We discuss the gravitational creation of superheavy particles χ in an inflationary scenario with a quartic potential and a non-minimal coupling between the inflaton ϕ and the Ricci curvature: ξϕ2R/2. ...We show that for large constants ξ≫1, there can be abundant production of particles χ with masses largely exceeding the inflationary Hubble rate Hinfl, up to (afew)×ξHinfl, even if they are conformally coupled to gravity. We discuss two scenarios involving these gravitationally produced particles χ. In the first scenario, the inflaton has only gravitational interactions with the matter sector and the particles χ reheat the Universe. In this picture, the inflaton decays only due to the cosmic expansion, and effectively contributes to dark radiation, which can be of the observable size. The existing limits on dark radiation lead to an upper bound on the reheating temperature. In the second scenario, the particles χ constitute Dark Matter, if substantially stable. In this case, their typical masses should be in the ballpark of the Grand Unification scale.
Gravitational instability in classical Jeans theory, General Relativity, and modified gravity is considered. The background density increase leads to a faster growth of perturbations in comparison ...with the standard theory. The transition to the Newtonian gauge in the case of coordinate dependent background metric functions is studied. For modified gravity a new high frequency stable solution is found.
Cosmic ray production in modified gravity Arbuzova, E. V.; Dolgov, A. D.; Reverberi, L.
European physical journal. C, Particles and fields,
06/2018, Letnik:
78, Številka:
6
Journal Article
Recenzirano
Odprti dostop
This paper is a reply to the criticism of our work on particle production in modified gravity by Gorbunov and Tokareva. We show that their arguments against efficient particle production are invalid.
...F
(
R
) theories can lead to an efficient generation of high energy cosmic rays in contracting systems.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The discovery of the accelerated expansion of the Universe has had a vast resonance on a number of physical disciplines. In recent years a few viable modified gravity models have been proposed, which ...naturally lead to a late-time de Sitter stage while reducing to General Relativity in the early Universe. We study two of these models during the contraction of a homogeneous cloud of pressureless dust. We show how the increasing energy/mass density may lead to a curvature singularity and derive the typical timescales for its development.
Cosmological evolution in R 2 gravity Arbuzova, E.V; Dolgov, A.D; Reverberi, L
Journal of cosmology and astroparticle physics,
02/2012, Letnik:
2012, Številka:
2
Journal Article
It is shown that
F
(
R
)-modified gravitational theories lead to curvature oscillations in astrophysical systems with rising energy density. The frequency and the amplitude of such oscillations could ...be very high and would lead to noticeable production of energetic cosmic ray particles.
Cosmological evolution in R{sup 2} gravity Arbuzova, E.V.; Dolgov, A.D.; Reverberi, L.
Journal of cosmology and astroparticle physics,
02/2012, Letnik:
2012, Številka:
2
Journal Article
Recenzirano
The universe evolution during the radiation-dominated epoch in the R{sup 2}-extended gravity theory is considered. The equations of motion for R and H are solved analytically and numerically. The ...particle production rate by the oscillating curvature is calculated in one-loop approximation and the back-reaction of particle production on the evolution of R is taken into account. Possible implications of the model for cosmological creation of non-thermal dark matter is discussed.
Spherically symmetric solutions in F(R) theories in astronomical systems with rising energy density are studied. The range of parameters is established for which the flat space–time approximation for ...the background metric is valid. For the solutions in which the curvature scalar oscillates with large amplitude and high frequency, found in our previous papers, it is shown that the analysis of the Jeans instability is strongly modified. It is discovered that for large astronomical objects modified gravity can be repulsive, so such objects would shrink forming relatively thin shells instead of quasi uniform bodies.
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