arXiv subjects

Alessandro Drago

Publications and source records attributed to Alessandro Drago.

At least 19 recordsLinked to original sources

arXiv2026

Is the coexistence of strange quark stars and hadronic stars favored by astrophysical data? A Bayesian analysis

Hadronic stars and strange quark stars could coexist within the so-called two-families scenario. In this respect, hadronic matter and strange quark matter correspond to two distinct equilibrium phases described by two different equations of state. We perform here the first detailed Bayesian analysis that makes use of astrophysical and laboratory data in order to constrain the equations of state adopted within the two-families scenario for hadronic and strange quark matter. In particular, in hadronic matter we consider the possible formation of hyperons and delta resonances (beside nucleons) within a class of non linear relativistic mean field models and in quark matter we consider the possible formation of a color-superconducting phase within a bag-like model. Results of the analysis indicate that while at the moment both the one-family and the two-families scenarios are compatible with the data, by comparing the Bayes factors of both models, the two-families scenario is favored with respect to the one-family scenario. Specifically, the two-families framework naturally relieves the tension between the intermediate-density softness of the equation of state required by small-radius objects and the high-density stiffness needed to support massive pulsars. Ultimately, future detections of even more massive compact objects, very compact ordinary-mass objects, or precise measurements of two distinct masses with the same radius, will provide strong indications in favor of the two-families scenario.

nucl-th↗

arXiv2025

Upper Bound on the Cosmic Baryon Chemical Potential from Lepton-Flavor Asymmetry

We study the early Universe trajectory around the QCD transition in lepton-flavor-asymmetric cases with small total lepton asymmetry ($|\ell|\lesssim 10^{-2}$), while allowing large individual lepton asymmetries. For each temperature, we find an upper bound on the baryon chemical potential $μ_{\mathrm B}(T)$: $τ$--$μ$ asymmetric cases exhibit a local maximum, whereas $μ$--$e$ cases approach a limiting curve. Thus, even extreme lepton-flavor asymmetry alone cannot reach a first-order region, unless the critical point is moved to a substantially lower $μ_\mathrm{B}/T$ because of the nonzero $μ_\mathrm{Q}$. Therefore, we constrain the QCD-era relic to the standard scenario of a chiral crossover transition.

hep-ph↗

arXiv2025

Role of thermal fluctuations in nucleation of three-flavor quark matter

We present a framework that aims to investigate the role of thermal fluctuations of the matter composition and color-superconductivity in the nucleation of three-flavor deconfined quark matter in the typical conditions of high-energy astrophysical systems related to compact stars. It is usually assumed that the flavor composition is locally fixed during the formation of the first seed of deconfined quark matter since weak interaction acts too slowly to re-equilibrate flavors. However, the matter composition fluctuates around its average equilibrium values at the typical temperatures of high-energy astrophysical processes. Here, we extend our previous two-flavor nucleation formalism to a three-flavor case. We develop a thermodynamic framework incorporating finite-size effects and thermal fluctuations of local composition to compute the nucleation probability as the product of droplet formation and composition fluctuation rates. Moreover, we discuss the role of color-superconductivity in nucleation, arguing that it can play a role only in systems larger than the typical coherence length of diquark pairs. We found that thermal fluctuations of the matter composition lead to lowering the potential barrier between the metastable hadronic phase and the stable quark phase. Moreover, the formation of diquark pairs reduces the critical radius and thus the potential barrier in the low baryon density and temperature regime.

nucl-th↗

arXiv2025

Cosmic Trajectories calculation with state of the art lattice QCD equation of state

We compute the full cosmic trajectories of the early Universe across the QCD phase diagram as the plasma cools from $T\simeq500\,$MeV to $30\,$MeV, assuming $β$-equilibrated matter. The trajectories are obtained by simultaneously solving baryon-number, electric-charge, and lepton-asymmetry conservation, closed by a state-of-the-art lattice-QCD equation of state: a fourth-order Taylor expansion in the chemical potentials that merges the latest $(2\!+\!1)$-flavor susceptibilities with charm-quark contributions, thus delivering a consistent $(2\!+\!1\!+\!1)$-flavor equation of state. Results are compared with an ideal quark-gluon plasma and with a hadron-resonance gas to highlight interaction effects. Two cases of primordial lepton asymmetries are analyzed: a symmetric configuration $(\ell_e=\ell_μ=\ell_τ=\ell/3)$ and an asymmetric one $(\ell_e=0,\;\ell_μ=-\ell_τ)$. Increasing $|\ell|$ systematically drives the trajectories toward larger values of $μ_B$ and more negative $μ_Q$. In the asymmetric case, a non-monotonic bounce develops when the $τ$ chemical potential reaches $m_τ$, generating a maximum in $μ_B(T)$, the position of which depends on $\ell_τ$. Assuming a modest $μ_{Q}$-dependence of the lattice-QCD critical end point estimates (obtained at $μ_{Q} = 0$), the trajectories for all lepton asymmetries explored ($|\ell|\lesssim 0.1$) lie to their left, implying that in a standard cosmological scenario the QCD transition is almost certainly a smooth crossover. Nevertheless, we estimate the magnitude of baryon and lepton asymmetries needed to obtain a cosmic trajectory closer to the QCD critical point, providing inputs for future studies of the strong-interaction epoch.

astro-ph.CO↗

arXiv2025

Strange quark matter as dark matter: 40 years later, a reappraisal

Forty years ago Witten suggested that dark matter could be composed of macroscopic clusters of strange quark matter. This idea was very popular for several years, but it dropped out of fashion once lattice QCD calculations indicated that the confinement/deconfinement transition, at small baryonic chemical potential, is not first order, which seemed to be a crucial requirement in order to produce large clusters of quarks. Here we revisit the conditions under which strangelets can be produced in the Early Universe. We discuss the impact of an instability in the hadronic phase separating a low density, positive-strange-charge phase from a high-density phase with a negative strange charge. This second phase can rapidly stabilize by forming color-superconducting gaps. The strangelets then undergo partial evaporation. In this way, we obtain distributions of their sizes in agreement with the observational constraints and we discuss the many astrophysical and cosmological implications of these objects. Finally, we examine the most promising techniques to detect this type of strangelets. We also show that strangelets can exist with masses $\lesssim10^{17} \mathrm g$, while primordial black holes are ruled out in that mass range, allowing us to distinguish between these two dark matter candidates.

hep-ph↗

arXiv2024

Thermal fluctuations of matter composition and quark nucleation in compact stars

At the extreme densities reached in the core of neutron stars, it is possible that quark deconfined matter is produced. The formation of this new phase of strongly interacting matter is likely to occur via a first-order phase transition for the typical temperatures reached in astrophysical processes. The first seeds of quark matter would then form through a process of nucleation within the metastable hadronic phase. Here we address the role of the thermal fluctuations in the hadronic composition on the nucleation of two-flavour quark matter. At finite temperature, thermodynamic quantities in a system fluctuate around average values. Being nucleation a local process, it is possible that it occurs in a subsystem whose composition makes the nucleation easier. We will consider the total probability of the nucleation as the product between the probability that a subsystem has a certain hadronic composition different from the average in the bulk, and the nucleation probability in that subsystem. We will show how those fluctuations of the hadronic composition can increase the efficiency of nucleation already for temperatures $\sim (0.1-1)$ keV. However, for temperatures $\lesssim (1-10)$ MeV, the needed overpressure exceeds the maximum pressure reached in compact stars. Finally, for even larger temperatures the process of nucleation can take place, even taking into account finite size effects.

nucl-th↗

arXiv2024

A Proposal for a Fast Infrared Bursts Detector

The gravitational wave GW170817 from a binary neutron star merger and the simultaneous electromagnetic detection of the GRB170817A by Fermi Gamma-Ray Space Telescope, opened a new era in the multi-messenger astronomy. Furthermore, the GRBs (Gamma-Ray Bursts) and the mysterious FRBs (Fast Radio Bursts) have sparked interest in the development of new detectors and telescopes dedicated to the time-domain astronomy across the electromagnetic spectrum. Time-domain astronomy aims to acquire fast astronomical bursts in temporal range between a few seconds down to 1 ns. Fast InfraRed Bursts (FIRBs) have been relatively understudied, often due to the lack of appropriate tools for observation and analysis. In this scientific scenario, the present contribution proposes a new detection system for ground-based reflecting telescopes working in the mid-infrared (mid-IR) range to search for astronomical FIRBs. Experience developed in the diagnostics for lepton circular accelerators can be used to design temporal devices for astronomy. Longitudinal diagnostic instruments acquire bunch-by-bunch particle shifts in the direction of flight, that is equivalent to temporal. Transverse device integrates the beam signal in the horizontal and vertical coordinates, as standard telescopes. The proposed instrument aims to work in temporal mode. Feasibility study tests have been carried out at SINBAD, infrared beam line of DAFNE, the $e^+e^-$ collider of INFN. SINBAD releases pulsed infrared synchrotron light with 2.7 ns separation. The frontend detector system has been evaluated to detect temporal fast infrared signals with 2-12 micron wavelengths and 1 ns rise times. The present contribute aims to be a step toward a feasibility study report.

astro-ph.HE↗

arXiv2024

Strange Dwarfs: a review on the (in)stability

White dwarfs are the remnants of stars not massive enough to become supernovae. This review explores the concept of strange dwarfs, a unique class of white dwarfs which contain cores of strange quark matter. Strange dwarfs have different sizes, masses, and evolutionary paths with respect to white dwarfs. They might form through the accumulation of normal matter on strange quark stars or by capture of strangelets. The stability of strange dwarfs has been debated, with initial studies suggesting stability, while later analyses indicated potential instability. This review revisits these discussions, focusing on the critical role of boundary conditions between nuclear and quark matter in determining stability. It also offers insights into their formation, structure, and possible detection in the universe.

astro-ph.SR↗

arXiv2024

Is the compact object associated with HESS J1731-347 a strange quark star?

The analysis of the central compact object within the supernova remnant HESS J1731-347 suggests that it has a small radius and, even more interestingly, a mass of the order or smaller than one solar mass. This raises the question of which astrophysical process could lead to such a small mass, since the analysis of various types of SN explosions indicate that is it not possible to produce a neutron star with a mass smaller than about $1.17 M_\odot$. Here we show that masses of the order or smaller than one solar mass can be obtained in the case of strange quark stars and that it is possible to build a coherent model explaining not only the mass and the radius of that object, but also its slow cooling suggested in various analyses. We also show that an astrophysical path exists which leads to the formation of such an object, and we discuss the role played in that scenario by strangelets assumed to constitute the dark matter.

astro-ph.HE↗

arXiv2023

Black Hole - Neutron Star mergers: using kilonovae to constrain the equation of state

The merging of a binary system involving two neutron stars (NSs), or a black hole (BH) and a NS, often results in the emission of an electromagnetic (EM) transient. One component of this EM transient is the epic explosion known as a kilonova (KN). The characteristics of the KN emission can be used to probe the equation of state (EoS) of NS matter responsible for its formation. We predict KN light curves from computationally simulated BH-NS mergers, by using the 3D radiative transfer code \texttt{POSSIS}. We investigate two EoSs spanning most of the allowed range of the mass-radius diagram. We also consider a soft EoS compatible with the observational data within the so-called 2-families scenario in which hadronic stars coexist with strange stars. Computed results show that the 2-families scenario, characterized by a soft EoS, should not produce a KN unless the mass of the binary components are small ($M_{\rm BH} \leq 6M_{\odot}$, $M_{\rm NS} \leq 1.4M_{\odot}$) and the BH is rapidly spinning ($χ_{\rm BH} \geq 0.3$). In contrast, a strong KN signal potentially observable from future surveys (e.g. VRO/LSST) is produced in the 1-family scenario for a wider region of the parameter space, and even for non-rotating BHs ($χ_{\rm BH} = 0$) when $M_{\rm BH} = 4M_{\odot}$ and $M_{\rm NS} = 1.2M_{\odot}$. We also provide a fit that allows for the calculation of the unbound mass from the observed KN magnitude, without running timely and costly radiative transfer simulations. Findings presented in this paper will be used to interpret light curves anticipated during the fourth observing run (O4), of the advanced LIGO, advanced Virgo and KAGRA interferometers and thus to constrain the EoS of NS matter.

astro-ph.HE↗

arXiv2023

Stability and instability of strange dwarfs

More than 20 years ago, Glendenning, Kettner and Weber proposed the existence of stable white dwarfs with a core of strange quark matter. More recently, by studying radial modes, Alford, Harris and Sachdeva concluded instead that those objects are unstable. We aim to clarify this issue. We investigate the stability of these objects by looking at their radial oscillations while incorporating boundary conditions at the quark-hadron interface, corresponding to either a rapid or a slow conversion of hadrons into quarks. Our analysis shows that objects of this type are stable if the star is not strongly perturbed, and ordinary matter cannot transform into strange quark matter because of the Coulomb barrier separating the two components. On the other hand, ordinary matter can be transformed into strange quark matter if the star undergoes a violent process, as in the preliminary stages of a type Ia supernova, and this causes the system to become unstable and to collapse into a strange quark star. In this way, accretion-induced collapse of strange dwarfs can be facilitated, and km-sized objects with subsolar masses can be produced.

astro-ph.SR↗

arXiv2022

Formation and evaporation of strangelets during the merger of two compact stars

We study the partial fragmentation of a strange quark star into strangelets during the process of merger of two strange quark stars. We discuss the fate of the fragments considering their possible evaporation into nucleons. We show that only a rather small amount of large size strangelets, ejected from the spiral arms in the post-merger, survives a total evaporation into nucleons. In this way we demonstrate that: 1) the density of strangelets in the galaxy is too low to trigger the conversion of all neutron stars into strange quark stars and it allows the co-existence of both types of compact objects; 2) the probability of direct detection of a strangelet is negligible and therefore its nondetection is compatible with the strange quark matter hypothesis; 3) most of the matter ejected during and after the merger of two strange quark stars evaporates into nucleons and therefore it can generate a kilonova-like signal.

astro-ph.HE↗

arXiv2022

Merger of a Neutron Star with a Black Hole: one-family vs. two-families scenario

A kilonova signal is generally expected after a Black Hole - Neutron Star merger. The strength of the signal is related to the equation of state of neutron star matter and it increases with the stiffness of the latter. The recent results obtained by NICER from the analyses of PSR J0740+6620 suggest a rather stiff equation of state and the expected kilonova signal is therefore strong, at least if the mass of the Black Hole does not exceed $\sim 10 \mathrm{\,M}_\odot$ and if the adimensional spin parameter is not too small and the orbit is prograde. We compare the predictions obtained by considering equations of state of neutron star matter satisfying the most recent observations and assuming that only one family of compact stars exists with the results predicted in the two-families scenario. In the latter a soft hadronic equation of state produces very compact stellar objects while a rather stiff quark matter equation of state produces massive strange quark stars, satisfying NICER results. The expected kilonova signal in the two-families scenario is very weak: in particular the Hadronic Star - Black Hole merger produces a much weaker signal than in the one-family scenario because the hadronic equation of state is very soft. Moreover, according to the only existing simulation, the Strange Quark Star - Black Hole merger does not produce a kilonova signal because the amount of mass ejected is negligible. These predictions will be easily tested with the new generation of detectors if Black Holes with an adimensional spin parameter $χ_\mathrm{BH}\gtrsim 0.2$ or a mass $\mathrm M_\mathrm{BH} \lesssim 4 \mathrm M_\odot$ can be present in the merger.

astro-ph.HE↗

arXiv2021

Analytic continuation of nucleon electromagnetic form factors in the time-like region

The possibility to compute nucleon electromagnetic form factors in the time-like region by analytic continuation of their space-like expressions has been explored in the framework of the Skyrme model. We have developed a procedure to solve analytically Fourier transforms of the nucleon electromagnetic current and hence to obtain form factors defined in all kinematical regions and fulfilling the first-principles requirements. The results are discussed and compared to data, both in space-like and time-like region.

hep-ph↗

arXiv2021

Speed of sound in dense matter and two families of compact stars

The existence of massive compact stars $(M\gtrsim 2.1 M_{\odot})$ implies that the conformal limit of the speed of sound $c_s^2=1/3$ is violated if those stars have a crust of ordinary nuclear matter. Here we show that, if the most massive objects are strange quark stars, i.e. stars entirely composed of quarks, the conformal limit can be respected while observational limits on those objects are also satisfied. By using astrophysical data associated with those massive stars, derived from electromagnetic and gravitational wave signals, we show, within a Bayesian analysis framework and by adopting a constant speed of sound equation of state, that the posterior distribution of $c_s^2$ is peaked around 0.3, and the maximum mass of the most probable equation of state is $\sim 2.13 M_{\odot}$. We discuss which new data would require a violation of the conformal limit even when considering strange quark stars, in particular we analyze the possibility that the maximum mass of compact stars is larger than $2.5M_{\odot}$, as it would be if the secondary component of GW190814 is a compact star and not a black hole. Finally, we discuss how the new data for PSR J0740+6620 obtained by the NICER collaboration compare with our analysis (not based on them) and with other possible interpretations.

astro-ph.HE↗

arXiv2020

Why can hadronic stars convert into strange quark stars with larger radii

The total binding energy of compact stars is the sum of the gravitational binding energy $(BE)_g$ and the nuclear binding energy $(BE)_n$, the last being related to the microphysics of the interactions. While the first is positive (binding) both for hadronic stars and for strange quark stars, the second is large and negative for hadronic stars (anti-binding) and either small and negative (anti-binding) or positive (binding) for strange quark stars. A hadronic star can convert into a strange quark star with a larger radius because the consequent reduction of $(BE)_g$ is over-compensated by the large increase in $(BE)_n$. Thus, the total binding energy increases due to the conversion and the process is exothermic. Depending on the equations of state of hadronic matter and quark matter and on the baryonic mass of the star, the contrary is obviously also possible, namely the conversion of hadronic stars into strange quark stars having smaller radii, a situation more often discussed in the literature. We provide a condition that is sufficient and in most of the phenomenologically relevant cases also necessary in order to form strange quark stars with larger radii while satisfying the exothermicity request. Finally, we compare the two schemes in which quark stars are produced (one having large quark stars and the other having small quark stars) among themselves and with the third-family scenario and we discuss how present and future data can discriminate among them.

nucl-th↗

arXiv2020

Intra-bunch feedback system developments at DAFNE

This paper presents history and evolution of the intra-bunch feedback system for circular accelerators. This pro-ject has been presented by John D. Fox (SLAC/Stanford Un.) at the IPAC2010 held in Kyoto. The idea of the pro-posal is to build a flexible and powerful instrument to mit-igate the parasitic e-cloud effects on the proton (and poten-tially positron) beams in storage rings. Being a new and ambitious project, the financial issues have been quite im-portant. US LHC Accelerator Research Program (LARP) and other institution funding sources have assured the de-velopment of the design for implementing the feedback in the SPS ring at CERN. Here the intra-bunch feedback sys-tem has been installed and tested in the frame of the LIU (LHC Injector Upgrade) program. After the end of the LARP funding, a possible new inter-esting chance to continue the R&D activity, could be by implementing the system in a lepton storage ring affected by e-cloud effects. For achieving this goal, a possible ex-periment could be carried out in the positron ring of DAFNE at Frascati, Italy. The feasibility of the proposal is evaluated in the following sections. In case of approval of the experiment, indeed the project could be inserted in the DAFNE-TF (DAFNE Test Facility) program that is fore-seen after the 2020 for the following 3-5 years.

physics.acc-ph↗

arXiv2020

Suppression of the longitudinal coupled bunch instability in DA$Φ$NE in collisions with a crossing angle

In DAFNE, the Frascati $e^+e^-$ collider operating since 1998, an innovative collision scheme, the crab waist, has been successfully implemented during the years 2008-09. During operations for the Siddharta experiment an unusual synchrotron oscillation damping effect induced by beam-beam collisions has been observed. Indeed, when the longitudinal feedback is off, the positron beam becomes unstable with currents above 200-300 mA due to coupled bunch instability. The longitudinal instability is damped by colliding the positron beam with a high current electron beam (of the order of 2 A). A shift of about -600 Hz in the residual synchrotron sidebands is observed. Precise measurements have been performed by using both a commercial spectrum analyzer and the diagnostic capabilities of the longitudinal bunch-by-bunch feedback. The damping effect has been observed in DAFNE for the first time during collisions with the crab waist scheme. Our explanation, based both on theoretical consideration and modeling simulation, is that beam collisions with a large crossing angle produce longitudinal tune shift and spread, providing Landau damping of synchrotron oscillations.

physics.acc-ph↗