Gravitational radiation from cosmic (super)strings: Bursts, stochastic background, and observational windows

Abstract

The gravitational wave (GW) signals emitted by a network of cosmic strings are reexamined in view of the possible formation of a network of cosmic superstrings at the end of brane inflation. The reconnection probability p of intersecting fundamental or Dirichlet strings might be much smaller than 1, and the properties of the resulting string network may differ significantly from those of ordinary strings (which have p = 1). In addition, it has been recently suggested that the typical length of newly formed loops may differ by a factor ǫ ≪ 1 from its standard estimate. Here, we analyze the effects of the two parameters p and ǫ on the GW signatures of strings. We consider both the GW bursts emitted from cusps of oscillating string loops, which have been suggested as candidate sources for the LIGO/VIRGO and LISA interferometers, and the stochastic GW background, which may be detectable by pulsar timing observations. In both cases we find that previously obtained results are quite robust, at least when the loop sizes are not suppressed by many orders of magnitude relative to the standard scenario. We urge pulsar observers to reanalyze a recently obtained 17-year combined data set to see whether the large scatter exhibited by a fraction of the data might be due to a transient GW burst activity of some sort, e.g. to a near cusp event.

Lumps in the throat

“…Reducing P would increase the number density of cosmic strings at the final scaling regime. This also results in a stronger gravitational wave signal which may be detected in upcoming gravity waves experiments such as LIGO and LISA [52].…”

Reconnection of non-abelian cosmic strings

“…For fundamental strings moving in d compactified dimensions of string theory, one expects the classical probability of reconnection to be suppressed by the geometric factor l d s /V , where V is the volume of the extra dimensions and l s = √ α ′ is the width of the string [8]. Together with the inherent probability P ∼ g 2 s of fundamental string reconnection [15,16] 2 , this leads to a reduced string cross-section, the net result of which is to increase the number of cosmic strings seen in the sky [18,19,2].…”

“…Similarly, D-strings may also pass through each other, reconnecting with probability P < 1 [16,17]. A reduced probability for reconnection affects the scaling solution for the string network, resulting in a larger concentration of strings in the sky [18,19,2]. Given enough data, it is not implausible that one could extract the probability P from observation.…”

“…On the observational side there is optimism that the next generation of gravitational wave detectors, Advanced LIGO and LISA, will be able to detect the characteristic signature of cosmic string loops as they twist and whip into cusps [1,2]. Moreover, there exist tantalizing gravitational lensing events, most notably CSL1 and its companion images [3], which point at the existence of a cosmic string with tension Gµ ∼ 4 × 10 −7 .…”

Interactions of cosmic superstrings

“…There is now vast literature on gravitational radiation from classical cosmic strings (see for example [16] [19] [20]). This is computed by Fourier transforming the functional derivative of the string action, 16) Note that this can be interpreted as a graviton vertex operator integrated over the worldsheet.…”