It is shown that, contrary to the widespread opinion, particle collisions considerably increase accretion rate from the cosmological background onto 5D primordial black holes formed during the high-energy phase of the Randall-Sundrum Type II braneworld scenario. Increase of accretion rate leads to much tighter constraints on initial primordial black hole mass fraction imposed by the critical density limit and measurements of high-energy diffuse photon background and antiproton excess.PACS numbers: PACS: 98.80.Cq, 04.50.+h, 04.70.Dy, It is well known that primordial black holes (PBHs) open up a way to obtain information on earliest era of the Universe [1,2]. Recent works [3,4,5,6,7,8] show that PBHs can also be a probe of braneworld cosmologies. The Hawking temperature drop [3] and considerable PBH mass growth due to radiation dominated background accretion occur [4] in the simplest braneworld cosmology of the Randall-Sundrum Type II (RS2). These modifications of PBH properties provide new constraints on the initial PBH mass fraction [6,7,8]. PBH mass growth is exponentially sensitive to the accretion efficiency. However, authors of [6, 7, 8] considered the accretion efficiency as a free parameter. In fact, they started with F equals 1 in the case of collisionless radiative background and assumed that it can only decrease when relativistic particle scattering length is small. They also predicted that a sufficiently low value of F leads to weaker constraints than those obtained in the standard 4D cosmology. It also allow the restriction of the RS2 curvature radius l from below. Meanwhile, according to the theory of spherical accretion of nonrelativistic particles [9], the hydrodynamic accretion theory [10] should be used instead of collisionless accretion theory [11,12] for small scattering length. Since "the presence of collisions between particles restricts tangential motion and funnels particles effectively in the radial direction for efficient capture" [9], the hydrodynamic accretion rate substantially exceeds the collisionless one in the case of nonrelativistic particles. The aim of the present paper is to demonstrate that collisions of relativistic particles analogously increase the accretion rate of the radiation dominated background and lead to the new, much tighter, constraints.Let us remind the reader that in the RS2 model our Universe is a 4D Lorentz metric hypersurface called a brane, embedded in a Z 2 symmetric 5D anti-de Sitter spacetime called the bulk, characterized by the curvature * vvtikh@mail.ru † skytec@mail.ru radius l, presently bound [13] by condition l ≤ 0.2mm. A black hole (BH) behaves as an essentially 5D object described by the metric [3,4,5,6,7,8] (1) where dΩ 2 2 is the line element on a unit 2-sphere, if its modified Schwarzchild radiusis much smaller than l. We use the units where c = G = 1 and introduce 4D Planck scale quantities l 4 , M 4 and t 4 for convenience. The high energy brane regime is characterized [3] by scale factor, energy density, horizon mass, and duration a = a h t ...

We calculate the quasi-uniform gravitational field of a disk in the weak-field approximation and demonstrate an inappropriateness of preceding results. The Riemann tensor of this field is determined. A nonexistence of the uniform gravitational field is proven. It is shown that a difference between equations of a particle motion and a spin rotation in the accelerated frame and in the quasi-uniform gravitational field of a disk does not violate the Einstein equivalence principle.