The standard DFSZ axion model features stable domain walls, so requires a pre-inflationary axion. This means the density of axion dark matter depends on an unknowable initial misalignment angle and thus predictivity is compromised compared to the post-inflationary axion case. I present a systematic classification of flavour-dependent DFSZ Peccei-Quinn symmetry variants that have no domain wall...
Spectator fields which provide additional tensor degrees of freedom, on top of the standard metric tensor perturbations, can produce significant amounts of gravitational waves (GWs). Employing the effective field theory approach for spin-2 fields, we find a universal prediction that linear mixing between the metric and extra tensor modes inevitably induces oscillatory features in the GW...
I discuss the PQ quality and scale hierarchy of extra dimensional axions in the context of 5-dimensional orbifold field theory on S^1/Z_2.
We propose a scenario for the cogenesis of baryon asymmetry and dark matter, realizing spontaneous leptogenesisby by Majoron in Type I seesaw model.
This mechanism requires significant kinetic motion, which we demonstrate can naturally arise from conventional misalignment under conditions of symmetry non-restoration
The recent determination of the primordial abundance of He4 suggests that our universe has a large lepton asymmetry. We consider the Q-ball scenario that produces the large lepton asymmetry without generating a large baryon asymmetry. We also discuss the enhancement of gravitational waves and resonant production of sterile neutrinos in the scenario.
Using the tanh potential as an example, we present a new class of real time instantons corresponding to general equivalence classes. The Euler-Lagrange equation solutions to saddle points are not unique for complex saddles: any contour in the equivalence classes maps to the same action due to Cauchy’s theorem. This new tool resolves a number of existing puzzles, including curved space particle...
Stochastic gravitational wave backgrounds have become a hot topic in cosmology. However, very few studies have been done on gravitational waves on intergalactic scales. I discuss possible sources on these scales which could even be parity violating, and present a method to probe such gravitational waves.
The grand unified theory (GUT) provides a rationale for the arbitrariness of the Standard Model (SM) and explains many enigmas of nature at the outset of a single gauge group. The GUTs predict the proton decay, and the spontaneous symmetry breaking (SSB) of the higher symmetry group may lead to the formation of topological defects, which are indispensable in the context of cosmological...
SABRE is an international collaboration that will operate similar particle detectors in the Northern (SABRE North) and Southern Hemispheres (SABRE South). This innovative approach aims to distinguish potential dark matter signals from seasonal backgrounds: a pioneering strategy only feasible with a Southern Hemisphere experiment. SABRE South is located at the Stawell Underground Physics...
General Relativity is based on Riemannian geometry, where gravity is solely represented by the metric degrees of freedom. This framework can be generalized by introducing torsion and nonmetricity into the underlying geometry. In this talk, I will describe how to construct such theories and how these geometrical quantities might lead to new effects on astrophysical and cosmological scales. I...
Scalar field theory on de Sitter space suffers from infrared (IR) divergences, highlighting the necessity of nonperturbative methods for IR resummation.
A well-known triad of statements encapsulates the IR issue:
(1) the massless Bunch–Davies vacuum breaks de Sitter invariance;
(2) the coincident limit of the two-point correlator exhibits secular growth; and
(3) stochastic inflation...
