In recent years, the area of observable consequences of extra dimensions has attracted a strong interest. The field is still in rapid development, so there still does not exist a `standard phenomenology'. The topic is also fairly new in PYTHIA, and currently only a first scenario is available.
The , introduced as new particle code 5000039, is intended to represent the lowest excited graviton state in a Randall-Sundrum scenario [Ran99] of extra dimensions. The lowest-order production processes by fermion or gluon fusion are found in 391 and 392. The further processes 393-395 are intended for the high- tail in hadron colliders. As usual, it would be double-counting to have both sets of processes switched on at the same time. Processes 391 and 392, with initial-state showers switched on, are appropriate for the full cross section at all values, and gives a reasonable description also of the high- tail. Processes 393-395 could be useful e.g. for the study of invisible decays of the , where a large imbalance would be required. It also serves to test/confirm the shower expectations of different spectra for different production processes [Bij01].
Decay channels of the to , , , and contribute to the total width. The correct angular distributions are included for decays to a fermion, or pair in the lowest-order processes, whereas other decays currently are taken to be isotropic.
The mass is to be considered a free parameter. The other degree of freedom in this scenario is a dimensionless coupling; see PARP(50).