Non-Gaussianity in the Cosmic Microwave Background temperature fluctuations from cosmic (super-)strings

Abstract

We compute analytically the small-scale temperature fluctuations of the cosmic microwave background from cosmic (super-)strings and study the dependence on the string intercommuting probability P . We develop an analytical model which describes the evolution of a string network and calculate the numbers of string segments and kinks in a horizon volume. Then we derive the probability distribution function (pdf) which takes account of finite angular resolution of observation. The resultant pdf consists of a Gaussian part due to frequent scatterings by long string segments and a non-Gaussian tail due to close encounters with kinks. The dispersion of the Gaussian part is reasonably consistent with that obtained by numerical simulations by Fraisse et al.. On the other hand, the non-Gaussian tail contains two phenomenological parameters which are determined by comparison with the numerical results for P = 1. Extrapolating the pdf to the cases with P < 1, we predict that the non-Gaussian feature is suppressed for small P .

Analytical model for CMB temperature angular power spectrum from cosmic (super-)strings

“…We first give basic equations governing string network incorporating intercommuting probability P , following [19,20]. A string worldsheet can be described by…”

“…The characteristic time scale for loop formation is ∼ ξ/(P v rms ) and the energy loss can be described as ∼cP v rms ρ seg /ξ where we have introduced c as a constant which represents the efficiency of loop formation. Assuming a(t) ∝ t β with the physical time t = a(η)dη, the equations of motion for γ and v rms are given by [19,20] …”

“…In [19,20], we computed the one-point probability distribution function (pdf) with a simple model of long curved string segments and kinks. It was found that the one-point pdf is dominated by a Gaussian component due to frequent scatterings by long straight segments, together with small non-Gaussian tails due to close encounters with kinks and a small asymmetry, namely skewness, from the correlation between curvatures and velocities of string segments.…”

Constraints on cosmic string tension imposed by the limit on the stochastic gravitational wave background from the European Pulsar Timing Array

“…Cosmic strings have a wide range of astrophysical signatures including: ultra high energy cosmic rays [20,21], gamma ray bursts [22,23], radio bursts and synchrotron radiation [24,25], Aharonov-Bohm radiation [26,27], gravitational lensing (strong/micro) [28][29][30], CMB imprints (non-gaussianity, small/large-scale anisotropies, B-mode polarization) [31][32][33][34][35][36][37][38], effects on matter power spectra in 21-cm surveys [39,40]. So far no detection has been possible, but an interesting opportunity lies in their imprint on the stochastic gravitational wave background (SGWB) [41][42][43][44][45][46][47][48].…”

Full-sky formulae for weak lensing power spectra from total angular momentum method

“…Assuming the network approaches a scaling solution, the quantities γ s and v rms stay constant. Taking the probabilistic nature of the intercommuting process into account [56][57][58][59], γ s and v rms are approximately described by γ s ≈ (π √ 2/3cP ) 1/2 and v 2 rms ≈ (1 − π/3γ s )/2 [57] , wherẽ c ≈ 0.23 quantifies the efficiency of the loop formation [54], and P is the intercommuting probability. In order to compute the weak lensing power spectra, we need to evaluate the correlation between the string segments, for which we adopt simple analytic model developed by [60][61][62].…”