Related papers: Axion as a cold dark matter candidate: Proof to fu…
We review the current status of axions as dark matter. Motivation, models, constraints and experimental searches are outlined. The axion remains an excellent candidate for the dark matter and future experiments, particularly the Axion Dark…
The dynamics of spin in external electromagnetic, gravitational, and axion fields is analysed in the framework of the gravitoelectromagnetism approach in Einstein's general relativity theory. We consistently extend the recent studies from…
Is the usual treatment of axion dark matter as a classical field reliable? We show that the answer is subtle: the axion field could well be in a quantum state that has no complete classical description, but realistic detectors cannot tell…
We study the time evolution of the quantum fluctuations of the axion field for both the QCD axion as well as axions arising in the context of supergravity and string theories. We explicitly keep track not only of the coherently oscillating…
In addition to the second-order Einstein equations on four-dimensional homogeneous isotropic background universe filled with the single perfect fluid, we also derived the second-order perturbations of the continuity equation and the Euler…
We formulate axion-electrodynamics and magnetohydrodynamics (MHD) in the cosmological context assuming weak gravity. The two formulations are made for a general scalar field with general $f(\phi)$-coupling, and an axion as a massive scalar…
In all supersymmetric theories, gravitinos, with mass suppressed by the Planck scale, are an obvious candidate for dark matter; but if gravitinos ever reached thermal equilibrium, such dark matter is apparently either too abundant or too…
We propose simple scenarios where the observed dark matter abundance arises from decays and scatterings of heavy quarks through freeze-in of an axion-like particle with mass in the $10 {\rm \, keV} - 1 {\rm \, MeV}$ range. These models can…
One of the intriguing properties characteristic to three-dimensional topological materials is the topological magnetoelectric phenomena arising from a topological term called the $\theta$ term. Such magnetoelectric phenomena are often…
Dark matter axions form a rethermalizing Bose-Einstein condensate. This provides an opportunity to distinguish axions from other forms of dark matter on observational grounds. I show that if the dark matter is axions, tidal torque theory…
The dynamics of self-gravitating fluids is analyzed within the framework of a collisionless Boltzmann equation in the presence of gravitational fields and Poisson equation. Two cases are analyzed: a system with baryonic and dark matter in a…
We point out that a well known axion model with an explicit Z(N) symmetry breaking term predicts both dark energy and cold dark matter. We estimate the parameters of this model which fit the observed densities of the dark components of the…
Gauge invariant treatments of the second order cosmological perturbation in a four dimensional homogeneous isotropic universe filled with the perfect fluid are completely formulated without any gauge fixing. We derive all components of the…
Under the main assumption that the axion scalar field mainly composes the dark matter in the Universe, in this paper we shall extend the formalism of kinetic axion $R^2$ gravity to include Gauss-Bonnet terms non-minimally coupled to the…
The dynamic world model and its linear perturbations were first studied in Einstein's gravity. In the system without pressure the relativistic equations coincide exactly with the later known ones in Newton's gravity. Here we prove that,…
The axino is a promising candidate for dark matter in the Universe. It is electrically and color neutral, very weakly interacting, and could be - as assumed in this study - the lightest supersymmetric particle, which is stable for unbroken…
We present fully nonlinear and exact cosmological perturbation equations in the presence of multiple components of fluids and minimally coupled scalar fields. We ignore the tensor-type perturbation. The equations are presented without…
Most matter in the Universe is invisible and unknown, which is called dark matter. A candidate of dark matter is axion, which is an ultra-light particle motivated as a solution for the CP problem. Axions form clouds in a galactic halo,…
It is well known that couplings occur among the scalar-, vector-, and tensor-type perturbations of Friedmann world model in the second perturbational order. Here, we prove that, except for the gravitational wave contribution, the…
The axion has emerged as the most attractive solution to two fundamental questions in modern physics related to the charge-parity invariance in strong interactions and the invisible matter component of our universe. Over the past decade,…