Gravitational wave observations have a high potential to probe cosmology.
Several processes operating in the early universe can act as sources of a stochastic gravitational wave background. Because of the weakness of the gravitational interaction, a stochastic gravitational wave background of cosmological origin forms a fossil radiation that in its amplitude, spectral shape and frequency range contains information on the nature of the source that generated it. The detection of this fossil background would have a profound impact on our knowledge of the early universe, possibly similar to the impact that the measurement of the Cosmic Microwave Background and of its temperature fluctuations had in the last decades.
By means of LISA we will be able to probe the characteristics of the particle physics model underlying the universe up to scales higher than those presently reached at the LHC. For instance, the shape of the stochastic background can unveil the nature of the electroweak sector, test the occurrence of high energy phase transitions and the formation of topological defects, and provide new information on the theory of inflation. Gravitational wave sources such as binaries inspirals can be used as standard sirens (the gravitational wave analogue of standard candles) to measure the rate of expansion of the universe and the equation of state of dark energy. The gravitational wave emission from compact binaries and the propagation of the waves through the perturbed universe can test gravitational theories beyond General Relativity.
The primary task of the Cosmology Working Group is to precisely assess the potential of the LISA mission to probe cosmology. It is also a task of the group to identify and discuss research topics that are in a broad sense relevant in the context of gravitational wave science and its connection to cosmology.
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