M.C. David Marsh

Senior Research Associate/Stephen Hawking Advanced Fellow
Centre For Theoretical Cosmology, DAMTP,
University of Cambridge


My research endeavours to confront theoretically well-motivated ideas about high-energy particle physics with observations from cosmology and astrophysics. The enormous energy density of the early, Big Bang universe provides a unique window to physics at scales not readily accessible through terrestrial experiments. Our relatively nearby surroundings contain fascinating astrophysical environments such as small, solar mass black holes and huge clusters of galaxies, from which signs of the fundamental structure of the universe may be gleamed. Darkness pervades the universe: most of the matter is of an unknown "dark" type, and observations give strong evidence for the existence of a "dark energy", or cosmological constant, driving the present universe to expand at an ever faster pace.

String theory combines quantum theory and gravity in a unified framework. Much of my work is focussed on deriving the cosmological and astrophysical properties of string theory models, and to use these models to interpret observational data.

Compactifications' cosmological consequences

String theory is naturally formulated in 10 or 11 spacetime dimensions, and can be connected to the observed four-dimensional spacetime by compactifying the extra dimensions. The geometry of the compactification manifold determines many of the properties of the low-energy theory. Size and shape deformations of the compactification manifold appear at in the four-dimensional effective theory as scalar, “moduli”, fields that interact with gravitational strength couplings. Typical compactification manifolds have a large number of moduli, and these crucially affect the cosmology and phenomenology of the theory.

Motivated by this, I have in the past introduced a novel framework for studying many-field inflation; tailored the statistical techniques of random matrix theory to compute the frequency of metastable de Sitter vacua in random ensembles of supergravity theories with many fields (it's very very small!); discovered corners of the moduli space of string theory where the low-energy theory exhibits universal properties that are insensitive to many details of the compactification; found a mechanism in string theory that make de Sitter vacua much more frequent than in random supergravities; studied the effects of moduli on the matter/antimatter asymmetry; determined their effects on supersymmetry breaking and so-called sequestering in string models.

Axions' astrophysical aspects

The axion is a type of (pseudo-)scalar particle that was first introduced to address one of the conceptually most challenging problems of Quantum Chromodynamics, the "strong CP-problem". Axions and more general "axion-like particles" appear frequently in compactifications of string theory, and can give rise to a vast array of cosmological and astrophysical effects. Among the most interesting: if travelling through a magnetic field these particles have a non-vanishing probability of converting into photons, which may then be detected. Galaxy clusters, it turns out, provide an ideal environment for such conversions to happen. Together with Joseph Conlon in Oxford, and others, I have determined the X-ray signals (and constraints) of light axion-like particles from clusters of galaxies. According to these results, upcoming and on-going X-ray satellite missions may shed light on the nature and couplings of dark matter, and the fundamental particle constituents of the universe. It's all very exciting!



DAMTP, Centre for Mathematical Sciences
Wilberforce Road
Cambridge, United Kingdom

Citizenship: Swedish
Hometown: Frösön: "Storsjöns pärla, Jämtlands Jamaica".

m.c.d.marsh(add at damtp.cam.ac.uk)
+44(0)1223 766873

Positions Held

(2015-present) Senior Research Associate/Stephen Hawking Advanced Fellow
Centre for Theoretical Cosmology,
Department of Applied Mathematics and Theoretical Physics, University of Cambridge.
(2012-2015) Postdoctoral Research Associate (4-year position),
Rudolph Peierls Centre for Theoretical Physics,
University of Oxford.


(2012) Ph.D. in Physics, Cornell University.
Adviser: Liam McAllister.
(2007) M.Sc. in Physics, Uppsala University.
Thesis adviser: Antti Niemi.


(2012) Olle Engqvist fellowship.
(2012) Fellow of the Carl-Erik Levin Foundation.
(2011) Fellow of the Gålö Foundation.
(2008) Graduate fellowship from the Swedish-American Society.
(2007) Graduate fellowship from the Thanks to Scandinavia Foundation.
(2005-2007) Thun's fellowship (fourfold recipient).

University Seminars

I have given >40 research seminars over the past few years. Here are the slides from a few of them.

(2016) Stanford University,
"Genericity and universality in the string theory landscape" (pdf, 2.8MB).
(2015) Stockholm University,
"ALPs and galaxy cluster X-rays as a window to the dark sector" (pdf, 8MB).
(2012) Institute for Advanced Study, Princeton,
"On sequestering and decoupling in stabilized string models" (pdf, 2.3MB).
Columbia University,
"The Wasteland of Random supergravities" (pdf, 2.6MB).
(2011) Ecole Polytechnique,
"Sequestering in string compactifications" (pdf, 1.5MB).

Conference Presentations

I have presented my research at numerous conferences and workshops. Slides from a few of them are linked below.

(2016) The May Dutch Theoretical Cosmology Meeting,
Groningen. Invited talk.
"Simple emergent power spectra from complex inflationary physics" (pdf, 2.8MB).
(2015) Off-the-Beaten-Track Dark Matter and Astrophysical Probes of Fundamental Physics,
ICTP, Trieste. Invited plenary.
"ALPs and galaxy cluster X-rays as a window to the dark sector" (pdf, 9.4MB).
Galileo Galilei institute, Florence. Invited contribution.
"The Type IIB Flux Landscape v. Random Matrix Theory" (pdf, 1.6MB).
(2014) String Phenomenology 2014,
ICTP, Trieste. Invited plenary.
"A string theory Cosmic Axion Background and the cluster soft X-ray excess" (pdf, 8MB).
Supersymmetry breaking in string theory,
Newton Institute, Cambridge. Invited contribution.
"Decoupling in stabilised type IIB models" (pdf, 2.2MB).
(2013) COSMO 2013,
Centre for Theoretical Cosmology, DAMTP, Cambridge.
"Charting an inflationary landscape with Random Matrix theory" (pdf, 1MB).
(2011) String Phenomenology 2011,
University of Wisconsin, Madison.
"Towards constraining Affleck-Dine baryogenesis" (pdf, 0.8MB).

Teaching Experience

(2016 -...) PhD advisor of Theodor Björkmo, DAMTP, University of Cambridge.
(2016) Lecturer, Part II Principles of Quantum Mechanics, DAMTP, University of Cambridge.
5 lectures on spin and angular momentum.
(2015, 2016) Lecturer, Part III Cosmology, DAMTP, University of Cambridge.
10 lectures on thermal history and the quantum origin of the structure of the universe.
Fourth year thesis adviser for Callum Brodie, University of Oxford.
Developed into publication in JHEP (2016).
(2014) Visiting Lecturer, M.Sc. Particle Physics, Birzeit University, Palestine (2 months).
Lectures, tutorials, examinations. Course organised by the ICTP.
(2013-2014) Stipendiary Lecturer, St John's College, Oxford.
Tutorials with first and second year students, internal examinations, college admissions.
(2010) Co-lecturer in Statistical Physics, Cornell University.
10 lectures for third year physics majors, examinations.
(2009-2012) Teaching Assistant, Cornell University.
Electromagnetism and Waves, Statistical Physics, and General Relativity (4 terms).

My pre-grad school teaching experience include three terms as a leader of Supplemental Instructions for junior undergraduates in the core physics courses, two weeks of teaching at the mathematics prep-course for incoming students at Uppsala University, and one year as a secondary school language teacher at Storsjöskolan, Östersund.

Service, Outreach

Referee: JCAP, JHEP, EPJ-C, ICP.
(2016) "The Palestinian Advanced Physics School", Jenin, Palestine.
(2015-2016)"The Cambridge Cosmology Journal Club", University of Cambridge.
(2012-2013)"The Particles and Fields Seminar", University of Oxford.
(2009-2011) Student string theory journal club, Cornell University.

(2016) "Naked Astronomy", podcast broadcasted on BBC radio and available online, discussing (the big bang and) gravitational waves.
(2014) "Stargazing Oxford", staff.
"Saturday Morning Theoretical Physics", University of Oxford. Outreach talk for former physics students. Video and pdf can be found through this link.
(2010) Hersby gymnasium, Stockholm, lecture on cosmology and string theory.

Publication list