Extra Dimensions

ISUB =

391	$\mathrm{f}\overline{\mathrm{f}}\to \mathrm{G}^*$
392	$\mathrm{g}\mathrm{g}\to \mathrm{G}^*$
393	$\mathrm{q}\overline{\mathrm{q}}\to \mathrm{g}\mathrm{G}^*$
394	$\mathrm{q}\mathrm{g}\to \mathrm{q}\mathrm{G}^*$
395	$\mathrm{g}\mathrm{g}\to \mathrm{g}\mathrm{G}^*$

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 $\mathrm{G}^*$, 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-$p_{\perp}$ 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 $p_{\perp}$ values, and gives a reasonable description also of the high-$p_{\perp}$ tail. Processes 393-395 could be useful e.g. for the study of invisible decays of the $\mathrm{G}^*$, where a large $p_{\perp}$ imbalance would be required. It also serves to test/confirm the shower expectations of different $p_{\perp}$ spectra for different production processes [Bij01].

Decay channels of the $\mathrm{G}^*$ to $\mathrm{f}\overline{\mathrm{f}}$, $\mathrm{g}\mathrm{g}$, $\gamma\gamma$, $\mathrm{Z}^0 \mathrm{Z}^0$ and $\mathrm{W}^+ \mathrm{W}^-$ contribute to the total width. The correct angular distributions are included for decays to a fermion pair in the lowest-order processes, whereas other decays currently are taken to be isotropic.

The $\mathrm{G}^*$ mass is to be considered a free parameter. The other degree of freedom in this scenario is a dimensionless coupling, see PARP(50).