Lorentz invariant dark-spinor and inflation

TL;DR

This paper explores how Lorentz invariant dark spinor fields can drive cosmic inflation, analyzing their perturbations and comparing results with Lorentz-violating theories, revealing constraints on the spinor field and implications for observable parameters.

Contribution

It introduces a Lorentz invariant non-standard spinor as a driver of inflation and analyzes its complex perturbation dynamics, extending previous Lorentz-violating models.

Findings

Dark spinors can drive inflation with a small tensor-to-scalar ratio.

The spectral index constrains the background NSS-field values.

Perturbation sound speed varies with time, unlike canonical scalar fields.

Abstract

We investigate the possibility of the inflation driven by a Lorentz invariant non-standard spinor field. As these spinors are having dominant interaction via gravitational field only, they are considered as \emph{Dark Spinors}. We study how these dark-spinors can drive the inflation and investigate the cosmological (scalar) perturbations generated by them. Though the dark-spinors obey a Klein-Gordon like equation, the underlying theory of the cosmological perturbations is far more complex than the theories which are using a canonical scalar field. For example the sound speed of the perturbations is not a constant but varies with time. We find that in order to explain the observed value of the spectral-index $n_s$ one must have upper bound on the values of the background NSS-field. The tensor to scalar ratio remains as small as that in the case of canonical scalar field driven inflation because the correction to tensor spectrum due to NSS is required to be very small. In addition we discuss the relationship of results with previous results obtained by using the Lorentz invariance violating theories.