The energy density of relic gravitational waves (GWs) emitted by primordial black holes (PBHs) is calculated. We estimate the intensity of GWs produced at quantum and classical scattering of PBHs, the classical graviton emission from the PBH binaries in the early Universe, and the graviton emission due to PBH evaporation. If nonrelativistic PBHs dominated the cosmological energy density prior to their evaporation, the probability of formation of dense clusters of PBHs and their binaries in such clusters would be significant and the energy density of the generated gravitational waves in the present-day universe could exceed that produced by other known mechanisms. The intensity of these gravitational waves would be maximal in the GHz frequency band of the spectrum or higher and makes their observation very difficult by present detectors but also gives a rather good possibility to investigate it by present and future high-frequency gravitational waves electromagnetic detectors. However, the low-frequency part of the spectrum in the range f$\sim${}0.1\char21{}10\,\,Hz may be detectable by the planned space interferometers DECIGO/BBO. For sufficiently long duration of the PBH matter-dominated stage, the cosmological energy fraction of GWs from inflation would be noticeably diluted.

Possible existence of baryo-dense (BD) stars and antistars, which might be created in the very early Universe in the frameworks of a slightly modified Affleck–Dine scenario of baryogenesis is studied. We discuss phenomenology, observational manifestations, and bounds on such antistars and show that they are allowed to be abundant in the Galaxy. New constraints on the possible number of compact antimatter objects are derived. We point out that explosion of an antistar as a type Ia supernova produces a remnant with relatively low annihilation signal. Another important conclusion is the strong reduction of the annihilation flux from antistars in the gaseous disk of the Galaxy due to the high velocities of BD stars in general, and antistars in particular. The contemporary observational data do not exclude significant amount of antimatter in the Galaxy (and in other galaxies) in the form of the BD stars with relatively low mass.

Sufficiently light primordial black holes (PBH) could evaporate in the very early universe and dilute the preexisting baryon asymmetry and/or the frozen density of stable relics. The effect is especially strong in the case that PBHs decayed if and when they dominated the cosmological energy density. The size of the reduction is first calculated analytically under the simplifying assumption of the delta-function mass spectrum of PBH and instant decay approximation. In the realistic case of exponential decay and for an extended mass spectrum of PBH the calculations are made numerically. Resulting reduction of the frozen number density of the supersymmetric relics opens for them a wider mass window to become viable dark matter candidate.