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Home > Physics Letters B (Elsevier) > Axion cosmology, lattice QCD and the dilute instanton gas |

Borsanyi, Sz. (Department of Physics, Wuppertal University, Gaussstrasse 20, Wuppertal, D-42119, Germany) ; Dierigl, M. (Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, Hamburg, D-22607, Germany) ; Fodor, Z. (Department of Physics, Wuppertal University, Gaussstrasse 20, Wuppertal, D-42119, Germany) (IAS/JSC, Forschungszentrum Jülich, Jülich, D-52425, Germany) (Institute for Theoretical Physics, Eötvös University, Pázmány Peter sétany 1/A, Budapest, H-1117, Hungary) ; Katz, S.D. (Institute for Theoretical Physics, Eötvös University, Pázmány Peter sétany 1/A, Budapest, H-1117, Hungary) (MTA-ELTE Lendület Lattice Gauge Theory Research Group, Budapest, Hungary) ; Mages, S.W. (University of Regensburg, Regensburg, D-93053, Germany) (IAS/JSC, Forschungszentrum Jülich, Jülich, D-52425, Germany) ; Nogradi, D. (Institute for Theoretical Physics, Eötvös University, Pázmány Peter sétany 1/A, Budapest, H-1117, Hungary) (MTA-ELTE Lendület Lattice Gauge Theory Research Group, Budapest, Hungary) (Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA, 93106-4030, USA) ; Redondo, J. (Departamento de Física Teórica, Universidad de Zaragoza, Pedro Cerbuna 12, Zaragoza, E-50009, Spain) (Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, München, D-80805, Germany) ; Ringwald, A. (Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, Hamburg, D-22607, Germany) ; Szabo, K.K. (Department of Physics, Wuppertal University, Gaussstrasse 20, Wuppertal, D-42119, Germany) (IAS/JSC, Forschungszentrum Jülich, Jülich, D-52425, Germany)

11 November 2015

**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.

**Published in: ****Physics letters B (2015)**
**Published by: **Elsevier

**DOI: **10.1016/j.physletb.2015.11.020

**License: **CC-BY-3.0