Deformed compact objects in modified gravity

Abstract We study equilibrium configurations of compact stars by combining two effects that are usually investigated separately: deviations from spherical symmetry and matter–geometry coupling in f ( R , T ) gravity. We derive a generalized, TOV-like set of stellar structure equations that extends the standard hydrostatic balance to deformed configurations within the broad class $$f(R,T)= R + f(T)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>f</mml:mi> <mml:mo>(</mml:mo> <mml:mi>R</mml:mi> <mml:mo>,</mml:mo> <mml:mi>T</mml:mi> <mml:mo>)</mml:mo> <mml:mo>=</mml:mo> <mml:mi>R</mml:mi> <mml:mo>+</mml:mo> <mml:mi>f</mml:mi> <mml:mo>(</mml:mo> <mml:mi>T</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> , and then specialize to the minimal coupling model $$f(R,T)= R + 2\lambda T$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>f</mml:mi> <mml:mo>(</mml:mo> <mml:mi>R</mml:mi> <mml:mo>,</mml:mo> <mml:mi>T</mml:mi> <mml:mo>)</mml:mo> <mml:mo>=</mml:mo> <mml:mi>R</mml:mi> <mml:mo>+</mml:mo> <mml:mn>2</mml:mn> <mml:mi>λ</mml:mi> <mml:mi>T</mml:mi> </mml:mrow> </mml:math> . We compute stellar sequences and compare the resulting mass–radius relations and internal profiles with the General Relativity limit. To probe different compositions, we consider representative equations of state for hadronic matter and for self-bound quark matter. We find that deviations from spherical symmetry can significantly shift the maximum mass and radius of stable configurations, while the coupling matter $$\lambda $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>λ</mml:mi> </mml:math> induces additional systematic changes in both neutron star and strange star sequences.