14,189 research outputs found
The full Schwinger-Dyson tower for random tensor models
We treat random rank- tensor models as -dimensional quantum field
theories---tensor field theories (TFT)---and review some of their
non-perturbative methods. We classify the correlation functions of complex
tensor field theories by boundary graphs, sketch the derivation of the
Ward-Takahashi identity and stress its relevance in the derivation of the tower
of exact, analytic Schwinger-Dyson equations for all the correlation functions
(with connected boundary) of TFTs with quartic pillow-like interactions.Comment: Proceedings: Corfu 2017 Training School "Quantum Spacetime and
Physics Models
The Spectral Action on quivers
We consider quiver representations not on vector spaces, as traditional, but
on a different target category, which emerges in the context of noncommutative
geometry. The equivalence between quiver representations and path algebra
modules -- established here for the new category -- inspired the following
construction: Only from representation theory data, we build the Dirac operator
(of a spectral triple) on a quiver and evaluate the spectral action functional
from a general formula over closed paths derived here. We apply this
construction to gauge theories on lattice-quivers and obtain all the exact
Weisz-Wohlert-type cells in the context of Symanzik's improvement to the
Wilsonian Yang-Mills lattice gauge theory. We show that a hermitian Higgs field
emerges from the self-loops of the quiver and derive the Yang-Mills--Higgs
theory on flat space as a limit of certain quivers. We worked in arbitrary
dimension and, concerning paths on lattices, we proved some combinatorial
claims, which might be useful elsewhere.Comment: 34 pp, many quivers; v2 some typos and minor correction
Computing the spectral action for fuzzy geometries: from random noncommutative geometry to bi-tracial multimatrix models
A fuzzy geometry is a certain type of spectral triple whose Dirac operator
crucially turns out to be a finite matrix. This notion was introduced in [J.
Barrett, J. Math. Phys. 56, 082301 (2015)] and accommodates familiar fuzzy
spaces like spheres and tori. In the framework of random noncommutative
geometry, we use Barrett's characterization of Dirac operators of fuzzy
geometries in order to systematically compute the spectral action for -dimensional fuzzy geometries. In contrast to the
original Chamseddine-Connes spectral action, we take a polynomial with
as in order to obtain a well-defined path
integral that can be stated as a random matrix model with action of the type
, being and noncommutative polynomials in
complex matrices that parametrize the Dirac operator
. For arbitrary signature---thus for any admissible KO-dimension---formulas
for 2-dimensional fuzzy geometries are given up to a sextic polynomial, and up
to a quartic polynomial for 4-dimensional ones, with focus on the octo-matrix
models for Lorentzian and Riemannian signatures. The noncommutative polynomials
and are obtained via chord diagrams and satisfy: independence of
; self-adjointness of the main polynomial (modulo cyclic reordering of
each monomial); also up to cyclicity, either self-adjointness or
anti-self-adjointness of and simultaneously, for fixed .
Collectively, this favors a free probabilistic perspective for the large-
limit we elaborate on.Comment: 51 pages (45+6), some figures. v5. Minor amend to Prop. 4.1 and
syntax of Def. 2.
Ultrasonic cavity solitons
We report on a new type of localized structure, an ultrasonic cavity soliton,
supported by large aspect-ratio acoustic resonators containing viscous media.
The spatio-temporal dynamics of this system is analyzed on the basis of a
generalized Swift-Hohenberg equation, derived from the microscopic equations
under conditions close to nascent bistability. These states of the acoustic and
thermal fields are robust structures, existing whenever a spatially uniform
solution and a periodic pattern coexist. An analytical solution for the
ultrasonic cavity soliton is also presented
Self collimation of ultrasound in a 3D sonic crystal
We present the experimental demonstration of self-collimation (subdiffractive
propagation) of an ultrasonic beam inside a three-dimensional sonic crystal.
The crystal is formed by two crossed steel cylinders structures in a
woodpile-like geometry disposed in water. Measurements of the 3D field
distribution show that a narrow beam which diffractively spreads in the absence
of the sonic crystal is strongly collimated in propagation inside the crystal,
demonstrating the 3D self-collimation effect.Comment: 3 figures, submitted to Applied Physics Letter
New light on the formation and evolution of bars:Trends in the stellar line-strength indices distribution inside the bar region
Aims. Our aim is to study the stellar content of the bar region to constrain its formation and evolution.Methods. Line-strength indices in the bar region of a sample of 6 barred galaxies were employed to derive age and metallicity gradients along the bars using stellar population models.Results. We find clear radial gradients in the line-strength indices for all the galaxies. We find positive gradients within the bar region in the metal indices in four of the six galaxies and opposite trends in the other two. These two galaxies are classified as SAB, and they present exponential bar light profiles. For all the galaxies, we find a positive gradient in the Balmer indices. There is a clear correlation between the position of morphological features inside the bar region with changes in the slope and value of the indices, which indicate changes in the stellar populations, when using stellar population analysis. Therefore, it seems that the bar regions show a gradient in both age and metallicity, changing radially to younger and more meta-rich populations for all the galaxies except for the two with exponential profiles.</p
Discovery of a wide companion near the deuterium burning mass limit in the Upper Scorpius association
We present the discovery of a companion near the deuterium burning mass limit
located at a very wide distance, at an angular separation of 4.6+/-0.1 arcsec
(projected distance of ~ 670 AU) from UScoCTIO108, a brown dwarf of the very
young Upper Scorpius association. Optical and near-infrared photometry and
spectroscopy confirm the cool nature of both objects, with spectral types of M7
and M9.5, respectively, and that they are bona fide members of the association,
showing low gravity and features of youth. Their masses, estimated from the
comparison of their bolometric luminosities and theoretical models for the age
range of the association, are 60+/-20 and 14^{+2}_{-8} MJup, respectively. The
existence of this object around a brown dwarf at this wide orbit suggests that
the companion is unlikely to have formed in a disk based on current planet
formation models. Because this system is rather weakly bound, they did not
probably form through dynamical ejection of stellar embryos.Comment: 10 pages, including 4 figures and 2 table
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