My research area is Particle Cosmology. Cosmology is the study of the Universe as a system. Modern Cosmology is based on the Hot Big Bang (HBB) model, which provides a successful description of the Universe history as far back as the first second of its existence. However, the HBB leaves many questions unanswered. The answers hide in the elusive primordial era, when the Universe was so dense and hot that its evolution was determined by High Energy Physics phenomena. In fact, since the energy scale of the cosmology in the Early Universe is much higher than the scale of electroweak unification, one needs to employ Physics beyond the Standard Model to investigate the remaining mysteries. Particle Cosmology uses what is known or conjectured about the fundamental interactions in the context of Particle Theory for the study of the Early Universe.
One of my main areas of research is Cosmic Inflation. This can be defined as a period of accelerated expansion of space in the Early Universe. Inflation is a compelling solution to the problems of the HBB that have to do with why the Universe appears to be so big and so uniform on very large scales. It also provides an elegant way to generate the small perturbations in the density of the Universe, which are necessary for the formation of structures such as galaxies and galactic clusters. The existence and the characteristics of these Primordial Density Perturbations (PDP) have been observationally determined because they reflect themselves on the Cosmic Microwave Background Radiation (CMBR) by generating anisotropies and polarisation.
My research regarding Inflation aims to construct and study the dynamics of realistic inflationary models based on Particle Theory. I am also interested in the generation of the PDP during Inflation, which can be explored by investigating the behaviour and evolution of suitable fields, belonging to simple extensions of the Standard Model. These fields may or may not be related to inflationary expansion itself (if not they are called Curvatons). At this level there is also considerable interface between cosmology and String Theory, Branes and Large Extra Dimensions. It should be noted that recent, precise CMBR observations from the WMAP satellite, have confirmed the basic predictions of Inflation. Hence, Cosmic Inflation is now considered a necessary extension of HBB cosmology.
Another open issue for cosmologists today is the recent observation that the Universe seems to be engaging into an era of accelerated expansion at present. This is attributed to a mysterious Dark Energy substance, whose nature and origin is unknown. The simplest choice of Dark Energy is a Cosmological Constant. However, such a constant has to be incredibly fine-tunned (by hundreds of orders of magnitude) to explain the observations. Alternatively, it has been suggested that the Universe is undergoing a late period of inflation, driven by a scalar field called Quintessence; the fifth element after Dark Matter, neutrinos, photons and baryons. In my research I concentrate on the possibility that the field that drives Cosmic Inflation in the Early Universe is the same with Quintessence. The study of such Quintessential Inflation is not only economical but has the advantage of using a single theoretical framework to determine the global evolution of the Universe from extremely early times until the present.
Primordial Magnetic Fields
Another area of my research is the possible generation of large-scale Primordial Magnetic Fields (PMFs) in the Early Universe. Such fields can be responsible for the observed intergalactic magnetic fields as well as the magnetic fields of the galaxies themselves. One can generate PMFs only in out-of thermal equilibrium conditions, because they break isotropy. Such opportunities exist during Phase Transitions in the Early Universe (at the breaking of symmetries of the fundamental interactions) and during Cosmic Inflation (when the Universe is supercooled because any preexisting entropy is inflated away).
Cosmic Vector Fields
Finally, in recent years I have pioneered the study of the effects of vector boson fields (such as the photon, i.e. the quantum of the electromagnetic field) on the PDP and CMBR. Such fields are produced in a similar manner as PMFs during Cosmic Inflation. I have shown that, under certain circumstances, vector boson fields can contribute significantly or even be solely responsible for the generation of the PDP. In contrast to scalar fields to which the PDP was attributed until now, vector boson fields have been observed in CERN (e.g. the W and Z massive gauge bosons). Moreover, they can give rise to distinct observational signatures on the CMBR, namely statistical anisotropy. This amounts to direction dependent patterns, which select a preferred direction on the microwave sky. Indeed, in recent years there is tantalising observational evidence that such a preferred direction may exist (manifested as alignment of the low multipoles of CMBR). Beyond the CMBR, statistical anisotropy may also reflect itself in the distribution of cosmic structures (e.g. rows of galaxies). Statistical anisotropy may well be observed in the near future by the Planck satellite, which was launched by ESA in May 2009. If so then one would have to involve vector boson fields in model-building inflation and in the generation of the PDP. This is the aim of my research. Theories beyond the Standard Model include many suitable candidates for cosmic vector fields such as the supermassive gauge bosons in Grand Unified Theories or fluxes in the extra dimensions needed for their stabilisation in String Theory.
Research output: Contribution to journal › Journal article
Research output: Contribution to journal › Journal article
Research output: Contribution in Book/Report/Proceedings › Paper