Constraints on cosmic strings using data from the first Advanced LIGO observing run

Abstract

Cosmic strings are topological defects which can be formed in grand unified theory scale phase transitions in the early universe. They are also predicted to form in the context of string theory. The main mechanism for a network of Nambu-Goto cosmic strings to lose energy is through the production of loops and the subsequent emission of gravitational waves, thus offering an experimental signature for the existence of cosmic strings. Here we report on the analysis conducted to specifically search for gravitational-wave bursts from cosmic string loops in the data of Advanced LIGO 2015-2016 observing run (O1). No evidence of such signals was found in the data, and as a result we set upper limits on the cosmic string parameters for three recent loop distribution models. In this paper, we initially derive constraints on the string tension Gμ and the intercommutation probability, using not only the burst analysis performed on the O1 data set but also results from the previously published LIGO stochastic O1 analysis, pulsar timing arrays, cosmic microwave background and big-bang nucleosynthesis experiments. We show that these data sets are complementary in that they probe gravitational waves produced by cosmic string loops during very different epochs. Finally, we show that the data sets exclude large parts of the parameter space of the three loop distribution models we consider.

Probing the gravitational wave background from cosmic strings with LISA

“…In fact, these small loops dominate the stochastic GW spectrum at high frequencies, as was already discussed in ref. [84], and hence can lead to very different constraints on Gµ to that of the BOS model in the high frequency regime. Indeed, the energy density in these small loops is very large, so the question of energy balance between the long string network and the loop distribution -at least as described by eq.…”

“…Determining the average number of cusps and kinks for the loop network is a very non-trivial task and the subject of ongoing work, and given this uncertainty it is common to take N c = N k = O(1). However, one can also consider a situation in which there will be contributions from all these types of events [82,84,104], namely N c number of cusps, N k kinks and N kk number of kink-kink collisions (with N kk = N 2 k /4, on assuming that there are equal numbers of left-and right-going kinks). We then impose that the sum of all these events to the averaged total power of the loop, Γ, is equal to the value used in the expression for the loop number density 11 .…”

“…Cusps and kinks generate gravitational wave bursts [50,51], and these play a significant role in the SGWB emitted by string networks. (One should note that a complementary strategy to the detection of the stochastic background is therefore to search for such individual transient signals, see [84,86]. )…”

Extending and calibrating the velocity dependent one-scale model for cosmic strings with one thousand field theory simulations

“…As such, understanding what processes will predominantly drive network evolution and how energy is transferred from large to small * Jose.Correia@astro.up.pt † Carlos. Martins@astro.up.pt scales is important for current [6,7] as well as future constraints [8,9]. It is thus unfortunate that for decades the two main types of cosmic string simulations (field theory Abelian Higgs [10,11] and Goto-Nambu connected segments [12][13][14][15]) largely disagree in terms of loop production (a key energy loss mechanism), the amount of small-scale structure on the strings [16,17] and the resulting large-scale properties of the network [10,18].…”

Continuous gravitational waves and magnetic monopole signatures from single neutron stars

“…Recent observation of gravitational waves (GWs) by the LIGO-VIRGO collaboration [1,2] have ushered in a new era of multi-messenger astronomy. Apart from its significant astrophysical [3][4][5] and cosmological [6,7] implications, gravitational wave astronomy also has the potential to illuminate many important questions in fundamental physics [8][9][10][11][12]. A fast emerging area in this context is the endeavour to detect continuous GWs from single neutron stars.…”