**Publication date:** Nov 2011

**Abstract:**

Extremely Compact Stars (ECS) contain trapped null geodesics. When such

objects enter the evolution period admitting geodetical motion of

neutrinos, certain part of neutrinos produced in their interior will be

trapped influencing their neutrino luminosity and thermal evolution. We

study neutrino trapping in the braneworld ECS, assuming uniform

distribution of neutrino emissivity and massless neutrinos. We give the

efficiency of the neutrino trapping effects in the framework of the

simple model of the internal spacetime with uniform distribution of

energy density, and external spacetime described by the

Reissner-Nordström geometry characterized by the braneworld "tidal"

parameter b. For b < 0 the external spacetime is of the black-hole

type, while for b > 0 the external spacetime can be of both

black-hole and naked-singularity type. Then the ECS surface radius R can

be located also above the unstable (outer) photon circular orbit. Such

basically new types of the spacetimes strongly alter the trapping

phenomena as compared to the standard case of b = 0. It is shown that

the neutrino trapping effects are slightly lowered by the presence of

physically more plausible case of b < 0, as compared to the standard

internal Schwarzschild spacetime, while they can be magnified by

positive tidal charges if b < 1 and lowered for b > 1. However,

potential astrophysical relevance of the trapping phenomena is strongly

enhanced for negative tidal charges enabling a significant enlargement

of the ECS surface radius to values coherent with recent observations.

**Authors:**

Stuchlík, Zdeněk; Hladík, Jan; Urbanec, Martin;