Aims. We present a new microscopic hadron-quark hybrid equation of state model for astrophysical applications, from which compact hybrid star configurations are constructed. These are composed of a quark core and a hadronic shell with a first-order phase transition at their interface. The resulting mass-radius relations are in accordance with the latest astrophysical constraints.Methods. The quark matter description is based on a quantum chromodynamics (QCD) motivated chiral approach with higher-order quark interactions in the Dirac scalar and vector coupling channels. For hadronic matter we select a relativistic mean-field equation of state with density-dependent couplings. Since the nucleons are treated in the quasi-particle framework, an excluded volume correction has been included for the nuclear equation of state at suprasaturation density which takes into account the finite size of the nucleons.Results. These novel aspects, excluded volume in the hadronic phase and the higher-order repulsive interactions in the quark phase, lead to a strong first-order phase transition with large latent heat, i.e. the energy-density jump at the phase transition, which fulfils a criterion for a disconnected third-family branch of compact stars in the mass-radius relationship. These twin stars appear at high masses (~2 M ⊙) that are relevant for current observations of high-mass pulsars.Conclusions. This analysis offers a unique possibility by radius observations of compact stars to probe the QCD phase diagram at zero temperature and large chemical potential and even to support the existence of a critical point in the QCD phase diagram.

We study the role of finite-size effects at the hadron-quark phase transition in a new hybrid equation of state constructed from an ab initio Brückner-Hartree-Fock equation of state with the realistic Bonn-B potential for the hadronic phase and a covariant nonlocal Nambu–Jona-Lasinio model for the quark phase. We construct static hybrid star sequences and find that our model can support stable hybrid stars with an onset of quark matter below $2M_{\odot }$ and a maximum mass above $2.17M_{\odot }$ in agreement with recent observations. If the finite-size effects are taken into account the core is composed of pure quark matter. Provided that the quark vector channel interaction is small, and the finite size effects are taken into account, quark matter appears at densities 2–3 times the nuclear saturation density. In that case the proton fraction in the hadronic phase remains below the value required by the onset of the direct URCA process, so that the early onset of quark matter shall affect on the rapid cooling of the star.

We compute the cross section for photons emitted from sea quarks in proton-nucleus collisions at collider energies. The computation is performed within the dilute-dense kinematics of the Color Glass Condensate (CGC) effective field theory. Albeit the result obtained is formally at next-to-leading order in the CGC power counting, it provides the dominant contribution for central rapidities. We observe that the inclusive photon cross section is proportional to all-twist Wilson line correlators in the nucleus. These correlators also appear in quark-pair production; unlike the latter, photon production is insensitive to hadronization uncertainties and therefore more sensitive to multi-parton correlations in the gluon saturation regime of QCD. We demonstrate that k_⊥ and collinear factorized expressions for inclusive photon production are obtained as leading twist approximations to our result. In particular, the collinearly factorized expression is directly sensitive to the nuclear gluon distribution at small x. Other results of interest include the realization of the Low-Burnett-Kroll soft photon theorem in the CGC framework and a comparative study of how the photon amplitude is obtained in Lorenz and light-cone gauges.

We analyze a classically scale invariant extension of the Standard Model with a dark gauge U(1)X broken by a doubly charge scalar Φ leaving a remnant Z 2 symmetry. Dark fermions are introduced as dark matter candidates and for anomaly reasons we introduce two chiral fermions. Due to classical scale invariance, bare mass term that would mix these two states is absent and they end up as stable Majorana fermions N 1 and N 2. We calculate cross sections for N a N a → ϕϕ, N a N a → X μ ϕ and N 2N 2 → N 1N 1 annihilation channels. We put constraints to the model from the Higgs searches at the LHC, dark matter relic abundance and dark matter direct detection limits by LUX. The dark gauge boson plays a crucial role in the Coleman-Weinberg mechanism and has to be heavier than 680 GeV. The viable mass region for dark matter is from 470 GeV up to a few TeV. In the case when the two Majorana fermions have different masses, two dark matter signals at direct detection experiments could provide a distinctive signature of this model.

We explore the possibility of obtaining heavy hybrid stars within the framework of the two flavor Nambu-Jona-Lasinio model that includes 8-quark interactions in the scalar and in the vector channel. The main impact of the 8-quark scalar channel is to reduce the onset of quark matter, while the 8-quark vector channel acts to stiffen the equation of state at high densities. Within the parameter space where the 4-quark vector channel is small, and the 8-quark vector channel sizeable, stable stars with masses of 2 M _⊙ and above are found to hold quark matter in their cores.

We show that for the lower branch of the quark condensate and values higher than approximately $$-${}(250\text{ }\text{ }\text{MeV}{)}^{3}$ the chiral critical endpoint in the Nambu\char21{}Jona-Lasinio model does not occur in the phase diagram. By using lattice motivated nonlocal quark interactions, we demonstrate that the critical endpoint can be recovered. We study this behavior for a range of condensate values and find that the variation in the position of the critical endpoint is more pronounced as the condensate is increased.