Neutron stars in $$f(\mathtt {R,L_m})$$ gravity with realistic equations of state: joint-constrains with GW170817, massive pulsars, and the PSR J0030+0451 mass-radius from NICER data

Abstract In this work, we investigate neutron stars (NS) in $$f(\mathtt {R,L_m})$$ <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:msub><mml:mi>L</mml:mi><mml:mi>m</mml:mi></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:math> theory of gravity for the case $$f(\mathtt {R,L_m})= \mathtt {R}+ \mathtt {L_m}+ \sigma \mathtt {R}\mathtt {L_m}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>f</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mi>R</mml:mi><mml:mo>,</mml:mo><mml:msub><mml:mi>L</mml:mi><mml:mi>m</mml:mi></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mo>=</mml:mo><mml:mi>R</mml:mi><mml:mo>+</mml:mo><mml:msub><mml:mi>L</mml:mi><mml:mi>m</mml:mi></mml:msub><mml:mo>+</mml:mo><mml:mi>σ</mml:mi><mml:mi>R</mml:mi><mml:msub><mml:mi>L</mml:mi><mml:mi>m</mml:mi></mml:msub></mml:mrow></mml:math> , where $$\mathtt {R}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>R</mml:mi></mml:math> is the Ricci scalar and $$\mathtt {L_m}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>L</mml:mi><mml:mi>m</mml:mi></mml:msub></mml:math> the Lagrangian matter density. In the term $$\sigma \mathtt {R}\mathtt {L_m}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>σ</mml:mi><mml:mi>R</mml:mi><mml:msub><mml:mi>L</mml:mi><mml:mi>m</mml:mi></mml:msub></mml:mrow></mml:math> , $$\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>σ</mml:mi></mml:math> represents the coupling between the gravitational and particles fields. For the first time the hydrostatic equilibrium equations in the theory are solved considering realistic equations of state and NS masses and radii obtained are subject to joint constrains from massive pulsars, the gravitational wave event GW170817 and from the PSR J0030+0451 mass-radius from NASA’s Neutron Star Interior Composition Explorer ( NICER ) data. We show that in this theory of gravity, the mass-radius results can accommodate massive pulsars, while the general theory of relativity can hardly do it. The theory also can explain the observed NS within the radius region constrained by the GW170817 and PSR J0030+0451 observations for masses around $$1.4~M_{\odot }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>1.4</mml:mn><mml:mspace/><mml:msub><mml:mi>M</mml:mi><mml:mo>⊙</mml:mo></mml:msub></mml:mrow></mml:math> .

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