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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.

Understanding the suppression of structure formation from dark matter-dark energy momentum coupling (2020)
Journal Article
Chamings, F. N., Avgoustidis, A., Copeland, E. J., Green, A. M., & Pourtsidou, A. (2020). Understanding the suppression of structure formation from dark matter-dark energy momentum coupling. Physical Review D, 101(4), https://doi.org/10.1103/physrevd.101.043531

Models in which scalar field dark energy interacts with dark matter via a pure momentum coupling have previously been found to potentially ease the structure formation tension between early-and late-universe observations. In this article we explore t... Read More about Understanding the suppression of structure formation from dark matter-dark energy momentum coupling.

Inflation in loop quantum cosmology (2019)
Journal Article
Bhardwaj, A., Copeland, E. J., & Louko, J. (2019). Inflation in loop quantum cosmology. Physical Review D, 99(6), Article 063520. https://doi.org/10.1103/physrevd.99.063520

We develop a consistent analytic approach to determine the conditions under which slow-roll inflation can arise when the inflaton is the same scalar field that is responsible for the bounce in loop quantum cosmology (LQC). We find that the requiremen... Read More about Inflation in loop quantum cosmology.

Symmetron scalar fields: modified gravity, dark matter, or both? (2019)
Journal Article
Burrage, C., Copeland, E. J., Käding, C., & Millington, P. (2019). Symmetron scalar fields: modified gravity, dark matter, or both?. Physical Review D, 99(4), Article 043539. https://doi.org/10.1103/physrevd.99.043539

Scalar fields coupled to gravity through the Ricci scalar have been considered both as dark matter candidates and as a possible modified gravity explanation for galactic dynamics. It has recently been demonstrated that the dynamics of baryonic matter... Read More about Symmetron scalar fields: modified gravity, dark matter, or both?.

Dark Energy after GW170817 Revisited (2019)
Journal Article
Copeland, E. J., Kopp, M., Padilla, A., Saffin, P. M., & Skordis, C. (2019). Dark Energy after GW170817 Revisited. Physical Review Letters, 122(6), Article 061301. https://doi.org/10.1103/physrevlett.122.061301

We revisit the status of scalar-tensor theories with applications to dark energy in the aftermath of the gravitational wave signal GW170817 and its optical counterpart GRB170817A. At the level of the cosmological background, we identify a class of th... Read More about Dark Energy after GW170817 Revisited.

Fifth forces, Higgs portals and broken scale invariance (2018)
Journal Article
Burrage, C., Copeland, E. J., Millington, P., & Spannowsky, M. (2018). Fifth forces, Higgs portals and broken scale invariance. Journal of Cosmology and Astroparticle Physics, 2018(11), 1-31. https://doi.org/10.1088/1475-7516/2018/11/036

© 2018 IOP Publishing Ltd and Sissa Medialab. We study the relationship between the strength of fifth forces and the origin of scale breaking in the Standard Model (SM) of particle physics. We start with a light scalar field that is conformally coupl... Read More about Fifth forces, Higgs portals and broken scale invariance.

Dynamical systems applied to cosmology: dark energy and modified gravity (2018)
Journal Article
Bahamonde, S., Böhmer, C. G., Carloni, S., Copeland, E. J., Fang, W., & Tamanini, N. (2018). Dynamical systems applied to cosmology: dark energy and modified gravity. Physics Reports, 775-777, 1-122. https://doi.org/10.1016/j.physrep.2018.09.001

The Nobel Prize winning confirmation in 1998 of the accelerated expansion of our Universe put into sharp focus the need of a consistent theoretical model to explain the origin of this acceleration. As a result over the past two decades there has been... Read More about Dynamical systems applied to cosmology: dark energy and modified gravity.

Gravitational waves from asymmetric oscillon dynamics? (2018)
Journal Article
Amin, M. A., Braden, J., Copeland, E. J., Giblin, J. T., Solorio, C., Weiner, Z. J., & Zhou, S.-Y. (2018). Gravitational waves from asymmetric oscillon dynamics?. Physical Review D, 98(2), 1-6. https://doi.org/10.1103/physrevd.98.024040

It has been recently suggested that oscillons produced in the early universe from certain asymmetric potentials continue to emit gravitational waves for a number of e-folds of expansion after their formation, leading to potentially detectable gravita... Read More about Gravitational waves from asymmetric oscillon dynamics?.

The shape dependence of chameleon screening (2018)
Journal Article
Burrage, C., Copeland, E. J., Moss, A., & Stevenson, J. A. (2018). The shape dependence of chameleon screening. Journal of Cosmology and Astroparticle Physics, 2018(1), https://doi.org/10.1088/1475-7516/2018/01/056

Chameleon scalar fields can screen their associated fifth forces from detection by changing their mass with the local density. These models are an archetypal example of a screening mechanism, and have become an important target for both cosmological... Read More about The shape dependence of chameleon screening.

Radiative screening of fifth forces (2016)
Journal Article
Burrage, C., Copeland, E. J., & Millington, P. (2016). Radiative screening of fifth forces. Physical Review Letters, 117(21), Article 211102. https://doi.org/10.1103/PhysRevLett.117.211102

© 2016 American Physical Society. We describe a symmetron model in which the screening of fifth forces arises at the one-loop level through the Coleman-Weinberg mechanism of spontaneous symmetry breaking. We show that such a theory can avoid current... Read More about Radiative screening of fifth forces.

A proposed experimental search for chameleons using asymmetric parallel plates (2016)
Journal Article
Burrage, C., Copeland, E. J., & Stevenson, J. A. (2016). A proposed experimental search for chameleons using asymmetric parallel plates. Journal of Cosmology and Astroparticle Physics, 2016(8), https://doi.org/10.1088/1475-7516/2016/08/070

Light scalar fields coupled to matter are a common consequence of theories of dark energy and attempts to solve the cosmological constant problem. The chameleon screening mechanism is commonly invoked in order to suppress the fifth forces mediated by... Read More about A proposed experimental search for chameleons using asymmetric parallel plates.

CMB constraints on cosmic strings and superstrings (2016)
Journal Article
Charnock, T., Avgoustidis, A., Copeland, E. J., & Moss, A. (2016). CMB constraints on cosmic strings and superstrings. Physical Review D - Particles, Fields, Gravitation and Cosmology, 93(12), Article 123503. https://doi.org/10.1103/PhysRevD.93.123503

We present the first complete MCMC analysis of cosmological models with evolving cosmic (super)string networks, using the Unconnected Segment Model in the unequal-time correlator formalism. For ordinary cosmic string networks, we derive joint constra... Read More about CMB constraints on cosmic strings and superstrings.

Using atom interferometry to detect dark energy (2015)
Journal Article
Burrage, C., & Copeland, E. J. (in press). Using atom interferometry to detect dark energy. Contemporary Physics, 57(2), https://doi.org/10.1080/00107514.2015.1060058

We review the tantalising prospect that the first evidence for the dark energy driving the observed acceleration of the Universe on giga-parsec scales may be found through metre scale laboratory based atom interferometry experiments. To do that, we f... Read More about Using atom interferometry to detect dark energy.

Asymptotically safe Starobinsky inflation (2015)
Journal Article
Copeland, E. J., Rahmede, C., & Saltas, I. D. (2015). Asymptotically safe Starobinsky inflation. Physical Review D, 91(10), https://doi.org/10.1103/PhysRevD.91.103530

We revisit Starobinsky inflation in a quantum gravitational context, by means of the exact renormalization group (RG). We calculate the nonperturbative beta functions for Newton’s “constant” G and the dimensionless R^2 coupling, and show that there e... Read More about Asymptotically safe Starobinsky inflation.

Ellipticity weakens chameleon screening (2015)
Journal Article
Burrage, C., Copeland, E. J., & Stevenson, J. (2015). Ellipticity weakens chameleon screening. Physical Review D, D91(6), Article 065030. https://doi.org/10.1103/PhysRevD.91.065030

The chameleon mechanism enables a long-range fifth force to be screened in dense environments when nontrivial self-interactions of the field cause its mass to increase with the local density. To date, chameleon fifth forces have mainly been studied f... Read More about Ellipticity weakens chameleon screening.

Probing dark energy with atom interferometry (2015)
Journal Article
Burrage, C., Copeland, E. J., & Hinds, E. A. (2015). Probing dark energy with atom interferometry. Journal of Cosmology and Astroparticle Physics, 2015(3), Article 042. https://doi.org/10.1088/1475-7516/2015/03/042

© 2015 IOP Publishing Ltd and Sissa Medialab srl. Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here... Read More about Probing dark energy with atom interferometry.

Charge-swapping q balls (2014)
Journal Article
Copeland, E. J., Saffin, P. M., & Zhou, S. Y. (2014). Charge-swapping q balls. Physical Review Letters, 113(23), https://doi.org/10.1103/PhysRevLett.113.231603

© 2014 American Physical Society. Q balls are nontopological solitonic solutions to a wide class of field theories that possess global symmetries. Here we show that in these same theories there also exists a tower of novel composite Q-ball solutions... Read More about Charge-swapping q balls.

The cosmology of the Fab-Four (2012)
Journal Article
Copeland, E. J., Padilla, A., & Saffin, P. M. (2012). The cosmology of the Fab-Four. Journal of Cosmology and Astroparticle Physics, 2012(12), Article 026. https://doi.org/10.1088/1475-7516/2012/12/026

We have recently proposed a novel self tuning mechanism to alleviate the famous cosmological constant problem, based on the general scalar tensor theory proposed by Horndeski. The self-tuning model ends up consisting of four geometric terms in the ac... Read More about The cosmology of the Fab-Four.

Self-tuning and the derivation of a class of scalar-tensor theories (2012)
Journal Article
Charmousis, C., Copeland, E. J., Padilla, A., & Saffin, P. M. (2012). Self-tuning and the derivation of a class of scalar-tensor theories. Physical Review D, 85(10), Article 104040. https://doi.org/10.1103/PhysRevD.85.104040

We have recently proposed a special class of scalar tensor theories known as the Fab Four. These arose from attempts to analyse the cosmological constant problem within the context of Horndeski's most general scalar tensor theory. The Fab Four togeth... Read More about Self-tuning and the derivation of a class of scalar-tensor theories.

General second-order scalar-tensor theory and self-tuning (2012)
Journal Article
Charmousis, C., Copeland, E. J., Saffin, P. M., & Padilla, A. (2012). General second-order scalar-tensor theory and self-tuning. Physical Review Letters, 108(5), Article 051101. https://doi.org/10.1103/PhysRevLett.108.051101

Starting from the most general scalar-tensor theory with second order field equations in four dimensions, we establish the unique action that will allow for the existence of a consistent self-tuning mechanism on FLRW backgrounds, and show how it can... Read More about General second-order scalar-tensor theory and self-tuning.

Evolution and stability of cosmic string loops with Y-junctions (2009)
Journal Article
Bevis, N., Copeland, E. J., Martin, P.-Y., Niz, G., Pourtsidou, A., Saffin, P. M., & Steer, D. (2009). Evolution and stability of cosmic string loops with Y-junctions. Physical Review D, 80(12), https://doi.org/10.1103/PhysRevD.80.125030

We study the evolution of non-periodic cosmic string loops containing Y-junctions, such as may form during the evolution of a network of (p,q) cosmic superstrings. We set up and solve the Nambu-Goto equations of motion for a loop with junctions, focu... Read More about Evolution and stability of cosmic string loops with Y-junctions.

Cosmological constraints on f(G) dark energy models (2009)
Journal Article
Zhou, S.-Y., Copeland, E. J., & Saffin, P. M. (2009). Cosmological constraints on f(G) dark energy models. Journal of Cosmology and Astroparticle Physics, 2009(7), https://doi.org/10.1088/1475-7516/2009/07/009

Modified gravity theories with the Gauss-Bonnet term G=R2−4RμνRμν+RμνρσRμνρσ have recently gained a lot of attention as a possible explanation of dark energy. We perform a thorough phase space analysis on the so-called f(G) models, where f(G) is some... Read More about Cosmological constraints on f(G) dark energy models.

No resonant tunneling in standard scalar quantum field theory (2008)
Journal Article
Copeland, E. J., Padilla, A., & Saffin, P. M. (2008). No resonant tunneling in standard scalar quantum field theory. Journal of High Energy Physics, 2008(1), https://doi.org/10.1088/1126-6708/2008/01/066

We investigate the nature of resonant tunneling in Quantum Field Theory. Following the pioneering work of Banks, Bender and Wu, we describe quantum field theory in terms of infinite dimensional quantum mechanics and utilize the ``Most probable escape... Read More about No resonant tunneling in standard scalar quantum field theory.