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| 3 | <title>SUSY Les Houches Accord</title> |
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| 28 | <form method='post' action='SUSYLesHouchesAccord.php'> |
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| 29 | |
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| 30 | <h2>SUSY Les Houches Accord</h2> |
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| 31 | |
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| 32 | The PYTHIA 8 program does not contain an internal spectrum calculator |
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| 33 | (a.k.a. RGE package) to provide supersymmetric couplings, mixing angles, |
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| 34 | masses and branching ratios. Thus the SUSY Les Houches Accord (SLHA) |
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| 35 | [<a href="Bibliography.php" target="page">Ska04</a>][<a href="Bibliography.php" target="page">All08</a>] is the only way of |
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| 36 | inputting SUSY models, and SUSY processes (see |
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| 37 | the <?php $filepath = $_GET["filepath"]; |
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| 38 | echo "<a href='SUSYProcesses.php?filepath=".$filepath."' target='page'>";?>SUSYProcesses</a> page) |
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| 39 | cannot be run unless such an input has taken place. |
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| 40 | |
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| 41 | <p/> |
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| 42 | The SLHA input format can also be extended for use with more general BSM |
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| 43 | models, beyond SUSY. Information specific to how to use the SLHA |
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| 44 | interface for generic BSM models is collected below, |
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| 45 | under <a href="#generic">Using SLHA for generic BSM Models</a>, with |
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| 46 | more elaborate explanations and examples in [<a href="Bibliography.php" target="page">Des11</a>]. |
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| 47 | |
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| 48 | <p/> |
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| 49 | Most of the SUSY implementation in PYTHIA 8 is compatible with both the |
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| 50 | SLHA1 [<a href="Bibliography.php" target="page">Ska04</a>] and SLHA2 [<a href="Bibliography.php" target="page">All08</a>] |
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| 51 | conventions (with some limitations for the NMSSM |
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| 52 | in the latter case). Internally, PYTHIA 8 uses the |
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| 53 | SLHA2 conventions and translates SLHA1 input to these when necessary. |
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| 54 | See the section on SUSY Processes and [<a href="Bibliography.php" target="page">Des11</a>] for more |
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| 55 | information. |
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| 56 | |
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| 57 | <p/> |
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| 58 | When reading LHEF files, Pythia automatically looks for SLHA information |
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| 59 | between <code><slha>...</slha></code> tags in the header of such |
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| 60 | files. When running Pythia without LHEF input (or if reading an LHEF |
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| 61 | file that does not contain SLHA information in the header), a separate |
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| 62 | file containing SLHA information may be specified using |
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| 63 | <code>SLHA:file</code> (see below). |
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| 64 | |
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| 65 | <p/> |
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| 66 | Normally the LHEF would be in uncompressed format, and thus human-readable |
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| 67 | if opened in a text editor. A possibility to read gzipped files has |
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| 68 | been added, based on the Boost and zlib libraries, which therefore |
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| 69 | have to be linked appropriately in order for this option to work. |
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| 70 | See the <code>README</code> file in the main directory for details |
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| 71 | on how to do this. |
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| 72 | |
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| 73 | <p/> |
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| 74 | Finally, the SLHA input capability can of course also be used to input |
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| 75 | SLHA-formatted <code>MASS</code> and <code>DECAY</code> tables for |
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| 76 | other particles, such as the Higgs boson, furnishing a less |
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| 77 | sophisticated but more universal complement to the |
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| 78 | standard PYTHIA 8-specific methods for inputting such information (for the |
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| 79 | latter, see the section on <?php $filepath = $_GET["filepath"]; |
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| 80 | echo "<a href='ParticleData.php?filepath=".$filepath."' target='page'>";?>Particle Data</a> |
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| 81 | and the <?php $filepath = $_GET["filepath"]; |
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| 82 | echo "<a href='ParticleDataScheme.php?filepath=".$filepath."' target='page'>";?>scheme</a> to modify it). This |
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| 83 | may at times not be desirable, so a few options can be used to curb the right |
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| 84 | of SLHA to overwrite particle data. |
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| 85 | |
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| 86 | <p/> |
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| 87 | The reading-in of information from SLHA or LHEF files is handled by the |
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| 88 | <code>SusyLesHouches</code> class, while the subsequent calculation of |
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| 89 | derived quantities of direct application to SUSY processes is done in the |
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| 90 | <code>CoupSUSY</code>, <code>SigmaSUSY</code>, |
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| 91 | and <code>SUSYResonanceWidths</code> classes. |
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| 92 | |
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| 93 | <h3>SLHA Switches and Parameters</h3> |
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| 94 | |
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| 95 | <p/><code>mode </code><strong> SLHA:readFrom </strong> |
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| 96 | (<code>default = <strong>1</strong></code>; <code>minimum = 0</code>; <code>maximum = 2</code>)<br/> |
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| 97 | Controls from where SLHA information is read. |
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| 98 | <br/><code>option </code><strong> 0</strong> : is not read at all. Useful when SUSY is not simulated |
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| 99 | and normal particle properties should not be overwritten. |
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| 100 | <br/><code>option </code><strong> 1</strong> : read in from the <code><slha>...</slha></code> |
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| 101 | block of a LHEF, if such a file is read during initialization, and else |
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| 102 | from the <code>SLHA:file</code> below. |
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| 103 | <br/><code>option </code><strong> 2</strong> : read in from the <code>SLHA:file</code> below. |
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| 104 | |
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| 105 | |
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| 106 | <br/><br/><table><tr><td><strong>SLHA:file </td><td></td><td> <input type="text" name="1" value="void" size="20"/> (<code>default = <strong>void</strong></code>)</td></tr></table> |
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| 107 | Name of an SLHA (or LHEF) file containing the SUSY/BSM model definition, |
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| 108 | spectra, and (optionally) decay tables. Default <code>void</code> |
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| 109 | signals that no such file has been assigned. |
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| 110 | |
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| 111 | |
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| 112 | <br/><br/><strong>SLHA:keepSM</strong> <input type="radio" name="2" value="on" checked="checked"><strong>On</strong> |
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| 113 | <input type="radio" name="2" value="off"><strong>Off</strong> |
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| 114 | (<code>default = <strong>on</strong></code>)<br/> |
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| 115 | Some programs write SLHA output also for SM particles where normally |
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| 116 | one would not want to have masses and decay modes changed unwittingly. |
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| 117 | Therefore, by default, known SM particles are ignored in SLHA files. |
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| 118 | To be more specific, particle data for identity codes in the ranges |
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| 119 | 1 - 24 and 81 - 999,999 are ignored. Notably this includes <i>Z^0</i>, |
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| 120 | <i>W^+-</i> and <i>t</i>. The SM Higgs is modified by the SLHA input, |
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| 121 | as is other codes in the range 25 - 80 and 1,000,000 - . If you |
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| 122 | switch off this flag then also SM particles are modified by SLHA input. |
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| 123 | |
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| 124 | |
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| 125 | <br/><br/><table><tr><td><strong>SLHA:minMassSM </td><td></td><td> <input type="text" name="3" value="100.0" size="20"/> (<code>default = <strong>100.0</strong></code>)</td></tr></table> |
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| 126 | This parameter provides an alternative possibility to ignore SLHA input |
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| 127 | for all particles with identity codes below 1,000,000 (which mainly |
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| 128 | means SM particle, but also includes e.g. the Higgses in |
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| 129 | two-Higgs-doublet scenarios) whose default masses in PYTHIA lie below |
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| 130 | some threshold value, given by this parameter. The default value of |
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| 131 | 100.0 allows SLHA input to modify the top quark, but not, e.g., the |
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| 132 | <i>Z^0</i> and <i>W^+-</i> bosons. |
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| 133 | |
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| 134 | |
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| 135 | <h3>SLHA DECAY Tables</h3> |
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| 136 | |
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| 137 | <br/><br/><strong>SLHA:useDecayTable</strong> <input type="radio" name="4" value="on" checked="checked"><strong>On</strong> |
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| 138 | <input type="radio" name="4" value="off"><strong>Off</strong> |
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| 139 | (<code>default = <strong>on</strong></code>)<br/> |
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| 140 | Switch to choose whether to read in SLHA <code>DECAY</code> tables or not. |
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| 141 | If this switch is set to off, PYTHIA will ignore any decay tables found |
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| 142 | in the SLHA file, and all decay widths will be calculated internally by |
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| 143 | PYTHIA. If switched on, SLHA decay tables will be read in, and will |
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| 144 | then supersede PYTHIA's internal calculations, with PYTHIA only |
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| 145 | computing the decays for particles for which no SLHA decay table is |
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| 146 | found. (To set a particle stable, you may either omit an SLHA |
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| 147 | <code>DECAY</code> table for it and then |
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| 148 | use PYTHIA's internal <code>id:MayDecay</code> switch for that |
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| 149 | particle, or you may include an SLHA <code>DECAY</code> table for it, |
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| 150 | with the width set explicitly to zero.) |
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| 151 | |
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| 152 | |
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| 153 | <br/><br/><table><tr><td><strong>SLHA:minDecayDeltaM </td><td></td><td> <input type="text" name="5" value="1.0" size="20"/> (<code>default = <strong>1.0</strong></code>)</td></tr></table> |
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| 154 | This parameter sets the smallest allowed mass difference (in GeV, |
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| 155 | between the mass of the mother and the sum of the daughter masses) |
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| 156 | for a decay mode in a DECAY table to be switched on inside PYTHIA. The |
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| 157 | default is to require at least 1 GeV of open phase space, but this can |
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| 158 | be reduced (at the user's risk) for instance to be able to treat |
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| 159 | decays in models with very small mass splittings. |
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| 160 | |
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| 161 | |
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| 162 | <h3>Internal SLHA Variables</h3> |
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| 163 | |
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| 164 | <p/><code>mode </code><strong> SLHA:verbose </strong> |
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| 165 | (<code>default = <strong>1</strong></code>; <code>minimum = 0</code>; <code>maximum = 3</code>)<br/> |
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| 166 | Controls amount of text output written by the SLHA interface, with a |
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| 167 | value of 0 corresponding to the most quiet mode. |
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| 168 | |
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| 169 | |
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| 170 | The following variables are used internally by PYTHIA as local copies |
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| 171 | of SLHA information. User changes will generally have no effect, since |
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| 172 | these variables will be reset by the SLHA reader during initialization. |
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| 173 | |
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| 174 | <br/><br/><strong>SLHA:NMSSM</strong> <input type="radio" name="6" value="on"><strong>On</strong> |
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| 175 | <input type="radio" name="6" value="off" checked="checked"><strong>Off</strong> |
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| 176 | (<code>default = <strong>off</strong></code>)<br/> |
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| 177 | Corresponds to SLHA block MODSEL entry 3. |
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| 178 | |
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| 179 | |
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| 180 | <a name="generic"></a> |
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| 181 | <h2>Using SLHA for generic BSM Models</h2> |
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| 182 | |
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| 183 | </p> |
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| 184 | Using the <code>QNUMBERS</code> extension [<a href="Bibliography.php" target="page">Alw07</a>], the SLHA |
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| 185 | can also be used to define new particles, with arbitrary quantum |
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| 186 | numbers. This already serves as a useful way to introduce new |
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| 187 | particles and can be combined with <code>MASS</code> and |
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| 188 | <code>DECAY</code> tables in the usual |
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| 189 | way, to generate isotropically distributed decays or even chains of |
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| 190 | such decays. (If you want something better than isotropic, sorry, you'll |
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| 191 | have to do some actual work ...) |
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| 192 | </p> |
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| 193 | |
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| 194 | </p> |
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| 195 | A more advanced further option is to make use of the possibility |
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| 196 | in the SLHA to include user-defined blocks with arbitrary |
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| 197 | names and contents. Obviously, standalone |
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| 198 | PYTHIA 8 does not know what to do with such information. However, it |
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| 199 | does not throw it away either, but instead stores the contents of user |
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| 200 | blocks as strings, which can be read back later, with the user |
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| 201 | having full control over the format used to read the individual entries. |
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| 202 | </p> |
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| 203 | |
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| 204 | <p> |
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| 205 | The contents of both standard and user-defined SLHA blocks can be accessed |
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| 206 | in any class inheriting from PYTHIA 8's <code>SigmaProcess</code> |
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| 207 | class (i.e., in particular, from any semi-internal process written by |
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| 208 | a user), through its SLHA pointer, <code>slhaPtr</code>, by using the |
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| 209 | following methods: |
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| 210 | <a name="method1"></a> |
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| 211 | <p/><strong> </strong> <br/> |
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| 212 | bool slhaPtr->getEntry(string blockName, double& val); |
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| 213 | |
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| 214 | <strong> </strong> <br/> |
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| 215 | bool slhaPtr->getEntry(string blockName, int indx, double& val); |
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| 216 | |
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| 217 | <strong> </strong> <br/> |
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| 218 | bool slhaPtr->getEntry(string blockName, int indx, int jndx, double& val); |
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| 219 | |
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| 220 | <strong> </strong> <br/> |
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| 221 | bool slhaPtr->getEntry(string blockName, int indx, int jndx, int |
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| 222 | kndx, double& val); |
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| 223 | |
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| 224 | </p> |
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| 225 | |
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| 226 | <p> |
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| 227 | This particular example assumes that the user wants to read the |
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| 228 | entries (without index, indexed, matrix-indexed, or 3-tensor-indexed, |
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| 229 | respectively) in the user-defined block <code>blockName</code>, |
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| 230 | and that it should be interpreted as |
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| 231 | a <code>double</code>. The last argument is templated, and hence if |
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| 232 | anything other than a <code>double</code> is desired to be read, the |
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| 233 | user has only to give the last argument a different type. |
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| 234 | If anything went wrong (i.e., the block doesn't |
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| 235 | exist, or it doesn't have an entry with that index, or that entry |
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| 236 | can't be read as a double), the method returns false; true |
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| 237 | otherwise. This effectively allows to input completely arbitrary |
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| 238 | parameters using the SLHA machinery, with the user having full control |
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| 239 | over names and conventions. Of course, it is then the user's |
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| 240 | responsibility to ensure complete consistency between the names and |
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| 241 | conventions used in the SLHA input, and those assumed in any |
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| 242 | user-written semi-internal process code. |
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| 243 | </p> |
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| 244 | |
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| 245 | <p> |
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| 246 | Note that PYTHIA 8 always initializes at least |
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| 247 | the SLHA blocks MASS and SMINPUTS, starting from its internal |
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| 248 | SM parameters and particle data table values (updated to take into |
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| 249 | account user modifications). These blocks can therefore be accessed |
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| 250 | using the <code>slhaPtr->getEntry()</code> methods even in the absence |
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| 251 | of SLHA input. |
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| 252 | Note: in the SMINPUTS block, PYTHIA outputs physically correct |
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| 253 | (i.e., measured) values of <i>GF</i>, <i>m_Z</i>, and |
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| 254 | <i>alpha_EM(m_Z)</i>. However, if one attempts to compute, e.g., |
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| 255 | the W mass, at one loop from these quantities, a value of 79 GeV results, |
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| 256 | with a corresponding value for the weak mixing angle. We advise to |
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| 257 | instead take the physically measured W mass from block MASS, and |
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| 258 | recompute the EW parameters as best suited for the application at hand. |
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| 259 | </p> |
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| 260 | |
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| 261 | <input type="hidden" name="saved" value="1"/> |
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| 262 | |
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| 263 | <?php |
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| 264 | echo "<input type='hidden' name='filepath' value='".$_GET["filepath"]."'/>"?> |
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| 265 | |
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| 266 | <table width="100%"><tr><td align="right"><input type="submit" value="Save Settings" /></td></tr></table> |
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| 267 | </form> |
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| 268 | |
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| 269 | <?php |
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| 270 | |
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| 271 | if($_POST["saved"] == 1) |
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| 272 | { |
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| 273 | $filepath = $_POST["filepath"]; |
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| 274 | $handle = fopen($filepath, 'a'); |
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| 275 | |
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| 276 | if($_POST["1"] != "void") |
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| 277 | { |
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| 278 | $data = "SLHA:file = ".$_POST["1"]."\n"; |
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| 279 | fwrite($handle,$data); |
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| 280 | } |
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| 281 | if($_POST["2"] != "on") |
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| 282 | { |
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| 283 | $data = "SLHA:keepSM = ".$_POST["2"]."\n"; |
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| 284 | fwrite($handle,$data); |
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| 285 | } |
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| 286 | if($_POST["3"] != "100.0") |
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| 287 | { |
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| 288 | $data = "SLHA:minMassSM = ".$_POST["3"]."\n"; |
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| 289 | fwrite($handle,$data); |
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| 290 | } |
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| 291 | if($_POST["4"] != "on") |
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| 292 | { |
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| 293 | $data = "SLHA:useDecayTable = ".$_POST["4"]."\n"; |
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| 294 | fwrite($handle,$data); |
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| 295 | } |
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| 296 | if($_POST["5"] != "1.0") |
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| 297 | { |
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| 298 | $data = "SLHA:minDecayDeltaM = ".$_POST["5"]."\n"; |
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| 299 | fwrite($handle,$data); |
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| 300 | } |
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| 301 | if($_POST["6"] != "off") |
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| 302 | { |
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| 303 | $data = "SLHA:NMSSM = ".$_POST["6"]."\n"; |
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| 304 | fwrite($handle,$data); |
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| 305 | } |
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| 306 | fclose($handle); |
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| 307 | } |
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| 308 | |
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| 309 | ?> |
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| 310 | </body> |
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| 311 | </html> |
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| 312 | |
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| 313 | <!-- Copyright (C) 2012 Torbjorn Sjostrand --> |
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| 314 | |
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| 315 | |
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