Research Interests

In my research activity (mostly initiated when I was at DAMTP - University of Cambridge) I work on Superstring Effects in Early Universe Scenarios.

The physical background is as follows. 10-dimensional superstring theory is one of the most promising candidates for the ultimate theory of the quantum gravitational field, incorporating the hope that quantum gravity is unified with the other fundamental interactions. Five distinct consistent string theories are known, related by important transformation properties denoted by S, T and U - dualities. It now seems they can be interpreted as different realisations of a deeper new theory called M-theory, where 11-dimensional supergravity is also present. This is indeed quite fascinating, opening new grounds to explore, culminating (or leading) many of the new theoretical developments in the XXth century into new (often changing) borders. The status of current research is so exciting that it may suggestively remind the words of L. Wittgenstein: "In order to draw a limit to thinking, we should have to think both sides of that limit", in: Tractatus Logico-Philosophicus (1961).

A natural arena where Superstring-Supergravity-M-theory concepts may be tested is given by early universe cosmology. Indeed, early universe cosmology should be re-examined in the context of Supergravity/Superstring theory since the field equations have a different structure from Einstein equations. Moreover, symmetries of string theory provide an alternative picture (with an higher dimensional spacetime). In this context, part of my recent research has focused on

Quantum Cosmological Models in Superstring Theory and M-Theory:

(See the mentioned papers for a more detailed description of the achieved results, as well as subsequently proposed new directions that are currently being investigated)

  1. Employing inhomogenous perturbations of the metric and dilaton fields, I have searched for new (quantum) states, which would have a physical significance regarding a period of evolution from String/Supergravity cosmological physics towards a semi-classical stage. In particular, identifying the existence of any (quantum) state associated with dilaton-inflation and to structure formation.
  2. Quite recently, numerical simulations regarding inhomogenous cosmological models in string cosmology have been investigated. However, they have not provided a full agreement or a consistent scenario. My purpose is to further investigate these models within the general scenario of scalar-tensor theories, where the dilaton kinetic term is multiplied by a constant factor.
  3. Pre Big-Bang cosmologies (extracted from string inspired theories) quantized from the point of view of a de Broglie-Bohm approach predict classical scenarios for small values of the scale-factor, in contrast with conventional views of quantum cosmology. I aim to further investigated these systems in the presence of dilaton potentials and extra spatial dimensions.

  4. I have been analysing the canonical and quantum cosmological implications of a spatially flat, 4-D Friedmann-Robertson-Walker (FRW) model that is derived from the M-theory effective action . Investigation was directed in studying whether and how axions and form fields influence a four-dimensional FRW spacetime, first contracting from a strong coupling regime and then expanding to a weak coupling regime, while the internal space ever contracts.

  5. I also became interested in issues relating (A)dS stability and large extra dimensions. For this purpose, a non-linear gravitational model with a multidimensional warped product geometry and quadratic scalar curvature terms was considered together with p-form fields. The 4--dimensional effective cosmological constant as well as the bulk cosmological constant may become negative or positive for actual times but more needs to be investigated.

  6. Actions of the Born-Infeld (BI) type have been the subject of wide interest in the context of M/string theory. This comes from the result that the effective action for the open string ending on D-branes can be written in a BI form. If either string or brane effects are present, it can be expected that they may bring modifications and elucidate on current problems. Closed FRW models in the presence of a SO(N) gauge sector described by a non-Abelian Born-Infeld action have been investigated. Applications of Born-Infeld cosmology to early evolution, quintessence and alpha-varying effects were discussed recently by myself.

In addition, I have also investigated quantum gravity, under the effects of matter, by means of a scalar (spin-0) field. I have been studying a wider range of situations, allowing for the realistic presence of fermionic partners, within a supersymmetric context. More specifically, I have been focusing on the following topic:

upersymmetric quantum cosmology (SQC)

(See the mentioned papers for a more detailed description of the achieved results, as well as subsequantly proposed new directions that are currently being investigated)

  1. Examining how the presence of duality transformations induces the existence of SUSY invariance. Previous studies involving FRW models (that is, isotropic) have suggested N=2 SUSY. We will test this assertion towards a larger range by analysing Bianchi models, which are not isotropic.

  2. Analysing Bianchi models derived N=1 supergravity, where a fermionic matter sector is explicitly present. This an urgent and pertinent issue: previous results with other models and different matter contents have pointed instead to N=4 SUSY.

  3. Investigating the validity of minisuperspace approximation in supersymmetric quantum cosmology: A minisuperspace is a truncation in the inhomogenous modes of the field variables. How does this affect a supersymmetric theory and what does supersymmetry brings about as far as minisuperspace approach is concerned?

  4. Addressing the existence of physical states in the full theory of N=1 supergravity (without truncations), namely analysing a recent conjecture. It seems only a wormhole state can be obtained in the infinite fermionic sector but not a Hartle-Hawking (no-boundary) solution.

  5. Investigating the possibility of constructing conserved currents in locally supersymmetric minisuperspaces.

  6. Investigating the scenario of spontaneous supersymmetry breaking from a canonical quantization point of view: How does the presence or absence of a potential influences the quantum mechanical description (e.g., the wave function of the universe) for a specific cosmomogical model?

More details of my current and forthcoming research activity can be found here, where the above mentioned and may other original papers (with the journals site) are also included.

Finally, I would like to stress I have received three prizes for research in three international competitions/events:

As far as my research aspirations are concerned, I have more information about my research projects separately (found here!). I would like to stress my total commitment to continue my research in quantum gravity and cosmology, the physics of the very early universe and structure formation. These are indeed fascinating and active subjects with a plethora of open issues, and where I wish to contribute enthusiastically.

My aspirations also include establishing more contacts with other gravity groups, especially in Europe, and starting or participating in the formation of Research Networks. If you are a researcher with common or similar interests (at some point) do contact me. Maybe we could produce a joint proposal to get some funding, as well as produce some really interesting research papers.

And, yes, you are indeed quite right! This is the cover of J. Saramago (1999 Literature Nobel prize winner) recent book "A CAVERNA" (The cave). As you can see, it is signed by him(!), where he also wrote To Paulo Monizand for the ADS/CFT. For those eager to see what is ADS/CFT, what possible relation to Plato, the cave and all that, in view of avant-garde research in theoretical physics, click here or there.

And have fun!!!

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