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Christophe Ringeval
External collaborator. Funding: UCL.
Member since September 2006
My personal homepage
UCL member card
People responsibilities
André Füzfa (FUNDP), member since October 2006
Professor at FUNDP, working in theoretical cosmology: interpretations of dark energy, observational constraints from structure formation, Hubble diagram, CMB, ... and on complex systems in general relativity: dynamical systems, multi-physics N-body simulations, numerical relativity.

Former members
Jose Beltran Jimenez (ARC), Postdoc in CP3 from October 2012 to January 2015
Current position: Post-doctoral position at CPT, Marseille University.

Antonio De Felice (PAI), Postdoc in CP3 from October 2007 to October 2009
Current position: Associate Professor at Yukawa Institute for Theoretical Physics, Kyoto.

Vittoria Demozzi (ESA-Prodex), Postdoc in CP3 from October 2011 to September 2012
Current position: Department of Electrical Engineering and IT, Patent Attorneys' office Hoffmann-EitlePatent, Munich.

Marie-Hélène Deproost (ARC), Visitor in CP3 from September 2013 to December 2013

Anne-Sylvie Deutsch, Master student in CP3 from October 2011 to September 2012
Current position: PhD student at Penn State University.

Martin Evrard, Master student in CP3

Geoffrey Feraut, Master student in CP3 from September 2013 to September 2014

Christian Fidler (PAI), Postdoc in CP3 from October 2014 to September 2017
Current position: Postdoc at RWTH, AAchen University, Germany.

David Frenay, Master student in CP3 from September 2010 to June 2011

Francois Kinard, Master student in CP3 from September 2012 to September 2013

Marc Lilley (FSR), Postdoc in CP3 from March 2010 to September 2010
Current position: Post-doctoral position at IAP, Paris.

Larissa Lorenz (PAI), Postdoc in CP3 from September 2009 to July 2011
Current position: Researcher in Future Technologies and Innovation (Bauhaus Luftfahrt e.V., Munich).

Marcello Musso (ESA-Prodex), Postdoc in CP3 from January 2012 to December 2014

Sandrine Schlögel (FRIA), PhD student in CP3 from January 2013 to October 2016

Vincent Spies, Master student in CP3 from February 2014 to August 2014

Teruaki Suyama (FSR), Postdoc in CP3 from October 2008 to March 2010
Current position: Professor at RESCUE, the University of Tokyo.

Hiroyuki Tashiro (PAI), Postdoc in CP3 from October 2009 to August 2011
Current position: Lecturer at the department of Physics and Astrophysics, Nagoya University.

Research statement
Within Cosmology, our research interests range from the understanding of the early universe, the place and time at which the candidate unified theories of Nature may have been at work, to data analysis and model testing with cosmological observables.

In this respect, we have been involved in the Planck data analysis of the Cosmic Microwave Background (CMB) while our current interests are in CMB polarization measurements, large scale structures (Euclid satellite), gravitational waves (eLISA satellites) and forecasts for future 21cm surveys.

My research directions are diversified and motivated by both theoretical results and observational discoveries.
Past projects
Hide past projects.

I am involved in the following research directions:

Averaging problem

Due to the non-commutation of spatial averaging and temporal evolution, inhomogeneities and anisotropies (cosmic structures) influence the evolution of the averaged Universe via the cosmological backreaction mechanism. We study the dynamics of backreaction effects and further introduce a relative entropy to characterize the structure formation in the perturbed Universe. We show this entropy increases during the cosmological evolution.

Backreaction in modified cosmologies and gravities

Our universe is homogeneous an isotropic on very large scales. However, when we go down to smaller scales inhomogeneities become more and more important. Given that Einstein equations are non-linear, it is clear than averaging and time-evolution are operations that do not commute. Thus, it is a crucial question to be addressed the importance of the non-commutativity of these two operations when we measure observables of the background cosmology. In General Relativity and a universe dominated by dust, there seems to be a general consensus that these corrections are small. However, when we consider modified cosmologies (either multifluid scenarios or alternative theories of gravity), the issue remains unclear. Moreover, this will need to be addressed to be able to use the next generation of high precision cosmological data to constrain such alternative scenarios.

External collaborators: Peter Dunsby (University of Cape Town), Alvaro de la Cruz Dombriz (Universidad Complutense de Madrid), Diego Saez (University of the Basque Country.

Cosmic inflation

The first measurements of acoustic peaks in the CMB anisotropies strongly suggest that the birth of cosmological fluctuations may have taken place during an early inflationary era of the universe.
In this domain, our activities deal with the construction of explicit models of inflation as well as the extraction of their observable consequences. Our fields of expertise comprise some actively debated subjects as the existence of features (e.g. trans-Planckian effects), inflation with non-minimally coupled scalar fields, DBI- and brane inflation as in the context of String Theory.
For all these theories, we are maintaining various numerical tools such as the ASPIC and FieldInf librairies allowing to compute reheating-consistent predictions for comparison with cosmological data.

External collaborators: Jérôme Martin (IAP, Paris, France), Vincent Vennin (Portsmouth, U.K.), Sébastien Clesse (RWTH, Aachen, Germany).

Cosmic strings

Based on our knowledge of particle physics at very high energy, cosmic strings are a natural consequence of the symmetry breaking mechanism and are expected to be formed during the cooling of the universe. However, they have not been observed yet and our research is concentrated into the various effects they may have in cosmology. The technical difficulties to deal with such systems are overcome using super-computer numerical simulations. We are focusing our present work to the effects induced in the CMB and in other astrophysical observables.

External collaborators: Jun'ichi Yokoyama (University of Tokyo, Japan), Daisuke Yamauchi (RESCUE, Tokyo, Japan), Mairi Sakellariadou (King's College London, U.K.), Patrick Peter, François Bouchet (Institut d'Astrophysique de Paris, France).

Cosmological data

Our expertise on inflation and cosmic strings is involved in the CMB data analysis of the PLANCK satellite.
Our current efforts concern the study of future CMB polarization experiments, ground based, and in space, as the CORE satellite.
We are part of the EUCLID collaboration and interested in the impact of high precision measurements of the matter power spectra of the large scale structures for cosmic inflation.
We are also involved in the LISA project, the giant space interferometer dedicated to gravitational wave astronomy, which should open a new window on cosmic string physics and other early universe phenomena.
Another direction concerns the 21cm cosmological radiation. This radiation is emitted by neutral hydrogen atoms and should shed light into the so-called "dark ages": from the recombination to the reionisation of the universe by the first stars. This new observable is expected to be sensitive to the nature of dark matter as well as to some properties of the inflationary era.

External collaborators: Sébastien Clesse (RWTH, Aachen), V. Vennin (Portsmooth, U.K.), CORE Coll., Euclid Coll., eLISA Coll.

Dark energy

Although the undergoing cosmic acceleration may be explained by a non-vanishing cosmological constant in Einstein gravity, various dynamical effects could very well explain current observations, all dubbed as dark energy.

Quintessence, as a light scalar field minimally coupled to gravity, is a dark energy candidate to explain the recent acceleration of the Universe expansion. The Ratra-Peebles potential and its corrected form in supergravity are under study. Using a modified version of CAMB, including perturbations of the scalar field, we use the latest SNIa and CMB observations to select acceptable points in the parameter space. Starting with the associated matter power spectrum, in collaboration with the LUTh (Paris-Meudon Obs., France) we run N-body simulations of growth of large scale structures where the background evolution is modified by quintessence. We are involved in the Dark Energy Universe Simulation Series (DEUSS) collaboration.

Another dark energy candiate involves cosmic inflation, currently the best explanation of the origin of large scale structures and CMB anisotropies. Similarly, if dark energy is a light scalar field, the current acceleration can be the consequence of quantum fluctuations during cosmic inflation, provided this one occurs at TeV scale.

External collaborators: Jean-Michel Alimi, Yann Rasera, Pier Stefano Corasaniti (Observatoire de Paris-Meudon, France). Teruaki Suyama (The University of Tokyo, Japan), Tomo Takahashi (Saga University, Japan), Masahide Yamaguchi (Tokyo Institute of Technology, Japan), Shuichiro Yokoyama (Nagoya University, Japan).


It is possible to construct classical models of extra-dimensions based on Field Theory and General Relativity. The goal is to gain deeper understanding into these systems based on tractable and well known theories. In particular, the so-called Randall-Sundrum (RS) models in various dimensions can be modelised as hyper-dimensional topological defects. Our present studies concern the realisation of the Dvali-Gabadadze-Porrati mechanism inside hyper-dimensional monopoles, in which four-dimensional gravity can be obtained by trapping gravitons.

External collaborators: Antonio De Felice (The University of Tokyo, Japan).

Large Scale Structures

The statistical properties of large scale structures contain a large amount of information on cosmological observables. The abundance of halos of given mass is sensitive to various cosmological observables such as the equation of state of dark energy, to the amount of primordial non-Gaussianity as well as to the mass and cross section of the dark matter particles. Various of our activities and research are equally focused to the future EUCLID satellite mission.

External collaborators: M. Musso.

Modifications of gravity

The recent acceleration of the universe is explained in the standard model by the presence of a non-vanishing cosmological constant. However, one may also question the validity of General Relativity on length scales that have never been so accurately tested so far. However, it is not trivial to modify gravity and to build at the same time a model which can survive all the experimental tests. In collaboration with S. Capozziello, we looked for cosmological exact solutions for modifications of gravity in the form f(R) where f possesses a constant of motion during the evolution of the universe. In the future we plan to look for the subset of solutions which can describe experimental data from radiation domination up to today's accelerated expansion.

I have been working also in the so called f(G) gravity. This is a work made in collaboration with Shinji Tsujikawa, which aims to give some necessary conditions for a cosmologically viable f(G) gravity, where G is the Gauss-Bonnet scalar, that is a particular quadratic combination of the Riemann tensor. This scalar, G, has the property that, if not coupled, it can be written as a total derivative. Along with these conditions, we provide also some toy-models which fulfill them.

Modified gravity

Born-Infeld inspired theories. Although General Relativity has proven to be very successful in the scales where it has been tested, when going to high curvature regimes it is commons the appearance of singularities like the Big Bang and/or black holes singularities. This motivates the modification of gravity in such a regime to try to regularize those singularities. We study a natural extension of these models and study their predictions in cosmology and astrophysics

External collaborators: Jose Beltran Jimenez (CPT, Université de Marseille), Lavinia Heisenberg (University of Stockholm), Gonzalo Olmo (University of Valencia).


The forthcoming cosmological experiments should provide new insights on the amount of non-Gaussianity eventually present in the Cosmic Microwave Background fluctuations and large scale structures surveys. We study various early universe models that could potentially let some imprints in these observables and especially cosmic strings.

External collaborators: Teruaki Suyama (The University of Tokyo, Japan), Mark Hindmarsh (Sussex University, U.K.), Stéphane Colombi, François Bouchet (Institut d'Astrophysique de Paris, France).

Primordial magnetic fields

Observations show that magnetic fields are present everywhere in the universe. Planets, galaxies, clusters carry magnetic fields of varying strength and coherence size. There are evidences of their presence also in the intergalactic medium and this strongly suggests that their origin might be primordial. A promising candidate for the generation of primordial magnetic fields is inflation. Our work concerns the construction of efficient inflationary mechanisms which could produce the large-scale magnetic fields observed today and it deals in particular with the possible effects that such mechanisms have on the physics of the universe after inflation.

External collaborators: Chiara Caprini (CEA Saclay, France), Teruaki Suyama (The University of Tokyo, Japan).


When computing cosmological predictions it is often assumed that reionisation is homogenous and completely described by only one parameter, it's optical depth. However, reionisation is driven by the local collapse of matter and therefore highly inhomogeneous.
The above method is therefore only an approximation and large corrections can be expected for quantities which depend on the exact dynamics of reionisation.
We study more realistic models on reionisation and their impact on the cosmic microwave background, especially in polarization.

SONG -- Simulations of the early Universe

We work on the development and update of the numerical code SONG which solves the dynamics of the primordial Universe after Inflation. The computational methods used are comparable to the ones employed in the public codes CLASS and CAMB, but we solve the equations of motion beyond the linear order approximation, providing greater precision.
This is crucial for several dynamical effects which are absent in the leading order equations such as the generation of B-mode polarization and non-Gaussianity.

Furthermore, the code plays a central role in the recently developed Newtonian motion gauge framework. In this framework, a Newtonian N-body simulation can be promoted to a full relativistic simulation by interpreting it on the space-time of a specific Newtonian motion gauge. SONG can be used to compute the structure of these space-times up to second order in perturbation theory, thereby including for example the impact of relativity on the dark matter bispectrum.

External collaborators: Guido W. Pettinari, Thomas Tram, Cyril Pitrou (IAP, France).

Publications in CP3
All my publications on Inspire


Optical Follow-up of Planck Cluster Candidates with Small Instruments
Vincent Boucher, Simon de Visscher and Christophe Ringeval
[Abstract] [PDF] [Journal]
Refereed paper. 15th January.


Multi-Scale Pipeline for the Search of String-Induced CMB Anisotropies
A. Vafaei Sadr, S. Movahed, M. Farhang, C. Ringeval and F. R. Bouchet
[Abstract] [PDF] [Journal]
Refereed paper. 3rd October.
Stochastic gravitational waves from cosmic string loops in scaling
Christophe Ringeval and Teruaki Suyama
[Abstract] [PDF] [Journal] Published in JCAP 1712 (2017) 027
Refereed paper. 13th September.
CMB anisotropies from patchy reionisation and diffuse Sunyaev-Zel'dovich effects
Christian Fidler and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in JCAP 1710 (2017) 026
Refereed paper. 6th September.
Exploring Cosmic Origins with CORE: Survey requirements and mission design
Delabrouille, J. and others
[Abstract] [PDF] [Journal]
Refereed paper. 16th June.
Exploring Cosmic Origins with CORE: Inflation
Finelli, Fabio and others
[Abstract] [PDF] [Journal]
Refereed paper. 10th January.


Exploring Cosmic Origins with CORE: Cosmological Parameters
Di Valentino, Eleonora et al.
[Abstract] [PDF] [Journal]
Refereed paper. 2nd December.
Wavelet-Bayesian inference of cosmic strings embedded in the cosmic microwave background
J. D. McEwen, S. M. Feeney, H. V. Peiris, Y. Wiaux, C. Ringeval and F. R. Bouchet
[Abstract] [PDF] [Journal]
Refereed paper. 2nd December.
Shortcomings of New Parametrizations of Inflation
Jerome Martin, Christophe Ringeval and Vincent Vennin
[Abstract] [PDF] [Journal] Published in Phys. Rev. D94, 123521 (2016).
Refereed paper. 16th September.
Information Gain on Reheating: the One Bit Milestone
Jérôme Martin, Christophe Ringeval and Vincent Vennin
[Abstract] [PDF] [Journal] Published in Phys. Rev. D93, 103532 (2016)
Refereed paper. 9th March.


Cosmic inflation and model comparison
Vincent Vennin, Jérôme Martin and Christophe Ringeval
[Journal] [Full text] Published in Comptes Rendus Physique, Volume 16, Issue 10, December 2015, Pages 960–968
Refereed paper. 11th December.
Large scale CMB anomalies from thawing cosmic strings
Christophe Ringeval, Daisuke Yamauchi, Jun'ichi Yokoyama and François R. Bouchet
[Abstract] [PDF] [Journal] Published in JCAP 1602 (2016) 033
Refereed paper. 8th October.
Cascading dust inflation in Born-Infeld gravity
Jose Beltran Jimenez, Lavinia Heisenberg, Gonzalo J. Olmo and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in JCAP 1511 (2015) 046
Refereed paper. 22nd September.


Observing the Inflationary Reheating
Jerome Martin, Christophe Ringeval and Vincent Vennin
[Abstract] [PDF] [Journal] Published in Phys. Rev. Lett. 114, 081303 (2015)
Refereed paper. 30th October.
How Well Can Future CMB Missions Constrain Cosmic Inflation?
Jerome Martin, Christophe Ringeval and Vincent Vennin
[Abstract] [PDF] [Journal] Published in JCAP 1410 (2014) 038
Refereed paper. 16th July.
Planck 2013 results. I. Overview of products and scientific results
Ade, P.A.R. and others
[Abstract] [PDF] [Journal] Published in Astron. Astrophys, 571, A1 (2014)
Refereed paper. 11th July.
Compatibility of Planck and BICEP2 in the Light of Inflation
Jerome Martin, Christophe Ringeval, Roberto Trotta and Vincent Vennin
[Abstract] [PDF] [Journal] Published in in Phys. Rev. D90, 063501 (2014)
Refereed paper. 1st June.


The Best Inflationary Models After Planck
Jerome Martin, Christophe Ringeval, Roberto Trotta and Vincent Vennin
[Abstract] [PDF] [Journal] Published in JCAP 1403 (2014) 039
Refereed paper. 13th December.
Fast Bayesian inference for slow-roll inflation
Christophe Ringeval
[Abstract] [PDF] [Journal] Published in MNRAS 439, 3253 (2014)
Refereed paper. 10th December.
Encyclopaedia Inflationaris
Jerome Martin, Christophe Ringeval and Vincent Vennin
[Abstract] [PDF] [Journal] Published in Phys. Dark Univ. 003, 01 (2014)
Refereed paper. 25th March.
Planck 2013 results. XV. CMB power spectra and likelihood
Planck Collaboration
[Abstract] [PDF] [Journal] Published in Astron. Astrophys, 571, A15 (2014)
Refereed paper. 25th March.
Planck 2013 results. XXV. Searches for cosmic strings and other topological defects
Planck Collaboration
[Abstract] [PDF] [Journal] Published in Astron. Astrophys, 571, A25 (2014)
Refereed paper. 25th March.
Exact Mapping between Tensor and Most General Scalar Power Spectra
Jose Beltran Jimenez, Marcello Musso and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in Phys. Rev. D88, 043524 (2013)
Refereed paper. 15th March.
K-inflationary Power Spectra at Second Order
Jerome Martin, Christophe Ringeval and Vincent Vennin
[Abstract] [PDF] [Journal] Published in JCAP 06 (2013) 021
Refereed paper. 12th March.
Magneto-reheating constraints from curvature perturbations
Christophe Ringeval, Teruaki Suyama and Jun'ichi Yokoyama
[Abstract] [PDF] [Journal] Published in JCAP 09 (2013) 020
Refereed paper. 26th February.
A Boltzmann treatment for the vorton excess problem
Patrick Peter and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in JCAP 05 (2013) 005
Refereed paper. 6th February.
Early Universe Tomography with CMB and Gravitational Waves
Sachiko Kuroyanagi, Christophe Ringeval and Tomo Takahashi
[Abstract] [PDF] [Journal] Published in Phys. Rev. D87, 083502 (2013)
Refereed paper. 10th January.


Dark energy from inflation
Christophe Ringeval
[Journal] [Full text] Published in J.Phys.Conf.Ser. 485, 012023 (2014)
Contribution to proceedings. 12th September.
Background reionization history from omniscopes
Sebastien Clesse, Laura Lopez-Honorez, Christophe Ringeval, Hiroyuki Tashiro and Michel H. G. Tytgat
[Abstract] [PDF] [Journal] Published in Phys. Rev. D86, 123506 (2012)
Refereed paper. 21st August.
Searching for Standard Clocks in the Primordial Universe
Xingang Chen and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in JCAP 08 (2012) 014
Refereed paper. 29th May.
All sky CMB map from cosmic strings integrated Sachs-Wolfe effect
Christophe Ringeval and François R. Bouchet
[Abstract] [PDF] [Journal] Published in Phys. Rev. D86, 023513 (2012)
Refereed paper. 24th April.
Reheating constraints in inflationary magnetogenesis
Vittoria Demozzi and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in JCAP 05 (2012) 009
Refereed paper. 15th February.


Hunting Down the Best Model of Inflation with Bayesian Evidence
Jerome Martin, Christophe Ringeval and Roberto Trotta
[Abstract] [PDF] [Journal] Published in Phys. Rev. D83, 063524 (2011)
Refereed paper. 22nd September.
Cosmic string loop distribution on all length scales and at any redshift
Larissa Lorenz, Christophe Ringeval and Mairi Sakellariadou
[Abstract] [PDF] [Journal] Published in JCAP 10 (2010) 003
Refereed paper. 7th June.
Dark energy from primordial inflationary quantum fluctuations
Christophe Ringeval, Teruaki Suyama, Tomo Takahashi, Masahide Yamaguchi, Shuichiro Yokoyama
[Abstract] [PDF] [Journal] Published in Phys. Rev. Lett. 105, 121301 (2010)
Refereed paper. 3rd June.
Cosmic strings and their induced non-Gaussianities in the cosmic microwave background
Christophe Ringeval
[Abstract] [PDF] [Journal] Published in Advances in Astronomy, vol. 2010, Article ID 380507 (2010)
Refereed paper. 27th May.
First CMB constraints on the inflationary reheating temperature
Jerome Martin and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in Phys. Rev. D82, 023511 (2010)
Refereed paper. 3rd May.
Graviton confinement inside hypermonopoles of any dimension
Seán Murray, Christophe Ringeval and Simone Zonetti
[Abstract] [PDF] [Journal] Published in JCAP 09 (2010) 015
Refereed paper. 26th February.


CMB temperature trispectrum of cosmic strings
Mark Hindmarsh, Christophe Ringeval and Teruaki Suyama
[Abstract] [PDF] [Journal] Published in Phys. Rev. D81, 063505 (2010)
Refereed paper. 6th November.
Dirac-Born-Infeld and k-inflation: the CMB anisotropies from string theory
Christophe Ringeval
[Abstract] [PDF] [Journal] Published in J. Phys. Conf. Ser. 203, 012056 (2010)
Contribution to proceedings. 12th October.
Fractal initial conditions and natural parameter values in hybrid inflation
Sébastien Clesse, Christophe Ringeval, Jonathan Rocher
[Abstract] [PDF] [Journal] Published in Phys. Rev. D80, 123534 (2009)
Refereed paper. 2nd September.
CMB temperature bispectrum induced by cosmic strings
Mark Hindmarsh, Christophe Ringeval and Teruaki Suyama
[Abstract] [PDF] [Journal] Published in Phys. Rev. D80, 083501 (2009)
Refereed paper. 4th August.
Charged seven-dimensional spacetimes with spherically symmetric extra-dimensions
Antonio De Felice and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in Phys. Rev. D79, 123525 (2009)
Refereed paper. 2nd April.


Massive gravitons trapped inside a hypermonopole
Antonio De Felice and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in Physics Letters B 671, 158-161 (2009)
Refereed paper. 2nd September.
K-inflationary power spectra in the uniform approximation
Larissa Lorenz, Jerome Martin and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in Phys. Rev. D78, 083513 (2008)
Refereed paper. 18th July.
Constraints on kinetically modified inflation from WMAP5
Larissa Lorenz, Jerome Martin and Christophe Ringeval
[Abstract] [PDF] [Journal] Published in Phys. Rev. D78, 063543 (2008)
Refereed paper. 15th July.


Brane inflation and the WMAP data: a Bayesian analysis
Larissa Lorenz, Jérôme Martin, Christophe Ringeval
[Abstract] [PDF] [Journal] Published in JCAP 04 (2008) 001.
Refereed paper. 24th September.
Small-angle CMB temperature anisotropies induced by cosmic strings
Aurélien Fraisse, Christophe Ringeval, David Spergel and François Bouchet
[Abstract] [PDF] [Journal] Published in Phys. Rev. D78 (2008) 043535
Refereed paper. 13th August.
Cosmological evolution of cosmic string loops
Christophe Ringeval, Mairi Sakellariadou, François R. Bouchet
[Abstract] [PDF] [Journal] Published in JCAP 0702 (2007) 023.
Refereed paper. 19th February.
The exact numerical treatment of inflationary models
Christophe Ringeval
[Abstract] [PDF] [Journal] Published in Lect. Notes Phys 738, 243-273 (2008)
Refereed paper. 14th January.

[UCLouvain] - [SST] [IRMP] - [SC]
Contact : Jérôme de Favereau
Job opportunities Post-doctoral positions in BSM phenomenology at colliders and in astrophysics
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