Cosmic void abundance in a spherical boundary model

Cosmic voids are large and underdense structures that fill up most of the volume of the universe, and are potentially a powerful probe of dark energy and modified gravity. By developing a void model that accounts for both the boundary and interior evolution, we discover that shell-crossing is an inaccurate description for void formation, correcting a misconception that has accompanied void studies for decades. In addition, the model directly incorporate selection criterion acting on the significance of voids, making it possible to relate the theoretical prediction to voids identified in observations/simulations. The new model is also compatible with the existence of the largest voids observed in galaxy surveys, which is forbidden in the previous widely used model.