We introduce a generalised form of an emergent dark energy model with one degree of freedom for the dark energy sector that has the flexibility to include both $Λ$CDM model as well as the Phenomenologically Emergent Dark Energy (PEDE) model proposed by Li & Shafieloo (2019) as two of its special limits. The free parameter for the dark energy sector, namely $Δ$, has the value of $0$ for the case of the $Λ$ and $1$ for the case of PEDE. Fitting the introduced parametric form to Planck CMB data and most recent $H_0$ results from local observations of Cepheids and Supernovae, we show that the $Δ=0$ associated with the $Λ$CDM model would fall out of 4$σ$ confidence limits of the derived posterior of the $Δ$ parameter. Moreover, $H_0$ tensions will be alleviated with emergent dark energy model and this model can satisfy the combination of Planck CMB data and local $H_0$ observations with $Δ{\rm{DIC}}\,=\,-2.88$ compared with $\LCDM$ model.
We investigate a generalized form of the phenomenologically emergent dark energy model, known as generalized emergent dark energy (GEDE), introduced by Li and Shafieloo [Astrophys. J. {\bf 902}, 58 (2020)] in light of a series of cosmological probes and considering the evolution of the model at the level of linear perturbations. This model introduces a free parameter $Δ$ that can discriminate between the $Λ$CDM (corresponds to $Δ=0$) or the phenomenologically emergent dark energy (PEDE) (corresponds to $Δ=1$) models, allowing us to determine which model is preferred most by the fit of the obse…
A cosmological scenario where dark matter interacts with a variable vacuum energy for a spatially flat Friedmann-Robertson-Walker space-time is proposed and analysed to show that with a linear equation of state and a particular interaction in the dark sector it is possible to get a model of an Emergent Universe. In addition, the viability of two particular models is studied by taking into account recent observations. The updated observational Hubble data and the JLA supernovae data are used in order to constraint the cosmological parameters of the models and estimate the amount of dark energy …
A cosmic potential which can relax the vacuum energy is proposed in a framework of scalar-tensor gravity. In the phase of the gravity scalar field around the evolution with an approximate emergent conformal symmetry, we have obtained a set of cosmological equations with the dark energy regulated to the order of a conformal anomaly parameter. Through a role of the cosmic potential, the vacuum energy which could be generated in matter Lagrangian does not contribute to the dark energy in the phase.
The nonlinear affine Goldstone model of the emergent gravity, built on the nonlinearly realized/hidden affine symmetry, is concisely revisited. Beyond General Relativity, the explicit violation of general invariance/relativity, under preserving general covariance, is exposed. Dependent on a nondynamical affine connection, a generally covariant second-order effective Lagrangian for metric gravity is worked out, with the general relativity violation and the gravitational dark matter serving as the signatures of emergence.
We present the radial distribution of the dark matter in two massive, X-ray luminous galaxy clusters, Abell~2142 and Abell~2319, and compare it with the quantity predicted as apparent manifestation of the baryonic mass in the context of the "Emergent Gravity" scenario, recently suggested from Verlinde (2016). Thanks to the observational strategy of the \xmm\ Cluster Outskirt Programme (X-COP), using the X-ray emission mapped with \xmm\ and the SZ signal in the Planck survey, we recover the gas density, temperature and thermal pressure profiles up to $\sim R_{200}$, allowing to constrain at unp…
We have found a mechanism which regulates the dark energy in our universe. With an emergent conformal symmetry, the dark energy density is regulated to the order of a conformal anomaly parameter in the conformally coupled gravity. In the late time cosmological evolution, we have obtained a set of exact cosmological equations which deviate from the Friedmann equations significantly. Based on the recent observational cosmic expansion data, it is shown that the dark energy density is about 1/4 of the matter density at present, which is quite smaller than determined by General Relativity. The jerk…
The Phenomenologically Emergent Dark Energy model, a dark energy model with the same number of free parameters as the flat $Λ$CDM, has been proposed as a working example of a minimal model which can avoid the current cosmological tensions. A straightforward question is whether or not the inclusion of massive neutrinos and extra relativistic species may spoil such an appealing phenomenological alternative. We present the bounds on $M_ν$ and $N_{\rm eff}$ and comment on the long standing $H_0$ and $σ_8$ tensions within this cosmological framework with a wealth of cosmological observations. Inter…
We introduce a modified form of the Phenomenologically Emergent Dark Energy (PEDE) model by showing a very elegant approach. The model is named as Modified Emergent Dark Energy (MEDE) to distinguish from PEDE model and it includes $Λ$CDM, PEDE model, Chevallier-Polarski-Linder model and other cosmological models of interest. We show that the present article offers a very fantastic route to construct other PEDE models in a simple but very elegant way. The model has seven free parameters where the six parameters are the same as in $Λ$CDM or PEDE model and the remaining one parameter `$α$' quanti…
In the general frameworks of an earlier introduced quartet-metric/multi-component gravity, a theory of a massive scalar graviton supplementing the massless tensor one is consistently deduced. The peculiarities of the scalar-graviton field compared to the canonical scalar one are demonstrated. The light scalar graviton is treated as an emergent dark substance of the Universe: dark matter and/or dark energy depending on the solution. The case with scalar graviton as dark energy responsible for the late-time accelerated expansion of the Universe is studied in more detail. In particular, it is sho…
Recently \citet{PEDE:2019ApJ} proposed a phenomenologically emergent dark energy (PEDE) which consider that the dark energy density evolves as $\widetildeΩ_{\rm{DE}}(z)\,=\,Ω_{\rm{DE,0}}\left[ 1 - {\rm{tanh}}\left( {\log}_{10}(1+z) \right) \right]$ with the advantage that it does not have degree of freedom. Later on, \citet{PEDE:2020} proposed a generalized model by adding one degree of freedom to the PEDE model, encoded in the parameter $Δ$. Motivated by these proposals, we constrain the parameter space ($h,Ω_m$) and ($h,Ω_m, Δ$) for PEDE and Generalized Emergent Dark Energy (GEDE) respective…
The ten-parameter, quadratic Poincaré gauge theory of gravity is a plausible alternative to general relativity. We show that the rich background cosmology of the gauge theory is described by a non-canonical bi-scalar-tensor theory in the Jordan frame: the `metrical analogue'. This provides a unified framework for future investigation by the broader community. For many parameter choices, the non-canonical term reduces to a Cuscuton field of the form $\smash{\sqrt{|X^{ϕϕ}|}}$. The Einstein-Cartan-Kibble-Sciama theory maps to a pure quadratic Cuscuton, whereas the teleparallel theory maps to the …
We consider the cosmological dynamics of a scalar field in a potential with multiple troughs and peaks. We show that the dynamics of the scalar field will evolve from light dark matter-like behaviour (such as that of a light axion) to a combination of heavy dark matter-like and dark energy-like behaviour. We discuss the phenomenology of such a model, explaining how it can give rise to the cosmological constant, as well as how it can decouple the dark sector densities between the time of recombination and today, for both the homogeneous background and perturbations. The final form of the dark m…
Motivated by the recent increased interest in energy non-conserving models in cosmology, we extend the analysis of the cosmological consequences of the Classical Channel Model of Gravity (CCG). This model is based on the classical-quantum interaction between a test particle and a metric (classical) and results in a theory with a modified Wheeler-deWitt equation that in turn leads to non conservation of energy. We show that CCG applied to a cosmological scenario with primordial matter leads to an emergent dark fluid that at late times behaves as a curvature term in the Friedmann equations, show…
In this work we examine the recently proposed phenomenological emergent dark energy (PEDE) model by \cite{Li:2019yem}, using the latest observational data in both expansion and perturbation levels. Applying the statistical Bayesian evidence as well as the AIC and BIC information criteria, we compare the PEDE model with the concordance $Λ$CDM model in both flat and non-flat universes. We combine the observational datasets as (i) expansion data (except CMB), (ii) expansion data (including CMB) and (iii) expansion data jointed to the growth rate dataset. Our statistical results show that the flat…
A specific class of flat Emergent Universe (EU) is considered and its viability is tested in view of the recent observations. Model parameters are constrained from Stern data for Hubble Parameter and Redshift ($H(z)$ vs. $z$) and from a model independent measurement of BAO peak parameter. It is noted that a composition of Exotic matter, dust and dark energy, capable of producing an EU, can not be ruled out with present data. Evolution of other relevant cosmological parameters, viz. density parameter ($Ω$), effective equation of state (EOS) parameter ($ω_{eff}$) are also shown.
A natural geometric framework of noncommutative spacetime is symplectic geometry rather than Riemannian geometry. The Darboux theorem in symplectic geometry then admits a novel form of the equivalence principle such that the electromagnetism in noncommutative spacetime can be regarded as a theory of gravity. Remarkably the emergent gravity reveals a noble picture about the origin of spacetime, dubbed as emergent spacetime, which is radically different from any previous physical theory all of which describe what happens in a given spacetime. In particular, the emergent gravity naturally explain…
There is sufficient amount of internal evidence in the nature of gravitational theories to indicate that gravity is an emergent phenomenon like, e.g, elasticity. Such an emergent nature is most apparent in the structure of gravitational dynamics. It is, however, possible to go beyond the field equations and study the space itself as emergent in a well-defined manner in (and possibly only in) the context of cosmology. In the first part of this review, I describe various pieces of evidence which show that gravitational field equations are emergent. In the second part, I describe a novel way of s…
We discuss a scenario that the dark matter in late time universe emerges as part of the holographic stress-energy tensor on the hypersurface in higher dimensional flat spacetime. Firstly we construct a toy model with a de Sitter hypersurface as the holographic screen in the flat bulk. After adding the baryonic matter on the screen, we assume that both of the dark matter and dark energy can be described by the Brown-York stress-energy tensor. From the Hamiltonian constraint equation in the flat bulk, we find an interesting relation between the dark matter and baryonic matter's energy density pa…
A limiting temperature of a species can cause the Universe to asymptote to it yielding a deSitter (dS) phase due to macroscopic emergent behavior. The limiting temperature is generic for theories slightly shifted from their conformal point. We demonstrate such behavior in the example of unparticles/Banks-Zaks theory. The unparticles behave like radiation at high energies reducing the Hubble tension, and a cosmological constant (CC) at low energies yielding a model that follows closely ΛCDM model but due to collective phenomenon. It is technically natural and avoids the no-dS conjecture. The mo…
We illustrate that $Λ$MOND cosmology following from E. Verlinde's emergent gravity idea which contains only constant dark energy and baryonic matters governed by linear inverse gravitation forces at and beyond galaxy scales fit with the luminosity distance v.s. redshift relationship, i.e. $d_\ell(z)$ of type Ia supernovae equally well as the standard $Λ$CDM cosmology does. But in a rather broad and reasonable parameter space, $Λ$MOND gives too strong baryon acoustic oscillation, i.e. BAO signals on the matter power spectrum contradicting with observations from various galaxy survey and countin…
We propose a one-parameter extension to $Λ$CDM, expected to strongly affect cosmological tensions. An effective dark radiation component in the early universe redshifts away as hot dark matter, then quintessence, tracking the dominant equation-of-state parameter and leaving a falsifiable torsion field in the current epoch. This picture results from a new Poincaré gauge theory (PGT), one of the most promising among the latest batch of 58 PGTs found to be both power-counting renormalisable and free from ghosts and tachyons. We systematically categorise the cosmologies of 33 of these PGTs, as spe…
Motivated by the current status of the cosmological observations and significant tensions in the estimated values of some key parameters assuming the standard $Λ$CDM model, we propose a simple but radical phenomenological emergent dark energy model where dark energy has no effective presence in the past and emerges at the later times. Theoretically, in this phenomenological dark energy model with zero degree of freedom (similar to a $Λ$CDM model), one can derive that the equation of state of dark energy increases from $-\frac{2}{3 {\rm{ln}}\, 10} -1$ in the past to $-1$ in the future. We show …
We study a model of the emergent dark universe, which lives on the time-like hypersurface in a five-dimensional bulk spacetime. The holographic fluid on the hypersurface is assumed to play the role of the dark sector, mainly including the dark energy and apparent dark matter. Based on the modified Friedmann equations, we present a Markov-Chain-Monte-Carlo analysis with the observational data, including type Ia Supernova and the direct measurement of the Hubble constant. We obtain a good fitting result and the matter component turns out to be small enough, which matches well with our theoretica…
In general, non-minimal models of the dark sector such as Dynamical Dark Matter posit the existence of an ensemble of individual dark components with differing masses, cosmological abundances, and couplings to the Standard Model. Perhaps the most critical among these features is the spectrum of masses, as this goes a long way towards determining the cosmological abundances and lifetimes of the corresponding states. Many different underlying theoretical structures can be imagined for the dark sector, each giving rise to its own mass spectrum and corresponding density of states. In this paper, b…
Quantum gravity computations suggest the existence of an ultraviolet and an infrared fixed point where quantum scale invariance emerges as an exact symmetry. We discuss a particular variable gravity model for the crossover between these fixed points which can naturally account for inflation and dark energy, using a single scalar field. In the Einstein-frame formulation the potential can be expressed in terms of Lambert functions, interpolating between a power-law inflationary potential and a mixed-quintessence potential. For two natural heating scenarios, the transition between inflation and r…
We propose a new scenario where dark matter belongs to a secluded sector coupled to the Standard Model through energy--momentum tensors. Our model is motivated by constructions where gravity {\it emerges} from a hidden sector, the graviton being identified by the kinetic term of the fields in the secluded sector. Supposing that the lighter particle of the secluded sector is the dark component of the Universe, we show that we can produce it in a sufficiently large amount despite the suppressed couplings of the theory, thanks to large temperatures of the thermal bath in the early stage of the Un…
Verlinde's theory of Emergent Gravity (EG) describes gravity as an emergent phenomenon rather than a fundamental force. Applying this reasoning in de Sitter space leads to gravity behaving differently on galaxy and galaxy cluster scales; this excess gravity might offer an alternative to dark matter. Here we test these ideas using the data from the Coma cluster and from 58 stacked galaxy clusters. The X-ray surface brightness measurements of the clusters at $0.1 < z < 1.2$ along with the weak lensing data are used to test the theory. We find that the simultaneous EG fits of the X-ray and weak l…
Metastability in Emergent Dark Energy: A New Framework Confronting Cosmological Observations
College of Physics, Hebei Normal University（河北师范大学物理学院）；School of Physics and Optoelectronic, Yangtze University（长江大学物理与光电工程学院）；Liaoning Key Laboratory of Cosmology and Astrophysics, College of Sciences, Northeastern University（东北大学理学院）；Korea Astronomy and Space Science Institute（韩国天文学与空间科学研究所）；University of Science and Technology（科学技术大学）；National Centre for Nuclear Research（波兰国家核研究中心）
We present a new mechanism for transferring a pre-existing lepton or baryon asymmetry to a dark matter asymmetry that relies on mass mixing which is dynamically induced in the early universe. Such mixing can succeed with only generic scales and operators and can give rise to distinctive relationships between the asymmetries in the two sectors. The mixing eliminates the need for the type of additional higher-dimensional operators that are inherent to many current asymmetric dark matter models. We consider several implementations of this idea. In one model, mass mixing is temporarily induced dur…
Addressing the discrepancy between the late and early time measurements of the Hubble parameter, $H_0$, and the so-called $S_8$ parameter has been a challenge in precision cosmology. Several models are present to address these tensions, but very few of them can do so simultaneously. In the past, we have suggested Banks-Zaks/Unparticles as an emergent Dark Energy model and claimed that it can ameliorate the Hubble tension. In this work, we test this claim and perform a likelihood analysis of the model and its parameters are given current data and compare it to $Λ$CDM. The model offers a possibl…
In a recent paper \cite{Artymowski:2020zwy} we suggested the possibility that the present acceleration of the Universe is due to thermodynamical behavior of unparticles. The model is free of scalar fields, modified gravity, a Cosmological Constant (CC), the coincidence problem, initial conditions problem and possesses interesting distinct predictions regarding the equation of state of Dark Energy, the growth rate and the number of relativistic degrees of freedom at BBN and CMB decoupling. In this work, we relate to a recent paper \cite{Abchouyeh:2021wey}, which discusses a similar setup of unp…
We discuss a novel explanation of the dark energy as a manifestation of macroscopic non-locality coming from quantum gravity, as proposed by Markopoulou. It has been previously suggested that in a transition from an early quantum geometric phase of the universe to a low temperature phase characterized by an emergent spacetime metric, locality might have been "disordered". This means that there is a mismatch of micro-locality, as determined by the microscopic quantum dynamics and macro-locality as determined by the classical metric that governs the emergent low energy physics. In this paper we …
When Dark Energy Turns On: Constraints on a Critical Emergence Model
Univ. La Sapienza（罗马第一大学）；K.N. Toosi University of Technology（K.N.托伊西理工大学）；Kharazmi University（哈拉兹米大学）；University of Sheffield（谢菲尔德大学）；Presidency University（总统大学）；Durban University of Technology（德班科技大学）
Verlinde (2016) has recently proposed that spacetime and gravity may emerge from an underlying microscopic theory. In a de Sitter spacetime, such emergent gravity (EG) contains an additional gravitational force due to dark energy, which may explain the mass discrepancies observed in galactic systems without the need of dark matter. For a point mass, EG is equivalent to Modified Newtonian Dynamics (MOND). We show that this equivalence does not hold for finite-size galaxies: there are significant differences between EG and MOND in the inner regions of galaxies. We confront theoretical prediction…
We use a sample of 23 galaxy clusters to test the predictions of emergent gravity (EG) as alternative to dark matter. Our sample has both weak-lensing inferred total mass profiles as well as x-ray inferred baryonic gas mass profiles. Using nominal assumptions about the weak-lensing and x-ray mass profiles, we find that the EG predictions (based on no dark matter) are acceptable fits only near the virial radius. In the cores and in the outskirts, the mass profile shape differences allow us to confirm previous results that the EG model can be ruled out at $>5σ$. However, when we account for syst…
No preference for generalized emergent dark energy from current cosmological data
Lovely Professional University（洛维专业大学）；Babeș-Bolyai University（巴贝什-波约依大学）；Khazar University（阿塞拜疆卡扎尔大学）；Università di Napoli “Federico II”（那不勒斯费德里科二世大学）；Istituto Nazionale di Fisica Nucleare (INFN)（意大利国家核物理研究所）；Scuola Superiore Meridionale（南方高等学院）；Madhabdev University（马德哈伯德夫大学）；Zhejiang Normal University（浙江师范大学）；Walailak University（瓦拉莱克大学）
We propose a dark energy model based on the physics of critical phenomena which is consistent with both the Planck's CMB and the Riess et al.'s local Hubble measurements. In this model the dark energy density behaves like the magnetization of the Ising model. This means the dark energy is an emergent phenomenon and we named it critically emergent dark energy model, CEDE. In CEDE, dark energy emerges at a transition redshift, $z_c$, corresponding to the critical temperature in critical phenomena. Combining the Planck CMB data and local measurement of the Hubble constant from Riess et al. (2019)…
In the same base setup as Sakharov's induced gravity, we investigate emergence of gravity in effective quantum field theories (QFT), with particular emphasis on the gauge sector in which gauge bosons acquire anomalous masses in proportion to the ultraviolet cutoff $Λ_\wp$. Drawing on the fact that $Λ_\wp^2$ corrections explicitly break the gauge and Poincare symmetries, we find that it is possible to map $Λ_\wp^2$ to spacetime curvature as a covariance relation and we find also that this map erases the anomalous gauge boson masses. The resulting framework describes gravity by the general relat…
We consider FRW cosmology in $f(R)= R+ γR^2+δR^3$ modified framework. The Palatini approach reduces its dynamics to the simple generalization of Friedmann equation. Thus we study the dynamics in two-dimensional phase space with some details. After reformulation of the model in the Einstein frame, it reduces to the FRW cosmological model with a homogeneous scalar field and vanishing kinetic energy term. This potential determines the running cosmological constant term as a function of the Ricci scalar. As a result we obtain the emergent dark energy parametrization from the covariant theory. We s…
In a recent paper, Erik Verlinde has developed the interesting possibility that spacetime and gravity may emerge from the entangled structure of an underlying microscopic theory. In this picture, dark matter arises as a response to the standard model of particle physics from the delocalized degrees of freedom that build up the dark energy component of the Universe. Dark matter physics is then regulated by a characteristic acceleration scale $a_0$, identified with the radius of the (quasi)-de Sitter universe we inhabit. For a point particle matter source, or outside an extended spherically symm…
Fermi measurements of the high-latitude gamma-ray background strongly constrain a decaying-dark-matter origin for the 1--100 GeV Galactic positron anomaly measured with PAMELA. Inverse-Compton scattering of the microwave background by the emergent positrons produces a bump in the diffuse 100-200 MeV gamma-ray background that would protrude from the observed background at these energies. The positrons are thus constrained to emerge from the decay process at a typical energy between ~100 GeV and ~250 GeV. By considering only gamma-ray emission of the excess positrons and electrons, we derive a m…
In order to bypass the big bang singularity, we develop an emergent universe scenario within a covariant extension of General Relativity known as \emph{"Energy-Momentum Squared Gravity"}. The extra terms of the model emerge in the high energy regime. Considering dynamics in a Friedmann-Lemaître-Robertson-Walker background, critical points, representing stable Einstein static states of the phase space, result as solutions. It then turns out that as the equation of state parameter $ω$ gradually declines from a constant value as $t\rightarrow-\infty$, eventually some of the static past eternal so…
