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UID:news675@dmi.unibas.ch
DTSTAMP;TZID=Europe/Zurich:20190212T225615
DTSTART;TZID=Europe/Zurich:20160310T110000
SUMMARY:Seminar Algebra and Geometry: Alexander Perepechko (Moscow)
DESCRIPTION:It is well known that A1-fibrations are of particular interest 
 in the  study of automorphism groups of affine surfaces. That is\, descrip
 tion of  automorphism groups is based on subgroups preserving A1-fibration
 s\,  except for surfaces without such fibrations. We provide a method to  
 directly compute these subgroups in terms of a boundary divisor of an  SNC
 -completion. We also use the concepts of arc spaces and formal  neighbourh
 oods. This allows us to establish the following structure of a  subgroup p
 reserving a A1-fibration. Up to a finite index\, it is a  semidirect produ
 ct of an abelian unipotent subgroup acting by  translations on fibers and 
 of a finite-dimensional subgroup that fixes a  certain section.In particul
 ar\, we derive an example of a surface with infinite discrete automorphism
  group.
X-ALT-DESC: It is well known that A1-fibrations are of particular interest 
 in the  study of automorphism groups of affine surfaces. That is\, descrip
 tion of  automorphism groups is based on subgroups preserving A1-fibration
 s\,  except for surfaces without such fibrations. We provide a method to  
 directly compute these subgroups in terms of a boundary divisor of an  SNC
 -completion. We also use the concepts of arc spaces and formal  neighbourh
 oods. This allows us to establish the following structure of a  subgroup p
 reserving a A1-fibration. Up to a finite index\, it is a  semidirect produ
 ct of an abelian unipotent subgroup acting by  translations on fibers and 
 of a finite-dimensional subgroup that fixes a  certain section.<br />In pa
 rticular\, we derive an example of a surface with infinite discrete automo
 rphism group.
DTEND;TZID=Europe/Zurich:20160310T120000
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