Time: 2pm

Place: 2N36

# Events

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

*The purpose of this meeting is to bring together experts working at the interface of cosmology, string theory and particle physics for a few days of informal talks and exchanges of ideas. The schedule will allow ample time for impromptu discussions and collaborations. Each talk includes ~60mins worth of presentation and interruptions, plus 30mins worth of questions/discussions.*

**Place:** DRL 4N12

**Thursday, December 3:**

**10:30-11am:** Welcome coffee

**11am -12:30pm:** Juan Maldacena (IAS)

Title: "Quantum mechanics and Cosmology: Entanglement and interference effects”

**12:30pm-2pm:** Catered lunch (in 4N12)

**2-3:30pm:** Erik Verlinde (Amsterdam)

Title: “Emergent Gravity and the Dark Universe”

**3:30-4pm**: Coffee

**4-5:30pm:** Liam McAllister (Cornell)

Title: "Planckian Axions and Quantum Gravity"

**6:30pm:** Conference dinner at Han Dynasty

**Friday, December 4:**

**10:30-11am:** Welcome coffee

**11am -12:30pm:** Gregory Gabadadze (NYU)

Title: "Metamorphosis of the Cosmological Constant"

**12:30pm-2pm:** Catered lunch (in 4N12)

**2-3:30pm:** Savdeep Sethi (Chicago)

Title: “Bounding the String Landscape”

**3:30-4pm**: Coffee

**4-5:30pm:** Mariangela Lisanti (Princeton)

Title: "Searching for Signals of Dark Matter in the Inner Galaxy"

**End of the workshop**

Time: 2pm

Place: 2N36

Title: F-Theorem and the Epsilon Expansion

Abstract:

I will discuss the dimensional continuation of the sphere free energy in conformal field theory. This provides an interpolation between a-anomaly coefficients in even dimensions and F-values in odd dimensions, and smoothly connects the existing a-theorems and F-theorems. As concrete applications, I will explain how to use the Wilson-Fisher epsilon expansion to find the value of F for the 3d Ising CFT and related O(N) symmetric models, and for the conformal phase of the 3d QED with N_f massless fermions.

Time: 2pm

Place: 2N36

Title: Witten Diagrams Revisited: The AdS Geometry of Conformal Blocks

Time: 2pm

Place: 2N36

Title: Matter Transitions and Heterotic/F-theory duality

Abstract:

We explore a novel type of transition in certain 6D and 4D Heterotic/F-theory dual pairs, in which the matter content of the theory changes while the gauge group and other parts of the spectrum remain invariant. Such transitions can occur, for example, for SU(6), SU(7), and SU(8) gauge groups, where matter in a three-index antisymmetric

representation is exchanged in the transition for matter in a

two-index antisymmetric representation. These matter transitions are

realized by passing through superconformal theories at the transition

point. We also briefly describe some other situations,

with groups such as Sp(3), SO(12), and SU(3), where analogous matter

transitions can occur between different representations. For SU(3),

in particular, we find a matter transition between adjoint matter and

matter in the symmetric representation, giving an explicit Weierstrass

model for the F-theory description of the symmetric representation

that complements other recent analogous constructions.

Time: 2pm

Place: 2N36

Title: The Future is Stochastic

Abstract: Precision calculations in de Sitter space (such as of inflationary predictions for primordial fluctuations) are often plagued by infrared problems and issues of secular time dependence. Similar issues about the breakdown of perturbation theory also arise for information loss in black holes. This talk briefly summarizes what is known about when these problems do (and do not) arise, and how similar problems are dealt with in other areas (like optics). It is argued that Master-Equation techniques used there also apply to cosmology (and possibly black holes) and can tell us how to extract reliably late-time predictions. Applied to inflation they lead to Starobinsky's stochastic methods (plus potential corrections). This is argued to provide an explanation for why stochastic inflation seems to resum IR effects in simple examples, and allows these tools to be generalized to other systems. I mention in passing the relevance of these tools to the problem of Schrodinger's Cosmologist! : how primordial fluctuations decohere sometime between their production during inflation and their observation early in the present Big Bang Epoch.

Time: 2pm

Place: 2N36

Title: "Effective string theory for vortex lines in fluids and superfluids"

Time: 2pm

Place: 2N36

Title: “Thriving from the vacuum”

Abstract: Theories of modified gravity in the infrared usually come hand in hand with additional degrees of freedom which couple to matter at gravitational strength and carry a low strong-coupling scale. By including non-trivial effects from the vacuum I will show how the strong-coupling scale can be raised while keeping the theory fundamentally Lorentz-invariant. This can lead to new features and may alleviate the need for a screening mechanism.

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