Red or Blue Tensor Spectrum from GW170817-compatible Einstein-Gauss-Bonnet Theory: A Detailed Analysis

In this work we shall prove that the tensor spectral index of the primordial tensor perturbations for GW170817-compatible Einstein-Gauss-Bonnet theories, takes the approximate simplified form $n_{\mathcal{T}}\simeq 2\left(-1+\frac{1}{\lambda(\phi)} \right)\epsilon_1$ at leading order, with $\lambda (\phi)$ being a function of the scalar field which depends on the scalar field potential and the second derivative of the scalar-Gauss-Bonnet coupling $\xi''(\phi)$. With our analysis we aim to provide a definitive criterion for selecting Einstein-Gauss-Bonnet models that can provide a blue-tilted inflationary phenomenology, by simply looking at the scalar potential and the scalar-Gauss-Bonnet coupling. We shall prove this using two distinct approaches and as we show the tilt of the tensor spectral index is determined by the values of the potential $V(\phi)$ and of scalar-Gauss-Bonnet coupling at first horizon crossing. Specifically the blue-tilted tensor spectral index can occur when $\xi''(\phi_*)V(\phi_*)>0$ at first horizon crossing.Comment: EPL Accepte

Kinetic Axion Dark Matter in String Corrected f(R)f(R) Gravity

Under the main assumption that the axion scalar field mainly composes the dark matter in the Universe, in this paper we shall extend the formalism of kinetic axion $R^2$ gravity to include Gauss-Bonnet terms non-minimally coupled to the axion field. As we demonstrate, this non-trivial Gauss-Bonnet term has dramatic effects on the inflationary phenomenology and on the kinetic axion scenario. Specifically, in the context of our formalism, the kinetic axion ceases to be kinetically dominated at the end of the inflationary era, since the condition $\dot{\phi}\simeq 0$ naturally emerges in the theory. Thus, unlike the case of kinetic axion $R^2$ gravity, the Gauss-Bonnet corrected kinetic axion $R^2$ gravity leads to an inflationary era which is not further extended and the reheating era commences right after the inflationary era, driven by the $R^2$ fluctuations.Comment: Published in the Physics of the Dark Univers

Fractional Action Cosmology with Power Law Weight Function

Motivated by an earlier work on fractional-action cosmology with a periodic weight function [1], we extend it by choosing a power-law weight function in the action. In this approach, we obtain a varying gravitational coupling constant. We then model dark energy in this paradigm and obtain relevant cosmological parameters.Comment: 12 pages, 9 figures, Contributed talk published in the proceedings of "3rd Italian-Pakistani Workshop on Relativistic Astrophysics

Modified Chaplygin Gas and Solvable F-essence Cosmologies

The Modified Chaplygin Gas (MCG) model belongs to the class of a unified models of dark energy and dark matter. In this paper, we have modeled MCG in the framework of f-essence cosmology. By constructing an equation connecting the MCG and the f-essence, we solve it to obtain explicitly the pressure and energy density of MCG. As special cases, we obtain both positive and negative pressure solutions for suitable choices of free parameters. We also calculate the state parameter which describes the phantom crossing.Comment: 12 pages, (Invited Review), accepted for publication in "Astrophysics and Space Science" DOI: 10.1007/s10509-011-0870-

Biological protection of spring wheat from root rot in the forest-steppe zone of Eastern Siberia

We present the results of the trial of the biological drug BisolbiSan (Bacillus subtillis strain H-13, isolated by the All-Russian Research Institute of Agricultural Microbiology) for treatment of spring wheat seeds in comparison with the widely popular chemical fungicides Maxim and Maxim Plus in the forest-steppe zone of Eastern Siberia in 2016–2018. BisolbiSan contributed to a decrease in total seed contamination by 2.4 times compared to control, which was practically at the level of the chemical fungicide Maxim. Maxim and Maxim Plus oppressed the growth of the sprout and the main germ line, while BisolbiSan stimulated the growth and development of the root system, and did not inhibit the growth of the sprout. The prevalence of root rot in the variant with BisolbiSan was lower compared to control by 54 %, effectiveness of which was not significantly inferior to that of chemical protectants. In comparison with control variant, BisolbiSan increased vitreous content of grain by 16.9 %, the content of crude gluten by 3.9 %, contributed to obtaining a statistically reliable increase in the yield of 0.38 tons per hectare, which did not differ significantly from the increase in the variant with chemical protectants. In our experiment, the payback of 1 ruble of costs when treating seeds with BisolbiSan was 1.7, which is 0.5 and 0.2 rubles higher compared to Maxim and Maxim Plus, respectively. The profitability of the yield increase using BisolbiSan was 70.9 %, which is 54.5 % and 20.6 % more than when using Maxim and Maxim Plus, respectively

Probing Our Universe’s Past Using Earth’s Geological and Climatological History and Shadows of Galactic Black Holes

In this short review, we discuss how Earth’s climatological and geological history and also how the shadows of galactic black holes might reveal our Universe’s past evolution. Specifically we point out that a pressure singularity that occurred in our Universe’s past might have left its imprint on Earth’s geological and climatological history and on the shadows of cosmological black holes. Our approach is based on the fact that the H0 tension problem may be resolved if some sort of abrupt physics change occurred in our Universe 70–150 Myrs ago, an abrupt change that deeply affected the Cepheid parameters. We review how such an abrupt physics change might have been caused in our Universe by a smooth passage of it through a pressure finite-time singularity. Such finite-time singularities might occur in modified gravity and specifically in F(R) gravity, so we show how modified gravity might drive this type of evolution, without resorting to peculiar cosmic fluids or scalar fields. The presence of such a pressure singularity can distort the elliptic trajectories of bound objects in the Universe, causing possible geological and climatological changes on Earth, if its elliptic trajectory around the Sun might have changed. Also, such a pressure singularity affects directly the circular photon orbits around supermassive galactic black holes existing at cosmological redshift distances, thus the shadows of some cosmological black holes at redshifts z≤0.01, might look different in shape, compared with the SgrA* and M87* supermassive black holes. This feature however can be checked experimentally in the very far future

EPJ Plus your physics journal G-essence cosmologies with scalar-fermion in- teractions G-essence cosmologies with scalar-fermion interactions

Abstract. We study the two particular models of g-essence with Yukawa-type interactions between a scalar field φ and a classical Dirac field ψ. For the homogeneous, isotropic and flat Friedmann-Robertson-Walker universe filled with the such g-essence; some exact solutions of these models are found. Moreover, we reconstruct the corresponding scalar and fermionic potentials