Particles, Volume 2, Issue 3 (September 2019) – 4 articles

We give a pedagogical review of the properties of the various meson condensation phases triggered by a large isospin or strangeness imbalance. We argue that these phases are extremely interesting and powerful playground for exploring the properties of hadronic matter. The reason is that they are realized in a regime in which various theoretical methods overlap with increasingly precise numerical lattice QCD simulations, providing insight on the properties of color confinement and of chiral symmetry breaking. Full article

Nonlocal quantum field theory (QFT) of one-component scalar field $\phi$ in D-dimensional Euclidean spacetime is considered. The generating functional (GF) of complete Green functions $\mathcal{Z}$ as a functional of external source j, coupling constant g and spatial measure $d\mu$ is studied. An expression for GF $\mathcal{Z}$ in terms of the abstract integral over the primary field $\phi$ is given. An expression for GF $\mathcal{Z}$ in terms of integrals over the primary field and separable Hilbert space (HS) is obtained by means of a separable expansion of the free theory inverse propagator $\widehat{L}$ over the separable HS basis. The classification of functional integration measures $\mathcal{D}\left[\phi \right]$ is formulated, according to which trivial and two nontrivial versions of GF $\mathcal{Z}$ are obtained. Nontrivial versions of GF $\mathcal{Z}$ are expressed in terms of 1-norm and 0-norm, respectively. In the 1-norm case in terms of the original symbol for the product integral, the definition for the functional integration measure $\mathcal{D}\left[\phi \right]$ over the primary field is suggested. In the 0-norm case, the definition and the meaning of 0-norm are given in terms of the replica-functional Taylor series. The definition of the 0-norm generator $\Psi$ is suggested. Simple cases of sharp and smooth generators are considered. An alternative derivation of GF $\mathcal{Z}$ in terms of 0-norm is also given. All these definitions allow to calculate corresponding functional integrals over $\phi$ in quadratures. Expressions for GF $\mathcal{Z}$ in terms of integrals over the separable HS, aka the basis functions representation, with new integrands are obtained. For polynomial theories ${\phi }^{2n},n=2,3,4,\dots ,$ and for the nonpolynomial theory ${sinh}^4\phi$ , integrals over the separable HS in terms of a power series over the inverse coupling constant $1/\sqrt{g}$ for both norms (1-norm and 0-norm) are calculated. Thus, the strong coupling expansion in all theories considered is given. “Phase transitions” and critical values of model parameters are found numerically. A generalization of the theory to the case of the uncountable integral over HS is formulated—GF $\mathcal{Z}$ for an arbitrary QFT and the strong coupling expansion for the theory ${\phi }^4$ are derived. Finally a comparison of two GFs $\mathcal{Z}$ , one on the continuous lattice of functions and one obtained using the Parseval–Plancherel identity, is given. Full article

The gravitational wave and electromagnetic signatures connected to the merger of two neutron stars allow us to test the nature of matter at supranuclear densities. Since the Equation of State governing the interior of neutron stars is only loosely constrained, there is even the possibility that strange quark matter exists inside the core of neutron stars. We investigate how strange quark matter cores affect the binary neutron star coalescence by performing numerical relativity simulations. Interestingly, the strong phase transition can cause a reduction of the convergence order of the numerical schemes to first order if the numerical resolution is not high enough. Therefore, an additional challenge is added in producing high-quality gravitational wave templates for Equation of States with a strong phase transition. Focusing on one particular configuration of an equal mass configuration consistent with GW170817, we compute and discuss the associated gravitational wave signal and some of the electromagnetic counterparts connected to the merger of the two stars. We find that existing waveform approximants employed for the analysis of GW170817 allow describing this kind of systems within the numerical uncertainties, which, however, are several times larger than for pure hadronic Equation of States, which means that even higher resolutions have been employed for an accurate gravitational wave model comparison. We also show that for the chosen Equation of State, quasi-universal relations describing the gravitational wave emission after the moment of merger seem to hold and that the electromagnetic signatures connected to our chosen setup would not be bright enough to explain the kilonova associated to GW170817. Full article

Using the light-cone sum rules at leading order, we present an approach to perform the preliminary upper estimation for the nucleon gravitational form factor $\mathbb{D}\left(t\right)$ (D-term contribution). Comparison with the experimental data and with the results of different models is discussed. Full article