Related papers: The Quality/Cosmology Tension for a Post-Inflation…
The QCD axion needs not be an exact pseudoscalar for solving the strong CP problem. Its imperfectness can play a profound role cosmologically. We propose effective operators, where the Peccei-Quinn field linearly couples to Standard Model…
The post-inflationary Peccei-Quinn symmetry-breaking scenario provides a rich theoretical framework to study axion dark matter production through the dynamics oftopological defects. Accurate predictions for the axion abundance require a…
Composite axions offer a scenario where the axion emerges as a pion-like state, avoiding fine-tuning of elementary scalars and ameliorating the axion quality problem. Despite these advantages, their post-inflationary cosmology remains…
The QCD axion is the leading solution to the strong-CP problem, a dark matter candidate, and a possible result of string theory compactifications. However, for axions produced before inflation, symmetry-breaking scales of $f_a \gtrsim…
We investigate two cosmological axion problems (isocurvature fluctuations and domain-wall formation) in chaotic inflationary universe. It is believed that these problems are solved if potential for the Peccei-Quinn scalar field is very…
Theories in which the Peccei-Quinn phase transition occurs after inflation tend to suffer from problematic domain walls. One possible solution involves a small, explicit breaking ot the symmetry. But this raises other potential issues. We…
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…
Axion models have two serious cosmological problems, domain wall and isocurvature perturbation problems. In order to solve these problems we investigate the Linde's model in which the field value of the Peccei-Quinn (PQ) scalar is large…
We present a novel framework of the post-inflationary composite axion to address the strong CP problem without the cosmological domain wall problem. Conventional composite axion models lead to the domain wall number greater than one,…
We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry. Symmetry breaking during or after inflation results in the formation of a domain wall network which would cause cosmic…
We consider the scenario in which the Peccei-Quinn symmetry breaking is followed by a period of inflation. A particularly interesting case is that the string-domain wall network produced by the symmetry breaking enters the horizon after the…
We propose two novel solutions to the domain wall problem of the QCD axion by introducing a massless or light axion that also couples to gluons. The first solution applies when the new axion forms strings after inflation. Due to its mixing…
Axions are hypothetical pseudoscalar particles introduced initially as a solution to the Strong CP problem in Quantum Chromodynamics (QCD), and they also arise naturally in a broad class of low-energy compactifications of string theory.…
We explore the interplay of the post-inflationary QCD axion and a light scalar field for the axion domain wall decay and dark matter (DM). The scalar field possesses a nonzero vacuum expectation value (VEV) during inflation, so that its…
We examine the theoretical possibility for the heavy QCD axion to induce slow-roll inflation while solving the strong CP problem through the Peccei-Quinn mechanism. If the cancellation between contributions from a small-size instanton and…
Axion dark matter in high-scale inflation is subject to the isocurvature constraint, since quantum fluctuations of the axion field during inflation may exceed the current CMB bound. One conventional way to suppress these fluctuations is to…
We study the possibility that the axion Peccei-Quinn symmetry is spontaneously broken after the beginning of inflation. This scenario interpolates between pre-inflationary and post-inflationary axion cosmology with significant…
The QCD axion cosmology depends crucially on whether the QCD axion is present during inflation or not. We point out that contrary to the standard criterion, the Peccei-Quinn (PQ) symmetry could remain unbroken during inflation, even when…
It is known for some time that the cosmological bound on the invisible axion scale can be avoided by an early phase of strong QCD. While most approaches rely on theories where the strong coupling constant is determined through the…
The axion causes two serious cosmological problems, domain wall and isocurvature perturbation problems. Linde pointed that the isocurvature perturbations are suppressed when the Peccei-Quinn (PQ) scalar field takes a large value $\sim…