LISA can help us probe the unknown and test for new physics, such as the existence of extra dimensions or cosmic super-strings.
With LISA, we will continue our search for the (currently) unknown, in the hope of finding new physics. Amongst other things, we will be able to search for the existence of extra dimensions, cosmic superstrings predicted by string theory, and investigate the nature of dark matter.
The LISA frequency band corresponds to horizon scales in the early Universe at energies of the order of the TeV, where new physics, such as extra dimensions, is expected to become visible. One of the effects of the new physics are primordial first order phase transitions, proceeding through the explosive growth of broken phase bubbles, and leading to efficient gravitational wave production.
LISA will also provide a unique probe on cosmic (super-)strings, relics of the very early Universe at even higher energy scales, which are predicted in several theories unifying the fundamental interactions of nature, including string theory. Their detection would offer direct evidence for phenomena occurring at energies up to 1016 GeV and which are not observable with conventional astronomy.
Through gravitational wave detection, LISA is therefore capable of probing energy ranges much beyond the reach of present particle accelerators and gather informations on the state of the Universe at much earlier epochs than those directly probed by any other cosmological observation. Gravitational waves represent the next messenger to probe the very early Universe, after the use of the Cosmic Microwave Background.