derekeverett/freestream-milne

This C++ module performs the free streaming of massless particles, given an initial energy density, and assuming momentum isotropy in transverse plane and a thermally smeared boost invariant momentum dependence. The Energy-Momentum tensor is then Landau matched to a Viscous Hydro Decomposition.

freestream-milne (c) Derek Everett

Purpose

freestream-milne numerically solves the collisionless Boltzmann Equation assuming that

1. the particles are massless
2. initial distribution function is isotropic in azimuthal momentum space $px, py$
3. the initial distribution is a gaussian $(y - \eta)$ in 3D case, or delta function in $(y-\eta)$ in 2D case.

Given an initial energy density profile $T^{00}$, it computes the stress energy tensor $T^{\mu\nu}$ at a later time, and also a viscous hydrodynamic decomposition.

OpenMP is used to accelerate the computation.

Usage

Parameters and options can be set in freestream_input, which is read in at run time. They are described below OUTPUTFORMAT (int) 1 : disk , 2 : write to vectors in memory

BARYON (int) 0 : freestream the energy density, 1 : freestream the baryon density and energy density

IC_ENERGY (int) 1 : Smooth Gaussian, 2 : MC Guassian, 3: read tab delimited file for energy density, 4 : read superMC block format, 5 : read from vector in Memory

IC_BARYON (int) 1 : Smooth Gaussian, 2 : MC Guassian, 3: read tab delimited file for baryon density

ETA_WIDTH (float) used to create a 3D profile of energy density from 2D MC Glb (only for superMC block)

ETA_FLAT (float) used to create a 3D profile of energy density from 2D MC Glb (only for superMC block)

SIGMA (float) std. deviation of one particle distribution function f ~ exp((y - eta)^2 / 2 SIGMA^2)

SIGMA_B (float) std. deviation of one particle distribution function of baryon charges f_B ~ exp((y - eta)^2 / 2 SIGMA_B^2)

DIM_X (int) number of grid points in x

DIM_Y (int) number of grid points in y

DIM_ETA (int) number of grid points in eta

DIM_RAP (int) number of grid points in rapidity for riemann sum

DIM_PHIP (int) number of grid points in phi_p for riemann sum

DX (float) lattice spacing in x [fm]

DY (float) lattice spacing in y [fm]

DETA (float) lattice spacing in eta

DRAP (float) lattice spacing in rapidity (differential) DEPRECATED

DTAU (float) free streaming proper time interval [fm/c]

TAU0 (float) start of free streaming proper time [fm/c]

EOS_TYPE (int) 1 : conformal EoS, 2 : Wuppertal-Bhudapest Parameterization

E_FREEZE (float) [GeV/fm^3] used to calculate fraction of energy contained within surface of energy density > E_FREEZE

freestream-milne's Issues

integer overflow

check if integers indexing arrays can overflow for very large grids

Evolve Tmunu in steps

Add option to evolve Tmunu for several time steps, and save history in struct or to file