Low Momentum Research Articles

Relativistic Low Angular Momentum Advective Flows Onto Black Hole and Associated Observational Signatures

Abstract We present simulation results examining the presence and behavior of standing shocks in zero-energy low angular momentum advective accretion flows and explore their (in)stability properties, taking into account various values of specific angular momentum, λ 0. Within the range 10−50R g (where R g denotes the Schwarzschild radius), shocks are discernible for λ 0 ≥ 1.75. In the special relativistic hydrodynamic simulation when λ 0 = 1.80, we find the merger of two shocks resulted in a dramatic increase in luminosity. We present the impact of external and internal flow collisions from the funnel region on luminosity. Notably, oscillatory behavior characterizes shocks within 1.70 ≤ λ 0 ≤ 1.80. Using free–free emission as a proxy for analysis, we show that the luminosity oscillations between frequencies of 0.1−10 Hz for λ 0 range as 1.7 ≤ λ 0 ≤ 1.80. These findings offer insights into quasi-periodic oscillation emissions from certain black hole X-ray binaries, exemplified by GX 339-4. Furthermore, for the supermassive black hole at the Milky Way's center, Sgr A*, oscillation frequencies between 10−6 and 10−5 Hz were observed. This frequency range, translating to one cycle every few days, aligns with observational data from X-ray telescopes such as Chandra, Swift, and XMM-Newton.

Strongly Magnetized Accretion with Low Angular Momentum Produces a Weak Jet

Abstract We study the spherical accretion of magnetized plasma with low angular momentum onto a supermassive black hole, utilizing global general relativistic magnetohydrodynamic simulations. Black hole-driven feedback in the form of magnetic eruptions and jets triggers magnetized turbulence in the surrounding medium. We find that when the Bondi radius exceeds a certain value relative to the black hole’s gravitational radius, this turbulence restricts the subsequent inflow of magnetic flux, strongly suppressing the strength of the jet. Consequently, magnetically arrested disks and powerful jets are not a generic outcome of the accretion of magnetized plasma, even if there is an abundance of magnetic flux available in the system. However, if there is significant angular momentum in the inflowing gas, the eruption-driven turbulence is suppressed (sheared out), allowing for the presence of a powerful jet. Both the initially rotating and nonrotating flows go through periods of low and high gas angular momentum, showing that the angular momentum content of the inflowing gas is not just a feature of the ambient medium, but is strongly modified by the eruption and jet-driven black hole feedback. In the lower-angular-momentum states, our results predict that there should be dynamically strong magnetic fields on horizon scales, but no powerful jet; this state may be consistent with Sgr A* in the Galactic center.

Effects of the Arrangement and Height Variability of Roughness Obstacles on the Structure and Intensity of Tornado-Like Vortices

Abstract To reveal the effects of surface roughness on the structure and intensity of tornadic flow, we conducted numerical simulations, in which the horizontal density and height of obstacles were controlled independently. Simulation with a low external swirl ratio produced a tornado-like vortex with a narrow core radius. For this low-swirl vortex, when the horizontal density of obstacles was varied while the obstacle height was maintained, the lowest value of maximum tangential wind speed was achieved at a moderate horizontal density; a greater horizontal density led to an increase in the maximum tangential wind speed. By contrast, an increase in obstacle height always resulted in a lower maximum tangential wind speed. The mechanisms underlying such results were considered from the viewpoint of angular momentum depletion. Tall and moderately densely distributed obstacles generated a large amount of depleted angular momentum flux, which thickened the low angular momentum layer inside the corner flow region and the core region of the vortices. As a result, the maximum tangential wind speed decreased in association with the decrease in the radial gradient of angular momentum. Additional simulations were then run with a higher external swirl ratio, which resulted in vortices with a wider core radius. Even the roughness distribution with the highest and moderately dense obstacles did not notably reduce the intensity of the higher-swirl vortex, while the flow structure changed in larger scale. The results of this study suggest that urban roughness with a moderate density of tall buildings may weaken low swirl, thin tornadoes but does not preclude high swirl, wide tornadoes, at least through vortex-scale processes. Significance Statement In this study, we investigate the frictional effects of surface roughness on the intensity and the structure of tornado-like vortices in vortex-scale processes from computational fluid simulations that directly resolve the roughness obstacles. We show that the influence of roughness is maximized when tall obstacles are distributed at a moderate density, such as in urban terrain. This is considered to be because the intensity of the tornado-like vortices is dominated by the angular momentum stratification inside the central region of the vortices, which is strongly influenced by the surface flow at a depth of a similar length scale. This study indicates that small-scale topography, which is not always fully resolved in meteorological models, has a nonnegligible influence on tornado intensity.

J/ψ photoproduction and polarization in peripheral Pb−Pb collisions with ALICE

Ultrarelativistic heavy-ion collisions generate a powerful electromagnetic field that produces photonuclear reactions. These processes have been extensively studied in ultraperipheral collisions, in which the impact parameter is larger than twice the nuclear radius. Recently, coherent photoproduction of J/ψ has been observed in nucleus–nucleus (A–A) collisions with nuclear overlap, based on the measurement of an excess of production with respect to hadron-production expectations in the very low transverse momentum (pT). Such quarkonium measurements provide valuable information about the nuclear gluon distribution at low Bjorken x and high energy. In addition, they can constrain the theory describing photon-induced reactions in A–A collisions with nuclear overlap, including possible interactions of the measured probes with the formed and fast expanding Quark-Gluon Plasma. In order to confirm the photoproduction origin of the very low pT J/ψ yield excess, polarization measurements represent a suitable observable. It is expected that the produced quarkonium inherits the polarization of the incoming photon because of the s-channel helicity conservation. ALICE can measure inclusive and exclusive quarkonium production down to pT = 0, at forward rapidity (2.5 < y < 4) and midrapidity (|y| < 0.9). In this contribution, new preliminary measurement of the y-differential cross section and the first new polarization analysis at the LHC of coherently photoproduced J/ψ in peripheral Pb–Pb collisions will be presented. These measurements are conducted at forward rapidity in the dimuon decay channel. These results will be discussed together with the recent results on coherent photoproduction as a function of centrality at both mid and forward rapidities. Comparison with models will be shown whenever available.

First measurement of heavy flavour femtoscopy in Au+Au collisions at √sNN = 200 GeV by STAR

In the very beginning stages of heavy-ion collisions, hard partonic scatterings yield heavy quarks, which go through the entire Quark-Gluon Plasma medium evolution. Femtoscopic correlation is characterized as a two particle correlation at low relative momentum that depends on the size of the region from which the correlated particles are emitted and on the final-state interaction. Such correlations between identifiable charged hadrons and charmed mesons could provide insights into their interactions with the medium and charm quarks in the hadronic phase. We describe the first femtoscopic correlation measurements made by the STAR experiment between D0/D¯0 - π± pairs at mid-rapidity in Au+Au collisions at √sNN The discussion of the physics consequences involves a comparison to theory calculations.

Numerical Turbulence Modeling in a Transonic Boundary-Layer Ingestion Intake

The boundary–layer ingestion (BLI) engine concept is a possible solution to improve aircraft efficiency for the next decades. This concept enables an improvement in engine efficiency due to the lower momentum flow ingested at the air intake. In addition, the weight and drag reduction contributes to the overall improvement of aircraft performance. However, previous studies have shown that the efficiency benefit of a BLI engine is very sensitive to flow distortion and pressure losses. The intake curvature causes complex secondary flows that lead to total pressure distortions and swirl velocities at the engine face. The intent of this paper is to assess the accuracy of different turbulence models, Reynolds-averaged Navier–Stokes and zonal detached eddy simulation, to simulate the complex physical phenomena, such as flow recirculation, vortices, and secondary flows, associated with a BLI intake. The results are compared to experimental data obtained during the project, the objective of which is to study the BLI technology for civil aircraft applications.

Absorption-Emission Codes for Atomic and Molecular Quantum Information Platforms.

Diatomic molecular codes [V. V. Albert, J. P. Covey, and J. Preskill, Robust encoding of a qubit in a molecule, Phys. Rev. X 10, 031050 (2020).PRXHAE2160-330810.1103/PhysRevX.10.031050] are designed to encode quantum information in the orientation of a diatomic molecule, allowing error correction from small torques and changes in angular momentum. Here, we directly study noise native to atomic and molecular platforms-spontaneous emission, stray electromagnetic fields, and Raman scattering-and show that diatomic molecular codes fail against this noise. We derive simple conditions that are sufficient for codes to protect against such noise. We also identify existing and develop new absorption-emission (Æ) codes that are more practical than molecular codes, require lower average momentum, can directly protect against photonic processes up to arbitrary order, and are applicable to a broader set of atomic and molecular systems.

A Systematic Survey of Moon-forming Giant Impacts. II. Rotating Bodies

In the leading theory of lunar formation, known as the giant impact hypothesis, a collision between two planet-sized objects resulted in a young Earth surrounded by a circumplanetary debris disk from which the Moon later accreted. The range of giant impacts that could conceivably explain the Earth–Moon system is limited by the set of known physical and geochemical constraints. However, while several distinct Moon-forming impact scenarios have been proposed—from small, high-velocity impactors to low-velocity mergers between equal-mass objects—none of these scenarios have been successful at explaining the full set of known constraints, especially without invoking one or more controversial post-impact processes. Allowing for pre-impact rotation of the colliding bodies has been suggested as an avenue that may produce more promising collision outcomes. However, to date, only limited studies of pre-impact rotation have been conducted. Therefore, in this second paper of the series, we focus on pairwise impacts between rotating bodies. Using nonrotating collisions as a baseline, we systematically study the effects of rotation on collision outcomes. We consider nine distinct rotation configurations and a range of rotation rates up to the rotational stability limit. Notably, we identify a population of collisions that can produce low post-impact angular momentum (AM) budgets and massive, iron-poor protolunar disks. Furthermore, even when pre-impact rotation is included, we demonstrate that the canonical Moon-forming impact can only generate sufficiently massive protolunar disks in the presence of excessive post-impact AM budgets; this casts doubt on the canonical impact scenario.

Experimental Study on Liquid Jet Trajectory in Cross Flow of Swirling Air at Elevated Pressure Condition

Abstract Motivated by fuel atomization applications in gas turbine combustors, this paper presents an experimental examination of liquid jet trajectory and spray dynamics in crossflow of swirling air, at elevated pressure conditions. The study was conducted within an annular passage and was focused on momentum flux ratio and swirl number as the main parameters. The momentum flux ratio was varied from 2 to 25 through incremental adjustments to the liquid injection velocity and the swirl number values of 0.42 and 0.74 were used, representing typical gas turbine fuel atomization conditions. The jet trajectories were captured by imaging the three-dimensional (3D) helical path traced by the liquid jet using two mutually perpendicular optical windows. Radial penetration was quantified by solving the equations of a helix. The key findings revealed that radial penetration of the liquid jet is larger for higher momentum flux ratios and is influenced by the helical arc length. Notably, the radial penetration observed at low momentum flux ratios was larger for crossflow with lower swirl number and the radial penetration observed at high momentum flux ratios was more for crossflows with higher swirl number. In comparison to the spray characteristics in swirling crossflows at atmospheric pressure, condition of elevated gaseous pressure resulted in lower radial penetration, jet spread and jet area. The jet trajectory correlations for elevated pressure conditions are additionally presented, developed using curve fitting to the experimental data, which will be useful to the industry for estimation of spray trajectory in swirling crossflows at elevated pressure conditions.

Multijet event shape variables for Mueller-Navelet jet topologies

This paper presents a new set of multijet event shape variables introduced to further understand the Mueller-Navelet jet topology. This topology consists of having at least one pair of jets with a very large rapidity separation between them, treating additional jet activity inclusively. This multijet topology is expected to shed light on the radiation pattern that is expected in the high-energy limit of the strong interaction. The paper relies on a Monte Carlo event generator analysis. One set of predictions uses the ex event generator, which is based on Balitsky-Fadin-Kuraev-Lipatov (BFKL) perturbative quantum chromodynamics (pQCD) evolution with a resummation of large logarithms of energy at leading-logarithmic accuracy. The ex predictions are compared with a fixed-order next-to-leading order pQCD calculation using matched to the parton shower of ythia8 (NLO+PS), which is the standard for NLO generator predictions at the LHC. We find that both approaches lead to compatible results at current LHC energies, assuming the current experimental constraints for the reconstruction of low transverse momentum jets in ATLAS and CMS. This shows the reliability of the BFKL approach at describing the behavior of the strong interaction in the preasymptotic limit of high center-of-mass energies. Differences between the NLO+PS and the BFKL-based approaches are found when the jet multiplicity is increased or when the minimum transverse momentum of the jets is decreased. Published by the American Physical Society 2024

When does a Fermi puddle become a Fermi sea? Emergence of pairing in two-dimensional trapped mesoscopic Fermi gases

Pairing lies at the heart of superfluidity in fermionic systems. Motivated by recent experiments in mesoscopic Fermi gases, we study up to six fermionic atoms with equal masses and equal populations in two different spin states, confined in a quasi-two-dimensional harmonic trap. We couple a stochastic variational approach with the use of an explicitly correlated Gaussian basis set, which enables us to obtain highly accurate energies and structural properties. Utilising two-dimensional two-body scattering theory with a finite-range Gaussian interaction potential, we tune the effective range to model realistic quasi-two-dimensional scattering. We calculate the excitation spectrum, pair correlation function, and number of pairs as a function of increasing attractive interaction strength. For up to six fermions in the ground state, we find that opposite spin and momentum pairing is maximised well below the Fermi surface in momentum space. By contrast, corresponding experiments on twelve fermions have found that pairing is maximal at the Fermi surface and strongly suppressed beneath [M. Holten et al., Nature 606, 287-291 (2022)]. This suggests that the Fermi sea — which acts to suppress pairing at low momenta via Pauli blocking — emerges in the transition from six to twelve particles.

Heavy-quark diffusion in 2+1D and glasmalike plasmas: Evidence of a transport peak

We examine how plasma excitations affect the heavy-quark diffusion coefficient in 2+1-dimensional and glasmalike plasmas, akin to the preequilibrium matter describing relativistic heavy-ion collisions at early times. We find that the transport coefficient 2κ transverse to and κz along the beam direction display a qualitatively different evolution. We attribute this to the underlying excitation spectra of these systems, thus providing evidence for the existence of nonperturbative properties in the spectrum. This is accomplished by first reconstructing the diffusion coefficients using gauge-fixed correlation functions, which accurately reproduces the time evolution of 2κ and κz. We then modify these excitation spectra to study the impact of their nonperturbative features on the transport coefficients. In particular, we find evidence for a novel transport peak in the low-frequency spectrum that is crucial for heavy-quark diffusion. We also demonstrate that gluonic excitations are broad while scalar excitations associated with κz are narrow and strongly enhanced at low momenta. Our findings indicate that the large values and dynamical properties of transport coefficients in the glasma could originate from genuinely nonperturbative features in the spectrum. Published by the American Physical Society 2024

Exploring Ultraperipheral Heavy Ion Collisions in CMS Run III

Ultraperipheral collisions (UPCs) of heavy ions are a useful probe to study nuclear parton distribution functions (nPDFs) and, in particular, to characterize nuclear matter at Bjorken x < 10−3 and low squared momentum transfer Q2 (shadowing/saturation regime). In order to fully exploit these collisions, dedicated triggers on such event topologies were developed for the heavy ion data-taking period in 2023 by the CMS experiment. These triggers relied on the possibility of using the Zero Degree Calorimeter (ZDC) as a level-1 (L1) trigger detector for the first time. As a result, they allowed for an improved selection performance in addition to existing UPC triggers (as well as minimum-bias hadronic triggers), and enabled the study of hard processes (jets and heavy flavor hadrons) in photon-photon (γγ) and photon-nucleus (γN) scatterings [1].

The Future of Experimental Measurements of Light-by-Light Scattering

Light-by-light scattering is a relatively new area in experimental physics. Our recent, theoretical research shows that studying two photon measurements in regions with lower transverse momentum (pt,γ) and invariant mass (Mγγ) allows us to observe not only the main contribution of photon scattering, known as fermionic loops, but also mechanisms like the VDM–Regge. In addition, examining diphoton measurements in low invariant mass regions is crucial for researching light meson resonances in γγ → γγ scattering. We also focus on the interference between different contributions. For future experiments with the ALICE FoCal and ALICE 3 detectors, we have calculated background estimates and explored possibilities to minimize their impact.

Holographic zero sound for [formula omitted] SCFTs in 4d

We build up the notion of metallic holography for N=2 SCFTs in four dimensions, in the presence of a finite U(1) chemical potential. We compute two point correlation functions and study their properties in the regime of low frequency and low momentum. The color sector reveals gapless excitations, one of which propagates with a finite phase velocity while the other mode attenuates through scattering. The flavour sector, on the other hand, reveals spectrum that contains quasiparticle excitations which propagate with a definite phase velocity together with modes that propagate with a finite group velocity which quantum attenuates quite similar in spirit as that of Landau's zero sound modes. We also compute associated AC conductivities, which exhibit different characteristics for different (color and flavour) sectors of N=2 SCFTs.

GRASP Integrated 3D Plotter: GRIP.

In research on mesoscale structure and correlations, small-angle neutron scattering (SANS) is increasingly being employed to map fully three-dimensional distributions of scattered intensity at low momentum transfer. While traditionally SANS experiments and data analysis methods are designed to prioritize the determination of salient information in only one or two dimensions, the trend towards volumetric intensity mapping experiments calls for new software tools to assist with analyzing the resulting datasets. In this paper, we describe the development of a new software module, the GRASP Integrated 3D Plotter (GRIP). GRIP adds numerous features to GRASP, a widely used SANS analysis program that was written in MATLAB and developed at the Institut Laue-Langevin, France. The GRIP module provides multiple methods of three-dimensional SANS data visualization and new abilities to perform 1D and 2D cuts in various momentum-space coordinate systems, including reciprocal lattice units relevant for single-crystal studies. GRIP also includes the ability to fit diffraction peaks to a fully three-dimensional ellipsoidal Gaussian function to extract peak parameters including peak intensity, location and width, as well as a built-in calculator for estimating the resolution-deconvolved 3D coherence lengths in a sample. GRIP thus represents a significant addition to GRASP which extends the utility and application of SANS. Valuable advantages are provided, in particular, for 'small-angle neutron diffraction' studies of mesoscale correlations in single crystals, such as those due to incommensurate magnetic spin textures like spirals and topological skyrmion lattices.

A Kalman filter for track reconstruction in very large time projection chambers

This study introduces a Kalman Filter tailored for homogeneous gas Time Projection Chambers (TPCs), adapted from the algorithm utilized by the ALICE experiment. In order to describe semi-circular paths in the plane perpendicular to the magnetic field, we introduce a novel mirror rotation technique into the Kalman Filter algorithm, enabling effective tracking of trajectories of varying lengths, including those with multiple circular paths within the detector, also known as “loopers”. Demonstrated relative improvements of up to 80% in electron momentum resolution and up to 50% in muon and pion momentum resolution underscore the significance of this enhancement. Significant improvements in the reconstruction efficiency for relatively short low momentum “looper” tracks are also shown. Such advancements hold promise not only for the future of the ALICE TPC but also for neutrino high-pressure gas TPCs, where loopers become significant owing to the randomness of production points and their relatively low energies in neutrino interactions. In particular, an improvement in low energy electron reconstruction, for which the production of “looping” tracks is likely and the impact of the new algorithm is directly demonstrated, could significantly impact the quality of flux determination, which in accelerator neutrino experiments relies on the measurement of νe electron scatterings.

Searches for Pair-Produced Multijet Resonances Using Data Scouting in Proton-Proton Collisions at sqrt[s]=13 TeV.

Searches for pair-produced multijet signatures using data corresponding to an integrated luminosity of 128 fb^{-1} of proton-proton collisions at sqrt[s]=13 TeV are presented. A data scouting technique is employed to record events with low jet scalar transverse momentum sum values. The electroweak production of particles predicted in R-parity violating supersymmetric models is probed for the first time with fully hadronic final states. This is the first search for prompt hadronically decaying mass-degenerate higgsinos, and extends current exclusions on R-parity violating top squarks and gluinos.

Morphology and intervesicle distances in condensates of synaptic vesicles and synapsin

Synaptic vesicle clusters or pools are functionally important constituents of chemical synapses. In the so-called reserve and the active pools, neurotransmitter-loaded synaptic vesicles (SVs) are stored and conditioned for fusion with the synaptic membrane and subsequent neurotransmitter release during synaptic activity. Vesicle clusters can be considered as so-called membraneless compartments, which form by liquid-liquid phase separation. Synapsin as one of the most abundant synaptic proteins has been identified as a major driver of pool formation. It has been shown to induce liquid-liquid phase separation and form condensates on its own in solution, but also has been shown to integrate vesicles into condensates in vitro. In this process, the intrinsically disordered region of synapsin is believed to play a critical role. Here, we first investigate the solution structure of synapsin and SVs separately by small-angle x-ray scattering. In the limit of low momentum transfer q, the scattering curve for synapsin gives clear indication for supramolecular aggregation (condensation). We then study mixtures of SVs and synapsin-forming condensates, aiming at the morphology and intervesicle distances, i.e., the structure of the condensates in solution. To obtain the structure factor S(q) quantifying intervesicle correlation, we divide the scattering curve of condensates by that of pure SV suspensions. Analysis of S(q) in combination with numerical simulations of cluster aggregation indicates a noncompact fractal-like vesicular fluid with rather short intervesicle distances at the contact sites.

Electroweak corrections to Higgs boson pair production: the top-Yukawa and self-coupling contributions

We present results for the Yukawa-enhanced and Higgs self-coupling type electroweak corrections to di-Higgs production in gluon fusion. The calculation of the corresponding four-scale, two-loop amplitude is carried out retaining the exact symbolic dependence on all masses and scales during the reduction to master integrals. The resulting integrals are then evaluated at high precision using both the series expansion of the differential equations and sector decomposition. Differential cross sections for the di-Higgs invariant mass and the transverse momentum of a Higgs boson are shown, where we find that the corrections are most pronounced at low invariant mass and transverse momentum.