arXiv subjects

R. Fariello

Publications and source records attributed to R. Fariello.

8 recordsLinked to original sources

arXiv2026

Effects of the magnetic field on $π^0$ production in ultraperipheral Pb-Pb collisions

In this work, we study the effect of the magnetic field on the production of neutral pions in photon-photon interactions in ultraperipheral Pb-Pb collisions at the LHC. The calculation is performed within the equivalent photon approximation, including a magnetic-field dependence in the decay width $Γ(π^0\toγγ)$, from which the corresponding production cross section is computed. We find that the reduction of the two-photon decay width in the presence of a strong magnetic field leads to a substantial reduction (by a factor of about 2-3) of the $π^0$ production cross section at LHC energies.

hep-ph↗

arXiv2026

Soliton dynamics in the Ostrovsky equation with anomalous dispersion

We investigate the formation and interaction of solitons in the non-integrable Ostrovsky equation characterized by anomalous (positive) dispersion. This equation is relevant for describing wave phenomena in various media, including plasma, solids, and optical fibers. Our findings indicate that certain Ostrovsky solitons, which possess zero total ''mass'' and exhibit non-monotonic asymptotic behavior, can arise from initial perturbations of a pulse-like nature. These solitons may organize into regular trains, where they are arranged according to their amplitude, or they may form irregular, nonstationary configurations of bound interacting solitons, or even multi-soliton structures. Furthermore, we demonstrate that the interactions between solitons in the Ostrovsky equation are inelastic, resulting in the emergence of a dominant soliton, or ''soliton-champion,'' within closed systems, such as those with periodic boundary conditions. In such systems, the soliton with the highest amplitude acts as a ''terminator,'' annihilating smaller amplitude solitons and absorbing a portion of their energy. We also analyze the recurrence phenomenon and determine that, although it resembles that of the Korteweg-de Vries equation, it exhibits distinct features.

nlin.PS↗

arXiv2025

The sharpness of the quark-hadron transition and the properties of hybrid stars

We investigate the effects of the sharpness of the phase transition between hadronic matter and quark matter on various properties of neutron stars. We construct hybrid equations of state by combining a hadronic model with a quark model using a Gaussian function. This approach introduces a smooth transition characterized by two parameters: one representing the overpressure relative to the first-order phase transition point, and the other related to the range over which the hybrid region extends in baryon chemical potential. We find that the sharpness of the phase transition significantly influences the equation of state, which can deviate by several tens of $\text{MeV fm}^{-3}$ from the one with a sharp first-order transition. The speed of sound exhibits diverse behaviors, including drastic drops, pronounced peaks, and oscillatory patterns, depending on the sharpness parameters. In terms of stellar structure, while the maximum neutron star mass remains largely unaffected by the sharpness of the phase transition, the stellar radii can vary significantly. Smoother transitions lead to a leftward shift (up to 1 km) of the mass-radius curve segment corresponding to hybrid stars. The tidal deformability decreases with smoother transitions, especially for higher-mass stars. Our results are quite general and do not qualitatively depend on the specific hadronic and quark matter models employed. In fact, the hybrid equation of state and stellar properties derived from microscopic models of quark-hadron pasta phases display the same behavior as described above.

nucl-th↗

arXiv2023

Two and three photon fusion into charmonium in ultra-peripheral nuclear collisions

In this paper we investigate the production of charmonium states in two and three photon fusion processes in nucleus -- nucleus collisions at the CERN Large Hadron Collider (LHC) energies. Our results indicate that the experimental study of these processes is feasible and can be used to constrain the theoretical decay widths and give information on the non $c - \bar{c}$ components of these states.

hep-ph↗

arXiv2021

Tidal Deformability of Quark Stars with Repulsive Interactions

In an early work, we applied a QCD-based equation of state to the study of the stellar structure of self-bound strange stars, obtaining sequences with maximum masses larger than two solar masses and radii ranging from 8 to 12 Km. In this work, we update the previous calculations and compare them with the most recent data, including the very recent determination of the mass and radius of the massive pulsar PSR J0740+6620 performed by the NICER and XMM-Newton Collaborations. Our equation of state is similar to the MIT bag model one, but it includes repulsive interactions, which turn out to be essential to reproduce the accumulated experimental information. We find that our EOS is still compatible with all astrophysical observations but the parameter window is now narrower.

nucl-th↗

arXiv2020

The QCD Kondo phase in quark stars

We study light (u, d) quark matter with charm impurities. These impurities are added to the Lagrangian density. We derive the equation of state (EOS) of this kind of quark matter, which contains a Kondo phase. We explore this EOS and study the structure of stars, identifying the effects of the Kondo phase. Solving the TOV equations and computing the mass-radius diagram, we find that the presence of a Kondo phase leads to smaller and lighter stars.

nucl-th↗

arXiv2019

Evolution of non-stationary pulses in a cold magnetized quark-gluon plasma

We study weakly nonlinear wave perturbations propagating in a cold nonrelativistic and magnetized ideal quark-gluon plasma. We show that such perturbations can be described by the Ostrovsky equation. The derivation of this equation is presented for the baryon density perturbations. Then we show that the generalized nonlinear Schr{ö}dinger (NLS) equation can be derived from the Ostrovsky equation for the description of quasi-harmonic wave trains. This equation is modulationally stable for the wave number $k < k_m$ and unstable for $k > k_m$, where $k_m$ is the wave number where the group velocity has a maximum. We study numerically the dynamics of initial wave packets with the different carrier wave numbers and demonstrate that depending on the initial parameters they can evolve either into the NLS envelope solitons or into dispersive wave trains.

hep-ph↗

arXiv2016

Bubble dynamics and the quark-hadron phase transition in nuclear collisions

We study the nucleation of a quark gluon plasma (QGP) phase in a hadron gas at low temperatures and high baryon densities. This kind of process will presumably happen very often in nuclear collisions at FAIR and NICA. When the appropriate energy densities (or baryon densities) and temperatures are reached the conversion of one phase into another is not instantaneous. It is a complex process, which involves the nucleation of bubbles of the new phase. One important element of this transition process is the rate of growth of a QGP bubble. In order to estimate it we solve the Relativistic Rayleigh$-$Plesset equation which governs the dynamics of a relativistic spherical bubble in a strongly interacting medium. The baryon rich hadron gas is represented by the nonlinear Walecka model and the QGP is described by the MIT bag model and also by a mean field model of QCD.

hep-ph↗