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ihixs documentation

Running the code

The various features of ihixs are controlled by an input runcard, an ascii file than is edited by the user. To run with a given runcard as input type in the installation directory:

In case no runcard is given, the program runs on the default card (called `runcard') in the installation directory. When no output filename is given, the program writes the output in runcard_name.out.

The output consists of the total cross sections per perturbative order in QCD, together with the corresponding Monte-Carlo errors achieved and the PDF errors. Those are set to zero if no PDF uncertainty is requested in the runcard. The input runcard is also appended.

Setting options and variables

In the runcard anything after a hash symbol,`#', is considered as a comment and is ignored. The following options are available:

• pdf_provider : sets the PDF grid used. The user can choose between MSTW08, ABKM09, JR09, NNPDF21 (since version 1.1), ABM11, NNPDF21_as_00i (with i from 14 to 24, denoting the fixed value of the strong coupling constant that was used in the fit) (since version 1.3), CT10 and NNPDF23 (since version 1.3.3). Within the MSTW PDFs there is also the option to switch confidence level from 68% to 90% and to use the MSTW grids with the strong coupling constant varied by one standard deviation from the best fit value. The exact filenames of the grids available are stated in the default runcard.
• effective_theory_flag : set to 0 for the exact LO and NLO QCD effects and HQET approximation for NNLO. Set to 1 for the improved HQET approximation through LO, NLO, NNLO.
• no_error_flag: Set to 0 to calculate with PDF uncertainty, set to 1 to calculate without PDF uncertainty.
• collider: Set to `LHC' or `TEVATRON'
• Etot: The total center of mass collider energy. This option is ignored if the collider chosen above is Tevatron.
• mhiggs: The nominal mass of the Higgs boson.
• higgs_width_scheme : Set to 0 for the default finite width scheme (naive Breit-Wigner distribution). Set to 1 for the Seymour scheme. Set to 2 for the running width scheme and set to 3 for the Valencia-Willenbrock scheme (Phys. Rev. D 46, 2247–2251). For a description of the other schemes see section 4 of 1202.3638.
• higgs_width_grid: = The path (absolute or relative to the run directory) of the file with the grid for the width of the Higgs, and the branching ratios to diphoton, WW, WW and bottom quarks as a function of the Higgs mass. If no path is set the default grid is used, HdecayGrid.dat, constructed with Hdecay v.3.532 with arguments that can be read in the header of the file. If the user supplies a grid file of his own, operating requirements are that the maximum number of grid points cannot exceed 16200, that the first three lines of the file are reserved for comments (so they are not read) and that the format of each line is respected, i.e. that the data is given in the order Higgs mass, Total width,BR to diphoton, BR to WW, BR to ZZ, BR to bottom quarks.
• min_mh : Setting a minimum in the invariant mass of the Higgs boson. This allows the user to study the total cross section in the presence of kinematical cuts.
• max_mh : Setting a maximum in the invariant mass of the Higgs boson.
• bin_flag : Set to 1 to produce files with the bin-integrated Higgs invariant mass. Set to 0 not to produce it. The data files produced contain the cross section per bin, with the bin size set to 1 GeV, from 30 to 2000 GeV at LO, NLO and NNLO. The files are named ` masshisto\m_H.\order', so e.g. for m_H=200GeV the NLO file will be ` masshisto200.1 '.
• muf/mhiggs : The ratio of the factorization scale to the Higgs mass.
• mur/mhiggs : The ratio of the renormalization scale to the Higgs mass.
• DecayMode: Set to no_width for the zero width approximation total cross section, to ` total' for finite width total cross section, or to the decay modes ` gamma gamma', ` ZZ', ` WW', ` b b-bar'.
• ProductionMode: Set to ` gg' for gluon fusion or to ` bb' for bottom quark annihilation.
• K_ewk: This is a global rescaling factor for all electroweak corrections. Set to 0.0 to switch them off.
• K_ewk_real: Set to 0.0 to switch the electroweak corrections to H+j off.
• K_ewk_real_b: Set to 0.0 to switch the electroweak corrections to H+j that include diagrams with massive quarks or Higgs boson in the loop, off.
• m_top: the mass of the top quark.
• Gamma_top: the width of the top quark.
• Y_top : rescaling factor for the SM Yukawa coupling of the top. Note that this can be set to an arbitrarily small positive value, but not to 0.0 exactly.
• scheme_top : 0: The MSbar mass is used in all places where the top mass enters. m_top from above is interpreted as the 'MSbar mass at the MSbar mass' (usually about 10 GeV smaller than the top pole mass). 1: The pole scheme is used, and m_top from above is not run.
• m_bot: the mass of the bottom quark.
• Gamma_bot: the width of the bottom quark.
• Y_bot: rescaling factor for the SM Yukawa coupling of the bottom quark.
• scheme_bottom : 0: The MSbar mass is used in all places where the bottom mass enters. m_bot from above is interpreted as the MSbar mass at 10 GeV. 1: The pole scheme is used, and m_bot from above is not run.
• heavy quark: Optional extra quarks in the model. The argument of this option should be formatted as m_Q:Width_Q:Y_Q:scheme where Y_Q is the rescaling factor from a SM-like Yukawa coupling m_Q/v. For example, adding an extra 300GeV quark with width 1.2GeV and a Yukawa coupling that is 5.7m_Q/v, with the mass treated in the on-shell scheme, the user should type:
  ` heavy quark = 300.0 : 1.2 : 5.7 : 1'
• m_Z: the mass of the Z boson.
• Gamma_Z: the width of the Z boson
• m_W: the mass of the W boson
• Gamma_W: the width of the W boson
• epsrel: Sets the relative Monte-Carlo integration error.
• epsabs: Sets the absolute Monte-Carlo integration error.
• nstart : Sets the number of points per Vegas iteration.
• nincrease: Set the number of points by which the number of points per iteration increases
• mineval: Set the minimum number of points before ending the Monte-Carlo integration
• maxeval: Set the maximum number of points after which the integration ends.
• adapt to central only: Set to 0 to force Vegas to adapt to all integrand. Set to 1 to adapt to the central integrand only. This is useful when running with PDF errors. Then each member of the PDF grid is treated as a separate integral. Adapting to the central only assumes that the peak structures of all integrals is similar which is a good approximation, and saves some CPU time.
• vegas_verbose: Set to 0 for silent Vegas output. Set to 2 to have information about each iteration printed in the standard output (the console).