Observational Constraints on Cosmic String Production During Brane Inflation

TL;DR

This paper examines how current cosmological data constrain cosmic string production during brane inflation, finding that a small contribution from cosmic strings remains possible and could be detected with future precise measurements.

Contribution

It provides the first detailed analysis of observational constraints on cosmic strings specifically produced during brane inflation, highlighting the potential for future detection.

Findings

Current data cannot exclude a ~10% contribution from cosmic strings.

Upper bound on string tension: Gμ ≲ 3.5×10⁻⁷.

Future measurements of B-mode polarization and spectral index could confirm or rule out cosmic string contributions.

Abstract

Overall, brane inflation is compatible with the recent analysis of the WMAP data. Here we explore the constraints of WMAP and 2dFGRS data on the various brane inflationary scenarios. Brane inflation naturally ends with the production of cosmic strings, which may provide a way to distinguish these models observationally. We argue that currently available data cannot exclude a non-negligible contribution from cosmic strings definitively. We perform a partial statistical analysis of mixed models that include a sub-dominant contribution from cosmic strings. Although the data favor models without cosmic strings, we conclude that they cannot definitively rule out a cosmic-string-induced contribution of $\sim 10 %$ to the observed temperature, polarization and galaxy density fluctuations. These results imply that $G\mu \lesssim 3.5\times 10^{-7}(\lambda/0.25)\sqrt{B/0.1}$, where $\lambda$ is a dimensionless parameter related to the interstring distance, and $B$ measures the importance of perturbations induced by cosmic strings. We argue that, conservatively, the data available currently still permit $B\lesssim 0.1$. Precision measurements sensitive to the B-mode polarization produced by vector density perturbation modes driven by the string network could provide evidence for these models. Accurate determinations of $n_s(k)$, the scalar fluctuation index, could also distinguish among various brane inflation models.