Limits on Entanglement Effects in the String Landscape from Planck and BICEP/Keck Data

We consider observational limits on a proposed model of the string landscape in inflation. In this scenario, effects from the decoherence of entangled quantum states in long-wavelength modes in the universe result in modifications to the Friedmann Equation and a corresponding modification to inflationary dynamics. Previous work by Holman, Mersini-Houghton, and Takahashi suggested that such effects could provide an explanation for well-known anomalies in the Cosmic Microwave Background (CMB), such as the lack of power on large scales and the "cold spot" seen by both the WMAP and Planck satellites. In this paper, we compute limits on these entanglement effects from the Planck CMB data combined with the BICEP/Keck polarization measurement, and find no evidence for observable modulations to the power spectrum from landscape entanglement, and no sourcing of observable CMB anomalies. The originally proposed model with an exponential potential is ruled out to high significance. Assuming a Starobinsky-type $R^2$ inflation model, which is consistent with CMB constraints, data place a $2\sigma$ lower bound of $b > 6.46 \times 10^7\ {\rm GeV}$ on the Supersymmetry breaking scale associated with entanglement corrections.Comment: 21 pages, 19 figures (v2: version published in JCAP

Attractor Solutions in Tachyacoustic Cosmology

We study the dynamical stability of "tachyacoustic" cosmological models, in which primordial perturbations are generated by a shrinking sound horizon during a period of decelerating expansion. Such models represent a potential alternative to inflationary cosmology, but the phase-space behavior of tachyacoustic solutions has not previously been investigated. We numerically evaluate the dynamics of two non-canonical Lagrangians, a cuscuton-like Lagrangian and a Dirac-Born-Infeld Lagrangian, which generate a scale-invariant spectrum of perturbations. We show that the power-law background solutions in both cases are dynamical attractors.Comment: Some references and comments added. Accepted for publication in Physical Review

Symmetron Inflation

We define a new inflationary scenario in which inflation starts naturally after the Big Bang when the energy density drops below some critical value. As a model, we use recently proposed symmetron field whose effective potential depends on the energy density of the environment. At high densities, right after the Big Bang, the potential for the symmetron is trivial, and the field sits in equilibrium at the bottom of the potential. When the density drops below some critical value, the potential changes its shape into a symmetry breaking potential, and the field starts rolling down. This scenario does not require any special initial conditions for inflation to start. We also construct a concrete model with two fields, i.e. with symmetron as an inflaton and an additional scalar field which describes the matter content in the early universe. For the simplest coupling, the amplitude and shape of the power spectrum are the same as in the single field slow-roll inflation.Comment: Published in JCAP 01(2014)02

Inflation From Symmetry Breaking Below the Planck Scale

We investigate general scalar field potentials \hbox{$V\left(\phi\right)$} for inflationary cosmology arising from spontaneous symmetry breaking. We find that potentials which are dominated by terms of order $\phi^m$ with \hbox{$m > 2$} can satisfy observational constraints at an arbitrary symmetry breaking scale. Of particular interest, the spectral index of density fluctuations is shown to be independent of the specific form of the potential, depending only on the order $m$ of the lowest non-vanishing derivative of $V(\phi)$ near its maximum. The results of a model with a broken ${\rm SO(3)}$ symmetry illustrate these features.Comment: Submitted to Phys. Rev. Letters. 7 Pages, REVTeX. No figure