Seminario teoría de grupos UAM-ICMAT 
 
María Pe Pereira 
(Universidad Complutense de Madrid) 
 
"Curve monodromy, quasi-periodic diffeomorphism and tête-à-tête graphs" 
Lunes 29/1/2018, 14:30, Aula 520, UAM 
 
Resumen: I will report about a joint work with J. Fernández de Bobadilla and P. Portilla 
which is also part of the PhD Thesis of the third author. 
Norbert A’Campo defined tête-à-tête graphs and showed that if the monodromy 
of a plane branch is periodic then it is a generalized Dehn twist along a tête-à-tête 
graph. 
We see that any periodic orientable diffeomorphisms of surfaces with non-empty 
boundary is induced by a generalized Dehn twist along a tête-à-tête graph. In this 
sense we generalize a result by Christian Graf. 
We also study the more general case of quasi-periodic homeomorphisms of sur- 
faces with boundary. Monodromy of an arbitrary plane curve is an example of 
them. To codify this type of homeomorphisms we introduce the notion of mixed 
tête-à-tête graph, improving a former version by A’Campo. We show that any 
quasi periodic homeomorphism, subject to certain combinatorial restriction, can 
be modelized with a mixed tête-à-tête graph. These restrictions are accomplished 
by the monodromy of unibranch plane curves. 
In this talk I will introduce the monodromy of plane branches, the quasi-periodic 
automorpisms, the tête-à-tête graphs and the mentioned characterizations.