We continue our presentation of an alternative cosmology based on conformal gravity, following our kinematical approach introduced in a recent paper. In line with the assumptions of our model, which proposes a closed-form expression for the cosmic scale factor R(t), we first revise the Hubble and deceleration parameters and also introduce modified cosmological distances, analyzing in particular the case of the luminosity distance.
Our kinematical conformal cosmology is then able to explain the anomalous acceleration of the Pioneer spacecraft, as due to a local region of gravitational blueshift. From the reported values of the Pioneer anomaly we also compute the current value of our first fundamental parameter, gamma_{0} = 1.94 x 10^{-28} cm^{-1}, in line with the original estimate by P. Mannheim of this quantity.
Our second fundamental parameter, delta_{0} = 3.83 x 10^{-5}, interpreted as the current value of a cosmological time variable, is derived from a detailed fitting of type Ia Supernovae "gold-silver" data, producing Hubble plots of the same quality of those obtained by standard cosmology, but without requiring any dark matter or dark energy contribution.
If further experiments will confirm the presence of an anomalous frequency blueshift in the outer region of the Solar System, as described by our model, kinematical conformal cosmology might become a viable alternative to standard cosmological theories.
We present an alternative cosmology based on conformal gravity, as originally introduced by H. Weyl and recently revisited by P. Mannheim and D. Kazanas. Unlike past similar attempts our approach is a purely kinematical application of the conformal symmetry to the Universe, through a critical reanalysis of fundamental astrophysical observations, such as the cosmological redshift and others. As a result of this novel approach we obtain a closed-form expression for the cosmic scale factor R(t) and a revised interpretation of the space-time coordinates usually employed in cosmology. New fundament…
We explore the effects of a positive cosmological constant on astrophysical and cosmological configurations described by a polytropic equation of state. We derive the conditions for equilibrium and stability of such configurations and consider some astrophysical examples where our analysis may be relevant. We show that in the presence of the cosmological constant the isothermal sphere is not a viable astrophysical model since the density in this model does not go asymptotically to zero. The cosmological constant implies that, for polytropic index smaller than five, the central density has to e…
It is stressed that the kinematical problems of the standard cosmological model can be solved by a phase of accelerated contraction of the cosmic scale factor. Such a behaviour is only a particular case of a more general ``pre-big-bang" inflationary scenario, arising naturally in a string cosmology context, and driven asymptotically by the free dilaton field without any self-interaction potential and/or vacuum contribution.
Cosmological consequences of a string-motivated dark energy scenario featuring a scalar field coupled to the Gauss-Bonnet invariant are investigated. We study the evolution of the universe in such a model, identifying its key properties. The evolution of the homogeneous background and cosmological perturbations, both at large and small scales, are calculated. The impact of the coupling on galaxy distributions and the cosmic microwave background is examined. We find the coupling provides a mechanism to viably onset the late acceleration, to alleviate the coincidence problem, and furthermore to …
Albert Einstein postulated the equivalence of energy and mass, developed the theory of special relativity, explained the photoelectric effect, and described Brownian motion in five papers, all published in 1905, 100 years ago. With these papers, Einstein provided the framework for understanding modern astrophysical phenomena. Conversely, astrophysical observations provide one of the most effective means for testing Einstein's theories. Here, I review astrophysical advances precipitated by Einstein's insights, including gravitational redshifts, gravitational lensing, gravitational waves, the Le…
We discuss fits of cosmological dark energy models to the available data on high-redshift supernovae. We consider a conventional model with Cold Dark Matter and a cosmological constant (LambdaCDM), a model invoking super-horizon perturbations (SHCDM) and models based on Liouville strings in which dark energy is provided by a rolling dilaton field (Q-cosmology). We show that a complete treatment of Q-cosmology requires a careful discussion of non-equilibrium situations (off-shell effects). The two main high-redshift supernova data sets give compatible constraints on LambdaCDM and the other mode…
The spontaneous breaking of local Lorentz invariance in the early Universe, associated with a first order phase transition at a critical time $t_c$, generates a large increase in the speed of light and a superluminary communication of information occurs, allowing all regions in the Universe to be causally connected. This solves the horizon problem, leads to a mechanism of monopole suppression in cosmology and can resolve the flatness problem. After the critical time $t_c$, local Lorentz (and diffeomorphism) invariance is restored and light travels at its presently measured speed. The kinematic…
We review astrophysical, cosmological and terrestrial evidence for and against the constancy of fundamental parameters of particle physics, and discuss theoretical issues of unification and scalar-mediated forces, finding that the current rate of variation is bounded by limits on violations of the weak equivalence principle.
An extraordinary event took place recently in Ireland. A group of independent and professional researchers met to discuss an old heterodox topic with important consequences in astrophysics and, especially, in cosmology: possible causes of the redshifts in the spectra of astrophysical objects other than a Doppler or expanding universe mechanism. Many decades of work have been devoted to this kind of research, most of it forgotten by the greater part of the astrophysical community nowadays. But the question is still open, the debate is still alive, as was shown by the participants in the present…
The state of our understanding of cosmology is reviewed from an astrophysical cosmologist point of view with a particular emphasis given to recent observations and their impact. Discussion is then presented on the implications for particle physics.
Formation of primordial black holes (PBHs) on astrophysical mass scales is a natural consequence of inflationary cosmology if the primordial perturbation spectrum has a large and negative running of the spectral index as observationally inferred today, because double inflation is required to explain it and fluctuations on some astrophysical scales are enhanced in the field oscillation regime in between. It is argued that PBHs thus produced can serve as intermediate-mass black holes (IMBHs) which act as the observed ultraluminous X-ray sources (ULXs) by choosing appropriate values of the model …
In these Lectures I review possible constraints on particle physics models, obtained by means of combining the results of collider measurements with astrophysical data. I emphasize the theoretical-model dependence of these results. I discuss supersymmetric dark matter constraints at colliders (mainly LHC) in various theoretical contexts: the standard Cosmological-Constant-Cold-Dark-Matter (Lambda-CDM) model, (super)string-inspired ones and non-equilibrium relaxation dark energy models. I then investigate the capability of LHC measurements in asserting whether supersymmetric matter (if discover…
Astrophysical and cosmological consequences of a standard $ν_τ$ of (15 +- 3) keV/c^{2} mass are discussed in the light of the recent results of the solar, atmospheric and LSND neutrino experiments and theoretical prejudices.
The different phases of QCD at finite temperature and density lead to interesting effects in cosmology and astrophysics. In this work I review some aspects of the cosmological QCD transition and of astrophysics at high baryon density.
Spatially averaged inhomogeneous cosmologies in classical general relativity can be written in the form of effective Friedmann equations with sources that include backreaction terms. In this paper we propose to describe these backreaction terms with the help of a homogeneous scalar field evolving in a potential; we call it the `morphon field'. This new field links classical inhomogeneous cosmologies to scalar field cosmologies, allowing to reinterpret, e.g., quintessence scenarios by routing the physical origin of the scalar field source to inhomogeneities in the Universe. We investigate a one…
A system of effective Einstein equations for spatially averaged scalar variables of inhomogeneous cosmological models can be solved by providing a `cosmic equation of state'. Recent efforts to explain Dark Energy focus on `backreaction effects' of inhomogeneities on the effective evolution of cosmological parameters in our Hubble volume, avoiding a cosmological constant in the equation of state. In this Letter it is argued that, if kinematical backreaction effects are indeed of the order of the averaged density (or larger as needed for an accelerating domain of the Universe), then the state of…
The quality of astronomical spectra is now so high that the accuracy of the laboratory data is getting more and more important for the analysis and interpretation. Both in astrophysics and cosmology the needs for accurate laboratory wavelengths have increased with the development of new ground-based and air-borne telescopes and spectrographs. The high resolution UV Fourier Transform spectrometer at Lund Observatory is being used for studying laboratory spectra of astrophysically important elements. Measurements of accurate laboratory UV and IR wavelengths have been made for cosmological and as…
The study of sterile neutrinos has recently acquired a different flavor: being now excluded as the dominant solution for the solar or atmospheric conversions, sterile neutrinos, still attractive for many other reasons, have thus become even more elusive. The present relevant questions are: which subdominant role can they have? Where (and how) can they show up? Cosmology and supernovae turn out to be powerful tools to address these issues. With the most general mixing scenarios in mind, I present the analysis of many possible effects on BBN, CMB, LSS, and in SN physics due to sterile neutrinos.…
Recent cosmological observations of unprecented accuracy, by WMAP in particular, have established a `Standard Model' of cosmology, just as LEP established the Standard Model of particle physics. Both Standard Models raise open questions whose answers are likely to be linked. The most fundamental problems in both particle physics and cosmology will be resolved only within a framework for Quantum Gravity, for which the only game in town is string theory. We discuss novel ways to model cosmological inflation and late acceleration in a non-critical string approach, and discuss possible astrophysic…
The extreme luminosity and their fairly unique temporal behaviour have made supernovae a superb tool to measure distances in the universe. As complex astrophysical events they provide interesting insights into explosion physics, explosive nucleosynthesis, hydrodynamics of the explosion and radiation transport. They are an end product of stellar evolution and provide clues to the stellar composition. Since they can be observed at large distances they have become critical probes to further explore astrophysical effects, like dust properties in external galaxies and the star formation history of …
We review current cosmological constraints on the axion. We describe the basic mechanisms by which axions are created in the early universe, focussing on the standard thermal scenario where the dominant process is through axion radiation by a string network. A dark matter axion in this case would have a mass $\ma \sim 100 \microeV$, with specified large uncertainties. This cosmological lower bound leaves a viable window for the axion below the astrophysical upper limit, $\ma \lapp 1-10 \meV$. We also discuss alternative axion cosmologies which allow a much wider, but indefinite, mass range.
We present an up-to-date review of Big Bang Nucleosynthesis (BBN). We discuss the main improvements which have been achieved in the past two decades on the overall theoretical framework, summarize the impact of new experimental results on nuclear reaction rates, and critically re-examine the astrophysical determinations of light nuclei abundances. We report then on how BBN can be used as a powerful test of new physics, constraining a wide range of ideas and theoretical models of fundamental interactions beyond the standard model of strong and electroweak forces and Einstein's general relativit…
