Covariant spectator theory for the electromagnetic three-nucleon form factors: Complete impulse approximation

TL;DR

This paper calculates the electromagnetic form factors of helium-3 and tritium using Covariant Spectator Theory, highlighting the impact of scalar meson-nucleon off-shell coupling within the complete impulse approximation framework.

Contribution

First application of Covariant Spectator Theory to three-nucleon form factors, exploring sensitivity to off-shell coupling and relativistic effects in the complete impulse approximation.

Findings

Relativistic effects significantly influence form factors.

Scalar meson-nucleon off-shell coupling affects three-body binding energy.

Results compare favorably with non-relativistic calculations with relativistic corrections.

Abstract

We present the first calculations of the electromagnetic form factors of $^3$He and $^3$H within the framework of the Covariant Spectator Theory (CST). This first exploratory study concentrates on the sensitivity of the form factors to the strength of the scalar meson-nucleon off-shell coupling, known from previous studies to have a strong influence on the three-body binding energy. Results presented here were obtained using the complete impulse approximation (CIA), which includes contributions of relativistic origin that appear as two-body corrections in a non-relativistic framework, such as "Z-graphs", but omits other two and three-body currents. We compare our results to non-relativistic calculations augmented by relativistic corrections of ${\cal O}(v/c)^2$.