Roberto A. Sussman

• Ph.D
• National Autonomous University of Mexico

A recent study tested 20 electronic cigarette (e-cigarette) samples and reported that e-cigarette use was associated with far higher exposure to benzene, toluene, and total xylenes compared to Permissible Exposure Limits (PELs) for working environments. However, we noticed several errors in that study, such as incorrect conversions of measuring uni...

The InExpose system manufactured by SCIREQ® is valuable equipment for conducting preclinical studies in the laboratory. It generates e-cigarette (EC) aerosol by puffing the box mod of a high-powered third-generation device (JoyeTech® EVIC Mini), with its atomizer replaced by a custom-made 70 mL tank. We examined the experimental quality of aerosol...

We propose a new phenomenological second order gravity theory to be denoted as ‘Schouten–Codazzi’ Gravity’ (SCG), as it is based on Schouten and Codazzi tensors. The theory is related, but is clearly distinct from Cotton gravity. By assuming as source the energy momentum of General Relativity, we form a second order system with its geometric sector...

We propose a new phenomenological second order gravity theory to be denoted as ''Schouten-Codazzi' Gravity'' (SCG), as it is based on Schouten and Codazzi tensors. The theory is related, but is clearly distinct from Cotton Gravity. By assuming as source the energy momentum of General Relativity, we form a second order system with its geometric sect...

We provide an extensive review of 14 studies (11 independent and three industry-funded) on emissions generated by Electronic Cigarettes (ECs), specifically focusing on the evaluation of carbonyls present in these emissions and emphasizing a meticulous evaluation of their analytical methods and experimental procedures. Since the presence of carbonyl...

We present numerical solutions to Einstein’s equations describing large spherical cosmic voids constituted by two components; dark matter and baryons, with a non-vanishing initial relative velocity, in an asymptotically homogeneous background compatible with the ΛCDM concordance model. We compute numerically the evolution of such configurations in t...

We provide an extensive review of 17 independent and industry-funded studies targeting carbonyls in aerosol emissions of Heated Tobacco Products (HTPs), focusing on quality criteria based on the reproducibility of experiments, appropriate analytic methods, and puffing regimes. Most revised studies complied with these requirements, but some were unr...

We provide an extensive review of 17 independent and industry-funded studies targeting carbonyls in aerosol emissions of Heated Tobacco Products (HTPs), focusing on quality criteria based on the reproducibility of experiments, appropriate analytic methods, and puffing regimes. Most revised studies complied with these requirements, but some were unr...

We provide an extensive review of 17 independent and industry-funded studies targeting carbonyls in aerosol emissions of Heated Tobacco Products (HTPs), focusing on quality criteria based on the reproducibility of experiments, appropriate analytic methods, and puffing regimes. Most revised studies complied with these requirements, but some were unr...

We provide an extensive review of 17 independent industry-funded studies targeting carbonyls in aerosol emissions of Heated Tobacco Products (HTPs), focusing on quality criteria based on the reproducibility of experiments, appropriate analytic methods, and puffing regimes. Most revised studies complied with these requirements, but some were unrepro...

We present numerical solutions to Einstein's equations describing large spherical cosmic voids constituted by two components; dark matter and baryons, with a non-vanishing initial relative velocity, in an asymptotically homogeneous background compatible with the $\Lambda$CDM concordance model. We compute numerically the evolution of such configurat...

We review the literature on laboratory studies quantifying the production of potentially toxic organic byproducts (carbonyls, carbon monoxide, free radicals and some nontargeted compounds) in e-cigarette (EC) aerosol emissions, focusing on the consistency between their experimental design and a realistic usage of the devices, as determined by the p...

Developing a self-consistent notion of gravitational entropy in the context of cosmological structure formation has been so far an elusive task. Various theoretical proposals have been presented, initially based on Penrose’s Weyl Curvature Hypothesis, and variations of it. A more recent proposal by Clifton, Ellis, and Tavakol (CET) considered a nov...

The inhalation of metallic compounds in e-cigarette (EC) aerosol emissions presents legitimate concerns of potential harms for users. We provide a critical review of laboratory studies published after 2017 on metal contents in EC aerosol, focusing on the consistency between their experimental design, real life device usage and appropriate evaluatio...

In this paper, we consider inhomogeneous spherically symmetric models based on the Lemaître–Tolman–Bondi (LTB) metric, assuming as its source an interactive mixture of ordinary baryonic matter, cold dark matter and dark energy with a coupling term proportional to the addition of energy densities of both dark fluids. We reduce Einstein’s field equat...

It is well known that airborne transmission of COVID-19 in indoor spaces occurs through various respiratory activities: breathing, vocalizing, coughing, and sneezing. However, there is a complete lack of knowledge of its possible transmission through exhalations of e-cigarette aerosol (ECA), which is also a respiratory activity. E-cigarettes have b...

Gravitational entropy is an elusive concept. Various theoretical proposals have been presented, initially based on Penrose's Weyl Curvature Hypothesis, and variations of it. A more recent proposal by Clifton, Ellis, and Tavakol (CET) considered a novel approach by defining such entropy from a Gibbs equation constructed from an effective stress-ener...

In this paper, we explore the possibility to find exact solutions for Teleparallel Gravity (TG) of the type of spherically symmetric Lemaître–Tolman–Bondi (LTB) dust models. We apply to the LTB metric the formalism of Teleparallel Gravity in its extension to [Formula: see text] models, which can be seen as the analagous from the Schwarzschild solut...

We consider inhomogeneous spherically symmetric models based on the Lema\^{i}tre-Tolman-Bondi (LTB) metric, assuming as its source an interactive mixture of ordinary baryonic matter, cold dark matter and dark energy with a coupling term proportional to the addition of energy densities of both dark fluids. We reduce Einstein's field equations to a f...

In this paper we explore the possibility to find exact solutions for Teleparallel Gravity (TG) of the type of spherically symmetric Lema\^\i tre-Tolman-Bondi (LTB) dust models. We apply to the LTB metric the formalism of Teleparallel Gravity in its extension to $f(T,B)$ models, which can be seen it as the analagous from the Schwarzschild solution i...

We examine the plausibility of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets that might be carried by exhaled e-cigarette aerosol (ECA). Given the lack of empiric evidence on this phenomenon, we consider available evidence on cigarette smoking and respiratory droplet emission from mouth breathing thr...

We examine in this paper the possibility of finding exact solutions for Teleparallel Gravity (TG) of the type of spherically symmetric Lemaître-Tolman-Bondi (LTB) dust models. We apply to the LTB metric, as obtained from the Schwarzschild solution in General Relativity, the formalism of Teleparallel Gravity in its extension to f(T,B) models. An exa...

We examine in this paper the possibility of finding exact solutions for Teleparallel Gravity (TG) of the type of spherically symmetric Lema\^\i tre-Tolman-Bondi (LTB) dust models. We apply to the LTB metric, as obtained from the Schwarzschild solution in General Relativity, the formalism of Teleparallel Gravity in its extension to $f(T,B)$ models....

Two recently published papers (J.D. Barrow and A. Paliathanasis, Eur. Phys. J. C. (2018, 2019)) claim to have found exact solutions of Einstein's field equations belonging to the class of non-trivial Szekeres models, whose source is a mixture of dust and a homogeneous time-dependent scalar field, where the energy-momentum tensors of both mixture co...

We examine the evolution of peculiar velocities of cold dark matter (CDM) in localized arrays of inhomogeneous cosmic structures in a $$\varLambda $$ Λ CDM background that can be identified as a frame comoving with the Cosmic Microwave (CMB). These arrays are constructed by smoothly matching to this cosmological background regions of Szekeres-II mo...

Background. E-cigarettes are an important harm reduction tool that provides smokers an alternative for nicotine consumption that is much safer than smoking. It is important to asses its safety under preventive and containment measures undertaken during the COVID-19 pandemic.Methods. We develop a theoretical risk model to assess the contagion risk b...

Background. E-cigarettes are an important harm reduction tool that provides smokers an alternative for nicotine consumption that is much safer than smoking. It is important to asses its safety under preventive and containment measures undertaken during the COVID-19 pandemic. Methods. We develop a theoretical risk model to assess the contagion risk...

Two recently published papers (J.D. Barrow and A. Paliathanasis, Eur. Phys. J. C. (2018, 2019)) claim to have found exact solutions of Einstein's field equations belonging to the class of non-trivial Szekeres models, whose source is a mixture of dust and a homogeneous time-dependent scalar field, where the energy-momentum tensors of both mixture co...

We discuss the implications of possible contagion of COVID-19 through e-cigarette aerosol (ECA) for prevention and mitigation strategies during the current pandemic. This is a relevant issue when millions of vapers (and smokers) must remain under indoor confinement and/or share public outdoor spaces with non-users. The fact that the respiratory flo...

We discuss the implications of possible contagion of COVID-19 through e-cigarette aerosol (ECA) for prevention and mitigation strategies during the current pandemic. This is a relevant issue when millions of vapers (and smokers) must remain under indoor confinement and/or share public outdoor spaces with non-users. The fact that the respiratory flo...

We examine a novel class of toy models of cosmological inhomogeneities by smoothly matching along a suitable hypersurface an arbitrary number of sections of ‘quasi flat’ inhomogeneous and anisotropic Szekeres-II models to sections of any spatially flat cosmology that can be described by the Robertson–Waker metric (including de Sitter, anti de Sitte...

We discuss the implications of possible contagion of COVID-19 through e-cigarette aerosol (ECA) for prevention and mitigation strategies during the current pandemic. This is a relevant issue when millions of vapers (and smokers) must remain under indoor confinement and/or share public outdoor spaces with non-users. The fact that the respiratory flo...

We discuss the implications of possible contagion of COVID-19 through e-cigarette aerosol (ECA) for prevention and mitigation strategies during the current pandemic. This is a relevant issue when millions of vapers (and smokers) must remain under indoor confinement and/or share public outdoor spaces with non-users. The fact that the respiratory flo...

We examine the plausibility, scope and risks of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets carried by exhaled e–cigarette aerosol (ECA). Observational and laboratory data suggests considering cigarette smoking and mouth breathing through a mouthpiece as convenient proxies to infer the respiratory...

The plausibility, extent and risk of transmission of SARS-CoV-2 virus through respiratory droplets potentially carried by e-cigarette aerosol (ECA) exhaled by infected vapers are discussed. Taking into account observational data on mouth breathing droplet emission rates as a proxy model for this transmission, droplet diameters should be overwhelmin...

We discuss the plausibility, scope and risk for SARS-CoV-2 virus transmission through respiratory droplets potentially carried by e-cigarette aerosol (ECA) exhaled by infected vapers. Considering observational data on droplet emission rates of mouth breathing as a proxy model for this transmission, droplet diameters should be overwhelmingly in the...

We examine the evolution of peculiar velocities of arrays of inhomogeneous cosmic structures in a ΛCDM background identified as a comoving CMB frame. These arrays are constructed by smoothly matching to this cosmological background regions of Szekeres-II models with their imperfect fluid energy-momentum tensor reinterpreted as non-comoving dust, ke...

We examine a novel class of toy models of cosmological inhomogeneities by smoothly matching along a suitable hypersurface an arbitrary number of sections of "quasi flat" inhomogeous and anisotropic Szekeres-II models to sections of any spatially flat cosmology that can be described by the Robertson-Waker metric (including de Sitter, anti de Sitter...

Background There is insufficient information about risk factors for COVID-19 diagnosis and adverse outcomes from low and middle-income countries (LMICs). Objectives We estimated the association between patients’ characteristics and COVID-19 diagnosis, hospitalisation and adverse outcome in Mexico. Methods This retrospective case series used a pub...

Background: There is insufficient information about risk factors for COVID-19 diagnosis and adverse outcomes from low and middle-income countries (LMICs). Objectives: We estimated the association between patients characteristics and COVID-19 diagnosis, hospitalization and adverse outcome in Mexico. Methods: This retrospective case series used a pub...

We examine the implementation of Buchert’s and Green & Wald’s averaging formalisms in exact spherically symmetric and plane symmetric dust-filled cosmological models. We find that, given a cosmological space-time, Buchert’s averaging scheme gives a faithful way of interpreting the large-scale expansion of space, and explicit terms that precisely qu...

We propose in this letter a relativistic coordinate independent interpretation for Milgrom's acceleration $a_{0}=1.2 \times 10^{-8} \hbox{cm/s}^{2}$ through a geometric constraint obtained from the product of the Kretschmann invariant scalar times the surface area of 2--spheres defined through suitable characteristic length scales for local and cos...

We examine the implementation of Buchert's and Green & Wald's averaging formalisms in exact spherically symmetric and plane symmetric dust-filled cosmological models. We find that, given a cosmological space-time, Buchert's averaging scheme gives a faithful way of interpreting the large-scale expansion of space, and explicit terms that precisely qu...

We examine the fully relativistic evolution of cosmic voids constituted by baryons and cold dark matter (CDM), represented by two non-comoving dust sources in a \(\varLambda \)CDM background. For this purpose, we consider numerical solutions of Einstein’s field equations in a fluid-flow representation adapted to spherical symmetry and multiple comp...

We examine the fully relativistic evolution of cosmic voids constituted by baryons and cold dark matter (CDM), represented by two non-comoving dust sources in a $\Lambda$CDM background. For this purpose, we consider numerical solutions of Einstein's field equations in a fluid-flow representation adapted to spherical symmetry and multiple components...

Current observations suggest that our Universe is not incompatible with a small positive spatial curvature that can be associated with rest frames having a “closed” standard topology. We examine a toy model generalisation of the \(\varLambda \)CDM model in the form of ever expanding Lemaître–Tolman–Bondi (LTB) models with positive spatial curvature...

Current observations suggest that our Universe is not incompatible with a small positive spatial curvature that can be associated with rest frames having a "closed" standard topology. We examine a toy model generalisation of the $\Lambda$CDM model in the form of ever expanding Lema\^{i}tre-Tolman-Bondi (LTB) models with positive spatial curvature....

We examine the gravitational collapse and black hole formation of multiple non--spherical configurations constructed from Szekeres dust models with positive spatial curvature that smoothly match to a Schwarzschild exterior. These configurations are made of an almost spherical central core region surrounded by a network of "pancake-like" overdensiti...

We examine the gravitational collapse and black hole formation of multiple non--spherical configurations constructed from Szekeres dust models with positive spatial curvature that smoothly match to a Schwarzschild exterior. These configurations are made of an almost spherical central core region surrounded by a network of "pancake-like" overdensiti...

We derive a class of non-static inhomogeneous dust solutions in f(R) gravity described by the Lemaitre-Tolman-Bondi (LTB) metric. The field equations are fully integrated for all parameter subcases and compared with analogous subcases of LTB dust solutions of GR. Since the solutions do not admit regular symmetry centres, we have two possibilities:...

Recently we have studied in great detail a model of Hybrid Natural Inflation (HNI) by constructing two simple effective field theories. These two versions of the model allow inflationary energy scales as small as the electroweak scale in one of them or as large as the Grand Unification scale in the other, therefore covering the whole range of possi...

Quasi--local scalar variables approach is applied to a spherically symmetric inhomogeneous Lema\^\i tre--Tolman--Bondi metric containing a mixture of non-relativistic cold dark matter and coupled dark energy with constant equation of state. The quasi--local coupling term considered is proportional to the quasi--local cold dark matter energy density...

We examine the evolution of an inhomogeneous mixture of non-relativistic pressureless cold dark matter (CDM), coupled to dark energy (DE) characterised by the equation of state parameter $w<-1/3$, with the interaction term proportional to the DE density. This coupled mixture is the source of a spherically symmetric Lema\^\ itre-Tolman-Bondi (LTB) m...

We examine the evolution of an inhomogeneous mixture of non-relativistic pressureless cold dark matter (CDM), coupled to dark energy (DE) characterised by the equation of state parameter $w<-1/3$, with the interaction term proportional to the DE density. This coupled mixture is the source of a spherically symmetric Lema\^\ itre-Tolman-Bondi (LTB) m...

We derive a class of non-static inhomogeneous dust solutions in f(R) gravity described by the Lemaitre-Tolman-Bondi (LTB) metric. The field equations are fully integrated for all parameter subcases and compared with analogous subcases of LTB dust solutions of GR. Since the solutions do not admit regular symmetry centres, we have two possibilities:...

Recently we have studied in great detail a model of Hybrid Natural Inflation (HNI) by constructing two simple effective field theories. These two versions of the model allow inflationary energy scales as small as the electroweak scale in one of them or as large as the Grand Unification scale in the other, therefore covering the whole range of possi...

Quasi--local scalar variables approach is applied to a spherically symmetric inhomogeneous Lema\^\i tre--Tolman--Bondi metric containing a mixture of non-relativistic cold dark matter and coupled dark energy with constant equation of state. The quasi--local coupling term considered is proportional to the quasi--local cold dark matter energy density...

Understanding the observations of dynamical tracers and the trajectories of lensed photons at galactic scales within the context of General Relativity (GR), requires the introduction of a hypothetical dark matter dominant component. The onset of these gravitational anomalies, where the Schwarzschild solution no longer describes observations, closel...

We describe how an exact solution of Einstein's equations (the Szekeres models) can be used to construct assorted configurations of multiple non-spherical self-gravitating cold dark matter structures (over-densities and voids) that evolve from realistic initial data. Since the dynamical freedom of the Szekeres models allow (under certain restrictio...

We study the differences and equivalences between the non-perturbative description of the evolution of cosmic structure furnished by the Szekeres dust models (a non-spherical exact solution of Einstein's equations) and the dynamics of Cosmological Perturbation Theory (CPT) for dust sources in a $\Lambda$CDM background. We show how the dynamics of S...

We study the differences and equivalences between the non-perturbative description of the evolution of cosmic structure furnished by the Szekeres dust models (a non-spherical exact solution of Einstein's equations) and the dynamics of Cosmological Perturbation Theory (CPT) for dust sources in a $\Lambda$CDM background. We show how the dynamics of S...

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We take a pragmatic, model independent approach to single field slow-roll canonical inflation by imposing conditions, not on the potential, but on the slow-roll parameter $\epsilon$ and its derivatives $\epsilon^{\prime }$ and $\epsilon^{\prime\prime }$, thereby extracting general conditions on the tensor $r$ and the running $n_{sk}$. Of particula...

We show that the full dynamical freedom of the well known Szekeres models allows for the description of elaborated 3–dimensional networks of cold dark matter structures (over–densities and/or density voids) undergoing “pancake” collapse. By reducing Einstein’s field equations to a set of evolution equations, which themselves reduce in the linear lim...

We undertake a hydrodynamical study of a magnetised cosmic fluid between the end of the leptonic era and the beginning of the radiation-dominated epoch. We assume this fluid to be the source of a Bianchi I model and to be a mixture of tightly coupled primordial radiation, neutrinos, baryons, electrons and positrons, together with a gas of already d...

We analyse the evolution of a magnetised Universe in a stage between the leptonic era and the beginning of the radiationdominated epoch using an anisotropic BianchiI model. In our description the cosmic fluid is made of primordial radiation, neutrinos, magnetic field, non-interacting already decoupled dark matter (WIMPS), baryons, electrons, and po...

We examine the spatial extrema (local maxima, minima and saddle points) of the covariant scalars (density, Hubble expansion, spatial curvature and eigenvalues of the shear and electric Weyl tensors) of the quasispherical Szekeres dust models. Sufficient conditions are obtained for the existence of distributions of multiple extrema in spatial comovi...

We undertake a non-perturbative study of the evolution of the "gravitational entropy" proposed by Clifton, Ellis and Tavakol (CET) on local expanding cosmic CDM voids of $\sim 50-100$ Mpc size described as spherical under-dense regions with negative spatial curvature, whose dynamics is determined by Lemaitre-Tolman-Bondi (LTB) dust models asymptoti...

We examine the spatial extrema (local maxima, minima and saddle points) of the covariant scalars (density, Hubble expansion, spatial curvature and eigenvalues of the shear and electric Weyl tensors) of the quasi-spherical Szekeres dust models. Sufficient conditions are obtained for the existence of distributions of multiple extrema in spatial comov...

We examine the relation between the dynamics of Lema\^{\i}tre-Tolman-Bondi (LTB) dust models (with and without $\Lambda$) and the dynamics of dust perturbations in two of the more familiar formalisms used in cosmology: the metric based Cosmological Perturbation Theory (CPT) and the Covariant Gauge Invariant (GIC) perturbations. For this purpose we...

We apply a recent proposal to define “gravitational entropy” to the expansion of cosmic voids within the framework of nonperturbative General Relativity. By considering CDM void configurations compatible with basic observational constraints, we show that this entropy grows from post-inflationary conditions towards a final asymptotic value in a late...

We analyse Hybrid Natural Inflation in view of the recent results for the tensor index reported by BICEP2. We find that it predicts a large running of the scalar spectrum which is potentially detectable by large scale structure and $21\, \mathrm{cm} $ observations. The running of the running is also relatively large becoming close to $10^{-2}$. Alo...

We consider generic Lemaitre-Tolman-Bondi (LTB) dust models to probe the gravitational entropy proposal of Clifton, Ellis and Tavakol (CET) and of Hosoya and Buchert (HB). We also consider a variant of the HB proposal based on a suitable quasi-local scalar weighted average. We show that the conditions for entropy growth for all proposals are direct...

We analize Hybrid Natural Inflation in view of the recent results for the tensor index reported by BICEP2. We start by studying some general features of inflationary models: in the context of single field inflation based on the slow-roll paradigm we find constraint equations among the obsevables which make no use of the specific form of the potenti...

A "gravitational entropy" can be defined for a gravitational field, in the context of General Relativity, as an independent concept from the entropy of its sources (thermal fluids or black holes). We probe two proposals of this gravitational entropy in generic spherically symmetric Lemaı̂tre-Tolman-Bondy (LTB) models with a dust source. The conditi...

We obtain covariant expressions that generalize the growing and decaying density modes of linear perturbation theory of dust sources by means of the exact density perturbation from the formalism of quasi--local scalars associated to weighed proper volume averages in LTB dust models. The relation between these density modes and theoretical propertie...

We consider a formalism of weighed proper volume scalar averages (the "q-average") for the study of quasi-spherical Szekeres models. We show that the q-average of the main fluid flow covariant scalars are spherically symmetric and satisfy FLRW evolution laws, so that fluctuations and perturbations with respect to these averages provide a full descr...

We examine the dynamics of a self-gravitating magnetized fermion gas at finite temperature near the collapsing singularity of a Bianchi-I spacetime. Considering a general set of appropriate and physically motivated initial conditions, we transform Einstein–Maxwell field equations into a complete and self-consistent dynamical system amenable for num...

We introduce a weighed scalar average formalism ("q-average") for the study of the theoretical properties and the dynamics of spherically symmetric Lemaitre-Tolman-Bondi (LTB) dust models models. The "q-scalars" that emerge by applying the q-averages to the density, Hubble expansion and spatial curvature (which are common to FLRW models) are direct...

We examine the exact perturbations that arise from the q-average formalism that was applied in the preceding article (part I) to Lemaitre-Tolman-Bondi (LTB) models. By introducing an initial value parametrization, we show that all LTB scalars that take a FLRW "look alike" form (frequently used in the literature dealing with LTB models) follow as q-...

We examine the near collapse dynamics of a self-gravitating magnetized electron gas at finite temperature, taken as the source of a Bianchi-I spacetime described by the Kasner metric. The set of Einstein-Maxwell field equations reduces to a complete and self-consistent system of non-linear autonomous ODE's. By considering a representative set of in...

We obtain an elegant and useful description of the dynamics of Szekeres dust models (in their full generality) by means of `quasi-local' scalar variables constructed by suitable integral distributions that can be interpreted as weighed proper volume averages of the local covariant scalars. In terms of these variables, the field equations and basic...

The Szekeres inhomogeneous models are used in order to fit supernova combined data sets. We show that with a choice of the spatial curvature function that is guided by current observations, the models fit the supernova data almost as well as the LCDM model without requiring a dark energy component. The Szekeres models were originally derived as an...

If our cosmic location lies within a large-scale under-dense region or "void", then current cosmological observations can be explained without resorting to a cosmological constant or to an exotic and elusive source like "dark energy". If we further assume this void region to be spherical (as almost all current void models do), then fitting observat...

We use the Szekeres inhomogeneous relativistic models in order to fit supernova combined data sets. We show that with a choice of the spatial curvature function that is guided by current observations, the models fit the supernova data almost as well as the Lambda-CDM model without requiring a dark energy component. The Szekeres models were original...

Inhomogeneous cosmological models are able to fit cosmological observations without dark energy under the assumption that we live close to the “center” of a very large-scale under-dense region. Most studies fitting observations by means of inhomogeneities also assume spherical symmetry, and thus being at (or very near) the center may imply being lo...

We provide a thorough examination of the conditions for the existence of back-reaction and an 'effective' acceleration (in the context of Buchert's averaging formalism) in regular generic spherically symmetric Lemaître–Tolman–Bondi (LTB) dust models. By considering arbitrary spherical comoving domains,we verify rigorously the fulfillment of these c...

We consider spherically symmetric inhomogeneous dust models with a positive cosmological constant, Λ, given by the Lemaître–Tolman–Bondi metric. These configurations provide a simple but useful generalization of the Λ-CDM model describing cold dark matter (CDM) and a Λ term, which seems to fit current cosmological observations. The dynamics of thes...

An effective acceleration, which mimics the effect of dark energy, may arise in the context of Buchert’s scalar averaging formalism. We examine the conditions for such an acceleration to occur in the asymptotic radial range in generic spherically symmetric Lemaître‐Tolman‐Bondi (LTB) dust models. By looking at the behavior of covariant scalars alon...

The application of the second order Extended Irreversible Thermodynamics (EIT) to self-gravitating systems can be effectively considered as the coupling of Einstein's field equations to the transport equations of EIT for the main dissipative fluxes: bulk and shear viscosity and heat flux. A simplified dynamical system approach to this coupling is o...

We examine the radial asymptotic behavior of spherically symmetric Lemaître–Tolman–Bondi dust models by looking at their covariant scalars along radial rays, which are spacelike geodesics parametrized by proper length ℓ, orthogonal to the 4-velocity and to the orbits of SO(3). By introducing quasi-local scalars defined as integral functions along t...

We undertake a comprehensive and rigorous analytic study of the evolution of radial profiles of covariant scalars in regular Lemaitre-Tolman-Bondi dust models. We consider specifically the phenomenon of "profile inversions" in which an initial clump profile of density, spatial curvature or the expansion scalar, might evolve into a void profile (and...

Quasi-local (QL) scalar variables are introduced for spherically symmetric LTB models in order to examine the “back-reaction” term Q in the context of Buchert's scalar averaging formalism. Since QL scalars defined as functionals become weighed averages that generalize the standard proper volume averages, we are able to provide rigorous proof that b...

We introduce quasi-local integral scalar variables for the study of spherically symmetric Lemaitre-Tolman-Bondi (LTB) dust models. Besides providing a covariant, and theoretically appealing, interpretation for the parameters of these models, these variables allow us to study their dynamics (in their full generality) by means of fluid flow evolution...

We introduce quasi‐local (QL) scalar variables in spherically symmetric LTB models. If the QL scalars are defined as functionals, they become weighed averages that generalize the standard proper volume averages on space slices orthogonal to the 4‐velocity. We examine the connection between QL functions and functionals and the “back‐reaction” term...

We interpret as shear viscosity the anisotropic pressure that emerges in inhomogeneous spherically symmetric spacetimes described by the Lemaitre-Tolman-Bondi (LTB) metric in a comoving frame. By assuming that local isotropic pressure and energy density satisfy a generic ideal gas equation of state, we reduce the field equations to a set of evoluti...

A numerical approach is considered for spherically symmetric spacetimes that generalize Lemaître–Tolman–Bondi dust solutions to nonzero pressure (“LTB spacetimes”). We introduce quasilocal (QL) variables that are covariant LTB objects satisfying evolution equations of Friedman–Lemaître–Robertson–Walker (FLRW) cosmologies. We prove rigorously that r...

We examine the dynamics of a self--gravitating magnetized neutron gas as a source of a Bianchi I spacetime described by the Kasner metric. The set of Einstein-Maxwell field equations can be expressed as a dynamical system in a 4-dimensional phase space. Numerical solutions of this system reveal the emergence of a point--like singularity as the fina...