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 {mathcal{V}}^{alpha }{M}_{mathrm{Planck}} , α = 1, 3/2, 5/3 where mathcal{V} is the volume of the extra dimensions. Macroscopic compact objects from ultra-light string axions are realised with masses of order {e}^{mathcal{V}2/3} MPlanck. 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 {mathcal{V}}^{beta } with β > 2 and non-linear effects cannot be neglected.
Highlights
String theory, being a fundamental theory of gravity, has the potential to make physical predictions that can be tested only through gravitational couplings
We explore the possibility that (Bose-Einstein) condensation of scalar fields from string compactifications can lead to long-lived compact objects
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
Summary
In order to give rise to a long-lived compact objects, the corresponding particle has to be quasi-stable and could contribute to dark matter. String theory offers many dark matter candidates and quasi-stable particles, to name a few: matter fields from a hidden sector, moduli (including the dilaton and the many axions), the gravitino (see for instance [22]). Some conversion rules 1 GeV 1.8 × 10−24 g 5 × 1013 cm−1 1.5 × 1024 Hz
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