Cosmic Constraints Research Articles

Intermediate redshift calibration of gamma-ray bursts and cosmic constraints in non-flat cosmology

ABSTRACT We propose a new method to calibrate gamma-ray burst (GRB) correlations employing intermediate redshift data sets, instead of limiting to z ≃ 0 catalogues, and applied it to the well-consolidated Amati correlation. This model-independent calibration technique is based on the Bézier polynomial interpolation of the most updated observational Hubble data and baryonic acoustic oscillations (BAO) and alleviates de facto the well-known circularity problem affecting GRB correlations. In doing so, we also investigate the influence of the BAO scales rs, got from Planck results, and $r_{\rm s}^{\rm fid}$, got from the considered fiducial cosmology, by considering the cases $(r_{\rm s}/r_{\rm s}^{\rm fid})=1$ and $(r_{\rm s}/r_{\rm s}^{\rm fid})\ne 1$. We get constraints on the cosmic parameters, using Markov chain–Monte Carlo simulations, first fixing and then leaving free the spatial curvature density parameter Ωk. Compared to previous literature, we obtain tighter constraints on the mass density parameter Ωm. In particular, our findings turn out to be highly more compatible with those got from standard candle indicators within the Lambda cold dark matter paradigm. Finally, we critically re-examine the recent H0 tension in view of our outcomes.

Cosmic Gamma Ray Constraints on the Indirect Effects of Dark Matter

The observed anomalous excess of high-energy cosmic ray (CR) positrons is widely discussed as possible indirect evidence for dark matter (DM). However, any source of cosmic positrons is inevitably the source of gamma radiation. The least model dependent test of CR anomalies interpretation via DM particles decays (or annihilation) is connected with gamma-ray background due to gamma overproduction in such processes. In this work, we impose an observational constraint on gamma ray production from DM. Then, we study the possible suppression of gamma yield in the DM decays into identical final fermions. Such DM particles arise in the multi-component dark atom model. The influence of the interaction vertices on the gamma suppression was also considered. No essential gamma suppression effects are found. However, some minor ones are revealed.

Cosmic Constraints to the wCDM Model from Strong Gravitational Lensing**Supported by the National Natural Science Foundation of China under Grant No 11275035.

We study the cosmic constraint to the wCDM (cold dark matter with a constant equation of state w) model via 118 strong gravitational lensing systems which are compiled from SLACS, BELLS, LSD and SL2S surveys, where the ratio between two angular diameter distances Dobs = DA(zl, zs)/DA(0, zs) is taken as a cosmic observable. To obtain this ratio, we adopt two strong lensing models: one is the singular isothermal sphere model (SIS) and the other one is the power-law density profile (PLP) model. Via the Markov chain Monte Carlo method, the posterior distribution of the cosmological model parameters space is obtained. The results show that the cosmological model parameters are not sensitive to the parameterized forms of the power-law index γ. Furthermore, the PLP model gives a relatively tighter constraint to the cosmological parameters than that of the SIS model. The predicted value of Ωm = 0.31−0.24+0.44 by the SIS model is compatible with that obtained by Planck2015: Ωm = 0.313 ± 0.013. However, the value of Ωm = 0.15−0.11+0.13 based on the PLP model is smaller and has 1.25σ tension with that obtained by Planck2015.

A Time-DependentΛandGCosmological Model Consistent with Cosmological Constraints

The prevailing constantΛ-Gcosmological model agrees with observational evidence including the observed red shift, Big Bang Nucleosynthesis (BBN), and the current rate of acceleration. It assumes that matter contributes 27% to the current density of the universe, with the rest (73%) coming from dark energy represented by the Einstein cosmological parameterΛin the governing Friedmann-Robertson-Walker equations, derived from Einstein’s equations of general relativity. However, the principal problem is the extremely small value of the cosmological parameter (~10−52 m2). Moreover, the dark energy density represented byΛis presumed to have remained unchanged as the universe expanded by 26 orders of magnitude. Attempts to overcome this deficiency often invoke a variableΛ-Gmodel. Cosmic constraints from action principles require that either bothGandΛremain time-invariant or both vary in time. Here, we propose a variableΛ-Gcosmological model consistent with the latest red shift data, the current acceleration rate, and BBN, provided the split between matter and dark energy is 18% and 82%.Λdecreases (Λ~τ-2, whereτis the normalized cosmic time) andGincreases (G~τn) with cosmic time. The model results depend only on the chosen value ofΛat present and in the far future and not directly onG.

Revisiting the vacuum energy scenario from the renormalization group method of the QFT theory

In this paper the vacuum energy scenario (or time-dependent cosmological constant) from the renormalization group (RG) equation is studied. By considering the renormalization group scale described by the Hubble parameter, we apply the current observational data to constrain this RG dark energy model. Concretely, the different combinations of cosmic observational data, including the kinematical and the dynamical part, are investigated to constrain the RG model. For comparison we also consider the cosmic constraints on the dark model by taking the Ricci scalar as the renormalization group scale. In addition, we compare these two RG dark energy models with the cosmological constant.

An accelerated universe from Brans-Dicke theory in the Einstein frame

The current acceleration of the universe is not consistent with the theory of general relativity (GR). The substitutes of GR have been studied widely. One of them is the Brans-Dicke (BD) theory. Thereinto, most studies of BD theory are in the frame of Jordan representation. In this paper we investigate the accelerating cosmology from BD theory in the other frame, i.e. in the Einstein frame, where it indicates the interaction between the matter and the BD scalar field. We apply the Markov Chain Monte Carlo method to study the cosmic constraints on BD theory according to the current experiment data from the kinematical observations: the Union2 dataset of type supernovae Ia (SNIa) and the observational Hubble data (OHD), and the dynamical observations: the baryon acoustic oscillation (BAO), the cosmic microwave background (CMB) data, and the cluster X-ray gas mass fraction. It is shown that an expanded universe from deceleration to acceleration is given in this theory. And the constraint results on BD model parameters are β = −0.0067(±0.2268) −0.2372−0.4407 +0.2395+0.4168 , γ = 0.0237(±0.0342) −0.0329−0.0647 +0.0326+0.0715 , e = −0.0063(±0.0073) −0.0073−0.0130 +0.0072+0.0158 ; and the constraints values of some correlative cosmological parameters are the dimensionless matter density Ω 0m = 0.2853(±0.0132) −0.0133−0.0247 +0.0132+0.0262 , the cosmic age = 13.5699(±0.2398) −0.2374−0.4568 +0.2371+0.4806 Gyr, and the current Hubble parameter H 0 = 70.2623(±1.2695) −1.2675−2.5150 +1.2749+2.4532 .

Modified Chaplygin gas as a unified dark matter and dark energy model and cosmic constraints

A modified Chaplygin gas model (MCG), $\rho_{MCG}/\rho_{MCG0}=[B_{s}+(1-B_{s})a^{-3(1+B)(1+\alpha)}]^{1/(1+\alpha)}$, as a unified dark matter model and dark energy model is constrained by using current available cosmic observational data points which include type Ia supernovae, baryon acoustic oscillation and the seventh year full WMAP data points. As a contrast to the consideration in the literatures, we {\it do not} separate the MCG into two components, i.e. dark mater and dark energy component, but we take it as a whole energy component-a unified dark sector. By using Markov Chain Monte Carlo method, a tight constraint is obtained: $\alpha= 0.000727_{- 0.00140- 0.00234}^{+ 0.00142+ 0.00391}$, $B=0.000777_{- 0.000302- 0.000697}^{+ 0.000201+ 0.000915}$ and $B_s= 0.782_{- 0.0162- 0.0329}^{+ 0.0163+ 0.0307}$ .}

Unified dark fluid with constant adiabatic sound speed and cosmic constraints

As is known above 90% of the energy content in Universe is made of unknown dark component. Usually this dark fluid is separated into two parts: dark matter and dark energy. However, it may be a mixture of these two energy components, or just one exotic unknown fluid. This property is dubbed as dark degeneracy. With this motivation, in this paper, a unified dark fluid having constant adiabatic sound speed $c_s^2=\alpha$, which is in the range $[0,1]$, is studied. At first, via the energy conservation equation, its energy density, $\rho_d/\rho_{d0}=(1-B_s)+B_s a^{-3(1+\alpha)}$ where $B_s$ is related to integration constant from energy conservation equation as another model parameter, is presented. Then by using Markov Chain Monte Carlo method with currently available cosmic observational data sets which include type Ia supernova Union 2, baryon acoustic oscillation and WMAP 7-year data of cosmic background radiation, we show that small values of $\alpha$ are favored in this unified dark fluid model. Furthermore, we show that smaller values of $\alpha<10^{-5}$ are required to match matter (baryon) power spectrum from SDSS DR7.

MATTER INSTABILITIES IN GENERAL GAUSS-BONNET GRAVITY

We study the evolution of cosmological perturbations in [Formula: see text] gravity, where the Lagrangian is the sum of a Ricci scalar R and an arbitrary function f in terms of a Gauss-Bonnet term [Formula: see text]. We derive the equations for perturbations assuming matter to be described by a perfect fluid with a constant equation of state w. We show that density perturbations in perfect fluids exhibit negative instabilities during both the radiation and the matter domination, irrespective of the form of [Formula: see text]. This growth of perturbations gets stronger on smaller scales, which is difficult to be compatible with the observed galaxy spectrum unless the deviation from General Relativity is very small. Thus [Formula: see text] cosmological models are effectively ruled out from this Ultra-Violet instability, even though they can be compatible with the late-time cosmic acceleration and local gravity constraints.

TIME VARIABLE COSMOLOGICAL CONSTANT FROM RENORMALIZATION GROUP EQUATIONS

In this paper, a time variable cosmological constant (CC) from renormalization group equations (RGEs) is explored, where the renormalization scales μ2 = Ḣ + 2H2 and μ2 = - Ḣ are taken respectively. The cosmological parameters, such as dimensionless energy density, deceleration parameter and effective equation of state of CC etc., are derived. Also, the cosmic observational constraints are implemented to test the model's consistency. The results show that it is compatible with cosmic data. So, it would be a viable dark energy model.

Cosmic constraints rule out s-wave annihilation of light dark matter

Light dark matter annihilating into electron-positron pairs emits a significant amount of internal bremsstrahlung that may contribute to the cosmic gamma-ray background. The amount of emitted gamma-rays depends on the dark matter clumping factor. Recent calculations indicate that this value should be of order ${10}^{6}\ensuremath{-}{10}^{7}$. That allows us to calculate the expected gamma-ray background contribution from dark matter annihilation. We find that the light dark matter model can be ruled out if a constant thermally-averaged cross section is assumed (s-wave annihilation). For more massive dark matter candidates like neutralinos, however, cosmic constraints are weaker.

Semi-analytic modelling of galaxy evolution in the IR/submm range

This paper proposes a new semi-analytic modelling of galaxy properties in the IR/submm wavelength range, which is explicitly set in a cosmological framework. This type of approach has had some success in reproducing the optical properties of galaxies. We hereafter propose a simple extension to the IR/submm range. We estimate the IR/submm luminosities of ``luminous UV/IR galaxies'', and we explore how much star formation could be hidden in heavily--extinguished, ``ultraluminous IR galaxies'' by designing a family of evolutionary scenarios which are consistent with the current status of the ``cosmic constraints'', as well as with the IRAS luminosity function and faint counts, but with different high-z IR luminosity densities. However, these scenarios generate a Cosmic Infrared Background whose spectrum falls within the range of the isotropic IR component detected by Puget et al. (1996) and revisited by Guiderdoni et al. (1997). We give predictions for the faint galaxy counts and redshift distributions at IR and submm wavelengths. The submm range is very sensitive to the details of the evolutionary scenarios. As a result, the on-going and forthcoming observations with ISO and SCUBA (and later with SIRTF, SOFIA, FIRST and PLANCK) will put strong constraints on the evolution of galaxies at z=1 and beyond.

The extinction of starlight revisited

The rigorous Kerker-Matijevic formulae for light scattering by co-axial double cylinders are used to calculate the extinction properties of hollow organic grains. A size distribution of such particles together with iron whiskers of radii 0.01 μm, silica spheres of radius 0.03 μm and free aromatic molecular clusters comprised of 50–100 atoms yield excellent agreement with data on the extinction of starlight. The mass ratios of silica to organics and of iron to organics are in good accord with cosmic abundance constraints.