Evidence of Hidden dimensions could be revealed with high frequency gravitational wave detectors

Researchers from the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam found that hidden dimensions – as predicted by string theory – could influence gravitational waves. In a recently published paper they study the consequences of extra dimensions on these ripples in space-time, and predict whether their effects could be detected.

LIGO’s first detection of gravitational waves from a black-hole binary in September 2015 has opened a new window onto the universe. Now it looks like with this new observing tool physicists cannot only trace black holes and other exotic astrophysical objects but also understand gravity itself. “Compared to the other fundamental forces like, e.g. electromagnetism, gravity is extremely weak,” explains Dr. David Andriot, one of the authors of the study. The reason for this weakness could be that gravity interacts with more than the three dimensions in space and one dimension in time that are part of our everyday experience.

The researchers discovered that extra dimensions should have two different effects on gravitational waves: they would modify the “standard” gravitational waves and would cause additional waves at high frequencies above 1000 Hz. However, the observation of the latter is unlikely since the existing ground-based gravitational wave detectors are not sensitive enough at high frequencies.

On the other hand, the effect that extra dimensions can make a difference in how “standard” gravitational waves stretch and shrink space-time might be easier to detect by making use of more than one detector. Since the Virgo detector will join the two LIGO detectors for the next observing run this might happen after late 2018/beginning of 2019.

The predicted gravitational frequency values are much higher than the typical one of the recently observed gravitational waves, around 150 Hz. They are also much higher than the upper sensitivity bound of LIGO, of the order of 1000 to ten thousand Hz. In addition, future detectors seem to be planned, rather, to probe lower frequencies. This disfavors the direct detection of signals with such high frequencies, which would require a new type of apparatus. On top of being sensitive to a higher frequency range, the latter should have a much smaller strain sensitivity, to get a signal-to-noise ratio comparable to LIGO: for now this looks quite challenging. If such a detector were available, however, one could hop for a very clean signal, since there is no known astrophysical process emitting gravitational waves with frequencies much greater than 1000 Hz. Such high frequencies may thus be clear
symptoms of new physics.

Merging black holes generate gravitational waves. These ripples in space-time might be used to unveil hidden dimensions. © Simulating eXtreme Spacetimes (SXS)

Arxiv – Signatures of extra dimensions in gravitational waves