Scientific Series

In this talk I’ll discuss an exotic theory of gravity known as “partially massless” gravity.  The linear partially massless theory displays many features analogous to those of electromagnetism, including an electric/magnetic duality.  However, the structure of gauge charges is much richer than in E&M.  I’ll present the analogues of electric point charges and Dirac monopoles.

An algebraic view allows one to compute properties of physical states without having to introduce an explicit Hilbert space. In relational systems without absolute time, a state cannot be completely positive once a choice for a (possibly local) internal time has been made. A more general class of `almost-positive' states is introduced in this talk, together with a discussion of their constrained dynamics.

We hope to find clues about the particle physics of the primordial (inflationary?) universe in the statistics of the cosmological perturbations. However, if the fluctuations are non-Gaussian the statistics we observe can differ significantly from the global, mean predictions of an inflationary model. I will discuss how the conclusions we draw about the primordial degrees of freedom can be affected in interesting ways by the finiteness of our observable universe.

After a short review of the gauge gravity duality, we will discuss black holes.  We will explain what the duality tells us about black holes as viewed from the outside.  We will review some of the puzzles that arise when we try to describe the black hole  interior. We will describe wormholes and their interpretation in the dual field theory as entangled states.

Matrix product operators form a natural language for describing topological quantum order. I will discuss how they arise as symmetries in PEPS, how anyon excitations arise as end points on them, and how the virtual indices of the MPO's provide a tensor product structure for the logical qubits in topological quantum computation.

We evaluate the one-graviton loop contribution to the vacuum polarization on de Sitter background in a 1-parameter family of exact, de Sitter invariant gauges. Our result is computed using dimensional regularization and fully renormalized with BPHZ counterterms, which must include a noninvariant owing to the time-ordered interactions.

Because the graviton propagator engenders a physical breaking of de Sitter invariance two structure functions are needed to express the result. In addition to its relevance for the gauge issue this is the first time a covariant gauge graviton propagator has been used to compute a noncoincident loop.

We study 5d and 6d SCFTs with eight supercharges by using 5-brane web diagrams in Type IIB string theory. There are two important properties of the web diagram. One is that it enables us to compute the exact partition function of the 5d theory on the 5-brane web. Even though the web diagram is not dual to a toric geometry, we develop a technique to compute the partition function by using the topological vertex. The other is that a new class of the 5-brane web diagram is conjectured to imply that the corresponding 5d theory has a 6d superconformal fixed point at high energies. Such a web diagram is called Tao web diagram. By using the Tao web diagram, we conjecture new 5d theories whose UV completion is a 6d SCFT. Moreover, we can show that a brane configuration realizing the 6d SCFT may reduce to the Tao web diagram, giving a direct way of identifying the 6d description of the 5d theory. This construction also indicates various dualities of the 5d theories.

Using the method of flux fusion anomaly test recently developed by M. Hermele and X. Chen (arXiv:1508.00573), we show that the possible ways of fractionalize crystal symmetry is greatly restricted if we assume the spin liquid has an SU(2) spin rotation symmetry and the spinon carries a half-integer spin. For a Z_2 spin liquid, under these assumptions the vison can only take the crystal symmetry fractionalization described by the Ising gauge theory. For a chiral spin liquid these assumptions imply that the spinon must also take fractionalized quantum numbers of crystal symmetries.

Extensions of the Standard Model (SM) Higgs sector often predict the existence of new vacua and can feature novel patterns of symmetry breaking in the early universe. In this talk, I will discuss the implications of such scenarios for electroweak scale cosmology, baryogenesis, and Higgs phenomenology. I will focus on two classes of models, one involving a gauge singlet scalar field and the other an inert SU(2) doublet scalar. The former can give rise to a strong first-order electroweak phase transition, but also to rapidly expanding bubbles which can pose a problem for viable electroweak baryogenesis. In the latter, electroweak symmetry can be spontaneously broken by a first-order phase transition to an exotic vacuum, allowing for successful electroweak baryogenesis decoupled from the Standard Model-like Higgs field. Nevertheless, this class of scenarios generically predicts modifications of the SM-like Higgs couplings within reach of present-day collider experiments.

The existence of observables that are incompatible or not jointly measurable is a characteristic feature of quantum mechanics, which is the root of a number of nonclassical phenomena, such as uncertainty relations, wave--particle dual behavior, Bell-inequality violation, and contextuality.

However,  no intuitive  criterion  is available for determining  the compatibility of even two (generalized) observables, despite the overarching importance of this problem  and intensive efforts of many researchers over more than 80 years.

Here we introduce an information theoretic  paradigm together with an intuitive geometric picture for decoding incompatible observables,

starting from two simple ideas:   Every  observable can only provide

limited  information and   information is monotonic  under data

processing. By virtue of quantum estimation theory, we introduce a family of universal criteria for detecting incompatible observables and a natural measure of incompatibility, which are applicable to arbitrary number of arbitrary observables. Based on this framework, we derive a family of universal  measurement uncertainty relations, provide a simple information theoretic explanation of quantitative wave--particle duality, and offer new perspectives for understanding Bell nonlocality, contextuality, and quantum precision limit.

In this talk, we will analyze the properties of the bosonic $\nu = 1$ Moore-Read state when used to build a state
which is strongly believed to be a non-Abelian spin-1 chiral spin liquid state [1]. In this state the bosonic $\nu = 1$
Moore-Read Pfaffian wavefunction is interpreted as a wavefunction for a gas of bosons on a 2D square lattice with one flux quantum per plaquette. We investigate the properties of this wavefunction for the case of planar geometry and for the case of the system living on a torus. For the latter case, there are three distinct states corresponding to the three-fold degeneracy of the $\nu = 1$
bosonic Moore-Read state [2]. Our results show that correlation functions in these states become identical in the limit of large system size. Further issues investigated include the result that the three wavefunctions on the torus are linearly independent and orthogonal in the thermodynamic limit. Additionally, the Renyi entanglement entropy is also calculated for different system partitions in order to extract the topological entanglement entropy $\gamma$.

[1] M. Greiter and R. Thomale, Phys. Rev. Lett. 102, 207203 (2009).
[2] S. B. Chung and M. Stone, J. Phys. A: Math. Theor. 40, 4923 (2007).

A pedagogic introduction will be given to: i) Emergent Majorana fermions and Majorana zero modes in certain condensed matter models and ii) Kondo insulators. This will be followed by discussion of a remarkable Quantum Oscillation Anomaly seen in recent experiments in SmB6, a Kondo insulator, by the Cambridge group [1], as providing evidence [2] for presence of Majorana fermi sea, in an unexpected place. We show a counter intuitive result that these Majorana fermions though neutral, exhibit Landau diamagnetism.

[1] B.S. Tan et al., Science, vol.349, pp. 287-29 (2015), arXiv:1507.01129 [1] G. Baskaran, arXiv:1507.03477