Related papers: Cosmic ray production in modified gravity
Begun as part of a promotion of accelerator-based nuclear astrophysics, research toward this goal has shifted to cosmic ray production within the solar system. This has been motivated by the high quality of data collected recently by…
Modified f(R) gravity is one of the most promising candidates for dark energy, and even for the unification of the whole cosmological evolution, including the inflationary phase. Within this class of theories, the so-called viable modified…
We consider FLRW cosmological models for perfect fluid (with rho as the energy density) in the frame work of the f(rho) modified theory of gravity [V. N. Tunyak, Russ. Phys. J. 21, 1221 (1978); J. R. Ray, L. L. Smalley, Phys. Rev. D. 26,…
We review modified $F(R)$ gravity as realistic candidate to describe the observable universe expansion history. We show that recent cosmic acceleration, radiation/matter-dominated epoch and inflation could be realized in the framework of…
Modified gravity theories have received increased attention lately due to combined motivation coming from high-energy physics, cosmology and astrophysics. Among numerous alternatives to Einstein's theory of gravity, theories which include…
In this work we present a brief discussion about modified and extended cosmological models using current observational tests. We show that according to these astrophysical samples based in late universe measurements, theories like $f(R)$…
We study the matter stability in modified teleparallel gravity or $f(T)$ theories. We show that there is no Dolgov-Kawasaki instability in these types of modified teleparallel gravity theories. This give the $f(T)$ theories a great…
The paper is devoted to the analysis of particle acceleration in Gamma-Ray Bursts and its radiative consequences. Therefore we get on one hand constraints on the physics and on the other hand possible signatures of particle acceleration…
Solar flare observations are used to demonstrate the new technique of abundance determination based on gamma ray line emission produced by accelerated particle bombardment. Some of the implications of similar gamma ray line emission…
Multidimensional modification of gravity with a smaller mass scale of the gravitational interaction is considered. Stable by assumption dark matter particles could decay via interactions with virtual black holes. The decay rates of such…
Two processes of matter creation after inflation: 1) gravitational creation of superheavy (quasi)stable particles, and 2) non-thermal phase transitions leading to formation of topological defects, may be relevant to the resolution of the…
We consider a class of metric f(R) modified gravity theories, analyze them in the context of a Friedmann-Robertson-Walker cosmology and confront the results with some of the known constraints imposed by observations. In particular, we focus…
We consider modified gravity which may describe the early-time inflation and/or late-time cosmic acceleration of the universe. In particular, we discuss the properties of $F(R)$, $F(G)$, string-inspired and scalar-Einstein-Gauss-Bonnet…
We propose that nearly every accelerated CR was part of the parallel current that maintains all force-free (f-f) magnetic fields. Charged particles are accelerated by the E-parallel (to the magnetic filed B) produced by reconnection. The…
Cosmic rays are deemed to be generated by a process known as ``Fermi acceleration", in which charged particles scatter against magnetic fluctuations in astrophysical plasmas. The process itself is however universal, has both classical and…
We discuss the modified gravity which may produce the current cosmic aceleration of the universe and eliminates the need for dark energy. It is shown that such models where the action quickly grows with the decrease of the curvature define…
This thesis is devoted to the study of gravitational theories which can be seen as modifications or generalisations of General Relativity. The motivation for considering such theories, stemming from Cosmology, High Energy Physics and…
In Phys. Rev. D 102, 024057 (2020), the authors studied energy conditions in $f(Q)$ theory following the same path as researchers handled the energy conditions in the curvature-based modified gravity theories, like $f(R)$ or $f(R,G)$…
One of the most striking astrophysical phenomena today is the existence of cosmic ray particles with energies in excess of 10^20 eV. While their presence has been confirmed by a number of experiments, it is not clear where and how these…
We address some current theoretical issues around ultra-high energy cosmic rays. We recall that scenarios producing more gamma-rays than cosmic rays up to high redshift can in general only provide a sub-dominant contribution to the…