QCD equations of state and speed of sound in neutron stars

Neutron stars are cosmic laboratories to study dense matter in quantum chromodynamics (QCD). The observable mass-radius relations of neutron stars are determined by QCD equations of state and can reflect the properties of QCD phase transitions. In the last decade, there have been historical discoveries in neutron stars; the discoveries of two-solar mass neutron stars and neutron star merger events, which have imposed tight constraints on equations of state. While a number of equations of state are constructed to satisfy these constraints, a theoretical challenge is how to reconcile those constructions with the microphysics expected from the hadron physics and in-medium calculations. In this short article, we briefly go over recent observations and discuss their implications for dense QCD matter, referring to QCD constraints in the low- and high-density limits, QCD-like theories, and lattice QCD results for baryon-baryon interactions.

The potential of $$\varLambda $$ and $$\varXi ^-$$ studies with PANDA at FAIR

The antiproton experiment PANDA at FAIR is designed to bring hadron physics to a new level in terms of scope, precision and accuracy. In this work, its unique capability for studies of hyperons is outlined. We discuss ground-state hyperons as diagnostic tools to study non-perturbative aspects of the strong interaction, and fundamental symmetries. New simulation studies have been carried out for two benchmark hyperon-antihyperon production channels: $${\bar{p}}p \rightarrow {\bar{\varLambda }}\varLambda $$ p ¯ p → Λ ¯ Λ and $${\bar{p}}p \rightarrow {\bar{\varXi }}^+\varXi ^-$$ p ¯ p → Ξ ¯ + Ξ - . The results, presented in detail in this paper, show that hyperon-antihyperon pairs from these reactions can be exclusively reconstructed with high efficiency and very low background contamination. In addition, the polarisation and spin correlations have been studied, exploiting the weak, self-analysing decay of hyperons and antihyperons. Two independent approaches to the finite efficiency have been applied and evaluated: one standard multidimensional efficiency correction approach, and one efficiency independent approach. The applicability of the latter was thoroughly evaluated for all channels, beam momenta and observables. The standard method yields good results in all cases, and shows that spin observables can be studied with high precision and accuracy already in the first phase of data taking with PANDA.

The interaction of glueball and heavy-light flavoured meson in holographic QCD

We construct the D4/D8 brane configuration in the Witten–Sakai–Sugimoto model by introducing a pair of heavy flavour brane with a heavy-light open string. The multiplets created by the heavy-light string acquire mass due to the finite separation of the heavy and light flavour branes thus they could be identified as the heavy-light meson fields in this model. On the other hand the glueball field is identified as the gravitational fluctuations carried by the close string in the bulk, so this model is able to describe the interaction of glueball and heavy-light meson through the open-close string interaction in gauge-gravity duality. We explicitly derive the effective action for the various glueballs and heavy-light mesons then numerically evaluate the associated lowest coupling constants. Afterwards the decay/production widths of various glueballs involving the lowest heavy-light meson, which is identified as $$D^{0}$$ D 0 meson, are calculated by using our effective action which might be remarkable to theoretically study the charm oscillation e.g. $$D^{0}-{\bar{D}}^{0}$$ D 0 - D ¯ 0 , $$B_{s}-{\bar{B}}_{s}$$ B s - B ¯ s decay/production in hadron physics. This work extends the previous investigations of glueball in holographic QCD and it is also a further prediction of glueball-meson interaction.