Calculation of the axion mass based on high-temperature lattice quantum chromodynamics.
Unlike the electroweak sector of the standard model of particle physics, quantum chromodynamics (QCD) is surprisingly symmetric under time reversal. As there is no obvious reason for QCD being so symmetric, this phenomenon poses a theoretical problem, often referred to as the strong CP problem. The most attractive solution for this requires the existence of a new particle, the axion-a promising dark-matter candidate. Here we determine the axion mass using lattice QCD, assuming that these particles are the dominant component of dark matter. The key quantities of the calculation are the equation of state of the Universe and the temperature dependence of the topological susceptibility of QCD, a quantity that is notoriously difficult to calculate, especially in the most relevant high-temperature region (up to several gigaelectronvolts). But by splitting the vacuum into different sectors and re-defining the fermionic determinants, its controlled calculation becomes feasible. Thus, our twofold prediction helps most cosmological calculations to describe the evolution of the early Universe by using the equation of state, and may be decisive for guiding experiments looking for dark-matter axions. In the next couple of years, it should be possible to confirm or rule out post-inflation axions experimentally, depending on whether the axion mass is found to be as predicted here. Alternatively, in a pre-inflation scenario, our calculation determines the universal axionic angle that corresponds to the initial condition of our Universe.
Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.
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Borsanyi
Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.|Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany.|Institute for Theoretical Physics, Eötvös University, H-1117 Budapest, Hungary.
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Fodor
Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.
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Guenther
Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.
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Kampert
Institute for Theoretical Physics, Eötvös University, H-1117 Budapest, Hungary.|MTA-ELTE Lendület Lattice Gauge Theory Research Group, H-1117 Budapest, Hungary.
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Katz
Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany.
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Kawanai
Institute for Nuclear Research of the Hungarian Academy of Sciences, H-4026 Debrecen, Hungary.
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Kovacs
Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany.
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Mages
Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.
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Pasztor
Institute for Theoretical Physics, Eötvös University, H-1117 Budapest, Hungary.|MTA-ELTE Lendület Lattice Gauge Theory Research Group, H-1117 Budapest, Hungary.
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Pittler
University of Zaragoza, E-50009 Zaragoza, Spain.|Max Planck Institut für Physik, D-80803 Munich, Germany.
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Redondo
Deutsches Elektronen-Synchrotron DESY, D-22607 Hamburg, Germany.
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Ringwald
Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.|Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany.
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Szabo