Supernova Cosmology Project Research Articles

FRW cosmology in f(Q,T) gravity

In this paper, we considered the study of Friedmann–Robertson–Walker (FRW) model in the framework of [Formula: see text] gravity, an extension of symmetric teleparallel gravity, recently defined by Xu et al. [[Formula: see text] gravity, Eur. Phys. J. C 79 (2019) 708]. The nonlinear model [Formula: see text], where [Formula: see text] and [Formula: see text] are constants, is taken into account. The equation of state of perfect fluid is assumed and 31 points of Hubble data are used to constrain the value of model parameter. To explore the evolution of the universe, the numerical solutions of cosmological implications, such as Hubble parameter, deceleration parameter, apparent magnitude and luminosity distance, are determined and the energy conditions are examined. The theoretical results of Hubble parameter are compared with [Formula: see text]CDM model. Further, 57 Supernova data (42 from Supernova cosmology project and 15 from Calán/Tolono supernova survey) are also used to have consistent results of apparent magnitude and luminosity distance.

Estimation of cosmological parameters, stability analysis and energy conditions in viable modified gravity

In the present paper, we have investigated the Friedmann-Robertson-Walker (FRW) model in viable f(R, T) gravity with f(R, T) function proposed as f(R,T)=R+ξT1/2, where ξ is an arbitrary constant, R is the scalar curvature and T is the trace of stress energy tensor. Defining the scale factor, the field equations are solved numerically and the energy conditions are analyzed. Further, determining Hubble parameter and deceleration parameter, their present values are estimated. Furthermore, 57 redshift data (42 redshift data from Supernova Cosmology project and 15 redshift data from Calán/ Tolono Supernova survey) are used to estimate the age of the universe and to find the best fit curves for luminosity distance and apparent magnitude.

See Change: VLT spectroscopy of a sample of high-redshift Type Ia supernova host galaxies

ABSTRACT The Supernova Cosmology Project has conducted the ‘See Change’ programme, aimed at discovering and observing high-redshift (1.13 ≤ z ≤ 1.75) Type Ia supernovae (SNe Ia). We used multifilter Hubble Space Telescope (HST) observations of massive galaxy clusters with sufficient cadence to make the observed SN Ia light curves suitable for a cosmological probe of dark energy at z > 0.5. This See Change sample of SNe Ia with multi-colour light curves will be the largest to date at these redshifts. As part of the See Change programme, we obtained ground-based spectroscopy of each discovered transient and/or its host galaxy. Here, we present Very Large Telescope (VLT) spectra of See Change transient host galaxies, deriving their redshifts, and host parameters such as stellar mass and star formation rate. Of the 39 See Change transients/hosts that were observed with the VLT, we successfully determined the redshift for 26, including 15 SNe Ia at z > 0.97. We show that even in passive environments, it is possible to recover secure redshifts for the majority of SN hosts out to z = 1.5. We find that with typical exposure times of 3−4 h on an 8-m-class telescope we can recover ∼75 per cent of SN Ia redshifts in the range of 0.97 < z < 1.5. Furthermore, we show that the combination of HST photometry and VLT spectroscopy is able to provide estimates of host galaxy stellar mass that are sufficiently accurate for use in a mass-step correction in the cosmological analysis.

The Evidence for the accelerating universe: endorsement and robust consistency

The 2011 Nobel Prize in Physics was awarded to researchers from the Supernova Cosmology Project and the High-z Supernova Search Team for the discovery of the accelerating expansion of the universe. In this paper, I provide a historical analysis of the supernova cosmology evidence put forward by these teams for the accelerating universe, in terms of an iterative model of scientific progress developed by Hasok Chang in the context of his study of the development of measurement standards. I argue, using the key concept of epistemic iteration, that the iterative model adequately accounts for evidence production in experimental science as well. In order to apply Chang’s model to the experimental evidence for the accelerating universe, I introduce the concept of endorsement as a particular mode of progress, and argue that supernova scientists produced an endorsed measurement system to claim evidence for their discovery. Furthermore, I show that the credibility of the evidence was not based on a particular measurement, rather, what proved to be decisive was the “robust consistency” of many individual results.

FRW cosmology in f(R,T) gravity

In the present paper, the work of Moreas et al. [P. H. R. S. Moraes, G. Ribeiro and R. A. C. Correa, A transition from a decelerated to an accelerated phase of the universe expansion from the simplest non-trivial polynomial function of T in the [Formula: see text] formalism, Astrophys. Space Sci. 361 (2016) 227–231] is extended to study the FRW model in [Formula: see text] gravity. The expressions for deceleration and Hubble parameters are determined in terms of redshift. The age of the universe is established using [Formula: see text] high-redshift type Ia supernovae data from the Supernova cosmology project and 15 low-redshift type Ia supernovae data from the Calán/Tolono Supernova survey [S. Permutter et al., Measurements of Omega and Lambda from 42 High-Redshift Supernovae, Astrophys. J. 517 (1999) 565–585]. For these redshifts, the data of observed apparent magnitude and luminosity distance are used for the comparison with the obtained theoretical values.

How the Dirac Sea Idea May Apply to a Spatially-Flat Universe Model (A Brief Review)

The famous Dirac sea idea can be resurrected if one replaces the concept of positive and negative matter mass with positive and negative energy. Utilizing this concept, the perpetually spatially-flat matter-generating FSC model can be shown to be a realistic Milne “empty universe” model. Furthermore, this may be why Rh = ct cosmological models like FSC show an excellent statistical fit with the accumulated data of the Supernova Cosmology Project.

Anisotropic Bianchi-V dark energy model under the new perspective of accelerated expansion of the universe in Brans–Dicke theory of gravitation

In this paper, we have proposed a cosmological model, which is consistent with the new findings of ‘The Supernova Cosmology project’ headed by Saul Perlmutter, and the ‘High-Z Supernova Search team’, headed by Brian Schimdt. According to these new findings, the universe is undergoing an expansion with an increasing rate, in contrast to the earlier belief that the rate of expansion is constant or the expansion is slowing down. We have considered spatially homogeneous and anisotropic Bianchi-V dark energy model in Brans–Dicke theory of gravitation. We have taken the scale factor $$a(t)=k t^\alpha e^{\beta t}$$ , which results into variable deceleration parameter (DP). The graph of DP shows a transition from positive to negative, which shows that universe has passed through the past decelerated expansion to the current accelerated expansion phase. In this context, we have also calculated and plotted various parameters and observed that these are in good agreement with physical and kinematic properties of the universe and are also consistent with recent observations.

How a Realistic Linear <i>R<sub>h</sub> = ct </i> Model of Cosmology Could Present the Illusion of Late Cosmic Acceleration

Realistic FLRW cosmic coasting models which contain matter now appear to be a reasonable alternative in explaining the accumulated Supernova Cosmology Project data since 1998. In sharp contrast to the unrealistic original classic Milne universe, which was entirely devoid of matter, these modified Milne-type models containing matter, often referred to as realistic linear Rh = ct models, have rapidly become the primary competition with standard cosmology. This paper compares the expected relative luminosity distances and relative angular diameter distances for given magnitudes of redshift within these two competing models. A simple ratio formula is derived, which explains how expected luminosity distances and angular diameter distances for given magnitudes of redshift within a realistic Milne-type cosmic expansion could create the illusion (for standard model proponents) of cosmic acceleration where none exists.

Study of the observational compatibility of an inhomogeneous cosmology with linear expansion according to SNe Ia

Most of current cosmological theories are built combining an isotropic and homogeneous manifold with a scale factor that depends on time. If one supposes a hyperconical universe with linear expansion, an inhomogeneous metric can be obtained by an appropriate transformation that preserves the proper time. This model locally tends to a flat Friedman-Robertson-Walker metric with linear expansion. The objective of this work is to analyze the observational compatibility of the inhomogeneous metric considered. For this purpose, the corresponding luminosity distance was obtained and was compared with the observations of 580 SNe Ia, taken from the Supernova Cosmology Project. The best fit of the hyperconical model obtains ${\ensuremath{\chi}}_{0}^{2}=562$, the same value as the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. Finally, a possible relationship is found between both theories.

On the concordance of cosmological data in the case of the generalized Chaplygin gas

The generalized Chaplygin gas cosmology provides a prime example for the class of unified dark matter models, which substitute the two dark components of the standard cosmological ΛCDM concordance model by a single dark component. The equation of state of the generalized Chaplygin gas is characterised by a parameter α such that the standard ΛCDM model is recovered in the case α=0 with respect to the background dynamics and the cosmic microwave background (CMB) statistics. This allows to investigate the concordance of different cosmological data sets with respect to α. We compare the supernova data of the Supernova Cosmology Project, the data of the baryon oscillation spectroscopic survey (BOSS) of the third Sloan digital sky survey (SDSS-III) and the CMB data of the Planck 2015 data release. The importance of the BOSS Lyman α forest BAO measurements is investigated. It is found that these data sets possess a common overlap of the confidence domains only for Chaplygin gas cosmologies very close to the ΛCDM model.

Frequency-based redshift for cosmological observation and Hubble diagram from the 4-D spherical model in comparison with observed supernovae

According to the formerly reported 4-D spherical model of the universe, factors on Hubble diagrams are discussed. The observed redshift is not the prolongation of wavelength from that of the source at the emission but from the wavelength of spectrum of the present atom of the same element. It is equal to the redshift based on the shift of frequency from the time of emission. We demonstrate that the K-correction corresponds to conversion of the light propagated distance (luminosity distance) to the proper distance at present (present distance). Comparison of the graph of the present distance times 1 + z versus the frequency-based redshift with the reported Hubble diagrams from the Supernova Cosmology Project, which were time-dilated by 1 + z and K-corrected, showed an excellent fit for the Present Time (the radius of 4-D sphere) being c.a. 0.7 of its maximum.

Molecules Can Explain the Expansion of the Universe

The Hubble diagram continues to remain one of the most important graphical representations in the realm of astronomy and cosmology right from its genesis that depicts the velocity-distance relation for the receding large-scale structures within the Universe; it is the diagram that helps us to understand the Universe’s expansion. In this paper I introduce the molecular expansion model in order to explain the expansion of the Universe. The molecular expansion model considers the large-scale structures as gas molecules undergoing free expansion into the vacuum. Large-scale structures being ensemble of atoms must behave like molecules possessing finite amount of energy. Since metric expansion of space cannot be tested practically and can only be observed indirectly due to the presence of observable entities, therefore, instead of considering the metaphysics of expanding space, the paper emphasizes upon the actual recession of large-scale structures as the most natural reason to explain the observed expansion. I show in this paper that the linear velocity-distance relation or the Hubble diagram is actually a natural and a characteristic feature of different gas molecules undergoing free expansion into the vacuum at the same time. Different gas molecules have different velocities, and, molecules being natural entities provide a natural and a scientifically-viable explanation better than metaphysics. The study conducted in this paper finds the recessional behaviour of large-scale structures to be consistent with the recessional behaviour of molecules. The free expansion of different gas molecules into the vacuum is found to be homogeneous, isotropic and in agreement with the Copernican principle. Redshift-distance relationship has been plotted for 580 type Ia supernovae from the Supernova Cosmology Project data and the reason for the deviation of the Hubble diagram from linearity at high redshifts has been explained without any acceleration by introducing the concept of differential molecular expansion.

Open Supernova Catalog objects subsample characteristics

The homogeneous subsample characteristics understanding is necessary for the investigation of any astrophysical objects redshift distribution, for example, gamma-ray bursts. The type Ia supernovae considered as a homogeneous subsample because of suggestion that these luminous events might be used as standard candles for cosmological measurements occurs since the earliest studies of supernovae in 1938. The parameters of our Metagalaxy Ω and Λ were determine due sample of Ia supernovae from the Supernova Cosmology Project analysis in 1998. Since then more than 4000 supernovae were added. The results of the redshift distribution analysis for supernova from the two catalogues (Asiago Supernova Catalogue and Open Supernova Catalog) are presented in this work. The ability to use an analyzed dataset as homogeneous subsample also is discussed

Cosmological Distance Scale. Part 5. Metrological Expert Opinion on Type SN Ia Supernovae

The detection of the accelerated expansion of the universe by the High-Z SN Search Team and the Supernova Cosmology Project is analyzed from the standpoint of solving the structural-parametric identification problem for the red-shift cosmological distance scale in the Friedman–Robertson–Walker model based on combined data for type SN Ia supernovae. A similar solution is given for the interpolation model.

Supernova constraints on higher-dimensional cosmology with a phantom field

We use observational data on the magnitude-redshift relation for Type Ia supernovae (SNeIa) together with constraints on the ages of the oldest stars to rule out a higher-dimensional extension of General Relativity with a negative kinetic energy scalar field. This theory is of considerable physical interest because it produces accelerated expansion at both early and late times with a single new field, as in quintessential inflation scenarios. It is also of mathematical interest because it is characterized by an analytic expression for the macroscopic scale factor [Formula: see text]. We show that cosmological solutions of this theory can be usefully parametrized by a single quantity, the lookback time [Formula: see text] corresponding to the transition from deceleration to acceleration. Supernovae data from the recently released Supernova Cosmology Project (SCP) Union 2.1 compilation single out a narrow range of values for [Formula: see text]. In the context of the theory, however, these same values of [Formula: see text] imply that the universe is much older than the oldest observed stars.

Light propagated distance and redshift of a distant star

According to the formerly reported 4-D spherical model of the time and universe, factors affecting the redshift are discussed. In addition to the factor from the space expansion, two other factors derived from the light speed variation are proposed. One is the energy density factor of the wave medium, which was formerly reported to determine the light speed. The second is a newly proposed factor caused by the electromagnetic interaction of light with substances in the 3-D space. Subsequently the direct correlation of the light propagated distance with the redshift is given. Superimposed graphs of it on the real observed data from the Supernova Cosmology Project exhibited an excellent fit for a case that the current radius (equal to our observed time) of the universe is between 0.7 and 0.8 of its maximum. This could be an important ground for a possibility of the 4-D spherical model, which implies that the universe has been expanding at a constant speed by our observed time.

Cosmographic analysis of the equation of state of the universe through Padé approximations

Cosmography is used in cosmological data processing in order to constrain the kinematics of the universe in a model-independent way, providing an objective means to evaluate the agreement of a model with observations. In this paper, we extend the conventional methodology of cosmography employing Taylor expansions of observables by an alternative approach using Pad\'e approximations. Due to the superior convergence properties of Pad\'e expansions, it is possible to improve the fitting analysis to obtain numerical values for the parameters of the cosmographic series. From the results, we can derive the equation of state parameter of the universe and its first derivative and thus acquire information about the thermodynamic state of the universe. We carry out statistical analyses using observations of the distance modulus of type 1a supernovae, provided by the union 2.1 compilation of the supernova cosmology project, employing a Markov chain Monte Carlo approach with an implemented Metropolis algorithm. We compare the results of the original Taylor approach to the newly introduced Pad\'e formalism. The analyses show that experimental data constrain the observable universe well, finding an accelerating universe and a positive jerk parameter. We demonstrate that the Pad\'e convergence radii are greater than standard Taylor convergence radii, and infer a lower limit on the acceleration of the universe solely by requiring the positivity of the Pad\'e expansion. We obtain fairly good agreement with the Planck results, confirming the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model at small redshifts, although we cannot exclude a dark energy density varying in time with negligible speed of sound.

Chasing the phantom: A closer look at type Ia supernovae and the dark energy equation of state

Some recent observations provide $> 2\sigma$ evidence for phantom dark energy -- a value of the dark energy equation of state less than the cosmological-constant value of $-1$. We focus on constraining the equation of state by combining current data from the most mature geometrical probes of dark energy: Type Ia supernovae (SNe Ia) from the Supernova Legacy Survey (SNLS3), the Supernova Cosmology Project (Union2.1), and the Pan-STARRS1 survey (PS1); cosmic microwave background measurements from Planck and WMAP9; and a combination of measurements of baryon acoustic oscillations. The combined data are consistent with $w = -1$ for the Union2.1 sample, though they present moderate ($\sim 1.9\sigma$) evidence for a phantom value when either the SNLS3 or PS1 sample is used instead. We study the dependence of the constraints on the redshift, stretch, color, and host galaxy stellar mass of SNe, but we find no unusual trends. In contrast, the constraints strongly depend on any external $H_0$ prior: a higher adopted value for the direct measurement of the Hubble constant ($H_0 \gtrsim 71~\text{km/s/Mpc}$) leads to $\gtrsim 2\sigma$ evidence for phantom dark energy. Given Planck data, we can therefore make the following statement at $2\sigma$ confidence: either the SNLS3 and PS1 data have systematics that remain unaccounted for or the Hubble constant is below 71 km/s/Mpc; else the dark energy equation of state is indeed phantom.

The Accelerated universe. On the Nobel Prize in Physics 2011 awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess

Since the end of the 1920s we have known that distant galaxies are receding from us. The observations that led to this conclusion were mainly those of Edwin Hubble. The history of the universe has been one of continuous expansion and cooling, marked by several critical events. In a matter-dominated universe, it is quite intuitive that the expansion will eventually slow down; in other words, the universe should decelerate. And yet two teams, the Supernova Cosmology Project and the High-z Supernova Search Team, used a subset of supernova-type Ia (SNIa)-and reached the same surprising result: the universe is accelerating. But what, then, is producing theobserved cosmological acceleration? This article discusses the 2011 Nobel Prize for Physics, awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess for the discovery of the accelerating expansion of the universe through observations of distant supernovae, and reviews the cosmological context of the discovery and the use of supernovae as standard candles. Some of the consequences of the discovery are presented as well.

χ2versus median statistics in supernova type Ia data analysis

In this paper we compare the performances of the chi-square and median likelihood analysis in the determination of cosmological constraints using type Ia supernovae data. We perform a statistical analysis using the 307 supernovae of the Union 2 compilation of the Supernova Cosmology Project and find that the chi-square statistical analysis yields tighter cosmological constraints than the median statistic if only supernovae data is taken into account. We also show that when additional measurements from the Cosmic Microwave Background and Baryonic Acoustic Oscillations are considered, the combined cosmological constraints are not strongly dependent on whether one applies the chi-square statistic or the median statistic to the supernovae data. This indicates that, when complementary information from other cosmological probes is taken into account, the performances of the chi-square and median statistics are very similar, demonstrating the robustness of the statistical analysis.