Harko, TiberiuTiberiuHarkoLobo, Francisco S. N.Francisco S. N.LoboMak, Man KwongMan KwongMak2026-10-082026-10-082026-08-10Harko, Tiberiu; Lobo, Francisco S. N.; Mak, Man Kwong (2026-08-10). Exact general relativistic solutions for a cylindrically symmetric stiff fluid matter source. The European Physical Journal C, 86(8), 960. https://doi.org/10.1140/epjc/s10052-026-16225-71434-6052https://hdl.handle.net/20.500.12740/24923Abstract In this work, we derive the general solutions for a cylindrically symmetric space-time filled with a cosmological perfect fluid obeying $$p=\gamma \rho $$ p = γ ρ ( $$0\le \gamma \le 1$$ 0 ≤ γ ≤ 1 ), where $$\gamma =1$$ γ = 1 represents a stiff or Zeldovich fluid. Using Marder’s metric with coefficients depending on t and r , we obtain explicit solutions of the gravitational field equations for the three cases $$\delta = 1, 0, -1,$$ δ = 1 , 0 , - 1 , corresponding to exponential, power-law, and trigonometric behaviors of the metric functions. The resulting space-times exhibit anisotropic evolution, nontrivial expansion and shear, and curvature singularities, with energy density and pressure profiles determined by the integration constants. These solutions provide a comprehensive framework for modeling cylindrically symmetric cosmologies, offering insights into early-universe dynamics and anisotropic gravitational phenomena. The versatility of the solutions also opens avenues for extensions to higher-dimensional or modified gravity scenarios, making them a valuable tool for both theoretical and phenomenological studies in general relativity.http://purl.org/coar/access_right/c_abf2https://creativecommons.org/licenses/by/4.0Elementary Particles, Quantum Field TheoryNuclear Physics, Heavy Ions, HadronsQuantum Field Theories, String TheoryMeasurement Science and InstrumentationAstronomy, Astrophysics and CosmologyNuclear EnergyArticulohttps://doi.org/10.1140/epjc/s10052-026-16225-7