On Monday, the European Space Agency unveiled a microwave map of the universe, the result of the first 10 months of observations by the Planck satellite.
When Planck completes its mission next year, it'll provide the best picture yet of the universe just after the big bang. But what it finds could have serious implications for the Large Hadron Collider.
Two of the biggest prizes in physics today – the detection of gravitational waves (one of Planck's aims) and the discovery of a new set of particles (which the LHC is after) – could be at odds. Success for one could mean disappointment for the other. New Scientist explains why.
How can Planck detect gravitational waves?
Indirectly. Planck is studying the photons that make up the cosmic microwave background (CMB), the radiation left over from the big bang. These photons were released when the universe was about 380,000 years old and they contain imprints of events that took place in the first instants after the big bang.
For example, an episode called inflation – a period of exponential expansion when the cosmos was about 10-36 seconds old – should have created enormous fluctuations in the fabric of space-time called gravitational waves. These would have polarised the photons of the CMB in a specific manner, and Planck could detect this polarisation (arxiv.org/abs/1004.2504).
What's this got to do with the LHC?
Among other things, the LHC is trying to find phenomena that go beyond the standard model of particle physics, the theory that describes all known particles and forces apart from gravity. There's ample reason to believe that such new physics exists.
One favoured model of new physics is supersymmetry, which says that for every particle in the standard model there exists a heavier partner particle. However, if Planck were to find the imprint of gravitational waves in the CMB, it could mean that the LHC will be unlikely to find any supersymmetric particles.
Why are the two discoveries linked?
Cosmologist Andrei Linde of Stanford University in California and his colleagues have shown a relationship between the energy density of space-time during inflation and the mass of the gravitino, a particle that is hypothesised in supersymmetric theories (arxiv.org/abs/hep-th/0411011). Planck's instruments will be able to spot signs of relatively powerful gravitational waves, so if they pick such evidence up, the energy scale of inflation must have been relatively high, and so the mass of the gravitino would be greater than about 1 teraelectronvolt (TeV).
In supersymmetric theories, such a high mass for the gravitino would mean that the other supersymmetric partner particles would also be correspondingly massive, probably putting them beyond the reach of the LHC: it would not have the energy required to create such particles.
On the other hand, if the LHC discovers some supersymmetric particles, this would suggest that the mass of the gravitino is relatively small, less than 1 TeV. According to Linde, this implies that the energy scale of inflation was low too – creating gravitational waves too weak to be detected by Planck.
No comments:
Post a Comment