# Normal forms of bireversible vector fields

## TL;DR

This paper develops a method to derive normal forms for a specific class of smooth bireversible vector fields, preserving symmetries and linear structure, with applications to Hamiltonian systems.

## Contribution

It adapts an existing normal form method to bireversible vector fields with nilpotent and semisimple parts, providing an algebraic, algorithmic approach.

## Key findings

- Normal forms preserve reversing symmetries and linearization.
- Applicable to Hamiltonian systems without resonance.
- Method simplifies calculations for complex vector fields.

## Abstract

In this paper we adapt the method of [P. H. Baptistelli, M. Manoel and I. O. Zeli. Normal form theory for reversible equivariant vector fields. Bull. Braz. Math. Soc., New Series 47 (2016), no. 3, 935-954] to obtain normal forms of a class of smooth bireversible vector fields. These are vector fields reversible under the action of two linear involution and whose linearization has a nilpotent part and a semisimple part with purely imaginary eigenvalues. We show that these can be put formally in normal form preserving the reversing symmetries and their linearization. The approach we use is based on an algebraic structure of the set of this type of vector fields. Although this can lead to extensive calculations in some cases, it is in general a simple and algorithmic way to compute the normal forms. We present some examples, which are Hamiltonian systems without resonance for one case and other cases with certain resonances.