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New User Input Parameters

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Kay Lehnert edited this page Feb 24, 2026 · 20 revisions

To assess the model using Markov chain Monte Carlo techniques, the free variables need to be accessible through the python wrapper, i.e. additional input parameters are necessary. I created the following additional parameters in input.c to be set by the user in the *.ini-file respectively through the python wrapper:

int model_cdm; // CDM model (0:standard, 1: Hubbleian, 2: interacting)
double cdm_c;  // constant in the hyperbolic DM model
int scf_potential // type of scalar field potential

Dark Matter

model_cdm can take three values:

  • 0, which is the default value and corresponds to CDM
  • 1, which corresponds to Hubbleian DM and is set by using any word that starts with h or H in the *.ini-file
  • 2, which corresponds to DM that depends on the scalar field and is set by any word that starts with i or I in the *.ini-file

cdm_c corresponds to the constant $\mathfrak{c}$ in the expression

$$m\left(\phi\right)=\frac{m_0}{2}\left[1-\tanh\left(\mathfrak{c}\phi\right)\right].$$

Scalar Field

scf_potential indicates which scalar field potential is to be used. The options are

  1. power-law: $V\left(\phi\right) = c_1^{(4-c_2)} \phi^{c_2} + c_3$
  2. cosine: $V\left(\phi\right) = c_1 \cos\left(c_2 \phi\right)$
  3. hyperbolic: $V\left(\phi\right) = c_1 \left[1 - \tanh\left(c_2 \phi\right)\right]$
  4. pNG: $V\left(\phi\right) = c_1^4 \left[1 + \cos\left(\frac{\phi}{c_2}\right)\right]$
  5. iPL: $V\left(\phi\right) = c_1^{(4+c_2)} \phi^{-c_2}$
  6. exponential: $V\left(\phi\right) = c_1 \exp\left(-c_2 \phi\right)$
  7. SqE: $V\left(\phi\right) = c_1^{(c_2+4)} \phi^{-c_2} \exp\left(c_1 \phi^2\right)$
  8. Bean: $V\left(\phi\right) = c_1 \left[\left(c_4 - \phi\right)^2 + c_2\right] \exp\left(-c_3 \phi\right)$
  9. DoubleExp: $V\left(\phi\right) = c_1 \left(\exp\left(-c_2 \phi\right) + c_3 \exp\left(-c_4 \phi\right)\right)$

Furthermore, I implemented changes to the scalar field parameters, which also govern the generalised coupling between DM and DE. For scalar fields, CLASS takes all input parameters as a comma-separated list from a single line. I extended this line to obtain all 4 free constants in the scalar field potential, the 6 free coupling parameters between DM and DE, as well as the initial field values for $\phi$ and $\phi\prime$:

#        The scalar field parameters are given as a list of parameters with the following format:
#        [0]     = c_1
#        [1]     = c_2
#        [2]     = c_3
#        [3]     = c_4
#        [4]     = q_1 (coupling)
#        [5]     = q_2
#        [6]     = q_3
#        [7]     = q_4
#        [8]     = coupling_exponent_1
#        [9]     = coupling_exponent_2
#        [10]    = phi_ini
#        [11]    = phi_prime_ini
scf_parameters = 1.0, 2.0, 3.0, 4.0, 0.1, 0.2, 0.3, 0.4, e-1, e-2, 10.0, 1.0

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