Elena V. Arbuzova

A reduction mechanism of the theoretically predicted excessive abundance of ⁷ Li via baryons evaporated by primordial black holes is suggested. It is shown that the fraction of ⁷ Li with respect to the number density of baryons can be diminished down to the observed value via the process of ⁷ Li transformation by neutron or proton capture. The created in this process ⁸ Li or ⁸ Be quickly decay into a pair of ⁴ He nuclei.

The scenario of gravitational baryogenesis modified through adding an R² term into the model is explored. This modification allows eliminating the cosmological instability inherent to the canonical version of gravitational baryogenesis. In the updated model, the exponential growth of the curvature is transformed into high-frequency oscillations, which, in turn, results in forming super-heavy dark matter particles. Slow decay of these particles through virtual black holes can contribute to the flux of ultra-high-energy cosmic rays.

The instability problem of the gravitational baryogenesis (GBG) is analysed. It is shown that the explosive growth of the curvature scalar, inherent to GBG, can be terminated by introducing the $R^2$-term into the classical action of General Relativity. As a result, the exponential rising curvature is transformed into a quickly oscillating one. The high-frequency curvature oscillations lead to the production of energetic particles which, according to the estimates presented, could make a noticeable contribution to ultra high energy cosmic rays (UHECR).

The search for supersymmetric partners at Large Hadron Collider revealed negative result. Though, strictly speaking, it does not exclude low energy supersymmetry, but still it leads to strong constraints of the parameter space. Therefore the search for supersymmetric particles at higher energies becomes of interest. It is shown that in $R^2$-modified cosmology heavy particles with the interaction strength typical for supersymmetry could be promising candidates for carriers of dark matter. We consider the heating of the Universe at the postinflationary stage via particle production by oscillating curvature scalar (scalaron). The bounds on the masses of dark matter particles are obtained for different dominant decay modes of the scalaron. Possible impact of superheavy particle decays on the spectrum of ultra high energy cosmic rays (UHECR) is discussed.

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 processes are estimated. It is shown that with the proper fixation of the parameters the decays of these ultra-massive particles can give noticeable contribution to the flux of high energy cosmic rays in particular, near the Greisen–Zatsepin–Kuzmin limit. Such particles can also create neutrinos of very high energies observed in the existing huge underwater or ice-cube detectors.

The search for supersymmetric partners at Large Hadron Collider revealed negative result. Though, strictly speaking, it does not exclude low energy supersymmetry, but still it leads to strong constraints of the parameter space. Therefore the search for supersymmetric particles at higher energies becomes of interest. It is shown that in $R^2$-modified cosmology heavy particles with the interaction strength typical for supersymmetry could be promising candidates for carriers of dark matter. We consider the heating of the Universe at the post-inflationary stage via particle production by oscillating curvature scalar (scalaron). The bounds on the masses of dark matter particles are obtained for different dominant decay modes of the scalaron. Possible impact of superheavy particle decays on the spectrum of ultra high energy cosmic rays is discussed.