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Linear Breit-Wheeler: use amrex::Math::powi and _prt literals #7191

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Merged
EZoni merged 1 commit into from
Aug 25, 2026
Merged

Linear Breit-Wheeler: use amrex::Math::powi and _prt literals #7191

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12 changes: 5 additions & 7 deletions ...e/Particles/Collision/BinaryCollision/LinearBreitWheeler/LinearBreitWheelerCrossSection.H
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@

#include "Utils/WarpXConst.H"

#include <AMReX_Math.H>
#include <AMReX_REAL.H>

#include <cmath>
Expand All @@ -35,18 +36,15 @@ amrex::ParticleReal LinearBreitWheelerCrossSection (const amrex::ParticleReal& E

if (E_star < me*c2) {return 0._prt;}

constexpr auto one_half_pr = amrex::ParticleReal(1./2.);
constexpr amrex::ParticleReal pi = MathConst::pi;
constexpr amrex::ParticleReal re2 = PhysConst::r_e * PhysConst::r_e;
auto constexpr pow2 = [](auto const x) { return x*x; };
auto constexpr pow4 = [](auto const x) { return x*x*x*x; };

const amrex::ParticleReal s = pow2(E_star/(me * c2));
const amrex::ParticleReal s = amrex::Math::powi<2>(E_star/(me * c2));
const amrex::ParticleReal beta = std::sqrt(1._prt-1._prt/s);

const amrex::ParticleReal term1 = (3._prt-pow4(beta))*std::log((1._prt+beta)/(1._prt-beta));
const amrex::ParticleReal term2 = 2._prt*beta*(pow2(beta)-2._prt);
const amrex::ParticleReal cross_section = one_half_pr*pi*re2*(1._prt-pow2(beta))*(term1+term2);
const amrex::ParticleReal term1 = (3._prt-amrex::Math::powi<4>(beta))*std::log((1._prt+beta)/(1._prt-beta));
const amrex::ParticleReal term2 = 2._prt*beta*(amrex::Math::powi<2>(beta)-2._prt);
const amrex::ParticleReal cross_section = 0.5_prt*pi*re2*(1._prt-amrex::Math::powi<2>(beta))*(term1+term2);

return cross_section;
}
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4 changes: 1 addition & 3 deletions Source/Particles/Collision/BinaryCollision/LinearBreitWheeler/LinearBreitWheelerUtil.H
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Expand Up @@ -62,8 +62,6 @@ namespace {
constexpr auto c2 = PhysConst::c2_v<amrex::ParticleReal>;
constexpr auto inv_c2 = PhysConst::inv_c2_v<amrex::ParticleReal>;
constexpr amrex::ParticleReal me = PhysConst::m_e;
constexpr auto one_half_pr = amrex::ParticleReal(1./2.);
constexpr auto one_pr = amrex::ParticleReal(1.);

// Compute momenta
const amrex::ParticleReal p1x_in = u1x_in * me;
Expand All @@ -80,7 +78,7 @@ namespace {

// Energy squared of each of the two colliding photons in the center of momentum frame,
// calculated using the Lorentz invariance of the total four-momentum norm
const amrex::ParticleReal E_star_sq = one_half_pr*c2*p1_in*p2_in*(one_pr - cos_ang);
const amrex::ParticleReal E_star_sq = 0.5_prt*c2*p1_in*p2_in*(1._prt - cos_ang);

// Square of the norm of the momentum of the products in the center of mass frame
// Formula obtained by inverting E^2 = p^2*c^2 + m^2*c^4 in the COM frame for each particle:
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