Bounds on higher derivative f(R,□R,T) models from energy conditions

This paper studies the viable regions of some cosmic models in a higher derivative [Formula: see text] theory with the help of energy conditions (where [Formula: see text], [Formula: see text] and [Formula: see text] are the Ricci scalar, d’Alembert’s operator and trace of energy–momentum tensor, respectively). For this purpose, we assume a flat Friedmann–Lemaître–Robertson–Walker metric which is assumed to be filled with perfect fluid configurations. We take two distinct realistic models that might be helpful to explore stable regimes of cosmological solutions. After taking some numerical values of cosmic parameters, like crackle, snap, jerk (etc.) as well as viable constraints from energy conditions, the viable zones for the under observed [Formula: see text] models are examined.

Energy conditions in higher derivative f(R,□R,T) gravity

In this paper, we examined the viability bounds of a higher derivative [Formula: see text] theory through analyzing energy conditions (where [Formula: see text] and [Formula: see text] are the Ricci scalar, d’Alemberts operator and trace of energy–momentum tensor, respectively). We take flat Friedmann–Lemaître–Robertson–Walker spacetime coupled with ideal configurations of matter content. We consider three different realistic models of this gravity, that could be utilized to understand the stability of cosmological solutions. After constructing certain bounds mediated by energy conditions, more specifically the weak energy condition, we discuss viable zones of the under considered modified models in an environment of recent estimated numerical choices of the cosmic parameters.

Hawking and the Universe

First, the limits of Science, Philosophy and Theology, and the proper methodologies of each field of knowledge must he recalled in order to speak meaningfully of material reality, living or non-living. The existence of infinite universes as the theoretical reason why Einstein’s cosmological constant is so close to zero is impossible to verify for those other universes. Eddington, Dicke, Carter, Barrow, Wheeler and Hawking himself have underlined the need for most precise values of the different cosmic parameters (Anthropic Principle). Finality is a metaphysical problem when we speak of the Universe and to deny it leaves us with an absurd. We should admit that there is no scientific answer as yet for any of the important questions posed by biology. “The Emperor’s New Mind” of artificial intelligence is a fraud, as pointed out by Penrose. In “The Great Design”, their authors present the multiplicity of undetectable universes (than appear out of “nothing”) as the explanation of the fact that the one we detect is suitable for life. No Science can predict what I will do next minute. Neither can it predict the free activity of the Creator who holds the Universe in existence.

COSMIC VOIDS: STRUCTURE, DYNAMICS AND GALAXIES

In this contribution we review and discuss several aspects of Cosmic Voids. Voids are a major component of the large scale distribution of matter and galaxies in the Universe. Their instrumental importance for understanding the emergence of the Cosmic Web is clear. Their relatively simple shape and structure makes them into useful tools for extracting the value of a variety cosmic parameters, possibly including even that of the influence of dark energy. Perhaps most promising and challenging is the issue of the galaxies found within their realm. Not only does the pristine environment of voids provide a promising testing ground for assessing the role of environment on the formation and evolution of galaxies, the dearth of dwarf galaxies may even represent a serious challenge to the standard view of cosmic structure formation.

ALFALFA: HI Cosmology in the Local Universe

For the last 25 years, the 21 cm line has been used productively to investigate the large–scale structure of the Universe, its peculiar velocity field and the measurement of cosmic parameters. In February 2005 a blind HI survey that will cover 7074 square degrees of the high latitude sky was started at Arecibo, using the 7-beam feed L-band feed array (ALFA). Known as the Arecibo Legacy Fast ALFA (ALFALFA) Survey, the program is producing a census of HI-bearing objects over a cosmologically significant volume of the local Universe. With respect to previous blind HI surveys, ALFALFA offers an improvement of about one order of magnitude in sensitivity, 4 times the angular resolution, 3 times the spectral resolution, and 1.6 times the total bandwidth of HIPASS. ALFALFA can detect 7×104D2M⊙of HI, whereDis the source distance in Mpc. As of mid 2007, 44% of the survey observations and 15% of the source extraction are completed. We discuss the status of the survey and present a few preliminary results, in particular with reference to the proposed “dark galaxy” VirgoHI21.

The large number coincidence, the cosmic coincidence and the critical acceleration

The coincidence problem among the pure numbers of order near 10 40 is resolved with the Raychaudhuri and Friedmann–Robertson–Lemaitre–Walker equations and a trivial relationship involving the fine structure constant. The fact that the large number coincidence occurs only in the same epoch in which other coincidences among cosmic parameters occur could be considered a distinct coincidence problem suggesting an underlying physical connection. A natural set of scaling laws for the cosmological constant and the critical acceleration is identified that would resolve the coincidence among cosmic coincidences.