arXiv subjects

Luca Teodori

Publications and source records attributed to Luca Teodori.

10 recordsLinked to original sources

arXiv2026

Gravitational lensing time delay beyond the Shapiro/geometry split

Time delays are a key observable in strong gravitational lensing systems. Their theoretical expression is usually written as a sum of a geometrical delay and a Shapiro delay, with cosmology entering through angular diameter distances and a redshift prefactor. In this work we derive this structure from the exact null geodesics of the Schwarzschild-de Sitter metric. The standard formula is recovered as the leading term in a small-angle expansion, and we identify the first correction to the usual geometrical-plus-Shapiro split. Such correction does not introduce any new cosmological dependence: it corresponds instead to a higher-order correction intrinsic to the Schwarzschild part of the metric. As a consequence, up to this order, the cosmological constant enters only through the unlensed angular diameter distances and the unlensed lens-redshift prefactor.

astro-ph.CO↗

arXiv2026

Influence of tides and self-gravity on Ultra-Light Dark Matter Bounds from Dwarf Galaxies

Dwarf spheroidal galaxies provide some of the most sensitive astrophysical probes of ultra-light dark matter (ULDM), but the inferred constraints can be affected by two important systematics: tidal interactions with the Milky Way, which reduce ULDM-induced dynamical heating, and stellar self-gravity, which can become relevant if the stellar component was more compact at earlier times. In this work, we attempt to estimate both effects by reconstructing dwarf-galaxy orbital histories in a Milky-Way potential, adopting a simple and approximate tidal-susceptibility diagnostic that we argue provides a conservative description of tidal stripping, and explicitly including stellar self-gravity in our numerical simulations. Within our framework, which we apply to five different dwarf galaxies, we find that ULDM with masses $5\times 10^{-22} \lesssim m/{\rm eV} \lesssim 5\times 10^{-21}$ remains in tension with current data.

hep-ph↗

arXiv2026

The approximate gravitational lensing multiple plane mass sheet degeneracy

Strong gravitational lensing has to deal with many modeling degeneracies, the most notable being the Mass Sheet Degeneracy (MSD). We review the MSD when one needs to model more lens planes, each one with an internal mass sheet. We take into account the non-linear lens-lens coupling and line of sight effects, the latter treated as external mass sheets with associated shear. If second order shear terms on external and internal mass sheets can be neglected, we show that the MSD is always retained, and the mass sheets influence can be reabsorbed in the redefinition of angular diameter distances. In particular, internal and external mass sheets can be placed on the same footing. The version of the MSD discussed here does not require any particular relation between the internal mass sheets in the different planes. Even when including time delays from all sources, a residual degeneracy involving time delays, mass sheets and $ H_0 $ remains. We develop a framework which shows what can actually be constrained in multiple plane lens systems.

astro-ph.GA↗

arXiv2025

Bracketing the soliton-halo relation of ultralight dark matter

In theories of ultralight dark matter, solitons form in the inner regions of galactic halos. The observational implications of these depend on the soliton mass. Various relations between the mass of the soliton and properties of the halo have been proposed. We analyze the implications of these relations, and test them with a suite of numerical simulations. The relation of Schive et al. 2014 is equivalent to $(E/M)_{\rm sol}=(E/M)_{\rm halo}$ where $E_{\rm sol (halo)}$ and $M_{\rm sol (halo)}$ are the energy and mass of the soliton (halo). If the halo is approximately virialized, this relation is parametrically similar to the evaporation/growth threshold of Chan et al. 2022, and it thus gives a rough lower bound on the soliton mass. A different relation has been proposed by Mocz et al. 2017, which is equivalent to $E_{\rm sol}=E_{\rm halo}$, so is an upper bound on the soliton mass provided the halo energy can be estimated reliably. Our simulations provide evidence for this picture, and are in broad consistency with the literature, in particular after accounting for ambiguities in the definition of $E_{\rm halo}$ at finite volume.

astro-ph.CO↗

arXiv2025

Ultra-Light Dark Matter Simulations and Stellar Dynamics: Tension in Dwarf Galaxies for $m < 5\times10^{-21} $ eV

We present numerical simulations of dark matter and stellar dynamics in ultra light dark matter halos tailored to mimic dwarf galaxies. An important effect we observe is the dynamical evolution of the stellar half-light radius and velocity dispersion, which makes previous equilibrium models significantly incomplete. Based on half-light radius dynamical evolution, as well as velocity peaks due to soliton core condensation, we show that data from the Fornax, Carina, and Leo II dwarf galaxies disfavores particle masses in the range $ 5\times 10^{-22} \text{ eV} \lesssim m \lesssim 5\times10^{-21}$ eV. Smaller boson masses, around $m\approx1\times10^{-22}$ eV, could cause strong dynamical heating, but we caution that tidal stripping by the Milky Way could moderate the effect. A caveat in our analysis is the omission of stellar self-gravity, which could affect extrapolation back in time if the stellar body was much more compact in the past.

astro-ph.GA↗

arXiv2024

AxionH0graphy: hunting for ultralight dark matter with cosmographic H$_0$ signal

If ultralight boson fields exist, then vacuum misalignment populates them with nonzero relic abundance. For a broad range of particle mass $m$ the field condenses into fuzzy cores in massive galaxies. We use numerical simulations to test this idea, extending previous work (Blum and Teodori 2021) and focusing on ultralight dark matter (ULDM) that makes-up a subdominant fraction of the total dark matter density, consistent with observational constraints. Our simulations mimic galactic halos and explore different initial conditions and levels of sophistication in the modeling of the halo potential. For $m\sim10^{-25}$ eV ULDM cores act as approximate internal mass sheets in strong gravitational lensing, and could first be detected as an $H_0$ bias in cosmography: a scenario we dub AxionH0graphy. The mass sheet degeneracy is broken by finite core radius and by the dynamical displacement of cores from the halo center of mass, which introduce imaging distortions and restrict the $H_0$ bias limit of AxionH0graphy to $m\lesssim5\times10^{-25}$ eV. Cosmological simulations are called for to sharpen the predicted connection between the amplitude of ULDM galactic cores and the ULDM cosmological fraction.

astro-ph.CO↗

arXiv2023

Host group degeneracy in gravitational lensing time delay determination of $H_0$

Massive elliptical galaxies, that serve as lenses in gravitational lensing time delay measurements of the Hubble parameter $H_0$, often reside in a host group. We consider degeneracies in the modeling of the group halo. When the group effect on imaging can be summarized by its flexion (the next order term beyond shear in the tidal expansion), the posterior likelihood map can develop disjoint local minima, associated with an approximate discrete symmetry of a dominant flexion term. Monte-Carlo Markov Chain (MCMC) algorithms that are not designed to explore a rich posterior landscape can miss some of the minima, introducing systematic bias. We study mock data and demonstrate that the bias in $H_0$ can exceed $10\%$, and pulls the inference value of $H_0$ above its truth value, for a reason that can be traced to the structure of a mismodeled flexion term. MCMC algorithms that are designed to cope with a rich posterior landscape can uncover the structure. If the group is X-ray bright enough, X-ray data may also help to resolve the degeneracy, by pinpointing the group's center of mass. Finally, we show that some implementations in the literature used an inaccurate kinematical prior, mis-modeling the group velocity dispersion by as much as $20\%$

astro-ph.CO↗

arXiv2022

Comments on the mass sheet degeneracy in cosmography analyses

We make a number of comments regarding modeling degeneracies in strong lensing measurements of the Hubble parameter $H_0$. The first point concerns the impact of weak lensing associated with different segments of the line of sight. We show that external convergence terms associated with the lens-source and observer-lens segments need to be included in cosmographic modeling, in addition to the usual observer-source term, to avoid systematic bias in the inferred value of $H_0$. Specifically, we show how an incomplete account of some line of sight terms biases stellar kinematics as well as ray tracing simulation methods to alleviate the mass sheet degeneracy. The second point concerns the use of imaging data for multiple strongly-lensed sources in a given system. We show that the mass sheet degeneracy is not fully resolved by the availability of multiple sources: some degeneracy remains because of differential external convergence between the different sources. Similarly, differential external convergence also complicates the use of multiple sources in addressing the approximate mass sheet degeneracy associated with a local ("internal") core component in lens galaxies. This internal-external degeneracy is amplified by the non-monotonicity of the angular diameter distance as a function of redshift. For a rough assessment of the weak lensing effects, we provide estimates of external convergence using the nonlinear matter power spectrum, paying attention to non-equal time correlators.

astro-ph.CO↗

arXiv2021

lenstronomy II: A gravitational lensing software ecosystem

lenstronomy is an Astropy-affiliated Python package for gravitational lensing simulations and analyses. lenstronomy was introduced by Birrer and Amara (2018) and is based on the linear basis set approach by Birrer et a. (2015). The user and developer base of lenstronomy has substantially grown since then, and the software has become an integral part of a wide range of recent analyses, such as measuring the Hubble constant with time-delay strong lensing or constraining the nature of dark matter from resolved and unresolved small scale lensing distortion statistics. The modular design has allowed the community to incorporate innovative new methods, as well as to develop enhanced software and wrappers with more specific aims on top of the lenstronomy API. Through community engagement and involvement, lenstronomy has become a foundation of an ecosystem of affiliated packages extending the original scope of the software and proving its robustness and applicability at the forefront of the strong gravitational lensing community in an open source and reproducible manner.

astro-ph.CO↗

arXiv2021

Gravitational lensing $H_0$ tension from ultralight axion galactic cores

Gravitational lensing time delays offer an avenue to measure the Hubble parameter $H_0$, with some analyses suggesting a tension with early-type probes of $H_0$. The lensing measurements must mitigate systematic uncertainties due to the mass modelling of lens galaxies. In particular, a core component in the lens density profile would form an approximate local mass sheet degeneracy and could bias $H_0$ in the right direction to solve the lensing tension. We consider ultralight dark matter as a possible mechanism to generate such galactic cores. We show that cores of roughly the required properties could arise naturally if an ultralight axion of mass $m\sim10^{-25}$ eV makes up a fraction of order ten percent of the total cosmological dark matter density. A relic abundance of this order of magnitude could come from vacuum misalignment. Stellar kinematics measurements of well-resolved massive galaxies (including the Milky Way) may offer a way to test the scenario. Kinematics analyses aiming to test the core hypothesis in massive elliptical lens galaxies should not, in general, adopt the perfect mass sheet limit, as ignoring the finite extent of an actual physical core could lead to significant systematic errors.

astro-ph.CO↗