Two seminars next week

[Cond.Matt. & Stat.Mech.Section]

JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR

 

Tuesday, 19 April    -    11:00 a.m.

 

 SISSA, Santorio Building,   Room 129 (1st Floor)

  

Iacopo MASTROMATTEO   ( SISSA )

 

"On the criticality of inferred models"

 

Abstract

Advanced inference techniques allow one to reconstruct the pattern of interaction from high dimensional data sets.  We focus here on the statistical properties of inferred models and argue that inference procedures are likely to yield models which are close to a phase transition.  On one side, we show that the reparameterization invariant metrics in the space of probability distributions of these models (the Fisher Information) is directly related to the model's susceptibility.  As a result, distinguishable models tend to accumulate close to critical points, where the susceptibility diverges in infinite systems.  On the other, this region is the one where the estimate of inferred parameters is most stable.  In order to illustrate these points, we discuss inference of interacting point processes with application to financial data and show that sensible choices of observation time-scales naturally yield models which are close to criticality.

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SEMINAR on    Disorder and strong electron correlations

 

Thursday, 21 April -  11:30 a.m.

 

Luigi Stasi Seminar Room,  Leonardo Building - first floor

 

Victor GURARIE     ( University of Colorado at Boulder )

 

"Bulk-boundary correspondence of  topological insulators"

 



Abstract

 

Topological insulators are noninteracting gapful fermionic systems which have gapless boundary excitations.  They are characterized by topological invariants.  The topological invariants can be written in many different ways, including in terms of the Green’s functions.  We show that the existence of the boundary states directly follows, and can be derived by simple manipulations, from the existence of the bulk topological invariant written in terms of the Green’s functions, for all types of topological insulators in all spatial dimensions.  At the same time, the same procedure explains why topological insulators, once the interactions are turned on, can lose their boundary states.