Related papers: 0.5 eV QCD Axion Cosmology
Based on the assumption that some apparent properties of the observable universe are accurate at a reasonable level of approximation, a tentative is made to independently derive the values of the baryon density parameter, the Hubble…
Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion the physical cause of which is a mystery. Formally, this requires the inclusion of a term acting as a negative pressure in the…
We show that Dark Matter consisting of bosons of mass of about 1eV or less has critical temperature exceeding the temperature of the universe at all times, and hence would have formed a Bose-Einstein condensate at very early epochs. We also…
The current cosmological constraints on a dark matter axion are reviewed. We describe the basic mechanisms by which axions are created in the early universe, both in the standard thermal scenario in which axion strings form and in…
Cosmology is nowadays going through a true revolution in the quantity and quality of observations that are capable of providing crucial information about the origin and evolution of the universe. In the first years of the next millenium we…
Motivated by the observed cosmic matter distribution, we present the following conjecture: due to the formation of voids and opaque structures, the average matter density on the path of the light from the well-observed objects changes from…
This chapter aims to present an introduction to current research on the nature of the cosmological dark matter and the origin of galaxies and large scale structure within the standard theoretical framework: gravitational collapse of…
Hidden axions may be coupled to the standard model particles through a kinetic or mass mixing with QCD axion. We study a scenario in which a hidden axion constitutes a part of or the whole of dark matter and decays into photons through the…
We study the potential of a future, large-volume photometric survey to constrain the axion mass $m_a$ in the hot dark matter limit. Future surveys such as Euclid will have significantly more constraining power than current observations for…
I discuss the possibility that the difference in the measured Hubble constant Ho between the current, Late, and the z ~1100, Early, epochs is due to the emergence in between of a new particle. I connect that difference with a change in the…
If primordial black holes (PBHs) had come to dominate the energy density of the early Universe when oscillations in the axion field began, we show that the relic abundance and expected mass range of the QCD axion would be greatly modified.…
The age of the Universe at a given redshift is a fundamental relationship in cosmology. For many years, the uncertainties in it were dauntingly large, close to a factor of 2. In this age of precision cosmology, they are now at the percent…
A measurement of the expansion rate of the Universe (that is the Hubble constant, H0) is derived here using the gamma-ray attenuation observed in the spectra of gamma-ray sources produced by the interaction of extragalactic gamma-ray…
The cosmological vacuum decay scenario recently proposed by Wang and Meng \cite{wm} is rediscussed. From thermodynamic arguments it is found that the $\epsilon$ parameter quantifying the vacuum decay rate must be positive in the presence of…
The QCD axion offers a natural resolution to the strong CP problem and provides a compelling dark matter candidate. If the QCD axion constitutes all the dark matter, the simplest models pick out a narrow range of masses around $100\,\mu{\rm…
Observational constraints guide one forcefully to examine models in which the matter density is substantially less than critical density. Particularly noteworthy are those which are consistent with inflation. For these models, microwave…
We present a possible understanding to the issues of cosmological constant, inflation, matter and coincidence problems based only on the Einstein equation and Hawking particle production. The inflation appears and results agree to…
For two decades the hot big-bang model has been referred to as the standard cosmology -- and for good reason. For just as long cosmologists have known that there are fundamental questions that are not addressed by the standard cosmology and…
This is a review and statistical analysis of the evidence supporting the existence of a cosmological constant in the early 1990s, before its discovery made with distant supernovae in 1998. The earlier evidence was derived from newly precise…
Axion as a coherently oscillating scalar field is known to behave as a cold dark matter in all cosmologically relevant scales. For conventional axion mass with 10^{-5} eV, the axion reveals a characteristic damping behavior in the evolution…