From Classical To Quantum Gravity: Introduction to Loop Quantum Gravity

We present an introduction to the canonical quantization of gravity performed in loop quantum gravity, based on lectures held at the 3rd quantum geometry and quantum gravity school in Zakopane in 2011. A special feature of this introduction is the inclusion of new proposals for coupling matter to gravity that can be used to deparametrize the theory, thus making its dynamics more tractable. The classical and quantum aspects of these new proposals are explained alongside the standard quantization of vacuum general relativity in loop quantum gravity.Comment: 56 pages. Contribution to the Proceedings of the 3rd Quantum Geometry and Quantum Gravity School in Zakopane (2011). v2: Typos corrected, various small changes in presentation, version as published in Po

Regularity of conjugacies of linearizable generalized interval exchange transformations

We consider generalized interval exchange transformations (GIETs) of d intervals ($d\geq 2$) which are linearizable, i.e. differentiably conjugated to standard interval exchange maps (IETs) via a diffeomorphism h of [0, 1] and study the regularity of the conjugacy h. Using a renormalisation operator obtained accelerating Rauzy-Veech induction, we show that, under a full measure condition on the IET obtained by linearization, if the orbit of the GIET under renormalisation converges exponentially fast in a $C^2$ distance to the subspace of IETs, there exists an exponent $0 < \alpha < 1$ such that h is $C^{1+{\alpha}}$. Combined with the results proved by the authors in [4], this implies in particular the following improvement of the rigidity result in genus two proved in previous work by the same authors (from $C^1$ to $C^{1+{\alpha}}$ rigidity): for almost every irreducible IET $T_0$ with d = 4 or d = 5, for any GIET which is topologically conjugate to $T_0$ via a homeomorphism h and has vanishing boundary, the topological conjugacy h is actually a $C^{1+{\alpha}}$ diffeomorphism, i.e. a diffeomorphism h with derivative Dh which is $\alpha$-H\"older continuous.Comment: 28 pages, 4 figure

Singularities of plane complex curves and limits of K\"ahler metrics with cone singularities. I: Tangent Cones

We construct and classify, in the case of two complex dimensions, the possible tangent cones at points of limit spaces of non-collapsed sequences of K\"ahler-Einstein metrics with cone singularities.Comment: Reference to Panov's Polyhedral Kahler Manifolds adde

Deformed Lorentz Symmetry and High-Energy Astrophysics (I)

An updated discussion of Lorentz symmetry violation in particle physics at very high energy is presented, focusing on applications of models of deformed Lorentz symmetry to high-energy astrophysics.Comment: Updated version of a talk given at the ICRC 1999 Conferenc

Quantum Configuration and Phase Spaces: Finsler and Hamilton Geometries

In this paper, we review two approaches that can describe, in a geometrical way, the kinematics of particles that are affected by Planck-scale departures, named Finsler and Hamilton geometries. By relying on maps that connect the spaces of velocities and momenta, we discuss the properties of configuration and phase spaces induced by these two distinct geometries. In particular, we exemplify this approach by considering the so-called $q$-de Sitter-inspired modified dispersion relation as a laboratory for this study. We finalize with some points that we consider as positive and negative ones of each approach for the description of quantum configuration and phases spaces.Comment: 22 pages. Matches published version. Invited contribution for Physics. Special Issue "New Advances in Quantum Geometry

Quantum simulation of (1+1)D QED via a Zn lattice Gauge theory

La simulazione di un sistema quantistico complesso rappresenta ancora oggi una sfida estremamente impegnativa a causa degli elevati costi computazionali. La dimensione dello spazio di Hilbert cresce solitamente in modo esponenziale all'aumentare della taglia, rendendo di fatto impossibile una implementazione esatta anche sui più potenti calcolatori. Nel tentativo di superare queste difficoltà, sono stati sviluppati metodi stocastici classici, i quali tuttavia non garantiscono precisione per sistemi fermionici fortemente interagenti o teorie di campo in regimi di densità finita. Di qui, la necessità di un nuovo metodo di simulazione, ovvero la simulazione quantistica. L'idea di base è molto semplice: utilizzare un sistema completamente controllabile, chiamato simulatore quantistico, per analizzarne un altro meno accessibile. Seguendo tale idea, in questo lavoro di tesi si è utilizzata una teoria di gauge discreta con simmetria Zn per una simulazione dell'elettrodinamica quantistica in (1+1)D, studiando alcuni fenomeni di attivo interesse di ricerca, come il diagramma di fase o la dinamica di string-breaking, che generalmente non sono accessibili mediante simulazioni classiche. Si propone un diagramma di fase del modello caratterizzato dalla presenza di una fase confinata, in cui emergono eccitazioni mesoniche ed antimesoniche, cioè stati legati particella-antiparticella, ed una fase deconfinata

(Broken) Gauge Symmetries and Constraints in Regge Calculus

We will examine the issue of diffeomorphism symmetry in simplicial models of (quantum) gravity, in particular for Regge calculus. We find that for a solution with curvature there do not exist exact gauge symmetries on the discrete level. Furthermore we derive a canonical formulation that exactly matches the dynamics and hence symmetries of the covariant picture. In this canonical formulation broken symmetries lead to the replacements of constraints by so--called pseudo constraints. These considerations should be taken into account in attempts to connect spin foam models, based on the Regge action, with canonical loop quantum gravity, which aims at implementing proper constraints. We will argue that the long standing problem of finding a consistent constraint algebra for discretized gravity theories is equivalent to the problem of finding an action with exact diffeomorphism symmetries. Finally we will analyze different limits in which the pseudo constraints might turn into proper constraints. This could be helpful to infer alternative discretization schemes in which the symmetries are not broken.Comment: 32 pages, 15 figure