Vincent B. Klaer, Guy D. Moore

We evaluate the efficiency of axion production from spatially random initial conditions in the axion field, so a network of axionic strings is present. For the first time, we perform numerical simulations which fully account for the large short-distance contributions to the axionic string tension, and the resulting dense network of high-tension axionic strings. We find nevertheless that the total axion production is somewhat less efficient than in the angle-averaged misalignment case. Combining our results with a recent determination of the hot QCD topological susceptibility (Borsanyi et al 2016), we find that if the axion makes up all of the dark matter, then the axion mass is m_a = 26.2 +-3.4 micro-electron volts.

Deng Wang, Xin-He Meng

We perform a comprehensive study of the dark energy equation of state (EoS) utilizing the model-independent Gaussian processes (GP). Using a combination of the Union 2.1 data set, the 30 newly added H(z) cosmic chronometer data points and Planck's shift parameter, we modify the usual GaPP code and provide a tighter constraint on the dark energy EoS than the previous literature about GP reconstructions. Subsequently, we take the "controlling variable method" to investigate directly the effects of variable matter density parameter $\Omega_{m0}$, variable cosmic curvature $\Omega_{k0}$ and variable Hubble constant $H_0$ on the dark energy EoS, respectively. We find that too small or large $\Omega_{m0}$, $\Omega_{k0}$ and $H_0$ are all disfavored by our GP reconstructions based on current cosmological observations. Subsequently, we find that variable $\Omega_{m0}$ and $\Omega_{k0}$ affect the reconstructions of the dark energy EoS, but affect hardly the reconstructions of the normalized comoving distance $D(z)$ and its derivatives $D'(z)$ and $D"(z)$. However, variable $H_0$ affects the reconstructions of the dark energy EoS by affecting obviously those of $D(z), D'(z)$ and $D"(z)$. Furthermore, we find that the results of our reconstructions support substantially the recent local measurement of $H_0$ reported by Riess et al.

Hannes R. Rüter, David Hilditch, Marcus Bugner, Bernd Brügmann, University of Jena, Jena, Germany, (2) CENTRA, University of Lisbon, Lisboa, Portugal)

We show how the basic idea of parabolic Jacobi relaxation can be modified to obtain a new class of hyperbolic relaxation schemes that are suitable for the solution of elliptic equations. Some of the analytic and numerical properties of hyperbolic relaxation are examined. We describe its implementation as a first order system in a pseudospectral evolution code, demonstrating that certain elliptic equations can be solved within a framework for hyperbolic evolution systems. Applications include various initial data problems in numerical general relativity. In particular we generate initial data for the evolution of a massless scalar field, a single neutron star, and binary neutron star systems.

Alexandros Papageorgiou, Marco Peloso

We compute the gravitational leptogenesis generated from the parity-violating gravitational waves sourced by an abelian gauge field coupled to a pseudo-scalar inflation. We show that, once the CMB bound on the tensor-to-scalar ratio is enforced, the lepton asymmetry produced by this mechanism during inflation is too small to account for the observed baryon asymmetry of the universe, irrespectively of the inflaton potential, the strength of its coupling to the gauge field, and the details of reheating.

Shohei Saga, Hiroyuki Tashiro, Shuichiro Yokoyama

We provide a new bound on the amplitude of primordial magnetic fields (PMFs) by using a novel mechanism, named {\it magnetic reheating}. Before the epoch of recombination, PMFs induce the fluid motions in a photon-baryon plasma through the Lorentz force. Due to the viscosity in the plasma, such induced fluid motions would be damped and this means the dissipation of PMFs. In the early Universe with $z \gtrsim 2 \times 10^6$, cosmic microwave background (CMB) photons are quickly thermalized with the dissipated energy and shift to a different Planck distribution with a new temperature. In other words, the energy injection due to the dissipation of PMFs changes the baryon-photon number ratio during this era and we name such a process {\it magnetic reheating}. By using the current results of the baryon-photon number ratio obtained from the Big Bang nucleosynthesis and CMB observations, we put a strongest constraint on the amplitude of PMFs on small scales which we can not access through CMB anisotropy and CMB distortions, $B_{0} \lesssim 1.0 \; \mu{\rm G}$ at the scales $10^{4} \; h{\rm Mpc}^{-1} < k < 10^{8} \; h{\rm Mpc}^{-1}$. Moreover, when the spectrum of PMFs is given by the power-law, the magnetic reheating puts a quite strong constraint in the case of the blue-tilted spectrum, for example, $B_0 \lesssim 10^{-17} \;{\rm nG}$, $10^{-23} \;{\rm nG}$, and $10^{-29} \;{\rm nG}$ at 1~comoving Mpc for $n_{B}=1.0$, $2.0$, and $3.0$, respectively. This constraint would give an impact on generation mechanisms of PMFs in the early Universe.