TY - JOUR
T1 - An ultralight pseudoscalar boson
AU - Kim, Jihn E.
AU - Marsh, David J.E.
N1 - Publisher Copyright:
© 2016 American Physical Society.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2016/1/27
Y1 - 2016/1/27
N2 - Using a fundamental discrete symmetry, ZN, we construct a two-axion model with the QCD axion solving the strong-CP problem, and an ultralight axion (ULA) with mULA≈10-22 eV providing the dominant form of dark matter (DM). The ULA is light enough to be detectable in cosmology from its imprints on structure formation, and may resolve the small-scale problems of cold DM. The necessary relative DM abundances occur without fine-tuning in constructions with decay constants fULA∼1017 GeV, and fQCD∼1011 GeV. An example model achieving this has N=24, and we construct a range of other possibilities. We compute the ULA couplings to the standard model, and discuss prospects for direct detection. The QCD axion may be detectable in standard experiments through the E→·B→ and GG couplings. In the simplest models, however, the ULA has identically zero coupling to both GG of QCD and E→·B→ of electromagnetism due to vanishing electromagnetic and color anomalies. The ULA couples to fermions with strength g1/fULA. This coupling causes spin precession of nucleons and electrons with respect to the DM wind with period t∼ months. Current limits do not exclude the predicted coupling strength, and our model is within reach of the CASPEr-Wind experiment, using nuclear magnetic resonance.
AB - Using a fundamental discrete symmetry, ZN, we construct a two-axion model with the QCD axion solving the strong-CP problem, and an ultralight axion (ULA) with mULA≈10-22 eV providing the dominant form of dark matter (DM). The ULA is light enough to be detectable in cosmology from its imprints on structure formation, and may resolve the small-scale problems of cold DM. The necessary relative DM abundances occur without fine-tuning in constructions with decay constants fULA∼1017 GeV, and fQCD∼1011 GeV. An example model achieving this has N=24, and we construct a range of other possibilities. We compute the ULA couplings to the standard model, and discuss prospects for direct detection. The QCD axion may be detectable in standard experiments through the E→·B→ and GG couplings. In the simplest models, however, the ULA has identically zero coupling to both GG of QCD and E→·B→ of electromagnetism due to vanishing electromagnetic and color anomalies. The ULA couples to fermions with strength g1/fULA. This coupling causes spin precession of nucleons and electrons with respect to the DM wind with period t∼ months. Current limits do not exclude the predicted coupling strength, and our model is within reach of the CASPEr-Wind experiment, using nuclear magnetic resonance.
UR - http://www.scopus.com/inward/record.url?scp=84956661285&partnerID=8YFLogxK
U2 - 10.1103/PhysRevD.93.025027
DO - 10.1103/PhysRevD.93.025027
M3 - Article
AN - SCOPUS:84956661285
SN - 2470-0010
VL - 93
JO - Physical Review D
JF - Physical Review D
IS - 2
M1 - 025027
ER -