Research Repository

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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. doi:10.1088/1475-7516/2018/11/036

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 coupled to a toy SM matter sector through a Weyl re... Read More

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. doi: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

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. (2018). Gravitational waves from asymmetric oscillon dynamics?. Physical Review D, 98(2), 1-6. doi: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

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), doi:10.1088/1475-7516/2018/01/056. ISSN 1475-7516

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

Radial acceleration relation from symmetron fifth forces (2017)
Journal Article
Burrage, C., Copeland, E. J., & Millington, P. (2017). Radial acceleration relation from symmetron fifth forces. Physical Review D, D95(6), doi:10.1103/PhysRevD.95.064050. ISSN 2470-0010

We show that the radial acceleration relation for rotationally supported galaxies may be explained, in the absence of cold dark matter, by a nonminimally coupled scalar field, whose fifth forces are partially screened on galactic scales by the symmet... Read More

Highly excited strings I: Generating function (2017)
Journal Article
Skliros, D. P., Copeland, E. J., & Saffin, P. M. (in press). Highly excited strings I: Generating function. Nuclear Physics B, doi:10.1016/j.nuclphysb.2016.12.022. ISSN 0550-3213

This is the first of a series of detailed papers on string amplitudes with highly excited strings (HES). In the present paper we construct a generating function for string amplitudes with generic HES vertex operators using a fixed-loop momentum forma... Read More

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), doi:10.1103/PhysRevLett.117.211102. ISSN 0031-9007

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 constraints on the existence of fi... Read More

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), doi:10.1088/1475-7516/2016/08/070. ISSN 1475-7516

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

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), doi:10.1103/PhysRevD.93.123503. ISSN 1550-7998

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

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), doi:10.1080/00107514.2015.1060058. ISSN 0010-7514

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

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), doi:10.1103/PhysRevD.91.103530. ISSN 2470-0010

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

Parametrized post-Friedmannian framework for interacting dark energy theories (2015)
Journal Article
Skordis, C., Pourtsidou, A., & Copeland, E. J. (2015). Parametrized post-Friedmannian framework for interacting dark energy theories. Physical Review D, 91(8), doi:10.1103/PhysRevD.91.083537. ISSN 2470-0010

We present the most general parametrization of models of dark energy in the form of a scalar field which is explicitly coupled to dark matter. We follow and extend the parametrized post-Friedmannian approach, previously applied to modified gravity th... Read More

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, 1503(3), doi:10.1088/1475-7516/2015/03/042. ISSN 1475-7516

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 we show that individual atoms are too small to scr... Read More

Gravitational waves from oscillon preheating (2013)
Journal Article
Zhou, S., Copeland, E. J., Easther, R., Finkel, H., Mou, Z., & Saffin, P. M. (2013). Gravitational waves from oscillon preheating. Journal of High Energy Physics, 2013, doi:10.1007/JHEP10(2013)026. ISSN 1029-8479

Oscillons are long-lived, localized excitations of nonlinear scalar fields which may be copiously produced during preheating after inflation, leading to a possible oscillon-dominated phase in the early Universe. For example, this can happen after axi... Read More

Duality and decay of macroscopic F-strings (2013)
Journal Article
Skliros, D. P., Copeland, E. J., & Saffin, P. M. (2013). Duality and decay of macroscopic F-strings. Physical Review Letters, 111(4), doi:10.1103/PhysRevLett.111.041601. ISSN 0031-9007

We study the decay of fundamental string loops of arbitrary size L/min(n,m)≫√α′, labeled by (n, m; λn, ¯λm), where n, m correspond to left- and right-mover harmonics and λn, ¯λm to polarization tensors, and find that a description in terms of the rec... Read More

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), doi:10.1088/1475-7516/2012/12/026. ISSN 1475-7516

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

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), doi:10.1103/PhysRevD.85.104040. ISSN 2470-0010

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