Evolution of a system of cosmic strings

Topological defects: A problem for cyclic universes?

“…Again we note that the latter is also the scaling law for the correlation length in the matterdominated, expanding universe (but again the behaviour of the velocities is very different in the two cases). This highlights the different roles played by loop production in the scaling behaviour of a cosmic string network in the radiation and matter eras, a point which has been noticed long ago [9,12] in the usual expanding case. A strong argument can be made, however, for an important relativistic correction to the loop production term in the evolution equation for the correlation length.…”

“…Two different but complementary approaches are available to study the evolution of a cosmic string network: one can resort to large numerical simulations [14,15,16] (which are intrinsically difficult and time consuming, as one is dealing with highly non-linear objects), or one can develop analytic tools [9,11,12,13,39,43] which provide an averaged (or 'thermodynamical') description of the basic properties of the network. In what follows we shall briefly describe the best motivated of these analytic models, the velocity-dependent one-scale (VOS) model [11,12,13,39], and try to use it to deduce the basic properties of a cosmic string network during a phase of contraction.…”

“…For this reason, if defects do exist in these models, it is crucial to understand their evolution and consequences in both the expanding and collapsing phases. Up to now * Electronic address: ppavelin@fc.up.pt † Electronic address: C.J.A.P.Martins@damtp.cam.ac.uk ‡ Electronic address: cssilva@fc.up.pt § Electronic address: E.P.S.Shellard@damtp.cam.ac.uk all these studies, be they analytic [9,10,11,12,13] or numerical [14,15,16], have only been undertaken for the expanding case, and it is clear that while some results may be expected to carry over to the contracting phase, some others clearly won't. This will have consequences not only for the standard string seeded (or hybrid) structure formation scenario [17], but also for other 'non-standard' scenarios involving defects, such as the production of adiabatic and nearly Gaussian density fluctuations [18,19], or those involving anisotropic or inhomogeneous universes [20,21].…”

Cosmic Strings and Cosmic Superstrings

“…The first analytical studies of the evolution of a cosmic string network have shown [12] the existence of scaling, in the sense that the string network can be characterised by a single length scale, roughly the persistence length or the interstring distance ξ which grows with the horizon. This important property of cosmic strings renders them cosmologically acceptable, in contrast to local monopoles or domain walls.…”

Scaling laws for nonintercommuting cosmic string networks

“…The evolution of standard cosmic strings has been extensively studied, both by numerical [6,7,8,9] and by analytic means [10,11,12,13,14,15,16,17,18,19]. Here one finds that after an initial transient period (whose duration depends on the string mass scale, being shorter for heavier strings) the network will evolve in a linear scaling regime, with a characteristic length (or correlation length) being a constant fraction of the horizon, L ∝ t, and the RMS velocity being also constant.…”