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# Hyperbolicity and determinantal representations for higher-codimensional subvarieties

## Hot Topics: Kadison-Singer, Interlacing Polynomials, and Beyond March 09, 2015 - March 13, 2015

March 13, 2015 (03:30 PM PDT - 04:30 PM PDT)
Speaker(s): Victor Vinnikov (Ben Gurion University of the Negev)
Location: MSRI: Simons Auditorium
Tags/Keywords
• algebraic geometry

• Grassmannians

• Schubert cells

• combinatorial geometry

• Lax conjecture

• Kadison-Singer theorem

• Marcus-Spielman-Srivastava theorem

Primary Mathematics Subject Classification
Secondary Mathematics Subject Classification No Secondary AMS MSC
Video

#### 14194

Abstract

Let $X$ be a real subvariety of codimension $\ell$ in the complex projective space ${\mathbb P}^d$.
We say that $X$ is hyperbolic with respect to a real linear space $V$ of dimension $\ell-1$
if $X \cap V = \emptyset$ and $X$ intersects any real linear space of dimension $\ell$ through $V$
in real points only.
Alternatively, if $Y$ is the associated hypersurface of $X$ in the Grassmanian ${\mathbb G}(\ell-1,d)$
of $\ell-1$-dimensional linear spaces in ${! \mathbb P}^d$, then $V \not\in Y$ and $Y$ intersects any
real one-dimensional Schubert cycle through $V$ in real points only.

In the case $\ell=1$, i.e., $X$ is a hypersurface, this simply means that $X$ is the zero locus of a homogeneous
hyperbolic polynomial.

I will discuss hyperbolic subvarieties of a higher codimension, the analogues of hyperbolicity cones,
and a class of definite Hermitian determinantal representations that witnesses hyperbolicity.
It turns out that the analogue of the Lax conjecture holds --- any real curve in ${\mathbb P}^d$ that is hyperbolic
with respect to some $d-2$-dimensional linear space admits a definite Hermitian, or even real symmetric, determinantal representation.

Supplements
 Gurvits.Abstract 130 KB application/pdf Download
Video/Audio Files

#### 14194

 H.264 Video 14194.mp4 355 MB video/mp4 rtsp://videos.msri.org/data/000/023/119/original/14194.mp4 Download
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