Browsing by Author "Nguyen, Hoang Ky"

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    A Stationary Axisymmetric Vacuum Solution for Pure R2 Gravity
    (2023) Azreg Ainou, Mustapha; Nguyen, Hoang Ky; 0000-0002-3244-7195
    The closed-form expression for pure R-2 vacuum solution obtained in Phys. Rev. D 107, 104 008 (2023) lends itself to a generalization to axisymmetric setup via the modified Newman-Janis algorithm. We adopt the procedure put forth in Phys. Rev. D 90, 064 041 (2014) bypassing the complexification of the radial coordinate. The procedure presumes the existence of Boyer-Lindquist coordinates. Using the Event Horizon Telescope Collaboration results, we model the central black hole M87* by the thus obtained exact rotating metric, depending on the mass, rotation parameter and a third dimensionless parameter. The latter is constrained upon investigating the shadow angular size assuming mass and rotation parameters are those of M87*. Stability is investigated.
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    Traversable Morris-Thorne-Buchdahl Wormholes in Quadratic Gravity
    (2023) Nguyen, Hoang Ky; Azreg-Ainou, Mustapha; 0000-0002-3244-7195
    The special Buchdahl-inspiredmetric obtained in a recent paper [Phys. Rev. D 107, 104008 (2023)] describes asymptotically flat spacetimes in pure R-2 gravity. The metric depends on a new (Buchdahl) parameter (k) over tilde of higher-derivative characteristic, and recovers the Schwarzschild metric when (k) over tilde = 0. It is shown that the special Buchdahlinspired metric supports a two-way traversable MorrisThorne wormhole for (k) over tilde is an element of (-1, 0) in which case the Weak Energy Condition is formally violated, a naked singularity for (k) over tilde is an element of (-infinity,-1). (0,+infinity), and a non-Schwarzschild structure for (k) over tilde = -1.