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Primordial black holes and stochastic inflation beyond slow roll. Part I. Noise matrix elements (2023)
Journal Article
Mishra, S. S., Copeland, E. J., & Green, A. M. (2023). Primordial black holes and stochastic inflation beyond slow roll. Part I. Noise matrix elements. Journal of Cosmology and Astroparticle Physics, 2023(September 2023), Article 005. https://doi.org/10.1088/1475-7516/2023/09/005

Primordial Black Holes (PBHs) may form in the early Universe, from the grav-itational collapse of large density perturbations, generated by large quantum fluctuations during inflation. Since PBHs form from rare over-densities, their abundance is sens... Read More about Primordial black holes and stochastic inflation beyond slow roll. Part I. Noise matrix elements.

CMB constraints on monodromy inflation at strong coupling (2022)
Journal Article
Copeland, E. J., Cunillera, F., Moss, A., & Padilla, A. (2022). CMB constraints on monodromy inflation at strong coupling. Journal of Cosmology and Astroparticle Physics, 2022(09), Article 080. https://doi.org/10.1088/1475-7516/2022/09/080

We carry out a thorough numerical examination of field theory monodromy inflation at strong coupling. We perform an MCMC analysis using a Gaussian likelihood, fitting multiparameter models using CMB constraints on the spectral index and the tensor to... Read More about CMB constraints on monodromy inflation at strong coupling.

Generalised scalar-tensor theories and self-tuning (2022)
Journal Article
Copeland, E. J., Ghataore, S., Niedermann, F., & Padilla, A. (2022). Generalised scalar-tensor theories and self-tuning. Journal of Cosmology and Astroparticle Physics, 2022(3), Article 004. https://doi.org/10.1088/1475-7516/2022/03/004

We explore a family of generalised scalar-tensor theories that exhibit self-tuning to low scale anti de Sitter vacua, even in the presence of a large cosmological constant. We are able to examine the linearised fluctuations about these vacua and comp... Read More about Generalised scalar-tensor theories and self-tuning.

Fifth forces and broken scale symmetries in the Jordan frame (2022)
Journal Article
Copeland, E. J., Millington, P., & Sevillano Muñoz, S. (2022). Fifth forces and broken scale symmetries in the Jordan frame. Journal of Cosmology and Astroparticle Physics, 2022(02), Article 016. https://doi.org/10.1088/1475-7516/2022/02/016

We study the origin of fifth forces in scalar-tensor theories of gravity in the so-called Jordan frame, where the modifications to the gravitational sector are manifest. We focus on theories of Brans-Dicke type in which an additional scalar field is... Read More about Fifth forces and broken scale symmetries in the Jordan frame.

Dark energy loopholes some time after GW170817 (2020)
Journal Article
Bordin, L., Copeland, E. J., & Padilla, A. (2020). Dark energy loopholes some time after GW170817. Journal of Cosmology and Astroparticle Physics, 2020(11), Article 063. https://doi.org/10.1088/1475-7516/2020/11/063

We revisit the constraints on scalar tensor theories of modified gravity following the purge of GW170817. We pay particular attention to dynamical loopholes where the anomalous speed of propagation of the gravitational wave can vanish on-shell, when... Read More about Dark energy loopholes some time after GW170817.

Constraints on primordial gravitational waves from the cosmic microwave background (2020)
Journal Article
Clarke, T. J., Copeland, E. J., & Moss, A. (2020). Constraints on primordial gravitational waves from the cosmic microwave background. Journal of Cosmology and Astroparticle Physics, 2020(10), Article 002. https://doi.org/10.1088/1475-7516/2020/10/002

Searches for primordial gravitational waves have resulted in constraints in a large frequency range from a variety of sources. The standard Cosmic Microwave Background (CMB) technique is to parameterise the tensor power spectrum in terms of the tenso... Read More about Constraints on primordial gravitational waves from the cosmic microwave background.

Classical decay rates of oscillons (2020)
Journal Article
Zhang, H.-Y., Amin, M. A., Copeland, E. J., Saffin, P. M., & Lozanov, K. D. (2020). Classical decay rates of oscillons. Journal of Cosmology and Astroparticle Physics, 2020(07), 055-055. https://doi.org/10.1088/1475-7516/2020/07/055

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) exceptiona... Read More about Classical decay rates of oscillons.

Shift-symmetric orbital inflation: Single field or multifield? (2020)
Journal Article
Achúcarro, A., Copeland, E. J., Iarygina, O., Palma, G. A., Wang, D.-G., & Welling, Y. (2020). Shift-symmetric orbital inflation: Single field or multifield?. Physical Review D, 102(2), Article 021302(R). https://doi.org/10.1103/physrevd.102.021302

We present a new class of two-field inflationary attractor models, known as shift-symmetric orbital inflation, whose behavior is strongly multifield but whose predictions are remarkably close to those of single-field inflation. In these models, the f... Read More about Shift-symmetric orbital inflation: Single field or multifield?.

Constraints on the cosmic string loop collapse fraction from primordial black holes (2020)
Journal Article
James-Turner, C., Weil, D. P. B., Green, A. M., & Copeland, E. J. (2020). Constraints on the cosmic string loop collapse fraction from primordial black holes. Physical Review D, 101(12), Article 123526. https://doi.org/10.1103/physrevd.101.123526

A small fraction, f , of cosmic string loops can collapse to form Primordial Black Holes (PBHs). Constraints on the abundance of PBHs can therefore be used to constrain f. We update these calculations, taking into account the PBH extended mass functi... Read More about Constraints on the cosmic string loop collapse fraction from primordial black holes.