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Institute
We study equilibrium as well as out-of-equilibrium properties of the strongly interacting QGP medium under extreme conditions of high temperature T and high baryon densities or baryon chemical potentials μB within a kinetic approach. We present the thermodynamic and transport properties of the QGP close to equilibrium in the framework of effective models with Nf=3 active quark flavours such as the Polyakov extended Nambu-Jona Lasinio (PNJL) and dynamical quasiparticle model with the CEP (DQPM-CP). Considering the transport coefficients and the EoS of the QGP phase, we compare our results with various results from the literature. Furthermore, out-of equilibrium properties of the QGP medium and in particular, the effect of a μB- dependence of thermodynamic and transport properties of the QGP are studied within the Parton-Hadron-String-Dynamics (PHSD) transport approach, which covers the full evolution of the system during HICs. We find that bulk observables and flow coefficients for strange hadrons as well as for antiprotons are more sensitive to the properties of the QGP, in particular to the μB - dependence of the QGP interactions.
Presolar grain isotopic ratios as constraints to nuclear physics inputs for s-process calculations
(2023)
The isotopic abundances in presolar SiC grains of AGB origin provide important and precise constraints to those star nucleosynthesis models. By comparing the values of the s-element abundances resulting from calculations with the ones measured in these dust grains, it turns out that new measurements of weak-interaction rates in ionized plasmas, as well as of neutron-capture cross sections, are needed, especially in the region near the neutron magic numbers 50 and 82.
Results on proton and Λ flow, calculated with the UrQMD model that incorporates different realistic density dependent equations of state, are presented. It is shown that the proton and hyperon flow shows sensitivity to the equation of state and especially to the appearance of a phase transition at densities below 4n0. Even though qualitatively hyperons and protons exhibit the same beam energy dependence of the flow, the quantitative results are different. In this context it is suggested that the hyperon measurements can be used to study the density dependence of the hyperon interaction in high density QCD matter.
This thesis aims to investigate the properties of hadronic matter by analyzing fluctuations of conserved charges. A transport model (SMASH) is used for these studies to achieve this. The first part of this thesis focuses on examining transport coefficients, specifically the diffusion coefficients of conserved charges and the shear viscosity. The second part investigates equal-time correlations of particle numbers in the form of cumulants. The last chapter studies different aspects of the isobar collision systems Ru and Zr.
As a first step, the hadronic medium and interactions between its constituents are introduced, and simultaneously, their impact on transport coefficients is investigated. The methodology is verified by comparing the results of SMASH with Chapman-Enskog calculations, followed by examining 3-to-1 multi-particle reactions, revealing their influence on shear viscosity and electrical diffusion. The analysis of the full hadron gas considers angle-dependent cross-sections and additional elastic cross-sections via the AQM description, showing significant impacts on transport coefficients. The dependency on the number of degrees of freedom is explored, with noticeable effects on diffusion coefficients but a smaller influence on the shear viscosity. At non-zero baryon chemical potential, the diffusion coefficients are strongly influenced, while the shear viscosity remains unaffected. Overall, the study underscores the importance of individual cross-sections and the modeling of interactions on transport coefficients.
The following chapter explores fluctuations of conserved charges, crucial for understanding phase transitions in heavy-ion collision from the quark-gluon plasma to the hadronic phase. Using SMASH, the impact of global charge conservation on particle number cumulants in subvolumes of boxes simulating infinite matter is studied. Comparisons with simpler systems highlights the influence of hadronic interactions on cumulants, especially via charge annihilation processes and the results from SMASH shows agreement with analytical calculations. Calculations at finite baryon chemical potential reveals a transition from a Poisson to Skellam distribution within the net proton cumulants. It is shown that an unfolding procedure to obtain the net baryon fluctuations from the net proton ones deviates from the actual net baryon result, particularly in larger volumes. Finally, net proton correlations at vanishing baryon chemical potential align with ALICE measurements and the net proton cumulants are unaffected by deuteron formation.
In the next step, the goal is to investigate critical fluctuations in the hadronic medium. Therefore, the hadronic system is initialized with critical equilibrium fluctuations by coupling the hadron resonance gas with the 3D Ising model. The single-particle probability distributions are derived from the principle of maximum entropy. Evolving these distributions in SMASH, their development in an expanding sphere adjusted to experimental conditions can be analyzed. It reveals resonance decay and formations as the primary source that affects the particle cumulants. Because of isospin randomization processes, critical fluctuations are better preserved in net nucleon numbers. However, for the strongest coupling investigated in this work, correlations of the critical field are still present in the final state of the evolution in the net proton fluctuations. Examining cumulant dependence on rapidity windows shows a non-monotonic trend.
In the third part, collisions involving the isobars Ru and Zr are studied at a center-of-mass energy of 200 GeV. Initially, SMASH is used to study the initial conditions to hydrodynamical simulations, emphasizing the importance of the nuclear structure of isobars on the geometry of the collision area. It is found that the deformation parameters notably influence the initial state. Correlations between nucleon-nucleon pairs on eccentricity fluctuations yield no significant effect. Subsequently, the hydrodynamic model vHLLE evolves the previously explored initial conditions and for the transition between the hydrodynamic and kinetic descriptions, the Cooper-Frye formula is used. Usage of the canonical ensemble ensures the exact conservation of the conserved charges B, Q, and S. The neutron skin effect, which changes the charge distribution within Ru nuclei, is additionally considered. Fluctuations are assessed, revealing suppression in large rapidity windows due to global charge conservation. The hadronic phase modifies fluctuations of net pions, net kaons, and net protons via annihilation processes, yet fluctuations remain unaffected by the neutron skin effect.
The equation of state (EoS) of matter at extremely high temperatures and densities is currently not fully understood, and remains a major challenge in the field of nuclear physics. Neutron stars harbor such extreme conditions and therefore serve as celestial laboratories for constraining the dense matter EoS. In this thesis, we present a novel algorithm that utilizes the idea of Bayesian analysis and the computational efficiency of neural networks to reconstruct the dense matter equation of state from mass-radius observations of neutron stars. We show that the results are compatible with those from earlier works based on conventional methods, and are in agreement with the limits on tidal deformabilities obtained from the gravitational wave event, GW170817. We also observe that the resulting squared speed of sound from the reconstructed EoS features a peak, indicating a likely convergence to the conformal limit at asymptotic densities, as expected from quantum chromodynamics. The novel algorithm can also be applied across various fields faced with computational challenges in solving inverse problems. We further examine the efficiency of deep learning methods for analyzing gravitational waves from compact binary coalescences in this thesis. In particular, we develop a deep learning classifier to segregate simulated gravitational wave data into three classes: signals from binary black hole mergers, signals from binary neutron star mergers, or white noise without any signals. A second deep learning algorithm allows for the regression of chirp mass and combined tidal deformability from simulated binary neutron star mergers. An accurate estimation of these parameters is crucial to constrain the underlying EoS. Lastly, we explore the effects of finite temperatures on the binary neutron star merger remnant from GW170817. Isentropic EoSs are used to infer the frequencies of the rigidly rotating remnant and are noted to be significantly lower compared to previous estimates from zero temperature EoSs. Overall, this thesis presents novel deep learning methods to constrain the neutron star EoS, which will prove useful in future, as more observational data is expected in the upcoming years.
We have investigated the systematic differences introduced when performing a Bayesian-inference analysis of the equation of state (EOS) of neutron stars employing either variable- or constant-likelihood functions. The former has the advantage of retaining the full information on the distributions of the measurements, making exhaustive usage of the data. The latter, on the other hand, has the advantage of a much simpler implementation and reduced computational costs. In both approaches, the EOSs have identical priors and have been built using the sound speed parameterization method so as to satisfy the constraints from X-ray and gravitational waves observations, as well as those from chiral effective theory and perturbative quantum chromodynamics. In all cases, the two approaches lead to very similar results and the 90% confidence levels essentially overlap. Some differences do appear, but in regions where the probability density is extremely small and are mostly due to the sharp cutoff on the binary tidal deformability L˜ 720 set in the constant-likelihood approach. Our analysis has also produced two additional results. First, an inverse correlation between the normalized central number density, nc,TOV/ns, and the radius of a maximally massive star, RTOV. Second, and most importantly, it has confirmed the relation between the chirp mass and the binary tidal deformability. The importance of this result is that it relates chirp, which is measured very accurately, and L˜ , which contains important information on the EOS. Hence, when chirp is measured in future detections, our relation can be used to set tight constraints on L˜ .
The amplification of magnetic fields plays an important role in explaining numerous astrophysical phenomena associated with binary neutron star mergers, such as mass ejection and the powering of short gamma-ray bursts. Magnetic fields in isolated neutron stars are often assumed to be confined to a small region near the stellar surface, while they are normally taken to fill the whole star in numerical modeling of mergers. By performing high-resolution, global, and high-order general-relativistic magnetohydrodynamic simulations, we investigate the impact of a purely crustal magnetic field and contrast it with the standard configuration consisting of a dipolar magnetic field with the same magnetic energy but filling the whole star. While the crust configurations are very effective in generating strong magnetic fields during the Kelvin–Helmholtz-instability stage, they fail to achieve the same level of magnetic-field amplification of the full-star configurations. This is due to the lack of magnetized material in the neutron-star interiors to be used for further turbulent amplification and to the surface losses of highly magnetized matter in the crust configurations. Hence, the final magnetic energies in the two configurations differ by more than 1 order of magnitude. We briefly discuss the impact of these results on astrophysical observables and how they can be employed to deduce the magnetic topology in merging binaries.
Post-merger gravitational-wave signal from neutron-star binaries: a new look at an old problem
(2023)
The spectral properties of the post-merger gravitational-wave signal from a binary of neutron stars encodes a variety of information about the features of the system and of the equation of state describing matter around and above nuclear saturation density. Characterizing the properties of such a signal is an “old” problem, which first emerged when a number of frequencies were shown to be related to the properties of the binary through “quasiuniversal” relations. Here we take a new look at this old problem by computing the properties of the signal in terms of the Weyl scalar ψ4. In this way, and using a database of more than 100 simulations, we provide the first evidence for a new instantaneous frequency, y f0 4, associated with the instant of quasi-time-symmetry in the dynamics, and which also follows a quasi-universal relation. We also derive a new quasi-universal relation for the merger frequency f h mer, which provides a description of the data that is 4 times more accurate than previous expressions while requiring fewer fitting coefficients. Finally, consistent with the findings of numerous studies before ours, and using an enlarged ensemble of binary systems, we point out that the ℓ = 2, m = 1 gravitational-wave mode could become comparable with the traditional ℓ = 2, m = 2 mode on sufficiently long timescales, with strain amplitudes in a ratio |h21|/|h22| ∼ 0.1–1 under generic orientations of the binary, which could be measured by present detectors for signals with a large signal-to-noise ratio or by third-generation detectors for generic signals should no collapse occur.
The core of this work is represented by the investigation of the chiral phase transition, using Monte Carlo simulations and unimproved staggered fermions, both in the weak and strong coupling regimes of Quantum Chromodynamics. Based on recent results from Monte Carlo simulations, both using unimproved staggered fermions and Wilson fermions, the chiral phase transition in the continuum and chiral limit shows compatibility with a second-order phase transition for Nf (number of flavours) in range [2:7], at zero baryon chemical potential. This achievement relies on the analytic continuation of Nf to non-integer values on the lattice, which allows to make use of extrapolation techniques to the chiral limit, where simulations are not possible. Furthermore, these results provide a resolution to the ambiguous scenario for Nf = 2 in the chiral limt. The first part of this thesis is devoted to the investigation of the chiral phase transition when a non-zero imaginary baryon chemical potential is involved, whose value corresponds to the 81% of the Roberge-Weiss one. Using the same extrapolation techniques aforementioned, the order of the chiral phase transition in the continuum and chiral limit shows compatibility with a second-order phase transition for Nf in range [2:6], highlighting a lack of dependence of the order of the chiral phase transition on the imaginary baryon chemical potential value. The second part of this thesis is about the study of the extension of the first-order chiral region in the strong coupling regime, at zero baryon chemical potential. Using Monte Carlo techniques, this can be done by investigating the Z2 boundary on a coarse lattice, whose temporal extent reads Nt = 2, and simulations are realised for Nf = 4, 8. The results in the weak coupling regime show, for $Nt = 8, 6, 4 and fixed Nf value, an inflating first-order chiral region. As in the strong coupling limit a second-order chiral phase transition is expected, the first-order chiral region has to shrink as the strong coupling regime is approached, resulting in a non-monotonic behaviour of the Z2 boundary. For Nf = 8, a critical mass on the Z2 boundary has been obtained, confirming the expected non-monotonic behaviour. For Nf = 4 the results do not provide a unique conclusion: Either a Z2 boundary at extremely low bare quark mass or a second-order chiral phase transition in the O(2) universality class in the chiral limit can take place. In addition to the two main topics, the performances of the second-order minimum norm integrator (2MN) and the fourth-order minimum norm integrator (4MN) have been compared, after implementing the 4MN one in the CL2QCD code used to realise our simulations. The 2MN integrator had already been implemented in the code since the first version was released. The two integrators belong to the class of symplectic integrators and represent an essential component of the RHMC algorithm, involved in our investigation. This step is extremely important, in order to guarantee the best quality when collecting data from simulations, and the results of the comparison suggested to favor the 2MN integrator, for both the topics.
In the framework of the LHC Injectors Upgrade Project (LIU), the CERN Proton Synchrotron Booster (PSB) went through major upgrades resulting in new effects to study, challenges to overcome and new parameter regimes to explore. To assess the achievable beam brightness limit of the machine, a series of experimental and computational studies in the transverse planes were performed. In particular, the new injection scheme induces optics perturbations that are strongly enhanced near the half-integer resonance. In this thesis, methods for dynamically measuring and correcting these perturbations and their impact on the beam performance will be presented. Additionally, the quality of the transverse beam distributions and strategies for improvement will be addressed. Finally, the space charge effects when dynamically crossing the half-integer resonance will be characterized. The results of these studies and their broader significance beyond the PSB will be discussed.
DNA binding redistributes activation domain ensemble and accessibility in pioneer factor Sox2
(2023)
More than 1600 human transcription factors orchestrate the transcriptional machinery to control gene expression and cell fate. Their function is conveyed through intrinsically disordered regions (IDRs) containing activation or repression domains but lacking quantitative structural ensemble models prevents their mechanistic decoding. Here we integrate single-molecule FRET and NMR spectroscopy with molecular simulations showing that DNA binding can lead to complex changes in the IDR ensemble and accessibility. The C-terminal IDR of pioneer factor Sox2 is highly disordered but its conformational dynamics are guided by weak and dynamic charge interactions with the folded DNA binding domain. Both DNA and nucleosome binding induce major rearrangements in the IDR ensemble without affecting DNA binding affinity. Remarkably, interdomain interactions are redistributed in complex with DNA leading to variable exposure of two activation domains critical for transcription. Charged intramolecular interactions allowing for dynamic redistributions may be common in transcription factors and necessary for sensitive tuning of structural ensembles.
We show examples of the impact of the Maxwellian averaged capture cross sections determined at n_TOF over the past 20 years on AGB stellar nucleosynthesis models. In particular, we developed an automated procedure to derive MACSs from evaluated data libraries, which are subsequently used as input to stellar models computed by means of the FuNS code. In this contribution, we present a number of s-process abundances obtained using different data libraries as input to stellar models, with a focus on the role of n_TOF data.
Subensemble is a type of statistical ensemble which is the generalization of grand canonical and canonical ensembles. The subensemble acceptance method (SAM) provides general formulas to correct the cumulants of distributions in heavy-ion collisions for the global conservation of all QCD charges. The method is applicable for an arbitrary equation of state and sufficiently large systems, such as those created in central collisions of heavy ions. The new fluctuation measures insensitive to global conservation effects are presented. The main results are illustrated in the hadron resonance gas and van der Waals fluid frameworks.
Present nuclear reaction network computations for astrophysical simulations involve many different types of rates, including neutron-capture reactions of interest for the modeling of heavy-element nucleosynthesis. While for many of them we still have to rely on theoretical calculations, an increasing number of experimentally-determined cross sections have now become available. In this contribution, we present “ASTrophysical Rate and rAw data Library” (ASTRAL), a new online database for neutron-capture cross sections based on experimental results, mainly obtained through activation and timeof-flight measurements. For the evaluation process, cross sections were re-calculated starting from raw data and by considering recent changes in physical properties of the involved isotopes (e.g., half-life and γ-ray intensities). We show the current status of the database, the techniques adopted to derive the recommended Maxwellian-averaged cross sections, and future developments.
Prediction for hyper nuclei multiplicities from GSI to LHC energies from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model combined with a final state coalescence approach is presented and compared to the thermal model. The influence of the coalescence radius on the collision energy and centrality dependence of the Λ3H/ΛΛ3H/Λ ratio is discussed.
This article summarizes some of the current theoretical developments and the experimental status of hypernuclei in relativistic heavy-ion collisions and elementary collisions. In particular, the most recent results of hyperhydrogen of mass A = 3 and 4 are discussed. The highlight at SQM2022 in this perspective was the discovery of the anti-hyperhydrogen-4 by the STAR Collaboration, in a large data set consisting of different collision systems. Furthermore, the production yields of hyperhydrogen-4 and hyperhelium-4 from the STAR Collaboration can be described nicely by the thermal model when the excited states of these hypernuclei are taken into account. In contrast, the production measurements in small systems (pp and p–Pb) from the ALICE Collaboration tends to favour the coalescence model over the thermal description. New measurements from STAR, ALICE and HADES Collaborations of the properties, e.g. lifetime, of A = 3 and 4 hypernuclei give similar results of these properties. Also the anti-hyperhydrogen-4 lifetime is in rather good agreement with previous measurements. Interestingly, the new STAR measurement on the R3 value, that is connected to the branching ratio, points to a Λ separation energy that is below 100 keV but definitely consistent with the value of 130 keV assumed since the 70s.
Asymptotic giant branch (AGB) stars are responsible for the production of the main component of the solar s-process distribution. Despite enormous progress in the theoretical modeling of these objects over the last few decades, many uncertainties remain. The still-unknown mechanism leading to the production of 13C neutron source is one example. The nucleosynthetic signature of AGB stars can be examined in a number of stellar sources, from spectroscopic observations of intrinsic and extrinsic stars to the heavy-element isotopic composition of presolar grains found in meteorites. The wealth of available observational data allows for constraining the processes occurring in AGB interiors. In this view, we discuss recent results from new AGB models including the effects of mixing triggered by magnetic fields, and show comparisons of the related s-process nucleosynthesis with available observations.
Lattice QCD and functional methods are making significant progress in constraining the QCD phase diagram. As an important milestone, the chiral phase transition with massless u, d-quarks at zero density is now understood to be of second order for all strange quark masses, and a smooth crossover as soon as mu,d, ≠ 0. Together with information on fluctuations and refined reweighted simulations, this bounds a possible critical point to be at µB/T ≲3. On the other hand, an approximately chiral-spin symmetric temperature window has been discovered above the chiral crossover, Tch<T ≳3Tch, with distinct correlator multiplet patterns and a pion spectral function suggesting resonance-like degrees of freedom, which dissolve graduallly with temperature.
In this work we study the 3+1-dimensional Nambu-Jona-Lasinio (NJL) model in the mean field-approximation. We carry out calculations using five different regularization schemes (two continuum and three lattice regularization schemes) with particular focus on inhomogeneous phases and condensates. The regularization schemes lead to drastically different inhomogeneous regions. We provide evidence that inhomogeneous condensates appear for all regularization schemes almost exclusively at values of the chemical potential and with wave numbers, which are of the order of or even larger than the corresponding regulators. This can be interpreted as indication that inhomogeneous phases in the 3+1-dimensional NJL model are rather artifacts of the regularization and not a consequence of the NJL Lagrangian and its symmetries.