Wormholes in R2R^2-gravity within the f(R,T)f(R,T) formalism

We propose, as a novelty in the literature, the modelling of wormholes within the particular case of the $f(R,T)$ gravity, namely $f(R,T)=R+\alpha R^{2}+\lambda T$, with $R$ and $T$ being the Ricci scalar and trace of the energy-momentum tensor, respectively, while $\alpha$ and $\lambda$ are constants. Although such a functional form application can be found in the literature, those concern to compact astrophysical objects, such that no wormhole analysis has been done so far. The quadratic geometric and linear material corrections of this theory make the matter content of the wormhole to remarkably be able to obey the energy conditions.Comment: Published versio

AdS_3, Black Holes and Higher Derivative Corrections

Using AdS/CFT correspondence and the Euclidean action formalism for black hole entropy Kraus and Larsen have argued that the entropy of a BTZ black hole in three dimensional supergravity with (0,4) supersymmetry does not receive any correction from higher derivative terms in the action. We argue that as a consequence of AdS/CFT correspondence the action of a three dimensional supergravity with (0,4) supersymmetry cannot receive any higher derivative correction except for those which can be removed by field redefinition. The non-renormalization of the entropy then follows as a consequence of this and the invariance of Wald's formula under a field redefinition.Comment: LaTeX file, 12 pages; v2: reference adde

Synthesis and characterization of BaMnO3multiferroic ceramics

In the present study, BaMnO3 ceramic oxide has been prepared and analysed using various experimental techniques. The proposed material has been prepared using high temperature solid state reaction route. The structural (XRD), microstructural (FESEM), compositional (EDX) and dielectric properties have been studied extensively. X-ray diffraction (XRD) analysis confirms the formation of compound. Field Emission Scanning Electron Micrograph (FESEM) shows thenon-homogenous distribution of grains ranging from 1-1.5��mwhich are densely packed. Energy Dispersive X-ray (EDX) spectroscopic analysis shows the presence of all the elemental in BaMnO3. The ferroelectric to paraelectric phase transition is observed from temperature dependent dielectric analysis. The loss tangent is found to be increases with increase in temperature. DC and AC conductivity decreases with increase in temperatur