Matching WMAP 3-yrs results with the Cosmological Slingshot Primordial Spectrum

We consider a recently proposed scenario for the generation of primordial cosmological perturbations, the so called Cosmological Slingshot scenario. We firstly obtain a general expression for the Slingshot primordial power spectrum which extends previous results by including a blue pre-bounce residual contribution at large scales. Starting from this expression we numerically compute the CMB temperature and polarization power spectra arising from the Slingshot scenario and show that they excellently match the standard WMAP 3-years best-fit results. In particular, if the residual blue spectrum is far above the largest WMAP observed scale, the Slingshot primordial spectrum fits the data well by only fixing its amplitude and spectral index at the pivot scale k_p=10^{-3}h x Mpc^{-1}. We finally show that all possible distinctive Slingshot signatures in the CMB power spectra are confined to very low multipoles and thus very hard to detect due to large cosmic variance dominated error bars at these scales.Comment: 9 pages, 4 figures; v3 clarifications added, version accepted for publication in Gen. Rel. Grav. 200

Curvature perturbation spectrum from false vacuum inflation

In the inflationary cosmology it occurs frequently that the inflaton field is trapped in a local, transient minimum with non-zero vacuum energy. The difficulty regarding the curvature perturbation produced during such a stage is that classically the inflaton does not move so that the comoving hypersurfaces are not well defined at linear order in the scalar field perturbation. In this paper, assuming a mechanism of trapping which resembles a high temperature correction to the potential, we explicitly calculate for the first time the resulting power spectrum of the curvature perturbation by evaluating the quantum two-point correlation function directly. The spectrum is steeply blue with the spectral index n_R = 4.Comment: (v1) 17 pages, no figure; (v2) 18 pages, more clarifications and discussions added, to appear in JCA

Conditions for Successful Extended Inflation

We investigate, in a model-independent way, the conditions required to obtain a satisfactory model of extended inflation in which inflation is brought to an end by a first-order phase transition. The constraints are that the correct present strength of the gravitational coupling is obtained, that the present theory of gravity is satisfactorily close to general relativity, that the perturbation spectra from inflation are compatible with large scale structure observations and that the bubble spectrum produced at the phase transition doesn't conflict with the observed level of microwave background anisotropies. We demonstrate that these constraints can be summarized in terms of the behaviour in the conformally related Einstein frame, and can be compactly illustrated graphically. We confirm the failure of existing models including the original extended inflation model, and construct models, albeit rather contrived ones, which satisfy all existing constraints.Comment: 8 pages RevTeX file with one figure incorporated (uses RevTeX and epsf). Also available by e-mailing ARL, or by WWW at http://star-www.maps.susx.ac.uk/papers/infcos_papers.html; Revised to include extra references, results unchanged, to appear Phys Rev

Power Spectrum in Krein Space Quantization

The power spectrum of scalar field and space-time metric perturbations produced in the process of inflation of universe, have been presented in this paper by an alternative approach to field quantization namely, Krein space quantization [1,2]. Auxiliary negative norm states, the modes of which do not interact with the physical world, have been utilized in this method. Presence of negative norm states play the role of an automatic renormalization device for the theory.Comment: 8 pages, appear in Int. J. Theor. Phy

Observational constraints on braneworld chaotic inflation

We examine observational constraints on chaotic inflation models in the Randall-Sundrum Type II braneworld. If inflation takes place in the high-energy regime, the perturbations produced by the quadratic potential are further from scale-invariance than in the standard cosmology, in the quartic case more or less unchanged, while for potentials of greater exponent the trend is reversed. We test these predictions against a data compilation including the WMAP measurements of microwave anisotropies and the 2dF galaxy power spectrum. While in the standard cosmology the quartic potential is at the border of what the data allow and all higher powers excluded, we find that in the high-energy regime of braneworld inflation even the quadratic case is under strong observational pressure. We also investigate the intermediate regime where the brane tension is comparable to the inflationary energy scale, where the deviations from scale-invariance prove to be greater.Comment: 5 pages RevTeX4 file with three figures incorporated. Minor changes to match version accepted by Physical Review

Primordial black hole production due to preheating

During the preheating process at the end of inflation the amplification of field fluctuations can lead to the amplification of curvature perturbations. If the curvature perturbations on small scales are sufficiently large, primordial black holes (PBHs) will be overproduced. In this paper we study PBH production in the two-field preheating model with quadratic inflaton potential. We show that for many values of the inflaton mass m, and coupling g, small scale perturbations will be amplified sufficiently, before backreaction can shut off preheating, so that PBHs will be overproduced during the subsequent radiation dominated era.Comment: 5 pages, 3 eps figures. Minor changes to match version to appear in PRD as a rapid communicatio

The Tensor to Scalar Ratio of Phantom Dark Energy Models

We investigate the anisotropies in the cosmic microwave background in a class of models which possess a positive cosmic energy density but negative pressure, with a constant equation of state w = p/rho < -1. We calculate the temperature and polarization anisotropy spectra for both scalar and tensor perturbations by modifying the publicly available code CMBfast. For a constant initial curvature perturbation or tensor normalization, we have calculated the final anisotropy spectra as a function of the dark energy density and equation of state w and of the scalar and tensor spectral indices. This allows us to calculate the dependence of the tensor-to-scalar ratio on w in a model with phantom dark energy, which may be important for interpreting any future detection of long-wavelength gravitational waves.Comment: 5 pages, 4 figure

CMB Power Spectrum from Noncommutative Spacetime

Very recent CMB data of WMAP offers an opportunity to test inflation models, in particular, the running of spectral index is quite new and can be used to rule out some models. We show that an noncommutative spacetime inflation model gives a good explanation of these new results. In fitting the data, we also obtain a relationship between the noncommutative parameter (string scale) and the ending time of inflation.Comment: 8 pages, 2 figures; v2: refs. added and minor corrections; v3: further minor correctio

Inflation in Gauged 6D Supergravity

In this note we demonstrate that chaotic inflation can naturally be realized in the context of an anomaly free minimal gauged supergravity in D=6 which has recently been the focus of some attention. This particular model has a unique maximally symmetric ground state solution, $R^{3,1} \times S^2$ which leaves half of the six-dimensional supersymmetries unbroken. In this model, the inflaton field $\phi$ originates from the complex scalar fields in the D=6 scalar hypermultiplet. The mass and the self couplings of the scalar field are dictated by the D=6 Lagrangian. The scalar potential has an absolute munimum at $\phi = 0$ with no undetermined moduli fields. Imposing a mild bound on the radius of $S^2$ enables us to obtain chaotic inflation. The low eenrgy equations of motion are shown to be consistent for the range of scalar field values relevant for inflation.Comment: one reference adde

Effects of f(R) Model on the Dynamical Instability of Expansionfree Gravitational Collapse

Dark energy models based on f(R) theory have been extensively studied in literature to realize the late time acceleration. In this paper, we have chosen a viable f(R) model and discussed its effects on the dynamical instability of expansionfree fluid evolution generating a central vacuum cavity. For this purpose, contracted Bianchi identities are obtained for both the usual matter as well as dark source. The term dark source is named to the higher order curvature corrections arising from f(R) gravity. The perturbation scheme is applied and different terms belonging to Newtonian and post Newtonian regimes are identified. It is found that instability range of expansionfree fluid on external boundary as well as on internal vacuum cavity is independent of adiabatic index $\Gamma$ but depends upon the density profile, pressure anisotropy and f(R) model.Comment: 26 pages, no figure. arXiv admin note: text overlap with arXiv:1108.266