Accelerating Universes from Compactification on a Warped Conifold

Abstract

We find a cosmological solution corresponding to the compactification of 10D supergravity on a warped conifold that easily circumvents the ''no-go'' theorem given for a warped or flux compactification, providing new perspectives for the study of supergravity or superstring theory in cosmological backgrounds. With fixed volume moduli of the internal space, the model can explain a physical Universe undergoing an accelerated expansion in the 4D Einstein frame, for a sufficiently long time. The solution found in the limit that the warp factor dependent on the radial coordinate y is extremized (giving a constant warping) is smooth and it supports a flat four-dimensional Friedmann-Robertson-Walker cosmology undergoing a period of accelerated expansion with slowly rolling or stabilized volume moduli. , not only provide emerging evidence for the ongoing accelerated expansion of the Universe but also provide support for the concept of inflation, or a rapid exponential expansion of large magnitude in a much earlier cosmological epoch. Although it is not difficult to construct cosmological models that exhibit these features, one would prefer any such model to be derivable from a fundamental, and mathematically consistent microscopic theory of (de Sitter) quantum gravity, such as string theory. Superstring theory lives in ten dimensions but we live in a four-dimensional Universe. Clearly, any attempt to derive a viable cosmology from string or M theory (compactification) must produce a four-dimensional de Sitter Universe similar to ours and the size of extra dimensions should remain much smaller than the physical three dimensions.The past few years have witnessed significant progress in building of inflation models within string theory via flux compactifications of the ten-or eleven-dimensional spacetime of superstring or M theory with the desire to find models for late-time cosmology [3-5] supporting a small positive cosmological constant. If one wishes to stay within the realm of low energy supergravity models derived from superstrings, cosmic inflation is ruled out for warped flux compactifications of classical supergravities on the basis of a ''no-go '' theorem [6,7], which forbids accelerating solutions for warped (and static) extra dimensions. For a way out, one may possibly include higher curvature corrections [8] to the leading order Lagrangian in 0 expansion or extended sources (branes, antibranes) that are present in string theory [9] or even invoke certain nonperturbative effects (such as, gaugino condensate and Euclidian D3 branes) [3]. These all achieve some limited success in overcoming the no-go theorem. However, there is no good reason to suppose that all these string effects are available at much lower energy scale, such as vac 10 ÿ3 eV or H 10 ÿ60 M Pl . There is another particular

Bianchi type-VI0 cosmological models with anisotropic dark energy

“…Astronomical observations indicate that our universe is flat and currently consists of approximately 2/3 dark energy and 1/3 dark matter. The nature of dark energy as well as dark matter is unknown, and many radically different models have been proposed, such as, a tiny positive cosmological constant, quintessence (Caldwell et al 1998;Liddle and Scherrer 1999;Steinhardt et al 1999), DGP branes (Dvali et al 2000;Deffayet 2001), the non-linear F(R) models (Capozziello et al 2003;Carroll et al 2003;Nojiri and Odintsov 2003), and dark energy in brane worlds, among many others (Townsend and Wohlfarth 2003;Gibbons 2001;Ohta 2003aOhta , 2003bWohlfarth 2003;Roy 2003;Webb et al 2001;Cline and Vinet 2003;Chen et al 2003;Bergshoeff 2004;Gong and Wang 2006;Neupane andWiltshire 2005a, 2005b;Maeda and Ohta 2005;Neupane 2007;Gong et al 2008;Pereira et al 2006;Brandt et al 2007); see also the review articles (Copeland et al 2006;Padmanabhan 2007), and references therein. As mentioned before, the existence of dark energy fluids comes from the observations of the accelerated expansion of the universe and the isotropic pressure cosmological models give the best fitting of the observations.…”

Warped compactification to de Sitter space

“…In recent years, many authors have constructed varieties of time-dependent solutions. One of the motivations for this has been that the original no-go theorem required time independence of the internal space, so one could look for time-dependent solutions in higher dimensions [19][20][21][22][23][24][25]. Through many examples discussed in the literature, we have learnt that higher-dimensional theories with time-dependent metric moduli generally give rise to a transient acceleration (of the universe).…”

Kaluza–klein Cosmological Models With Anisotropic Dark Energy

“…Astronomical observations indicate that our universe is flat and currently consists of approximately 2/3 dark energy and 1/3 dark matter. The nature of dark energy as well as dark matter is unknown, and many radically different models have been proposed, such as, a tiny positive cosmological constant, quintessence, 12,37,69 DGP branes, 24,22 the nonlinear F (R) models, 13,14,44 and dark energy in braneworlds, among many others 26,73,71,[45][46][47]75,63,18,15,8,27,42,40,43,28,51,11 ; see also the review articles, 20,49 and references therein. As mentioned before, the existence of dark energy fluids comes from the observations of the accelerated expansion of the universe and the isotropic pressure cosmological models give the best fitting of the observations.…”