  In our solar system, Mars-sized protoplanets frequently collided with each
other during the last stage of terrestrial planet formation called the giant
impact stage. Giant impacts eject a large amount of material from the colliding
protoplanets into the terrestrial planet region, which may form debris disks
with observable infrared excesses. Indeed, tens of warm debris disks around
young solar-type stars have been observed. Here, we quantitatively estimate the
total mass of ejected materials during the giant impact stages. We found that
$\sim$0.4 times the Earth's mass is ejected in total throughout the giant
impact stage. Ejected materials are ground down by collisional cascade until
micron-sized grains are blown out by radiation pressure. The depletion
timescale of these ejected materials is determined primarily by the mass of the
largest body among them. We conducted high-resolution simulations of giant
impacts to accurately obtain the mass of the largest ejected body. We then
calculated the evolution of the debris disks produced by a series of giant
impacts and depleted by collisional cascades to obtain the infrared excess
evolution of the debris disks. We found that the infrared excess is almost
always higher than the stellar infrared flux throughout the giant impact stage
($\sim$100 Myr) and is sometimes $\sim$10 times higher immediately after a
giant impact. Therefore, giant impact stages would explain the infrared excess
from most observed warm debris disks. The observed fraction of stars with warm
debris disks indicates that the formation probability of our solar system-like
terrestrial planets is approximately 10%.
