DGP Braneworld Model Research Articles

Softly higher-derivative massive gravity

In this work, we study the higher-derivative massive gravity in D-dimensional space-time with the mass term arisen due to a 2-brane embedded in a 4D Minkowski spacetime. We consider the effect of a resonance mass term from the DGP braneworld model for the higher-derivative massive gravity. Moreover, we add the gravitational Chern–Simons and Ricci–Cotton terms to this model and evaluate the graviton propagator using a basis of Barnes–Rivers spin projectors. Using the obtained propagator, we proceed with discussing the consistency of the model, writing the dispersion relations, and analyzing causality and unitarity.

Towards an accurate model of small-scale redshift-space distortions in modified gravity

ABSTRACT The coming generation of galaxy surveys will provide measurements of galaxy clustering with unprecedented accuracy and data size, which will allow us to test cosmological models at much higher precision than achievable previously. This means that we must have more accurate theoretical predictions to compare with future observational data. As a first step towards more accurate modelling of the redshift space distortions (RSD) of small-scale galaxy clustering in modified gravity (MG) cosmologies, we investigate the validity of the so-called Skew-T (ST) probability distribution function (PDF) of halo pairwise peculiar velocities in these models. We show that, combined with the streaming model of RSD, the ST PDF substantially improves the small-scale predictions by incorporating skewness and kurtosis, for both Λ cold dark matter (ΛCDM) and two leading MG models: f(R) gravity and the DGP braneworld model. The ST model reproduces the velocity PDF and redshift-space halo clustering measured from MG N-body simulations very well down to $\sim 5 \, h^{-1}\, \mathrm{Mpc}$. In particular, we investigate the enhancements of halo pairwise velocity moments with respect to ΛCDM for a larger range of MG variants than previous works, and present simple explanations to the behaviours observed. By performing a simple Fisher analysis, we find a significant increase in constraining power to detect modifications of General Relativity by introducing small-scale information in the RSD analyses.

Braneworld Inspires Cosmological Implications of Barrow Holographic Dark Energy

In the present manuscript, the evolution of the cosmic parameters and planes are being investigated in the framework of the DGP braneworld model. In this scenario, the interaction Γ between the Barrow holographic dark energy model (whose infrared cutoff scale is set by Hubble and event horizons) and pressureless dark matter are considered. We check the behavior of different cosmological parameters such as Hubble, equation of state, deceleration and squared speed of sound from the early matter-dominated era until the late-time acceleration. It is found that the range of Hubble parameter lies in the interval 95−35+35 (for Hubble horizon) and 97−23+23 (for event horizon). For both horizons, the equation of state parameter favors the phantom dominant era as well as the ΛCDM model while the deceleration parameter illustrates the accelerated expansion of the universe. Furthermore, stability of the underlying model is found through squared speed of sound. Furthermore, it is observed that ω−ωϑ′ plane corresponds to freezing and thawing region for Hubble and event horizons, respectively. Furthermore, statefinder plane shows the ΛCDM and Chaplygin gas behavior for both models. Finally, we investigate the thermodynamical nature of the underlying model through Barrow entropy as horizon entropy and found validity for both horizons.

Holographic inflation in f(T) and DGP braneworld

In this paper, we investigate the holographic inflation in the framework of two gravitational theories like [Formula: see text] gravity, where [Formula: see text] corresponds to the torsion scalar and DGP braneworld model which is based on the idea that our four-dimensional FRW universe located on five-dimensional manifold. The modified infrared cutoff is used to explore all the inflationary parameters as slow-roll parameters [Formula: see text], number of [Formula: see text]-folds [Formula: see text], scalar spectral index [Formula: see text], tensor-to-scalar ratio [Formula: see text] and running of the scalar spectral index [Formula: see text]. Also, we investigate the behavior of inflationary parameters [Formula: see text] and [Formula: see text] through graphical presentation. The behavior of these parameters shows the consistency with Planck data [Formula: see text].

Stability analysis of DGP brane-world model with agegraphic dark energy

The aim of this work is to apply the dynamical system approach to study the linear dynamics of the normal DGP brane-world model with agegraphic dark energy. The stability analysis of the model will be investigated and the phase plane portrait will be illustrated. The nature of critical points will be analyzed by evaluating the eigenvalues of a linearized Jacobi matrix. Also, the statefinder diagnostic procedure will be applied to show the slight deviation of our model from the ΛCDM model. One of the most interesting results of this work is the great alleviation of the coincidence problem.

Robust numerical computation of the 3D scalar potential field of the cubic Galileon gravity model at solar system scales

Direct detection of dark energy or modified gravity may finally be within reach due to ultrasensitive instrumentation such as atom interferometry capable of detecting incredibly small scale accelerations. Forecasts, constraints and measurement bounds can now too perhaps be estimated from accurate numerical simulations of the fifth force and its Laplacian field at solar system scales. The cubic Galileon gravity scalar field model (CGG), which derives from the DGP braneworld model, describes modified gravity incorporating a Vainshtein screening mechanism. The nonlinear derivative interactions in the CGG equation suppress the field near regions of high density, thereby restoring general relativity (GR) while far from such regions, field enhancement is comparable to GR and the equation is dominated by a linear term. This feature of the governing PDE poses some numerical challenges for computation of the scalar potential, force and Laplacian fields even under stationary conditions. Here we present a numerical method based on finite differences for solution of the static CGG scalar field for a 2D axisymmetric Sun-Earth system and a 3D Cartesian Sun-Earth-Moon system. The method relies on gradient descent of an integrated residual based on the normal attractive branch of the CGG equation. The algorithm is shown to be stable, accurate and rapidly convergent toward the global minimum state. We hope this numerical study, which can easily be extended to include smaller bodies such as detection satellites, will prove useful to future measurement of modified gravity force fields at solar system scales.

Modelling the matter bispectrum at small scales in modified gravity

Future large-scale structure surveys will measure three-point statistics with high statistical significance. This will offer significant improvements on our understanding of gravity, provided we can model these statistics accurately. {We assess the performance of several schemes for theoretical modelling of the matter bispectrum, including halo-model based approaches and fitting formulae. We compare the model predictions against N-body simulations, considering scales up to kmax = 4 h/Mpc, well into non-linear regime of structure formation. Focusing on the equilateral configuration, we conduct this analysis for three theories of gravity: general relativity, f(R) gravity, and the DGP braneworld model. Additionally, we compute the lensing convergence bispectrum for these models. We find that all current modelling prescriptions in modified gravity, in particular for theories with scale-dependent linear growth, fail to attain the accuracy required by the precision of the Stage IV surveys such as Euclid. Among these models, we find that a halo-model corrected fitting formula achieves the best overall performance.}

Dynamical system analysis of brane induced gravity with tachyon field

In this manuscript we use the dynamical system approach to study the linear dynamics of a normal DGP brane-world model with a tachyon field as the dark energy component. Our focus is on a Gaussian tachyonic potential in which the parameter , goes to infinity. One of the most important results of this study is that we find critical submanifolds which indicate the effect of extra dimension.

Thermodynamics of gravitationally induced particle creation scenario in DGP braneworld

In this paper, we discuss the thermodynamical analysis for gravitationally induced particle creation scenario in the framework of DGP braneworld model. For this purpose, we consider apparent horizon as the boundary of the universe. We take three types of entropy such as Bakenstein entropy, logarithmic corrected entropy and power law corrected entropy with ordinary creation rate Gamma . We analyze the first law and generalized second law of thermodynamics analytically for these entropies which hold under some constraints. The behavior of total entropy in each case is also discussed which implies the validity of generalized second law of thermodynamics. Also, we check the thermodynamical equilibrium condition for two phases of creation rate, that is constant and variable Gamma and found its vitality in all cases of entropy.

Probing the Lambda-DGP Braneworld model

We study cosmic dynamics in the context of the normal branch of the DGP braneworld model. Using current Planck data, we find the best fitting model and associated cosmological parameters in non-flat ΛDGP. With the transition redshift as a basic variable and statefinder parameters, our result shows that the Universe starts its accelerated expansion phase slightly earlier than expected in ΛCDM cosmology. The result also alleviates the coincidence problem of the ΛCDM model.

EVOLUTION OF THE DENSITY PARAMETER IN THE ANISOTROPIC DGP COSMOLOGY

Evolution of the density parameter in the anisotropic DGP braneworld model is studied. The role of shear and cross-over scale in the evolution of Ωρ is examined for both the branches of solution in the DGP model. The evolution is modified significantly compared to the FRW model and further it does not depend on the value of γ alone. Behavior of the cosmological density parameter Ωρ is unaltered in the late universe. The study of decceleration parameter shows that the entry of the universe into self-accelerating phase is determined by the value of shear. We also obtain an estimate of the shear parameter [Formula: see text], which is in agreement with the constraints obtained in the literature using data.

Reconstruction of Potentials as Well as Dynamics of Scalar Fields in DGP Braneworld Model

Here, we investigate the cosmological implications of Holographic Dark Energy (HDE) in the DGP braneworld model of the universe. Taking HDE in DGP braneworld, we investigate the model of non-interacting dark energy and derive its equation of state. Subsequently, we study the correspondence between k-essence, tachyon, dilaton, hessence and DBI-essence dark energy with the non-interacting HDE in a flat DGP braneworld and reconstruct the corresponding scalar potentials which describe the dynamics of the scalar fields. Also we study the correspondence between above mentioned scalar potentials and effective dark energy coming from DGP braneworld in the absence of HDE and in this situation, the potentials are reconstructed.

Equivalence principle implications of modified gravity models

Theories that attempt to explain the observed cosmic acceleration by modifying general relativity all introduce a new scalar degree of freedom that is active on large scales, but is screened on small scales to match experiments. We demonstrate that if such screening occurs via the chameleon mechanism, such as in $f(R)$ theory, it is possible to have order unity violation of the equivalence principle, despite the absence of explicit violation in the microscopic action. Namely, extended objects such as galaxies or constituents thereof do not all fall at the same rate. The chameleon mechanism can screen the scalar charge for large objects but not for small ones (large/small is defined by the depth of the gravitational potential and is controlled by the scalar coupling). This leads to order one fluctuations in the ratio of the inertial mass to gravitational mass. We provide derivations in both Einstein and Jordan frames. In Jordan frame, it is no longer true that all objects move on geodesics; only unscreened ones, such as test particles, do. In contrast, if the scalar screening occurs via strong coupling, such as in the Dvali-Gabadadze-Porrati braneworld model, equivalence principle violation occurs at a much reduced level. We propose several observational tests of the chameleon mechanism: 1. small galaxies should accelerate faster than large galaxies, even in environments where dynamical friction is negligible; 2. voids defined by small galaxies would appear larger compared to standard expectations; 3. stars and diffuse gas in small galaxies should have different velocities, even if they are on the same orbits; 4. lensing and dynamical mass estimates should agree for large galaxies but disagree for small ones. We discuss possible pitfalls in some of these tests. The cleanest is the third one where the mass estimate from HI rotational velocity could exceed that from stars by 30% or more. To avoid blanket screening of all objects, the most promising place to look is in voids.

The cosmology of asymmetric brane modified gravity

We consider the asymmetric branes model of modified gravity, which can produce late time acceleration of the universe and compare the cosmology of this model to the standard ΛCDM model and to the DGP braneworld model. We show how the asymmetric cosmology at relevant physical scales canbe regarded as a one-parameter extension of the DGP model, andinvestigate the effect of this additional parameter on the expansionhistory of the universe.

Constraining the cosmological constant and the DGP gravity with the double pulsar PSR J0737-3039

We consider the double pulsar PSR J0737-3039A/B binary system as a laboratory to locally test the orbital effects induced by an uniform cosmological constant Λ in the framework of the known general relativistic laws of gravity, and the DGP braneworld model of gravity independently of the cosmological acceleration itself for which they were introduced. We, first, construct the ratio R = Δ ω ˙ / Δ P of the discrepancies between the phenomenologically determined periastron rate ω ˙ and orbital period P b and their predicted values from the 1PN ω ˙ 1 PN approximation and the third Kepler law P ( 0 ) . Then, we compare its value | R | = ( 0.3 ± 4 ) × 10 - 11 s - 2 , compatible with zero within the errors, to the ratios R Λ and R DGP of the effects induced on the apsidal rate and the orbital period by Λ and the DGP gravity; we find them neatly incompatible with R being R Λ = ( 3.4 ± 0.3 ) × 10 - 8 s - 2 and R DGP = ( 1.4 ± 0.1 ) × 10 - 7 s - 2 , respectively. Such a result, which for the case of Λ is valid also for any other Hooke-like exotic force proportional to r, is in agreement with other negative local tests recently performed in the Solar System with the ratios of the non-Newtonian/Einsteinian perihelion precessions for several pairs of planets.

Large scale structure formation of the normal branch in the DGP brane world model

In this paper, we study the large scale structure formation of the normal branch in the DGP model (Dvail, Gabadadze, and Porrati brane world model) by applying the scaling method developed by Sawicki, Song, and Hu for solving the coupled perturbed equations of motion of on-brane and off-brane. There is a detectable departure of perturbed gravitational potential from the cold dark matter model with vacuum energy even at the minimal deviation of the effective equation of state w{sub eff} below -1. The modified perturbed gravitational potential weakens the integrated Sachs-Wolfe effect which is strengthened in the self-accelerating branch DGP model. Additionally, we discuss the validity of the scaling solution in the de Sitter limit at late times.

The Three Burials of Melquiades DGP

In this talk I review three fatal flaws of the DGP braneworld model, which has been put forward as a possible model for late time acceleration without a cosmological constant: Ghosts, Cosmological Crashes, and Instability of the 5D vacuum. The talk is based on work in collaboration with Charmousis, Kaloper, Myers and Padilla.

Observational constrains on the DGP brane-world model with a Gauss–Bonnet term in the bulk

Using the data coming from the new 182 Gold type Ia supernova samples, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey and the H(z) data, we have performed a statistical joint analysis of the DGP brane-world model with a high curvature Gauss–Bonnet term in the bulk. Consistent parameters estimations show that the Gauss–Bonnet-induced gravity model is a viable candidate to explain the observed acceleration of our universe.

Warm inflation in the DGP brane-world model

Warm inflationary universe models on a warped Dvali–Gabadadze–Porrati brane are studied. General conditions required for these models to be realizable are derived and discussed. By using an effective exponential potential we develop models for constant and variable dissipation coefficient ratio r = Γ 3 H . We use recent astronomical observations for constraining the parameters appearing in our models.

Brane universes with Gauss-Bonnet-induced-gravity

The DGP brane world model allows us to get the observed late time acceleration via modified gravity, without the need for a ``dark energy'' field. This can then be generalised by the inclusion of high energy terms, in the form of a Gauss-Bonnet bulk. This is the basis of the Gauss-Bonnet-Induced-Gravity (GBIG) model explored here with both early and late time modifications to the cosmological evolution. Recently the simplest GBIG models (Minkowski bulk and no brane tension) have been analysed. Two of the three possible branches in these models start with a finite density ``Big-Bang'' and with late time acceleration. Here we present a comprehensive analysis of more general models where we include a bulk cosmological constant and brane tension. We show that by including these factors it is possible to have late time phantom behaviour.