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Laura Tolos

Publications and source records attributed to Laura Tolos.

At least 91 records · Page 5Linked to original sources

Propagation of heavy baryons in heavy-ion collisions

The drag and diffusion coefficients of heavy baryons ($Λ_c$ and $Λ_b$) in the hadronic phase created in the latter stage of the heavy-ion collisions at RHIC and LHC energies have been evaluated recently. In this work we compute some experimental observables, such as the nuclear suppression factor $R_{AA}$ and the elliptic flow $v_2$ of heavy baryons at RHIC and LHC energies, highlighting the role of the hadronic phase contribution to these observables, which are going to be measured at Run 3 of LHC. For the time evolution of the heavy quarks in the QGP and heavy baryons in the hadronic phase we use the Langevin dynamics. For the hadronization of the heavy quarks to heavy baryons we employ Peterson fragmentation functions. We observe a strong suppression of both the $Λ_c$ and $Λ_b$. We find that the hadronic medium has a sizable impact on the heavy-baryon elliptic flow whereas the impact of hadronic medium rescattering is almost unnoticeable on the nuclear suppression factor. We evaluate the $Λ_c/D$ ratio at RHIC and LHC. We find that $Λ_c/D$ ratio remain unaffected due to the hadronic phase rescattering which enable it as a nobel probe of QGP phase dynamics along with its hadronization.

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Twin Stars within the SU(3) Chiral Quark-Meson Model

We present new stable solutions of the Tolman Oppenheimer Volkoff equations for quark stars using a quark matter equation of state based on the SU(3) Quark-Meson model that exhibits the onset of the chiral phase transition. These new solutions appear as two stable branches in the mass-radius relation allowing for so called twin stars, i.e. two stable quark star solutions with the same mass, but distinctly different radii. We find solutions which are compatible with causality, the stability conditions of dense matter, the astrophysical constraints of the rotation of the millisecond pulsar PSR J1748-2446ad and the 2$M_{\odot}$ pulsar mass constraint.

astro-ph.HE↗

Equation of State for Nucleonic and Hyperonic Neutron Stars with Mass and Radius Constraints

We obtain a new equation of state for the nucleonic and hyperonic inner core of neutron stars that fulfills the 2$M_{\odot}$ observations as well as the recent determinations of stellar radii below 13 km. The nucleonic equation of state is obtained from a new parametrization of the FSU2 relativistic mean-field functional that satisfies these latest astrophysical constraints and, at the same time, reproduces the properties of nuclear matter and finite nuclei while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions. On the one hand, the equation of state of neutron star matter is softened around saturation density, which increases the compactness of canonical neutron stars leading to stellar radii below 13 km. On the other hand, the equation of state is stiff enough at higher densities to fulfill the 2$M_{\odot}$ limit. By a slight modification of the parametrization, we also find that the constraints of 2$M_{\odot}$ neutron stars with radii around 13 km are satisfied when hyperons are considered. The inclusion of the high magnetic fields present in magnetars further stiffens the equation of state. Hyperonic magnetars with magnetic fields in the surface of $ \sim 10^{15}$ G and with values of $\sim 10^{18}$ G in the interior can reach maximum masses of 2$M_{\odot}$ with radii in the 12-13 km range.

astro-ph.HE↗

Transport coefficients of heavy baryons

We compute the transport coefficients (drag and momentum diffusion) of the low-lying heavy baryons $Λ_c$ and $Λ_b$ in a medium of light mesons formed at the later stages of high-energy heavy-ion collisions. We employ the Fokker-Planck approach to obtain the transport coefficients from unitarized baryon-meson interactions based on effective field theories that respect chiral and heavy-quark symmetries. We provide the transport coefficients as a function of temperature and heavy-baryon momentum, and analyze the applicability of certain nonrelativistic estimates. Moreover we compare our outcome for the spatial diffusion coefficient to the one coming from the solution of the Boltzmann-Uehling-Uhlenbeck transport equation and we find a very good agreement between both calculations. The transport coefficients for $Λ_c$ and $Λ_b$ in a thermal bath will be used in a subsequent publication as input in a Langevin evolution code for the generation and propagation of heavy particles in heavy-ion collisions at LHC and RHIC energies.

hep-ph↗

Measuring the neutron star equation of state using X-ray timing

One of the primary science goals of the next generation of hard X-ray timing instruments is to determine the equation of state of the matter at supranuclear densities inside neutron stars, by measuring the radius of neutron stars with different masses to accuracies of a few percent. Three main techniques can be used to achieve this goal. The first involves waveform modelling. The flux we observe from a hotspot on the neutron star surface offset from the rotational pole will be modulated by the star's rotation, giving rise to a pulsation. Information about mass and radius is encoded into the pulse profile via relativistic effects, and tight constraints on mass and radius can be obtained. The second technique involves characterising the spin distribution of accreting neutron stars. The most rapidly rotating stars provide a very clean constraint, since the mass-shedding limit is a function of mass and radius. However the overall spin distribution also provides a guide to the torque mechanisms in operation and the moment of inertia, both of which can depend sensitively on dense matter physics. The third technique is to search for quasi-periodic oscillations in X-ray flux associated with global seismic vibrations of magnetars (the most highly magnetized neutron stars), triggered by magnetic explosions. The vibrational frequencies depend on stellar parameters including the dense matter equation of state. We illustrate how these complementary X-ray timing techniques can be used to constrain the dense matter equation of state, and discuss the results that might be expected from a 10m$^2$ instrument. We also discuss how the results from such a facility would compare to other astronomical investigations of neutron star properties. [Modified for arXiv]

astro-ph.HE↗

Strangeness At Extremes

We study the properties of strange mesons in vacuum and in the hot nuclear medium within unitarized coupled-channel effective theories. We determine transition probabilities, cross sections and scattering lengths for strange mesons. These scattering observables are of fundamental importance for understanding the dynamics of strangeness production and propagation in heavy-ion collisions.

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Heavy mesons in a hadronic medium: interaction and transport coefficients

We review the recent results of heavy meson diffusion in thermal hadronic matter. The interactions of D and B-bar mesons with other hadrons (light mesons and baryons) are extracted from effective field theories based on chiral and heavy-quark symmetries. When these guiding principles are combined with exact unitarity, physical values of the cross sections are obtained. These cross sections (which contain resonant contributions) are used to calculate the drag and diffusion coefficients of heavy mesons immersed in a thermal and dense medium. The transport coefficients are computed using a Fokker-Planck reduction of the Boltzmann equation.

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Strange meson-baryon interaction in hot and dense medium: recent progress for a road to GSI/FAIR

We report recent results on the dynamics of strange hadrons in two-body reactions relevant for near-threshold production in heavy-ion collisions at GSI/FAIR and NICA-Dubna. In particular, $\bar K N$ scattering in hot and dense nuclear matter is studied within a chiral unitary framework in coupled channels, setting up the starting point for implementations in microscopic off-shell transport approaches. We focus on the calculation of transition rates with special attention to the excitation of hyperon resonances and isospin effects. Additionally, we explore "unconventional" strangeness generation by meson-meson and meson-baryon interactions in connection with recent HADES observations of deep sub-threshold $ϕ$ and $Ξ$ production.

hep-ph↗

Heavy Hadrons in Dense Matter

We study the behavior of dynamically-generated baryon resonances with heavy-quark content within a unitarized coupled-channel theory in matter that fulfills heavy-quark spin symmetry constraints. We analyze the implications for the formation of charmed mesic nuclei and the propagation of heavy mesons in heavy-ion collisions from RHIC to FAIR.

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Tomography of the Quark-Gluon-Plasma by Charm Quarks

We study charm production in ultra-relativistic heavy-ion collisions by using the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm quarks are produced by the Pythia event generator tuned to fit the transverse momentum spectrum and rapidity distribution of charm quarks from Fixed-Order Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses and widths are given by the Dynamical Quasi-Particle Model (DQPM) which reproduces the lattice QCD equation-of-state in thermal equilibrium. The relevant cross section are calculated in a consistent way by employing the effective propagators and couplings from the DQPM. Close to the critical energy density of the phase transition, the charm quarks are hadronized into $D$ mesons through coalescence and/or fragmentation depending on transverse momentum. The hadronized $D$ mesons then interact with the various hadrons in the hadronic phase with cross sections calculated in an effective lagrangian approach with heavy-quark spin symmetry. Finally, the nuclear modification factor $\rm R_{AA}$ and the elliptic flow $v_2$ of $D^0$ mesons from PHSD are compared with the experimental data from the STAR Collaboration for Au+Au collisions at $\sqrt{s_{\rm NN}}$ =200 GeV. We find that in the PHSD the energy loss of $D$ mesons at high $p_T$ can be dominantly attributed to partonic scattering while the actual shape of $\rm R_{AA}$ versus $p_T$ reflects the heavy quark hadronization scenario, i.e. coalescence versus fragmentation. Also the hadronic rescattering is important for the $\rm R_{AA}$ at low $p_T$ and enhances the $D$-meson elliptic flow $v_2$.

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Charmed baryonic resonances in medium

We discuss the behavior of dynamically-generated charmed baryonic resonances in matter within a unitarized coupled-channel model consistent with heavy-quark spin symmetry. We analyze the implications for the formation of $D$-meson bound states in nuclei and the propagation of $D$ mesons in heavy-ion collisions from RHIC to FAIR energies.

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Transport coefficients in superfluid neutron stars

We study the shear and bulk viscosity coefficients as well as the thermal conductivity as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state and the gap of the system. The shear viscosity due to phonon scattering is compared to calculations of that coming from electron collisions. We also comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars. We finally obtain a temperature-independent thermal conductivity from phonon collisions and compare it with the electron-muon thermal conductivity in superfluid neutron stars.

astro-ph.SR↗

Thermal conductivity due to phonons in the core of superfluid neutron stars

We compute the contribution of phonons to the thermal conductivity in the core of superfluid neutron stars. We use effective field theory techniques to extract the phonon scattering rates, written as a function of the equation of state of the system. We also calculate the phonon dispersion law beyond linear order, which depends on the gap of superfluid neutron matter. With all these ingredients, we solve the Boltzmann equation numerically using a variational approach. We find that the thermal conductivity $κ$ is dominated by combined small and large angle binary collisions. As in the color-flavor-locked superfluid, we find that our result can be well approximated by $κ\propto 1/ Δ^6$, where $Δ$ is the neutron gap, the constant of proportionality depending on the density. We further comment on the possible relevance of electron and superfluid phonon collisions in obtaining the total contribution to the thermal conductivity in the core of superfluid neutron stars.

astro-ph.SR↗

Anti-strange meson-baryon interaction in hot and dense nuclear matter

We present a study of in-medium cross sections and (off-shell) transition rates for the most relevant binary reactions for strange pseudoscalar meson production close to threshold in heavy-ion collisions at FAIR energies. Our results rely on a chiral unitary approach in coupled channels which incorporates the $s$- and $p$-waves of the kaon-nucleon interaction. The formalism, which is modified in the hot and dense medium to account for Pauli blocking effects, mean-field binding on baryons, and pion and kaon self-energies, has been improved to implement full unitarization and self-consistency for both the $s$- and $p$-wave interactions at finite temperature and density. This gives access to in-medium amplitudes in several elastic and inelastic coupled channels with strangeness content $S=-1$. The obtained total cross sections mostly reflect the fate of the $Λ(1405)$ resonance, which melts in the nuclear environment, whereas the off-shell transition probabilities are also sensitive to the in-medium properties of the hyperons excited in the $p$-wave amplitudes [$Λ$, $Σ$ and $Σ^*(1385)$]. The single-particle potentials of these hyperons at finite momentum, density and temperature are also discussed in connection with the pertinent scattering amplitudes. Our results are the basis for future implementations in microscopic transport approaches accounting for off-shell dynamics of strangeness production in nucleus-nucleus collisions.

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Heavy Mesons in Nuclear Matter and Nuclei

Heavy mesons in nuclear matter and nuclei are analyzed within different frameworks, paying a special attention to unitarized coupled-channel approaches. Possible experimental signatures of the properties of these mesons in matter are addressed, in particular in connection with the future FAIR facility at GSI.

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$D$-mesons propagation in hadronic matter and consequences on heavy-flavor observables in ultrarelativistic heavy-ion collisions

We employ recently published cross sections for $D$-mesons with hadrons and calculate the drag and diffusion coefficients of $D$-mesons in hadronic matter as a function of the momentum of $D$-mesons as well as of the temperature of the medium. Calculating in our approach the spatial diffusion coefficient, $D_x$, at zero chemical potential we see a very smooth transition between our calculations for the hadron gas and the lattice QCD calculations. Applying the results for the transport coefficients of $D$-mesons in a Fokker-Planck equation, which describes the evolution of $D$-mesons during the expansion of a hadron gas created in ultrarelativistic heavy-ion collisions, we find that the value of $R_{AA}$ is little influenced by hadronic rescattering, whereas in the elliptic flow the effects are stronger. We extend our calculations to the finite chemical potentials and calculate the spatial diffusion coefficients of $D$-mesons propagating through the hadronic medium following isentropic trajectories, appropriate at future FAIR and NICA heavy-ion experiments. For the isentropic trajectory with $s/ρ_B^{\rm net}=20$ we find a perfect matching of results for $D$-mesons in hadronic matter and for charm quarks in partonic matter treated within the DQPM approach.

hep-ph↗

Dynamically-generated baryon resonances with heavy flavor

We study baryon resonances with heavy flavor in a molecular approach, thus as dynamically generated by meson-baryon scattering. This is accomplished by using a unitary coupled-channel model taking, as bare interaction, the extension to four flavors and spin symmetry of the Weinberg-Tomozawa interaction potential. A special attention is paid to the inclusion of heavy-quark spin symmetry and to the studies of the generated baryon resonances which complete the heavy-quark spin multiplets. We reproduce few charmed and strange baryon resonances found experimentally, that is, Λ_c(2595), Λ_c(2625), Ξ_c(2790), Ξ_c(2815), and make predictions for more states. The bottom-flavored Λ_b(5912) and Λ_b(5920) states, found by the LHCb collaboration, are also obtained by our model, thus these resonances can be interpreted as molecular states. We also study Ξ_b resonances, which belong to the same SU(3) x HQSS multiplets as the observed Λ_b particles. Finally we analyze hidden-charm baryon resonances. In this sector, we predict seven N-like and five Δ-like states with masses around 4 GeV, most of them as bound states, and compare them with predictions from other models. The predicted states can be searched for in future experiments that involve studies of heavy-flavor physics, e.g. PANDA/FAIR, where charm physics will be analyzed.

hep-ph↗

Open bottom states and the anti-B meson propagation in hadronic matter

The interaction and propagation of anti-B mesons with light mesons, N and Delta baryons is studied within a unitarized approach based on effective models that are compatible with chiral and heavy-quark symmetries. We find several heavy-quark spin doublets in the open-bottom sectors, where anti-B and anti-B* mesons are present. In the meson sector we find several resonant states, among them, a B0 and a B1 with masses 5530 MeV and 5579 MeV as well as Bs0* and Bs1* narrow states at 5748 MeV and 5799 MeV, respectively. They form two doublets with no experimental identification yet, the first one being the bottom counterpart of the D0(2400) and D1(2430) states, and the second bottom doublet associated to the ubiquitous Ds0* (2317) and the Ds1 (2460). In the baryon sector, several Lambda_b and Sigma_b doublets are identified, among them the one given by the experimental Lambda_b(5910) and Lambda*_b(5921). Moreover, one of our states, the Sigma_b*(5904), turns out to be the bottom counterpart of the Sigma*(1670) and Sigma_c*(2549), which is a case for discovery. We finally analyze different transport coefficients for the anti-B meson in hot matter, such as formed in heavy-ion collisions at RHIC and LHC. For RHIC/LHC energies, the main contribution to the coefficients comes from the interaction of anti-B mesons with pions. However, we also include the effects of baryonic density which might be sizable at temperatures T < 100 MeV, as the chemical potential is expected to increase in the last stages of the expansion. We conclude that although the relaxation time decreases with larger baryonic densities, the anti-B meson does not thermalize at RHIC/LHC energies, representing an ideal probe for the initial bottom distribution.

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