Related papers: More Axions from Strings
We argue that the QCD axion can arise from many aligned axions with decay constants much smaller than the conventional axion window. If the typical decay constant is of {\cal O}{(100)} GeV to 1 TeV, one or more of the axions or saxions may…
Cosmic strings are topological defects possibly formed in the early Universe, which may be observable due to their gravitational effects on the cosmic microwave background radiation or gravitational wave experiments. To this effect it is…
Axions and axion-like particles (ALPs) are a prominent dark matter candidate, drawing motivation in part from the axiverse of string theory. Axion-like particles can also arise as composite degrees of freedom of a dark sector, for example,…
String scenarios generically predict that we live in a so called axiverse: the Universe with about a hundred of light axion species which are decoupled from the Standard Model particles. However, the axions can couple to the inflaton which…
Laboratory experiments have the capacity to detect the QCD axion in the next decade, and precisely measure its mass, if it composes the majority of the dark matter. In type IIB string theory on Calabi-Yau threefolds in the geometric regime,…
We propose a relaxation mechanism for the initial misalignment angle of the pre-inflationary QCD axion with a large decay constant. The proposal addresses the challenges posed to the axion dark matter scenario by an overabundance of axions…
Axion strings are horizon-size topological defects that may be produced in the early Universe. Ultra-light axion-like particles may form strings that persist to temperatures below that of big bang nucleosynthesis. Such strings have been…
Two populations of axions can contribute to cold dark matter: the classical field produced via the misalignment mechanism, and the modes produced in the decay of strings. The classical field has extra pressure, as compared to WIMPs, which…
Consistent frameworks of quantum gravity often predict the existence of large numbers of ultralight pseudoscalar degrees of freedom, forming the phenomenological landscape of the String Axiverse. The complexity of the extra-dimensional…
In this talk, I review briefly a scenario for the evolution of a string-inspired cosmological model, in which condensates of primordial gravitational waves (GW), formed at the very early eras after the Big Bang, are considered responsible…
A consequence of QCD axion dark matter being born after inflation is the emergence of small-scale substructures known as miniclusters. Although miniclusters merge to form minihalos, this intrinsic granularity is expected to remain imprinted…
String theory suggests the simultaneous presence of many ultralight axions possibly populating each decade of mass down to the Hubble scale 10^-33eV. Conversely the presence of such a plenitude of axions (an "axiverse") would be evidence…
Dark gauge sectors and axions are well-motivated in string theory. We demonstrate that if a confining gauge sector gives rise to dark glueballs that are a fraction of the dark matter, and the associated axion has a decay constant near the…
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…
String theoretic axion is a prime candidate for the QCD axion solving the strong CP problem. For a successful realization of the QCD axion in string theory, one needs to stabilize moduli including the scalar partner (saxion) of the QCD…
In theories of axion dark matter with large axion decay constant, temperature variations in the CMB are extremely sensitive to perturbations in the initial axion field, allowing one to place a lower bound on the total amount of inflation.…
We discuss key aspects of the nature of radiation from global strings and its impact on the relic axion density. Using a simple model we demonstrate the dependence on the spectrum of radiation emitted by strings. We then study the radiation…
The model independent axion of string theory has a decay constant of order of the Planck scale. We explore the properties of this quintessence candidate (quintaxion) in the scheme of hidden sector supergravity breakdown. In models allowing…
A QCD axion with a time-dependent decay constant has been known to be able to accommodate high-scale inflation without producing topological defects or too large isocurvature perturbations on CMB scales. We point out that a dynamical decay…
Axions as dark matter is an increasingly important subject in astrophysics and cosmology. Experimental and observational searches are mounting across the mass spectrum of axion-like particles, many of which require detailed knowledge of…