### Abstract

Axions are one of the most attractive dark matter candidates. The evolution of their number density in the early universe can be determined by calculating the topological susceptibility χ(T) of QCD as a function of the temperature. Lattice QCD provides an ab initio technique to carry out such a calculation. A full result needs two ingredients: physical quark masses and a controlled continuum extrapolation from non-vanishing to zero lattice spacings. We determine χ(T) in the quenched framework (infinitely large quark masses) and extrapolate its values to the continuum limit. The results are compared with the prediction of the dilute instanton gas approximation (DIGA). A nice agreement is found for the temperature dependence, whereas the overall normalization of the DIGA result still differs from the non-perturbative continuum extrapolated lattice results by a factor of order ten. We discuss the consequences of our findings for the prediction of the amount of axion dark matter.

Original language | English |
---|---|

Pages (from-to) | 175-181 |

Number of pages | 7 |

Journal | Physics Letters B |

Volume | 752 |

DOIs | |

Publication status | Published - Jan 10 2016 |

### Fingerprint

### Keywords

- Axion dark matter
- Instantons
- QCD on the lattice

### ASJC Scopus subject areas

- Nuclear and High Energy Physics

### Cite this

*Physics Letters B*,

*752*, 175-181. https://doi.org/10.1016/j.physletb.2015.11.020

**Axion cosmology, lattice QCD and the dilute instanton gas.** / Borsanyi, Sz; Dierigl, M.; Fodor, Z.; Katz, S.; Mages, S. W.; Nogradi, D.; Redondo, J.; Ringwald, A.; Szabo, K. K.

Research output: Contribution to journal › Article

*Physics Letters B*, vol. 752, pp. 175-181. https://doi.org/10.1016/j.physletb.2015.11.020

}

TY - JOUR

T1 - Axion cosmology, lattice QCD and the dilute instanton gas

AU - Borsanyi, Sz

AU - Dierigl, M.

AU - Fodor, Z.

AU - Katz, S.

AU - Mages, S. W.

AU - Nogradi, D.

AU - Redondo, J.

AU - Ringwald, A.

AU - Szabo, K. K.

PY - 2016/1/10

Y1 - 2016/1/10

N2 - Axions are one of the most attractive dark matter candidates. The evolution of their number density in the early universe can be determined by calculating the topological susceptibility χ(T) of QCD as a function of the temperature. Lattice QCD provides an ab initio technique to carry out such a calculation. A full result needs two ingredients: physical quark masses and a controlled continuum extrapolation from non-vanishing to zero lattice spacings. We determine χ(T) in the quenched framework (infinitely large quark masses) and extrapolate its values to the continuum limit. The results are compared with the prediction of the dilute instanton gas approximation (DIGA). A nice agreement is found for the temperature dependence, whereas the overall normalization of the DIGA result still differs from the non-perturbative continuum extrapolated lattice results by a factor of order ten. We discuss the consequences of our findings for the prediction of the amount of axion dark matter.

AB - Axions are one of the most attractive dark matter candidates. The evolution of their number density in the early universe can be determined by calculating the topological susceptibility χ(T) of QCD as a function of the temperature. Lattice QCD provides an ab initio technique to carry out such a calculation. A full result needs two ingredients: physical quark masses and a controlled continuum extrapolation from non-vanishing to zero lattice spacings. We determine χ(T) in the quenched framework (infinitely large quark masses) and extrapolate its values to the continuum limit. The results are compared with the prediction of the dilute instanton gas approximation (DIGA). A nice agreement is found for the temperature dependence, whereas the overall normalization of the DIGA result still differs from the non-perturbative continuum extrapolated lattice results by a factor of order ten. We discuss the consequences of our findings for the prediction of the amount of axion dark matter.

KW - Axion dark matter

KW - Instantons

KW - QCD on the lattice

UR - http://www.scopus.com/inward/record.url?scp=84947814107&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84947814107&partnerID=8YFLogxK

U2 - 10.1016/j.physletb.2015.11.020

DO - 10.1016/j.physletb.2015.11.020

M3 - Article

AN - SCOPUS:84947814107

VL - 752

SP - 175

EP - 181

JO - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

JF - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

SN - 0370-2693

ER -