Related papers: Relaxing Axions
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…
Nonlinearities in a realistic axion field potential may play an important role in the cosmological dynamics. In this paper we use the Boltzmann code CLASS to solve the background and linear perturbations evolution of an axion field and…
We report that the hypothesis that the upper bound on the axion decay constant can be moved up beyond $10^{12}$ GeV in models with a stronger QCD in the early universe is not realized. This proof is possible by studying the superpotential…
A mechanism is introduced to reduce a large cosmological constant to a sufficiently small value consistent with observational upper limit. The basic ingradient in this mechanism is a distinction which has been made between the two unit…
Axions arise in many theoretical extensions of the Standard Model of particle physics, in particular the "string axiverse". If the axion masses, $m_a$, and (effective) decay constants, $f_a$, lie in specific ranges, then axions contribute…
We investigate cosmological constraints on the original relaxion scenario proposed by Graham, Kaplan and Rajendran. We first discuss the appropriate sign choice of the terms in the scalar potential, when the QCD axion is the relaxion with a…
Theoretically, the running of the cosmological constant in the IR region is not ruled out. On the other hand, from the QFT viewpoint, the energy released due to the variation of the cosmological constant in the late universe cannot go to…
An alternative cosmological model is presented, which avoids the requirement of dark energy and dark matter. Based on the proposition that energy conservation should be valid not only locally but also globally, the energy tensor of general…
We propose a natural solution to the cosmological constant problem consistent with the standard cosmology and successful over a broad range of energies. This solution is based on the existence of a new field, the devaluton, with its…
We study novel solitonic solutions to Einstein-Klein-Gordon theory in the presence of a periodic scalar potential arising in models of axion-like particles. The potential depends on two parameters: the mass of the scalar field $m_a$ and the…
A special class of conformal gravity theories is proposed to solve the long standing problem of the fine-tuned cosmological constant. In the proposed model time evolution of the inflaton field leaves behind a nearly vanishing, but finite…
We study the cosmology of complex multi-axion theories. With O(100) fields and GUT scale energies these theories contain a vast number of vacua, inflationary trajectories and a natural dark matter candidate. We demonstrate that the vacua…
Theories with several hundred axion fields have enormous numbers of distinct meta-stable minima. A small fraction of these local minima have vacuum energy compatible with current measurements of dark energy. The potential also contains…
Recent cosmological observations suggest the presence of small but nonzero cosmological constant $\Lambda_{cos}^4 \simeq (2 \times 10^{-3} eV)^4$. It is an intriguing possibility that such a small cosmological constant is supplied by the…
String theory axions appear to be promising candidates for explaining cosmological constant via quintessence. In this paper, we study conditions on the string compactifications under which axion quintessence can happen. For sufficiently…
The observed properties of stars and especially the neutrino signal of the supernova 1987A provide an upper limit to the axion mass, while the age and expansion rate of the universe provide a lower limit. There remains a "window of…
We propose a novel and generalized mechanism, dubbed stochastic axion mixing. In a multi-axion framework, this mixing occurs naturally provided that the masses of all ultra-light axion-like particles (ALPs) are distinct and lighter than the…
A mechanism for suppressing the cosmological constant is developed, based on an analogy with a superconducting phaseshift in which free fermions coupled perturbatively to a weak gravitational field are in an unstable false vacuum state. The…
Relic thermal axions could play the role of an extra hot dark matter component in cosmological structure formation theories. By combining the most recent observational data we improve previous cosmological bounds on the axion mass m_a in…
We examine if the cosmological relaxation mechanism, which was proposed recently as a new solution to the hierarchy problem, can be compatible with high reheating temperature well above the weak scale. As the barrier potential disappears at…