Primordial non-Gaussianity from two curvaton decays

We study a model where two scalar fields, that are subdominant during inflation, decay into radiation some time after inflation has ended but before primordial nucleosynthesis. Perturbations of these two curvaton fields can be responsible for the primordial curvature perturbation. We write down the full non-linear equations that relate the primordial perturbation to the curvaton perturbations on large scales, calculate the power spectrum of the primordial perturbation, and finally go to second order to find the non-linearity parameter, fNL. We find large positive values of fNL if the energy densities of the curvatons are sub-dominant when they decay, as in the single curvaton case. But we also find a large fNL even if the curvatons dominate the total energy density in the case when the inhomogeneous radiation produced by the first curvaton decay is diluted by the decay of a second nearly homogeneous curvaton. The minimum value min(fNL)=-5/4 which we find is the same as in the single-curvaton case.Comment: 20 pages, 5 figure

Modulated curvaton decay

We study primordial density perturbations generated by the late decay of a curvaton field whose decay rate may be modulated by the local value of another isocurvature field, analogous to models of modulated reheating at the end of inflation. We calculate the primordial density perturbation and its local-type non-Gaussianity using the sudden-decay approximation for the curvaton field, recovering standard curvaton and modulated reheating results as limiting cases. We verify the Suyama-Yamaguchi inequality between bispectrum and trispectrum parameters for the primordial density field generated by multiple field fluctuations, and find conditions for the bound to be saturated.Comment: 16 pages, 8 figure

Hepatitis C elimination among people living with HIV

Background: Hepatitis C virus (HCV) is a major cause of liver-related morbidity and mortality among people living with HIV globally. Aims: The broad aim of this research was to evaluate progress towards HCV elimination among people living with HIV in Australia. Specific aims included evaluating incidence and factors associated with HCV reinfection and patterns of drug use and sexual risk behaviours after treatment and characterizing the HCV cascade of care and factors associated with engagement in HCV care among people living with HIV in Australia. Methods: In Chapter Two, the risk of HCV reinfection following successful therapy among people living with HIV was evaluated in a global systematic review and meta-analysis, with factors associated with reinfection assessed using meta-regression. In Chapter Three, patterns of drug use and sexual risk behaviours and HCV reinfection incidence were assessed before and after direct-acting antiviral (DAA) scale-up in Australia among people with HIV/HCV coinfection enrolled in CEASE. In Chapter Four, the HCV cascade of care, including HCV testing and treatment, among people living with HIV was characterized in the pre (2010–2015) and post (2016–2018) DAA era in a population-based linkage study including all people living with HIV in New South Wales, Australia with an HCV notification. Factors associated with HCV testing and DAA treatment were assessed using logistic regression. Key Findings: Globally, HCV reinfection incidence following treatment among people living with HIV was similar following interferon-based and DAA therapy, with the highest risk among men who have sex with men and those with recent HCV infection. Following unrestricted DAA access and broad treatment uptake among people living with xviii HIV in Australia, HCV reinfection incidence was low despite stable pattens of risk behaviours before and after DAA treatment. The HCV care cascade among people living with HIV demonstrated high HCV RNA testing coverage (91%) and treatment uptake following DAA availability (7% pre DAA, 73% post DAA). Younger age, female gender, and rural region of residence were negatively associated with testing; no factors were associated with DAA treatment. Conclusion: To maintain progress towards HCV elimination, ongoing HCV screening and treatment of (re)infection among people living with HIV will be required. Enabling access to and ensuring broad coverage of HCV testing, treatment and prevention will be essential

Gravitational waves from an early matter era

We investigate the generation of gravitational waves due to the gravitational instability of primordial density perturbations in an early matter-dominated era which could be detectable by experiments such as LIGO and LISA. We use relativistic perturbation theory to give analytic estimates of the tensor perturbations generated at second order by linear density perturbations. We find that large enhancement factors with respect to the naive second-order estimate are possible due to the growth of density perturbations on sub-Hubble scales. However very large enhancement factors coincide with a breakdown of linear theory for density perturbations on small scales. To produce a primordial gravitational wave background that would be detectable with LIGO or LISA from density perturbations in the linear regime requires primordial comoving curvature perturbations on small scales of order 0.02 for Advanced LIGO or 0.005 for LISA, otherwise numerical calculations of the non-linear evolution on sub-Hubble scales are required.Comment: 23 pages, 2 figure