Time: 2pm

Place: 2N36

# Events

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 4N9

Title: Black Holes in Higher-Derivative Gravity and Einstein-Scalar Gravity

Title: Incidence geometry and resolutions of Weierstrass models

Time: 2pm

Place: 4N9

Abstract: In this talk, I will present several new results in the geometry of elliptic fibrations:

In the first part of the talk, I will introduce an incidence geometry described by a representation of a given Lie algebra and explain how it contains a natural poset structure reminiscent of a Gelfand-Tsetlin pattern. This poset provides a simple counting of flats and ensembles of the incidence geometry. For an elliptic fibration, it is understood as a counting of (partial) crepant resolutions. In a physical context, the counting is interpreted as a detailed enumeration of mixed Coulomb-Higgs branches of a five dimensional gauge theory with 8 supercharges. In particular, I will present a generating function counting the mixed Coulomb-Higgs phases of a U(n) gauge theories with matter in the fundamental and anti-fundamental representations.

In the second part of the talk, I will describe the network of crepant resolutions of a SU(2) SU(3) gauge theory modeled by an elliptic fibration. This provides a fully resolved description of models studied recently by Grassi-Halverson-Shanesonn-Taylor. I will explain how representation theory aspects are retrieved by a simple analysis of intersection numbers.

Time: 2pm

Place: 2N36

Title: *Resurgence in quantum field theory: handling the Devil's invention.*

Abstract:Renormalized perturbation theory for QFTs typically produces divergent series, because the series coefficients grow factorially at high order. It has been a historical challenge to understand the asymptotic nature of perturbative series, and it has been unclear in what precise sense semiclassical expansions capture the physics of even weakly-coupled QFTs. I will discuss a recent conjecture that the semiclassical expansion of path integrals for asymptotically free QFTs yields well-defined answers once the implications of resurgence theory are taken into account. Resurgence theory relates expansions around different saddle points of a path integral to each other, and has the striking practical implication that the high-order divergences of perturbative series encode precise information about the non-perturbative physics of a QFT. These ideas will be discussed in the context of several QCD-like theories, where systematic semiclassical control over the dynamics is achieved using adiabatic compactifications on a circle. Fitting a conjecture by ’t Hooft, understanding the origin of the notorious renormalon divergences of perturbation theory of asymptotically-free QFTs allows us to see the microscopic origin of the mass gap of these QFTs in the semiclassical domain.

Time: 2pm

Place: 2N36

Title: *New Ekpyrotic Quantum Cosmology*

Abstract: This talk will present recent results in the quest to construct a viable cosmological model devoid of singularities and infinities. More specifically: the no-boundary proposal provides a compelling theory for the initial conditions of our universe. In this context, the recently discovered ekpyrotic instantons describe the creation of a classically contacting universe out of nothing. One notable consequence is that the ekpyrotic attractor can explain how the universe became classical. However, up to now these instantons ended in a big crunch singularity. We show how this can be remedied by adding higher-derivative terms, allowing a smooth bounce into an expanding phase to take place. Remarkably, and although there is a non-trivial evolution during the bounce, the wavefunction of the universe is ``classical'' in a WKB sense just as much after the bounce as before. These new non-singular instantons can thus form the basis for a fully non-singular and calculable (ekpyrotic) history of the universe, from creation until now.

Time: 2pm

Place: 2N36

Time: 2pm

Place: 4N36

Title: Shifting around cosmology

Time: 2pm

Place: 2N36

Title: Logarithmic Corrections to Black Hole Entropy V2.0

Time: 2pm

Place: 2N36

Title: New ghost-free matter couplings and derivative interactions in massive gravity and multigravity

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Title: Living beyond the edge -- Higgs inflation, metastable vacua, and importance of radiative corrections

Time: 2pm

Place: 2N36

Abstract: The measurements of the Higgs mass and the top Yukawa coupling indicate that we live in a very special Universe, at the edge of the absolute stability of the electroweak vacuum. While fully stable situation allows for simple Higgs Inflationary setup, boundary and unstable situations turn out to be also very interesting, and also allow for inflation and successful Universe evolution. The key point is taking into account radiative corrections to the couplings at the energy scale $M_P/\xi$. Then, the inflationary potential can appear even for metastable SM vacuum, and the temperature potential at preheating prevents the Universe to settle in the high scale vacuum.

Title: Self-dual strings of six-dimensional SCFTs

Time: 2pm

Place: 2N36

Abstract: A distinctive feature of six-dimensional superconformal field theories is the existence of self-dual strings whose interactions encode the SCFTs' dynamics. A deep understanding of these SCFTs is still lacking, primarily due to a poor understanding of the properties of their strings, which are intrinsically strongly-coupled and can form bound states. I will explain how in several cases (including the theory of N+1 parallel M5 branes and the theory of a small E8 instanton) the strings can be described by suitable two dimensional quiver gauge theories. In particular, this makes it possible to compute the elliptic genera of these strings and of their bound states. For SCFTs for which a quiver gauge theory description is not available, I will explain how topological string theory still provides a way to study the corresponding strings.

Title: Cosmological billiards and hyperbolic Weyl groups

Time: 2pm

Place: 2N36

Abstract: The BKL analysis of spacelike singularities in cosmology gives evidence for a chaotic behavior of the four-dimensional spacetime metric near the singularity. This can be understood as a billiard motion in the Weyl chamber of a hyperbolic Kac-Moody algebra, which is an infinite-dimensional extension of the Lie algebra sl(2,R). Thus the billiard motion is controlled by the Weyl group of the hyperbolic algebra, which can be realized as the modular group PGL(2,Z). The billiard description can be applied also to 11-dimensional supergravity, the low energy limit of M-theory. In this case sl(2,R) is replaced by the exceptional Lie algebra E8, with the hyperbolic extension E10. I will in my talk explain how the modular realization of the Weyl group can be extended to the E10 case by generalizing the rational integers Z to an integer version of the eight-dimensional algebra of octonions.