Jose Antonio de Freitas Pacheco

We investigate the equilibrium and stability properties of self-gravitating bosonic congurations in the nonrelativistic regime by numerically solving the nonlinear Gross-Pitaevskii-Poisson (GPP) system of equations. By adopting a suitable coordinate transformation and a specic gauge choice for the gravitational potential, the GPP equations are cast into a dimensionless form independent of the physical parameters of the model. In this formulation, equilibrium congurations are uniquely characterized by the central value of the dimensionless wave function, which determines the central density once physical units are restored. We compute sequences of stationary solutions including both ground-state and radially excited congurations and identify bifurcation points at which transitions between these states occur. The virial relation is employed as a diagnostic criterion for equilibrium, allowing us to determine a critical central density above which stationary congurations cease to exist. Excited-state solutions satisfying the virial relation are probably metastable and are expected to decay toward the ground state through gravitational cooling. The critical central density is associated with a maximum allowed particle number, leading to an estimate of the maximum stable mass of the conguration. For axion-like bosons with masses of order 10?5 eV, the resulting maximum mass is of the order of tens of Earth mass, while the characteristic size of the conguration is of order one meter. The compactness of these objects places them close to the limit of validity of the Newtonian approximation.

The possible presence of dimethyl sulfide (DMS) in the atmosphere of the exoplanet K2‑18b—an ocean‑bearing Hycean world candidate—has intensified the interest in its potential habitability. This sulfur compound, primarily produced by marine life on Earth, is considered a potential biosignature. We investigate whether the observed atmospheric DMS levels could plausibly originate from biological activity, assuming Earth‑like metabolic pathways. Through energy budget modeling, this study estimates the DMS production capacity of a hypothetical biosphere on K2‑18b and finding that, even under optimistic assumptions, biogenic DMS levels would fall several orders of magnitude short of those inferred from James Webb Space Telescope (JWST) observations. Additionally, we examine DMS atmospheric lifetimes under K2‑18b’s environmental conditions. The results suggest that, while the presence of DMS cannot be conclusively attributed to biological activity, its detection remains inconclusive as a biosignature due to possible non‑biological production mechanisms and uncertainties in spectral retrieval procedures. We conclude that current evidence does not support the presence of life on K2‑18b and emphasize the need for more refined observational data and atmospheric models.

We present a study of relic gravitational waves based on a foliated gauge field theory defined over a spacetime endowed with a noncommutative algebraic–geometric structure. As an ontological extension of general relativity—concerning manifolds, metrics, and fiber bundles—the conventional space and time coordinates, typically treated as classical numbers, are replaced by complementary quantum dual fields. Within this framework, consistent with the Bekenstein criterion and the Hawking–Hertog multiverse conception, singularities merge into a helix-like cosmic scale factor that encodes the topological transition between the contraction and expansion phases of the universe analytically continued into the complex plane. This scale factor captures the essence of an intricate topological quantum-leap transition between two phases of the branching universe: a contraction phase preceding the now-surpassed conventional concept of a primordial singularity and a subsequent expansion phase, whose transition region is characterized by a Riemannian topological foliated structure. The present linearized formulation, based on a slight gravitational field perturbation, also reveals a high sensitivity of relic gravitational wave amplitudes to the primordial matter and energy content during the universe’s phase transition. It further predicts stochastic homogeneous distributions of gravitational wave intensities arising from the interplay of short- and long-spacetime effects within the non-commutative algebraic framework. These results align with the anticipated future observations of relic gravitational waves, expected to pervade the universe as a stochastic, homogeneous background.

A novel approach to cosmic inflation within the framework of a non-commutative Riemannian foliated quantum gravity, built upon a reverse Faddeev–Jackiw symplectic spacetime deformation of the conventional Poisson algebra, is investigated. Friedmann-type dynamical equations, analitycally continued to a complex non-commutative framework, incorporate a modified energy-momentum Riemann tensor and a non-commutative matter-energy potential, highlighting the emergence of quantum gravity topological fluctuation effects on the expansion dynamics of the universe. In this realm, the coupling of UV and IR scales play a central role, providing a natural topological mechanism for inflation and recursal evidences for the generation of relic gravitational waves. These predictions align with a self-consistent description of the transition between the primordial mirror-universe deceleration and present-universe acceleration phases as predict by the Riemann foliated quantum gravity, offering potential connections to observational cosmology.

We present a study of relic gravitational waves based on a foliated gauge field theory defined over a spacetime endowed with a noncommutative algebraic-geometric structure. As an ontological extension of general relativity concerning manifolds, metrics and fiber bundles, the space and time coordinates, which conventionally correspond to classical numbers, are replaced in this formulation by complementary quantum dual fields. In this framework, consistently complying within the Bekenstein criterion, combined with the Hawking-Hertog multiverse conception, singularities merge, portrayed into a new cosmic helix-like scale factor, analytically continued to the complex plane. This scale-factor captures the essence of an intricate topological quantum-leap transition between two phases of the branching universe: a contraction phase preceding the surpassed conventional concept of a primordial singularity and a subsequent expansion phase whose transition region between the two phases is characterized by a Riemannian topological foliated structure. The present linearized formulation, underlying a slightly gravitational field perturbation reveals, during the universe phase transition, high sensitivity of the relic gravitational waves amplitudes to the primordial matter and energy content. The present formulation reveals a stochastic homogeneous distributions of gravitational-wave intensities arising from the capture of short and long spacetime scales within the noncommutative algebraic framework. These results are consistent with the expected anticipated future observations of relic gravitational waves, which are expected to fill the universe as a stochastic homogeneous background.

Neste artigo são discutidas as principais causas que podem ter sido responsáveis pelas grandes extinções de espécies observadas nos últimos 600 milhões de anos da história da Terra. Em geral, catástrofes cósmicas e um vulcanismo intenso tem sido as razões invocadas. Hoje, aceita-se que as causas são diversas e complexas. As extinções resultam de uma alteração importante e sobretudo rápida do habitat, como por exemplo o clima, impedindo que as espécies tenham tempo de se adaptar às condições do novo ambiente. Existem indícios preocupantes que estejamos presentemente no limiar de uma nova extinção massiva na qual a espécie humana, responsável por ela, pode sofrer graves consequências.

Neste trabalho é apresentado um modelo simples da evolução do nível de CO2 na atmosfera terrestre. Usando dados disponíveis das emissões de CO2 devidas a atividade humana e considerando uma estocagem do carbono por mecanismos agindo na biosfera, o tempo médio de residência do CO2 na atmosfera foi estimado em 120 anos. Supondo que a tendência observada nas emissões do CO2 sejam mantidas, a extrapolação dos resultados do modelo indicam no horizonte de 2050 uma concentração de CO2 da ordem de 513 ppm e um aumento de +2,6°C na temperatura global, acima do limite estabelecido pelo acordo de Paris.

We propose a novel extension to the recently developed non-commutative Riemannian foliated branch-cut quantum gravity (BCQG). On basis in an extended Faddeev–Jackiw symplectic deformation of the conventional Poisson algebra, we investigate non-commutativity effects on a symplectic topological manifold that provides a natural isomorphic setting composed by a triad of canonically conjugate scalar complex fields which comprise quantum complementary dualities. The resulting extended manifold spans the canonical BCQG cosmic scale factor and, in addition to its complementary quantum counterpart, outlined in the perfect fluid domain of Hermann Weyl, a scalar-complex inflaton-inspired field. By constructing a triad of quantized fields underlying a noncommutative spacetime, this extension allows the elaboration of a scenario where the original branch-cut domain coexists with a complex scalar inflaton-type field, settled on a plateau of a strong gravity interaction structure. Alongside shaping this structure settled on a background composed by the primordial energy, radiation-, quintessence-, stiff-, baryon- and dark matter, combined with the spacetime components of the scalar Ricci curvature at different orders, cosmic inflation is driven. The presence of the inflaton field in the present formulation transcends the character of a simple reference field, to the extent that its original motivation has been to driven inflation, a role played by the original formulation of the BCQG. The resulting symplectic algebraic extension allows additionally a liaison with primordial cosmic density perturbation predictions based on heuristic derivations of the scale invariance of the primordial spectrum of the Universe, as well as with eternal inflation and primordial chaotic cosmic mechanisms proposals. Given the peculiar characteristic of BCQG in overcoming the primordial singularity, the non-commutative symplectic extension proposal, due to the complex character of the constituent fields, additionally outlines the evolutionary process of the mirror Universe that encompasses analytically continued complex conjugate Friedmann's-type equations. This brings unique characteristics to the main scenario for the BCQG cosmic evolution, with a mirrored parallel evolutionary Universe, adjacent to ours, nested in the structure of space and time. The evolutionary process of the mirror Universe occurs in the negative sector of cosmological thermal time, and is characterized by a continuous cosmic contraction, with a systematic and continuous increase in temperature and a decrease in entropy before reaching the transition region to the current stage of the Universe. In contrast, the subsequent present evolutionary stage of cosmic expansion is characterized by a positive complex cosmological-time sector, accompanied by a systematic decrease in temperature and increase in entropy. On basis on complementary analytically continued Friedmann’s-type equation, combined with a quantum approach based on the Ho\v{r}awa-Lifshitz quantum gravity, we describe the dynamic evolution of the Universe’s wave function, unfolding unprecedented predictions for the cosmic evolution and inflation. This approach offers a new perspective to explain the accelerated cosmic expansion of the Universe, strongly suggesting that non-commutative algebra induces the late accelerated growth of the wave function of the Universe as well as of the corresponding scale factor and its complementary quantum counterparts. In contrast to the conventional inflationary model, where inflation requires a remarkably fine-tuned set of initial conditions in a patch of the Universe, non-commutative foliated quantum gravity, analytically continued to the complex plane, captures short and long scales of spacetime, leading to an evolutionary cosmic dynamic through a topological reconfiguration of the primordial cosmic matter and energy content. Still, we consider in this work the interplay between naturalness and a fine-tuning set constraining of the cosmological initial conditions. This result introduces new speculative framework elements regarding the reconfiguration of matter and energy due to an underlying non-commutative spatio-temporal structure as a driver of spacetime cosmic acceleration.