Sommerfeld Theory Colloquium (ASC)

We will review the beginning of experimental and theoretical studies of moire systems and their evolution up to present. We will show how thousands of p orbitals in a moire unit cell of graphene can create single Heavy fermion at moire scale, and how the interaction between such fermions can lead to a perfect quantum simulator of an Anderson model. We will then present a catalogue of possible twistable materials and show how a huge variety of strongly interacting models can be realized in twisted homo and hetero twiste bilayers and multilayers of these materials.

Gravitational waves open a new window into our universe. In this colloquium we discuss particle theorists' perspective on calculations directly relevant for gravitational-wave emission from compact objects, which is rooted in quantum field theory and builds on the idea that gravitational interactions are mediated by spin-2 particles. After reviewing some of the remarkable advances in our understanding of scattering amplitudes and in our ability to evaluate them, we show how these ideas produce state of the art results in weak-field fully-relativistic calculations for gravitational wave observables, including for the astrophysical binary black hole inspiral problem.

The conjectured relation between higher spin theories on anti de-Sitter (AdS) spaces and weakly coupled conformal �field theories is reviewed. I shall then outline the evidence in favour of a concrete duality of this kind, relating a speci�c higher spin theory on AdS3

to a family of 2d minimal model CFTs. Finally, I shall explain how

this relation �ts into the framework of the familiar stringy AdS/CFT correspondence.

The problem of understanding how gravity fits together with other fundamental interactions of matter has been at the forefront of the- oretical research for many decades, leading to the rich framework of string theory and M-theory. In this framework, many fundamen- tal questions are being resolved, but many remain quite mysterious, suggesting that search for novel concepts may be well justified. I review the recent concept of multicritical gravity with Lifshitz-type anisotropic scaling, and its applications in areas ranging from par- ticle phenomenology beyond the standard model to non-relativistic

versions of the holographic AdS/CFT correspondence.

Lorentz non-invariance in quantum field theory is reconsidered as well as its interplay with gravity, string theory, diffeomorphism invariance and changing reference frames. We clarify these issues, and argue that Lorentz violation is always an environmental effect. We provide a holographic view of the breaking, and its connection to Horava- Lifshitz type of gravitational theories. We also argue that dissipation is always a signal of Lorentz violation. We provide calculations of dissipation at strong coupling.

The "Inverse Ising Problem" refers to finding the parameters (the Jij's and the hi's) in an Ising model given the first and second moments (the magnetizations mi and the correlation functions cij).

This is of considerable interest in machine learning and data analysis whenever the data set and the number of variables is large, but the values taken by the variables can be taken to be "high" and "low". The maximum entropy distributions with given first and second moments then has the Ising form where the hi's and Jij's are Lagrange parameters.

Several perturbative methods to solve the inverse Ising problem approximately have been proposed in the last few years. I will give a survey of the situation, with a focus on what we have know about the applicability of these methods to data such as gene expression and recordings from many neurons, where an underlying exact description is surely not of the Ising form.

This is work with John Hertz and Yasser Roudi (Frontiers Comp Neuroscience, 2009) and work in progress.

Metagenomics has revealed hundreds to thousands of microbial species

coexisting in almost all microbiota. It is increasingly appreciated

that microbial communities condition their own environments.

To better understand the role of this environmental conditioning in

promoting diversity, we physically model the population dynamics of

microbes that compete for steadily supplied resources. In a model

where cells require multiple nutrients, we find that population dynamics

generally leads to the coexistence of different metabolic types,

which satisfy an extended competitive exclusion principle. Moreover,

we establish that these consortia of metabolic types act as cartels,

whereby population dynamics pins down resource concentrations at

values for which no other strategy can invade. Strikingly, these cartels

also yield maximum biomass, constituting a microbial example

of Adam Smith’s “invisible hand” leading to collective optimal usage

of resources. Curiously, in a model where only total resource acquisition

is considered, diversity can arbitrarily exceed that predicted by

the competitive exclusion principle.

Conformal interfaces are the long-distance limits of domain walls. They play a role in condensed-matter physics, and could be also rel- evant for theories of gravity. I will review some recently-developed techniques for analyzing their properties, and will discuss their pos- sible applications.

I describe the physics of black holes and show how the traditional

approach leads to the information paradox. I will then discuss some

of the proposed resolutions and the difficulties they need to overcome.

I then discuss soft black hole hair and describe how it may help to

resolve the information paradox. Finally, I will review the problems

that still need to be overcome.

In the next few years new data from ground and space will push the limit of cosmological observations to new frontiers. Combining CMB, weak lensing, redshift clustering and supernovae data, we will be able to constrain the properties of dark energy and its interactions from the background to the non-linear level. In this talk I discuss these methods and the future expected constraints on dark energy and modified gravity.