Search Talks

The Ryu-Takayanagi proposal (and generalizations) for holographic entanglement makes predictions for geometric CFT entanglement entropy (EE) that continue to hold for any CFT, regardless of existence of large-N limit or strong coupling. We establish this using a direct field theory calculation, thus providing a non-trivial check of the holographic proposal. This universality emerges for small perturbations of the EE of a ball shaped region. Einstein’s equations arise from the field theory calculation as a way to efficiently encode this perturbative CFT entanglement holographically in the geometry of a dual space-time.

We will present a reformulation of the Ryu-Takayanagi holographic entanglement entropy formula which does not involve the areas of surfaces. The reformulation leads to a picture of entanglement entropy of boundary regions being carried by Planck-thickness "bit threads" in the bulk. We will argue that this picture resolves a number of conceptual difficulties surrounding the RT formula.

We study a quantum information metric (or fidelity susceptibility) in conformal field theories with respect to a small perturbation by a primary operator. We argue that its gravity dual is approximately given by a volume of maximal time slice in an AdS spacetime when the perturbation is exactly marginal. We confirm our claim in several examples.

Due to the linearity of the field equations and the resulting bilinear structure of the Hamiltonian, quantum radiation effects such as black hole evaporation or particle creation in an expanding universe are typically described as (squeezing) processes where particles are created in pairs. Here, we address the following question: given a mode (e.g., wave-packet) corresponding to a created particle (e.g., as part of Hawking radiation), what is its partner, i.e., the other particle of the pair? After a general derivation of this partner mode, we will discuss some examples such as moving mirror radiation and speculate about possible implications for the black hole information puzzle.

Can high energy physics can be simulated by low-energy, nonrelativistic, many-body systems, such as ultracold atoms? Ultracold atomic systems lack the type of symmetries and dynamical properties of high energy physics models: in particular, they do not manifest local gauge invariance nor Lorentz invariance, which are crucial properties of the quantum field theories which are the building blocks of the standard model of elementary particles. However, it will be shown that there are ways to configure atomic system to manifest both local gauge invariance and Lorentz invariance. In particular, local gauge invariance can arise either as an effective, low energy, symmetry, or as an "exact" symmetry, following from the conservation laws in atomic interactions. Such quantum simulators may lead to new type of (table-top) experiments, to test various QCD phenomena, as the confinement of dynamical quarks, phase transitions, and other effects.

I will sketch a few interesting phenomena involving ideal plasmas, including helicity conservation, frozen flux, the Blandford-Znajek mechanism, and self-confined Poynting jets, using the language of differential forms.

This year marks the 40’th anniversary of the Unruh effect as described at the first Marcel Grossmann meeting in 1975. We revisit it with emphasis on the observability issue which might be a concern at first sight, since the linear acceleration needed to reach a temperature 1 K is of order 10^20 m/s^2 . We close the talk by emphasizing that the Unruh effect does not require any verification beyond that of relativistic free field theory itself. The Unruh effect lives among us.

The quantum Zeno effect is often very controversial in the context of consciousness problems. Frequent direct measurements of a quantum system freeze its time evolution. Then what happes if an observer continuously watches a Schrodinger's cat from the start of the experiment? Naively this looks like a yes-no measurement of a unstable atom decay, which emits a gamma ray as a trigger of the cat execution. If so, the continuous cat observation may prevent the ray emission as a Zeno effect. Consequently the cat can remain alive as long as the observation is maintained. However, this is clearly incorrect. In this talk, assuming some natural conditions, we generally prove the impossibility of quantum Zeno effects generated by indirect measurements by the observer's consciousness. Naively this is a yes-no experiment of a unstable atom decay, which emits a gamma ray as a trigger of the cat execution. If so, the continuous cat observation stops the ray emission as a Zeno effect. Consequently the cat remains alive as long as the observation is maintained. However, this is clearly incorrect. In this talk, assuming some natural conditions, I generally prove the impossibility of quantum Zeno effects generated by indirect measurements by the observer's consciousness

The problem of the gravitational collapse of small mass in the higher derivative and ghost free theories of gravity is discussed. It will be demonstrated how higher derivative and non-local modifications of gravity equations regularizes static and dynamical solutions. Boosting a static solution of the linearized equations for the gravitational potential of a point mass we obtain a solution for the field of the ultra-relativistic source (gyraton). Using the latter we construct solutions for the collapsing spherical (thin and thick) null shell. By analysing the obtained solutions we demonstrate that for small enough value of the mass M an apparent horizon is not formed for the gravitational collapse of small mass in the higher-derivative and ghost free theories of gravity. We demonstrate that this “mass gap” property is connected with the presence of the UV cut-off in such theories.

In 1981 Bill discovered an analogy between the propagation of fields in the vicinity of astrophysical black holes and the that of small excitations in fluids. He postulated that this analogy allows one to test, challenge and verify, in tabletop experiments, the elusive processes of black hole mass and angular momentum loss. Indeed, 34 years later analogue gravity experiments are carried out all over the world to implement his idea. I will first present a brief overview on analogue black hole experiments, and then discuss in more detail some of my earlier (in collaboration with Bill) and more recent experimental and theoretical results on the subject.