harmonicoscillatorrenormalisation.hh

#ifndef HARMONICOSCILLATORRENORMALISATION_HH
#define HARMONICOSCILLATORRENORMALISATION_HH                                   \
  HARMONICOSCILLATORRENORMALISATION_HH
#include "action/renormalisation.hh"
#include "lattice/lattice1d.hh"
#include <memory>

/** @file harmonicoscillatorrenormalisation.hh
 * @brief Header file for harmonic oscillator action renormalisation class
 */

/** @class RenormalisedHOParameters
 * @brief Renormalised coarse grid parameters for the harmonic oscillator
 *
 * Calculate the renormalised coarse grid mass and harmonic oscillator
 * potential parameter \f$\mu^2\f$
 *
 \f[
  m_0^{(c)} = m_0\left(1+\frac{a^2\mu^2}{2}\right)^{-1}
 \f]
 *
 \f[
  \left(\mu^{(c)}\right)^2 = \mu^2\left(1+\frac{a^2\mu^2}{4}\right)^{-1}
 \f]
 *
 * Instead of those exact formulae, the perturbative expansion in \f$\mu\f$
 * can also be used.
 */
class RenormalisedHOParameters : public RenormalisedParameters {
public:
  /** @brief Create new instance
   *
   * @param[in] lattice_ Underlying lattice
   * @param[in] m0_ Mass \f$m_0\f$
   * @param[in] mu2_ Harmonic oscillator potential parameter \f$\mu^2\f$
   * @param[in] renormalisation_ Type of renormalisation to use
   *              (0: none, 1: perturbative, 2: nonperturbative)
   */
  RenormalisedHOParameters(const std::shared_ptr<Lattice1D> lattice_,
                           const double m0_, const double mu2_,
                           const RenormalisationType renormalisation_)
      : RenormalisedParameters(renormalisation_), lattice(lattice_), m0(m0_),
        mu2(mu2_) {}

  /** @brief Renormalised coarse level mass \f$m_0^{(c)}\f$*/
  double m0_coarse() {
    double a_lat = lattice->geta_lat();
    double m0coarse;
    switch (renormalisation) {
    case RenormalisationNone:
      m0coarse = m0;
      break;
    case RenormalisationPerturbative:
      m0coarse = m0 * (1. - 0.5 * a_lat * a_lat * mu2);
      break;
    case RenormalisationNonperturbative:
      m0coarse = m0 / (1. + 0.5 * a_lat * a_lat * mu2);
      break;
    }
    return m0coarse;
  }
  /** @brief Renormalised coarse level oscillator parameter
   * \f$\left(\mu^{(c)}\right)^2\f$ */
  double mu2_coarse() {
    double a_lat = lattice->geta_lat();
    double mu2coarse;
    switch (renormalisation) {
    case RenormalisationNone:
      mu2coarse = mu2;
      break;
    case RenormalisationPerturbative:
      mu2coarse = mu2 * (1. + 0.25 * a_lat * a_lat * mu2);
      break;
    case RenormalisationNonperturbative:
      mu2coarse = mu2 * (1. + 0.25 * a_lat * a_lat * mu2);
      break;
    }
    return mu2coarse;
  }

private:
  /** @brief Mass \f$m_0\f$ */
  const double m0;
  /** @brief Harmonic oscillator potential parameter \f$\mu^2\f$*/
  const double mu2;
  /** @brief Underlying lattice */
  const std::shared_ptr<Lattice1D> lattice;
};

#endif // HARMONICOSCILLATORRENORMALISATION_HH