### Nico Hamaus

(USM/LMU Munich)

*Void Dynamics - Constraints on Cosmology and Gravity*

The universe is mostly composed of large and relatively empty domains known as cosmic voids, whereas its matter content is predominantly distributed along their boundaries. The remaining material inside them, either dark or luminous matter, is attracted to these boundaries and causes voids to expand faster and to grow emptier over time. Using the distribution of galaxies centered on voids identified in the SDSS and adopting minimal assumptions on their statistical motion, we constrain the average matter content in the universe and the linear growth rate of structure at z = 0.57. These measurements are robust to a battery of consistency tests. They surpass (and are complementary to) existing constraints by unlocking cosmological information on smaller scales through an accurate model of nonlinear clustering and dynamics in void environments. As such, our analysis furnishes a powerful probe of deviations from GR in the low density regime which has largely remained untested so far.