Related papers: The QCD Axion and Unification
We study the experimental constraints on a model of a two-component dark matter, consisting of the QCD axion, and a scalar particle, both contributing to the dark matter relic abundance of the Universe. The global Peccei-Quinn symmetry of…
It is shown that the post-inflationary quantum chromodynamics (QCD) axion need not lead to a unique one-parameter prediction for the dark matter abundance whenever small explicit Peccei-Quinn symmetry breaking becomes dynamically relevant…
Quantum Chromodynamics (QCD) is the theory of the strong interactions within the Standard Model of particle physics, which explains more than 99% of the mass of the visible Universe. However, there is evidence that a substantial portion of…
A simple yet compelling physical picture is proposed for the nature of dark matter, dark energy, and the Big Bang. The proposal leads to predictions, from first-principles with high precision, for the values of the Hubble constant,…
The QCD axion is one of the best motivated dark matter candidates. The misalignment mechanism is well known to produce an abundance of the QCD axion consistent with dark matter for an axion decay constant of order $10^{12}$ GeV. For a…
The QCD axion is a promising candidate of the dark matter. In this paper, we discuss elastic scattering processes between nucleons and the QCD axion dark matter. We point out that the cross section can be enhanced by more than…
The status of several current and proposed experiments to search for galactic dark-matter and solar axions is reviewed in the light of astrophysical and cosmological limits on the Peccei-Quinn scale.
We consider the possibility of an enlarged QCD color group, SU(3+$N^\prime$) spontaneously broken to SU(3)$_c\times$SU($N^\prime$) with extra vector-like quarks transforming in the fundamental representation. When the heavy quarks are…
The QCD axion is a leading dark matter candidate that emerges as part of the solution to the strong CP problem in the Standard Model. The coupling of the axion to photons is the most common experimental probe, but much parameter space…
We study for what specific values of the theoretical parameters the axion can form the totality of cold dark matter. We examine the allowed axion parameter region in the light of recent data collected by the WMAP5 mission plus baryon…
We investigate the level-crossing phenomenon in two-axion systems, where the mass eigenvalues intersect as the mass of one axion increases with the cooling of the universe. This phenomenon can significantly alter the abundance of axions in…
Axion dark matter coupled via QCD induces a non-zero differential acceleration between test masses of different composition. Tests of the equivalence principle, like the recent MICROSCOPE space mission, are sensitive to such a signal. We…
Axions solve the Strong CP Problem and are a cold dark matter candidate. The combined constraints from accelerator searches, stellar evolution limits and cosmology suggest that the axion mass is in the range $3 \cdot 10^{-3} > m_a >…
The clockwork axion refers to a family of aligned multi-axion models that lead to an exponential hierarchy between the scale of Peccei-Quinn symmetry breaking and the scale of the axion decay constant. The clockworking can bring the…
Murayama proposed a GeV-scale axion theory where the up-quark mass term is generated dynamically by the QCD chiral condensate, spontaneously breaking a Peccei-Quinn symmetry. It predicts a too large mass splitting between neutral and…
Composite axion scenarios offer a robust field theoretic justification for the existence of a Peccei-Quinn symmetry of high quality. We present a new class of realizations that are naturally embedded in Grand-Unified Theories, retain…
The QCD axion is one of the most compelling solutions of the strong CP problem. There are major current efforts into searching for an ultralight, invisible axion, which is believed to be the only phenomenologically viable realization of the…
We propose a grand unified model in five dimensions that addresses the strong CP problem. In this framework, the boundary conditions that break the unified gauge group into the Standard Model gauge group simultaneously explain the mass…
I discuss the implementation of the Peccei-Quinn mechanism in a minimal realization of the Pati-Salam partial unification scheme. The axion mass is shown to be related to the Pati-Salam breaking scale and it is predicted via a two-loop…
In an axiverse with numerous axions, the cosmological moduli problem poses a significant challenge because the abundance of axions can easily exceed that of dark matter. The well-established stochastic axion scenario offers a simple…