Modification of black-body radiance at low temperatures and frequencies

In contrast to earlier reports, where the spectrum of the {\sl energy density} of photonic black-body radiation modified by SU(2) effects was discussed, we discuss the low-frequency spectrum of the {\sl radiance} at temperatures ranging between 5 and 20 Kelvin. We conclude that compared to the conventional theory the only observable effect is associated with the spectral gap (total screening). We also discuss how a low-temperature black body cavity under the influence of a sufficiently strong static electric field is forced to emit according to Planck's radiation law (pure U(1) theory) even at low frequencies and how this effect can be utilized to measure SU(2) induced deviations.Comment: 10 pp, 5 figs; v2: slight changes in text, extended discussion of Rydberg-atom experimen

Chiral anomaly and strange-nonstrange mixing

As a first step, a simple and pedagogical recall of the $\eta$-$\eta'$ system is presented, in which the role of the axial anomaly, related to the heterochiral nature of the multiplet of (pseudo)scalar states, is underlined. As a consequence, $\eta$ is close to the octet and $\eta'$ to the singlet configuration. On the contrary, for vector and tensor states, which belong to homochiral multiplets, no anomalous contribution to masses and mixing is present. Then, the isoscalar physical states are to a very good approximation nonstrange and strange, respectively. Finally, for pseudotensor states, which are part of an heterochiral multiplet (just as pseudoscalar ones), a sizable anomalous term is expected: $\eta_2 (1645)$ roughly corresponds to the octet and $\eta_2 (1870)$ to the singlet.Comment: 4 pages. Prepared for the proceedings of MESON 2018, 15th International Workshop on Meson Physics, KRAK\'OW, POLAND, 7th - 12th June 201

Modelling glueballs

Glueballs are predicted in various theoretical approaches of QCD (most notably lattice QCD), but their experimental verification is still missing. In the low-energy sector some promising candidate for the scalar glueball exist, and some (less clear) candidates for the tensor and pseudoscalar glueballs were also proposed. Yet, for heavier gluonic states there is much work to be done both from the experimental and theoretical points of view. In these proceedings, we briefly review the current status of research of glueballs and discuss future developments.Comment: Proceedings of MESON2016, 14th International Workshop on Meson Production, Properties and Interaction KRAK\'OW, POLAND, 2-7/6/2016. 6 page

Revisiting the axial anomaly for light mesons and baryons

The axial anomaly is responsible for the masses and mixing of the mesons $\eta$ and $\eta'$. An open question is if (and to what extent) it affects also other hadrons. We show that anomalous terms can be important to understand the spectroscopy of the pseudotensor mesons $\eta_2 (1645)$ and $\eta_2 (1870)$. In fact, pseudotensor mesons belong to a so-called heterochiral multiplet, for which a quadratic mixing term between nonstrange and strange isoscalar members arises. On the contrary, for so-called homochiral multiplets, such as the ground-state (axial-)vector and tensor mesons, this mixing is not possible, hence one can easily understand why the isoscalar members of these multiplets are almost purely nonstrange and strange, respectively. Moreover, the axial anomaly can be also coupled to baryons (within the mirror assignment), and thus it helps to explain the large decay width $N^{\ast }(1535)\rightarrow N\eta$ and to clarify which baryons are chiral partners.Comment: 6 pages. Prepared for the proceedings of the XVII International Conference on Hadron Spectroscopy and Structure - Hadron2017, 25-29 September, 2017, University of Salamanca, Salamanca, Spai

Thermal ground state for pure SU(2) Yang-Mills thermodynamics

In this proceeding the emergence of a composite, adjoint-scalar field as an average over (trivial holonomy) calorons and anti-calorons is reviewed. This composite field acts as a background field to the dynamics of perturbative gluons, to which it is coupled via an effective, gauge invariant Lagrangian valid for temperatures above the deconfinement phase transition. Moreover a Higgs mechanism is induced by the composite field: two gluons acquire a quasi-particle thermal mass. On the phenomenological side the composite field acts as a bag pressure which shows a linear dependence on the temperature. As a result the linear rise with temperature of the trace anomaly is obtained and is compared to recent lattice studies