Cosmic Strings
Bodo Schwabe
University of Zaragoza
with adaptive mesh refinement
Axion Strings
strings = 1D-loops with phase changing 2pi around them
energy in phase gradient diverges - but decreasing modulus
Scale Separation
inter-string separation
string core size
axion decay constant
Hubble scale
10^{30}
- Cosmic expansion increases separation (solution PRS strings)
- not feasible on 3D uniform grids
- possible solution: adaptive mesh refinement around 1D strings (2048^3 root grid and 6 additional levels -> 11 e-folds)
[Buschmann et.al. arXiv:2108.05368]
[Drew, Shellard, arXiv:1910.01718]
Adaptive Mesh Refinement (AMR)
- Tag cells for refinement using string plaquettes [ Leesa Fleury, Guy D. Moore, 2015, arXiv:1509.00026 ] or gradients
- create new grids with progressively more resolution on higher levels
- Use MPI communication to transfer interpolated data between grids and levels
- subcycling: use smaller time steps on higher resolved levels
- possibly use different methods on different levels
We extended AxioNyx for AMR string simulations
Use AMR to keep string resolution fixed
[Buschmann et.al. arXiv:2108.05368]
AMR can improve current extrapolations
[Gorghetto et.al., arXiv: 1806.04677, 2007.04990 ]
[Buschmann et.al. arXiv:2108.05368]
[Buschmann et.al. arXiv:2108.05368]
q=1 \rightarrow m_a = 65 \pm 6 \mu eV
Potential issues
- Interpolation between levels
- higher frequency modes are discarded when propagating to coarser levels
- Spectrum only calculated on coarsest level
- lots of refinement if strings are too close together (physical strings are ideal as refinement levels increase while refined volume decreases)