Complex Scalar Field Dark Matter and the Stochastic Gravitational Wave Background from Inflation: New Cosmological Constraints and Detectability

Autor(en)

Bohua Li, Paul R. Shapiro, Tanja Rindler-Daller

Abstrakt

We consider an alternative to WIMP cold dark matter (CDM), ultralight bosonic dark matter (m≥10^-22 eV) described by a complex scalar field (SFDM), of which the comoving particle number density is conserved after particle production during standard reheating (w=p/ρ=0). In a ΛSFDM universe, SFDM starts relativistic, evolving from stiff (w=1) to radiation-like (w=1/3), before becoming nonrelativistic at late times (w=0). Thus, before the familiar radiation-dominated phase, there is an even earlier phase of stiff-SFDM-domination, during which the expansion rate is higher than in ΛCDM. The transitions between these phases, determined by SFDM particle mass m, and coupling strength λ, of a quartic self-interaction, are therefore constrained by cosmological observables, particularly N_eff, the effective number of neutrino species during BBN, and z_eq, the redshift of matter-radiation equality. Furthermore, since the homogeneous energy density contributed by the stochastic gravitational wave background (SGWB) from inflation is amplified during the stiff phase, relative to the other components, the SGWB can contribute a radiation-like component large enough to affect these observables. This same amplification makes possible detection of this SGWB at high frequencies by current laser interferometer experiments, e.g., aLIGO/Virgo, eLISA. For SFDM particle parameters that satisfy these cosmological constraints, the amplified SGWB is detectable by aLIGO, for values of tensor-to-scalar ratio r currently allowed by CMB polarization measurements, for a broad range of possible reheat temperatures T_re. For a given r, if SFDM parameters marginally satisfy cosmological constraints (maximizing total SGWB energy density), the SGWB is maximally detectable when modes that reenter the horizon when reheating ends have frequencies in the 10-50 Hz aLIGO band today. For example, if r=0.01, the maximally detectable model for (λ/(mc²)², m)=(10^-18 eV^-1cm³, 8×10^-20 eV) has T_re=10⁴ GeV, for which we predict aLIGO O1 run detection with SNR ~10. Nondetection by aLIGO O1 would provide a new cosmological constraint on SFDM. A wider range of SFDM parameters and T_re should be accessible to aLIGO/Virgo O5, which may detect this unique signature of SFDM.

Organisation(en)

Institut für Astrophysik

Externe Organisation(en)

University of Texas, Austin

Publikationsdatum

01-2017

ÖFOS 2012

103003 Astronomie, 103004 Astrophysik

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/3450b7a6-5f9d-4302-9a5d-7895c9c69026