Eyebrow Frozen After Lower Facelift, How is that Possible?

  Yes.  This can happen, just as other doctors have discussed with you.  But I am writing just to re-emphasize that in all likelihood this will get better with time.  It is VERY early after your procedure and the odds are STRONGLY in your favor that the brow elevation will return to normal over the next 6 months or so.

Temporary weakness of the face following facelift surgery is possible.  Don't panic at this early point.  The nerves can be stretched or stunned during surgery -- making the weakness temporary rather than permanent.  Give it time.  I would not surgically intervene for a minimum of 6-12 months.  Most people experience a return of function within that timeframe.

As others have noted, you probably have an injury to the frontal branch of the facial nerve.  This branch crosses the zygomatic arch in  a relatively superficial plane.  This is very likely to recover within the next few weeks to months.  Your Surgeon is likely to suggest Botox/Dysport to the normal side until recovery is complete.