Neutron stars phenomenology with scalar-tensor inflationary attractors

In this work we shall study the implications of a subclass of E-models cosmological attractors, namely of a-attractors, on hydrodynamically stable slowly rotating neutron stars. Specifically, we shall present the Jordan frame theory of the a-attractors, and by using a conformal transformation we shall derive the Einstein frame theory. We discuss the inflationary context of a-attractors in order to specify the allowed range of values for the free parameters of the model based on the latest cosmic-microwavebackground-based Planck 2018 data. Accordingly, using the notation and physical units frequently used in theoretical astrophysics contexts, we shall derive the Tolman-Oppenheimer-Volkoff equations in the Einstein frame. Assuming a piecewise polytropic equation of state, the lowest density part of which shall be chosen to be the WFF1, or APR or the SLy EoS, we numerically solve the TolmanOppenheimer-Volkoff equations using a double shooting python-based LSODA'' numerical code. The resulting picture depends on the value of the parameter a characterizing the a-attractors. As we show, for large values of a, which do not produce a viable inflationary era, the M-R graphs are nearly identical to the general relativistic result, and these two are discriminated at large central densities values. Also, for large a-values, the WFF1 equation of state is excluded, due to the GW170817 constraints on the radius of an M similar to 1.6M(circle dot) neutron star, which must be larger than R = 10.68(-0.04)(+15) km and on the radius corresponding to the maximum mass which must be larger than R = 9.6(-0.03)(+0.14) km. In addition, the small a cases produce larger masses and radii compared to the general relativistic case and are compatible with the GW170817 constraints on the radii of neutron stars. A notable feature is that as the parameter a decreases, the radii of the static hydrodynamically stable neutron stars increase. Our results indicate deep and not yet completely understood connections between non-minimal inflationary attractors and neutron stars phenomenology in scalar-tensor theory. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This work examines the implications of a subclass of E-models cosmological attractors, known as a-attractors, on hydrodynamically stable slowly rotating neutron stars. By numerically solving the Tolman-Oppenheimer-Volkoff equations in the Einstein frame, the study finds that the masses and radii of neutron stars vary with the parameter a characterizing the a-attractors. Results indicate a complex relationship between non-minimal inflationary attractors and neutron star phenomenology in scalar-tensor theory.