Browsing by Author "Kounnas, Costas"

Now showing items 1-12 of 12

    • Conference Object  

      Aspects of string cosmology 

      Kounnas, Costas; Toumbas, Nicolaos K. (Trieste, SISSA: Proceedings of Science., 2013)
      We review recent progress in string cosmology, where string dualities are applied so as to obtain complete cosmological evolutions, free of any essential singularities. Two classes of models are analyzed. The first class ...
    • Article  

      Cosmological perturbations across an S-brane 

      Brandenberger, R. H.; Kounnas, Costas; Partouche, Hervé; Patil, S. P.; Toumbas, Nicolaos K. (2014)
      Space-filling S-branes can mediate a transition between a contracting and an expanding universe in the Einstein frame. Following up on previous work that uncovered such bouncing solutions in the context of weakly coupled ...
    • Article  

      Induced superstring cosmologies and moduli stabilization 

      Catelin-Jullien, T.; Kounnas, Costas; Partouche, Hervé; Toumbas, Nicolaos K. (2009)
      We extend the analysis of the recently obtained stringy cosmological solutions induced by thermal and quantum effects, once space-time supersymmetry is spontaneously broken by geometrical fluxes. Cases in which more than ...
    • Article  

      Marginal deformations of vacua with massive boson-fermion degeneracy symmetry 

      Florakis, Ioannis G.; Kounnas, Costas; Toumbas, Nicolaos K. (2010)
      Two-dimensional string vacua with Massive Spectrum boson-fermion Degeneracy Symmetry, [MSDS]d=2, are explicitly constructed in Type II and Heterotic superstring theories. The study of their moduli space indicates the ...
    • Article  

      Non-singular string cosmology in a 2d hybrid model 

      Florakis, Ioannis G.; Kounnas, Costas; Partouche, Hervé; Toumbas, Nicolaos K. (2011)
      The existence of non-singular string cosmologies is established in a class of two-dimensional supersymmetric Hybrid models at finite temperature. The left-moving sector of the Hybrid models gives rise to 16 real (N4=4) ...
    • Article  

      R2 inflation from scale invariant supergravity and anomaly free superstrings with fluxes 

      Lüst, Dieter; Kounnas, Costas; Toumbas, Nicolaos K. (2015)
      The R2 scale invariant gravity theory coupled to conformally invariant matter is investigated. We show that in the non-supersymmetric case the conformally coupled scalars belong to an SO(1,1+n)/SO(1+n) manifold, while in ...
    • Article  

      Resolution of Hagedorn singularity in superstrings with gravito-magnetic fluxes 

      Angelantonj, Carlo; Kounnas, Costas; Partouche, Hervé; Toumbas, Nicolaos K. (2009)
      We consider closed type II and orientifold backgrounds where supersymmetry is spontaneously broken by asymmetric geometrical fluxes. We show that these can be used to describe thermal ensembles with chemical potentials ...
    • Article  

      S-brane to thermal non-singular string cosmology 

      Kounnas, Costas; Partouche, Hervé; Toumbas, Nicolaos K. (2012)
      We present a new class of non-singular string cosmologies in d spacetime dimensions. At very early times, τ τ c, the Universe is described by a flat σ-model metric, a constant maximal temperature T c and super-weak string ...
    • Article  

      Thermal and quantum superstring cosmologies 

      Catelin-Jullien, T.; Kounnas, Costas; Partouche, Hervé; Toumbas, Nicolaos K. (2008)
      We consider four dimensional heterotic string backgrounds for which supersymmetry is spontaneously broken via the Scherk-Schwarz mechanism on an internal spatial cycle and by finite temperature effects. We concentrate on ...
    • Article  

      Thermal duality and non-singular cosmology in d-dimensional superstrings 

      Kounnas, Costas; Partouche, Hervé; Toumbas, Nicolaos K. (2012)
      We are presenting the basic ingredients of a stringy mechanism able to resolve both the Hagedorn instabilities of finite temperature superstrings as well as the initial singularity of the induced cosmology in arbitrary ...
    • Article  

      Thermal/quantum effects and induced superstring cosmologies 

      Catelin-Jullien, T.; Kounnas, Costas; Partouche, Hervé; Toumbas, Nicolaos K. (2008)
      We consider classical superstring theories on flat four-dimensional space-times, and where N = 4 or N = 2 supersymmetry is spontaneously broken. We obtain the thermal and quantum corrections at the string one-loop level ...
    • Article  

      A wave-function for stringy universes 

      Kounnas, Costas; Troost, J.; Toumbas, Nicolaos K. (2007)