Search results for "Cosmological"
showing 10 items of 120 documents
Can interacting dark energy solve the $H_0$ tension?
2017
The answer is Yes! We indeed find that interacting dark energy can alleviate the current tension on the value of the Hubble constant $H_0$ between the Cosmic Microwave Background anisotropies constraints obtained from the Planck satellite and the recent direct measurements reported by Riess et al. 2016. The combination of these two datasets points towards an evidence for a non-zero dark matter-dark energy coupling $\xi$ at more than two standard deviations, with $\xi=-0.26_{-0.12}^{+0.16}$ at $95\%$ CL. However the $H_0$ tension is better solved when the equation of state of the interacting dark energy component is allowed to freely vary, with a phantom-like equation of state $w=-1.184\pm0.…
New reaction rates for the destruction of $^7$Be during big bang nucleosynthesis measured at CERN/n_TOF and their implications on the cosmological li…
2019
New measurements of the7Be(n,α)4He and7Be(n,p)7Li reaction cross sections from thermal to keV neutron energies have been recently performed at CERN/n_TOF. Based on the new experimental results, astrophysical reaction rates have been derived for both reactions, including a proper evaluation of their uncertainties in the thermal energy range of interest for big bang nucleosynthesis studies. The new estimate of the7Be destruction rate, based on these new results, yields a decrease of the predicted cosmological7Li abundance insufficient to provide a viable solution to the cosmological lithium problem.
Asymptotic Safety, Fractals, and Cosmology
2013
These lecture notes introduce the basic ideas of the asymptotic safety approach to quantum Einstein gravity (QEG). In particular they provide the background for recent work on the possibly multi-fractal structure of the QEG space-times. Implications of asymptotic safety for the cosmology of the early Universe are also discussed.
On the invariant symmetries of the D-metrics
2007
We analyze the symmetries and other invariant qualities of the $\mathcal{D}$-metrics (type D aligned Einstein Maxwell solutions with cosmological constant whose Debever null principal directions determine shear-free geodesic null congruences). We recover some properties and deduce new ones about their isometry group and about their quadratic first integrals of the geodesic equation, and we analyze when these invariant symmetries characterize the family of metrics. We show that the subfamily of the Kerr-NUT solutions are those admitting a Papapetrou field aligned with the Weyl tensor.
Non-Linear Relativistic Evolution of Cosmological Perturbations in Irrotational Dust
2008
Light majoron cold dark matter from topological defects and the formation of boson stars
2019
We show that for a relatively light majoron ($\ll 100 $ eV) non-thermal production from topological defects is an efficient production mechanism. Taking the type I seesaw as benchmark scheme, we estimate the primordial majoron abundance and determine the required parameter choices where it can account for the observed cosmological dark matter. The latter is consistent with the scale of unification. Possible direct detection of light majorons with future experiments such as PTOLEMY and the formation of boson stars from the majoron dark matter are also discussed.
The galaxy power spectrum take on spatial curvature and cosmic concordance
2020
The concordance of the $\Lambda$CDM cosmological model in light of current observations has been the subject of an intense debate in recent months. The 2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power spectrum measurements appear at face value to favour a spatially closed Universe with curvature parameter $\Omega_K<0$. This preference disappears if Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to break the geometrical degeneracy, although the reliability of this combination has been questioned due to the strong tension present between the two datasets when assuming a curved Universe. Here, we approach this issue from yet another point…
Symmetric frames on Lorentzian spaces
1991
Symmetric frames (those whose vectors are metrically indistinguishable) are studied both, from the algebraic and differential points of view. Symmetric frames which, in addition, remain indistinguishable for a given set of concomitants of the metric are analyzed, and the necessary and sufficient conditions for a space‐time to admit them are given. A new version of the cosmological principle then follows. Natural symmetric frames (induced by local charts) are also considered, and the space‐times admitting them are obtained.
Effective Field Theories for heavy probes in a hot QCD plasma and in the early universe
2016
International audience; There are many interesting problems in heavy-ion collisions and in cosmology that involve the interaction of a heavy particle with a medium. An example is the dissociation of heavy quarkonium seen in heavy-ion collisions. This was believed to be due to the screening of chromoelectric fields that prevents the heavy quarks from binding, however in the last years several perturbative and lattice computations have pointed out to the possibility that dissociation is due to the finite lifetime of a quarkonium state inside the medium. Regarding cosmology, the study of the behavior of heavy Majorana neutrinos in a hot medium is important to understand if this model can expla…
“Pensare con” i popoli indigeni dell’Amazzonia i rapporti tra uomo e cosmo
2020
Despite the devastation produced by centuries of European colonization, Amerindian societies have maintained worldviews and conceptions of humanity which present a great richness, originality and variety. As shown both by Lévi-Strauss (1992) and, in a study perspective closer to Eliade's approach, by Sullivan (1988), they share some common characteristics which it is useful to compare, by difference and analogy, with those of Euro-Western cosmologies. As Viveiros de Castro argued with specific reference to the indigenous cosmologies of the Amazon, the importance of the aspects of relationality of reality, its eminently transformative dynamic nature, the ontological multiplicity of its compo…