Related papers: Axions from string decay
We study the evolution of cosmic strings taking into account the frictional force due to the surrounding radiation. We consider small perturbations on straight strings, oscillation of circular loops and small perturbations on circular…
Starting with exact solutions to string theory on curved spacetimes we obtain deformations that represent gravitational shock waves. These may exist in the presence or absence of sources. Sources are effectively induced by a tachyon field…
At its very beginning, the universe is believed to have grown exponentially in size via the mechanism of inflation. The almost scale-invariant density perturbation spectrum predicted by inflation is strongly supported by cosmological…
We initiate a study on various cosmological imprints of string axions whose scalar potentials have plateau regions. In such cases, we show that a delayed onset of oscillation generically leads to a parametric resonance instability. In…
It is widely believed that axions are ubiquitous in string theory and could be the dark matter. The peculiar features of the axion dark matter are coherent oscillations and a coupling to the electromagnetic field through the Chern-Simons…
In the axiverse scenario, a massive scalar field (string axion) forms a cloud around a rotating black hole (BH) by superradiant instability and emits continuous gravitational waves (GWs). We examine constraints on the string axion…
In this master's thesis we study the production of axion dark matter through the so-called misalignment mechanism by considering that during that time, the universe was dominated by a new kind of fluid, different than radiation. We perform…
Assuming axion-like particles account for the entirety of the dark matter in the Universe, we study the possibility of detecting their decay into photons at radio frequencies. We discuss different astrophysical targets, such as dwarf…
The topic of cosmic strings provides a bridge between the physics of the very small and the very large. They are predicted by some unified theories of particle interactions. If they exist, they may help to explain some of the largest-scale…
The electric Weak Gravity Conjecture demands that axions with large decay constant $f$ couple to light instantons. The resulting large instantonic corrections pose problems for natural inflation. We explore an alternative argument based on…
We study the cosmology of axions in the post-inflationary scenario, where random initial conditions and the ensuing string-domain-wall network generate an isocurvature power spectrum. Axions radiated from strings behave as warm, wave-like…
We study the formation and evolution of topological defects in an aligned axion model with multiple Peccei-Quinn scalars, where the QCD axion is realized by a certain combination of the axions with decay constants much smaller than the…
Oscillons are extremely long-lived, spatially-localized field configurations in real-valued scalar field theories that slowly lose energy via radiation of scalar waves. Before their eventual demise, oscillons can pass through (one or more)…
Pre-big bang cosmology predicts tiny first-order dilaton and metric perturbations at very large scales. Here we discuss the possibility that other -- more copiously generated -- perturbations may act, at second order, as scalar seeds of…
We review applications of string theory to cosmology, from primordial times to the present-day accelerated expansion. Starting with a brief overview of cosmology and string compactifications, we discuss in detail moduli stabilisation,…
String scenarios typically not only predict axion-like particles (ALPs) but also significant amounts of ALP dark radiation originating from the decay of the inflaton or a more general modulus. In this paper, we study the decay of such…
Grand unified theories can admit cosmic strings with fermion zero modes. Such zero modes result in the string being current-carrying and the formation of stable remnants, vortons. However, the string zero modes do not automaticall survive…
A brief discussion is presented assessing the achievements and challenges of string phenomenology: the subfield dedicated to study the potential for string theory to make contact with particle physics and cosmology. Building from the well…
We derive constraints facing models of axion inflation based on decay constant alignment from a string-theoretic and quantum gravitational perspective. In particular, we investigate the prospects for alignment and `anti-alignment' of $C_4$…
We discuss exclusive decays of large spin mesons into mesons in models of large N_c quenched QCD at strong coupling using string theory. The rate of the processes are calculated by studying the splitting of a macroscopic string on the…