potentials.cc

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/*
 *
 *    Copyright (c) 2014-2018
 *      SMASH Team
 *
 *    GNU General Public License (GPLv3 or later)
 *
 */

#include "smash/potentials.h"

#include "smash/constants.h"
#include "smash/density.h"

namespace smash {

Potentials::Potentials(Configuration conf, const DensityParameters &param)
    : param_(param),
      use_skyrme_(conf.has_value({"Skyrme"})),
      use_symmetry_(conf.has_value({"Symmetry"})) {
  if (use_skyrme_) {
    skyrme_a_ = conf.take({"Skyrme", "Skyrme_A"});
    skyrme_b_ = conf.take({"Skyrme", "Skyrme_B"});
    skyrme_tau_ = conf.take({"Skyrme", "Skyrme_Tau"});
  }

  if (use_symmetry_) {
    symmetry_s_ = conf.take({"Symmetry", "S_Pot"});
  }
}

Potentials::~Potentials() {}

double Potentials::skyrme_pot(const double baryon_density) const {
  const double tmp = baryon_density / nuclear_density;
  /* U = U(|rho|) * sgn , because the sign of the potential changes
   * under a charge reversal transformation. */
  const int sgn = tmp > 0 ? 1 : -1;
  // Return in GeV
  return 1.0e-3 * sgn *
         (skyrme_a_ * std::abs(tmp) +
          skyrme_b_ * std::pow(std::abs(tmp), skyrme_tau_));
}

double Potentials::symmetry_pot(const double baryon_isospin_density) const {
  return 1.0e-3 * 2. * symmetry_s_ * baryon_isospin_density / nuclear_density;
}

double Potentials::potential(const ThreeVector &r, const ParticleList &plist,
                             const ParticleType &acts_on) const {
  double total_potential = 0.0;
  const bool compute_gradient = false;
  const auto scale = force_scale(acts_on);

  if (!acts_on.is_baryon()) {
    return total_potential;
  }

  if (use_skyrme_) {
    const double rho_eck = std::get<0>(
        rho_eckart(r, plist, param_, DensityType::Baryon, compute_gradient));
    total_potential += scale.first * skyrme_pot(rho_eck);
  }
  if (use_symmetry_) {
    const double rho_iso = std::get<0>(rho_eckart(
        r, plist, param_, DensityType::BaryonicIsospin, compute_gradient));
    const double sym_pot = symmetry_pot(rho_iso) * acts_on.isospin3_rel();
    total_potential += scale.second * sym_pot;
  }
  return total_potential;
}

std::pair<double, int> Potentials::force_scale(const ParticleType &data) const {
  double skyrme_scale = data.is_baryon() ? 1.0 : 0.0;
  if (data.pdgcode().is_hyperon()) {
    if (data.pdgcode().is_Xi()) {
      skyrme_scale = 1. / 3.;
    } else if (data.pdgcode().is_Omega()) {
      skyrme_scale = 0.;
    } else {
      skyrme_scale = 2. / 3.;
    }
  }
  skyrme_scale = skyrme_scale * data.pdgcode().baryon_number();
  const int symmetry_scale = data.pdgcode().baryon_number();
  return std::make_pair(skyrme_scale, symmetry_scale);
}

std::pair<ThreeVector, ThreeVector> Potentials::skyrme_force(
    const double density, const ThreeVector grad_rho, const ThreeVector dj_dt,
    const ThreeVector rot_j) const {
  const double MeV_to_GeV = 1.0e-3;
  ThreeVector E_component(0.0, 0.0, 0.0), B_component(0.0, 0.0, 0.0);
  if (use_skyrme_) {
    const double dV_drho =
        (skyrme_a_ + skyrme_b_ * skyrme_tau_ *
                         std::pow(density / nuclear_density, skyrme_tau_ - 1)) *
        MeV_to_GeV / nuclear_density;
    E_component -= dV_drho * (grad_rho + dj_dt);
    B_component += dV_drho * rot_j;
  }
  return std::make_pair(E_component, B_component);
}

std::pair<ThreeVector, ThreeVector> Potentials::symmetry_force(
    const ThreeVector grad_rho, const ThreeVector dj_dt,
    const ThreeVector rot_j) const {
  const double MeV_to_GeV = 1.0e-3;
  ThreeVector E_component(0.0, 0.0, 0.0), B_component(0.0, 0.0, 0.0);
  if (use_symmetry_) {
    const double dV_drho = MeV_to_GeV * 2. * symmetry_s_ / nuclear_density;
    E_component -= dV_drho * (grad_rho + dj_dt);
    B_component += dV_drho * rot_j;
  }
  return std::make_pair(E_component, B_component);
}

std::tuple<ThreeVector, ThreeVector, ThreeVector, ThreeVector>
Potentials::all_forces(const ThreeVector &r, const ParticleList &plist) const {
  const bool compute_gradient = true;
  auto F_skyrme =
      std::make_pair(ThreeVector(0., 0., 0.), ThreeVector(0., 0., 0.));
  auto F_symmetry =
      std::make_pair(ThreeVector(0., 0., 0.), ThreeVector(0., 0., 0.));

  if (use_skyrme_) {
    const auto density_and_gradient =
        rho_eckart(r, plist, param_, DensityType::Baryon, compute_gradient);
    const double rho = std::get<0>(density_and_gradient);
    const ThreeVector grad_rho = std::get<1>(density_and_gradient);
    const ThreeVector dj_dt = std::get<2>(density_and_gradient);
    const ThreeVector rot_j = std::get<3>(density_and_gradient);
    F_skyrme = skyrme_force(rho, grad_rho, dj_dt, rot_j);
  }

  if (use_symmetry_) {
    const auto density_and_gradient = rho_eckart(
        r, plist, param_, DensityType::BaryonicIsospin, compute_gradient);
    const ThreeVector grad_rho = std::get<1>(density_and_gradient);
    const ThreeVector dj_dt = std::get<2>(density_and_gradient);
    const ThreeVector rot_j = std::get<3>(density_and_gradient);
    F_symmetry = symmetry_force(grad_rho, dj_dt, rot_j);
  }

  return std::make_tuple(F_skyrme.first, F_skyrme.second, F_symmetry.first,
                         F_symmetry.second);
}

}  // namespace smash