String Cosmology: New Tools to connect String Theory with Cosmological Observations
Lead Research Organisation:
University of Portsmouth
Department Name: Institute of Cosmology and Gravitation
Abstract
Cosmology studies the origin of the Universe, and the main features of its evolution until today. The Universe expansion is mainly controlled by gravity, the force described by Einstein's General Relativity. This theory is extremely successful for describing gravitational phenomena that occur at large distances. However, when attempting to describe phenomena occurring at small scales, General Relativity apparently fails. Indeed, the best theories we have to describe short distance physics are based on Quantum Mechanics. But its principles lead to inconsistent results, when applied to gravitational phenomena following the rules of General Relativity. This problem is relevant for Cosmology, when trying to investigate epochs in which the Universe was very young, and then very small, in which quantum mechanical effects are important. For example, in the early epochs of our Universe, it is believed that cosmological expansion has experienced a phase of extremely fast acceleration, called Inflation. During this epoch, quantum effects are decisive to produce small inhomogeneities in the structure of the space-time, that seed large scale structures in the subsequent evolution of the Universe. The aim of consistently conjugate General Relativity with Quantum Mechanics is the main goal that motivated the development of String Theory. This theory introduces very unusual concepts: its consistency requires that our Universe has six dimensions more than the observed ones, that are wrapped on a small space, and unobservable by everyday experience. Also, it predicts the existence of membrane objects, fluctuating in a higher dimensional background, where the particle constituting our Universe can be localized. In order to check these beautiful ideas, however, we need to probe phenomena happening at extremely small scales. I find all these ideas extremely exciting, so I decided to study the relation between string theory and cosmology, with the main aim to find new ways to test string theory by cosmological observations. As explained before, phenomena occurring at early epochs, when the Universe was extremely small, are affected by short distance physics, and then possibly by String Theory. Inflation is the most important example: it is a process that leaves clear imprints in the pattern of the observed CMB radiation, and provides initial conditions affecting the subsequent evolution of the Universe. For these reasons part of my research is devoted to study models of inflation in String Theory. They can have peculiar properties, since they use many of the ingredients that the theory offers. The study of string models of inflation, then, offers unique opportunities to reveal effects that are characteristic of String Theory, and allows to test its ideas by means of cosmological observations. More specifically, the main objectives of my research activity can by summarized in the following. First, I plan to develop the theoretical tools allowing to compare observational results with string motivated cosmological models. This is a broad subject that requires the elaboration of existing techniques aimed to analyze the evolution of cosmological fluctuations, in order to apply them to string motivated cosmological models. Then, I will try to individuate the most promising cosmological models, based on string theory, that offer the best opportunities for being testable with future cosmological observations. Once this has been done, I will try to elaborate those models, in order to render them fully satisfactory from a theoretical point of view, and study in detail their predictions for cosmological quantities that will be tested by observations.
People |
ORCID iD |
Gianmassimo Tasinato (Principal Investigator / Fellow) |
Publications
Barclay L
(2012)
Lifshitz black holes in IIA supergravity
Barclay L
(2012)
Lifshitz black holes in IIA supergravity
in Journal of High Energy Physics
Barclay L
(2012)
Lifshitz black holes in IIA supergravity
Bartolo N
(2016)
Distinctive signatures of space-time diffeomorphism breaking in EFT of inflation
in Journal of Cosmology and Astroparticle Physics
Burgess C
(2015)
EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
in Journal of High Energy Physics
Byrnes C
(2012)
Inhomogeneous non-gaussianity
in Journal of Cosmology and Astroparticle Physics
Byrnes C
(2013)
Implications of the Planck bispectrum constraints for the primordial trispectrum
in EPL (Europhysics Letters)
Cannone D
(2015)
Generalised tensor fluctuations and inflation
in Journal of Cosmology and Astroparticle Physics
Cannone D
(2014)
Generalised tensor fluctuations and inflation
Cannone D
(2015)
Breaking discrete symmetries in the effective field theory of inflation
in Journal of Cosmology and Astroparticle Physics
Chagoya J
(2016)
Galileon Higgs vortices
in Journal of High Energy Physics
Chagoya J
(2014)
Galileons and strong gravity
in Journal of Cosmology and Astroparticle Physics
Chen H
(2010)
Towards multi-field D-brane inflation in a warped throat
in Journal of Cosmology and Astroparticle Physics
Cicoli M
(2011)
Poly-instanton inflation
in Journal of Cosmology and Astroparticle Physics
Cicoli M
(2012)
Natural quintessence in string theory
in Journal of Cosmology and Astroparticle Physics
Cicoli M
(2012)
Modulated reheating and large non-gaussianity in string cosmology
in Journal of Cosmology and Astroparticle Physics
Cicoli M
(2012)
Natural Quintessence in String Theory
Comelli D
(2015)
Cosmology of bigravity with doubly coupled matter
in Journal of Cosmology and Astroparticle Physics
Comelli D
(2015)
New Branches of Massive Gravity
Comelli D
(2015)
New branches of massive gravity
in Physical Review D
Emery J
(2013)
Mixed non-Gaussianity in multiple-DBI inflation
in Journal of Cosmology and Astroparticle Physics
Emery J
(2012)
Local non-Gaussianity from rapidly varying sound speeds
in Journal of Cosmology and Astroparticle Physics
Emery J
(2012)
Local non-Gaussianity from rapidly varying sound speeds
Emery J
(2013)
Mixed non-Gaussianity in multiple-DBI inflation
Erdmenger J
(2012)
Slow-walking inflation
Erdmenger J
(2013)
Slow-walking inflation
in Journal of Cosmology and Astroparticle Physics
Gerstenlauer M
(2011)
Inflationary correlation functions without infrared divergences
in Journal of Cosmology and Astroparticle Physics
Gregory R
(2010)
Lifshitz solutions in supergravity and string theory
in Journal of High Energy Physics
Hull M
(2015)
A Higgs mechanism for vector Galileons
in Journal of High Energy Physics
Hull M
(2016)
Covariantized vector Galileons
in Physical Review D
Hull M
(2015)
Covariantised Vector Galileons
Khosravi N
(2013)
Stability of the self-accelerating universe in massive gravity
in Journal of Cosmology and Astroparticle Physics
Koyama K
(2011)
Analytic Solutions in Nonlinear Massive Gravity
in Physical Review Letters
Koyama K
(2013)
Effective theory for the Vainshtein mechanism from the Horndeski action
in Physical Review D
KOYAMA K
(2012)
CAN THE GRAVITON HAVE A MASS?
in International Journal of Modern Physics D
Koyama K
(2011)
The self-accelerating universe with vectors in massive gravity
in Journal of High Energy Physics
Koyama K
(2011)
Strong interactions and exact solutions in nonlinear massive gravity
in Physical Review D
Nurmi S
(2013)
A non-Gaussian landscape
in Journal of Cosmology and Astroparticle Physics
Peloso M
(2014)
A falsely fat curvaton with an observable running of the spectral tilt
in Journal of Cosmology and Astroparticle Physics
Sbisà F
(2012)
Characterizing Vainshtein solutions in massive gravity
in Physical Review D
Tasinato G
(2013)
Loop corrections and a new test of inflation
in Physical Review D
Tasinato G
(2014)
Primordial non-Gaussianity in the bispectra of large-scale structure
in Journal of Cosmology and Astroparticle Physics
Tasinato G
(2013)
Primordial non-Gaussianity in the bispectra of large-scale structure
Tasinato G
(2015)
A scenario for inflationary magnetogenesis without strong coupling problem
in Journal of Cosmology and Astroparticle Physics
Tasinato G
(2014)
Cosmic acceleration from Abelian symmetry breaking
in Journal of High Energy Physics
Tasinato G
(2013)
Conformal couplings of Galileons to other degrees of freedom
in Journal of High Energy Physics
Tasinato G
(2014)
A small cosmological constant from Abelian symmetry breaking
in Classical and Quantum Gravity
Tasinato G
(2013)
Exact solutions in massive gravity
in Classical and Quantum Gravity
Tasinato G
(2012)
New symmetries in Fierz-Pauli massive gravity
in Journal of High Energy Physics
Tasinato G
(2013)
Vector instabilities and self-acceleration in the decoupling limit of massive gravity
in Physical Review D