Monday, February 19th, 2018

Tuesday, February 20th, 2018

Wednesday, February 21st, 2018

Physics Seminar: Austin Joyce

Time: 1:30 PM - 2:30 PM

Location: SCGP 313

Description: Title: Spin-2 scattering amplitudes and asymptotic superluminality

**Math Event:**Algebraic Geometry: Jian Xiao - Local positivity for curves

Time: 4:00 PM - 5:30 PM

Location: Math Tower P-131

Description: Title: Local positivity for curves

Speaker: Jian Xiao [Northwestern]

Abstract: One of the most important invariants measuring the local positivity of a nef line bundle is the local Seshadri function introduced by Demailly. We first give a brief introduction to this invariant. Then using the duality of positive cones, we show that applying the polar transform from convex analysis to local positivity invariants for divisors gives interesting and new local positivity invariants for curves. These new invariants, studied also independently by M. Fulger, have nice properties similar to those for divisors. In particular, this enables us to obtain a Seshadri type ampleness criterion for movable curves, and give a characterization of the divisorial components of the non-ample locus of a big class. (Joint work with N. McCleerey.)

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Speaker: Jian Xiao [Northwestern]

Abstract: One of the most important invariants measuring the local positivity of a nef line bundle is the local Seshadri function introduced by Demailly. We first give a brief introduction to this invariant. Then using the duality of positive cones, we show that applying the polar transform from convex analysis to local positivity invariants for divisors gives interesting and new local positivity invariants for curves. These new invariants, studied also independently by M. Fulger, have nice properties similar to those for divisors. In particular, this enables us to obtain a Seshadri type ampleness criterion for movable curves, and give a characterization of the divisorial components of the non-ample locus of a big class. (Joint work with N. McCleerey.)

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Thursday, February 22nd, 2018

**YITP Event:**Pheno seminar: Prateek Agrawal (Harvard). "The strong CP problem and UV instantons"

Time: 2:30 PM - 3:30 PM

Location:

Description: The absence of sizeable CP violation in the strong sector is a long standing puzzle. A class of solutions to this problem rely on a global U(1) symmetry that is anomalous with QCD. These solutions lead to robust low-energy predictions, for example a massless up quark or a light axion. I will present simple extensions to such solutions which can dramatically change these low-energy predictions. In our models, contributions from small instantons play a significant role in affecting the low-energy physics while preserving the solution to the strong CP problem.

**Math Event:**Math Colloquium: Nets Katz - Semialgebraic sets and the Kakeya Problem

Time: 4:00 PM - 5:00 PM

Location: Math Tower P-131

Description: Title: Semialgebraic sets and the Kakeya Problem

Speaker: Nets Katz [Caltech]

Abstract: In joint work with Keith Rogers, we study the connection between the Kakeya problem and the highlights of the theory of semialgebraic sets such as Tarski's projection theorem and Gromov's algebraic lemma.

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Speaker: Nets Katz [Caltech]

Abstract: In joint work with Keith Rogers, we study the connection between the Kakeya problem and the highlights of the theory of semialgebraic sets such as Tarski's projection theorem and Gromov's algebraic lemma.

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