Improved constraint on the primordial gravitational-wave density using recent cosmological data and its impact on cosmic string models

• Published in: Classical and Quantum Gravity
• Main Authors: Henrot-Versillé, S., Robinet, F., Leroy, N., Plaszczynski, Stéphane, Arnaud, N., Bizouard, M.-A., Cavalier, F., Christensen, N., Couchot, F., Franco, S., Hello, P., Huet, D., Kasprzack, M., Perdereau, O., Spinelli, M., Tristram, M.
• Other Authors: Laboratoire de l'Accélérateur Linéaire (LAL), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Department of Physics and Astronomy Northfield, Carleton College, Planck, Virgo
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: [SDU.ASTR.CO]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]; [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc]; [PHYS.HEXP]Physics [physics]/High Energy Physics - Experiment [hep-ex]; South pole
• Online Access: https://hal.in2p3.fr/in2p3-01107320; https://doi.org/10.1088/0264-9381/32/4/045003

International audience The production of a primordial stochastic gravitational-wave (GW) background by processes occuring in the early Universe is expected in a broad range of models. Observing this background would open a unique window onto the Universeʼs evolutionary history. Probes like the cosmic microwave background (CMB) or the baryon acoustic oscillations (BAO) can be used to set upper limits on the stochastic GW background energy density ${{\Omega }_{{\rm GW}}}$ for frequencies above 10−15 Hz. We perform a profile likelihood analysis of the Planck CMB temperature anisotropies and gravitational lensing data combined with WMAP low-ℓ polarization, BAO, South Pole Telescope and Atacama Cosmology Telescope data. We find that ${{\Omega }_{{\rm GW}}}{\rm h}_{0}^{2}\lt 3.8\times {{10}^{-6}}$ at a 95% confidence level for adiabatic initial conditions, which improves over the previous limit by a factor 2.3. Assuming that the primordial GW has been produced by a network of cosmic strings, we have derived exclusion limits in the cosmic string parameter space. If the size of the loops is determined by gravitational back-reaction, string tension values greater than ~4 × ${{10}^{-9}}$ are excluded for a reconnection probability of 10−3.