spectrum that results from a cold hidden sector. These transfer functions facilitate the quick computation of accurate matter power spectra in EMDE scenarios with initially hot hidden sectors and allow us to identify which models significantly enhance the microhalo abundance.
}, number={1}, journal={JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS}, author={Ganjoo, Himanish and Erickcek, Adrienne L. and Lin, Weikang and Mack, Katherine J.}, year={2023}, month={Jan} }