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Register a new userOn generalized wormhole in the Eddington inspired Born-Infeld (EiBI) gravity
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In this paper, we wish to investigate certain observable effects in the recently obtained wormhole solution of the EiBI theory, which generalizes the zero mass Ellis-Bronnikov wormhole of general relativity. The solutions of EiBI theory contain an extra parameter $kappa$ having the inverse dimension of the cosmological constant $Lambda$, and is expected to modify various general relativistic observables such as the masses of wormhole mouths, tidal forces and light deflection. A remarkable result is that a non-zero $kappa$ could prevent the tidal forces in the geodesic orthonormal frame from becoming arbitrarily large near a small throat radius $(r_0 sim {0})$ contrary to what happens near a small Schwarzschild horizon radius $(M sim 0)$. The role of $kappa$ in the flare-out and energy conditions is also analysed, which reveals that the energy conditions are violated. We show that the exotic matter in the EiBI wormhole cannot be interpreted as phantom $({omega}=(p_{r}/ rho)<-1)$ or ghost field ${phi} $ of general relativity due to the fact that both $rho$ and $p_{r}$ are negative for all $kappa$.
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Recently, Harko et al. (2014) derived an approximate metric of the galactic halo in the Eddington inspired Born-Infeld (EiBI) gravity. In this metric, we show that there is an upper limit $rho _{0}^{text{upper}}$ on the central density $rho _{0}$ of dark matter such that stable circular orbits are possible only when the constraint $rho _{0}leq rho_{0}^{text{upper}}$ is satisfied in each galactic sample. To quantify different $rho _{0}^{text{upper}}$ for different samples, we follow the novel approach of Edery & Paranjape (1998), where we use as input the geometric halo radius $R_{text{WR}}$ from Weyl gravity and equate it with the dark matter radius $R_{text{DM}}$ from EiBI gravity for the same halo boundary. This input then shows that the known fitted values of $rho _{0}$ obey the constraint $rho_{0}leqrho_{0}^{text{upper}}propto $ ($R_{text{WR}}$)$^{-2}$. Using the mass-to-light ratios giving $alpha $, we shall also evaluate $rho _{0}^{text{lower}}$ $propto $ $(alpha -1)M_{text{lum}}R_{text{WR}}^{-3}$ and the average dark matter density $leftlangle rhorightrangle ^{text{lower}}$. Quantitatively, it turns out that the interval $rho _{0}^{text{lower}}$ $leq rho _{0}leq $ $rho _{0}^{text{upper}}$ verifies reasonably well against many dark matter dominated low surface brightness (LSB) galaxies for which values of $rho _{0}$ are independently known. The interval holds also in the case of Milky Way galaxy. Qualitatively, the existence of a stability induced upper limit $rho _{0}^{text{upper}}$ is a remarkable prediction of the EiBI theory.
We investigate the tensor perturbation in the inflation model driven by a massive-scalar field in Eddington-inspired Born-Infeld gravity. For short wave-length modes, the perturbation feature is very similar to that of the usual chaotic inflation. For long wave-length modes, the perturbation exhibits a peculiar rise in the power spectrum which may leave a signature in the cosmic microwave background radiation.
We give the Buchdahl stability bound in Eddington-inspired Born-Infeld (EiBI) gravity. We show that this bound depends on an energy condition controlled by the model parameter $kappa$. From this bound, we can constrain $kappalesssim 10^{8}text{m}^2$ if a neutron star with a mass around $3M_{odot}$ is observed in the future. In addition, to avoid the potential pathologies in EiBI, a emph{Hagedorn-like} equation of state associated with $kappa$ at the center of a compact star is inevitable, which is similar to the Hagedorn temperature in string theory.
We construct an axially symmetric solution of Eddington-inspired Born-Infeld gravity coupled to an electromagnetic field in 2+1 dimensions including a (negative) cosmological constant term. This is achieved by using a recently developed mapping procedure that allows to generate solutions in certain families of metric-affine gravity theories starting from a known seed solution of General Relativity, which in the present case corresponds to the electrically charged Banados-Teitelboim-Zanelli (BTZ) solution. We discuss the main features of the new configurations, including the modifications to the ergospheres and horizons, the emergence of wormhole structures, and the consequences for the regularity (or not) of these space-times via geodesic completeness.
We investigate domain wall and other defect solutions in the weak-field limit of Eddington-inspired Born-Infeld gravity as a function of $kappa$, the only additional parameter of the theory with respect to General Relativity. We determine, both analytically and numerically, the internal structure of domain walls, quantifying its dependency on $kappa$ as well as the impact of such dependency on the value of the tension measured by an outside observer. We find that the pressure in the direction perpendicular to the domain wall can be, in contrast to the weak-field limit of General Relativity, significantly greater or smaller than zero, depending, respectively, on whether $kappa$ is positive or negative. We further show that the generalized von Laue condition, which states that the average value of the perpendicular pressure is approximately equal to zero in the weak-field limit of General Relativity, does not generally hold in EiBI gravity not only for domain walls, but also in the case cosmic strings and spherically symmetric particles. We argue that a violation of the generalized von Laue condition should in general be expected in any theory of gravity whenever geometry plays a significant role in determining the defect structure.
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