Talks

Although the typical physical system achieves an ordered state at low temperatures, spin liquids stay disordered even in their ground state. In addition to an increasing number of experimental candidates for spin liquids, recent numerical work from Meng, et. al and Yan, et. al. has supplied strong numerical evidence for natural Hamiltonians having spin liquid ground states. Their featureless nature, though, makes  learning about these states particularly difficult. In this talk, we explore what variational ansatz can teach us about them. Additionally, we examine whether the canonical theoretical framework makes sense in the context of the best wave-functions. Finally, we look at what other tools we have to make sense of spin liquids.

The entanglement spectrum denotes the eigenvalues of the reduced density matrix of a region in the ground state of a many-body system. Given these eigenvalues, one can compute the entanglement entropy of the region, but the full spectrum contains much more information. I will review geometric methods to extract this spectrum for special subregions in lorentz and conformally invariant field theories (and any theory whose universal low energy physics is captured by such a field theory). Using this technology, I give a new proof that the entanglement spectrum in quantum hall states is the same as that of a physical edge. I will discuss a number of other applications of the formalism, including, if there is time, a more complicated calculation of universal terms in the entanglement entropy at certain deconfined quantum critical points. The ultimate messages are that geometry is intimately bound up with entanglement and that the entanglement cut should be viewed as a physical cut.

In massive gravity the so-far-found black hole solutions on Minkowski space happen to convert horizons into a certain type of singularities. I will discuss whether these singularities can be avoided if space-time is not asymptotically Minkowskian. As an illustration, I will present an exact analytic black hole solution  which evades  the above problem by a transition at large scales to self-induced de Sitter space-time. The solution demonstrates that in massive GR, in the Schwarzschild coordinate system, a BH  metric has to be accompanied by the St\"uckelberg fields with nontrivial backgrounds to  prevent the horizons to convert into the singularities.

In this talk, I will discuss various aspects of UV-complete R-symmetric QFTs. In particular, I will focus on a small set of operators that are well-defined in many such theories, and I will argue that one can use these operators to get a (partial) non-perturbative handle on the deep IR physics, including, possibly, a handle on certain aspects of the emergent symmetries. Throughout, I will highlight applications to particle physics.

Rare earth pyrochlores, with a chemical formula A2B2O7, exhibit many interesting features in A site spin system. Depending on A site rare earth elements, spin ice and magnetically ordered phases are shown in several experiments. Moreover, they have been also focused as possible candidates of U(1) spin liquid. In order to explore such versatile phases, we study the pseudospin-1/2 model, which is quite generic to describe rare earth pyrochlores with integer spins, in the presence of spin-orbit coupling and crystalline electric field. Using a new "gauge mean field theory", we show the possible ground states, corresponding to several phases listed above.

I present a simple exactly solveable model of eternal inflation.  The correlation functions have a discrete analogue of conformal symmetry, which can be compactly expressed using the machinery of p-adic numbers.  I comment on the implications for actual cosmology, and in particular for holographic descriptions of eternal inflation.

The full machinery of supergravity (SUGRA) is required to fully understand many supersymmetric models. For the purpose of understanding phenomenology at colliders and in cosmology, the main concern is to ascertain the effects of SUGRA on the vacuum structure and particle spectrum. Practical calculations often require cumbersome manipulations of component field terms involving the full gravity multiplet. In this talk I will present an alternative gauge fixing for conformal SUGRA which decouples these gravity complications from SUGRA computations. This yields a simplified tree-level action for the matter fields in SUGRA which can be expressed compactly in terms of superfields and a modified conformal compensator. As a concrete application I will finally show the example of the mass spectrum of goldstini arising from a general admixture of F-term, D-term, and almost no-scale supersymmetry breaking.

Novel phases can result from the interplay of electronic interactions and spin orbit coupling. In the first part, we discuss a simple Hubbard model for the pyrochlore iridates, whose phase diagram contains topological insulator (TI) and various magnetic phases. The latter host the novel topological Weyl semimetal, whose excitations behave like Weyl fermions. In the second part we study a novel spin liquid that was proposed to arise in the iridates, the 3D topological Mott insulator: a fractionalized TI where the neutral spinons acquire a topologically non-trivial band structure. The low-energy behavior is dominated by the 2D surface spinons strongly coupled to a bulk gauge field. This phase is characterized by the helical nature of the spinon surface states and the dimensional mismatch between the latter and the gauge bosons. We discuss experimental signatures as well as the possibility of dyonic excitations and a non-trivial magneto-electric response.