We present predictions for scattering observables and femtoscopic correlation functions (CFs) of the <math altimg='si19.svg'><mrow><mi>I</mi><mo linebreak='goodbreak'>=</mo><mn>2</mn></mrow></math> <math altimg='si9.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>c</mi><mrow><mo>+</mo><mo>+</mo></mrow></msubsup><msup><mi>&#960;</mi><mo>+</mo></msup></mrow></math>, <math altimg='si20.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>c</mi><mn>0</mn></msubsup><msup><mi>&#960;</mi><mo>&#8722;</mo></msup></mrow></math> systems and its heavy-flavor counterpart <math altimg='si15.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>b</mi><mo>+</mo></msubsup><msup><mi>&#960;</mi><mo>+</mo></msup></mrow></math>. In both heavy-quark sectors, the strong interaction is formulated within two distinct theoretical frameworks, each constrained to reproduce the lowest-lying odd-parity isoscalar spin-1/2 resonances, &#923; <inf><italic>c</italic></inf>(2595) and &#923; <inf><italic>b</italic></inf>(5912), respectively. While the <math altimg='si20.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>c</mi><mn>0</mn></msubsup><msup><mi>&#960;</mi><mo>&#8722;</mo></msup></mrow></math> pair is governed solely by the strong interaction, electrostatic contributions are included in the other two channels involving charged particles through relativistic Coulomb wave functions. We show that the differences observed in the scattering observables between the two strong-interaction models arise mainly from the specific ultraviolet regularization schemes employed. The inclusion of Coulomb effects induces only a very small increase in both the scattering length and the effective range. The resulting CFs in the charm and bottom sectors display analogous global features, in agreement with expectations from heavy-quark flavor symmetry. Both, the <math altimg='si9.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>c</mi><mrow><mo>+</mo><mo>+</mo></mrow></msubsup><msup><mi>&#960;</mi><mo>+</mo></msup></mrow></math> and <math altimg='si15.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>b</mi><mo>+</mo></msubsup><msup><mi>&#960;</mi><mo>+</mo></msup></mrow></math> CFs, when computed including only the strong interaction, exhibits substantial discriminating power among the different models. However, once Coulomb effects are incorporated, the CFs become largely affected by the repulsive electrostatic interaction, which diminishes their sensitivity to the details of the underlying strong dynamics, thereby reducing the capability to differentiate between theoretical descriptions. Thus, the <math altimg='si20.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>c</mi><mn>0</mn></msubsup><msup><mi>&#960;</mi><mo>&#8722;</mo></msup></mrow></math> CF&#8212;being free from Coulomb effects&#8212;provides the most suitable observable for constraining the strong dynamics of the isotensor &#931; <inf><italic>c</italic></inf> <italic>&#960;</italic> system.

Spain

Mikel F. Barbat

Juan Nieves

Laura Tolos

Scattering and femtoscopic correlation functions of the <math altimg='si18.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>c</mi><mrow><mo>+</mo><mo>+</mo></mrow></msubsup><msup><mi>&#960;</mi><mo>+</mo></msup><mo>,</mo><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>c</mi><mn>0</mn></msubsup><msup><mi>&#960;</mi><mo>&#8722;</mo></msup></mrow></math> and <math altimg='si15.svg'><mrow><msubsup><mstyle mathvariant='normal'><mi>&#931;</mi></mstyle><mi>b</mi><mo>+</mo></msubsup><msup><mi>&#960;</mi><mo>+</mo></msup></mrow></math> systems

The capability of the ALICE@LHC and STAR@RHIC experiments to reconstruct <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi></math> mesons has enabled femtoscopic correlation measurements of open-charm mesons in both small and large systems. In this work, we present a theoretical calculation of the correlation functions of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>D</mi><mo stretchy="false">¯</mo></mover></math> mesons with nucleons, based on the Koonin-Pratt formalism. We employ an effective Lagrangian to model the interaction between charmed mesons and baryons and apply the TROY formalism to obtain the off-shell <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>T</mi></math>-matrix in coupled channels, incorporating the effect of the Coulomb interaction when the pair involves two charged particles. The resulting full coupled-channel wave function is inserted into the Koonin-Pratt equation with channel weights derived from a thermal model. Additionally, we compute the correlation functions using the Lednický-Lyuboshitz approximation with low-energy scattering parameters extracted from the unitarized amplitudes. We compare these two approaches and provide predictions for different correlated pairs. Our results can be tested against current and future experimental data from the ALICE and STAR Collaborations in both proton-proton and heavy-ion collisions.

Juan M. Torres-Rincon

Àngels Ramos

Femtoscopy of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>D</mi><mi>N</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>D</mi><mo stretchy="false">¯</mo></mover><mi>N</mi></math> systems

The dissipative properties of relativistic strongly interacting nuclear matter significantly influence the damping of stellar oscillations and density fluctuations during compact star mergers. In this work, we derive the evolution equation for the bulk viscous pressure in unpaired quark matter under small deviations from equilibrium. Our analysis reveals that it behaves like a two-component Burgers fluid. We identify four key transport coefficients—two relaxation times and two bulk viscosity coefficients—expressed in terms of equilibrium parameters and electroweak nonleptonic and semileptonic decay rates. The transport coefficients are evaluated for two distinct equations of state: one based on perturbative quantum chromodynamics and the other on a modified MIT bag model, valid in different density regimes. We also determine the temperature and density region where nonleptonic electroweak processes dominate the dissipation. Our formulation establishes a new way of describing bulk viscous effects in quark matter, applicable for numerical simulations of compact star mergers.

José Luis Hernández

Cristina Manuel

Saga Säppi

Burgers equation for the bulk viscous pressure of quark matter

We investigate the hyperonic equation of state within the non-linear derivative model that incorporates a momentum dependence on the interactions, with a special emphasis on properly establishing the conditions for hyperon appearance in neutron star matter. We demonstrate that hyperons can appear at finite momentum, even when they are absent at lower momenta, forming a so-called <italic>momentum-fragmented</italic> region. Our study shows that this phenomenon significantly alters the composition and equation of state of hyperonic matter as compared to the cases when it is disregarded, highlighting the importance of accurately treating the momentum dependence of the baryon fields in dense matter.

Hristijan Kochankovski

Momentum-fragmented hyperons in cold neutron stars

We investigate the influence of dark matter on hybrid stars. Using a two-fluid approach, where normal and dark matter components interact only gravitationally, we explore how dark matter can trigger the appearance of quark matter in neutron stars for unprecedented low masses. Our findings reveal that dark matter increases the central pressure of neutron stars, potentially leading to the formation of hybrid stars with quark cores even at very low compact star masses. The critical mass for the appearance of quark matter decreases with increasing dark matter content. We introduce the concept of “masquerading hybrid stars,” where dark matter admixed stars exhibit similar mass-radius relations to purely hadronic stars, making it challenging to distinguish between them based solely on these parameters. Additionally, we identify a unique class of objects termed “dark oysters,” characterized by a large dark matter halo and a small normal matter core, highlighting the diverse structural possibilities for compact stars influenced by dark matter.

Brazil

Carline Biesdorf

Germany

Jürgen Schaffner-Bielich

Masquerading hybrid stars with dark matter

We have studied the feasibility of the experimental determination of the width of a D meson in a nuclear medium by using the method of the nuclear transparency. The cross section for inclusive production of a <math><msup><mrow><mi>D</mi></mrow><mrow><mo>+</mo></mrow></msup></math> in different nuclei is evaluated, taking care of the <math><msup><mrow><mi>D</mi></mrow><mrow><mo>+</mo></mrow></msup></math> absorption in the nucleus, or equivalently, the survival probability of the <math><msup><mrow><mi>D</mi></mrow><mrow><mo>+</mo></mrow></msup></math> in its way out of the nucleus from the point of production. We use present values of the in medium width of D mesons and calculate ratios of the cross sections for different nuclei to the <math><mmultiscripts><mrow><mtext>C</mtext></mrow><mprescripts></mprescripts><none></none><mrow><mn>12</mn></mrow></mmultiscripts></math> nucleus as reference. We find ratios of the order of 0.6 for heavy nuclei, a large deviation from unity, which indicates that the method proposed is adequate to measure this relevant magnitude, so far only known theoretically.

Victor Montesinos

Japan

Natsumi Ikeno

Eulogio Oset

Miguel Albaladejo

On the determination of the Meson Width in the Nuclear Medium With the Transparency Ratio

We study the damping of density oscillations in the quark matter phase that might occur in compact stars. To this end we compute the bulk viscosity and the associated damping time in three-flavor quark matter, considering both nonleptonic and semileptonic electroweak processes. We use two different equations of state of quark matter, more precisely, the MIT bag model and perturbative QCD, including the leading-order corrections in the strong coupling constant. We analyze the dependence of our results on the density, temperature and value of strange quark mass in each case. We then find that the maximum of the bulk viscosity is in the range of temperature from 0.01 to 0.1 MeV for frequencies around 1 kHz, while the associated minimal damping times of the density oscillations at those temperatures might be in the range of few to hundreds milliseconds. Our results suggest that bulk viscous damping might be relevant in the postmerger phase after the collision of two neutron stars if deconfined matter is achieved in the process.

Damping of density oscillations from bulk viscosity in quark matter

Hadron femtoscopy has turned into a powerful tool for accessing space-time information of heavy-ion collisions as well as for studying final-state interactions of hadrons. Recently, heavy-flavor femtoscopy has become feasible using the ALICE detector at the LHC. We compute the correlation function of <math><mi>D</mi></math> mesons and light mesons using an off-shell <math><mi>T</mi></math>-matrix approach to access the two-meson wave function, and predict the correlation functions involving charged <math><msup><mi>D</mi><mo>+</mo></msup><mo>,</mo><msup><mi>D</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><mo>,</mo><msubsup><mi>D</mi><mi>s</mi><mo>+</mo></msubsup></math>, and <math><msubsup><mi>D</mi><mi>s</mi><mrow><mo>*</mo><mo>+</mo></mrow></msubsup></math> with <math><msup><mi>π</mi><mo>±</mo></msup></math> and <math><msup><mi>K</mi><mo>±</mo></msup></math>. From the obtained results—all of them accessible in <math><mi>p</mi><mo>+</mo><mi>p</mi></math> collision experiments—we point up the case of <math><msup><mi>D</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math>, which is sensitive to the lower state of the two-pole <math><msubsup><mi>D</mi><mn>0</mn><mo>*</mo></msubsup><mo>(</mo><mn>2300</mn><mo>)</mo></math> system. The presence of such poles imprints a depletion on the correlation function, which could potentially be detected in experiments. While preliminary ALICE data do not show evidence of this effect, we suggest to look into the <math><msubsup><mi>D</mi><mi>s</mi><mo>+</mo></msubsup><msup><mi>K</mi><mo>−</mo></msup></math> system to explore the higher pole of the <math><msubsup><mi>D</mi><mn>0</mn><mo>*</mo></msubsup><mo>(</mo><mn>2300</mn><mo>)</mo></math>, as the depletion in the correlation function is more pronounced. Using heavy-quark spin symmetry we also propose exploring the effect of the two poles of the <math><msub><mi>D</mi><mn>1</mn></msub><mo>(</mo><mn>2430</mn><mo>)</mo></math> and predict similar structures in the correlation functions of the <math><msup><mi>D</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><msup><mi>π</mi><mo>−</mo></msup></math> and <math><msubsup><mi>D</mi><mi>s</mi><mrow><mo>*</mo><mo>+</mo></mrow></msubsup><msup><mi>K</mi><mo>−</mo></msup></math> pairs.

Femtoscopy of <math><mi>D</mi></math> mesons and light mesons upon unitarized effective field theories

The properties of the <math><mi>X</mi><mo>(</mo><mn>3872</mn><mo>)</mo></math> and its spin partner, the <math><mi>X</mi><mo>(</mo><mn>4014</mn><mo>)</mo></math>, are studied both in vacuum and at finite temperature. Using an effective hadron theory based on the hidden-gauge Lagrangian, the <math><mi>X</mi><mo>(</mo><mn>3872</mn><mo>)</mo></math> is dynamically generated from the <math><mi>s</mi></math>-wave rescattering of a pair of pseudoscalar and vector charm mesons. By incorporating the thermal spectral functions of open charm mesons, the calculation is extended to finite temperature. Similarly, the properties of the <math><mi>X</mi><mo>(</mo><mn>4014</mn><mo>)</mo></math> are obtained out of the scattering of charm vector mesons. By applying heavy-quark flavor symmetry, the properties of their bottom counterparts in the axial-vector and tensor channels are also predicted. All the dynamically generated states show a decreasing mass and acquire an increasing decay width with temperature, following the trend observed in their meson constituents. These results are relevant in relativistic heavy-ion collisions at high energies, in analyses of the collective medium formed after hadronization, or in femtoscopic studies, and can be tested in lattice-QCD calculations exploring the melting of heavy mesons at finite temperature.

United States

Glòria Montaña

<math><mi>X</mi><mo>(</mo><mn>3872</mn><mo>)</mo></math>, <math><mi>X</mi><mo>(</mo><mn>4014</mn><mo>)</mo></math>, and their bottom partners at finite temperature

We extend the kinetic theory of <math><mi>D</mi></math> mesons to accommodate thermal and off-shell effects due to the medium modification of the heavy-meson spectral functions. From the Kadanoff-Baym approach we derive the off-shell Fokker-Planck equation which encodes the heavy-flavor transport coefficients. We analyze the thermal width (damping rate) of <math><mi>D</mi></math> mesons due to their scattering off light mesons, focusing on new in-medium effects: off-shell corrections, inelastic channels, and the contribution of the Landau cut. We obtain that the latter effect (absent for vacuum scattering amplitudes) brings sizable corrections at moderate temperatures. We discuss how the heavy-flavor transport coefficients, like the drag and diffusion coefficients, are modified in matter. We find that the <math><mi>D</mi></math>-meson spatial diffusion coefficient matches smoothly to the latest results of lattice-QCD calculations and Bayesian analyses at higher temperatures.