Related papers: Probing a QCD String Axion with Precision Cosmolog…
Axion scenarios in which the spontaneous breaking of the Peccei-Quinn symmetry takes place before or during inflation, and in which axion dark matter arises from the misalignment mechanism, can be constrained by Cosmic Microwave Background…
We compute the primordial scalar, vector and tensor metric perturbations arising from quantum field inflation. Quantum field inflation takes into account the nonperturbative quantum dynamics of the inflaton consistently coupled to the…
We discuss quantum gravitational effects in Einstein theory coupled to periodic axion scalars to analyze the viability of several proposals to achieve superplanckian axion periods (aka decay constants) and their possible application to…
String theory models of axion monodromy inflation exhibit scalar potentials which are quadratic for small values of the inflaton field and evolve to a more complicated function for large field values. Oftentimes the large field behaviour is…
If inflation occurs after the breaking of Peccei-Quinn symmetry then large values of the breaking scale $F$, which are forbidden in conventional axion cosmology, are permitted, provided that we inhabit a region of the Multiverse where the…
The latest Planck results show a power deficit in the temperature anisotropies near $\ell \approx 20$ in the cosmic microwave background (CMB). This observation can hardly be explained within the standard inflationary…
Large field excursions are required in a number of axion models of inflation. These models also possess global cosmic strings, around which the axion follows a path mirroring the inflationary trajectory. Cosmic strings are thus an…
We set constraints on moduli cosmology from the production of dark matter -- radiation and baryon -- radiation isocurvature fluctuations through modulus decay, assuming the modulus remains light during inflation. We find that the moduli…
We investigate the embedding of brane inflation into stable compactifications of string theory. At first sight a warped compactification geometry seems to produce a naturally flat inflaton potential, evading one well-known difficulty of…
Inflation universally produces classical almost scale free Gaussian inhomogeneities of any light scalars. Assuming the coupling constants at the time of inflation depend on some light moduli fields, we encounter the generation of modulated…
The nature of axion cosmology is usually said to depend on whether the Peccei-Quinn (PQ) symmetry breaks before or after inflation. The PQ symmetry itself is believed to be an accident, so there is not necessarily a symmetry during…
We explore the possibility of obtaining inflation in weakly coupled heterotic string theory, where the model dependent axions are responsible for driving inflation. This model can be considered as a certain extrapolation of…
The QCD axion has important connections to early universe cosmology. For example, it is often said that isocurvature limits rule out a combination of high axion decay constant, $f_a$, and high inflationary Hubble scale, $H_I$. High scales…
String theory abounds with light scalar fields (the dilaton and various moduli) which create a host of observational problems, and notably some serious cosmological difficulties similar to the ones associated with the Polonyi field in the…
In the scenario in which QCD axion dark matter is produced after inflation, the Universe is populated by large inhomogeneities on very small scales. Eventually, these fluctuations will collapse gravitationally to form dense axion…
The "central" region of moduli space of M- and string theories is where the string coupling is about unity and the volume of compact dimensions is about the string volume. Here we argue that in this region the non-perturbative potential…
We compute the primordial scalar, vector and tensor metric perturbations arising from quantum field inflation. Quantum field inflation takes into account the nonperturbative quantum dynamics of the inflaton consistently coupled to the…
In this paper, we consider a possibility that the temperature anisotropy of cosmic microwave background (CMB) is dominantly generated by the primordial fluctuations of QCD-axion like particles under a circumstance that inflaton's…
When Inflation is embedded in a fundamental theory, such as string theory, it typically begins when the Universe is already substantially larger than the fundamental scale [such as the one defined by the string length scale]. This is…
Inflationary cosmology provides a natural mechanism for the generation of primordial perturbations which seed the formation of observed cosmic structure and lead to specific signals of anisotropy in the cosmic microwave background…