Claudia de Rham, Scott Melville, Andrew J. Tolley, Shuang-Yong Zhou

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.

Philip F Hopkins, Andrew Wetzel, Dusan Keres, Claude-Andre Faucher-Giguere, Eliot Quataert, Michael Boylan-Kolchin, Norman Murray, Christopher C. Hayward, Shea Garrison-Kimmel, Cameron Hummels, Robert Feldmann, Paul Torrey, Xiangcheng Ma, Daniel Angles-Alcazar, Kung-Yi Su, Matthew Orr, Denise Schmitz, Ivanna Escala, Robyn Sanderson, Michael Y. Grudic, Zachary Hafen, Ji-Hoon Kim, Alex Fitts, James S. Bullock, Coral Wheeler, T.K. Chan, Oliver D. Elbert, Desika Narananan

The Feedback In Realistic Environments (FIRE) project explores the role of feedback in cosmological simulations of galaxy formation. Previous FIRE simulations used an identical source code (FIRE-1) for consistency. Now, motivated by the development of more accurate numerics (hydrodynamic solvers, gravitational softening, supernova coupling) and the exploration of new physics (e.g. magnetic fields), we introduce FIRE-2, an updated numerical implementation of FIRE physics for the GIZMO code. We run a suite of simulations and show FIRE-2 improvements do not qualitatively change galaxy-scale properties relative to FIRE-1. We then pursue an extensive study of numerics versus physics in galaxy simulations. Details of the star-formation (SF) algorithm, cooling physics, and chemistry have weak effects, provided that we include metal-line cooling and SF occurs at higher-than-mean densities. We present several new resolution criteria for high-resolution galaxy simulations. Most galaxy-scale properties are remarkably robust to the numerics that we test, provided that: (1) Toomre masses (cold disk scale heights) are resolved; (2) feedback coupling ensures conservation and isotropy, and (3) individual supernovae are time-resolved. As resolution increases, stellar masses and profiles converge first, followed by metal abundances and visual morphologies, then properties of winds and the circumgalactic medium. The central (~kpc) mass concentration of massive (L*) galaxies is sensitive to numerics, particularly how winds ejected into hot halos are trapped, mixed, and recycled into the galaxy. Multiple feedback mechanisms are required to reproduce observations: SNe regulate stellar masses; OB/AGB mass loss fuels late-time SF; radiative feedback suppresses instantaneous SFRs and accretion onto dwarfs. We provide tables, initial conditions, and the numerical algorithms required to reproduce our simulations.

Rachel A Rosen

When starting with a static, spherically-symmetric ansatz, there are two types of black hole solutions in dRGT massive gravity: (i) exact Schwarzschild solutions which exhibit no Yukawa suppression at large distances and (ii) solutions in which the dynamical metric and the reference metric are simultaneously diagonal and which inevitably exhibit coordinate-invariant singularities at the horizon. In this work we investigate the possibility of black hole solutions which can accommodate both a non-singular horizon and Yukawa asymptotics. In particular, by adopting a time-dependent ansatz, we derive perturbative analytic solutions which possess non-singular horizons. These black hole solutions are indistinguishable from Schwarzschild black holes in the limit of zero graviton mass. At finite graviton mass, they depend explicitly on time. However, we demonstrate that the location of the apparent horizon is not necessarily time-dependent, indicating that these black holes are not necessarily accreting or evaporating (classically). In deriving these results, we also review and extend known results about static black hole solutions in massive gravity.

Ning Bao, ChunJun Cao, Sean M. Carroll, Liam McAllister

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.

sxk1031

Exoplanets

Exoplanets Full

Kiyoshi Wesley Masui, Ue-Li Pen, Neil Turok

We show that three-dimensional information is critical to discerning the effects of parity violation in the primordial gravity-wave background. Helical gravity waves would induce parity-violating correlations in the cosmic microwave background (CMB) between parity-odd polarization $B$-modes and parity-even temperature anisotropies ($T$) or polarization $E$-modes. Unfortunately, $EB$ correlations are much weaker than would be naively expected, which we show is due to an approximate symmetry resulting from the two-dimensional nature of the CMB. The detectability of parity-violating correlations is exacerbated by the fact that the handedness of individual modes cannot be discerned in the two-dimensional CMB, leading to a noise contribution from scalar matter perturbations. In contrast, the tidal imprints of primordial gravity waves fossilized into the large-scale structure of the Universe will provide a three-dimensional probe of parity violation. Using such fossils the handedness of gravity waves may be determined on a mode-by-mode basis, permitting future surveys to probe helicity at the percent level if the amplitude of primordial gravity waves is near current observational upper limits.