We study cosmological dynamics and late-time evolution of an extended induced gravity braneworld scenario. In this scenario, curvature effects are taken into account via the Gauss-Bonnet term in the bulk action and there is also a Chaplygin gas component on the brane. We show that this model mimics an effective phantom behaviour in a relatively wider range of redshifts than previously formulated models. It also provides a natural framework for smooth crossing of the phantom-divide line due to presence of the Chaplygin gas component on the brane. We confront the model with observational data from Type Ia supernovae, cosmic microwave background and baryonic acoustic oscillations to constrain the model parameter space.

Lifetimes of protoplanetary disks (PPDs) are believed to be severely constrained by material depleting mechanisms, including photoevaporative winds due to the host star radiation or external radiation sources. Most previous studies focused on exploring the role of the winds in the exposed PPDs with a single star; however, exploring the evolution of the circumbinary disks with the photoevaporative winds driven by the host star radiation and external radiation sources deserves further investigation. In this study, we investigate the evolution of the circumbinary PPDs with the photoevaporative winds induced by external far ultraviolet (FUV) radiation field. We show that this mass-loss process can significantly constrain properties of a circumbinary PPD, including its lifetime, mass and radius. The lifetime of a circumbinary PPD, for instance, is found by a factor of about two longer than a similar circumstellar disk and this enhancement strongly depends on the viscosity parameter. But our model shows that viscosity dependence of the disk lifetime in the circumbinary case is more pronounced compared to the circumstellar case. We also show that dispersal of a circumbinary PPD occurs over a longer time as the disk temperature distribution becomes steeper. Our results also imply that dead zone in a photoevaporative circumbinary PPD extends over a larger radial range in comparison to a circumstellar disk counterpart. We also show that our calculations are in agreement with the observed circumbinary PPDs orbiting equal-mass binaries.

It has been shown recently that phantom-like effect can be realized on the normal branch of the DGP setup without introduction of any phantom matter neither in the bulk nor on the brane and therefore without violation of the null energy condition. It has been shown also that inclusion of the Gauss-Bonnet term in the bulk action modifies this picture via curvature effects. Here, based on the Lue-Starkman conjecture on the dynamical screening of the brane cosmological constant in the DGP setup, we extend this proposal to a general DGP-inspired f (R, φ) model that stringy effects in the ultraviolet sector of the theory are taken into account by inclusion of the Gauss-Bonnet term in the bulk action. We study cosmological dynamics of this setup, especially its phantom-like behavior and possible crossing of the phantom divide line especially with a non-minimally coupled quintessence field on the brane. In this setup, scalar field and curvature quintessence are treated in a unified framework. 95.36.+x, 98.80.Cq

It has been shown recently that phantom-like behavior of ΛDGP scenario can be extended by incorporation of the curvature effect via inclusion of the Gauss-Bonnet term in the bulk action. It is possible also to realize self-acceleration on the normal branch of the DGP scenario by modification of the induced gravity on the brane in the spirit of f (R) gravity. The purpose of the present study is to treat these issues in a unified manner: we study the phantom-like nature of a modified induced gravity in the presence of the Gauss-Bonnet effect.

So far the basic physical properties of matter forming a thin accretion disc in the static and spherically symmetric space-time metric of the vacuum f (R) modified gravity models (Pun et al. in Phys. Rev. D 78:024043, 2008) and building radiative models of thin accretion disks for both Schwarzschild and Kerr black holes in f (R) gravity (Perez et al. in Astron. Astrophys. 551:4, 2013) were addressed properly. Also von Zeipel surfaces and convective instabilities in f (R)-Schwarzschild(Kerr) background have been investigated recently (Alipour et al. in Mon. Not. R. Astron. Soc. 454:1992Soc. 454: , 2015. In this streamline, here we study the effects of radial and angular pressure gradients on thick accretion disks in Schwarzschild geometries in a constant curvature f (R) modified gravity. Since thick accretion disks have high accretion rate, we study configuration and structure of thick disks by focusing on the effect of pressure gradient on formation of the disks. We clarify our study by assuming two types of equation of state: polytropic and Clapeyron equation of states.