Repulsive gravitational effects of global monopoles

Abstract

A monopole formed as a consequence of the spontaneous breakdown of a global symmetry should have a mass that grows linearly with the distance off its core. It was recently shown by Barriola and Vilenkin that the gravitational effect of this configuration is equivalent to that of a deficit solid angle in the metric, plus that of a relatively tiny mass at the origin. Here we show that this small effective mass is negative. Global monopoles thus share with other topological defects, such as domain walls and global strings, a repulsive gravitational potential. We solve numerically the coupled equations for the metric and the scalar field, to precisely determine this repulsive potential and in order to analyze the solution when gravitational effects are already significant close to the monopole core. We study the motion of test particles in a monopole background, and discuss the possible implications of a negative effective mass.-

Vacuum polarization by a global monopole with finite core

“…Substituting eigenfunctions (17) and using the addition formula for the hyperspherical harmonics [24] …”

“…However, the realistic global monopole has a characteristic core radius determined by the symmetry braking scale at which the monopole is formed. A simplified model for the monopole core where the region inside the core is described by the de Sitter geometry is presented in [17]. The vacuum polarization effects due to a massless scalar field in the region outside the core of this model are investigated in Ref.…”

Global monopoles in the Brans-Dicke theory

“…When gravity is taken account the linearly divergent mass of a global momopole has an effect analogous to that of a tiny mass at the origin. Harari and Loustò [3], and Shi and Li [4] have shown that this small gravitational potential is actually repulsive. Recently, Li et.al.…”

Decay of massive scalar hair in the background of a black hole with a global monopole

“…The physical properties of the black-hole-global-monopole system have been studied extensively in recent years. These include, but are not limited to, the gravitational [9,10] and the vacuum polarization effects [11,12], the particle creation in the formation of the system [13], the black hole thermodynamics [14], and more recently the energy spectra of non-relativistic quantum system in the background [15].…”