Dvali-Gabadadze-Porrati Model Research Articles

A study of an embedding class-I traversable wormhole in Galileon Gravity

In this article, we examine the possibility of the creation of a traversable wormhole geometry in Galileon Gravity (GG). In this gravity, the alternation of gravity is determined by an effective scalar field ϕ, treated as the Galileon field. From a mechanism perspective, GG is developed by covariantizing the decoupling Lagrangian of the DGP (Dvali-Gabadadze-Porrati) model. Now, to achieve our aim, gravitational field equations have been constructed corresponding to a line element, which represents a static and spherically symmetric spacetime. Next, we have modified these field equations in the context of a Morris-Thorne traversable wormhole spacetime. In particular, we have used the ‘Karmarkar condition’ to evaluate the wormhole solutions in a general sense. Further, for a better understanding of our obtained wormhole solutions, 2-dimensional and 3-dimensional diagrams have been displayed. Later, we scrutinized the possible creation of a traversable wormhole based on the essential requirements, that is, the infraction of energy conditions in the neighborhood of the throat region, especially the Null Energy Condition (NEC). For this purpose, we have discussed three cases like Case-I: without the necessity of dark energy (DE), Case-II: with support of phantom-like DE and Case-III: with the SFDM profile of a dark matter (DM) halo. Next, we have examined the hydrostatic equilibrium position corresponding to our obtained wormhole system in GG. Furthermore, to examine the small and sufficient quantity of exotic matter, the possible formation of a traversable wormhole has been explored by a volume integral quantifier. Lastly, we have shown the nature of active mass. Finally, we have concluded that traversable wormhole solutions can also be established in the presence of an effective scalar field without any essential support of exotic matter in the neighborhood of the throat region by GG.

Charged Taub-NUT-de Sitter spacetime in DGP braneworld and its thermodynamics* *Supported by Lembaga Penelitian dan Pengabdian kepada Masyarakat Universitas Katolik Parahyangan (III/LPPM/2022-02/79-P)

We study a charged Taub-NUT spacetime solution in the Dvali-Gabadadze-Porrati (DGP) brane. We show that the Reissner-Nordstrom-Taub-NUT-de Sitter solution of Einstein-Maxwell gravity solves the corresponding equations of motion, where the cosmological constant is related to the cross-over scale in the DGP model. Following the approach by Teitelboim in discussing the thermodynamics of de Sitter spacetime and the proposal by Wu et al. for a conserved charge associated with the NUT parameter, we obtain the generalized Smarr mass formula and the first law of thermodynamics of the spacetime.

On Einstein equations with cosmological constant in braneworld models

In this paper, we investigate the Einstein equations with cosmological constant for Randall-Sundrum (RS) and Dvali-Gabadadze-Porrati (DGP) models to determine the warp functions in the context of warp product spacetimes. In RS model, it is shown that Einstein's equation in the bulk is reduced into the brane as a vacuum equation, having vacuum solution, which is not affected by the cosmological constant in the bulk. In DGP model, it is shown that the Einstein's equation in the bulk is reduced into the brane and along the extra dimension, where both equations are affected by the cosmological constant in the bulk. We have solved these equations in DGP model, subject to vanishing cosmological constants on the brane and along extra dimension, and obtained exact solutions for the warp functions. The solutions depend on the typical values of cosmological constant in the bulk as well as the dimension of the brane. So, corresponding to the typical values, some solutions have exponential behaviours which may be set to represent warp inflation on the brane, and some other solutions have oscillating behaviours which may be set to represent warp waves or branes waves along the extra dimension.

The impact of modified gravity on the Sunyaev–Zeldovich effect

ABSTRACT We study the effects of two popular modified gravity theories, which incorporate very different screening mechanisms, on the angular power spectra of the thermal (tSZ) and kinematic (kSZ) components of the Sunyaev–Zeldovich effect. Using the first cosmological simulations that simultaneously incorporate both screened modified gravity and a complete galaxy formation model, we find that the tSZ and kSZ power spectra are significantly enhanced by the strengthened gravitational forces in Hu-Sawicki f(R) gravity and the normal-branch Dvali–Gabadadze–Porrati model. Employing a combination of non-radiative and full-physics simulations, we find that the extra baryonic physics present in the latter acts to suppress the tSZ power on angular scales l ≳ 3000 and the kSZ power on all tested scales, and this is found to have a substantial effect on the model differences. Our results indicate that the tSZ and kSZ power can be used as powerful probes of gravity on large scales, using data from current and upcoming surveys, provided sufficient work is conducted to understand the sensitivity of the constraints to baryonic processes that are currently not fully understood.

Higher order spectra of weak lensing convergence maps in parametrized theories of modified gravity

ABSTRACT We compute the low-ℓ limit of the family of higher order spectra for projected (2D) weak lensing convergence maps. In this limit these spectra are computed to an arbitrary order using tree-level perturbative calculations. We use the flat-sky approximation and Eulerian perturbative results based on a generating function approach. We test these results for the lower order members of this family, i.e. the skew- and kurt-spectra against state-of-the-art simulated all-sky weak lensing convergence maps and find our results to be in very good agreement. We also show how these spectra can be computed in the presence of a realistic sky-mask and Gaussian noise. We generalize these results to 3D and compute the equal-time higher order spectra. These results will be valuable in analysing higher order statistics from future all-sky weak lensing surveys such as the Euclid survey at low-ℓ modes. As illustrative examples, we compute these statistics in the context of the Horndeski and beyond Horndeski theories of modified gravity. They will be especially useful in constraining theories such as the Gleyzes–Langlois–Piazza–Vernizzi (GLPV) theories and degenerate higher order scalar-tensor theories as well as the commonly used normal-branch of Dvali–Gabadadze–Porrati model, clustering quintessence models and scenarios with massive neutrinos.

Thermodynamic and observational constraints of DGP braneworld in the light of nonlinear electrodynamics

This paper deals with the study of the effect of Maxwell’s nonlinear electrodynamics (NLED) in the framework of Dvali–Gabadadze–Porrati (DGP) brane gravity for Friedmann–Robertson–Walker (FRW) Universe. Recently, the Hawking temperature and Bekenstein entropy have been modified for the validity of the thermodynamical laws at the event horizon. In this context, we test the validity of the generalized second law of thermodynamics (GSLT) at the apparent and event horizons. Here, the entropy of the horizon has been extracted for the following two cases: (i) by assuming the first law of thermodynamics (ii) by using modified entropy-area relation. In the case of apparent horizon, we consider the usual Hawking temperature. On the other hand, in the case of event horizon, we consider the modified Hawking temperature. Next, we discuss the geometrical parameters (deceleration, statefinder parameters and [Formula: see text] diagnostic) to explore the expansion of the accelerating Universe. From the general expression of GSLT, we find that for the apparent horizon, the GSLT always holds for any choice of model parameters in both the branches of the DGP model. However, the null energy condition must satisfy for the plausibility of GSLT at the event horizon. Finally, we use the recent observational data from Stern datasets, Baryon Acoustic Oscillations (BAO), Cosmic Microwave Background (CMB) and Type Ia Supernovae (SNIa) observations to hold down the model parameters. Our analysis reveals that the DGP braneworld is free from classical instability issues and also cannot be ruled out by present thermodynamical and observational constraints.

Bayesian comparison of nonstandard cosmologies using type Ia supernovae and BAO data

We use the most recent type Ia supernovae (SNe Ia) observations to perform a statistical comparison between the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model and its extensions [$w\mathrm{CDM}$ and $w(z)\mathrm{CDM}$] and some alternative cosmologies: namely, the Dvali-Gabadadze-Porrati (DGP) model, a power-law $f(R)$ scenario in the metric formalism and an example of vacuum decay [$\mathrm{\ensuremath{\Lambda}}(t)\mathrm{CDM}$] cosmology in which the dilution of pressureless matter is attenuated with respect to the usual ${a}^{\ensuremath{-}3}$ scaling due to the interaction of the dark matter and dark energy fields. We perform a Bayesian model selection analysis using the MultiNest algorithm. To obtain the posterior distribution for the parameters of each model, we use the joint light-curve analysis (JLA) SNe Ia compilation containing 740 events in the interval $0.01<z<1.3$ along with current measurements of baryon acoustic oscillations (BAO). The JLA data are analyzed with the SALT2 light-curve fitter and the model selection is then performed by computing the Bayesian evidence of each model and the Bayes factor of the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ cosmology related to the other models. The results indicate that the JLA data alone are unable to distinguish the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model from some of its alternatives but its combination with current measurements of baryon acoustic oscillations shows up an ability to distinguish them. In particular, the DGP model is practically not supported by both the BAO and the joint $\mathrm{JLA}+\mathrm{BAO}$ data sets compared to the standard scenario. Finally, we provide a rank order for the models considered.

Ghosts in the self-accelerating DGP branch with Gauss–Bonnet effect

The Dvali-Gabadadze-Porrati brane-world model provides a possible approach to address the late-time cosmic acceleration. However, it has subsequently been pointed out that a ghost instability will arise on the self-accelerating branch. Here, we carefully investigate whether this ghost problem could be possibly cured by introducing the Gauss-Bonnet term in the five-dimensional bulk action, a natural generalization to the Dvali-Gabadadze-Porrati model. Our analysis is carried out for a background where a de Sitter brane is embedded in an anti-de Sitter bulk. Our result shows that the ghost excitations cannot be avoided even in this modified model.

Testing Dvali–Gabadadze–Porrati gravity with Planck

Recently, the Planck Collaboration has released the first cosmological papers providing the highest resolution, full sky, maps of the cosmic microwave background (CMB) temperature anisotropies. It is crucial to understand that whether the accelerating expansion of our universe at present is driven by an unknown energy component (Dark Energy) or a modification to general relativity (Modified Gravity). In this Letter we study a phenomenological model which interpolates between the pure ΛCDM model and the Dvali–Gabadadze–Porrati (DGP) braneworld model with an additional parameter α. Firstly, we calculate the “distance information” of Planck data which includes the “shift parameter” R, the “acoustic scale” lA, and the photon decoupling epoch z⁎ in different cosmological models and find that this information is almost independent on the input models we use. Then, we compare the constraints on the free parameter α of the DGP model from the “distance information” of Planck and WMAP data and find that the Planck data with high precision do not improve the constraint on α, but give the higher median value and the better limit on the current matter density fraction Ωm. Then, combining the “distance information” of Planck measurement, baryon acoustic oscillations (BAO), Type Ia supernovae (SNIa) and the prior on the current Hubble constant (HST), we obtain the tight constraint on the parameter α<0.20 at 95% confidence level, which implies that the flat DGP model has been ruled out by the current cosmological data. Finally, we allow the additional parameter α<0 in our calculations and interestingly obtain α=−0.29±0.20 (68% C.L.), which means the current data slightly favor the effective equation of state weff<−1. More importantly, the tension between constraints on H0 from different observational data has been eased.

Testing modified gravity models with recent cosmological observations

We explore the cosmological implications of five modified gravity (MG) models by using the recent cosmological observational data, including the recently released SNLS3 type Ia supernovae sample, the cosmic microwave background anisotropy data from the Wilkinson Microwave Anisotropy Probe 7-yr observations, the baryon acoustic oscillation results from the Sloan Digital Sky Survey data release 7, and the latest Hubble constant measurement utilizing the Wide Field Camera 3 on the Hubble Space Telescope. The MG models considered include the Dvali-Gabadadze-Porrati(DGP) model, two $f(R)$ models, and two $f(T)$ models. We find that compared with the $\Lambda$CDM model, MG models can not lead to a appreciable reduction of the $\chi^2_{min}$. The analysis of AIC and BIC shows that the simplest cosmological constant model($\Lambda$CDM) is still most preferred by the current data, and the DGP model is strongly disfavored. In addition, from the observational constraints, we also reconstruct the evolutions of the growth factor in these models. We find that the current available growth factor data are not enough to distinguish these MG models from the $\Lambda$CDM model.

Cosmological probes of modified gravity: the nonlinear regime

We review the effects of modified gravity on large-scale structure in the nonlinear regime, focusing on f(R) gravity and the Dvali-Gabadadze-Porrati model, for which full N-body simulations have been performed. In particular, we discuss the abundance of massive halos, the nonlinear matter power spectrum and the dynamics within clusters and galaxies, with particular emphasis on the screening mechanisms present in these models.

Classical stability of the Galileon

We consider the classical equations of motion for a single Galileon field with generic parameters in the presence of non-relativistic sources. We introduce the concept of absolute stability of a theory: if one can show that a field at a single point---like infinity for instance---in spacetime is stable, then stability of the field over the rest of spacetime is guaranteed for any positive energy source configuration. The Dvali-Gabadadze-Porrati (DGP) model is stable in this manner, and previous studies of spherically symmetric solutions suggest that certain classes of the single field Galileon (of which the DGP model is a subclass) may have this property as well. We find, however, that when general solutions are considered this is not the case. In fact, when considering generic solutions there are no choices of free parameters in the Galileon theory that will lead to absolute stability except the DGP choice. Our analysis indicates that the DGP model is an exceptional choice among the large class of possible single field Galileon theories. This implies that if general solutions (non-spherically symmetric) exist they may be unstable. Given astrophysical motivation for the Galileon, further investigation into these unstable solutions may prove fruitful.

OBSERVATIONAL CONSTRAINTS ON PHANTOM CROSSING DGP GRAVITY

We study the observational constraints on the Phantom Crossing DGP model. We demonstrate that the crossing of the phantom divide does not occur within the framework of the original Dvali–Gabadadze–Porrati (DGP) model or the DGP model developed by Dvali and Turner. By extending their model in the framework of an extra dimension scenario, we study a model that realizes crossing of the phantom divide. We investigate the cosmological constraints obtained from the recent observational data of Type Ia supernovae, cosmic microwave background anisotropies, and baryon acoustic oscillations. The best-fit values of the parameters with 1σ (68%) errors for the Phantom Crossing DGP model are [Formula: see text]. We find that the Phantom Crossing DGP model is more compatible with the observations than the original DGP model or the DGP model developed by Dvali and Turner. Our model can realize late-time acceleration of the universe, similar to that of ΛCDM model, without dark energy due to the effect of DGP gravity. In our model, the crossing of the phantom divide occurs at a redshift of z ~ 0.2.

Modified holographic dark energy in DGP brane world

In this Letter, the cosmological dynamics of a modified holographic dark energy which is derived from the UV/IR duality by considering the black hole mass in higher dimensions as UV cutoff, is investigated in Dvali–Gabadadze–Porrati (DGP) brane world model. We choose Hubble horizon and future event horizon as IR cutoff respectively. And the two branches of the DGP model are both taken into account. When Hubble horizon is considered as IR cutoff, the modified holographic dark energy (HDE) behaves like an effect dark energy that modification of gravity in pure DGP brane world model acts and it can drive the expansion of the universe speed up at late time in ϵ=−1 branch which in pure DGP model cannot undergo an accelerating phase. When future event horizon acts as IR cutoff, the equation of state parameter of the modified HDE can cross the phantom divide.

Self-accelerating solutions in the cascading DGP braneworld

Abstract The self-accelerating branch of the Dvali–Gabadadze–Porrati (DGP) five-dimensional braneworld has provided a compelling model for the current cosmic acceleration. Recent observations, however, have not favored it so much. We discuss the solutions which contain a de Sitter 3-brane in the cascading DGP braneworld model, which is a kind of higher-dimensional generalizations of the DGP model, where a p-dimensional brane is placed on a ( p + 1 ) -dimensional one and the p-brane action contains the ( p + 1 ) -dimensional induced scalar curvature term. In the simplest six-dimensional model, we derive the solutions. Our solutions can be classified into two branches, which reduce to the self-accelerating and normal solutions in the limit of the original five-dimensional DGP model. In the presence of the six-dimensional bulk gravity, the ‘normal’ branch provides a new self-accelerating solution. The expansion rate of this new branch is generically lower than that of the original one, which may alleviate the fine-tuning problem.

Cosmic constraint to DGP brane model: Geometrical and dynamical perspectives

In this paper, the Dvali-Gabadadze-Porrati (DGP) brane model is confronted by current cosmic observational data sets from geometrical and dynamical perspectives. On the geometrical side, the recently released Union2 557 of type Ia supernovae (SN Ia), the baryon acoustic oscillation from the Sloan Digital Sky Survey and the Two Degree Galaxy Redshift Survey (transverse and radial to line-of-sight data points), the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations [shift parameters $R$, ${l}_{a}({z}_{*})$ and redshift at the last scatter surface ${z}_{*}$], ages of high redshifts galaxies, i.e., the lookback time and the high redshift gamma ray bursts are used. On the dynamical side, data points about the growth function of matter linear perturbations are used. Using the same data set combination, we also constrain the flat $\ensuremath{\Lambda}\mathrm{CDM}$ model as a comparison. The results show that current geometrical and dynamical observational data sets much favor the flat $\ensuremath{\Lambda}\mathrm{CDM}$ model and the departure from it is above $4\ensuremath{\sigma}(6\ensuremath{\sigma})$ for the spatially flat DGP model with (without) SN systematic errors. The consistence of growth function data points is checked in terms of a relative departure of redshift-distance relation.

Growth of linear matter perturbations and current observational constraints

We discuss, using a recently proposed parametrization for the growth index of linear matter perturbations, the observational constraints on the wCDM model and the Dvali–Gabadadze–Porrati (DGP) model with all current growth factor data. We find that the wCDM model is allowed by the observations at the 1σ confidence level, while the DGP model is only consistent with observations at 2σ confidence level.

Crossing the phantom divide in extended Dvali–Gabadadze–Porrati gravity

We propose a phantom crossing Dvali--Gabadadze--Porrati (DGP) model. In our model, the effective equation of state of the DGP gravity crosses the phantom divide line. We demonstrate crossing of the phantom divide does not occur within the framework of the original DGP model or the DGP model developed by Dvali and Turner. By extending their model, we construct a model that realizes crossing of the phantom divide. We find that the smaller the value of the new introduced parameter $\beta$ is, the older epoch crossing of the phantom divide occurs in. Our model can account for late-time acceleration of the universe without dark energy. We investigate and show the property of Phantom crossing DGP model.

Validity of generalised second law in holographic DGP brane

In this paper we study the validity of the generalised second law of thermodynamics (GSLT) of the universe bounded by the event horizon on the Dvali–Gabadadze–Porrati (DGP) brane world. The radius of the event horizon is calculated by establishing a correspondence between holographic dark energy and the effective energy density in the DGP brane world. It is shown that in the absence of cold dark matter (CDM), GSLT is always respected. In the presence of CDM, we take three different DGP models and find conditions under which GSLT holds.

Self-accelerating solutions in the cascading DGP braneworld

The self-accelerating branch of the Dvali–Gabadadze–Porrati (DGP) five-dimensional braneworld has provided a compelling model for the current cosmic acceleration. Recent observations, however, have not favored it so much. We discuss the solutions which contain a de Sitter 3-brane in the cascading DGP braneworld model, which is a kind of higher-dimensional generalizations of the DGP model, where a p-dimensional brane is placed on a (p+1)-dimensional one and the p-brane action contains the (p+1)-dimensional induced scalar curvature term. In the simplest six-dimensional model, we derive the solutions. Our solutions can be classified into two branches, which reduce to the self-accelerating and normal solutions in the limit of the original five-dimensional DGP model. In the presence of the six-dimensional bulk gravity, the ‘normal’ branch provides a new self-accelerating solution. The expansion rate of this new branch is generically lower than that of the original one, which may alleviate the fine-tuning problem.