Even simpler than PxrDirectLighting, the default integrator places a virtual light at the camera (the "headlamp integrator"). No shadows or indirect lighting are evaluated. A good option when all is black - this integrator can help narrow down where a problem is occurring (for example, when the fault is in the lighting, particularly). Like PxrDirectLighting, it is not designed to produce "final-quality" images.
PxrDefault has no parameters