# Inflation by spin and torsion in Poincare gauge theory of gravity

## TL;DR

This paper demonstrates that in Poincare gauge theory of gravity, spin and torsion can naturally induce an inflationary phase in the early universe without extra fields or fine-tuning, aligning with observational data.

## Contribution

It introduces a specific Lagrangian in Poincare gauge theory where spin and torsion drive inflation without additional fields or fine-tuning.

## Key findings

- Spin and torsion induce inflation in the early universe.
- The model's scalar spectral index matches observational data.
- No fine-tuning needed for the parameters.

## Abstract

In Poincare gauge theory of gravity, in addition to mass-energy content, spin is also a source for gravitational interactions. Although the effects of spin are negligible at low energies, they can play a crucial role at very early universe when the spin density was very high. In this paper by choosing a suitable Lagrangian for Poincare gauge theory of gravity, and suitable energy-momentum and spin density tensors, we show that the effects of spin and torsion can lead to a inflationary phase without the need for any additional fields. No fine tuning of parameters is required in this setup. We also calculate the scalar spectral index at the end of inflation and show that it agrees with the most recent observational data.