The revival of cosmic strings

Abstract

Key words early universe, cosmology, cosmic strings/superstrings PACS 98.80.Cq Cosmic strings are one-dimensional topological defects which could have been formed in the early stages of our Universe. They triggered a lot of interest, mainly for their cosmological implications: they could offer an alternative to inflation for the generation of density perturbations. It was shown however that cosmic strings lead to inconsistencies with the measurements of the cosmic microwave background temperature anisotropies. The picture is changed recently. It was shown that, on the one hand, cosmic strings can be generically formed in the framework of supersymmetric grand unified theories and that, on the other hand, cosmic superstrings could play the rôle of cosmic strings. There is also some possible observational support. All this lead to a revival of cosmic strings research and this is the topic of my lecture.

Local constraints on cosmic string loops from photometry and pulsar timing

“…We have checked numerically that giants and stars with photometrical distance estimates contribute little to the string density-constraining power of CoRoT data. Figure 3 shows the constraint on Ωs as a function of µ given by (10,11) assuming a non-detection of lensing signal in the light curves of stars listed in Table I. One can see that the presently available CoRoT data does not significantly constrain the density of cosmic string loops.…”

“…which is equivalent (cf. 23) to We are now ready to compute the constraints on the cosmic string loop density Ωs according to (10,11) based on the pulsar timing data collected in the Parkes Pulsar Timing Array (PPTA) [31] project as well as from Arecibo [33] and Green Bank Telescope (GBT) [34] observations. The details of these data are listed in Table II.…”

“…Simulations [1,9] suggest the energy fraction in strings has a scaling behavior: their density Ωs (in units of critical density ρ0 = 3H 2 0 /8πG) does not depend on cosmological time. Recent works suggest that strings contribute a subdominant fraction to the energy balance of the Universe [10]. This question has not been completely resolved yet.…”

The Geodesic Rule and the Spectrum of the Vacuum

“…Topological strings are of great importance methodologically [2], [3] due to their nonperturbative nature. What is even more important, they have severe experimental and observational implications [2], [3], [7] in models allowing their formation. Because of their great significance, a scheme leading to calculations of their density and distribution such as the geodesic rule has to be theoretically justified and its predictions have to be thoroughly tested.…”

“…Then issues of subtractions of infinity from Z (M,g) that arose from the existence of long loops on M no longer persist. Substituting (7) into (28), we get…”