Suppose I parametrize complex plane by coordinates,z=x+iy, ˉz=x−iy
then the upper half plane,
H+ is given by
y>0. I am looking for chiral coordinate transformations,
f(z), such that
1. they map the boundary (y=0) to itself,f(z)=ˉf(ˉz) whenever z=ˉz .
2.
z+ˉz>0⇔f(z)+ˉf(ˉz)>0 .
Since there is a conformal map between H+ and unit disc (Poincare disc), D={w:|w|<1}, where the above conditions become:
1. the coordinate transformations map the boundary of D (|w|=1) to itself,g(w)ˉg(ˉw)=1 whenever wˉw=1 .
2.
wˉw<1⇔g(w)ˉg(ˉw)<1 .
The Schwarz-Pick Lemma seems to suggest that a general holomorphic transformation brings the boundary of the disc closer than 1 in the Poincaré metric (I am interested in AdS2 so I can equivalently say that the *new* boundary after the coordinate transformation is at a finite distance from any interior point),g′(w)ˉg′(ˉw)(1−g(w)ˉg(ˉw))2dwdˉw≤1(1−wˉw)2dwdˉw
and the equality folds only for Mobius transformations (which can be seen as isometries of AdS
2).
- Is it correct to deduce that there are no (non-trivial, of course not the Mobius transformation) holomorphic transformations that satisfy the conditions 1 and 2 above, or am I interpreting the Schwarz-Pick lemma incorrectly?
- If my interpretation of Schwarz-Pick lemma is correct and there are no *holomorphic* maps with the given constraints, then what are the less restrictive class of functions that obey the above constraints?