It has been known for some time that the cosmological bound on the invisible axion scale can be avoided by an early phase of strong QCD. While most approaches rely on theories where the strong coupling constant is determined through the expectation value of some scalar field, we show that this mechanism can also be implemented into the benchmark Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky models when the early phase of strong QCD emerges by the modification of the running coupling during inflation. For both models the physics that are responsible for making QCD strong do not displace the axions minimum by too much, so that the efficiency of the relaxation is controlled by parameters of the theory and the number of inflationary <math><mi>e</mi></math>-folds. In particular, we consider the case of very efficient relaxation where the axion abundance is dominated by inflationary quantum and postinflationary thermal fluctuations. Within this situation we identify the parameter space compatible with all cosmological constrains and derive conditions on the reheating temperature and the QCD scale during inflation that result in the axion making up all the dark matter. Because of duality below the Peccei-Quinn scale and a minor influence of the Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky fields on the running, our findings also apply to a minimal two-form implementation of the axion.

Germany

Emmanouil Koutsangelas

Removing the cosmological bound on the axion scale in the Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky models

RENO (Reactor Experiment for Neutrino Oscillation) made a definitive measurement of the smallest neutrino mixing angle <math><msub><mrow><mi>θ</mi></mrow><mrow><mn>13</mn></mrow></msub></math> in 2012, based on the disappearance of reactor electron antineutrinos. The experiment has obtained a more precise value of the mixing angle and the first result on neutrino mass difference <math><mi>Δ</mi><msubsup><mrow><mi>m</mi></mrow><mrow><mi>ee</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math> from an energy and baseline dependent reactor neutrino disappearance using ∼500 days of data. Based on the ratio of inverse-beta-decay (IBD) prompt spectra measured in two identical far and near detectors, we obtain <math><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>⁡</mo><mo>(</mo><mn>2</mn><msub><mrow><mi>θ</mi></mrow><mrow><mn>13</mn></mrow></msub><mo>)</mo><mo>=</mo><mn>0.082</mn><mo>±</mo><mn>0.009</mn><mo>(</mo><mrow><mi>stat</mi></mrow><mo>.</mo><mo>)</mo><mo>±</mo><mn>0.006</mn><mo>(</mo><mrow><mi>syst</mi></mrow><mo>.</mo><mo>)</mo></math> and <math><mo>|</mo><mi>Δ</mi><msubsup><mrow><mi>m</mi></mrow><mrow><mi>ee</mi></mrow><mrow><mn>2</mn></mrow></msubsup><mo>|</mo><mo>=</mo><mo>[</mo><msubsup><mrow><mn>2.62</mn></mrow><mrow><mo>−</mo><mn>0.23</mn></mrow><mrow><mo>+</mo><mn>0.21</mn></mrow></msubsup><msubsup><mrow><mo>(</mo><mrow><mi>stat</mi></mrow><mo>.</mo><mo>)</mo></mrow><mrow><mo>−</mo><mn>0.13</mn></mrow><mrow><mo>+</mo><mn>0.12</mn></mrow></msubsup><mo>(</mo><mrow><mi>syst</mi></mrow><mo>.</mo><mo>)</mo><mo>]</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup><msup><mrow><mtext> eV</mtext></mrow><mrow><mn>2</mn></mrow></msup></math>. An excess of reactor antineutrinos near 5 MeV is observed in the measured prompt spectrum with respect to the most commonly used models. The excess is found to be consistent with coming from reactors. A successful measurement of <math><msub><mrow><mi>θ</mi></mrow><mrow><mn>13</mn></mrow></msub></math> is also made in an IBD event sample with a delayed signal of neutron capture on hydrogen. A precise value of <math><msub><mrow><mi>θ</mi></mrow><mrow><mn>13</mn></mrow></msub></math> would provide important information on determination of the leptonic CP phase if combined with a result of an accelerator neutrino beam experiment.