95 citations · 405 across the 26 of their papers we have counts for
23 papers · 1 filter
New astrophysical bounds on ultralight axionlike particles
Nilanjan Banik, Adam J. Christopherson, Pierre Sikivie +1
Motivated by tension between the predictions of ordinary cold dark matter (CDM) and observations at galactic scales, ultralight axionlike particles (ULALPs) with mass of the order…
The Rethermalizing Bose-Einstein Condensate of Dark Matter Axions
Nilanjan Banik, Adam Christopherson, Pierre Sikivie +1
The axions produced during the QCD phase transition by vacuum realignment, string decay and domain wall decay thermalize as a result of their gravitational self-interactions when t…
Recombination era magnetic fields from axion dark matter
Nilanjan Banik, Adam J. Christopherson
We introduce a new mechanism for generating magnetic fields in the recombination era. This Harrison-like mechanism utilizes vorticity in baryons that is sourced through the Bose-Ei…
Linear Newtonian perturbation theory from the Schrödinger-Poisson equations
Nilanjan Banik, Adam J. Christopherson, Pierre Sikivie +1
We obtain solutions to the coupled Schrödinger-Poisson equations. The solutions describe the evolution of cold dark matter density perturbations in an otherwise homogeneous expandi…
Stabilising the Planck mass shortly after inflation
Carsten van de Bruck, Adam J. Christopherson, Mathew Robinson
We consider a model of the early universe which consists of two scalar fields: the inflaton, and a second field which drives the stabilisation of the Planck mass (or gravitational…
Cosmological Perturbations: Vorticity, Isocurvature and Magnetic Fields
Adam J. Christopherson
In this paper I review some recent, interlinked, work undertaken using cosmological perturbation theory -- a powerful technique for modelling inhomogeneities in the Universe. The c…
A short note on the curvature perturbation at second order
Adam J. Christopherson, Ellie Nalson, Karim A. Malik
Working with perturbations about an FLRW spacetime, we compute the gauge-invariant curvature perturbation to second order solely in terms of scalar field fluctuations. Using the cu…
Effects of non-linearities on magnetic field generation
Ellie Nalson, Adam J. Christopherson, Karim A. Malik
Magnetic fields are present on all scales in the Universe. While we understand the processes which amplify the fields fairly well, we do not have a "natural" mechanism to generate…
The Poisson equation at second order in relativistic cosmology
Juan Carlos Hidalgo, Adam J. Christopherson, Karim A. Malik
We calculate the relativistic constraint equation which relates the curvature perturbation to the matter density contrast at second order in cosmological perturbation theory. This…
Isocurvature Perturbations and Reheating in Multi-Field Inflation
Ian Huston, Adam J. Christopherson
Inflationary models involving more than one scalar field naturally produce isocurvature perturbations. However, while these are fairly well studied, less is known about their evolu…
Quantifying the behaviour of curvature perturbations near Horizon Crossing
Ellie Nalson, Adam J. Christopherson, Ian Huston +1
How much does the curvature perturbation change after it leaves the horizon, and when should one evaluate the power spectrum? To answer these questions we study single field inflat…
The Evolution of Non-adiabatic Pressure Perturbations during Multi-field Inflation
Ian Huston, Adam J. Christopherson
Non-adiabatic pressure perturbations naturally occur in models of inflation consisting of more than one scalar field. The amount of non-adiabatic pressure present at the end of inf…
Vorticity from isocurvature in the early universe
Adam J. Christopherson, Karim A. Malik
Vorticity is ubiquitous in nature however, to date, studies of vorticity in cosmology and the early universe have been quite rare. In this paper, based on a talk in session CM1 of…
Modelling non-dust fluids in cosmology
Adam J. Christopherson, J. C. Hidalgo, Karim A. Malik
Currently, most of the numerical simulations of structure formation use Newtonian gravity. When modelling pressureless dark matter, or `dust', this approach gives the correct resul…
Quantifying the behaviour of curvature perturbations during inflation
Ellie Nalson, Adam J. Christopherson, Ian Huston +1
How much does the curvature perturbation change after it leaves the horizon, and when should one evaluate the power spectrum? To answer these questions we study single field inflat…
Calculating Non-adiabatic Pressure Perturbations during Multi-field Inflation
Ian Huston, Adam J. Christopherson
Isocurvature perturbations naturally occur in models of inflation consisting of more than one scalar field. In this paper we calculate the spectrum of isocurvature perturbations ge…
The future of cosmology and the role of non-linear perturbations
Adam J. Christopherson
Cosmological perturbation theory is a key tool to study the universe. The linear or first order theory is well understood, however, developing and applying the theory beyond linear…
The magnitude of the non-adiabatic pressure in the cosmic fluid
Iain A. Brown, Adam J. Christopherson, Karim A. Malik
Understanding the non-adiabatic pressure, or relative entropy, perturbation is crucial for studies of early-universe vorticity and Cosmic Microwave Background observations. We calc…
Applications of Cosmological Perturbation Theory
Adam J. Christopherson
Cosmological perturbation theory is crucial for our understanding of the universe. The linear theory has been well understood for some time, however developing and applying the the…
Comparing different formulations of non-linear cosmological perturbation theory
Adam J. Christopherson, Karim A. Malik, David R. Matravers +1
We compare and contrast two different metric based formulations of non- linear cosmological perturbation theory: the MW2009 approach in [K. A. Malik and D. Wands, Phys. Rept. 475 (…
Estimating the amount of vorticity generated by cosmological perturbations in the early universe
Adam J. Christopherson, Karim A. Malik, David R. Matravers
We estimate the amount of vorticity generated at second order in cosmological perturbation theory from the coupling between first order energy density and non-adiabatic pressure, o…
Gauge conditions in combined dark energy and dark matter systems
Adam J. Christopherson
When analysing a system consisting of both dark matter and dark energy, an often used practice in the literature is to neglect the perturbations in the dark energy component. Howev…
Vorticity generation at second order in cosmological perturbation theory
Adam J. Christopherson, Karim A. Malik, David R. Matravers
We show that at second order in cosmological perturbation theory vorticity generation is sourced by entropy gradients. This is an extension of Crocco's theorem to a cosmological se…