# Roton energy gap and spontaneous symmetry breaking

## TL;DR

This paper presents a theoretical calculation of the roton energy gap in superfluid helium-4 using spontaneous symmetry breaking, achieving results that closely match experimental data with less than 0.1% deviation.

## Contribution

The authors derive a relation for the roton energy gap at zero temperature based on spontaneous symmetry breaking, providing a highly accurate theoretical estimate.

## Key findings

- The theoretical roton gap is 8.707 K, very close to the experimental 8.712 K.
- The derived relation is Δ(0)/k_B T_λ = 4.
- Deviation between theory and experiment is less than 0.1%.

## Abstract

We study elementary excitations in superfluid helium-4 employing an approach based on the spontaneous symmetry breaking. In particular, we calculate the roton energy gap at zero temperature $\Delta (0)$. The relation that we have derived is $\Delta (0) / k_B T_\lambda = 4$. The theoretical value of $\Delta (0)/k_B$ is 8.707 K, which is significantly close to the experimental value of 8.712 K. The deviation between the theoretical and experimental values is less than 0.1%.