The GT seminar meets on Fridays
in Math 520, at 2 PM.

Organizer:
Walter Neumann.

Other
area seminars. Our e-mail
list. Archive of previous semesters

Date | Speaker | Title |
---|---|---|

Friday Sept 9 | Organizational meeting | 2pm Room 520 |

September 16 | Hung C Tran (UGA) | Geometric embedding properties of Bestvina-Brady subgroups |

September 22 THURSDAY 2:40pm! | BoGwang Jeon | The Unlikely Intersection Theory and the Cosmetic Surgery Conjecture |

September 30 | No GT seminar | |

October 7 | Henry Segerman, Oklahoma State | Connectivity of triangulations without degree one edges under 2-3 and 3-2 moves |

October 14 | Mehdi Yazdi (Princeton) | On Thurston's Euler class one conjecture |

October 21 | David Hume, MSRI and Oxford | TBA |

November 4 | No GT seminar | |

November 11 | Tim Susse, U Nebraska | TBA |

November 18 | Daniel Groves, UIC | TBA |

November 25 | No Seminar | Happy Thanksgiving |

December 2 | David Futer, Temple U | TBA |

December 9 | Hongbin Sun, UCB | TBA |

Spring Semester | Ahn Tran, UT Dallas |

## Abstracts

**Hung C Tran**, UGA

September 16

**Title**: Geometric embedding properties of Bestvina-Brady subgroups

We compute the subgroup distortion of Bestvina-Brady subgroups. We use
the result of this computation to show that for each integer $n\geq
3$, there is a free subgroup of rank $n$ of some right-angled Artin
group whose inclusion is not a quasi-isometric embedding. This
corollary answers the question of Carr about the minimum rank $n$ such
that some right-angled Artin group has a free subgroup of rank $n$
whose inclusion is not a quasi-isometric embedding. It is
also well-known that a right-angled Artin group $A_\Gamma$ is the
fundamental group of a graph manifold whenever the defining graph
$\Gamma$ is a tree. We show that the Bestvina-Brady subgroup
$H_\Gamma$ in this case is a horizontal surface subgroup.

**BoGwang Jeon**, Columbia

THURSDAY September 22, 2:40pm

**Title**: The Unlikely Intersection Theory and the Cosmetic Surgery Conjecture

The main result of this talk is the following theorem:
Let M be a 1-cusped hyperbolic 3-manifold whose cusp shape is not quadratic, and M(p/q) be its p/q-Dehn filled
manifold. If p/q is not equal to p'/q' for sufficiently large |p|+|q| and |p'|+|q'|, there is no orientation
preserving isometry between M(p/q) and M(p'/q').
This resolves the conjecture of C. Gordon, which is so called the Cosmetic Surgery Conjecture, for hyperbolic
3-manifolds belonging to the aforementioned class except for possibly finitely many exceptions for each manifold. We
also consider its generalization to more cusped manifolds. The key ingredient of the proof is the unlikely
intersection theory developed by E. Bombieri, D. Masser, and U. Zannier.

**Henry Segerman**, Oklahoma State U

October 7

**Title**: Connectivity of triangulations without degree one edges under 2-3 and 3-2
moves.

Matveev and Piergallini independently showed that, with a small number of known
exceptions, any triangulation of a three-manifold can be transformed into any
other triangulation of the same three-manifold with the same number of vertices,
via a sequence of 2-3 and 3-2 moves. We can interpret this as showing that the
"2-3 Pachner graph" of such triangulations is connected. This is useful for
defining invariants of a three-manifold based on the triangulation. However, there
are "would-be" invariants that can only be defined on triangulations with certain
properties, for example 1-efficiency or having only essential edges.
Unfortunately, there are no similar connectivity results for the subgraphs of the
Pachner graph with such properties. In this talk, I will describe a new
connectivity result for a weaker property than either 1-efficiency or essential
edges: that of a triangulation having no degree one edges.

**Mehdi Yazdi**, Princeton

October 14

**Title**: On Thurston's Euler class one conjecture

In 1976, Thurston proved that taut foliations on closed hyperbolic 3â€“manifolds have Euler class of norm at most one, and conjectured that, conversely, any
Euler class with norm equal to one is Euler class of a taut foliation. I construct counterexamples to this conjecture and suggest an alternative conjecture.

**David Hume**, MSRI and Oxford

October 21

**Title**: To be announced

Abstract

**Time Susse**, University of Nebraska

November 11

**Title**: To be announced

Abstract

**Daniel Groves**, University of Illinois at Chicago

November 18

**Title**: To be announced

Abstract

**David Futer**, Temple University

December 2

**Title**: To be announced

Abstract

**Hongbin Sun**, UCB

December 9

**Title**: To be announced

Abstract

**Ahn Tran**, UT Dallas

Spring Semester

**Title**:

/p>

# Other relevant information.

## Previous semesters:

Spring 2016, Fall 2015, Spring 2015, Fall 2014, Spring 2014, Fall 2013, Spring 2013, Fall 2012, Spring 2012, Fall 2011, 2010/11, Spring 2010, Fall 2009, Spring 2009, Fall 2008, Spring 2008, Fall 2007, Spring 2007, Fall 2006.## Other area seminars.

- Columbia Symplectic Geometry/Gauge Theory Seminar
- All Columbia Math Dept Seminars
- CUNY Geometry and Topology Seminar
- CUNY Complex Analysis & Dynamics Seminar
- CUNY Magnus Seminar
- Princeton Topology Seminar.