Scientific Series

A nonrotating black hole placed in a tidal environment (that is, subjected to the gravitational interactions produced by other nearby bodies) is not described by the Schwarzschild solution to the Einstein field equations. Instead, its metric is given by a perturbed version of this exact solution, and the spacetime is no longer stationary nor spherically symmetric. After reviewing the situation in Newtonian theory, I shall describe how the metric of a tidally distorted black hole is calculated. Special attention will be placed on the general description of the tidal environment, the choice of a good coordinate system to describe the perturbed black hole, and the consequences on the structure of the event horizon

Modified gravity models seem to have classical instabilities, ghosts degrees of freedom and superluminal modes. Besides these constraints new dynamical bounds have found to be typical of these models. The cosmological nature of all these constraints is discussed.

Existence of dark energy and nonzero nu mass are two most exciting discoveries of recent years. More excitingly, the similarity between the energy scales of these two raise the question: "Are they related?" I will explore how such connection could be there in nature and its cosmological consequences mainly in structure formation.

The exact boundary states for the rolling D-brane solution in two-dimensional black hole systems will be presented.I will study the physical significance of the solution in relation to the ``tachyon-radion correspondence\" and the ``black hole - string transition\". When the alpha\' corrections become larger, when at the same time the Hawking temperature coincide with the Hagedorn temperature, the phase transition occurs and the physics changes drastically. It also suggests the universal feature of the decaying D-brane and its failure in the strong quantum regime. The talk is based on my series of works hep-th/0605013, hep-th/0507040 in collaboration with Soo-jong Rey (SNU) and Yuji Sugawara (Tokyo).

We have previously isolated and characterized a multipotent precursor cell (termed SKPs for SKin-derived Precursors) from both rodent and human skin, and have shown that these stem cells share many characteristics with a multipotent stem cell that is found in the embryo termed a neural crest stem cell. Here I will discuss our current work with regard to the basic biology of these stem cells, with a focus on the “what, where and why”, and on their therapeutic potential with specific regard to the nervous system.

Most modern discussions of Bell's theorem take microscopic causality (the arrow of time) for granted, and raise serious doubts concerning realism and/or relativity. Alternatively, one may allow a weak form of backwards-in-time causation, by considering "causes" to have not only "effects" at later times but also "influences" at earlier times. These "influences" generate the correlations of quantum entanglement, but do not enable information to be transmitted to the past. Can one realize this scenario in a mathematical model? If macroscopic time-asymmetry is introduced by imposing initial conditions, such a model can not be deterministic. Stochastic Quantization (Parisi and Wu,1981) is a non-deterministic approach known to reproduce quantum field theory. Based on this, a search for models displaying quantum nonlocal correlations, while maintaining the principles of realism, relativity and macroscopic causality, is proposed.

It will be shown that eternal inflation of the random walk type is generically absent in the brane inflationary scenario. Eternal inflation will be analysed both in the context of KKLMMT and the DBI inflationary models. A Langevin analysis will be employed for a more careful treatment. The DBI action, and the relativistic nature of the brane motion in DBI inflationary model, leads to new subtleties in formulating a Langevin approach.

I will discuss some ambiguities involved in using the AdS/CFT correspondence to calculate the ultra-relativistic jet quenching parameter for quarks moving in an N=4 super Yang-Mills thermal bath. Along the way, I will investigate the behavior of various string configurations on a five-dimensional AdS black hole background.

In this talk, I will show how to efficiently generate graph states based on realistic linear optics (with imperfect photon detectors and source), how to do scalable quantum computation with probabilistic atom photon interactions, and how to simulate strongly correlated many-body physics with ultracold atomic gas.

I will explain how a quantum circuit together with measurement apparatuses and EPR sources can be fully verified without any reference to some other trusted set of quantum devices. Our main assumption is that the physical system we are working with consists of several identifiable sub-systems, on which we can apply some given gates locally. To achieve our goal we define the notions of simulation and equivalence. The concept of simulation refers to producing the correct probabilities when measuring physical systems. The notion of equivalence is used to enable the efficient testing of the composition of quantum operations. Unlike simulation, which refers to measured quantities (i.e., probabilities of outcomes), equivalence relates mathematical objects like states, subspaces or gates. Using these two concepts, we prove that if a system satisfies some simulation conditions, then it is equivalent to the one it is supposed to implement. In addition, with our formalism, we can show that these statements are robust, and the degree of robustness can be made explicit. Finally, we design a test for any quantum circuit whose complexity is linear in the number of gates and qubits, and polynomial in the required precision. Joint work with Frederic Magniez, Dominic Mayers and Harold Ollivier.