Kaluza-Klein gravity

Astrophysical observations are pointing out huge amounts of “dark matter” and “dark energy” needed to explain the observed large scale structure and cosmic dynamics. The emerging picture is a spatially flat, homogeneous Universe undergoing the today observed accelerated phase. Despite of the good quality of astrophysical surveys, commonly addressed as Precision Cosmology, the nature and the nurture of dark energy and dark matter, which should constitute the bulk of cosmological matter-energy, are still unknown. Furthermore, up to now, no experimental evidence has been found, at fundamental level, to explain such mysterious components. The problem could be completely reversed considering dark matter and dark energy as “shortcomings” of General Relativity in its simplest formulation (a linear theory in the Ricci scalar R, minimally coupled to the standard perfect fluid matter) and claiming for the “correct” theory of gravity as that derived by matching the largest number of observational data, without imposing any theory a priori. As a working hypothesis, accelerating behavior of cosmic fluid, large scale structure, potential of galaxy clusters, rotation curves of spiral galaxies could be reproduced by means of extending the standard theory of General Relativity. In other words, gravity could acts in different ways at different scales and the above “shortcomings” could be due to incorrect extrapolations of the Einstein gravity, actually tested at short scales and low energy regimes. After a survey of what is intended for Extended Theories of Gravity in the so called “metric” and “Palatini” approaches, we discuss some cosmological and astrophysical applications where the issues related to the dark components are addressed by enlarging the Einstein theory to more general f (R) Lagrangians, where f (R) is a generic function of Ricci scalar R, not assumed simply linear. Obviously, this is not the final answer to the problem of “dark-components” but it can be considered as an operative scheme whose aim is to avoid the addition of unknown exotic ingredients to the cosmic pie.

Extended theories of gravity and their cosmological and astrophysical applications

General introduction from fractal objects to fractal spaces fractal dimension of a quantum path the fractal structure of the quantum space-time towards a linear theory of scale relativity prospects.

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Fractal Space-Time And Microphysics: Towards A Theory Of Scale Relativity

Astronomy and Cosmogony

We consider particle decays during the cosmic dark ages with two aims: (1) to explain the high optical depth reported by the Wilkinson Microwave Anisotropy Probe (WMAP), and (2) to provide new constraints to the parameter space for decaying particles. We delineate the decay channels in which most of the decay energy ionizes and heats the intergalactic medium gas [and thus affects the cosmic microwave background (CMB)], and those in which most of the energy is carried away—e.g. photons with energies 100 keV<~E<~1 TeV—and thus appears as a contribution to diffuse x-ray and gamma-ray backgrounds. The new constraints to the decay-particle parameters from the CMB power spectrum thus complement those from the cosmic x-ray and gamma-ray backgrounds. Although decaying particles can indeed produce an optical depth consistent with that reported by WMAP, in so doing they produce new fluctuations in the CMB temperature and polarization power spectra. For decay lifetimes less than the age of the Universe, the induced power spectra generally violate current constraints, while the power spectra are usually consistent if the lifetime is longer than the age of the Universe.

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Particle decays during the cosmic dark ages

On the Origin of Inertia

Preface Part I. Dark Matter in Astronomy and Cosmology: 1. Dark matter in galaxies 2. Dark matter in clusters of galaxies 3. Dark matter in intergalactic space 4. The identity of the dark matter Part II. Ionisation Problems in Astronomy and Cosmology: 5. Diffuse ionisation in the Milky Way 6. Diffuse ionisation in spiral galaxies 7. The intergalactic flux of hydrogen-ionising photons Part III. Neutrino Decay and Ionisation in the Universe: 8. The radiative decay of massive neutrinos 9. Neutrino decay and the ionisation of the Milky Way 10. Neutrino decay and the ionisation of spiral galaxies 11. The intergalactic flux of ionising decay photons 12. The reionisation of the Universe Part IV. Observational Searches for the Neutrino Decay Line: 13. Observational searches for the neutrino decay line References Subject index.

Modern Cosmology and the Dark Matter Problem

The Physical Foundations of General Relativity

I purchased this boot six months ago. It was published in 2009. After picking it up I perused the index to see if proper homage was paid to Charles Darwin as is the custom with modern physics books for the masses. There was no entry for the great man of physics. Would this be the second physics book for the masses in a row that I have read in which I would not know the author’s religion or politics? On a closer look one finds that this publication is a reprint of the original published in 1959. That was before the discipline of physics expanded to embrace religion and politics. But what could one learn about the unity of the universe from fifty-year-old physics?

D. W. Sciama

Papers

On the Origin of Inertia

Modern Cosmology and the Dark Matter Problem

Modern Cosmology and the Dark Matter Problem

The Physical Foundations of General Relativity

The unity of the universe.