Dr. Antony Valentini

Imperial College London
Jonathan Halliwell,

*Imperial College London*
Hidden Variables in the Early Universe

The project will study the early universe from the viewpoint of "hidden-variables theories." These are theories in which the apparently random outcomes of quantum experiments are actually determined in advance, by hidden parameters that are presently outside our control. A particular theory due to de Broglie and Bohm is used as a model. A key idea is "quantum nonequilibrium," a state in which the values of the hidden entities have an anomalous distribution, so that the statistics predicted by quantum theory are violated (resulting in superluminal signals and violations of Heisenberg's uncertainty principle). In inflationary cosmology, nonequilibrium statistics in the early universe will leave signatures in the "cosmic microwave background" - the radiation left over from the big bang, coming from all over the sky. The project attempts to predict and find such signatures, by analysing the effects of quantum nonequilibrium during the earliest moments of the big bang.

Hidden-variables theories, such as de Broglie-Bohm theory, reproduce quantum theory for an `equilibrium' distribution of hidden parameters. But allowing arbitrary distributions (analogous to classical non-thermal distributions) raises the possibility of new `nonequilibrium' physics outside the quantum domain. This may have existed in the very early universe, with relaxation to `quantum equilibrium' taking place during the big bang. The project will use cosmological data to set limits on violations of quantum theory at early times, and attempt to predict where such violations might be found. The project has three components. (1) In inflationary cosmology, the primordial perturbations originate from quantum fluctuations, so current CMB data is sensitive to the magnitude and form of early quantum nonequilibrium. (2) I have derived a general `freezing inequality', which shows that, depending on the details of the expansion, relaxation for a scalar field can be suppressed for large-wavelength modes. I will use this result to try to make definite predictions (for example for a breaking of scale invariance in the CMB above a certain length scale). (3) The suppression of relaxation for largewavelength field modes suggests predictions for the presence of nonequilibrium in very low energy relic particles (such as gravitinos).

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