Supernova Type Ia Observations Research Articles

On the cosmic distance duality relation and strong gravitational lens power law density profile

Many new strong gravitational lensing (SGL) systems have been discovered in the last two decades with the advent of powerful new space and ground-based telescopes. The effect of the lens mass model (usually the power-law mass model) on cosmological parameters constraints has been performed recently in literature. In this paper, by using SGL systems and Supernovae type Ia observations, we explore if the power-law mass density profile (ρ ∝ r-γ) is consistent with the cosmic distance duality relation (CDDR), DL (1+z)-2/DA = η(z) = 1, by considering different lens mass intervals. It has been obtained that the verification of the CDDR validity is significantly dependent on lens mass interval considered: the sub-sample with σap ≥ 300 km/s (where σap is the lens apparent stellar velocity dispersion) is in full agreement with the CDDR validity, the sub-sample with intermediate σap values (200 ≤ σap < 300) km/s is marginally consistent with η = 1 and, finally, the sub-sample with low σap values (σap < 200 km/s) ruled out the CDDR validity with high statistical confidence. Therefore, if one takes the CDDR as guarantee, our results suggest that using a single density profile is not suitable to describe lens with low σap values and it is only an approximate description to lenses with intermediate mass interval.

Observational constraints on one-parameter dynamical dark-energy parametrizations and the H0 tension

The phenomenological parametrizations of dark-energy (DE) equation of state can be very helpful, since they allow for the investigation of its cosmological behavior despite the fact that its underlying theory is unknown. However, although there has been a large amount of research on DE parametrizations which involve two or more free parameters, the one-parameter parametrizations seem to be underestimated. We perform a detailed observational confrontation of five one-parameter DE models, with observational data from cosmic microwave background (CMB), Joint light-curve analysis sample from Supernovae Type Ia observations (JLA), baryon acoustic oscillations (BAO) distance measurements, and cosmic chronometers (CC). We find that all models favor a phantom DE equation of state at present time, while they lead to $H_0$ values in perfect agreement with its direct measurements and therefore they offer an alleviation to the $H_0$-tension. Finally, performing a Bayesian analysis we show that although $\Lambda$CDM cosmology is still favored, one-parameter DE models have similar or better efficiency in fitting the data comparing to two-parameter DE parametrizations, and thus they deserve a thorough investigation.

Projected distances to host galaxy reduce SNIa dispersion

We use multi-band imagery data from the Sloan Digital Sky Survey (SDSS) to measure projected distances of 302 supernova type Ia (SNIa) from the centre of their host galaxies, normalized to the galaxy's brightness scale length, with a Bayesian approach. We test the hypothesis that SNIas further away from the centre of their host galaxy are less subject to dust contamination (as the dust column density in their environment is smaller) and/or come from a more homogeneous environment. Using the Mann-Whitney U test, we find a statistically significant difference in the observed colour correction distribution between SNIas that are near and those that are far from the centre of their host. The local p-value is 3 x 10^{-3}, which is significant at the 5 per cent level after look-elsewhere effect correction. We estimate the residual scatter of the two subgroups to be 0.073 +/- 0.018 for the far SNIas, compared to 0.114 +/- 0.009 for the near SNIas -- an improvement of 30 per cent, albeit with a low statistical significance of 2sigma. This confirms the importance of host galaxy properties in correctly interpreting SNIa observations for cosmological inference.

Effect of dark energy on cosmological parameters with LVDP in lyra manifold

ABSTRACT We have constructed a model in Lyra manifold and time varying cosmological constant with perfect fluid using LVDP (Linear Varying Deceleration Parameter). Bianchi type-III metric is used as source of investigation. To get a deterministic solution of the field equation the expansion scalar (θ) is considered as proportional to the shear scalar (σ). The cosmological constant is found to be positive which satisfies the result obtained by supernova Type-Ia Observations [1999]. Here we analyse the behaviour of pressure and deceleration parameter by using different form of dark energy(DE). In addition to it, some physical and geometrical properties of the solutions are studied.

Correction to: Constraints on Janus Cosmological model from recent observations of supernovae type Ia

Correction to: Astrophys Space Sci (2018) 363:139 The original article has been updated for copyright reasons with Fig. 1 and a too vague formulation intended to give credit to Farnes (2017) for the originally displayed figure. The sentences “JCM explains the confinement of galaxies and their flat rotation curves, as recently showed by Farnes (2017), see Fig. 1. Mysterious dark matter is no longer required, while the mainstream model does.” have been replaced by “JCM explains the confinement of galaxies and the shape of their rotation curves. As we showed in Petit et al. (2001), if one introduces a surrounding repellent negative matter environment, it gives larger rotation velocities at distance, see Fig. 1. Mysterious dark matter is no longer required, while the mainstream model does.” Figure 1 has been replaced. The figure caption of the earlier Fig. 1 has been replaced by “ Circular velocity, after Petit et al. (2001). This can be compared with results from numerical simulations by Farnes (2017)” The original article has been corrected.

Constraints on Janus Cosmological model from recent observations of supernovae type Ia

From our exact solution of the Janus Cosmological equation we derive the relation of the predicted magnitude of distant sources versus their red shift. The comparison, through this one free parameter model, to the available data from 740 distant supernovae shows an excellent fit.

Dark matter with two- and many-body decays and supernovae type Ia

We present a decaying dark matter scenario where the daughter products are a single massless relativistic particle and a single, massive but possibly relativistic particle. We calculate the velocity distribution of the massive daughter particle and its associated equation of state and derive its dynamical evolution in an expanding universe. In addition, we present a model of decaying dark matter where there are many massless relativistic daughter particles together with a massive particle at rest. We place constraints on these two models using supernovae type Ia observations. We find that for a daughter relativistic fraction of 1% and higher, lifetimes of at least less than 10 Gyrs are excluded, with larger relativistic fractions constraining longer lifetimes.

Quintessence: a review

Quintessence is a canonical scalar field introduced to explain the late-time cosmic acceleration. The cosmological dynamics of quintessence is reviewed, paying particular attention to the evolution of the dark energy equation of state w. For the field potentials having tracking and thawing properties, the evolution of w can be known analytically in terms of a few model parameters. Using the analytic expression of w, we constrain quintessence models from the observations of supernovae type Ia, cosmic microwave background and baryon acoustic oscillations. The tracking freezing models are hardly distinguishable from the Λ-cold-dark-matter model, whereas in thawing models the today's field equation of state is constrained to be w0 < −0.7 (95% CL). We also derive an analytic formula for the growth rate of matter density perturbations in dynamical dark energy models, which allows a possibility of putting further bounds on w from the measurement of redshift-space distortions in the galaxy power spectrum. Finally, we review particle physics models of quintessence—such as those motivated by supersymmetric theories. The field potentials of thawing models based on a pseudo-Nambu–Goldstone boson or extended supergravity theories have a nice property that a tiny mass of quintessence can be protected against radiative corrections.

String cosmology in Bianchi type-VI0 dusty Universe with electromagnetic field

In this paper, the effect of electromagnetic field in the string Bianchi type-VI0 Universe is investigated. Einstein’s field equations have been solved exactly with suitable physical assumptions for two types of strings: (i) massive strings and (ii) Nambu strings. It is found that when the Universe is dominated by massive strings, the existence of electromagnetic field is necessary as it accelerates the expansion of the Universe. But when our Universe is dominated by Nambu strings, the electromagnetic field does not have significant effect on the evolution of the Universe. We have also shown that the early massive string-dominated Universe got converted to Nambu string-dominated Universe later. Our models are derived from an early deceleration phase to an accelerating phase which is consistent with the recent observations of supernovae type-Ia. The physical and geometrical behaviour of these models are also discussed.

Cosmological parameters constraints from galaxy cluster mass function measurements in combination with other cosmological data

We present the cosmological parameters constraints obtained from the combination of galaxy cluster mass function measurements (Vikhlinin et al. 2009a, 2009b) with new cosmological data obtained during last three years: updated measurements of cosmic microwave background anisotropy with Wilkinson Microwave Anisotropy Probe (WMAP) observatory, and at smaller angular scales with South Pole Telescope (SPT), new Hubble constant measurements, baryon acoustic oscillations and supernovae Type Ia observations. New constraints on total neutrino mass Σm ν and effective number of neutrino species are obtained. In models with free number of massive neutrinos the constraints on these parameters are notably less strong, and all considered cosmological data are consistent with non-zero total neutrino mass Σm ν ≈ 0.4 eV and larger than standard effective number of neutrino species, N eff ≈ 4. These constraints are compared to the results of neutrino oscillations searches at short baselines. The updated dark energy equation of state parameter constraints are presented. We show that taking in account systematic uncertanties, current cluster mass funstion data provide similarly powerful constraints on dark energy equation of state, as compared to the constraints from supernovae Type Ia observations.

String cosmology in LRS Bianchi type-II dusty Universe with time-decaying vacuum energy density Λ

A model of a cloud formed by massive strings is used as a source of LRS Bianchi type II with time decaying vacuum energy density $\Lambda$. To construct string cosmological models we have used the energy-momentum tensor for such string as formulated by Letelier (1983). The high nonlinear field equations have been solved for two types of strings, (i) Massive string and (ii) Nambu string. The expansion $\theta$ in the model is assumed to be proportional to the shear $\sigma$. This condition leads to $A=\beta B^{m}$, where $A$ and $B$ are the metric coefficients, $m$ is a constant and $\beta$ is an integrating constant. Our models are in accelerating phase which is consistent to the recent observations of supernovae type Ia. The physical and geometrical behavior of these models are also discussed.

Non-minimally coupled [formula omitted] cosmology

We investigate the consequences of non-minimal gravitational coupling to matter and study how it differs from the case of minimal coupling by choosing certain simple forms for the nature of coupling. The values of the parameters are specified at z=0 (present epoch) and the equations are evolved backwards to calculate the evolution of cosmological parameters. We find that the Hubble parameter evolves more slowly in non-minimal coupling case as compared to the minimal coupling case. In both the cases, the universe accelerates around present time, and enters the decelerating regime in the past. Using the latest Union2 dataset for supernova Type Ia observations as well as the data for baryon acoustic oscillation (BAO) from SDSS observations, we constraint the parameters of Linder exponential model in the two different approaches. We find that there is an upper bound on model parameter in minimal coupling. But for non-minimal coupling case, there is range of allowed values for the model parameter.

WMAP constraints on low redshift evolution of dark energy

Abstract The conceptual difficulties associated with a cosmological constant have led to the investigation of alternative models in which the equation of state parameter, w=p/ρ, of the dark energy evolves with time. We show that combining the supernova type Ia observations with the constraints from WMAP observations restricts large variation of ρ(z) at low redshifts. The combination of these two observational constraints is stronger than either one. The results are completely consistent with the cosmological constant as the source of dark energy.

Cosmological model with macroscopic spin fluid

We consider a Friedmann-Roberston-Walker cosmological model with some exotic perfect fluid with spin known as the Weyssenhoff fluid. The possibility that the dark energy may be described in part by the Weyssenhoff fluid is discussed. The observational constraint coming from supernovae type Ia observations is established. This result indicates that, whereas the cosmological constant is still needed to explain current observations, the model with a spin fluid is admissible. For high redshifts $z&gt;1$ the differences between the model with spin fluid and the cold dark matter model with a cosmological constant become detectable observationally for the flat case with ${\ensuremath{\Omega}}_{\mathrm{m},0}=0.3.$ From the maximum likelihood method we obtain the value of ${\ensuremath{\Omega}}_{\mathrm{s},0}=0.004\ifmmode\pm\else\textpm\fi{}0.016.$ This gives us the limit ${\ensuremath{\Omega}}_{\mathrm{s},0}&gt;\ensuremath{-}0.012$ at the $1\ensuremath{\sigma}$ level. While the model with ``brane effects'' is preferred by the supernovae Ia data, the model with a spin fluid is statistically admissible. For comparison, the limit on the spin fluid coming from cosmic microwave background anisotropies is also obtained. The uncertainties in the location of a first peak give the interval $\ensuremath{-}1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}&lt;{\ensuremath{\Omega}}_{\mathrm{s},0}&lt;\ensuremath{-}{10}^{\ensuremath{-}10}.$ From big bang nucleosynthesis we obtain the strongest limit, ${\ensuremath{\Omega}}_{\mathrm{s},0}\ensuremath{\gtrsim}\ensuremath{-}{10}^{\ensuremath{-}20}.$ The interconnection between the model considered and brane models is also pointed out.

Are domain walls ruled out?

Recent analysis of the combined data of cosmic microwave background, galaxy clustering and supernovae type Ia observations have set strong constraints on the equation of state parameter w X . The upper bound w X <−0.82 at 95% c.l. rules out an important class of models, the domain walls (−2/3< w X <−1/3). Here we revisit the issue of domain walls as a possible alternative to the standard Λ-CDM model by questioning the assumptions made in the choice of priors of the data analysis. The results of our investigation show that domain walls can provide a good fit to the WMAP data for a different choice of priors with “lower” values of the Hubble parameter ( h<0.65), (as indicated by Sunyaev–Zeldovich and time delays for gravitational lensing observations), and “higher” values of the matter density ( Ω m >0.35 ), (in agreement with recent measurements of the temperature–luminosity relation of distant clusters observed with the XMM-Newton satellite). In this new perspective, the existence of domain walls would lead to important implications for CMB constraints on cosmological and on inflationary parameters.

Evolution of perturbations in a domain wall cosmology

A fluid of domain walls may have an effective equation of state p w = -<img id="_x0000_i1026" src="../../../img/revistas/bjp/v33n4/a39img01.gif" align=absbottom>rhow. This equation of state is qualitatively in agreement with the supernova type Ia observations. We exploit a cosmological model where the matter content is given by a dust fluid and a domain wall fluid. The process of formation of galaxies is essentially preserved. On the other hand, the behaviour of the density contrast in the ordinary fluid is highly altered when domain walls begin to dominate the matter content of the Universe. This domain wall phase occurs at relative recent era, and its possible consequences are discussed, specially concerning the Sachs-Wolfe effect.

QUINTESSENCE AND COSMIC ACCELERATION

A cosmological model with perfect fluid and self-interacting quintessence field is considered in the framework of the spatially flat Friedmann–Robertson–Walker (FRW) geometry. By assuming that all physical quantities depend on the volume scale factor of the Universe, the general solution of the gravitational field equations can be expressed in an exact parametric form, with the volume taken as the parameter, and with the quintessence field as a free parameter. With an appropriate choice of the scalar field a class of exact parametric solutions is obtained, with an exponential type scalar field potential fixed via the gravitational field equations. The general physical behavior of the model is consistent with the recent cosmological scenario favored by supernova type Ia observations, indicating an accelerated expansion of the Universe.