1 <chapter name="SUSY Les Houches Accord">
3 <h2>SUSY Les Houches Accord</h2>
5 The PYTHIA 8 program does not contain an internal spectrum calculator
6 (a.k.a. RGE package) to provide supersymmetric couplings, mixing angles,
7 masses and branching ratios. Thus the SUSY Les Houches Accord (SLHA)
8 <ref>Ska04</ref><ref>All08</ref> is the only way of
9 inputting SUSY models, and SUSY processes cannot be run unless such an
10 input has taken place.
13 Most of the SUSY implementation in PYTHIA 8 is compatible with both the
14 SLHA1 and SLHA2 conventions (with the exception of R-parity violation and
15 the NMSSM extension in the latter case). Internally, PYTHIA 8 uses the
16 SLHA2 conventions and translates SLHA1 input to these when necessary.
17 See the section on SUSY Processes for more information.
20 When reading LHEF files, Pythia automatically looks for SLHA information
21 between <code><slha>...</slha></code> tags in the header of such
22 files. When running Pythia without LHEF input (or if reading an LHEF
23 file that does not contain SLHA information in the header), a separate
24 file containing SLHA information may be specified using
25 <code>SLHA:file</code> (see below).
28 With the so-called <code>QNUMBERS</code> extension <ref>Alw07</ref>, the
29 SLHA input format can also be used for more general BSM models, although
30 the implementation of this extension is not yet complete in PYTHIA 8.
33 Finally, the SLHA input capability can of course also be used to input
34 SLHA-formatted MASS and DECAY tables for other particles, such as the top
35 quark, furnishing a less sophisticated but more universal complement to the
36 standard PYTHIA 8-specific methods for inputting such information (for the
37 latter, see the section on <aloc href="ParticleData">Particle Data</aloc>
38 and the <aloc href="ParticleDataScheme">scheme</aloc> to modify it). This
39 may at times not be desirable, so a few options can be used to curb the right
40 of SLHA to overwrite particle data.
43 The reading-in of information from SLHA or LHEF files is handled by the
44 <code>SusyLesHouches</code> class, while the subsequent calculation of
45 derived quantities of direct application to SUSY processes is done in the
46 <code>CoupSUSY</code> class.
48 <h3>SLHA Switches and Parameters</h3>
50 <mode name="SLHA:readFrom" default="1" min="0" max="2">
51 Controls from where SLHA information is read.
52 <option value="0">is not read at all. Useful when SUSY is not simulated
53 and normal particle properties should not be overwritten.</option>
54 <option value="1">read in from the <code><slha>...</slha></code>
55 block of a LHEF, if such a file is read during initialization, and else
56 from the <code>SLHA:file</code> below.</option>
57 <option value="2">read in from the <code>SLHA:file</code> below.</option>
60 <word name="SLHA:file" default="void">
61 Name of an SLHA (or LHEF) file containing the SUSY/BSM model definition,
62 spectra, and (optionally) decay tables. Default <code>void</code>
63 signals that no such file has been assigned.
66 <flag name="SLHA:keepSM" default="on">
67 Some programs write SLHA output also for SM particles where normally
68 one would not want to have masses and decay modes changed unwittingly.
69 Therefore, by default, known SM particles are ignored in SLHA files.
70 To be more specific, particle data for identity codes in the ranges
71 1 - 24 and 81 - 999,999 are ignored. Notably this includes <ei>Z^0</ei>,
72 <ei>W^+-</ei> and <ei>t</ei>. The SM Higgs is modified by the SLHA input,
73 as is other codes in the range 25 - 80 and 1,000,000 - . If you
74 switch off this flag then also SM particles are modified by SLHA input.
77 <parm name="SLHA:minMassSM" default="100.0">
78 This parameter provides an alternative possibility to ignore SLHA input
79 for all particles with identity codes below 1,000,000 (which mainly
80 means SM particle, but also includes e.g. the Higgses in
81 two-Higgs-doublet scenarios) whose default masses in PYTHIA lie below
82 some threshold value, given by this parameter. The default value of
83 100.0 allows SLHA input to modify the top quark, but not, e.g., the
84 <ei>Z^0</ei> and <ei>W^+-</ei> bosons.
87 <mode name="SLHA:verbose" default="1" min="0" max="3">
88 Controls amount of text output written by the SLHA interface, with a
89 value of 0 corresponding to the most quiet mode.
92 <h3>Internal SLHA Variables</h3>
94 The following variables are used internally by PYTHIA as local copies
95 of SLHA information. User changes will generally have no effect, since
96 these variables will be reset by the SLHA reader during initialization.
98 <flag name="SLHA:NMSSM" default="off">
99 Corresponds to SLHA block MODSEL entry 3.
104 <!-- Copyright (C) 2010 Torbjorn Sjostrand -->