Towards the graviton from spinfoams: the 3d toy model

Recently, a proposal has appeared for the extraction of the 2-point function of linearised quantum gravity, within the spinfoam formalism. This relies on the use of a boundary state, which introduces a semi-classical flat geometry on the boundary. In this paper, we investigate this proposal considering a toy model in the (Riemannian) 3d case, where the semi-classical limit is better understood. We show that in this limit the propagation kernel of the model is the one for the harmonic oscillator. This is at the origin of the expected 1/L behaviour of the 2-point function. Furthermore, we numerically study the short scales regime, where deviations from this behaviour occur.Comment: 8 pages, 2 figures; v3 revised versio

A Case of Ciliate Protozoa Colpoda Spp. (Ciliata: Colpodidae) Detected In Human Urine

In the urine of a patient with chronic prostatitis, renal microlithiasis and acute cystitis we found the ciliate protozoa Colpoda spp., both in vegetative and cystic form. The entry point was most likely the urinary tract. Keeping in mind that only four more cases of Colpoda spp. existent in human urine have already been described, and that in the case of our patient the ciliate was present at repeated examinations of his urine, we presumed that it is not only a spurious infection of the urogenital tract. It still remains to be analyzed whether this ciliate belongs to a species of Colpoda adapted to parasitism in homeothermae and whether it can be pathogenic for humans

A simple background-independent hamiltonian quantum model

We study formulation and probabilistic interpretation of a simple general-relativistic hamiltonian quantum system. The system has no unitary evolution in background time. The quantum theory yields transition probabilities between measurable quantities (partial observables). These converge to the classical predictions in the $\hbar\to 0$ limit. Our main tool is the kernel of the projector on the solutions of Wheeler-deWitt equation, which we analyze in detail. It is a real quantity, which can be seen as a propagator that propagates "forward" as well as "backward" in a local parameter time. Individual quantum states, on the other hand, may contain only "forward propagating" components. The analysis sheds some light on the interpretation of background independent transition amplitudes in quantum gravity

Tecniche speditive per la ricostruzione tridimensionale dell’area archeologica di Villa Magna

The article presents the results of the GPS and photographic surveys conducted on the archaeological site of Villa Magna (Anagni, Lazio). The archaeological complex, identified as the imperial residence of Antoninus Pius, occupies an area of about 22 hectares. Presently, the visible remains are divided into two principal nuclei: the northern one, near the church of S. Pietro, and the southern one, occupied by a farmhouse. The aim of the survey was the reconstruction of the morphology of the terrain in order to produce a Digital Terrain Model and to highlight the relationship between natural elements and ancient structures. In order to speed up the work, a new procedure was used. It consists of a Differential GPS used in a kinematic way by mounting the rover antenna on a jeep. In this article the experimental method’s advantages and the problems of acquisition are analysed. Moreover, low altitude photographs of the archaeological excavations were taken using an aerostatic balloon. The photographic system was anchored to the balloon with a radio-controlled device called Picavet. Georeferenced photos can be very useful not only for documenting but also for presenting and exploiting the site

Background independence in a nutshell

We study how physical information can be extracted from a background independent quantum system. We use an extremely simple `minimalist' system that models a finite region of 3d euclidean quantum spacetime with a single equilateral tetrahedron. We show that the physical information can be expressed as a boundary amplitude. We illustrate how the notions of "evolution" in a boundary proper-time and "vacuum" can be extracted from the background independent dynamics.Comment: 19 pages, 19 figure

Spatially asymptotic S-matrix from general boundary formulation

We construct a new type of S-matrix in quantum field theory using the general boundary formulation. In contrast to the usual S-matrix the space of free asymptotic states is located at spatial rather than at temporal infinity. Hence, the new S-matrix applies to situations where interactions may remain important at all times, but become negligible with distance. We show that the new S-matrix is equivalent to the usual one in situations where both apply. This equivalence is mediated by an isomorphism between the respective asymptotic state spaces that we construct. We introduce coherent states that allow us to obtain explicit expressions for the new S-matrix. In our formalism crossing symmetry becomes a manifest rather than a derived feature of the S-matrix.Comment: 27 pages, LaTeX + revtex4; v2: various corrections, references update

Graviton propagator in loop quantum gravity

We compute some components of the graviton propagator in loop quantum gravity, using the spinfoam formalism, up to some second order terms in the expansion parameter.Comment: 41 pages, 6 figure

Broadband classification and statistics of echoes from aggregations of fish measured by long-range, mid-frequency sonar

Author Posting. © Acoustical Society of America, 2017. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 141 (2017): 4354, doi:10.1121/1.4983446.For horizontal-looking sonar systems operating at mid-frequencies (1–10 kHz), scattering by fish with resonant gas-filled swimbladders can dominate seafloor and surface reverberation at long-ranges (i.e., distances much greater than the water depth). This source of scattering, which can be difficult to distinguish from other sources of scattering in the water column or at the boundaries, can add spatio-temporal variability to an already complex acoustic record. Sparsely distributed, spatially compact fish aggregations were measured in the Gulf of Maine using a long-range broadband sonar with continuous spectral coverage from 1.5 to 5 kHz. Observed echoes, that are at least 15 decibels above background levels in the horizontal-looking sonar data, are classified spectrally by the resonance features as due to swimbladder-bearing fish. Contemporaneous multi-frequency echosounder measurements (18, 38, and 120 kHz) and net samples are used in conjunction with physics-based acoustic models to validate this approach. Furthermore, the fish aggregations are statistically characterized in the long-range data by highly non-Rayleigh distributions of the echo magnitudes. These distributions are accurately predicted by a computationally efficient, physics-based model. The model accounts for beam-pattern and waveguide effects as well as the scattering response of aggregations of fish.This research was supported by the U.S. Office of Naval Research, the National Oceanographic Partnership Program, NOAA, WHOI, and the Oceanographer of the U.S. Navy

Three dimensional loop quantum gravity: coupling to point particles

We consider the coupling between three dimensional gravity with zero cosmological constant and massive spinning point particles. First, we study the classical canonical analysis of the coupled system. Then, we go to the Hamiltonian quantization generalizing loop quantum gravity techniques. We give a complete description of the kinematical Hilbert space of the coupled system. Finally, we define the physical Hilbert space of the system of self-gravitating massive spinning point particles using Rovelli's generalized projection operator which can be represented as a sum over spin foam amplitudes. In addition we provide an explicit expression of the (physical) distance operator between two particles which is defined as a Dirac observable.Comment: Typos corrected and references adde

Physical boundary state for the quantum tetrahedron

We consider stability under evolution as a criterion to select a physical boundary state for the spinfoam formalism. As an example, we apply it to the simplest spinfoam defined by a single quantum tetrahedron and solve the associated eigenvalue problem at leading order in the large spin limit. We show that this fixes uniquely the free parameters entering the boundary state. Remarkably, the state obtained this way gives a correlation between edges which runs at leading order with the inverse distance between the edges, in agreement with the linearized continuum theory. Finally, we give an argument why this correlator represents the propagation of a pure gauge, consistently with the absence of physical degrees of freedom in 3d general relativity.Comment: 20 pages, 6 figure