A critical appraisal is presented of developments in MOND since its introduction by Milgrom in 1983 to the present day.

Earlier comparisons of galactic rotation curves with MOND have arrived at the conclusion that the parameter a 0 lies within ∼20% of cH 0 /2π, where c is the velocity of light and H 0 is the Hubble constant. It is proposed here that, for this value of H 0 , signals propagating around the periphery of the Universe are phase locked by the graviton–nucleon interaction.

A series of publications of the WASA Collaboration culminates in a recent paper of Pricking, Bashkanov and Clement (arXiv:1310.5532) claiming a ΔΔ dibaryon resonance at 2370 MeV. However, as explained here, there are logical flaws in this result. A natural alternative arises from the reaction pd → NN *(1440)p s , where ps is a spectator proton. There is supporting evidence from a recent experiment of Mielke et al. on dp → 3He π + π −.

A novel interpretation of modified Newtonian dynamics (MOND) is presented. For galactic data, in addition to Newtonian acceleration, there is an attractive acceleration peaking at Milgrom’s parameter, a 0 . The peak lies within experimental error where a 0 = cH 0 /2π; H 0 is the present-time value of the Hubble constant, and c the velocity of light. The physical interpretation of this relation and its connection to dark energy are discussed.

Belle data on gamma gamma -> eta'pi pi are refitted using a broad J(PC) = 0(-+) peaking in the mass range 2250-2300 and X(1835), but without eta(1760). There is the possibility that the broad 0(-+) signal may be identified with the 0(-+) glueball predicted originally by Morningstar and Peardon. The X(1835) is confirmed to have a resonant phase variation. DOI: 10.1103/PhysRevD.86.114006

The status of light I = 0, J(PC) = 2(++), and 0(++) mesons is discussed, particularly the separation of n (n) over bar and s (s) over bar states. They fall into a simple scheme except for f(2)(1810). A case is made that this has been confused with the f(0)(1790). It should be possible to check this with existing or forthcoming data.

A novel interpretation of MOND is presented. For galactic data, in addition to Newtonian acceleration, there is an attractive acceleration peaking at Milgrom's parameter a_0. The peak lies within experimental error where a_0 = cH_0/2\pi and H_0 is the present-time value of the Hubble constant. This peaking may be understood in terms of quantum mechanical mixing between Newtonian gravitation and the condensation mechanism. There are five pointers towards galaxies being Fermi-Dirac condensates.

Belle data on $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\pi}\ensuremath{\pi}$ are refitted using a broad ${J}^{PC}={0}^{\ensuremath{-}+}$ peaking in the mass range 2250--2300 and $X(1835)$, but without $\ensuremath{\eta}(1760)$. There is the possibility that the broad ${0}^{\ensuremath{-}+}$ signal may be identified with the ${0}^{\ensuremath{-}+}$ glueball predicted originally by Morningstar and Peardon. The $X(1835)$ is confirmed to have a resonant phase variation.

Masjuan, Arriola, and Broniowski [Phys. Rev. D85, 094006 (2012)] claim that the slope of the light-quark radial trajectories is 1.35 +- 0.04 GeV^2, disagreeing with the Crystal Barrel value 1.143 +- 0.013 GeV^2. There are defects in their choice of data. When these defects are revised, results come back close to the Crystal Barrel average for the slope. A revised average value is given here.

There is a large discrepancy between results of Crystal Barrel and WA102 for the branching ratio R = BR[eta(2)(1870) -> a(2)(1320)pi]/BR[eta(2)(1870) -> f(2)(1270)eta]. An extensive re-analysis of the Crystal Barrel data redetermines branching ratios for decays of eta(2)(1870), eta(2)(1645), eta(2)(2030) and f(2)(1910). This re-analysis confirms a small value for R of 1.60 +/- 0.39, inconsistent with the value 20.4 +/- 6.6 of WA102. The likely origin of the discrepancy is that the WA102 data contain a strong f(2)(1910) -> a(2)pi signal as well as eta(2)(1870). There is strong evidence that the eta(2)(1870) has resonant phase variation. A peak in f(2)(1270)a(0)(980) confirms closely the parameters of the a(2)(2255) resonance observed previously. A peak in eta(2)(2030)pi is interpreted naturally in terms of p2(2245) with reduced errors for mass and widthM = 2285 +/- 20(stat) +/- 25(syst) MeV, Gamma = 250 +/- 20(stat) +/- 25(syst) MeV.

There is a large discrepancy between results of Crystal Barrel and WA102 for the branching ratio R=BR[η 2(1870)→a 2(1320)π]/BR[η 2(1870)→f 2(1270)η]. An extensive re-analysis of the Crystal Barrel data redetermines branching ratios for decays of η 2(1870), η 2(1645), η 2(2030) and f 2(1910). This re-analysis confirms a small value for R of 1.60±0.39, inconsistent with the value 20.4±6.6 of WA102. The likely origin of the discrepancy is that the WA102 data contain a strong f 2(1910)→a 2 π signal as well as η 2(1870). There is strong evidence that the η 2(1870) has resonant phase variation. A peak in f 2(1270)a 0(980) confirms closely the parameters of the a 2(2255) resonance observed previously. A peak in η 2(2030)π is interpreted naturally in terms of π 2(2245) with reduced errors for mass and width M=2285±20(stat)±25(syst) MeV, Γ=250±20(stat)±25(syst) MeV.

The Y(4140) observed by CDF appears to have a novel explanation. Its mass and width coincide within experimental error with a two-step process. In the first step, Y(4140) -> D_sbar + pi + D_s where the pion is virtual. A loop diagram involving this virtual pion allows Y(4140) de-excitation to J/psi + phi. Its predicted spin-parity is JPC = 1++. The same mechanism for Dbar-D^* configurations predicts a similar structure at 3911-3918 MeV, consistent with the peak at 3915 +- 3 MeV observed in omega J/psi by Babar and Belle. Relative branching ratios observed for B+ -> phi J/psi K+ and B+ -> omega J/psi K+ require that this mechanism accelerates decays of Y(4140) by a factor ~ 10^4 compared with isospin-violating decays via Y(4140) -> D_sbar + D^*_s. Similar processes are well known in molecular chemistry.

Belle report data on Upsilon (5S) -> Upsilon(1S,2S,3S)-piplus-piminus and chi_b(1P,2P)-piplus-piminus; they observe peaks in Upsilon-pi and chi_b-pi consistent with J^P=1^+. They interpret the peaks as molecular states Z_b(10608) and Z_b(10653). Their masses are just above Bbar-B^* and B^*bar-B^* thresholds at 10604.6 and 10650.2 MeV. An explanation in terms of cusps at these thresholds is presented here. The product of the rising phase space for Bbar-B^* and B^*bar B^* with the cusps creates peaks a few MeV higher in Bbar-B^* and B^*bar-B^*, and these peaks can de-excite to piplus-piminus-Upsilon(1S,2S,3S) and piplus-piminus-chi_b(1P,2P).

There is a large discrepancy between results of Crystal Barrel and WA102 for the branching ratio R = BR [ η 2 (1870)→ a 2 (1320) π ]/ BR [ η 2 (1870)→ f 2 (1270) η ]. An extensive re-analysis of the Crystal Barrel data redetermines branching ratios for decays of η 2 (1870), η 2 (1645), η 2 (2030) and f 2 (1910). This re-analysis confirms a small value for R of 1.60±0.39, inconsistent with the value 20.4±6.6 of WA102. The likely origin of the discrepancy is that the WA102 data contain a strong f 2 (1910)→ a 2 π signal as well as η 2 (1870). There is strong evidence that the η 2 (1870) has resonant phase variation. A peak in f 2 (1270) a 0 (980) confirms closely the parameters of the a 2 (2255) resonance observed previously. A peak in η 2 (2030) π is interpreted naturally in terms of π 2 (2245) with reduced errors for mass and width M =2285±20( stat )±25( syst ) MeV, Γ =250±20( stat )±25( syst ) MeV.

A measurement of transverse polarisation in (p) over barp -> all-neutral final states would almost certainly determine a complete set of partial wave amplitudes over the mass range 1910 to 2410 MeV. This should identify all resonances in this mass range. The experiment is technically straightforward and cheap by present standards.

The X(1835) has been confirmed clearly in new BESIII data for J/Ψ→γ(η′ππ); the angular distribution of the photon is consistent with a pseudoscalar. This makes it a candidate for an ss¯ radial excitation of η′ and η(1440) (or one or both of η(1405) and η(1475)). However, a conspicuous feature of the BESIII data is the absence of evidence for η(1440)→η′ππ while it is well known that η(1440) appears in ηππ. Can these facts be reconciled? There is in fact a simple explanation. The channel η(1440)→ηππ may be explained by the two-step process η(1440)→[K⁎K¯]L=1 and [κK¯]L=0, followed by KK¯→a0(980)→ηπ. This process does not produce any significant η′π signal because of the Adler zero close to the η′π threshold. Some further comments are added on necessary points in fitting data on η(1440).

The eta(1835) is confirmed clearly in new BESIII data for J/Psi -> gamma (eta'-pi-pi); the angular distribution of the photon is consistent with a pseudoscalar. This makes it a candidate for an s-sbar radial excitation of eta' and eta(1440) (or one or both of eta(1405) and eta(1475)). However, a conspicuous feature of the BES III data is the absence of evidence for eta(1440) -> eta'-pi-pi while it is well known that eta(1440) appears in eta-pi-pi. Can these facts be reconciled? There is in fact a simple explanation. The channel eta(1440) -> eta-pi-pi may be explained by the two-step process eta(1440) -> [K*K]_{L=1} and [kappa K ]_{L=0}, followed by KK -> a0(980) -> eta-pi. This process does not produce any significant eta'-pi signal because of the Adler zero close to the eta'-pi threshold.