Kavli Affiliate: Lina Necib
| First 5 Authors: Dylan Folsom, Carlos Blanco, Mariangela Lisanti, Lina Necib, Mark Vogelsberger
| Summary:
The sensitivity of direct detection experiments depends on the phase-space
distribution of dark matter near the Sun, which can be modeled theoretically
using cosmological hydrodynamical simulations of Milky Way-like galaxies.
However, capturing the halo-to-halo variation in the local dark matter speeds
— a necessary step for quantifying the astrophysical uncertainties that feed
into experimental results — requires a sufficiently large sample of simulated
galaxies, which has been a challenge. In this work, we quantify this variation
with nearly one hundred Milky Way-like galaxies from the IllustrisTNG50
simulation, the largest sample to date at this resolution. Moreover, we
introduce a novel phase-space scaling procedure that endows every system with a
reference frame that accurately reproduces the local standard-of-rest speed of
our Galaxy, providing a principled way of extrapolating the simulation results
to real-world data. The predicted speed distributions are consistent with the
Standard Halo Model, a Maxwell-Boltzmann distribution peaked at the local
circular speed and truncated at the escape speed. The dark matter-nucleon cross
section limits placed by these speed distributions vary by ~60% about the
median. This places the 1-sigma astrophysical uncertainty at or below the level
of the systematic uncertainty of current ton-scale detectors, even down to the
energy threshold. The predicted uncertainty remains unchanged when
sub-selecting on those TNG galaxies with merger histories similar to the Milky
Way. Tabulated speed distributions, as well as Maxwell-Boltzmann fits, are
provided for use in computing direct detection bounds or projecting
sensitivities.
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