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Murat Metehan Türkoğlu

Publications and source records attributed to Murat Metehan Türkoğlu.

2 recordsLinked to original sources

Finite-domain inverse reconstruction of a Morris--Thorne-type wormhole candidate with a derivative-consistent $f(R)$ curvature sector

We present a finite-domain inverse reconstruction of a Morris--Thorne-type wormhole candidate as a methodological benchmark for constrained numerical model building in modified gravity. The throat condition and local flare-out behaviour are embedded analytically in the shape-function parameterization, while the redshift profile is kept finite by construction. Rather than fitting $f(R)$, $f_R(R)$, and $f_{RR}(R)$ as independent numerical arrays, a positive analytic generator is assigned to $f_{RR}(R)$ and integrated to obtain a derivative-consistent reconstructed curvature sector. The frozen reconstruction is evaluated on 10,019 radial nodes over $r\in[1,10^{5}]$. The corresponding Ricci-scalar trajectory spans $-1.1317\times10^{-9}\leq R\leq1.999999998$ and is weakly non-monotonic, so no inversion $r=r(R)$ is required. On the same finite grid, the reconstructed source variables retain positive pointwise energy-condition margins, the coordinate-radial null-energy integrals are positive both globally and in the near-throat band, and the maximum normalized tidal-curvature ratio is $0.8666<1$. The reconstructed source-side closure diagnostic has a maximum absolute residual of $5.3246\times10^{-5}$. The source closure is phenomenological rather than derived from a unique microphysical matter Lagrangian or a uniquely specified curvature--matter coupling function. Accordingly, the result is not presented as a full field-equation solution of a specified nonminimally coupled $f(R)$ theory, a stability proof, an exterior-matched global spacetime, or an observer-dependent safe-traversal model. It instead provides a finite-domain computational benchmark for auditable inverse reconstruction of Morris--Thorne-type geometries in modified gravity.

physics.gen-ph↗

What does a measurement of mass and/or radius of a neutron star constrain: Equation of state or gravity?

Neutron stars (NSs) are thought to be excellent laboratories for determining the equation of state (EoS) of cold dense matter. Their strong gravity suggests that they can also be used to constrain gravity models. The mass and radius (M-R) of a NS both depend on the choice of EoS and gravity, meaning that NSs cannot be simultaneously good laboratories for both of these questions. A measurement of M-R would constrain the less well known physics input. The assumption that M-R measurements can be used to constrain EoS-presumes general relativity (GR) is the ultimate model of gravity in the classical regime. We calculate the radial profile of compactness and curvature (square root of the full contraction of the Weyl tensor) within a NS and determine the domain not probed by the Solar System tests of GR. We find that, except for a tiny sphere of radius less than a millimeter at the center, the curvature is several orders of magnitude above the values present in Solar System tests. The compactness is beyond the solar surface value for r>10 m, and increases by 5 orders of magnitude towards the surface. With the density being only an order of magnitude higher than that probed by nuclear scattering experiments, our results suggest that the employment of GR as the theory of gravity describing the hydrostatic equilibrium of NSs is a rather remarkable extrapolation from the regime of tested validity, as opposed to that of EoS models. Our larger ignorance of gravity within NSs suggests that a measurement of M-R constrains gravity rather than EoS, and given that EoS has yet to be determined by nucleon scattering experiments, M-R measurements cannot tightly constrain the gravity models either. Near the surface the curvature and compactness attain their largest values, while EoS in this region is fairly well known. This renders the crust as the best site to look for deviations from GR.

astro-ph.HE↗