# Cosmological constraints on a unified dark matter-energy scalar field model with fast transition

## TL;DR

This paper investigates a single scalar field model that transitions rapidly from dark matter to dark energy behavior, constrained by cosmological data, showing it is comparable to the standard Lambda-CDM model in viability.

## Contribution

It introduces and constrains a k-essence scalar field model with a rapid transition, providing a viable alternative to Lambda-CDM with specific bounds on transition speed.

## Key findings

- Model has similar evidence to Lambda-CDM
- Fast transitions are favored over slow ones
- Lower bound on transition rapidity established

## Abstract

We test the viability of a single fluid cosmological model containing a transition from a dark-matter-like regime to a dark-energy-like regime. The fluid is a k-essence scalar field with a well-defined Lagrangian. We constrain its model parameters with a combination of geometric probes and conclude that the evidence for this model is similar to the evidence for $\Lambda$CDM. In addition, we find a lower bound for the rapidity of the transition, implying that fast transitions are favored with respect to slow ones even at background level.