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Galliano Valent

Publications and source records attributed to Galliano Valent.

At least 19 recordsLinked to original sources
arXiv2023

Axial Bianchi IX and its Lema{î}tre-Hubble diagram

We compute the Lema{î}tre-Hubble diagram for axial Bianchi IX universes with comoving dust. We motivate our choice by defining a {\it minimal} symmetry breaking of the cosmological principle. This criterium admits only two possibilities: the axial Bianchi I and IX universes. The latter have positive curvatures and reduce to the former in the zero curvature limit. Remarkably, negative curvatures are excluded by this minimal symmetry breaking in presence of comoving dust.

gr-qc↗
arXiv2023

The geodesic flow of the BGPP metric is Liouville integrable

We prove that the geodesics equations corresponding to the BGPP metric are integrable in the Liouville sense. The $\mathrm{SO}(3,\mathbb{R})$ symmetry of the model allows to reduce the system from four to two degrees of freedom. Moreover, solutions of the reduced system and its degenerations can be solved explicitly or reduced to a certain quadrature. In degenerated cases BGPP metric coincides with the Eguchi-Hanson metric and for this case the mentioned quadrature can be calculated explicitly in terms of elliptic integrals.

math-ph↗
arXiv2021

Superintegrable geodesic flows on the hyperbolic plane

In the framework laid down by Matveev and Shevchishin, superintegrability is achieved with one integral linear in the momenta (a Killing vector) and two extra integrals of of any degree above two in the momenta. However these extra integrals may exhibit either a trigonometric dependence in the Killing coordinate (a case we have already solved) or a hyperbolic dependence and this case is solved here. Unfortunately the resulting geodesic flow is {\em never} defined on the two-sphere, as was the case for Koenigs systems (with quadratic extra integrals). Nevertheless we give some sufficient conditions under which the geodesic flow is defined on the hyperbolic plane.

math-ph↗
arXiv2015

Global structure and geodesics for Koenigs superintegrable systems

Starting from the framework defined by Matveev and Shevchishin we derive the local and the global structure for the four types of super-integrable Koenigs metrics. These dynamical systems are always defined on non-compact manifolds, namely $\,{\mb R}^2\,$ and $\,{\mb H}^2$. The study of their geodesic flows is made easier using their linear and quadratic integrals. Using Carter (or minimal) quantization we show that the formal superintegrability is preserved at the quantum level and in two cases, for which all of the geodesics are closed, it is even possible to compute the discrete spectrum of the quantum hamiltonian.

math-ph↗
arXiv2014

Bianchi I meets the Hubble diagram

We improve existing fits of the Bianchi I metric to the Hubble diagram of supernovae and find an intriguing yet non-significant signal for anisotropy that should be verified or falsified in the near future by the Large Synoptic Survey Telescope. Since the literature contains two different formulas for the apparent luminosity as a function of time of flight in Bianchi I metrics, we present an independent derivation confirming the result by Saunders (1969). The present fit differs from earlier ones by Koivisto & Mota and by Campanelli et al. in that we use Saunders' formula, a larger sample of supernovae, Union 2 and JLA, and we use the general Bianchi I metric with three distinct eigenvalues.

astro-ph.CO↗
arXiv2013

On a class of integrable systems with a quartic first integral

We generalize, to some extent, the results on integrable geodesic flows on two dimensional manifolds with a quartic first integral in the framework laid down by Selivanova and Hadeler. The local structure is first determined by a direct integration of the differential system which expresses the conservation of the quartic observable and is seen to involve a finite number of parameters. The global structure is studied in some details and leads to a class of models living on the manifolds S^2, H^2 or R^2. As special cases we recover Kovalevskaya's integrable system and a generalization of it due to Goryachev.

nlin.SI↗
arXiv2011

A new integrable system on the sphere and conformally equivariant quantization

Taking full advantage of two independent projectively equivalent metrics on the ellipsoid leading to Liouville integrability of the geodesic flow via the well-known Jacobi-Moser system, we disclose a novel integrable system on the sphere $S^n$, namely the "dual Moser" system. The latter falls, along with the Jacobi-Moser and Neumann-Uhlenbeck systems, into the category of (locally) Stäckel systems. Moreover, it is proved that quantum integrability of both Neumann-Uhlenbeck and dual Moser systems is insured by means of the conformally equivariant quantization procedure.

math-ph↗
arXiv2011

Further results on non-diagonal Bianchi type III vacuum metrics

We present the derivation, for these vacuum metrics, of the Painlevé VI equation first obtained by Christodoulakis and Terzis, from the field equations for both minkowskian and euclidean signatures. This allows a complete discussion and the precise connection with some old results due to Kinnersley. The hyperkähler metrics are shown to belong to the Multi-Centre class and for the cases exhibiting an integrable geodesic flow the relevant Killing tensors are given. We conclude by the proof that for the Bianchi B family, excluding type III, there are no hyperkähler metrics.

gr-qc↗
arXiv2010

Explicit integrable systems on two dimensional manifolds with a cubic first integral

A few years ago Selivanova gave an existence proof for some integrable models, in fact geodesic flows on two dimensional manifolds, with a cubic first integral. However the explicit form of these models hinged on the solution of a nonlinear third order ordinary differential equation which could not be obtained. We show that an appropriate choice of coordinates allows for integration and gives the explicit local form for the full family of integrable systems. The relevant metrics are described by a finite number of parameters and lead to a large class of models on the manifolds ${\mb S}^2, {\mb H}^2$ and $P^2({\mb R})$ containing as special cases examples due to Goryachev, Chaplygin, Dullin, Matveev and Tsiganov.

math-ph↗
arXiv2010

Bianchi type II,III and V diagonal Einstein metrics re-visited

We present, for both minkowskian and euclidean signatures, short derivations of the diagonal Einstein metrics for Bianchi type II, III and V. For the first two cases we show the integrability of the geodesic flow while for the third case a somewhat unusual bifurcation phenomenon takes place: for minkowskian signature elliptic functions are essential in the metric while for euclidean signature only elementary functions appear.

math-ph↗
arXiv2008

Bianchi III and V Einstein metrics

We present diagonal Einstein metrics for Bianchi III and V, both for minkowskian and euclidean signatures and we show that the Einstein Bianchi III metrics have an integrable geodesic flow.

gr-qc↗
arXiv2006

Neumann-like integrable models

A countable class of integrable dynamical systems, with four dimensional phase space and conserved quantities in involution (H\_n,I\_n) are exhibited. For $n=1$ we recover Neumann sytem on T*S^2. All these systems are also integrable at the quantum level.

math-ph↗
arXiv2006

Integrable geodesic flows and Multi-Centre versus Bianchi A metrics

It is shown that most, but not all, of the four dimensional metrics in the Multi-Centre family with integrable geodesic flow may be recognized as belonging to spatially homogeneous Bianchi type A metrics. We show that any diagonal bi-axial Bianchi II metric has an integrable geodesic flow, and that the simplest hyperkähler metric in this family displays a finite dimensional W-algebra for its observables. Our analysis puts also to light non-diagonal Bianchi VI$_0$ and VII$_0$ metrics which seem to be new. We conclude by showing that the elliptic coordinates advocated in the literature do not separate the Hamilton-Jacobi equation for the tri-axial Bianchi IX metric.

math-ph↗
arXiv2005

Heun functions versus elliptic functions

We present some recent progresses on Heun functions, gathering results from classical analysis up to elliptic functions. We describe Picard's generalization of Floquet's theory for differential equations with doubly periodic coefficients and give the detailed forms of the level one Heun functions in terms of Jacobi theta functions. The finite-gap solutions give an interesting alternative integral representation which, at level one, is shown to be equivalent to their elliptic form.

math-ph↗