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Showing votes from 2020-05-05 11:30 to 2020-05-08 12:30 | Next meeting is Tuesday Aug 5th, 10:30 am.
We explore a model of the early universe in which the inflationary epoch is preceded by a cosmic bounce, and argue that this scenario provides a common origin to several of the anomalous features that have been observed at large angular scales in the cosmic microwave background (CMB). More concretely, we show that a power suppression, a dipolar asymmetry, and a preference for odd-parity correlations, with amplitude and scale dependence in consonance with observations, are expected from this scenario. The model also alleviates the tension in the lensing amplitude. These signals originate from the indirect effect that non-Gaussian correlations between CMB modes and super-horizon wavelengths induce in the power spectrum. We do not restrict to any specific theory, but rather derive features common to a family bouncing models.
Does space stretch its contents as the universe expands? Usually we say the answer is no - the stretching of space is not like the stretching of a rubber sheet that might drag things with it. In this paper we explore a potential counter example - namely we show that is is impossible to make an arbitrarily long ruler in an expanding universe, because it is impossible to hold the distant end of the ruler "stationary" with respect to us (as defined in the Friedmann-Lemaitre-Robertson-Walker metric). We show that this does not mean that expanding space has a force associated with it, rather, some fictitious forces arise due to our choice of a non-inertial reference frame. By choosing our usual time-slice (where all comoving observers agree on the age of the universe), we choose a global frame in which special relativity does not hold. As a result, simple relativistic velocity transforms generate an apparent acceleration, even where no force exists. This effect is similar to the fictitious forces that arise in describing objects in rotating reference frames, as in the case of the Coriolis effect.
We draw a figure from where it is possible to measure the number of e-folds of expansion of the universe with a ruler.
During inflation, there is a preferred reference frame in which the expansion of the background spacetime is spatially isotropic. In contrast to Minkowski spacetime, observables can depend on the velocity of the system with respect to this cosmic rest frame. We derive new constraints from radiative stability and unitarity on effective field theories with such spontaneously broken Lorentz symmetry. In addition to a maximum energy scale, there is now also a critical velocity at which the theory breaks down. The theory therefore has different resolving power in time and in space, and we show that these can only coincide if cubic Lorentz-violating interactions are absent. Applying these bounds to the Effective Field Theory of Inflation, we identify the region of parameter space in which inflation can be both single-field and weakly coupled on subhorizon scales. This can be implemented as a theoretical prior, and we illustrate this explicitly using Planck observational constraints on the primordial bispectrum.