arXiv subjects

M. Le Delliou

Publications and source records attributed to M. Le Delliou.

16 recordsLinked to original sources

arXiv2026

Fuzzy dark matter soliton as gravitational lens

The Schrödinger-Poisson (SP) equations predict fuzzy dark matter (FDM) solitons. Given the FDM mass $\sim10^{-20}\rm~{eV}/c^2$, the FDM soliton in the Milky Way is massive $\sim 10^7~M_{\odot}$ but diffuse $\sim 10{\rm~pc}$. Therefore, such FDM soliton can serve as a gravitational lens for gravitational waves (GWs) with frequency $\sim10^{-8}{\rm~Hz}$. In this paper, we investigate its gravitational lensing effects by numerical simulation of the propagation of GWs through it. We find that the maximum magnification factor of GWs is very small $\sim10^{-4}$, but the corresponding magnification zone is huge $\sim6{\rm~pc}$ for FDM with mass equal to $8\times10^{-21}\rm~{eV}/c^2$. Consequently, this small magnification factor compounding over such large magnification zone results in a small antisotropy of $\sim10^{-4}$ over a large solid angle in the GW background. That level of antisotropy is out of the sensitivity, $<20\%$, of the pulsar timing arrays today.

gr-qc↗

arXiv2026

Matching collapse and expansion across Matter Trapping surfaces in inhomogeneous $Λ$CDM models

In the present work we examine the MTS, for the restriction to spherical dust plus $Λ$, proving that it actually is a characteristic surface of the Cauchy problem (generated by its characteristic curves), which opens the possibility for infinite solutions. This translate as the MTS being a boundary between arbitrarily independent solutions, reminiscent of the Birkhoff theorem effects. This property is illustrated with combinations of 3 examples containing MTSs and $Λ$ ($Λ$CDM, Schwarzschild-de\,Sitter, Lemaître-Tolman-Bondi-de\,Sitter: LTBdS -- i.e. the inhomogeneous, spherically symmetric $Λ$CDM). The LTBdS model presents a static, stable MTS for the first time.

gr-qc↗

arXiv2026

Emergence of Dark Energy from topology and chiral spinors

Under the existence of a massless spinor with respect to the total connection in a spacetime modeled as a Lorentzian manifold with internal boundaries, such as finite volume semi-classical Black Holes, we show that a topological mechanism naturally induces terms in the Einstein-Cartan gravitational action that can be interpreted as General Relativity with dark energy. This may alleviate the problems of dark energy. The topological information is carried by a harmonic 1-form associated to the first co-holomology group of the spacetime, which induces a spacetime contortion acting on the horizontal bundle.

gr-qc↗

arXiv2025

Diversity of Fuzzy Dark Matter Solitons

According to the Schrödinger-Poisson equations, fuzzy dark matter (FDM) can form a stable equilibrium configuration, the so-called FDM soliton. In principle, given the FDM particle mass, the profile of the FDM soliton is fixed. In practice, however, there is a great diversity of structures in the Universe. Possible causes of such diversity can lie in such sources as the gravitoelectric field due to a central supermassive black hole, the gravitomagnetic field due to the system angular momentum, an extra denser and compact FDM soliton and an ellipsoidal baryon background. We find that the effects of the gravitomagnetic field due to the soliton's self-angular momentum are very weak while those of the other sources are considerable.

hep-ph↗

arXiv2024

Barions and $Λ$CDM Model Problems

We examine the inner profiles of the rotation curves of galaxies in the velocity range from dwarf galaxies to Milky-way like galaxies, having maximum of rotation, $V_{\rm max}$, in the range [30-250] km/s, whose diversity is much larger than that predicted by the $Λ$CDM model. After showing that the scatter in the observed rotation curves is much larger that that predicted by dark matter-only cosmologies, we show how taking into account baryons, through a semi-analytical code, allows to create a a variety of rotation curves in agreement with observation. Simultaneoulsy, we show that the the quoted discrepancy does not need for different form of dark matter as advocated by [1], and [2]. We finally show how our model can reobtain the rotation curve of remarkable outliers like IC 2574, a 8 kpc cored profile having a challenging, and extremely low rising rotation curve, and UGC 5721 a cusp-like rotation curve galaxy. We suggest treating baryonic physics properly before introducing new exotic features, albeit legitimate, in the standard cosmological model

astro-ph.GA↗

arXiv2022

Advanced General Relativity Notes

These lecture notes are intended as a guide to Graduate level readers that are already familiar with basic General Relativity. They present in a concise way some advanced concepts and problems encountered in the study of gravitation. In these notes are covered: Alternates forms of the Schwarzschild Black Hole solution, including the classic Kruskal extension; An account of the building of Conformal, Carter-Penrose, diagrams; A discussion of Birkhoff Theorem; A discussion of tools for Geodesics and congruences, including Energy Conditions; A discussion of Horizons and an approach to some of the singularity theorems; An exploration of the Kerr Black Hole solution properties, including the Penrose Process and Black Hole Thermodynamics; A discussion of the Eckart and Israel-Stewart Relativistic Thermodynamics; A discussion of Tetrads in Relativity, in Einstein-Cartan theory and in Newman-Penrose formalism; An explicitation of calculations on Geodesics approach from Hamilton-Jacobi Formalism; A derivation from Least action of the equation of Motion of a top in Relativity, the M.P.D. equations

gr-qc↗

arXiv2021

Cartan approach to Teleparallel Equivalent to General Relativity: a review

In previous works, questioning the mathematical nature of the connection in the translations gauge theory formulation of Teleparallel Equivalent to General Relativity (TEGR) Theory led us to propose a new formulation using a Cartan connection. In this review, we summarize the presentation of that proposal and discuss it from a gauge theoretic perspective.

gr-qc↗

arXiv2020

Teleparallel gravity as a gauge theory: coupling to matter with Cartan connection

We present a consistent and complete description of the coupling to matter in the Teleparallel Equivalent to General Relativity (TEGR) theory built from a Cartan connection, as we proposed in previous works. A first theorem allows us to obtain parallel transport from the Cartan connection into a proper Ehresmann connection, while a second ensures to link the TEGR-Cartan connection to the Ehresmann one-form that contains the Levi-Civita connection. This yields a coupling to matter in agreement with observations and the Equivalence Principle. As the fundamental fields proceed from the Cartan connection, if one insists on interpreting TEGR as a gauge theory of translations, such translation gauge field can be extracted from the consistent theory presented. However, this would entail a fundamental change in the structures known for gauge theory and a split between gauge field and connection is imperative. The willingness to take such a step is left to the reader.

gr-qc↗

arXiv2020

Is the Cosmological Constant of Topological Origin?

The observed value of the cosmological constant poses large theoretical problems. We find that topology of the Universe provides a natural source for it. Restricting dynamically an Einstein-Cartan gravity to General Relativity in our observed Universe allows topological invariants to induce an effective cosmological constant from dynamical quintessence-like topological fields. Its evaluation through the boundary of black holes yields a range compatible with the observed value, with uncertainty of three orders of magnitude. In turns, it provides a measurement of the Universe's isoperimetric constant.

gr-qc↗

arXiv2019

Teleparallel theory as a gauge theory of translations: comments and issues

The Teleparallel Equivalent to General Relativity (TEGR) is often presented as a gauge theory of translations, i.e., that uses \emph{only} the translation group $T_4 = (\setR^4, +)$ as its gauge group. In a previous work we argued against this \emph{translation-only} formalism on the basis of its mathematical shortcomings. We then provided an alternative proposal using a Cartan connection. Recently, a reply by some of the authors defending TEGR as a \emph{translation-only} gauge theory discussed our objections. Here, we first clarify our arguments, and give new proofs of some statements, to answer to these discussions, maintaining our first claim. We then amend one of the argument that originally led us to propose the Cartan connection in this context. This broadens the \emph{a priori} possible choices for a TEGR connection.

gr-qc↗

arXiv2019

Dark Energy from Topology

The concordance model of cosmology suffers from the major theoretical problems surrounding the observed value and recent emergence of a cosmological constant. In this paper we present a novel approach, which explains more naturally its value than that based on quantum vacuum energy, in the form of topological invariants characteristic classes, included as Lagrange multipliers in the action. The approach draws from topological as well as dynamical system consideration, generating as a byproduct an effective cosmological constant. General Relativity is recovered by canceling the torsion in a region containing the observable Universe, which boundary constraints the invariants, thus yielding the effective cosmological constant's form. As that form's denominator contains the total volume of the average black hole, calculated from a geometrical mean on the estimated black hole mass distribution and directly associated to the ratio of the total volume boundary of the space-time manifold and the dominant term in its Euler characteristic. The constant's small estimated value compared to the Planck scale is therefore natural and our evaluation fits remarkably well with the observed value.

gr-qc↗

arXiv2018

Teleparallel gravity (TEGR) as a gauge theory: Translation or Cartan connection?

In this paper we question the status of TEGR, the Teleparallel Equivalent of General Relativity,as a gauge theory of translations. We observe that TEGR (in its usual translation-gauge view) does not seem to realize the generally admitted requirements for a gauge theory for some symmetry group $G$: namely it does not present a mathematical structure underlying the theory which relates to a principal $G$-bundle and the choice of a connection on it (the gauge field). We point out that, while it is usually presented as absent, the gauging of the Lorentz symmetry is actually present in the theory, and that the choice of an Erhesmann connection to describe the gauge field makes the translations difficult to implement (mainly because there is in general no principal translation-bundle). We finally propose to use the Cartan Geometry and the Cartan connection as an alternative approach, naturally arising from the solution of the issues just mentioned, to obtain a more mathematically sound framework for TEGR.

gr-qc↗

arXiv2009

The Abell Cluster A586 and the Detection of the Equivalence Principle

We discuss the current bounds on the Equivalence Principle, in particular from structure formation and, reexamine in this context, the recent claim on the evidence of the interaction between dark matter and dark energy in the Abell Cluster A586 and the ensued violation of the Equivalence Principle.

astro-ph↗

arXiv2007

Dark Energy-Dark Matter Interaction and putative violation of the Equivalence Principle from the Abell Cluster A586

We show that the Abell Cluster A586 exhibits evidence of the interaction between dark matter and dark energy and argue that this interaction implies a violation of the Equivalence Principle. This violation is found in the context of two different models of dark energy-dark matter interaction. We also argue, based on the spherical symmetry of the Abell Cluster A586 that skewness is not the most general quantity to test the Equivalence Principle.

astro-ph↗

arXiv2005

The properties of Ly-alpha emitting galaxies in hierarchical galaxy formation models

We present detailed predictions for the properties of Ly-alpha-emitting galaxies in the framework of the Lambda-CDM cosmology, calculated using the semi-analytical galaxy formation model GALFORM. We explore a model which assumes a top-heavy IMF in starbursts, and which has previously been shown to explain the sub-mm number counts and the luminosity function of Lyman-break galaxies at high redshift. We show that this model, with the simple assumption that a fixed fraction of Ly-alpha photons escape from each galaxy, is remarkably successful at explaining the observed luminosity function of Ly-alpha emitters over the redshift range 3 7, a redshift range which is starting to be be probed by near-IR surveys and using new instruments such as DAzLE.

astro-ph↗

arXiv2002

Coarse Graining the Distribution Function of Cold Dark Matter

The density profiles established in the self-similar dynamical phase of dark matter haloes recollapse are all close to isothermal. This is steeper than the predictions of some n-body simulations for the central regions of the halo, which are in turn steeper than the profiles observed in the centre of some galaxies; particularly dwarfs and low surface brightness galaxies. The outer regions of galaxies both as observed and as simulated have density profiles steeper than the self-similar profile. Nevertheless there appears to be an intermediate region in most galaxies in which the inverse square behaviour is a good description. The outer deviations can be explained plausibly in terms of the transition from a self-gravitating extended halo to a Keplerian flow onto a dominant central mass (the isothermal distribution can not be complete), but the inner deviations are more problematic. Rather than attack this question directly, we use in this paper a novel coarse-graining technique combined with a shell code to establish both the distribution function associated with the self-similar density profile and the nature of the possible deviations in the central regions. In spherical symmetry we find that both in the case of purely radial orbits and in the case of orbits with non-zero angular momentum the self-similar density profile should flatten progressively near the centre of the system. The NFW limit of -1 seems possible. In a section aimed at demonstrating our technique for a spherically symmetric steady state, we argue that a Gaussian distribution function is the best approximation near the centre of the system.

astro-ph↗