Baryon Momentum Research Articles

Momentum Shell in Quarkyonic Matter from Explicit Duality: A Dual Model for Cold, Dense QCD.

We present a model of cold QCD matter that bridges nuclear and quark matter through the duality relation between quarks and baryons. The baryon number and energy densities are expressed as functionals of either the baryon momentum distribution, f_{B}, or the quark distribution, f_{Q}, which are subject to the constraints on fermions, 0≤f_{B,Q}≤1. The theory is ideal in the sense that the confinement of quarks into baryons is reflected in the duality relation between f_{Q} and f_{B}, while other possible interactions among quarks and baryons are all neglected. The variational problem with the duality constraints is formulated and we explicitly construct analytic solutions, finding two distinct regimes: a nuclear matter regime at low density and a quarkyonic regime at high density. In the quarkyonic regime, baryons underoccupy states at low momenta but form a momentum shell with f_{B}=1 on top of a quark Fermi sea. Such a theory describes a rapid transition from a soft nuclear equation of state to a stiff quarkyonic equation of state. At this transition, there is a rapid increase in the pressure.

Global Entropy Solutions and Newtonian Limit for the Relativistic Euler Equations

We analyze the relativistic Euler equations of conservation laws of baryon number and momentum with a general pressure law. The existence of global-in-time bounded entropy solutions for the system is established by developing a compensated compactness framework. The proof relies on a careful analysis of the entropy and entropy-flux functions, which are represented by the fundamental solutions of the entropy and entropy-flux equations for the relativistic Euler equations. Based on a careful entropy analysis, we establish the compactness framework for sequences of both exact solutions and approximate solutions of the relativistic Euler equations. Then we construct approximate solutions via the vanishing viscosity method and employ our compactness framework to deduce the global-in-time existence of entropy solutions. The compactness of the solution operator is also established. Finally, we apply our techniques to establish the convergence of the Newtonian limit from the entropy solutions of the relativistic Euler equations to the classical Euler equations.

The Atacama Cosmology Telescope: Probing the baryon content of SDSS DR15 galaxies with the thermal and kinematic Sunyaev-Zel’dovich effects

We present measurements of the average thermal Sunyaev Zel’dovich (tSZ) effect from optically selected galaxy groups and clusters at high signal-to-noise (up to 12σ) and estimate their baryon content within a 2.1′ radius aperture. Sources from the Sloan Digital Sky Survey Baryon Oscillation Spectroscopic Survey DR15 catalog overlap with 3,700 sq deg of sky observed by the Atacama Cosmology Telescope (ACT) from 2008 to 2018 at 150 and 98 GHz (ACT DR5), and 2,089 sq deg of internal linear combination component-separated maps combining ACT and Planck data (ACT DR4). The corresponding optical depths τ¯, which depend on the baryon content of the halos, are estimated using results from cosmological hydrodynamic simulations assuming an active galactic nuclei feedback radiative cooling model. We estimate the mean mass of the halos in multiple luminosity bins, and compare the tSZ-based τ¯ estimates to theoretical predictions of the baryon content for a Navarro-Frenk-White profile. We do the same for τ¯ estimates extracted from fits to pairwise baryon momentum measurements of the kinematic Sunyaev-Zel’dovich effect (kSZ) for the same dataset obtained in a companion paper. We find that the τ¯ estimates from the tSZ measurements in this work and the kSZ measurements in the companion paper agree within 1σ for two out of the three disjoint luminosity bins studied, while they differ by 2–3σ in the highest luminosity bin. The optical depth estimates account for one-third to all of the theoretically predicted baryon content in the halos across luminosity bins. Potential systematic uncertainties are discussed. The tSZ and kSZ measurements provide a step toward empirical Compton-y¯−τ¯ relationships to provide new tests of cluster formation and evolution models.2 MoreReceived 4 February 2021Accepted 27 May 2021DOI:https://doi.org/10.1103/PhysRevD.104.043503© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic microwave backgroundCosmological parametersCosmologyLarge scale structure of the UniverseGravitation, Cosmology & Astrophysics

Dynamic Equilibrium Sets of the Atomic Content of Galaxies across Cosmic Time

Abstract We analyze 88 independent, high-resolution, cosmological zoomed-in simulations of disk galaxies in the NIHAO simulations suite to explore the connection between the atomic gas fraction and angular momentum (AM) of baryons throughout cosmic time. The study is motivated by the analytical model of Obreschkow et al., which predicts a relation between the atomic gas fraction f atm and the integrated atomic stability parameter , where M and j are the mass and specific AM of the galaxy (stars+cold gas) and σ is the velocity dispersion of the atomic gas. We show that the simulated galaxies follow this relation from their formation (z ≃ 4) to the present within ∼0.5 dex. To explain this behavior, we explore the evolution of the local Toomre stability and find that 90%–100% of the atomic gas in all simulated galaxies is stable at any time. In other words, throughout the entire epoch of peak star formation until today, the timescale for accretion is longer than the timescale to reach equilibrium, thus resulting in a quasi-static equilibrium of atomic gas at any time. Hence, the evolution of f atm depends on the complex hierarchical growth history primarily via the evolution of q. An exception is galaxies subject to strong environmental effects.

Detection of the pairwise kinematic Sunyaev-Zel'dovich effect with BOSS DR11 and the Atacama Cosmology Telescope

We present a new measurement of the kinematic Sunyaev-Zel'dovich effect using data from the Atacama Cosmology Telescope (ACT) and the Baryon Oscillation Spectroscopic Survey (BOSS). Using 600 square degrees of overlapping sky area, we evaluate the mean pairwise baryon momentum associated with the positions of 50,000 bright galaxies in the BOSS DR11 Large Scale Structure catalog. A non-zero signal arises from the large-scale motions of halos containing the sample galaxies. The data fits an analytical signal model well, with the optical depth to microwave photon scattering as a free parameter determining the overall signal amplitude. We estimate the covariance matrix of the mean pairwise momentum as a function of galaxy separation, using microwave sky simulations, jackknife evaluation, and bootstrap estimates. The most conservative simulation-based errors give signal-to-noise estimates between 3.6 and 4.1 for varying galaxy luminosity cuts. We discuss how the other error determinations can lead to higher signal-to-noise values, and consider the impact of several possible systematic errors. Estimates of the optical depth from the average thermal Sunyaev-Zel'dovich signal at the sample galaxy positions are broadly consistent with those obtained from the mean pairwise momentum signal.

The Tully–Fisher and mass–size relations from halo abundance matching

The Tully-Fisher relation (TFR) expresses the connection between rotating galaxies and the dark matter haloes they inhabit, and therefore contains a wealth of information about galaxy formation. We construct a general framework to investigate whether models based on halo abundance matching are able to reproduce the observed stellar mass TFR and mass-size relation (MSR), and use the data to constrain galaxy formation parameters. Our model tests a range of plausible scenarios, differing in the response of haloes to disc formation, the relative angular momentum of baryons and dark matter, the impact of selection effects, and the abundance matching parameters. We show that agreement with the observed TFR puts an upper limit on the scatter between galaxy and halo properties, requires weak or reversed halo contraction, and favours selection effects that preferentially eliminate fast-rotating galaxies. The MSR constrains the ratio of the disc to halo specific angular momentum to be approximately in the range 0.6-1.2. We identify and quantify two problems that models of this nature face. (1) They predict too large an intrinsic scatter for the MSR, and (2) they predict too strong an anticorrelation between the TFR and MSR residuals. We argue that resolving these problems requires introducing a correlation between stellar surface density and enclosed dark matter mass. Finally, we explore the expected difference between the TFRs of central and satellite galaxies, finding that in the favoured models this difference should be detectable in a sample of ~700 galaxies.

The origin of discs and spheroids in simulated galaxies

The major morphological features of a galaxy are thought to be determined by the assembly history and net spin of its surrounding dark halo. In the simplest scenario, disc galaxies form predominantly in haloes with high angular momentum and quiet recent assembly history, whereas spheroids are the slowly rotating remnants of repeated merging events. We explore these assumptions using 100 systems with halo masses similar to that of the Milky Way, identified in a series of cosmological gasdynamical simulations: the Galaxies–Intergalactic Medium Interaction Calculation (gimic). At z= 0, the simulated galaxies exhibit a wide variety of morphologies, from dispersion-dominated spheroids to pure disc galaxies. Surprisingly, these morphological features are very poorly correlated with their halo properties: discs form in haloes with high and low net spin, and mergers play a negligible role in the formation of spheroids, whose stars form primarily in situ. With hindsight, this weak correlation between halo and galaxy properties is unsurprising given that a minority of the available baryons (∼40 per cent) end up in galaxies. More important to morphology is the coherent alignment of the angular momentum of baryons that accrete over time to form a galaxy. Spheroids tend to form when the spin of newly accreted gas is misaligned with that of the extant galaxy, leading to the episodic formation of stars with different kinematics that cancel out the net rotation of the system. Discs, on the other hand, form out of gas that flows in with similar angular momentum to that of earlier accreted material. Gas accretion from a hot corona thus favours disc formation, whereas gas that flows ‘cold’, often along separate, misaligned filaments, favours the formation of spheroids. In this scenario, many spheroids consist of the superposition of stellar components with distinct kinematics, age and metallicity, an arrangement that might survive to the present day given the paucity of major mergers. Since angular momentum is acquired largely at turnaround, morphology depends on the early interplay between the tidal field and the shape of the material destined to form a galaxy.

Do mergers spin-up dark matter haloes?

Abstract We use a large cosmological N-body simulation to study the origin of possible correlations between the merging history and spin of cold dark matter haloes. In particular, we examine claims that remnants of major mergers tend to have higher-than-average spins, and find that the effect is driven largely by unrelaxed systems: equilibrium dark matter haloes show no significant correlation between spin and merging history. Out-of-equilibrium haloes have, on average, higher spin than relaxed systems, suggesting that the virialization process leads to a net decrease in the value of the spin parameter. We find that this decrease is due to the internal redistribution of mass and angular momentum that occurs during virialization. This process is especially efficient during major mergers, when high angular momentum material is pushed beyond the virial radius of the remnant. Because such redistribution likely affects the angular momentum of baryons and dark matter unevenly, our findings question the common practice of identifying the specific angular momentum content of a halo with that of its embedded luminous component. Further work is needed to elucidate the true relation between the angular momentum content of baryons and dark matter in galaxy systems assembled hierarchically.

Fast and slow rotators: the build-up of the red sequence

AbstractUsing the unique dataset obtained within the course of theSAURONproject, a radically new view of the structure, dynamics and stellar populations of early-type galaxies has emerged. We show that galaxies come in two broad flavours (slow and fast rotators), depending on whether or not they exhibit clear large-scale rotation, as indicated via a robust measure of the specific angular momentum of baryons. This property is also linked with other physical characteristics of early-type galaxies, such as: the presence of dynamically decoupled cores, orbital structure and anisotropy, stellar populations and dark matter content. I here report on the observed link between this baryonic angular momentum and a mass sequence, and how this uniquely relates to the building of the red sequence via dissipative/dissipationless mergers and secular evolution.

Regularities in hadron systematics, Regge trajectories and a string quark model

An empirical principle for the construction of a linear relationship between the total angular momentum and squared-mass of baryons is proposed. In order to examine linearity of the trajectories, a rigorous least-squares regression analysis was performed. Unlike the standard Regge-Chew-Frautschi approach, the constructed trajectories do not have non-linear behaviour. A similar regularity may exist for lowest-mass mesons. The linear baryonic trajectories are well described by a semi-classical picture based on a spinning relativistic string with tension. The obtained numerical solution of this model was used to extract the (di)quark masses.

Elementary hadronic interactions at the CERN SPS

New data from the NA49 experiment at the CERN SPS concerning hadron+proton and hadron+nucleus interactions are discussed and compared to nucleus+nucleus collisions. Detailed information on baryonic momentum distributions and nuclear enhancement factors for kaons and cascade baryons are extracted.

An interacting parton model for quark and anti-quark distributions in the baryon

In this paper we study a 1+1 dimensional relativistic parton model for the structure of baryons. The quarks and anti-quarks interact through a linear potential. We obtain an analytic formula for the isospin averaged valence quark distribution in the chiral and large N c limits. The leading 1 N c and non-zero current quark mass corrections are estimated. Then we extend this model to include `sea' and anti-quarks. We find that the anti-quark content is small at a low value of Q 2. Using these distributions as initial conditions for Q 2 evolution, we compare with experimental measurements of the structure function xF 3( x, Q 2) and find reasonable agreement. The only parameters we can adjust are the fraction of baryon momentum carried by valence quarks and the initial scale Q 0 2.

A model of interacting partons for hadronic structure functions

We present a model for the structure of baryons in which the valence partons interact through a linear potential. This model can be derived from QCD in the approximation where transverse momenta are ignored. We compare the baryon structure function predicted by our model with those extracted from global fits to Deep Inelastic Scattering data. The only parameter we can adjust is the fraction of baryon momentum carried by valence partons. Our predictions agree well with data except for small values of the Bjorken scaling variable.

Baryon production in the string fragmentation picture

An improved version of the “pop-corn” model for baryon production in quark and gluon jets is presented. With a reduced number of parameters the model reproduces well both production rates for different baryon species and baryon momentum distributions. Predictions are presented for a set of baryon-antibaryon correlations.

Multiple-collision model for high-energy nucleus-nucleus collisions.

We use a Glauber multiple-collision model to examine the dynamics of nucleus-nucleus collisions. The model introduces a stopping law which describes how a baryon loses energy in a basic baryon-baryon collision and a particle production law which relates the distribution of produced particles to the baryon momentum loss. The model gives results which compare well with the recent WA80 experimental data of $^{16}\mathrm{O}$ on various targets at 60 and 200 GeV per projectile nucleon and reveals a high degree of stopping in these high-energy nuclear collisions.

Wave functions of octet baryons

The leading twist baryonic wave function ϕ(x1,x2,x3) describes the distribution of three quarks inside the baryon in the longitudinal momentum fractions 0≦xi≦1 atPz→∞. The properties of these wave functions for the baryons entering the nucleon octet are investigated using the QCD sum rules. The high asymmetry in the distribution of the baryon momentum between three quarks is found for all members of the octet. The properties of theSU(3)-symmetry breaking effects in baryonic wave functions are elucidated. The model wave functions are proposed which fulfil the sum rules requirements. The asymptotic behaviour of various baryon form factors (which can be measured ine+e−→\(\bar {\rm B}\)B) is found out.

The inclusive production of kaons in relativistic nucleus-nucleus collisions based on transport theory

We assume that in relativistic heavy-ion reactions positive kaons (K +) are produced in sequences of independent baryon-baryon collisions. The basic inputs into our calculation of the K + inclusive differential cross section thus are the baryon momentum distributions after a number n of collisions. These functions are, to a very good approximation, determined by their first and second moments which in turn are calculated by use of a transport theoretical approach. We compare our results with experimental data obtained from the reaction Ne + NaF at 2.1 GeV nucleon . This comparison is first made under the assumption that the kaons, once produced, escape from the participant region without further interactions. In this case, the observed K + total production cross section is reproduced quite well, but the corresponding differential cross sections are not. The inclusion of the K + elastic scattering on the surrounding baryons leads to a much better agreement with the experimental data. We also calculate the K + total production rate as a function of the bombarding energy per nucleon. At all energies, the number of kaons produced by multiply scattered baryons is seen to exceed by far that obtained from nucleons which scatter for the first time. The K + total production cross section remains sizeable in our approach even far below the threshold energy. For a very heavy system like Pb on Pb we estimate a cross section of 10 mb even 800 MeV below threshold.

Baryon momentum effects in resonance dominated strangeness changing nuclear reactions

Explicit inclusion of the baryon momentum operator in the input t K −N → Λπ amplitude in impulse approximation calculations of (K −, π −) reactions results in significant (angular dependent) reductions compared to earlier results. Agreement between theory and experiment is improved.

A study of the Λπ−pd final state produced in K−-meson interactions at rest in helium

Results are presented of a bubble chamber study of K−-meson interactions at rest in helium leading to the Λπ−pd final state. It is found that (75±1)% of this final state results from the two-step mechanism of internal Σ-Λ conversion via processes such as\(K^ - {\mathcal{N}} \to \Sigma \pi \) followed by\(\Sigma {\mathcal{N}} \to \Lambda {\mathcal{N}}\). The experimental results are compared to the predictions of a double-impulse model, in which a contribution has been included from a Σ-Λ conversion process involving two nucleons in order to reproduce the baryon momentum spectra. The model is capable of explaining the features of the invariant-mass distributions of the finalstate particles without invoking resonance production.