Bigger Rip with no dark energy
By studying a modified Friedmann equation which arises in an extension of general relativity which accommodates a time-dependent fundamental length L ( t ), we consider cosmological models where the scale factor diverges with an essential singularity at a finite future time. Such models have no dark energy in the conventional sense of energy possessing a simple pressure–energy relationship. Data on supernovae restrict the time from the present until the Rip to be longer than the current age of the Universe.

title: Isocurvature fluctuations in tracker quintessence models
abstract: We consider effects of the isocurvature perturbation in the framework of the tracker-type quintessence models. During the inflation, fluctuations in the amplitude of the quintessence field are generated, which provide isocurvature component of the cosmic density perturbation. Contrary to the conventional notion, it is shown that effects of the isocurvature fluctuation may become sizable in some cases, and in particular, the cosmic microwave background angular power spectrum may be significantly enhanced due to the effect of the isocurvature mode. Such an enhancement may be detectable in on-going and future experiments.

title: CMB constraint on non-Gaussianity in isocurvature perturbations
abstract: We study the CMB constraints on non-Gaussianity in CDM isocurvature perturbations. Non-Gaussian isocurvature perturbations can be produced in various models at the very early stage of the Universe. Since the isocurvature perturbations little affect the structure formation at late times, CMB is the best probe of isocurvature non-Gaussianity at least in the near future. In this paper, we focus on non-Gaussian curvature and isocurvature perturbations of the local-type, which are uncorrelated and in the form ζ = ζ{sub G}+(3/5)f{sub NL}(ζ{sub G}{sup 2}−(ζ{sub G}{sup 2})) and S = S{sub G}+f{sub NL}{sup (ISO)}(S{sub G}−(S{sub G}{sup 2})), and constrain the non-linearity parameter of isocurvature perturbations, f{sub NL}{sup (ISO)}, as well as the curvature one f{sub NL}. For this purpose, we employ several state-of-art techniques for the analysis of CMB data and simulation. Assuming that isocurvature perturbations are subdominant, we apply our method to the WMAP 7-year data of temperature anisotropy and obtain constraints on a combination α{sup 2}f{sub NL}{sup (ISO)}, where α is the ratio of the power spectrum of isocurvature perturbations to that of the adiabatic ones. When the adiabatic perturbations are assumed to be Gaussian, we obtained a constraint α{sup 2}f{sub NL}{sup (ISO)} = 40±66 assuming the power spectrum of isocurvaturemore » perturbations is scale-invariant. When we assume that the adiabatic perturbations can also be non-Gaussian, we obtain f{sub NL} = 38±24 and α{sup 2}f{sub NL}{sup (ISO)} = −8±72. We also discuss implications of our results for the axion CDM isocurvature model.« less

title: Correlated Isocurvature Fluctuation of Quintessence and Curvaton Scenario
abstract: We consider cosmic microwave background (CMB) anisotropy in models with quintessence taking into account of isocurvature fluctuation in the quintessence. It is shown that, if the primordial fluctuation of the quintessence has a correlation with the adiabatic density fluctuations, CMB angular power spectrum $C_l$ at low multipoles can be suppressed. Possible scenario of generating correlated mixture of the quintessence and adiabatic fluctuations is also discussed.

title: Spectator field models in light of spectral index after Planck
abstract: We revisit spectator field models including curvaton and modulated reheating scenarios, specifically focusing on their viability in the new Planck era, based on the derived expression for the spectral index in general spectator field models. Importantly, the recent Planck observations give strong preference to a red-tilted power spectrum, while the spectator field models tend to predict a scale-invariant one. This implies that, during inflation, either (i) the Hubble parameter varies significantly as in chaotic inflation, or (ii) a scalar potential for the spectator field has a relatively large negative curvature. Combined with the tight constraint on the non-Gaussianity, the Planck data provides us with rich implications for various spectator field models.

title: Non-Gaussianity and baryonic isocurvature fluctuations in the curvaton scenario
abstract: We discuss non-Gaussianity and baryonic isocurvature fluctuations in the curvaton scenario, assuming that the baryon asymmetry of the universe originates only from the decay products of the inflaton. When large non-Gaussianity is realized in such a scenario, non-vanishing baryonic isocurvature fluctuations can also be generated unless the baryogenesis occurs after the decay of the curvaton. We calculate the non-linearity parameter f NL and the baryonic isocurvature fluctuations, taking account of the primordial fluctuations of both the inflaton and the curvaton. We show that, although current constraints on isocurvature fluctuations are severe, the non-linearity parameter can be large as f NL ∼ O ( 10 – 100 ) without conflicting with the constraints.

title: Homotopy operators and identity-based solutions in cubic superstring field theory
abstract: We construct a class of nilpotent operators using the BRST current and ghost fields in superstring theory. The operator can be realized in cubic superstring field theory as a kinetic operator in the background of an identity-based solution. For a particular type of the deformed BRST operators, we find a homotopy operator and discuss its relationship to the cohomology in a similar way to the bosonic case, which has been elaborated by the authors.

title: Numerical solutions of open string field theory in marginally deformed backgrounds
abstract: We investigate numerical solutions of bosonic open string field theory in some marginally deformed backgrounds, which are obtained by expanding the action around an identity-based marginal solution with one parameter. We construct numerical solutions in the Siegel gauge and the Landau gauge corresponding to the tachyon vacuum. Their vacuum energy approximately cancels the D-brane tension for larger intervals of the parameter with increasing truncation level. The result is consistent with the previous expectation that the identity-based marginal solution has vanishing energy regardless of the values of the parameter. We also study the marginal branch (M-branch) and the vacuum branch (V-branch) and evaluate not only the vacuum energy but also the gauge invariant overlaps with the graviton and the closed tachyon. We observe that there is a finite bound for the value of the massless field of numerical solutions even in the marginally deformed background.

title: Marginal deformations and classical solutions in open superstring field theory
abstract: We construct a class of classical solutions in the Berkovits' open superstring field theory. The resulting solutions correspond to marginal boundary deformations in conformal field theory. The vacuum energy vanishes exactly for the solutions. Investigating the theory expanded around one of the solutions, we find that it reflects the effect of background Wilson lines. The solution has a well-defined Fock space expression and it is invariant under space-time supersymmetry transformation.

title: On nontrivial solutions around a marginal solution in cubic superstring field theory
abstract: A bstractWe construct tachyon vacuum and half-brane solutions, using an extension of KBc algebra, in the theory around a type of identity-based marginal solutions in modified cubic superstring field theory. With explicit computations, we find that their vacuum energies are the same as those of corresponding solutions around the original theory. It implies that the vacuum energy for the identity-based marginal solution vanishes although straightforward computation of it is subtle. We also evaluate the gauge invariant overlaps for those nontrivial solutions. The values for them are deformed according to the marginal solution in the same way as the case of bosonic string field theory.

title: Observables for identity-based tachyon vacuum solutions
abstract: We consider a modified KBc algebra in bosonic open string field theory expanded around identity-based scalar solutions. By use of the algebra, classical solutions on the background are constructed and observables for them, including energy densities and gauge invariant overlaps, are calculable. These results are applied to evaluate observables analytically for both of the identity-based trivial pure gauge solution and the identity-based tachyon vacuum solution.