The parameter space for A-term inflation is explored with W = λpϕp/pMPp−3. With p = 6 and λp∼1, the observed spectrum and spectral tilt can be obtained with soft mass of order 102 GeV but not with a much higher mass. The case p = 3 requires λp∼10−9 to 10−12. The ratio m/A requires fine-tuning, which may be justified on environmental grounds. An extension of the minimal supersymmetric standard model to include non-renormalizable terms and/or Dirac neutrino masses might support either A-term inflation or modular inflation.

A global monopole (or other topological defect) formed during a recent phase transition with core size comparable to the present Hubble scale, could induce the observed accelerating expansion of the Universe. In such a model, topological considerations trap the scalar field close to a local maximum of its potential in a cosmologically large region of space. We perform detailed numerical simulations of such an inhomogeneous dark energy system (topological quintessence) minimally coupled to gravity, in a flat background of initially homogeneous matter. We find that when the energy density of the field in the monopole core starts dominating the background density, the spacetime in the core starts to accelerate its expansion in accordance to a ÃCDM model with an effective inhomogeneous spherical dark energy density parameter à ðrÞ. The matter density profile is found to respond to the global monopole profile via an anticorrelation (matter underdensity in the monopole core). Away from the monopole core, the spacetime is effectively Einstein-de Sitter ( à ðr out Þ ! 0) while at the center à ðr ' 0Þ is maximum. We fit the numerically obtained expansion rate at the monopole core to the Union2 data and show that the quality of fit is almost identical to that of ÃCDM. Finally, we discuss potential observational signatures of this class of inhomogeneous dark energy models.

We generalize the small scale dynamics of the universe by taking into account models with an equation of state which evolves with time, and provide a complete formulation of the cluster virialization attempting to address the nonlinear regime of structure formation. In the context of the current dark energy models, we find that galaxy clusters appear to form at z ∼ 1 − 2, in agreement with previous studies. Also, we investigate thoroughly the evolution of spherical matter perturbations, as the latter decouple from the background expansion and start to "turn around" and finally collapse. Within this framework, we find that the concentration parameter depends on the choice of the considered dark energy (homogeneous or clustered). In particular, if the distribution of the dark energy is clustered then we produce more concentrated structures with respect to the homogeneous dark energy. Finally, comparing the predicted concentration parameter with the observed concentration parameter, measured for four massive galaxy clusters, we find that the scenario which contains a pure homogeneous dark energy is unable to reproduce the data. The situation becomes somewhat better in the case of an inhomogeneous (clustered) dark energy.PACS numbers: 98.80.-k, 95.35.+d, 95.36.+x

Curvaton reheating is studied in non-oscillatory (NO) models of inflation, with the aim to obtain bounds on the parameters of curvaton models and find out whether low scale inflation can be attained. Using a minimal curvaton model, it is found that the allowed parameter space is considerably larger than in the case of the usual oscillatory inflation models. In particular, inflation with Hubble scale as low as 1 TeV is comfortably allowed.

We rank the six latest Type Ia supernova (SnIa) datasets (Constitution (C), Union (U), ESSENCE (Davis) (E), Gold06 (G), SNLS 1yr (S) and SDSS-II (D)) in the context of the Chevalier-Polarski-Linder (CPL) parametrization w(a) = w0 + w1(1 − a), according to their Figure of Merit (FoM), their consistency with the cosmological constant (ΛCDM), their consistency with standard rulers (Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO)) and their mutual consistency. We find a significant improvement of the FoM (defined as the inverse area of the 95.4% parameter contour) with the number of SnIa of these datasets ((C) highest FoM, (U), (G), (D), (E), (S) lowest FoM). Standard rulers (CMB+BAO) have a better FoM by about a factor of 3, compared to the highest FoM SnIa dataset (C). We also find that the ranking sequence based on consistency with ΛCDM is identical with the corresponding ranking based on consistency with standard rulers ((S) most consistent, (D), (C), (E), (U), (G) least consistent). The ranking sequence of the datasets however changes when we consider the consistency with an expansion history corresponding to evolving dark energy (w0, w1) = (−1.4, 2) crossing the phantom divide line w = −1 (it is practically reversed to (G), (U), (E), (S), (D), (C)). The SALT2 and MLCS2k2 fitters are also compared and some peculiar features of the SDSS-II dataset when standardized with the MLCS2k2 fitter are pointed out. Finally, we construct a statistic to estimate the internal consistency of a collection of SnIa datasets. We find that even though there is good consistency among most samples taken from the above datasets, this consistency decreases significantly when the Gold06 (G) dataset is included in the sample.

We study the low-temperature limit of warm inflation in a hilltop model. This limit remains valid up to the end of inflation, allowing an analytic description of the entire inflationary stage. In the weak dissipative regime, if the kinetic density of the inflaton dominates after inflation, low scale inflation is attained with Hubble scale as low as 1 GeV. In the strong dissipative regime, the model satisfies the observational requirements for the spectral index with a mild tuning of the model parameters, while also overcoming the $\eta$-problem of inflation. However, there is some danger of gravitino overproduction unless the particle content of the theory is large.Comment: 9 pages, 2 figure

We solve analytically and numerically the generalized Einstein equations in scalar-tensor cosmologies to obtain the evolution of dark energy and matter linear perturbations. We compare our results with the corresponding results for minimally coupled quintessence perturbations. Our results for natural (O(1)) values of parameters in the Lagrangian which lead to a background expansion similar to ΛCDM are summarized as follows: 1. Scalar-Tensor dark energy density perturbations are amplified by a factor of about 10 4 compared to minimally coupled quintessence perturbations on scales less than about 1000h −1 Mpc (sub-Hubble scales). This amplification factor becomes even larger ( 10 6 ) for scales less than 100h −1 Mpc. On these scales dark energy perturbations constitute a fraction of about 10% compared to matter density perturbations. 2. Scalar-Tensor dark energy density perturbations are anti-correlated with matter linear perturbations on sub-Hubble scales. Thus clusters of galaxies are predicted to overlap with voids of dark energy. 3. This anti-correlation of matter with negative pressure perturbations induces a mild amplification of matter perturbations by about 10% on sub-Hubble scales. 4. The evolution of scalar field perturbations on sub-Hubble scales, is scale independent and therefore it corresponds to a vanishing effective speed of sound (csΦ = 0). It also involves large oscillations at early times induced by the amplified effective mass of the field. This mass amplification is due to the non-minimal coupling of the field to the Ricci curvature scalar and (therefore) to matter. No such oscillations are present in minimally coupled quintessence perturbations which are suppressed on sub-Hubble scales (csΦ = 1). We briefly discuss the observational implications of our results which may include predictions for galaxy and cluster halo profiles which are modified compared to ΛCDM . The observed properties of these profiles are known to be in some tension with the predictions of ΛCDM .PACS numbers: 98.80. Es,98.65.Dx,98.62.Sb

Quintessential inflation is studied using a string modulus as the inflaton -quintessence field. The modulus begins its evolution at the steep part of its scalar potential, which is due to non-perturbative effects (e.g. gaugino condensation). It is assumed that the modulus crosses an enhanced symmetry point (ESP) in field space. Particle production at the ESP temporarily traps the modulus resulting in a brief period of inflation. More inflation follows, due to the flatness of the potential, since the ESP generates either an extremum (maximum or minimum) or a flat inflection point in the scalar potential. Eventually, the potential becomes steep again and inflation is terminated. After reheating the modulus freezes due to cosmological friction at a large value, such that its scalar potential is dominated by contributions due to fluxes in the extra dimensions or other effects. The modulus remains frozen until the present, when it can become quintessence and account for the dark energy necessary to explain the observed accelerated expansion.