Confronting dark energy models with astrophysical data: Non-equilibrium vs. conventional cosmologies

Abstract

We discuss fits of cosmological dark energy models to the available data on high-redshift supernovae. We consider a conventional model with cold dark matter and a cosmological constant (KCDM), a model invoking super-horizon perturbations (SHCDM) and models based on Liouville strings in which dark energy is provided by a rolling dilaton field (Q-cosmology). We show that a complete treatment of Q-cosmology requires a careful discussion of non-equilibrium situations (off-shell effects). The two main high-redshift supernova data sets give compatible constraints on KCDM and the other models. We recover the well-known result that KCDM fits very well the combined supernova data sets, as does the super-horizon model. We discuss the model-dependent off-shell corrections to the Q-cosmology model that are relevant to the supernova data, and show that this model fits the data equally well. This analysis could be extended to other aspects of cosmological phenomenology, in particular to the CMB and baryon acoustic oscillations, which have so far been treated using on-shell models.

Dilaton and off-shell (non-critical string) effects in Boltzmann equation for species abundances

“…Essentially, the astrophysical data constraint severely in some cases the available phase-space distributions of favorite supersymmetric dark matter candidates such as neutralinos [16][17][18][19]. When off-equilibrium, non-critical string cosmologies are considered [1], which notably are consistent with the current astrophysical data from supernovae, as demonstrated recently [20], then there are significant modifications to the Boltzmann equation, stemming from extra sources (dilaton) and off-shell (non-critical, non equilibrium) terms, which affect the time evolution of the phase-space density of the species under consideration.…”

“…as a result of KaluzaKlein graviton modes in some brane cosmology scenarios. Such unconventional energy budget can still be made compatible at least with supernovae data [20]. It remains to be seen of course what constraints the CMB and structure formation data imply on such cosmologies, but it is evident from the above that string cosmology, and in particular supercritical string one, may lead to fascinating new results which may hide further surprises around the corner.…”

“…Also note that a preliminary comparison of such non-critical strings theories with astrophysical data, demonstrating consistency at present, is given in [20]. It should be remarked at this point that the solutions obtained in this study tend asymptotically to those presented in [8][9][10].…”

“…In realistic string models, the results depend crucially on many details of the underlying microscopic model, such as the compactification procedure, the details of supersymmetry breaking, the geometry of the bulk space in brane models, string loop corrections etc. Regarding the latter effects, we also mention that at late eras of the universe, the various scaling components of the energy density, such as a -4 , a -3 , etc, involve mixed contributions from both matter and gravitational/dilaton and radiation parts, in such a way that one may even have negative dust contributions during the present era in some models [20], e.g. as a result of KaluzaKlein graviton modes in some brane cosmology scenarios.…”

Constraints on Dissipative Non-Equilibrium Dark Energy Models From Recent Supernova Data

“…It is of outmost importance to confront the currently available precision astrophysical data with such non-equilibrium stringy cosmologies. The central purpose of this talk is to present a first step towards this direction, namely a confrontation of cosmological data on high-redshift supernovae 16,17 with Q-cosmologies and compare the results with the predictions of the conventional ΛCDM model 8 and the super-horizon model. 9 Care must be taken in interpreting the Q-cosmology scenario.…”