Axion dark matter with explicit Peccei-Quinn symmetry breaking in the axiverse

It is shown that the required high quality of the Peccei-Quinn (PQ) symmetry can be a natural outcome of the multiple QCD axion models. In the axiverse, a hypothetical mass mixing between the QCD axions and axion-like particles (ALPs) can occur, which leads to an interesting phenomenon called the level crossing. In this paper, we investigate this mass mixing between one QCD axion and one ALP with the explicit PQ symmetry breaking in the early Universe. The dynamics of the axions and their cosmological evolutions when the level crossing occurs in this scenario are studied in detail. Then we focus our attention on the axion dark matter (DM) abundance. With several typical parameter sets for level crossing, we find that in the presence of the explicit PQ symmetry breaking term in the mixing, the total axion DM abundance is dominated by ALP and significantly suppressed.Comment: 20 pages, 7 figure

New feature of low pTp_{T} charm quark hadronization in pppp collisions at s=7\sqrt{s}=7 TeV

Treating the light-flavor constituent quarks and antiquarks that can well describe the data of light-flavor hadrons in $pp$ collisions at $\sqrt{s}=7$ TeV as the underlying source of chromatically neutralizing the charm quarks of low transverse momenta ($p_{T}$), we show that the experimental data of $p_{T}$ spectra of single-charm hadrons $D^{0,+}$, $D^{*+}$ $D_{s}^{+}$, $\Lambda_{c}^{+}$ and $\Xi_{c}^{0}$ at mid-rapidity in the low $p_{T}$ range ($2\lesssim p_{T}\lesssim7$ GeV/$c$) in $pp$ collisions at $\sqrt{s}=7$ TeV can be well understood by the equal-velocity combination of perturbatively-created charm quarks and those light-flavor constituent quarks and antiquarks. This suggests a possible new scenario of low $p_{T}$ charm quark hadronization, in contrast to the traditional fragmentation mechanism, in $pp$ collisions at LHC energies. This is also another support for the exhibition of the effective constituent quark degrees of freedom for the small parton system created in $pp$ collisions at LHC energies.Comment: 7 pages, 5 figure