Dense Baryonic Matter Research Articles

Stability of evolving cluster of stars and exotic matter

AbstractThis paper discusses the phenomenon of evolving spherically symmetric cluster of stars in the presence of an exotic matter. To discuss evolutionary mechanism, we use the Starobinsky model of f(R) gravity as exotic matter and the structure scalars as evolutional parameters. We study various evolution modes such as isotropic pressure, quasi-homologous evolution, density homogeneity, and geodesic nature. The stability of homogeneous density of baryonic and non-baryonic matter is discussed using dissipation, tidal forces, anisotropic pressures, expansion and shear-effects. It is observed that the dark matter has remarkable impact on the evolutionary changes. Also, it is shown that the dissipation factor produces density inhomogeneity in expanding clusters with shear effects. We observe that high curvature geometry enhances quasi-homologous evolution in the presence of shear. We use star Her X-1 as test star to discuss physical behavior of Starobinsky model. It is found that the density of dark matter overcomes the density of matter for large values of dark matter parameter n.

Parity Doubling in Dense Baryonic Matter as an Emergent Phenomenon and Pseudo-Conformal Phase

The star matter composed of nucleons deep inside compact stars, such as neutron stars, is believed to be very dense, such that various types of new concepts and physical phenomena are naturally expected due to the nontrivial strong correlations between hadrons. The possibility of revealing the hidden scale symmetry in dense baryonic matter has been discussed recently, to uncover the pseudo-conformal phase in dense star matter. In the pseudo-conformal phase, the trace of the energy–momentum tensor becomes density-independent, and the speed of sound approaches the conformal velocity in scale symmetric matter. Interestingly, it is also observed that the effective nucleon mass becomes a density-independent finite quantity, which can be identified as the chiral invariant mass of the parity doublet model, indicating that the parity doubling is an emergent phenomenon. In this paper, we will discuss how parity-doubling symmetry emerges inside the core of a compact star as a consequence of the interplays between ω vector mesons and nucleons (or dilaton, χ, equivalently) and between the chiral symmetry and the scale symmetry.

Probing Dark Sectors with Neutron Stars

Tensions in the measurements of neutron and kaon weak decays, such as of the neutron lifetime, may speak to the existence of new particles and dynamics not present in the Standard Model (SM). In scenarios with dark sectors, particles that couple feebly to those of the SM appear. We offer a focused overview of such possibilities and describe how the observations of neutron stars, which probe either their structure or dynamics, limit them. In realizing these constraints, we highlight how the assessment of particle processes within dense baryonic matter impacts the emerging picture—and we emphasize both the flavor structure of the constraints and their broader connections to cogenesis models of dark matter and baryogenesis.

Constraints on Phase Transitions in Neutron Star Matter

Recent inference results of the sound velocity in the cores of neutron stars are summarized. Implications for the equation of state and the phase structure of highly compressed baryonic matter are discussed. In view of the strong constraints imposed by the heaviest known pulsars, the equation of state must be very stiff in order to ensure the stability of these extreme objects. This required stiffness limits the possible appearance of phase transitions in neutron star cores. For example, a Bayes factor analysis quantifies strong evidence for squared sound velocities cs2>0.1 in the cores of 2.1 solar-mass and lighter neutron stars. Only weak first-order phase transitions with a small phase coexistence density range Δρ/ρ<0.2 (at the 68% level) in a Maxwell construction still turn out to be possible within neutron stars. The central baryon densities in even the heaviest neutron stars do not exceed five times the density of normal nuclear matter. In view of these data-based constraints, much discussed issues such as the quest for a phase transition towards restored chiral symmetry and the active degrees of freedom in cold and dense baryonic matter, are reexamined.

Simulating collectivity in dense baryon matter with multiple fluids

A novel three-fluid dynamical model for simulations of heavy-ion collisions at RHIC Beam Energy Scan programme, called MUFFIN, has been developed. The novelty consists of modular inclusion of the Equation of State, use of hyperbolic coordinates that allow to simulate higher collision energies, and fluctuating initial conditions. The model reproduces rapidity and pt spectra of collisions from √SNN = 7.7 to 62.4 GeV. Ideal fluid is assumed, and the elliptic flow is over-predicted, particularly at lower collision energies.

Status of the CBM experiment at FAIR

The CBM experiment will explore dense baryonic matter at moderate temperatures with rare observables that could not be investigated so far for this type of matter. Experiments will be performed at the future FAIR facility with beams from SIS 100 exploring a range in √SNN from 2.3 - 5.3 GeV at interaction rates up to 10 MHz. Within the first few years energy scans in particular for dilepton and fluctuation observables are planned in order to search for the predicted first order phase transition and critical point. The status of the experimental preparations is reviewed in this contribution.

Status of the development of the RICH detector for CBM including a mRICH prototype in mCBM

The Compressed Baryonic Matter (CBM) experiment is being built at the future Facility for Antiproton and Ion Research (FAIR) next to GSI, Darmstadt, Germany. A RICH detector will provide clean and efficient electron identification in order to access di-electrons emitted from dense baryonic matter, one of the key measurements of CBM. The CBM RICH recently passed the threshold to construction with first mass production of part of the electronics. The readout electronics was developed together with the HADES experiment and is successfully operated there in the upgraded RICH detector which also makes use of approximately half of the H12700 MAPMTs of CBM. The readout electronics is also tested in a dedicated “mini-RICH” detector in the “mini-CBM” setup with prototypes of all subdetectors, however with an implementation of the full functionality of the future free-streaming readout. Besides finalizing the RICH readout, work is ongoing on full size prototypes of the RICH mirror mechanics and the photocamera including a full system test of the cooling concept. In this report, a brief update on the various developments and the status of the CBM RICH detector is given.

Observing gravitational redshift with X-ray emission in galaxy clusters withAthenaX-IFU

Context.The Doppler shift predicted by general relativity for light escaping a gravitational potential has been observed on Earth as well as in the direction of various stars and galaxy clusters at optical wavelengths.Aims.Observing the gravitational redshift in the X-ray band within galaxy clusters could provide information on their properties and, in particular, their gravitational potential. We present a feasibility study of such a measurement, using the capabilities of the next-generation European X-ray observatoryAthena.Methods.We used a simple generalized Navarro–Frenk–White potential model along with aβ-model for the density of baryonic matter, which sets the emission to provide an estimation of the observed redshift in the simplest of cases. We generated mock observations with theAthenaX-ray Integral Field Unit (X-IFU) for a nearby massive cluster, while seeking to recover the gravitational redshift along with other properties of the toy model cluster.Results.We investigated the observability of the gravitational redshift in an idealized test case of a nearby massive cluster with theAthenaX-IFU instrument, as well as its use in probing the properties of the potential well. We were also able to constrain the mass to a ∼20% level of precision and the cosmological redshift to less than ∼1%, within a simplified and idealized observational framework. More refined simulations accounting for further effects such as the internal gas motions and the actual shape of the potential well are required to fully investigate the feasibility of measuring the gravitational redshift for a single target or statistically over a sample of galaxy clusters.

Dark Universe phenomenology from Yukawa potential?

We argue that the effect of cold dark matter in the cosmological setup can be explained by the coupling between the baryonic matter particles in terms of the long-range force having a graviton mass mg via the Yukawa gravitational potential. Such a quantum-corrected Yukawa-like gravitational potential is characterized by the coupling parameter α, the wavelength parameter λ, which is related to the graviton mass via mg=ħ/(λc), that determines the range of the force and, finally, a Planck length quantity l0 that makes the potential regular at the centre. The modified Friedmann equations are obtained using Verlinde’s entropic force interpretation of gravity based on the holographic scenario and the equipartition law of energy. The parameter α modifies the Newton’s constant as Geff=G(1+α). Interestingly, we find an equation that relates the dark matter density, dark energy density, and baryonic matter density. It is given by ΩD=2ΩBΩΛ(1+z)3. We argue that dark matter is an apparent effect as no dark matter particle exists in this picture. Furthermore, the dark energy is also related to graviton mass and α; in particular, we point out that the cosmological constant can be viewed as a self-interaction effect between gravitons. We further show a precise correspondence with Verlinde’s emergent gravity theory, and due to the long-range force, the theory can be viewed as a non-local gravity theory. To this end, we performed the phase space analyses and estimated λ≃103 [Mpc] and α≃0.04, respectively. Finally, from these values, for the graviton mass, we get mg≃10−68 kg, and cosmological constant Λ≃10−52m−2. Further, we argue how this theory reproduces the MOND phenomenology on galactic scales via the acceleration of Milgrom a0≃10−10m/s2.

Towards the understanding of the genuine three-body interaction for p–p–p and p–p–Lambda

Three-body nuclear forces play an important role in the structure of nuclei and hypernuclei and are also incorporated in models to describe the dynamics of dense baryonic matter, such as in neutron stars. So far, only indirect measurements anchored to the binding energies of nuclei can be used to constrain the three-nucleon force, and if hyperons are considered, the scarce data on hypernuclei impose only weak constraints on the three-body forces. In this work, we present the first direct measurement of the p–p–p and p–p–Lambda systems in terms of three-particle correlation functions carried out for pp collisions at sqrt{s} = 13 TeV. Three-particle cumulants are extracted from the correlation functions by applying the Kubo formalism, where the three-particle interaction contribution to these correlations can be isolated after subtracting the known two-body interaction terms. A negative cumulant is found for the p–p–p system, hinting to the presence of a residual three-body effect while for p–p–Lambda the cumulant is consistent with zero. This measurement demonstrates the accessibility of three-baryon correlations at the LHC.

Toward the System Size Dependence of Anisotropic Flow in Heavy-Ion Collisions at sNN= 2–5 GeV

The study of the high-density equation of state (EOS) and the search for a possible phase transition in dense baryonic matter is the main goal of beam energy scan programs with relativistic heavy ions at energies sNN= 2–5 GeV. The most stringent constraints currently available on the high-density EOS of symmetric nuclear matter come from the present measurements of directed (v1) and elliptic flow (v2) signals of protons in Au + Au collisions. In this energy range, the anisotropic flow is strongly affected by the presence of cold spectators due to the sizable passage time. The system size dependence of anisotropic flow may help to study the participant–spectator contribution and improve our knowledge of the EOS of symmetric nuclear matter. In this work, we discuss the layout of the upgraded BM@N experiment and the anticipated performance for differential anisotropic flow measurements of identified hadrons at Nuclotron energies: sNN= 2.3–3.5 GeV.

Quantum Modified Gravity at Low Energy in the Ricci Flow of Quantum Spacetime

Quantum treatment of physical reference frame leads to the Ricci flow of quantum spacetime, which is a quite rigid framework to quantum and renormalization effect of gravity. The theory has a low characteristic energy scale described by a unique constant: the critical density of the universe. At low energy long distance (cosmic or galactic) scale, the theory modifies Einstein's gravity which naturally gives rise to a cosmological constant as a counter term of the Ricci flow at leading order and an effective scale dependent Einstein-Hilbert action. In the weak and static gravity limit, the framework gives rise to a transition trend away from Newtonian gravity and similar to the MOdified Newtonian Dynamics (MOND) around the characteristic scale. When local curvature is large, Newtonian gravity is recovered. When local curvature is low enough to be comparable with the asymptotic background curvature corresponding to the characteristic energy scale, the transition trend produces the baryonic Tully-Fisher relation. For intermediate general curvature around the background curvature, the interpolating Lagrangian function yields a similar transition trend to the observed radial acceleration relation of galaxies. When the baryonic matter density is much lower than the critical density at the outskirt of a galaxy, there may be a universal "acceleration floor" corresponding to the acceleration expansion of the universe, which differs from MOND at its deep-MOND limit. The critical acceleration constant $a_0$ introduced in MOND is related to the low characteristic energy scale of the theory. The cosmological constant gives a universal leading order contribution to it and the flow effect gives the next order scale dependent contribution, which equivalently induces the "cold dark matter" to the theory. $a_0$ is consistent with galaxian data when the "dark matter" is about 5 times the baryonic matter.

Kaon-meson condensation and Δ resonance in hyperonic stellar matter within a relativistic mean-field model

We study the equation of state of dense baryon matter within the relativistic mean-field model, and we include ${\Delta}$(1232) isobars into IUFSU model with hyperons and consider the possibility of kaon meson condensation. We find that it is necessary to consider the $\Delta$ resonance state inside the massive neutron star. The critical density of Kaon mesons and hyperons is shifted to a higher density region, in this respect an early appearance of $\Delta$ resonances is crucial to guarantee the stability of the branch of hyperonized star with the difference of the coupling parameter $x_{\sigma \Delta}$ constrained based on the QCD rules in nuclear matter. The $\Delta$ resonance produces a softer equation of state in the low density region, which makes the tidal deformability and radius consistent with the observation of GW170817. As the addition of new degrees of freedom will lead to a softening of the equation of state, the ${\sigma}$-cut scheme, which states the decrease of neutron star mass can be lowered if one assumes a limited decrease of the ${\sigma}$-meson strength at ${\rho_B}$($\rho_B > \rho_0$), finally we get a maximum mass neutron star with $\Delta$ resonance heavier than 2$M_{\odot}$.

Implementation of the Event Metadata System for physics analysis in the NICA experiments

NICA (Nuclotron-based Ion Collider fAcility) is a new accelerator complex, which is under construction at the Joint Institute for Nuclear Research in Dubna to study properties of dense baryonic matter. The experiments of the NICA projects have already generated and obtained substantial volumes of event data, and it is expected that the overall number of stored events will increase from the current value of hundreds of millions to several billion events per year. The developed Event Metadata System is required to store and index experimental event records obtained at NICA facilities, allowing to quickly search for only necessary events based on various criteria for further processing and physics analyses. The main aim of the information system that is described is to speed up desired physics analyses and data quality checks. In addition, it allows reducing the load of the NICA computing infrastructure. The Event Metadata System, which is presented in the paper, is integrated with other experimental and software systems, in particular, NICA ROOT-based frameworks and implemented Condition Database. An access and management of the event metadata in the Event Catalogue being used to select only events for a particular physics analysis are provided via several interfaces, such as REST API, Web UI, and a dedicated C++/ROOT interface. The detailed architecture of the system and developed services including monitoring are also presented.

Upgrade of the BM@N detector for studies of heavy ion interactions

In the next years the Baryonic Matter at Nuclotron (BM@N) experiment at Joint Institute for Nuclear Research (JINR) will carry out the physics program with heavy ion beams with energies up to 3.9 AGeV and intensities up to 2 [Formula: see text] ions/s. The experiment is devoted to measure observables sensitive to the equation of state of dense baryonic matter. To meet this goal the existing BM@N set-up will be upgraded with fast hybrid tracking system, which includes beam tracking detectors, a large aperture silicon tracking system, gas electron multiplier stations and cathode strip chambers. The measurement of the event plane and centrality will be achieved with a forward hadron calorimeter and granular hodoscopes. The physics program and configuration of the upgraded BM@N set-up are presented.

Algebraic approach to a quarkyoniclike configuration and stable diquarks in dense matter

We study the color-spin interaction energy of a quark, a diquark and a baryon with their surrounding baryons and/or quark matter. This is accomplished by classifying all possible flavor and spin states of the resulting multiquark configuration in both the flavor SU(2) and SU(3) symmetric cases. We find that while the baryon has the lowest interaction energy when there is only a single surrounding baryon, the quark has the lowest interaction energy when the surrounding has more than three baryons or becomes a quark gas. As the short range nucleon-nucleon interactions are dominated by the color-spin interactions, our finding suggests that the baryon modes near other baryons are suppressed due to larger repulsive energy compared to that of a quark and thus provides a quark model basis for the quarkyoniclike phase in dense matter. At the same time, when the internal interactions are taken into account, and the matter density is high so that the color-spin interaction becomes the dominant interaction, the diquark becomes the lowest energy configuration and will thus appear in both the dense baryonic and/or quark matter.

Exploring terra incognita in the phase diagram of strongly interacting matter—experiments at FAIR and NICA

The fundamental properties of dense nuclear matter, as it exists in the core of massive stellar objects, are still largely unknown. The investigation of the high-density equation of state (EOS), which determines mass and radii of neutron stars and the dynamics of neutron star mergers, is in the focus of astronomical observations and of laboratory experiments with heavy-ion collisions. Moreover, the microscopic degrees-of-freedom of strongly interacting matter at high baryon densities are also unknown. While Quantum-Chromo-Dynamics (QCD) calculations on the lattice find a smooth chiral crossover between hadronic matter and the quark-gluon plasma for high temperatures at zero baryon chemical potential, effective models predict a 1st order chiral transition with a critical endpoint for matter at large baryon chemical potentials. Up to date, experimental data both on the high-density EOS and on a possible phase transition in dense baryonic matter are very scarce. In order to explore this terra incognita, dedicated experimental programs are planned at future heavy-ion research centres: the CBM experiment at FAIR, and the MPD and BM@N experiments at NICA. The research programs and the layout of these experiments will be presented. The future results of these laboratory experiments will complement astronomical observations concerning the EOS, and, in addition, will shed light on the microscopic degrees of freedom of QCD matter at neutron star core densities.

Eigenmode analysis of perturbations in the primordial medium at and before recombination

Context. Anisotropies of the cosmic microwave background are thought to be due to perturbations of the primordial medium, which, post recombination, lead to the formation of galaxy clusters and galaxies Aims. The perturbation wave modes of the primordial medium at and before recombination, consisting of a fully ionised baryonic plasma, a strong black body radiation field, and cold dark matter, are analysed. Methods. We use the linear perturbation theory of the relativistic equations of motion, utilising a strict thermodynamic equilibrium model that relates the radiation energy density to the plasma temperature. Results. It is shown that a wave mode corresponding to the postulated baryon acoustic waves exists with a phase velocity close to the speed of light, but the participation of the dark matter in this mode is very small. Instead, the dark matter has its own dominant mode in the form of gravitational collapse, with very little participation by the baryonic plasma. Conclusions. In view of this very weak coupling between baryons and dark matter, the initial conditions postulated for computer simulations of large-scale structure and galaxy formation – which assume that after recombination, when galaxy formation is getting underway, baryon and dark matter density perturbations are spatially coincident and are equal in terms of fractional amplitude – may be unjustified. Additionally, the possible non-coincidence of baryon and dark matter perturbations at the last scattering surface has implications for the analysis of cosmic microwave background anisotropies.

Building a realistic neutron star from holography

We employ the recently improved description of dense baryonic matter within the Witten-Sakai-Sugimoto model to construct neutron stars. In contrast to previous holographic approaches, the presence of an isospin asymmetry allows us to implement beta equilibrium and electric charge neutrality. As a consequence, we are able to model the crust of the star within the same formalism and compute the location of the crust-core transition dynamically. After showing that a simple pointlike approximation for the baryons fails to satisfy astrophysical constraints, we demonstrate that our improved description does account for neutron stars that meet the current experimental constraints for mass, radius, and tidal deformability. However, we also point out tensions in the parameter fit and large-$N_c$ artifacts and discuss how to potentially resolve them in the future.

Baryogenesis from ultra-slow-roll inflation

The ultra-slow-roll (USR) inflation represents a class of single-field models with sharp deceleration of the rolling dynamics on small scales, leading to a significantly enhanced power spectrum of the curvature perturbations and primordial black hole (PBH) formation. Such a sharp transition of the inflationary background can trigger the coherent motion of scalar condensates with effective potentials governed by the rolling rate of the inflaton field. We show that a scalar condensate carrying (a combination of) baryon or lepton number can achieve successful baryogenesis through the Affleck-Dine mechanism from unconventional initial conditions excited by the USR transition. Viable parameter space for creating the correct baryon asymmetry of the Universe naturally incorporates the specific limit for PBHs to contribute significantly to dark matter, shedding light on the cosmic coincidence problem between the baryon and dark matter densities today.