Moduli stars

Abstract

We explore the possibility that (Bose-Einstein) condensation of scalar fields from string compactifications can lead to long-lived compact objects. Depending on the type of scalar fields we find different realisations of star-like and solitonic objects. We illustrate in the framework of type IIB string compactifications that closed string moduli can lead to heavy microscopic stars with masses of order V α M Planck , α = 1, 3/2, 5/3 where V is the volume of the extra dimensions. Macroscopic compact objects from ultra-light string axions are realised with masses of order e V 2/3 M Planck . Q-ball configurations can be obtained from open string moduli whereas the closed string sector gives rise to a new class of solutions, named PQ-balls, that arise in the two-field axion-modulus system. The stability, the potential for the formation, and the observability of moduli stars through gravitational waves are discussed. In particular we point out that during the early matter phase given by moduli domination, density perturbations grow by a factor V β with β > 2 and non-linear effects cannot be neglected.

De Sitter vs Quintessence in String Theory

“…It is then natural to have several candidates for dark energy but also for ultra‐light axion dark matter. Notice that these fields can also give rise to condensates (axion stars) with masses of order which can be as heavy as 10 20 solar masses . Moreover, as we shall show in Sec.…”

“…Notice that these fields can also give rise to condensates (axion stars) with masses of order M star ∼ M 2 p /m which can be as heavy as 10 20 solar masses. [161][162][163] Moreover, as we shall show in Sec. 3.4, notice that ultra-light axions oscillating around a minimum with positive vacuum energy can induce an oscillating equation of state parameter which yields a small modification of the standard CDM model.…”

A conjecture on the minimal size of bound states

“…The possible bearing of the swampland idea on boson stars has recently been discussed in [52,53]. In particular, the swampland distance and de Sitter conjectures attempt to constrain scalar dynamics and are hence relevant to what type of boson stars may exist [53].…”

A geometrical instability for ultra-light fields during inflation?

“…Ref. [13] however considered the case with V = V 0 e −k 1 φ 1 and f = f 0 e −k 2 φ 1 = f 0 e −k 1 k 2 N where f can decrease exponentially with the number of…”