Modification of Growth with CAMB
MGCAMB

By A. Hojjati, G.-B. Zhao, L. Pogosian and A. Silvestri

Our paper
Description
Download and Installation
Several examples
Implementation in CosmoMC
Version History
Referring to this code

Description

CAMB is a public fortran 90 code written by Antony Lewis and Anthony Challinor for evaluating cosmological observables. MGCAMB is a modified version of CAMB in which the linearized Einstein equations of General Relativity (GR) are modified. MGCAMB can also be used in CosmoMC to fit different modified-gravity (MG) models to data.

With scalar perturbations to FRW metric defined as

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the modifications to the linear order Einstein equations are introduced in terms of two general functions of scale and time (see our paper):

\text{[math]}

This parametrization is discussed in detail in the paper. The initial conditions for the evolution of linear perturbations are not modified in the current version of MGCAMB. A discussion of initial conditions can be found in the paper. Some of the widely used functional forms for such parametrization are reviewed and implemented in the code, while others can also be easily implemented. Several examples can be found here.

Download and Installation

There are two ways to get MGCAMB. The easy way is to replace some of the files in CAMB with the modified versions supplied here and re-compile the code. You should get the modified version of the following files:
params.ini inidriver.F90 equations.f90 In this case, attention must be paid for the compatibility of the version used.

The other way is to manually modify your existing code. For instructions, click here.

Implementation in CosmoMC

Using MGCAMB with Cosmomc requires passing the new MG variables to the CosmoMC routines. Again, you can download the modified files directly from here. You should get the following files :


params.ini

params_CMB.paramnames

source/driver.F90

source/settings.f90

source/CMB_Cls_simple.f90

source/cmbtypes.f90

source/params_CMB.f90

To manually modify your existing code, follow the steps here.

Version History

February, 1, 2012: MGCAMB, January-12 version.

January, 10, 2012: MGCAMB, October-11 version.

July, 15, 2011: MGCAMB, July-11 version.

This version (V.2) of MGCAMB is written based on CAMB (instead of CAMBsources) which makes it easier to use with Cosmomc. It also generalizes the previous parametrization making it applicable to the entire range of redshifts and includes different components of the energy-momentum tensor. It also includes other modified-gravity parametrizations introduced in the literature.

The previous version of MGCAMB written by G.B. Zhao, L. Pogosian, A. Silvestri and J. Zylberberg was based on CAMBsources. That version modified GR equations for z>30, i.e. at late times when the contribution of radiation is negligible.

Reference to this code

If you use MGCAMB, please cite the original CAMB paper and our paper.

The correct citation for the original version of MGCAMB code is this paper by G.-B. Zhao et al, as well as the CAMBsources paper.

If you have any questions or comments, or want to be notified of MGCAMB updates, please send an email to a_hojjati@sfu.ca