Scientific Series

Entropy plays a fundamental role in quantum information theory through applications ranging from communication theory to condensed matter physics.  These applications include finding the best possible communication rates over noisy channels and characterizing ground state entanglement in strongly-correlated quantum systems.  In the latter, localized entanglement is often characterized by an area law for entropy.  Long-range entanglement, on the other hand, can give rise to topologically ordered materials whose collective excitations are robust against local noise.  In this talk, I will present a property of quantum entropy for multipartite quantum systems that resolves several open questions in quantum information theory about entanglement measures, provides new algorithmic opportunities and makes nontrivial statements about the structure of states with vanishing - but nonzero - topological entropy.  I will also comment how extensions of this work could help our understanding of quantum communication over certain very noisy channels.

Supersymmetry is a popular candidate for the 'model beyond the Standard Model', however minimal versions of it are quite constrained by the first year of data from the LHC. In this talk I will focus on supersymmetry scenarios where the gaugino masses are Dirac rather than Majorana. This seemingly innocuous change has a profound impact on collider bounds -- reducing the bound on (1st and 2nd generation) squark masses by nearly a factor of two. In addition, Dirac gaugino scenarios have amazing flavor properties, smoking gun LHC signals, and cosmological implications.

This talk presents two results on the interplay between causality and quantum information flow. First I will discuss about the task of switching the connections among quantum gates in a network. In ordinary quantum circuits, gates are connected in a fixed causal sequence.  However, we can imagine a physical mechanism where the connections among gates are not fixed, but instead are controlled by the quantum state of a control system. Such a "quantum switch" mechanism is consistent with quantum theory but cannot be described with in the standard model of causally ordered circuits, where it would be equivalent to a deterministic time travel and hence would violate the causality principle. With respect to the standard circuit model, the quantum switch is a new primitive that enables new information-processing protocols, such as the perfect discrimination between two classes of channels that are not perfectly distinguishable in a single query by any ordinary quantum circuit. Second, I will discuss about the probabilistic simulation of impossible channels that take an input in the future and produce an output in the past. In this case, I will show that the maximum probability of success in such a simulation is determined by causality and is inversely proportional to the amount of information that the channel can transmit.

Observing lepton-number violating processes is a decisive step toward establishing the Majorana nature of the neutrino mass. We explore the prospects searching for Delta L = 2 processes and propose the tests for the three types of the Seesaw mechanisms. Potential signals at the LHC
are studied and correlations to the neutrino oscillation parameters are investigated.

Recent progress in massive gravity has made it possible to construct consistent theories of interacting spin-2 fields.  In this talk I'll describe these developments, focusing on the resolution of the Boulware-Deser ghost problem and the promotion of massive gravity to a bimetric theory of gravity with two dynamical, interacting spin-2 fields.  I'll then discuss the generalization of these bimetric theories to theories of multiple interacting spin-2 fields.

Quantum corrections to three-point functions of scalar single trace operators in planar ${\cal N}=4$ Super-Yang-Mills theory are studied using integrability. At one loop, we find  new algebraic structures that not only govern all two loop corrections to the mixing of the operators but also automatically incorporate all one loop diagrams correcting the tree level Wick contractions. Speculations about possible extensions of our construction to all loop orders are given. We also match our results with the strong coupling predictions in the classical (Frolov-Tseytlin) limit. 

I review the uses of effective field theory (EFT) techniques, originally developed in particle physics, to study gravitational dynamics. I will focus on the EFT approach to gravitational wave (GW) radiation, aka NRGR, and show how it has succeeded in producing the most accurate description of spinning binary systems to date, opening the door to a new era of precise astrophysical & cosmological measurements and tests of General Relativity via GW interferometry. I will also briefly discuss EFT applications for black hole dissipation/absorption, inflationary dynamics and  high energy gravitational scattering.

During the last couple of years Dupuis, Freidel, Livine, Speziale and Tambornino developed a twistorial formulation for loop quantum gravity.
Constructed from Ashtekar--Barbero variables, the formalism is restricted to SU(2) gauge transformations.
In this talk, I perform the generalisation to the full Lorentzian case, that is the group SL(2,C).
The phase space of SL(2,C) (i.e. complex or selfdual) Ashtekar variables on a spinnetwork graph is decomposed in terms of twistorial variables. To every link there are two twistors---one to each boundary point---attached. The formalism provides a clean derivation of the solution space of the reality conditions of loop quantum gravity.
Key features of the EPRL spinfoam model are perfectly recovered.
If there is still time, I'll scatch my current project concerning a twistorial path integral for spinfoam gravity as well. 

I will explain some recent exact developments in N=2 SUSY gauge theories on 3-sphere and its deformations. I will begin by the analysis of Killing spinors and their generalization which are necessary to construct SUSY theories on curved spaces. Then I will sketch the exact computation of partition function using SUSY localization and present a general formula. Some applications to the physics of M5-branes will also be discussed.

The standard cosmological model posits that the universe is homogeneous and statistically isotropic on its largest scales. However, there is no fundamental reason why these properties have to hold, and in fact they can be broken due to interesting new physics. Moreover, there is some evidence from recent WMAP observations for 'anomalies' - including departures from statistical isotropy - on the largest observable scales. Large-scale structure (LSS) - including the distribution of galaxies in the universe - presents a new frontier in testing statistical isotropy and homogeneity, and we are entering an epoch with orders-of-magnitude improvement in the statistics of LSS. In this talk I first review general tests of statistical isotropy using LSS. I then describe results from research done in collaboration with my student Cameron Gibelyou on testing aspects of the statistical isotropy - in particular, dipolar modulations of the galaxy counts - using existing LSS surveys.