The Gaussian Free Field, Conformal Field Theory, and Schramm-Loewner Evolution

Speaker: 

Tom Alberts

Institution: 

Cal Tech

Time: 

Tuesday, April 15, 2014 - 11:00am to 12:00pm

Location: 

RH 306

 I will review the recent mathematical approach to Conformal Field Theory proposed by my colleagues Nam-Gyu Kang and Nikolai Makarov. Their construction defines a certain class of algebraic operations on correlation functions of the Gaussian Free Field, and these operations can be used to give meaning to "vertex observables" and other well known objects in CFT. Using conformal transformation rules for the GFF these objects can be defined on any simply connected domain, and using Lie derivatives they can be analyzed when the domain evolves according to an infinitesimal flow. Using the flow of Loewner's differential equation produces a connection with the random curves of the Schramm-Loewner evolution, which I will describe along with some recent work in the case of multiple SLE curves.

Continuous Schrodinger Operators Associated to Aperiodic Subshifts

Speaker: 

Jake Fillman

Institution: 

Rice University

Time: 

Tuesday, April 29, 2014 - 1:00pm to 2:00pm

Host: 

Location: 

RH 340P

We will discuss continuum analogues of substitution Hamiltonians -- specifically, we will discuss Schrodinger operators on the real line whose potentials are described by an ergodic subshift over a finite alphabet and a rule that replaces symbols of the alphabet by compactly supported potential pieces. In this setting, the spectrum and the spectral type are almost surely constant, and one can identify the almost sure absolutely continuous spectrum with the Lebesgue essential closure of the set of energies with vanishing Lyapunov exponent. Using this and results of Damanik-Lenz and Klassert-Lenz-Stollmann, we can show that the spectrum is a Cantor set of zero Lebesgue measure if the subshift satisfies a precise combinatorial condition due to Boshernitzan. We will discuss the specific case of operators over the Fibonacci subshift in detail. This is joint work with D. Damanik and A. Gorodetski.

Self-genericity axioms IV

Speaker: 

Andres Forero

Institution: 

UCI

Time: 

Monday, April 14, 2014 - 4:00pm to 5:30pm

Host: 

Location: 

RH 440R

We continue the exposition on self-genericity axioms for ideals on P(Z) (Club Catch, Projective Catch and Stationary Catch). We have established some relations with forcing axioms and with the existence of certain regular forcing embeddings and projections, and also point out connections with Precipitousness. We give an rough overview of the method used for proving the existence of models with Woodin cardinals coming from these axioms, using the Core Model Theory. In this talk we explain one of the main technique used in the argument, namely the frequent extension argument.

Efficient operator factorizations for integral and differential equations

Speaker: 

Kenneth Ho

Institution: 

Stanford

Time: 

Monday, May 12, 2014 - 4:00pm to 5:00pm

Host: 

Location: 

RH306

Fast algorithms for elliptic PDEs are central to modern scientific computing. In this talk, we consider the efficient factorization of matrices associated with elliptic problems in both integral and differential form. A key starting point is the nested dissection multifrontal method for PDEs, which can be viewed as an LU factorization with a cost which grows with the spatial dimension. Our primary contributions are twofold: (1) a reformulation of previous fast direct solvers for integral equations as multifrontal-like generalized LU decompositions; and (2) a recursive dimensional reduction strategy to achieve optimal linear or nearly linear complexity in 2D and 3D. Our method is fully adaptive and can handle both boundary and volume problems, and furthermore reveals the close connection between structured dense matrices and sparse ones. This is joint work with Lexing Ying.

Self-genericity axioms III

Speaker: 

Andres Forero

Institution: 

UCI

Time: 

Monday, April 7, 2014 - 4:00pm to 5:30pm

Host: 

Location: 

RH 440R

We continue the exposition on self-genericity axioms for ideals on P(Z) (Club Catch, Projective Catch and Stationary Catch). We establish some relations with forcing axioms and with the existence of certain regular forcing embeddings, and also point out connections with Precipitousness. In particular we observe that if Projective Catch holds for an ideal, then that ideal is precipitous, and the converse holds for ideals that concentrate on countable sets. Finally we give an overview of the method used for proving the existence of models with Woodin cardinals coming from these axioms, using the Core Model Theory.

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