arXiv subjects

Renato Velozo Ruiz

Publications and source records attributed to Renato Velozo Ruiz.

9 recordsLinked to original sources

arXiv2026

Relatively non-degenerate integrated decay estimates for massless Vlasov fields on Schwarzschild spacetimes

In this article, we make use of a weight function capturing the concentration phenomenon of unstable future-trapped causal geodesics. A projection $V_+$, on the tangent space of the null-shell, of the associated symplectic gradient turns out to enjoy good commutation properties with the massless Vlasov operator. This reflects that $V_+f$ decays exponentially locally near the photon sphere, for any smooth solution $f$ to the massless Vlasov equation. By identifying a well-chosen modification of $V_+$, we are able to construct a $W_{x,p}^{1,1}$ weighted norm for which any smooth solution to the massless Vlasov equation verifies an integrated local energy decay estimate without relative degeneration. Together with the $r^p$-weighted energy method of Dafermos--Rodnianski, we establish time decay for the energy norm. This norm allows for the control of the energy-momentum tensor $\mathrm{T}[f]$ as well as all its first order derivatives. The method developed in this paper is in particular compatible with approaches recently developed for the study of quasi-linear wave equations on black hole spacetimes.

math.AP↗

arXiv2026

Future global stability of Maxwell-Jüttner equilibria and vacuum for the massless Boltzmann equation on FLRW spacetimes

In this work we study the general relativistic massless Boltzmann equation on Friedmann-Lemaître-Robertson-Walker spacetimes with spatial topology $\mathbb{T}^3$ in the linear and decelerated expanding regimes, where the scale factor is $t^{\mathfrak{q}}$ with $\mathfrak{q}\in [0,1]$. The massless Boltzmann equation on these backgrounds admits non-stationary Maxwell-Jüttner equilibria of the form $\exp(- |t^{2\mathfrak{q}}p|)$. For $0 \leq \mathfrak{q} \leq 1$, we prove future global-in-time existence and uniqueness of small perturbations of these equilibria in the case of hard ball interaction without symmetry assumptions. For $0\leq \mathfrak{q} < 1/3$, we prove that the perturbation -- measured in a suitable $L^2_p$ based energy norm -- decays at the superpolynomial time-decay rate of $t^{-3\mathfrak{q}}\exp(-t^{1-3\mathfrak{q}})$, whereas for $1/3< \mathfrak{q} \leq 1$ we obtain the polynomial time-decay rate of $t^{-3\mathfrak{q}}$. In the borderline case $\mathfrak{q}=1/3$, we show the time-decay of $t^{-3\mathfrak{q} -c}$ with a uniform constant $c>0$. Finally, for $\frac{1}{3}< \mathfrak{q}\leq 1$, we prove future global-in-time existence and uniqueness of small perturbations of the vacuum solution on $\mathbb{T}^3$.

gr-qc↗

arXiv2025

Phase mixing and the Vlasov equation in cosmology

We consider the Vlasov equation on slowly expanding isotropic homogeneous tori, described by the Friedmann--Lemaître--Robertson--Walker cosmological spacetimes. For expansion rate $t^q$, with $0< q<\frac{1}{2}$ (excluding certain exceptional values), we show that the spatial density decays at the rate $t^{-6q}$ and that, when the spatial average is removed, the density decays at an enhanced rate due to a phase mixing effect. This enhancement is polynomial for Sobolev initial data and super-polynomial, but sub-exponential, for real analytic initial data. We further show that, when the expansion rate is the borderline $t^{\frac{1}{2}}$ -- the rate which describes a radiation filled universe -- a degenerate phase mixing effect results in a logarithmic enhancement for Sobolev initial data and a super-logarithmic enhancement (in fact, a gain of $\exp(-μ(\log t)^ε)$ for some $μ,ε>0$) for analytic initial data. The proof is based on a collection of commuting vector fields, and certain combinatorial properties of an associated collection of differential operators. The vector fields are not explicit, but are shown to have good properties when $t$ is large with respect to the momentum support of the solution. A physical space dyadic localisation is employed to treat non-compactly supported (in particular, non-trivial real analytic) but suitably decaying solutions.

gr-qc↗

arXiv2024

Decay properties for massive Vlasov fields on Schwarzschild spacetime

In this paper, we obtain pointwise decay estimates in time for massive Vlasov fields on the exterior of Schwarzschild spacetime. We consider massive Vlasov fields supported on the closure of the largest domain of the mass-shell where timelike geodesics either cross $\mathcal{H}^+$, or escape to infinity. For this class of Vlasov fields, we prove that the components of the energy-momentum tensor decay like $v^{-\frac{1}{3}}$ in the bounded region $\{r\leq R\}$, and like $u^{-\frac{1}{3}}r^{-2}$ in the far-away region $\{r\geq R\}$, where $R>2M$ is sufficiently large. Here, $(u,v)$ denotes the standard Eddington--Finkelstein double null coordinate pair.

gr-qc↗

arXiv2024

Late-time asymptotics of small data solutions for the Vlasov-Poisson system

In this paper, we study the precise late-time asymptotic behaviour of small data solutions for the Vlasov-Poisson system in dimension three. First, we show that the spatial density and the force field satisfy asymptotic self-similar polyhomogeneous expansions. Moreover, we obtain an enhanced modified scattering result for this non-linear system. We show that the distribution function converges, with an arbitrary rate, to a regular distribution function along high order modifications to the characteristics of the linearised problem. We exploit a hierarchy of asymptotic conservation laws for the distribution function. As an application, we show late-time tails for the spatial density and the force field, where the coefficients in the tails are obtained in terms of the scattering state. Finally, we prove that the distribution function (up to normalisation) converges weakly to a Dirac mass on the zero velocity set.

math.AP↗

arXiv2024

A note on integrated local energy decay estimates for spherically symmetric black hole spacetimes

We present short proofs of integrated local energy decay estimates on Schwarzschild, extremal Reissner-Nordström, and Schwarzschild-de Sitter spacetimes. The proofs employ novel global physical space multipliers, which, besides their remarkable simplicity, (a) are directly derivable from the geodesic flow, (b) do not require decomposition into spherical harmonics, and (c) whose boundary terms can be controlled by the conserved $T$-energy alone. We also elaborate on the intimate connection between the multipliers of the present paper and the globally good commutators introduced by the first two authors.

gr-qc↗

arXiv2023

Decay properties of Vlasov fields on non-trapping asymptotically hyperbolic manifolds

In this paper, we study pointwise decay estimates in time for Vlasov fields on non-trapping asymptotically hyperbolic manifolds. We prove optimal decay estimates in time for the spatial density induced by Vlasov fields on these geometric backgrounds in dimension two. First, we show exponential decay for Vlasov fields on hyperbolic space supported away from the zero velocity set. In contrast, we obtain inverse polynomial decay for general Vlasov fields on hyperbolic space. In the second part of the article, we prove exponential decay for Vlasov fields on non-trapping asymptotically hyperbolic manifolds supported away from the zero velocity set. The proofs are obtained through a commuting vector field approach. We exploit the hyperbolicity of the geodesic flow in these geometric backgrounds, by making use of a commuting vector field in the unstable invariant distribution of phase space.

math.AP↗

arXiv2023

Modified scattering of small data solutions to the Vlasov-Poisson system with a trapping potential

In this paper, we study small data solutions to the Vlasov-Poisson system with the simplest external potential, for which unstable trapping holds for the associated Hamiltonian flow. First, we provide a new proof of global existence for small data solutions to the Vlasov-Poisson system with the trapping potential $\frac{-|x|^2}{2}$ in dimension two. We exploit the uniform hyperbolicity of the Hamiltonian flow, by making use of the commuting vector fields contained in the stable and unstable invariant distributions of phase space for the linearized system. In contrast with the proof in \cite{VV23}, we do not use modified vector field techniques. Moreover, we obtain small data modified scattering for this non-linear system. We show that the distribution function converges to a new regular distribution function along modifications to the characteristics of the linearized problem. We define the linearly growing corrections to the characteristic system, in terms of a precise effective asymptotic force field. We make use of the scattering state to obtain the late-time asymptotic behavior of the spatial density. Finally, we prove that the distribution function (up to normalization) converges weakly to a Dirac mass on the unstable manifold of the origin.

math.AP↗

arXiv2023

Small data solutions for the Vlasov-Poisson system with a trapping potential

In this paper, we study small data solutions for the Vlasov-Poisson system with the simplest external potential, for which unstable trapping holds for the associated Hamiltonian flow. We prove sharp decay estimates in space and time for small data solutions to the Vlasov-Poisson system with the unstable trapping potential $\frac{-|x|^2}{2}$ in dimension two or higher. The proofs are obtained through a commuting vector field approach. We exploit the uniform hyperbolicity of the Hamiltonian flow, by making use of the commuting vector fields contained in the stable and unstable invariant distributions of phase space for the linearized system. In dimension two, we make use of modified vector field techniques due to the slow decay estimates in time. Moreover, we show an explicit teleological construction of the trapped set in terms of the non-linear evolution of the force field.

math.AP↗