A tensor theory of space-time as a strained material continuum

The classical theory of strain in material continua is reviewed and generalized to space-time. Strain is attributed to "external" (matter/energy fields) and intrinsic sources fixing the global symmetry of the universe (defects in the continuum). A Lagrangian for space-time is worked out, adding to the usual Hilbert term an "elastic" contribution from intrinsic strain. This approach is equivalent to a peculiar tensor field, which is indeed part of the metric tensor. The theory gives a configuration of space-time accounting both for the initial inflation and for the late acceleration. Considering also the contribution from matter the theory is used to fit the luminosity data of type Ia supernovae, giving satisfactory results.Comment: Revised to match the version accepted for publication in Class. Quantum Gra

Massive gravitational waves from the Cosmic Defect theory

The Cosmic Defect theory (CD), which is presented elsewhere in this conference, introduces in the standard Einstein-Hilbert Lagrangian an elastic term accounting for the strain of space-time viewed as a four-dimensional physical continuum. In this framework the Ricci scalar acts as the kinetical term of the strain field whose potential is represented by the additional terms. Here we are presenting the linearised version of the theory in order to analyze its implications in the weak field limit. First we discuss the recovery of the Newtonian limit. We find that the typical static weak field limit imposes a constraint on the values of the two parameters (Lame coefficients) of the theory. Once the constraint has been implemented, the typical gravitational potential turns out to be Yukawa-like. The value for the Yukawa parameter is consistent with the constraints coming from the experimental data at the Solar system and galactic scales. We then come to the propagating solutions of the linearised Einstein equations in vacuo, i.e. to gravitational waves. Here, analogously with other alternative or extended theories of gravity, the presence of the strain field produces massive waves, where massive (in this completely classical context) means subluminal. Furthermore longitudinal polarization modes are allowed too, thus lending, in principle, a way for discriminating these waves from the plane GR ones.Comment: Proceedings of 'Invisible Universe International Conference', Paris, June 29- July 3, 200

Weak-Field Spherically Symmetric Solutions in f(T)f(T) gravity

We study weak-field solutions having spherical symmetry in $f(T)$ gravity; to this end, we solve the field equations for a non diagonal tetrad, starting from Lagrangian in the form $f(T)=T+\alpha T^{n}$, where $\alpha$ is a small constant, parameterizing the departure of the theory from GR. We show that the classical spherically symmetric solutions of GR, i.e. the Schwarzschild and Schwarzschild-de Sitter solutions, are perturbed by terms in the form $\propto r^{2-2n}$ and discuss the impact of these perturbations in observational tests.Comment: 11 pages, LaTeX; revised to match the version accepted for publication in Physical Review

Assessment of the Performance of Ionospheric Models with NavIC Observations during Geomagnetic Storms

The paper presents an assessment of the performances of the global empirical models: International Reference Ionosphere (IRI)-2016 and the NeQuick2 model derived ionospheric Total Electron Content (TEC) with respect to the Navigation with Indian Constellation (NavIC)/ Indian Regional Navigation Satellite System(IRNSS) estimated TEC under geomagnetic storm conditions. The present study is carried out over Indore (Geographic: 22.52$^{\circ}$N 75.92$^{\circ}$E and Magnetic Dip: 32.23$^{\circ}$N, located close to the northern crest of the Equatorial Ionization Anomaly (EIA) region of the Indian sector). Analysis has been performed for an intense storm (September 6-10, 2017), a moderate storm (September 26-30, 2017) and a mild storm (January 17-21, 2018) that fall in the declining phase of the present solar cycle. It is observed that both IRI-2016 and NeQuick2 derived TEC are underestimates when compared with the observed TEC from NavIC and therefore fail to predict storm time changes in TEC over this region and requires real data inclusion from NavIC for better prediction over the variable Indian longitude sector.Comment: 4 pages, 4 figures, accepted for publication in the proceedings of the 2020 URSI Regional Conference on Radio Science(URSI-RCRS 2020

Cosmological constraints for the Cosmic Defect theory

The Cosmic Defect theory has been confronted with four observational constraints: primordial nuclear species abundances emerging from the big bang nucleosynthesis; large scale structure formation in the universe; cosmic microwave background acoustic scale; luminosity distances of type Ia supernovae. The test has been based on a statistical analysis of the a posteriori probabilities for three parameters of the theory. The result has been quite satisfactory and such that the performance of the theory is not distinguishable from the one of the Lambda-CDM theory. The use of the optimal values of the parameters for the calculation of the Hubble constant and the age of the universe confirms the compatibility of the Cosmic Defect approach with observations.Comment: 13 pages, 1 figure, in press on IJMP