© The London Mathematical Society
Herman Rings and Arnold Disks
Laboratoire Emile Picard, Université Paul Sabatier 118 route de Narbonne, 31062 Toulouse Cedex, France buff{at}picard.ups-tlse.fr
Departimento de Matematica Aplicada i Analisi, Universitat de Barcelona Gran via 585, 08007 Barcelona, Spain e-mail: fagella{at}maia.ub.es
Department of Mathematics, Montana State University PO Box 172400, Bozeman, MT 59717-2400, USA geyer{at}math.montana.edu
Department of Mathematics, Technical University of Denmark Matematiktorvet, Building 303, DK-2800 Kgs. Lyngby, Denmark christian.henriksen{at}mat.dtu.dk
Received 19 May 2004. Revision received 8 March 2005.
For (
,a)
C* x C, let f
,a be the rational map defined by f
,a(z) =
z2 (az+1)/(z+a). If 
R/Z is a Brjuno number, we let D
be the set of parameters (
,a) such that f
,a has a fixed Herman ring with rotation number
(we consider that (e2i
,0)
D
). Results obtained by McMullen and Sullivan imply that, for any g
D
, the connected component of D
(C* x (C/{0,1})) that contains g is isomorphic to a punctured disk.
We show that there is a holomorphic injection F
:D
D
such that F
(0) = (e2i
,0) and
, where r
is the conformal radius at 0 of the Siegel disk of the quadratic polynomial z
e2i
z(1+z).
As a consequence, we show that for a
(0,1/3), if fl,a has a fixed Herman ring with rotation number
and if ma is the modulus of the Herman ring, then, as a
0, we have e
ma=(r
/a) + O(a).
We finally explain how to adapt the results to the complex standard family z
e(a/2)(z-1/z).