scholarly journals Do supernovae indicate an accelerating universe?

2021 ◽  
Author(s):  
Roya Mohayaee ◽  
Mohamed Rameez ◽  
Subir Sarkar
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
Bulk Flow ◽  
Expansion Rate ◽  
Accelerated Expansion ◽  
Accelerating Universe ◽  
Acoustic Oscillations ◽  
Independent Evidence ◽  
Peculiar Velocity ◽  
Hubble Expansion

AbstractIn the late 1990’s, observations of two directionally-skewed samples of, in total, 93 Type Ia supernovae were analysed in the framework of the Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology. Assuming these to be ‘standard(isable) candles’ it was inferred that the Hubble expansion rate is accelerating as if driven by a positive Cosmological Constant $$\varLambda $$ Λ in Einstein’s theory of gravity. This is still the only direct evidence for the ‘dark energy’ that is the dominant component of today’s standard $$\varLambda $$ Λ CDM cosmological model. Other data such as baryon acoustic oscillations (BAO) in the large-scale distribution of galaxies, temperature fluctuations in the cosmic microwave background (CMB), measurement of stellar ages, the rate of growth of structure, etc are all ‘concordant’ with this model but do not provide independent evidence for accelerated expansion. The recent discussions about whether the inferred acceleration is real rests on analysis of a larger sample of 740 SNe Ia which shows that these are not quite standard candles, and more importantly highlights the ‘corrections’ that are applied to analyse the data in the FLRW framework. The latter holds in the reference frame in which the CMB is isotropic, whereas observations are carried out in our heliocentric frame in which the CMB has a large dipole anisotropy. This is assumed to be of kinematic origin i.e. due to our non-Hubble motion driven by local inhomogeneity in the matter distribution which has grown under gravity from primordial density perturbations traced by the CMB fluctuations. The $$\varLambda $$ Λ CDM model predicts how this peculiar velocity should fall off as the averaging scale is raised and the universe becomes sensibly homogeneous. However observations of the local ‘bulk flow’ are inconsistent with this expectation and convergence to the CMB frame is not seen. Moreover, the kinematic interpretation implies a corresponding dipole in the sky distribution of high redshift quasars, which is rejected by observations at $$4.9\sigma $$ 4.9 σ . Hence the peculiar velocity corrections employed in supernova cosmology are inconsistent and discontinuous within the data. The acceleration of the Hubble expansion rate is in fact anisotropic at $$3.9\sigma $$ 3.9 σ and aligned with the bulk flow. Thus dark energy could be an artefact of analysing data assuming that we are idealised observers in an FLRW universe, when in fact the real universe is inhomogeneous and anisotropic out to distances large enough to impact on cosmological analyses.

scholarly journals ΛCDM periodic cosmology

2020 ◽  
Vol 494 (2) ◽  
pp. 2183-2190
Author(s):  
Stéphane Fay
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Density Parameter ◽  
Acoustic Oscillations ◽  
Microwave Background ◽  
Hubble Expansion ◽  
Background Data ◽  
Periodic Models ◽  
Cosmic Microwave Background Data

ABSTRACT We examine the possibility that Universe expansion be made of some Λ-cold dark matter (ΛCDM) expansions repeating periodically, separated by some inflation- and radiation-dominated phases. This so-called ΛCDM periodic cosmology is motivated by the possibility that inflation and the present phase of accelerated expansion be due to the same dark energy. Then, in a phase space showing the variation of matter density parameter Ωm with respect to this of the radiation Ωr, the curve Ωm(Ωr) looks like a closed trajectory that Universe could run through forever. In this case, the end of the expansion acceleration of the ΛCDM phase is the beginning of a new inflation phase. We show that such a scenario implies the coupling of matter and/or radiation to dark energy. We consider the simplest of these ΛCDM periodic models i.e. a vacuum energy coupled to radiation. From matter domination phase to today, it behaves like a ΛCDM model, then followed by an inflation phase. But a sudden and fast decay of the dark energy into radiation periodically ends the expansion acceleration. This leads to a radiation-dominated Universe preceding a new ΛCDM type expansion. The model is constrained with Markov Chain Monte Carlo simulations using supernovae, Hubble expansion, Baryon Acoustic Oscillations (BAO), and cosmic microwave background data and fits the data as well as the ΛCDM one.

DYNAMICS OF DARK ENERGY

2006 ◽  
Vol 15 (11) ◽  
pp. 1753-1935 ◽  
Author(s):  
EDMUND J. COPELAND ◽  
M. SAMI ◽  
SHINJI TSUJIKAWA
Keyword(s):  
Dark Energy ◽  
Particle Physics ◽  
Large Scale ◽  
Scalar Fields ◽  
Accelerated Expansion ◽  
Accelerating Universe ◽  
Late Time ◽  
Microwave Background ◽  
Energy Models ◽  
Expansion Of The Universe

We review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observational evidence for the current accelerated expansion of the universe and present a number of dark energy models in addition to the conventional cosmological constant, paying particular attention to scalar field models such as quintessence, K-essence, tachyon, phantom and dilatonic models. The importance of cosmological scaling solutions is emphasized when studying the dynamical system of scalar fields including coupled dark energy. We study the evolution of cosmological perturbations allowing us to confront them with the observation of the Cosmic Microwave Background and Large Scale Structure and demonstrate how it is possible in principle to reconstruct the equation of state of dark energy by also using Supernovae Ia observational data. We also discuss in detail the nature of tracking solutions in cosmology, particle physics and braneworld models of dark energy, the nature of possible future singularities, the effect of higher order curvature terms to avoid a Big Rip singularity, and approaches to modifying gravity which leads to a late-time accelerated expansion without recourse to a new form of dark energy.

scholarly journals FORMATION OF DARK MATTER HALOES IN A HOMOGENEOUS DARK ENERGY UNIVERSE

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1397-1403
Author(s):  
L. MARASSI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Large Scale ◽  
State Parameter ◽  
Mass Function ◽  
Accelerated Expansion ◽  
X Ray ◽  
Energy Models ◽  
Dark Energy Component ◽  
Standard Press

Several independent cosmological tests have shown evidences that the energy density of the universe is dominated by a dark energy component, which causes the present accelerated expansion. The large scale structure formation can be used to probe dark energy models, and the mass function of dark matter haloes is one of the best statistical tools to perform this study. We present here a statistical analysis of mass functions of galaxies under a homogeneous dark energy model, proposed in the work of Percival (2005), using an observational flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our analysis, the standard Press–Schechter (PS) approach (where a Gaussian distribution is used to describe the primordial density fluctuation field of the mass function), and the PL (power–law) mass function (where we apply a non-extensive q-statistical distribution to the primordial density field). We conclude that the PS mass function cannot explain at the same time the X-ray and the CMB data (even at 99% confidence level), and the PS best fit dark energy equation of state parameter is ω = -0.58, which is distant from the cosmological constant case. The PL mass function provides better fits to the HIFLUGCS X-ray galaxy data and the CMB data; we also note that the ω parameter is very sensible to modifications in the PL free parameter, q, suggesting that the PL mass function could be a powerful tool to constrain dark energy models.

scholarly journals Probing dark energy with braneworld cosmology in the light of recent cosmological data

2018 ◽  
Vol 27 (02) ◽  
pp. 1850006 ◽  
Author(s):  
Miguel A. García-Aspeitia ◽  
Juan Magaña ◽  
A. Hernández-Almada ◽  
V. Motta
Keyword(s):  
Dark Energy ◽  
Background Radiation ◽  
Big Bang ◽  
Accelerated Expansion ◽  
Joint Analysis ◽  
Brane Tension ◽  
Acoustic Oscillations ◽  
Brane Model ◽  
Baryon Acoustic Oscillations ◽  
The Universe

We investigate a brane model based on Randall–Sundrum scenarios with a generic dark energy component. The latter drives the accelerated expansion at late-times of the universe. In this scheme, extra terms are added into Einstein Field equations that are propagated to the Friedmann equations. To constrain the dark energy equation-of-state (EoS) and the brane tension we use observational data with different energy levels (Supernovae Type Ia, [Formula: see text], baryon acoustic oscillations, and cosmic microwave background radiation distance, and a joint analysis) in a background cosmology. Beside EoS being consistent with a cosmological constant at the [Formula: see text] confidence level for each dataset, the baryon acoustic oscillations probe favors an EoS consistent with a quintessence dark energy. Although we found different lower limit bounds on the brane tension for each dataset, being the most restricted for CMB, there is not enough evidence of modifications in the cosmological evolution of the universe by the existence of an extra dimension within observational uncertainties. Nevertheless, these new bounds are complementary to those obtained by other probes like table-top experiments, Big Bang Nucleosynthesis, and stellar dynamics. Our results show that a further test of the braneworld model with appropriate correction terms or a profound analysis with perturbations, may be needed to improve the constraints provided by the current data.

scholarly journals Observational constraints on interacting Tsallis holographic dark energy model

2019 ◽  
Vol 79 (9) ◽  
Author(s):  
Ehsan Sadri
Keyword(s):  
Dark Energy ◽  
Observational Data ◽  
Dark Energy Model ◽  
Large Scale ◽  
Gamma Ray ◽  
Holographic Dark Energy ◽  
Energy Model ◽  
Late Time ◽  
Acoustic Oscillations ◽  
Holographic Dark Energy Model

Abstract In this paper, we investigate a recent proposed model – so called the Tsallis holographic dark energy (THDE) model with consideration of the Hubble and the event future horizon as IR cutoffs. In this case, we consider the non-gravitational and phenomenological interaction between dark sectors. We fit the free parameters of the model using Pantheon Supernovae Type Ia data, Baryon Acoustic Oscillations, Cosmic Microwave Background, Gamma-Ray burst and the the local value of the Hubble constant. We examine the THDE model to check its compatibility with observational data using objective Information Criterion (IC). We find that the THDE models cannot be supported by observational data once the $$\Lambda $$ΛCDM is considered as the referring model. Therefore we re-examine the analysis with the standard holographic dark energy model (HDE) as another reference. Changing the $$\Lambda $$ΛCDM to main standard dark energy model (HDE), we observe the compatibility of the THDE models. Using the Alcock–Paczynski (AP) test we check the deviation of the model compared to $$\Lambda $$ΛCDM and HDE. Surveying the evolution of squared of sound speed $$v^2_s$$vs2 as an another test we check the stability of the interacting and non-interacting THDE models and we find that while the THDE model with the Hubble horizon as IR cutoff is unstable against the background perturbation, the future event horizon as IR cutoff show stability at the late time. In addition, using the modified version of the CAMB package, we observe the suppressing the CMB spectrum at small K-modes and large scale.

scholarly journals Dynamical Properties of Dark Energy Models in Fractal Universe

Symmetry ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1174
Author(s):  
Muhammad Umair Shahzad ◽  
Ayesha Iqbal ◽  
Abdul Jawad
Keyword(s):  
Dark Energy ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Accelerating Universe ◽  
Statefinder Parameters ◽  
Om Diagnostic ◽  
Energy Models ◽  
Expansion Of The Universe ◽  
Dynamical Properties ◽  
The Universe

In this paper, we consider the flat FRW spacetime filled with interacting dark energy and dark matter in fractal universe. We work with the three models of dark energy named as Tsallis, Renyi and Sharma–Mittal. We investigate different cosmological implications such as equation of state parameter, squared speed of sound, deceleration parameter, statefinder parameters, ω e f f - ω e f f ´ (where prime indicates the derivative with respect to ln a , and a is cosmic scale factor) plane and Om diagnostic. We explore these parameters graphically to study the evolving universe. We compare the consistency of dark energy models with the accelerating universe observational data. All three models are stable in fractal universe and support accelerated expansion of the universe.

scholarly journals Some Interacting Dark Energy Models

Symmetry ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 577 ◽  
Author(s):  
Martiros Khurshudyan ◽  
Asatur Khurshudyan
Keyword(s):  
Dark Energy ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Peak Position ◽  
Accelerated Expansion ◽  
Model Parameters ◽  
Acoustic Oscillations ◽  
Barotropic Fluid ◽  
Interacting Dark Energy Models ◽  
Parameter Values

In this paper, we study various cosmological models involving new nonlinear forms of interaction between cold dark matter (DM) and dark energy (DE) assuming that DE is a barotropic fluid. The interactions are nonlinear either due to log ( ρ d e / ρ d m ) or log ( ρ d m / ρ d e ) parameterizations, respectively. The main purpose of this paper is to demonstrate the applicability of the forms of suggested interactions to the problem of modern cosmology known as accelerated expansion of the Universe. Using the differential age of old galaxies expressed in terms of H ( z ) data, the peak position of baryonic acoustic oscillations (known as BAO data), the SN Ia data with strong gravitational lensing data, we obtain the best fit values of the model parameters for each case. Besides, using O m analysis and S 3 parameter from the statefinder hierarchy analysis, we also demonstrate that the considered models are clearly different from the Λ CDM model. We obtain that the models predict Hubble parameter values consistent to the estimations from gravitational lensing, which probes the expansion out to z ≤ 1.7 . We show that, with considered models, we can also explain PLANCK 2015 and PLANCK 2018 experiment results.

scholarly journals Cosmography and Large Scale Structure by -Gravity: New Results

2009 ◽  
Vol 2009 ◽  
pp. 1-34 ◽  
Author(s):  
Salvatore Capozziello ◽  
Vincenzo Salzano
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Large Scale ◽  
Galaxy Cluster ◽  
Weak Field ◽  
Accelerated Expansion ◽  
Final Theory ◽  
Weak Field Limit ◽  
Expansion Of The Universe ◽  
Analytic Models

The so-called -gravity has recently attracted a lot of interest since it could be, in principle, able to explain the accelerated expansion of the Universe without adding unknown forms of dark energy/dark matter but, more simply, extending the General Relativity by generic functions of the Ricci scalar. However, apart several phenomenological models, there is no final -theory capable of fitting all the observations and addressing all the issues related to the presence of dark energy and dark matter. An alternative approach could be to “reconstruct” the form of starting from data without imposing particular classes of model. Besides, adopting the same philosophy, we take into account the possibility that galaxy cluster masses, estimated at X-ray wavelengths, could be explained, without dark matter, reconstructing the weak-field limit of analytic models. The corrected gravitational potential, obtained in this approximation, is used to estimate the total mass of a sample of 12 well-shaped clusters of galaxies.

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