Quantum Circuit Cosmology: The Expansion of the Universe Since the First Qubit [CL]


We consider cosmological evolution from the perspective of quantum information. We present a quantum circuit model for the expansion of a comoving region of space, in which initially-unentangled ancilla qubits become entangled as expansion proceeds. We apply this model to the comoving region that now coincides with our Hubble volume, taking the number of entangled degrees of freedom in this region to be proportional to the de Sitter entropy. The quantum circuit model is applicable for at most 140 $e$-folds of inflationary and post-inflationary expansion: we argue that no geometric description was possible before the time $t_1$ when our comoving region was one Planck length across, and contained one pair of entangled degrees of freedom. This approach could provide a framework for modeling the initial state of inflationary perturbations.

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N. Bao, C. Cao, S. Carroll, et. al.
Fri, 24 Feb 17

Comments: 12 pages, 1 figure. Including appendix

BRS structure of Simple Model of Cosmological Constant and Cosmology [CL]


In arXiv:1601.02203, a simple model has been proposed in order to solve one of the problems related with the cosmological constant. The model is given by a topological field theory and the model has an infinite numbers of the BRS symmetries. The BRS symmetries are, however, spontaneously broken in general. In this paper, we investigate the BRS symmetry in more details and show that there is one and only one BRS symmetry which is not broken and the unitarity can be guaranteed. In the model, the quantum problem of the vacuum energy, which may be identified with the cosmological constant, reduces to the classical problem of the initial condition. In this paper, we investigate the cosmology given by the model and specify the region of the initial conditions which could be consistent with the evolution of the universe. We also show that there is a stable solution describing the de Sitter space-time, which may explain the accelerating expansion in the current universe.

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T. Mori, D. Nitta and S. Nojiri
Fri, 24 Feb 17

Comments: LaTeX 10 pages, 3 figures

Fifty years of cosmological particle creation [CL]


In the early sixties Leonard Parker discovered that the expansion of the universe can create particles out of the vacuum, opening a new and fruitfull field in physics. We give a historical review in the form of an interview that took place during the Conference ERE2014 (Valencia 1-5, September, 2014).

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L. Parker and J. Navarro-Salas
Fri, 24 Feb 17

Comments: 8 pages

Assessing the impact of bulk and shear viscosities on large scale structure formation [CEA]


It is analyzed the effects of both bulk and shear viscosities on the perturbations, relevant for structure formation in late time cosmology. It is shown that shear viscosity can be as effective as the bulk viscosity on suppressing the growth of perturbations and delaying the nonlinear regime. A statistical analysis of the shear and bulk viscous effects is performed and some constraints on these viscous effects are given.

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C. Barbosa, H. Velten, J. Fabris, et. al.
Fri, 24 Feb 17

Comments: 21 pages, 19 figures

Positivity Bounds for Scalar Theories [CL]


Assuming the existence of a local, analytic, unitary UV completion in a Poincar\'{e} invariant scalar field theory with a mass gap, we derive an infinite number of positivity requirements using the known properties of the amplitude at and away from the forward scattering limit. These take the form of bounds on combinations of the pole subtracted scattering amplitude and its derivatives. In turn, these positivity requirements act as constraints on the operator coefficients in the low energy effective theory. For certain theories these constraints can be used to place an upper bound on the mass of the next lightest state that must lie beyond the low energy effective theory if such a UV completion is to ever exist.

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C. Rham, S. Melville, A. Tolley, et. al.
Thu, 23 Feb 17

Comments: 5 pages

Chiral magnetic effect in the presence of electroweak interactions as a quasiclassical phenomenon [CL]


We provide the quasiclassical derivation of the modified chiral magnetic effect in the case when massless charged fermions moving in external electromagnetic fields interact by electroweak forces with the background matter. In our study we rely on the energy balance between the external electromagnetic field and charged particles. The obtained expression for the electric current along the external magnetic field appears to coincide with our previous results based on the purely quantum approach. We also compare our results with findings of other authors.

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M. Dvornikov and V. Semikoz
Wed, 22 Feb 17

Comments: 10 pages in LaTeX2e, 1 table

Getting Super-Excited with Modified Dispersion Relations [CL]


We demonstrate that in some regions of parameter space, modified dispersion relations can lead to highly populated excited states, which we dub as “super-excited” states. In order to prepare such super-excited states, we invoke dispersion relations that have negative slope in an interim sub-horizon phase at high momenta. This behaviour of quantum fluctuations can lead to large corrections relative to the Bunch-Davies power spectrum, which mimics highly excited initial conditions. We identify the Bogolyubov coefficients that can yield these power spectra. In the course of this computation, we also point out the shortcomings of the gluing method for evaluating the power spectrum and the Bogolyubov coefficients. As we discuss, there are other regions of parameter space, where the power spectrum does not get modified. Therefore, modified dispersion relations can also lead to so-called “calm excited states” as well. We conclude by commenting on the possibility of obtaining these modified dispersion relations within the Effective Field Theory of Inflation.

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A. Ashoorioon, R. Casadio, G. Geshnizjani, et. al.
Wed, 22 Feb 17

Comments: 1+19 pages, 4 figures