Just an illusion

• Giovanni Amelino-Camelia

Room: 132:028 I observe tha the physical content of all so-called 'space- time measurements' only requires timed particle detections. And I point out the aspects of our current theories that render the abstraction of a spacetime extremely covenient. Among these particularly significant is the role of the assumed triviality of the geometry of momentum space, which makes room for an observer- independent notion of locality. Starting from some recent studies of the quantum-gravity problem, which stumbled upon hints of a nontrivial geometry of momentum space, we might be led to renouncing to absolute locality, thereby loosing a good part of the convenience of abstracting a spacetime.

Relative locality in 3 dimensions

• Jerzy Kowalski-Glikman

Room: 132:028 In my talk I will discuss how the theory of gravity in 3 spacetime dimensions coupled to particles can be interpreted as a relative locality type of a theory.

Non-local charges, curved momentum space and fractal space-time

• Michele Arzano

Room: 132:028 Non-local currents and their associated conserved charges have been known and studied widely in two- dimensional field theories. Their main feature is that their action on product of fields is non-additive i.e. it follows a "deformed" Leibniz rule. Less appreciated is the fact that non-local charges appear in the context of three-dimensional Einstein gravity where they describe the energy-momentum of a "topologically" gravitating point particle. Here momenta are Lorentz group elements and the non-additive action is simply a consequence of the non-abelian structure of the group. After a brief introduction I will show how quantization of such relativistic point particle with group- valued momenta leads to a non-commutative field theory. As an application I will introduce a non- commutative heat-kernel, calculate the associated spectral dimension and comment on its non-trivial behaviour. Finally I will discuss how these structure can be extended to a 4d context and comment on some potential applications.

Non-locality in black hole evolution

• Larus Thorlacius

Room: 132:028 Hawking's information paradox arises when one considers the formation and subsequent evaporation of a black hole. It pits quantum mechanical unitarity against locality in spacetime and highlights the incompatibility between the world view offered by general relativity and that of quantum physics. In a gravity theory with a gauge theory dual, the information paradox must be resolved in favor of unitary evolution. The challenge is then to identify the non-local effects that implement unitarity on the gravity side.

Modifications to quantum theory, in light of the black hole information problem

• Jonathan Oppenheim

Room: 132:028 The origin of black hole entropy, and the black hole information problem provide important clues for trying to piece together a quantum theory of gravity. Thus far, discussions on this topic have generally assumed that in a consistent theory of gravity and quantum mechanics, quantum theory will be unmodified. This talk will examine the black hole information problem in the context of generalisations of quantum theory. The black hole information problem suggests that either information is fundamentally destroyed, or if information is preserved, the semi-classical description of black hole evaporation must be misleading. Two generalisations will be discussed, each one bolstering a different side in this debate. In one, information is fundamentally destroyed, but in a way which preserves conservation laws. In another, information is preserved, but can become delocalised, or remain in the black hole until the end of the evaporation process, while still respecting entropy bounds.

Discussion Session

• Convener: George Musser

Room: 132:028

Nonlocality and QFT

• Gariy Efimov

Room: 132:028 QFT and S-matrix. Ultraviolet divergences. Formfactor and unitarity. - Propagator and confinement. - Field equations, external fields and vacuum stability. - Bound states in QFT and effective Lagrangians. - Oscillator and field: local interaction - instability, nonlocal interaction - stability

Gauge theories on canonically deformed spaces

• Michael Wohlgenannt

Room: 132:028 We will briefly discuss noncommutative coordinates and explain UV/IR mixing in the context of scalar fields on (canonically) deformed Euclidean spaces. Based on the approach to scalar fields, models for noncommutative gauge theory and one-loop corrections are discussed. Finally, some connections to gravity, especially the so- called induced gravity and some open questions are raised.

Gravity from phase transitions

• Lorenzo Sindoni

Room: 132:028 I will present some ideas on the possibility that gravity is an emergent phenomenon in a class of combinatorial models, proposed within the framework of discretized models for quantum gravity, namely group field theories. I will discuss the ideas on the appearance of a continuum semiclassical phase (described in terms of local quantum field theories on a classical space-time) as well as possible deviations that might be relevant for observations (nonlocality, physics of the early universe etc.), from the point of view of phase transitions.

Black holes are quite non-local

• Ingemar Bengtsson (SU Fysikum)

Room: 132:028 Black holes are arguably the simplest things that exist. Their definition is very holistic. In recent years there has been a trend towards defining them "quasi-locally" using properties of trapped surfaces. This does solve a practical problem in numerical relativity, but in fact the definition remains quite non-local. (This talk is only a review talk.)

Nonlocal Quantum Gravity

• Leonardo Modesto

Room: 132:028 I introduce a perturbatively super-renormalizable and unitary theory of quantum gravity in any dimension D starting from the four dimensional case. The theory presents one entire function, a.k.a. "form factor", and a finite number of local operators required by the quantum consistency as well as unitarity of the theory itself. The theory is power-counting renormalizable at one loop and finite from two loops upward. I essentially present three classes of form factors, systematically showing the tree-level unitarity. It is right now under investigation a possible N=1 supersymmetric extension of the theory in four dimensions. Preliminary results indicate that the nonlocal supergravity theory is power-counting super-renormalizable and tree level unitary with the same particle content of the local N=1 supergravity. In contrast to the local (quadratic-)higher derivative supergravity in its nonlocal generalization all the states fill up in N=1 supergravity multiplet. We believe that the extended SO(N) supergravity, for N=4 and/or N=8, can be off-shell divergence-free also at one loop. At semiclassical level the gravitational potential is regular in r = 0 for all the choices of form factors compatible with renormalizability and unitarity. For two out of three form factors the black hole solutions are regular and the classical singularity is replaced by a "de Sitter-like core" in r=0. For one particular example of form factor, I prove that the D-dimensional "Newtonian cosmology" is singularity- free and the Universe spontaneously follows a de Sitter evolution at the "Planck scale" for any matter content. I conclude stating that, in the ultraviolet regime, the spectral dimension takes on different values for the three cases: less than or equal to "1" for the first case, "0" for the second one and "2" for the third one. Once the class of theories compatible with renormalizability and unitarity is defined, the spectral dimension has the same short-distance "critical value" or "accumulation point" for any value of the topological dimension D.

3D gravity and the deformation of particle kinematics

• Tomasz Trzesniewski

Room: 132:028 In my talk I would like to explain how gravitation in 3D makes kinematics of particles deformed. I will show that the effective theory of 3D gravity coupled to a particle (with mass and/or spin) describes the system with a curved momentum space and non-commutative spacetime, with the scale provided by the Newton's constant. The case of many particles and their 'topological' interactions will be briefly discussed.

Discussion Session

• Convener: TBA

Room: 132:028

A new look at entropy and gravity

• Olaf Dreyer

Room: 132:028 I will give a new description of the relationship of entropy to gravity. I will show that while gravity is not entirely entropic in origin it does receive an entropic correction. I calculate the entropic correction and the new gravitational constant. I then show that in simple cases the entropy of the whole spacetime can be calculated and it turns out to be proportional to an area. The implications for holography and non-locality are discussed.

Real clocks: a toy model for non-locality

• Luis Garay

Room: 132:028 Good clocks, which are naturally subject to fluctuations, can be characterized in statistical terms and the evolution of quantum systems according to these clocks obey a master equation. This master equation is diffusive and produces loss of coherence. Moreover, real clocks can be described in terms of effective interactions that are non-local in time. Alternatively, they can be modeled by an effective thermal bath coupled to the system. This may give interesting hints in the study of some aspects concerning the evolution of quantum low-energy fields in a foamlike spacetime, with involved topology at the Planck scale but with a smooth metric structure at large length scales, which also introduces nonlocal interactions that can be modeled by a quantum bath, and low-energy fields evolve according to a master equation.

Geometry on quantum spacetime

• Klaus Fredenhagen

Room: 132:028 Noncommutative spaces are natural candidates for spacetimes under the influence of quantum gravity. We discuss distances, areas and volumes on such a spacetime.