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Дата изменения: Tue Aug 15 14:21:26 2000
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Menu 6.

The View squared diagrams function is similar to the View diagram one of the previous menu but is applied to the set of squared diagrams. Each squared diagram is a graphic representation of $A B^{*}$ contribution in the squared matrix element, where $A$ and $B$ are some amplitudes corresponding to Feynman diagrams.

Let us summarize some features of CompHEP  squared diagrams generation:

• CompHEP  never constructs both $A B^{*}$ and $B A^{*}$ diagrams but only one of them. Instead, for simplicity, CompHEP  calculates $2*Re(A B^{*})$ on the symbolic and numerical levels.

• CompHEP  constructs only one representative of a set of diagrams which can be transformed one to another by permutation of identical outgoing particles. The needed symmetrization for such particles is performed later on, at the step of numerical or symbolic summation.

• Each CompHEP  diagram represents a set of squared diagrams where some physical particles are replaced by their ghosts in all possible ways according to the existing vertices of the model. To see the ghost squared diagrams for each displayed one just press the 'G' key.

If you browse the squared diagrams after usage of the Symbolic calculation function you will see that each of the squared diagrams is marked by one of the following labels CALC, ZERO, Out of memory, Del. They mean that the diagram has been successfully calculated; gives a zero contribution; cannot be calculated; or has been deleted, correspondingly.

The Symbolic calculation function starts symbolic evaluation of the generated squared diagrams. This evaluation is performed by the built-in symbolic calculator created specially in the framework of the CompHEP  project.

During the calculation the information about a number of calculated diagrams and about a step of evaluation of the current diagram is shown.

The Reduce program function creates a code of symbolic evaluation in the format of Reduce  language [Hearn&Fitch] separately for each squared diagram. These codes are not used for the further CompHEP  processing, but they can be useful for cross-checking the CompHEP  software. On one hand, one can investigate the Reduce  code to get conviction that it correctly calculates a contribution of the squared diagram. On the other hand, you may compare the result of the Reduce  evaluation of diagram code with the result of built-in symbolic calculator.

General purpose of a package like CompHEP  is to create the corresponding C  or Fortran  source code for further numerical processing and compile this code using the corresponding system facilities. User's control is not necessary for this step as well as for the step of symbolic calculations. CompHEP  provides the user with a possibility to perform the above steps in a non-interactive mode. To start the non-interactive session one could activate the Make n_comphep_c or Make n_comphep_f menu function. Then the current interactive session ends and a new batch process starts. See Section for details of the non-interactive calculations in CompHEP.

As the outcome, the executable file n_comphep_c or n_comphep_f is created for the further numerical precessing. You may find it in the results directory. For the time of batch calculation the LOCK file appears in the user working directory to prevent a double start of the CompHEP  package within the same place of the file system.

As a rule the System Administrator requires to start a large job in a special batch regime. The execution of one of the Make n_comphep_ functions may require large computer resources for some processes with large number of diagrams. In this case you could correct your comphep command file according to the System Administrator rules. The corresponding calls are disposed after labels 24) and 25) in this file.