Horndeski fermion-boson stars

TL;DR

This paper demonstrates the existence of static, spherically symmetric fermion-boson stars within (beyond) Horndeski theories, analyzing their properties and showing they can be more compact than traditional stars but below Buchdahl's limit.

Contribution

It introduces and characterizes fermion-boson stars in Horndeski theories, revealing two distinct families with unique properties and their relation to General Relativity.

Findings

Existence of static, spherically symmetric fermion-boson stars in Horndeski theories.

Identification of two families of configurations distinguished by parameter c_4.

Maximum compactness remains below Buchdahl's limit.

Abstract

We establish the existence of static and spherically symmetric fermion-boson stars, in a low energy effective model of (beyond) Horndeski theories. These stars are in equilibrium, and are composed by a mixing of scalar and fermionic matters that only interact gravitationally one with each other. Properties such as mass, radius, and compactness are studied, highlighting the existence of two families of configurations defined by the parameter $c_4$. These families have distinctive properties, although in certain limits both are reduced to their counterparts in General Relativity. Finally, by assuming the same conditions used in General Relativity, we find the maximum compactness of these hybrid stars and determine that it remains below the so-called Buchdahl's limit.