arXiv subjects

Lucas Lazzari

Publications and source records attributed to Lucas Lazzari.

4 recordsLinked to original sources

arXiv2024

How the QCD trace anomaly behaves at the core of twin stars?

We investigate the behavior of the dense and cold (normalized) QCD trace anomaly, $\Delta$, in the interior of twin neutron stars (obtained from several sets of equations of state in agreement with modern compact-star and multimessenger data) satisfying static and dynamic stability conditions. We scan the formed twin-star parameter space in order to look for effects caused by the presence of a strong first-order phase transition connecting hadron and quark phases by means of a Maxwell construction. We found robustly that $\Delta$ suffers an abrupt decrease around the transition point, even reaching large negative values ($\Delta\simeq-0.35$), in marked contrast to current studies pointing out a smooth behavior with $\Delta\gtrsim 0$ at all densities. Besides, we characterize the behavior of {the recently defined} conformal factor, $d_{c}$, in our four categories of twin stars for which we perform comparisons with theoretical constraints put, e.g. by Bayesian studies sometimes adjusted to agree with perturbative QCD at high densities. These analyses allow us to hypothesize modifications in the strong QCD coupling in dense nuclear matter with a strong thermodynamic discontinuity.

hep-ph↗

arXiv2023

Revisiting the stability of strange-dwarf stars and strange planets

The dynamical stability of strange-dwarf hybrid stars and strange planets, constituted by strange-quark-matter cores and dilute-nuclear-matter crusts, is revisited by analyzing the fundamental mode eigenfrequencies of the radial oscillation equations with boundary conditions for slow (rapid) conversions originating at the density-discontinuous interface characterizing extremely large (small) microscopic timescales compared to the oscillation periods. For the hadronic crust we used an analytic fit of the BPS results matched to the massless MIT bag model. For the rapid case, our calculations indicate that the zero mode is the so-called {\it reaction mode} whose frequency is a complex number, thus ruling out the existence of strange dwarfs (planets) in nature. On the other hand, slow conversions still provide a sizeable stability window which, interestingly, also reproduces the Glendenning-Kettner-Weber results. The robustness of our findings is demonstrated for different transition densities and using an equation of state from perturbative QCD for the ultra-dense core.

nucl-th↗

arXiv2022

Fundamental-mode eigenfrequencies of neutral and charged twin neutron stars

We investigate the effects of rapid and slow conversions on the fundamental-mode eigenfrequencies of hybrid neutron stars having highly discontinuous transitions between hadronic and quark matter, the so-called twin stars. We analyze some characteristic cases in the available parameter space of the equations of state for the hadronic and quark phases. Furthermore, we also consider the possibility that these stellar configurations are electrically charged. Our results indicate that for neutral configurations under rapid conversions the stability window coincides with the usual stability criterion, i.e. $\partial M/\partial p_c > 0$ and that the two branches are disconnected. This discontinuity remains when electric charge is considered, but the usual criterion is not sufficient to determine the star's stability. On the other hand, slow conversions connect initially disconnected branches and increase the stability window of the hybrid configurations. For both conversion speeds, the presence of electric charge diminishes the magnitude of the eigenfrequencies and its stability window.

nucl-th↗

arXiv2022

Impact of slow conversions on hybrid stars with sequential QCD phase transitions

In this paper, we investigate the impact of the phase conversion speed on the properties of hybrid stars with sequential sharp QCD phase transitions. We consider that these hybrid stars possess an inner (outer) core of CFL (2SC) quark matter surrounded by hadronic matter. Assuming that the phase conversions can be slow or rapid, we analyze the dynamical stability of these objects. In particular, we present our predictions for the mass-radius profile and the fundamental eigenfrequencies of hybrid stars with sequential QCD first order phase transitions. Our results demonstrate that the usual stability criteria i.e. $\partial M/ \partial P_0 \geq 0$, is sufficient only if both conversions are rapid. Moreover, we show that if any of the interfaces has a slow conversion speed, the fundamental eigenfrequencies are significantly modified.

nucl-th↗