In this paper we show that a pseudo-Nambu-Goldstone boson (PNGB) quintessence of spontaneous symmetry breaking (SSB) is responsible for an epoch of the late time cosmic acceleration. We suggest that an N=2 PNGB quintessence with SSB can give rise to the fast-roll cosmic acceleration in evolution of the Universe. In the N=2 PNGB quintessence model, the standard slow-roll condition in which the absolute value of the tachyonic mass squared $|m_q^2|$ of this model is much less than the square of the Hubble constant $H^2$, is broken down to the fast-roll condition, $|m_q^2|=O(H^2)$. However, it is shown that the fast-rolling associated with the N=2 PNGB quintessence of SSB can be led to the epoch of the late time cosmic acceleration. Indeed, in our PNGB model, this epoch can be quite long lasting since the mass of the N=2 PNGB quintessence field is extremely small as $m_q \approx 10^{-33} \rm{eV}$.
We review the pNGB quintessence models, and point out that the reason why the large decay constants $f_a \ga {\cal O}(1)M_{Pl}$ are really needed is to tame a tachyonic instability present for a wide range of initial $vev$s. Starting very close to potential maxima does not help because quantum fluctuations during early inflation at a scale $H_I$ perturb the quintessence $vev$, displacing it from the maxima. This issue is quite interesting for pNGB dark energy in light of the recently discussed difficulties with embedding models with $f_a > M_{Pl}$ in fundamental theory. A possible way around i…
A pseudo-Nambu Goldstone Boson (pNGB) arising from the breaking of a global symmetry ($G\rightarrow H$) can be one of the most promising candidates for the quintessence model, to explain the late-time acceleration of our universe. Motivated from the Composite Higgs scenario, we have investigated the case where the pNGB associated with $SO(N)/ SO(N-1)$ develops a potential through its couplings with the particles that do not form the complete representations of $G$. The Coleman Weinberg (CW) potential is generated via the external particles in the loop which are linked with the strongly interac…
A canonical pseudo-Nambu Goldstone Boson (pNGB) can play the role of a dark energy field responsible for present cosmic acceleration. Confronting with the recent cosmological data, we find that the pNGB field requires spontaneous symmetry breaking scale $f$ close to $M_P$ and the initial field value fine-tuned. It is difficult to achieve a large $f$ in a theoretically consistent set-up. A possible resolution can be achieved by increasing the Hubble friction in well motivated particle physics models in the general set-up of modified gravity theories. We show two phenomenological examples of thi…
A model consisting of quintessence scalar field interacting with cold dark matter is considered. Conditions required to reach $w_d=-1$ are discussed. It is shown that depending on the potential considered for the quintessence, reaching the phantom divide line puts some constraints on the interaction between dark energy and dark matter. This also may determine the ratio of dark matter to dark energy density at $w_d=-1$.
The string inspired tachyon field can serve as a candidate of dark energy. Its equation of state parameter $w$ varies from 0 to -1. In case of tachyon field potential $V(ϕ)\to 0$ slower(faster) than $1/ϕ^2$ at infinity, dark energy(dark matter) is a late time attractor. We investigate the tachyon dark energy models under the assumption that $w$ is close to -1. We find that all the models exhibit unique behavior around the present epoch which is exactly same as that of the thawing quintessence.
We investigate the dark matter annihilation in the brane-world and quintessence scenarios, in which the modified cosmological expansion rate can enhance the thermal relic density of dark matter. According to the observed dark matter abundance, we constrain the thermally averaged annihilation cross section <σv> in these two scenarios. In addition, the big bang nucleosynthesis and the partial-wave unitarity are also used to place bounds on <σv>. It is found that both scenarios can lead to a large annihilation cross section, so they can be used to explain the recent PAMELA, ATIC and PPB-BETS anom…
We study the models with radiative neutrino mass generation and explore the relation between the neutrino masses and dark energy. In these models, the pseudo-Nambu-Goldston bosons (pNGBs) arise at two-loop level via the Majorana neutrino masses. In particular, we demonstrate that the potential energy of the pNGB can be the dark energy potential and the observed value of the equation of state (EoS) parameter of the universe, $i.e.$, $w\simeq -1$, can be realized.
In this work we determine the correspondence between quintessence and tachyon dark energy models with a constant dark energy equation of state parameter, $w_e$. Although the evolution of both the Hubble parameter and the scalar field potential with redshift is the same, we show that the evolution of quintessence/tachyon scalar fields with redshift is, in general, very different. We explicity demonstrate that if $w_e \neq -1$ the potentials need to be very fine-tuned for the relative perturbation on the equation of state parameter, $Δw_e/(1+w_e) \ll 1$, to be very small around the present time.…
In a recent paper by C. Gao, M. Kunz, A. Liddle and D. Parkinson [arXiv:0912.0949], the unification of dark matter and dark energy was explored within a theory containing a scalar field of non-Lagrangian type. This scalar field, different from the classic quintessence, can be obtained from the scalar field representation of an interacting two-fluid mixture described in the paper by L.P. Chimento and M. Forte [arXiv:0706.4142]
Exponential Quintessence Model: Analytical Quantification of the Fine-Tuning Problem in Dark Energy
The Graduate University for Advanced Studies (SOKENDAI)（高级研究院（SOKENDAI））；National Astronomical Observatory of Japan（日本国立天文台）；University of Tokyo（东京大学）；KEK（高能加速器研究机构）；Kavli IPMU (WPI), UTIAS, University of Tokyo（东京大学木户宇宙物理数学研究所（ Kavli IPMU ））
Recently, a dark energy model characterized by the age of the universe, dubbed ``agegraphic dark energy'', was proposed by Cai. In this paper, a connection between the quintessence scalar-field and the agegraphic dark energy is established, and accordingly, the potential of the agegraphic quintessence field is constructed.
We introduce a natural model of quintessence in string theory where the light rolling scalar is radiatively stable and couples to Standard Model matter with weaker-than- Planckian strength. The model is embedded in an anisotropic type IIB compactification with two exponentially large extra dimensions and TeV-scale gravity. The bulk turns out to be nearly supersymmetric since the scale of the gravitino mass is of the order of the observed value of the cosmological constant. The quintessence field is a modulus parameterising the size of an internal four-cycle which naturally develops a potential…
We consider ideal fluid and equivalent scalar field dark energy universes where all four known types of finite-time, future singularities occur at some parameter values. It is demonstrated that pressure/energy density of such quintessence/phantom dark energy diverges in spherically-symmetric spacetime at finite radius or at the center. This may cause the instability of the relativistic star or black hole in such universe. The resolution of the problem via the extra modification of the equation of state is briefly discussed.
We present a novel dark energy candidate, based upon the existence and dynamics of Ghost D-branes in a warped compactification of type IIB string theory. Gp-branes cancel the combined BPS sectors of the Dp-branes, while they preserve the same supersymmetries. We show that this scenario can naturally lead to either quintessence or phantom-like behaviors, depending on the form of the involved potentials and brane tension.
We suggest a correspondence between interacting agegraphic dark energy models and the quintessence scalar field in a non-flat universe. We demonstrate that the agegraphic evolution of the universe can be described completely by a single quintessence scalar field. Then, we reconstruct the potential of the interacting agegraphic quintessence dark energy as well as the dynamics of the scalar field according to the evolution of the agegraphic dark energy.
In the present work, motivated by the work of Cai and Su [Phys. Rev. D {\bf 81}, 103514 (2010)], we propose a new type of interaction in dark sector, which can change its sign when our universe changes from deceleration to acceleration. We consider the cosmological evolution of quintessence and phantom with this type of interaction, and find that there are some scaling attractors which can help to alleviate the cosmological coincidence problem. Our results also show that this new type of interaction can bring new features to cosmology.
The origin of the neutrino mass, dark matter (DM), and dark energy (DE) are among the most challenging problems of fundamental physics. We address these questions from analyses of the models where the neutrino mass is generated via Yukawa coupling to the quintessence field which represents the DE. It has been shown in a recent work on the toy model with a single Dirac fermion coupled to the quintessence that by choosing parameters of the DE potential to match the present DE density, the model allows to lock the neutrino mass at m ~0.01 eV and yields consistent estimates for other parameters of…
The distinction between modified gravity and quintessence or dynamical dark energy is difficult. Many models of modified gravity are equivalent to models of coupled quintessence by virtue of variable transformations. This makes an observational differentiation between modified gravity and dark energy very hard. For example, the additional scalar degree of freedom in $f(R)$-gravity or non-local gravity can be interpreted as the cosmon of quintessence. Nevertheless, modified gravity can shed light on questions of interpretation, naturalness and simplicity. We present a simple model where gravity…
With a parametric form of the equation of state parameter of dark energy, a quintessence potential has been reconstructed. The potential is found to be a generalization of a double exponential potential. The constraints on the parameters are obtained by maximum likelihood analysis using observational Hubble data, type Ia supernova data, baryon acoustic oscillation data and the CMB shift parameter data. Th emodel shows preference towards the phantom behaviour of dark energy.
By analysing the cosmological dynamical system with a dark-sector interaction which changes sign during the cosmological evolution, we find a scaling attractor to help to alleviate the cosmic-coincidence problem. This result shows that this interaction can bring new features to the cosmology.
We examine dark energy models in which a quintessence or a phantom field, $ϕ$, rolls near the vicinity of a local minimum or maximum, respectively, of its potential $V(ϕ)$. Under the approximation that $(1/V)(dV/dϕ) \ll 1$, [although $(1/V)(d^2 V/dϕ^2)$ can be large], we derive a general expression for the equation of state parameter $w$ as a function of the scale factor for these models. The dynamics of the field depends on the value of $(1/V)(d^2 V/dϕ^2)$ near the extremum, which describes the potential curvature. For quintessence models, when $(1/V)(d^2 V/dϕ^2)<3/4$ at the potential minimum…
The string theory swampland proposes that there is no UV-completion for an effective field theory with an exact (metastable) de Sitter vacua, thereby ruling out standard $Λ$CDM cosmology if the conjecture is taken seriously. The swampland criteria have also been shown to be in sharp tension with quintessence models under current and forthcoming observational bounds. As a logical next step, we introduce higher derivative self-interactions in the low-energy effective Lagrangian and show that one can satisfy observational constraints as well as the swampland criteria for some specific models. In …
In the Einstein-Cartan gravitational theory with the chameleon field, changing its mass in dependence of a density of its environment, we analyze the Friedmann-Einstein equations for the Universe evolution with the expansion parameter $a$ dependent on time only. We analyze the problem of an identification of the chameleon field with quintessence, i.e. a canonical scalar field responsible for dark energy dynamics and for the acceleration of the Universe expansion. We show that since the cosmological constant, related to the relic dark energy density, is induced by torsion (Astrophys. J.829, 47 …
We introduce a new form of coupling between dark energy and dark matter that is quadratic in their energy densities. Then we investigate the background dynamics when dark energy is in the form of exponential quintessence. The three types of quadratic coupling all admit late-time accelerating critical points, but these are not scaling solutions. We also show that two types of coupling allow for a suitable matter era at early times and acceleration at late times, while the third type of coupling does not admit a suitable matter era.
We consider the coupling of quintessence to observable matter in supergravity and study the dynamics of both supersymmetry breaking and quintessence in this context. We investigate how the quintessence potential is modified by supersymmetry breaking and analyse the structure of the soft supersymmetry breaking terms. We pay attention to their dependence on the quintessence field and to the electroweak symmetry breaking, ie the pattern of fermion masses at low energy within the Minimal Supersymmetric Standard Model (MSSM) coupled to quintessence. In particular, we compute explicitly how the ferm…
The holographic dark energy model is an attempt for probing the nature of dark energy within the framework of quantum gravity. The dimensionless parameter $c$ determines the main property of the holographic dark energy. With the choice of $c\geq 1$, the holographic dark energy can be described completely by a quintessence scalar field. In this paper, we show this quintessential description of the holographic dark energy with $c\geq 1$ and reconstruct the potential of the quintessence as well as the dynamics of the scalar field.
We study evolution of perturbations in dark matter and dark energy for spherical collapse. We study Tachyon models of dark energy using the approach outlined in Rajvanshi and Bagla (2018). We work with models that are allowed by current observations. We find that as with Quintessence models allowed by observations, dark energy perturbations do not affect evolution of perturbations in dark matter in a significant manner. Perturbations in dark energy remain small for such models. In order to compare different classes of dark energy models, we use reconstruction of potentials and study dark matte…
The self-gravitating gas in the Newtonian limit is studied in the presence of dark energy with a linear and constant equation of state. Entropy extremization associates to the isothermal Boltzmann distribution an effective density that includes `dark energy particles', which either strengthen or weaken mutual gravitational attraction, in case of quintessence or phantom dark energy, respectively, that satisfy a linear equation of state. Stability is studied for microcanonical (fixed energy) and canonical (fixed temperature) ensembles. Compared to the previously studied cosmological constant cas…
While there is mounting evidence in all fronts of experimental cosmology for a non-vanishing dark energy component in the Universe, we are still far away from understanding its ultimate nature. A fundamental cosmological constant, Lambda, is the most natural candidate, but many dynamical mechanisms to generate an effective Lambda have been devised which postulate the existence of a peculiar scalar field (so-called quintessence, and generalizations thereof). These models are essentially ad hoc, but they lead to the attractive possibility of a time-evolving dark energy with a non-trivial equatio…
Using cosmic voids to probe the growth rate of cosmic structure, and hence the nature of dark energy, is particularly interesting in the context of modified gravity theories that rely on the screening mechanism. In this work we improve the modelling of redshift-space distortions around voids in the dark matter density field, and thus reduce systematic errors in the derivation of cosmological parameters. We also show how specific types of voids can be used to better probe the growth rate, using a flexible void finder. We apply our results to test for a quintessence type of dark energy vs. a LCD…
We study the dynamical properties of tracker quintessence models using a general parametrization of their corresponding potentials, and show that there is a general condition for the appearance of a tracker behavior at early times. Likewise, we determine the conditions under which the quintessence tracker models can also provide an accelerating expansion of the universe with an equation of state closer to $-1$. Apart from the analysis of the background dynamics, we also include linear density perturbations of the quintessence field in a consistent manner and using the same parametrization of t…
The quintessence dark energy potential is reconstructed in a model-independent way. Reconstruction relies on a Gaussian process and on available expansion-rate data. Specifically, 40-point values of $H(z)$ are used, consisting of a 30-point sample deduced from a differential age method and an additional 10-point sample obtained from the radial BAO method. Results are obtained for two kernel functions and for three different values of $H_{0}$. They shed light on the $H_{0}$ tension problem for a universe described with quintessence dark energy. They are also a clear indication that the tension …
We study the spherical collapse model in the presence of quintessence with negligible speed of sound. This case is particularly motivated for w<-1 as it is required by stability. As pressure gradients are negligible, quintessence follows dark matter during the collapse. The spherical overdensity behaves as a separate closed FLRW universe, so that its evolution can be studied exactly. We derive the critical overdensity for collapse and we use the extended Press-Schechter theory to study how the clustering of quintessence affects the dark matter mass function. The effect is dominated by the modi…
In this paper we implement the new agegraphic dark energy model with quintessence field. We demonstrate that the new agegraphic evolution of the universe can be described completely by a single quintessence field. Its potential as a function of the quintessence field is reconstructed numerically. In particular, the analytical solution of the new agegraphic quintessence dark energy model (NAQDE) is approximately obtained in the matter-dominated epoch. Furthermore, we investigate the evolution of the NAQDE model in the $ω-ω'$ phase plane. It turns out that by quantum corrections, the trajectory …
We propose an holographic quintessence and tachyon models of dark energy. The correspondence between the quintessence and tachyon energy densities with the holographic density, allows the reconstruction of the potentials and the dynamics for the quintessence and tachyon fields, in flat FRW background. The proposed infrared cut-off for the holographic energy density works for two cases of the constant $α$: for $α<1$ we reconstructed the holographic quintessence model in the region before the $ω=-1$ crossing for the EoS parameter. The cosmological dynamics for $α>1$ was also reconstructed for th…
We study the motion of a ring string in the background of the Bardeen-AdS black hole surrounded by the quintessence dark energy. The effects of the magnetic monopole charge, the quintessence state parameter, and the quintessence normalization parameter on the dynamical behavior of the ring string are respectively analyzed. Our numerical results show that the chaotic behavior of string generally becomes stronger with the increase of the quintessence normalization parameter. In particular, the conditions for the existence of chaos are distinctly diverse for two different quintessence state param…
We analyze the coupled quintessence in the light of the linear dynamical systems theory, with two different interactions: i) proportional to the energy density of the dark energy and ii) proportional to the sum of the energy densities of the dark matter and dark energy. The results presented here enlarge the previous analyses in the literature, wherein the interaction has been only proportional to the energy density of the dark matter. In the first case it is possible to get the well-known sequence of cosmological eras. For the second interaction only the radiation and the dark energy era can …
We use linear perturbation theory to study perturbations in dynamical dark energy models. We compare quintessence and tachyonic dark energy models with identical background evolution. We write the corresponding equations for different models in a form that makes it easier to see that the two models are very hard to distinguish in the linear regime, especially for models with $(1 + w) \ll 1$. We use Cosmic Microwave Background data and parametric representations for the two models to illustrate that they cannot be distinguished for the same background evolution with existing observations. Furth…
In standard cosmologies, dark energy interacts only gravitationally with dark matter. An extension to this picture is interacting quintessence (IQ) model, where scalar field coupled directly to cold dark matter. The percentage deviation is studied in IQ model wrt $Λ$CDM for varied values of interacting parameter W. We investigated the effect of interaction on matter, Kaiser and galaxy power spectrums. Deviation in power spectrum increases with interaction on both large and small scales. On small scale, variation is comparatively smaller than on large scale. On large scale, it is due to dark en…
Extended quintessence is obtained by coupling a normal scalar field to the Ricci scalar defined in the metric formalism. In this paper, we propose a new extended quintessence dark energy by introducing a non-minimal coupling between the quintessence and gravity, but with the Ricci scalar given from the Palatini formalism rather than the metric one. We find that the equation of state of the new extended quintessence can cross the phantom divide line, and moreover, it oscillates around the -1 line. We also show that the universe driven by the new extended quintessence will enter a dark energy do…
In this work we investigate corrections of the quintessence regime of the dark energy on the Joule-Thomson (JT) effect of the Reissner Nordström anti de Sitter (RNAdS) black hole. The quintessence dark energy has equation of state as $p_q=ωρ_q$ in which $-1<ω<-\frac{1}{3}.$ Our calculations are restricted to ansatz: $ω=-1$ (the cosmological constant regime) and $ω=-\frac{2}{3}$ (quintessence dark energy). To study the JT expansion of the AdS gas under the constant black hole mass, we calculate inversion temperature $T_i$ of the quintessence RNAdS black hole where its cooling phase is changed t…
In this paper we consider two models of quintessence scalar fields with different potentials. Interaction with generalized cosmic Chaplygin gas is also investigated. Cosmological parameters are studied and graphical behavior is analyzed. We find that our model is agree with observational data specially $Λ$CDM model.
We discuss some cosmological consequences of a general model of coupled quintessence in which the phenomenological coupling between the cold dark matter and dark energy is a function of the cosmic scale factor $ε(a)$. This class of models presents cosmological solutions in which the Universe is currently dominated by an exotic component, but will eventually be dominated by cold dark matter in the future. This dynamical behavior is considerably different from the standard $Λ$CDM evolution, and may alleviate some conflicts in reconciling the idea of the dark energy-dominated universe with observ…
We investigate the effects of quintessence dark energy on the shadows of black hole, surrounded by various profiles of accretions. For the thin disk accretion, the images of the black hole comprises the dark region and bright region, including direct emission, lensing rings and photon rings. Although their details depend on the form of the emission, generically, the direct emission plays a major role for the observed brightness of the black hole, while the lensing ring makes a small contribution and photon ring makes a negligible contribution. The existence of cosmological horizon also plays a…
We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-conventional kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the dark energy vanishes in the early universe and then grows with time. This constitutes an "…
Over the last few years the $R_{\mathrm{h}}=ct$ universe has received a lot of attention, particularly when observational evidence seems to favor this over the standard $Λ$ cold dark matter ($ΛCDM$) universe. Like the $ΛCDM$, the $R_{\mathrm{h}}=ct$ universe is based on a Friedmann-Robertson-Walker (FRW) cosmology where the total energy density $ρ$ and pressure $p$ of the cosmic fluid contain a dark energy component besides the usual (dark and baryonic) matter and radiation components. However unlike the $ΛCDM$ this model has the simple equation of state (EOS) $ρ+ 3p = 0$, i.e., its total acti…
A so called "ghost dark energy" was recently proposed to explain the present acceleration of the universe expansion. The energy density of ghost dark energy, which originates from Veneziano ghost of QCD, is proportional to the Hubble parameter, $ρ_D=αH$, where $α$ is a constant which is related to the QCD mass scale. In this paper, we establish the correspondence between ghost dark energy and quintessence scalar field energy density. This connection allows us to reconstruct the potential and the dynamics of the quintessence scalar field according to the evolution of ghost energy density.
In this paper, we study quintessence cosmology with an effective $Λ$-term in Lyra manifold. We consider three different models by choosing variable $Λ$ depend on time, the Hubble parameter and the energy density of dark matter and dark energy. Dark energy assumed as quintessence which interacts with the dark matter. By using numerical analysis we investigate behavior of cosmological parameters in three different models and compare our results with observational data. Statefinder diagnostic is also performed for all models.
Brans--Dicke scalar--tensor theory provides a conformally coupling of the scalar field with gravity in Einstein's frame. This model is equivalent to an interacting quintessence in which dark matter is coupled to dark energy. This provides a natural mechanism to alleviate the coincidence problem. We investigate the dynamics of this model and show that it leads to comparable dark energy and dark matter densities today.
In the context of the induced matter theory of gravity, we investigate the possibility of deriving a 4D quintessential scenario where an interaction between dark energy and dark matter is allowed, and the dark energy component is modeled by a minimally coupled scalar field. Regarding the Ponce de Leon metric, we found that it is possible to obtain such scenario on which the energy densities of dark matter and dark energy, are both depending of the fifth extra coordinate. We obtain that the 4D induced scalar potential for the quintessence scalar field, has the same algebraic form to the one fou…
In this Letter, we investigate the effects of dark energy on $P-V$ criticality of charged AdS black holes by considering the case of the RN-AdS black holes surrounded by quintessence. By treating the cosmological constant as thermodynamic pressure, we study its thermodynamics in the extended phase space. It is shown that quintessence dark energy does not affect the existence of small/large black hole phase transition. For the case $ω_q=-2/3$ we derive analytic expressions of critical physical quantities, while for cases $ω_q\neq-2/3$ we appeal to numerical method for help. It is shown that qui…
We examine the behavior of dark energy models in the plane defined by w (the equation of state parameter for the dark energy) and w' (the derivative of w with respect to the logarithm of the scale factor). For non-phantom barotropic fluids with positive squared sound speed, we find that w' < 3w(w+1), the opposite of the bound on quintessence models previously derived by Caldwell and Linder. Thus, these barotropic models and quintessence models for the dark energy occupy disjoint regions in the w - w' plane. We also derive two new bounds for quintessence models in the w - w' plane: the first is…
In this paper, we have presented a model of the FLRW universe filled with matter and dark energy fluids, by assuming an ansatz that deceleration parameter is a linear function of the Hubble constant. This results in a time-dependent DP having decelerating-accelerating transition phase of the universe. This is a quintessence model $ω_{(de)}\geq -1$. The quintessence phase remains for the period $(0 \leq z \leq 0.5806)$. The model is shown to satisfy current observational constraints. Various cosmological parameters relating to the history of the universe have been investigated.
