cppEGB

Description

Code for obtaining static neutron star solutions in regularized 4D Einstein-Gauss-Bonnet gravity¹, for tabulated EoS², using the KEH/CST numerical scheme³. A C++ version of the Savitzky-Golay filter⁴ is used, along with some modules from the BOOST C++ library⁵. In addition the C++ code is wrapped using SWIG⁶, 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.

EGB.exe takes 7 inputs in total. The parameters are specified using the following flags:

1. -f eos_name (The EoS file name).
2. -c coupling (The EGB coupling constant in km^2).
3. -e central_pressure (The central pressure in dyn/cm^2/10^35).
4. -t relative_error (The relative error for the iteration scheme).
5. -m maximum_iterations (The maximum number of iterations).
6. -l relaxation_factor
7. -p print_option:
   • 0: Prints gravitational mass M and radius R.
   • 1: Prints (0) along with the distance, metric, scalar, energy density and pressure profiles.

For example,

./EGB -f ppsly4.cold.rns1.1.txt -c 20.0 -e 10.0 -t 1e-05 -m 100 -l 0.2 -p 0

typical input parameter space:

• central pressure ~ 0.1-30.0 (10^35 dyn/cm^2)
• coupling ~ 0-70 (km^2)

Footnotes

1. https://iopscience.iop.org/article/10.1088/1475-7516/2022/02/033 ↩

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

3. https://academic.oup.com/mnras/article/237/2/355/976460, https://ui.adsabs.harvard.edu/abs/1992ApJ...398..203C/abstract, https://gitlab.com/niksterg/rns1-1/ ↩

4. https://github.com/arntanguy/sgsmooth ↩

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

6. https://github.com/swig/swig ↩