cppSTT

Description

Code for obtaining neutron star models for tabulated equations of state¹, in the context of Damour-Esposito-Farese (DEF) scalar tensor theory model and R^2 gravity model. The system of ODEs is solved by implementing a C++11 version of LSODA² and a C++ version of the Nelder-Mead method³, which is used for the optimization of the boundary conditions. Both of these libraries are slightly modified to fit the STT class in stt.h. Additionaly, some modules from the BOOST C++ library⁴ are used to interpolate the tabulated EoS. The code prints the model's parameters e.g. mass, radius, scalar charge, scalar at center and boundary minimization accuracy, for the corresponding input parameters.

The C++ code is wrapped using SWIG⁵, into a python library which can be imported and used in any way, as shown in swig/test.py.

Usage

Compile, using the provided makefile.

STT.exe takes 5 inputs in total. The parameters are specified using the following flags:

1. -m theory (DEF or R2)
2. -f eos name (EoS file name).
3. -c coupling (model's coupling constant).
4. -e central density (central energy density in CGS/10^15).

For example,

./STT -m DEF -f ppsly4.cold.rns1.1.txt -c -5.0 -e 1.5

./STT -m R2 -f ppsly4.cold.rns1.1.txt -c 20.0 -e 1.5

typical input parameter space:

• central density ~ 0.5-4.0 (10^15 gr/cm^3)
• coupling ~ (-5.0,-4.5) (DEF), (5,10^3) (R^2)

GR solutions may also be obtained simply by choosing "DEF" as theory and setting the coupling to zero.

Footnotes

1. https://ui.adsabs.harvard.edu/abs/2021PhRvD.103l3004B/abstract (table IX) ↩

2. https://github.com/dilawar/libsoda-cxx ↩

3. https://people.sc.fsu.edu/~jburkardt/cpp_src/asa047/asa047.html ↩

4. https://github.com/boostorg/boost ↩

5. https://github.com/swig/swig ↩