Helicity Formalism for Spin-2 Particles

TL;DR

The paper develops a helicity-based formalism for spin-2 particles (gravitons) and applies it to ADD large extra dimensions, enabling automated, wide-ranging calculations of processes involving gravitons. It extends the helicity method to spin-2, defines spinor bases, polarization tensors, and a building-block framework to construct amplitudes, and provides a complete set of Feynman rules for graviton interactions. The ADD model is implemented in AMEGIC++, with continuum KK sums for virtual exchange and Monte Carlo sampling for real graviton production, and the results are validated against established analytic benchmarks. This work delivers a practical, extensible tool for collider phenomenology of quantum gravity and sets the stage for future exploration of warped extra dimensions.

Abstract

We develop the helicity formalism for spin-2 particles and apply it to the case of gravity in flat extra dimensions. We then implement the large extra dimensions scenario of Arkani-Hamed, Dimopoulos and Dvali in the program AMEGIC++, allowing for an easy calculation of arbitrary processes involving the emission or exchange of gravitons. We complete the set of Feynman rules derived by Han, Lykken and Zhang, and perform several consistency checks of our implementation.

Figures (8)

• Figure 1: The triple-Higgs--KK vertex.
• Figure 2: The four-Higgs--KK vertex.
• Figure 3: The fermion--fermion--KK vertex.
• Figure 4: The two-gauge-boson--KK vertex.
• Figure 5: The scalar--scalar--KK vertex.