Conserved Quantum Numbers Research Articles

A test of strangeness quantum number conservation in proton-proton collisions

The study delves into the production of (multi-) strange hadrons in proton-proton collisions at LHC. Novel observables are proposed to distinguish between Epos4, based on core-corona separation between a thermalised QGP phase and a vacuum phase with global strangeness conservation, and Pythia 8.3, based on microscopic interactions between Lund strings that conserve strangeness locally. Correlations between a ϕ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi $$\\end{document} meson and (multi-)strange hadrons are shown to be an excellent discriminator between the two types of models.

Quantum number conservation: a tool in the design and analysis of high energy experiments

The Clifford Unification algebra Cl 7,7 is shown to provide a unified description of all the elementary fermions and hadrons in terms of seven binary quantum numbers. Four of these are defined in existing theories, namely spin-direction, fermion/anti-fermion pairing and the two commuting generators in the SU(3) description of quark colour. A Cl 3,3 sub-algebra integrates the Cl 1,3 space-time and Dirac algebras providing a new definition of time direction and identifying parity as a new quantum number. A further two quantum numbers are related to the commuting generators of an SU(3) description of fermion generations. All seven are conserved in the decays and interactions of charged particles, suggesting that quantum number conservation provides a useful tool in the design and interpretation of high energy experiments. This is especially relevant when neutral particles and parity are involved.

Chasing the onset of QCD thermalization with ALICE

In heavy-ion and hadronic collisions, indications of thermalization are detected in the yields of produced hadrons: these observations call for a detailed study of the hadronization processes. Novel observables are required to discriminate between the different hadronization models that successfully describe the average yields of hadrons. The ALICE Collaboration reports on the studies of event-by-event fluctuations of the net-Ξ± number, and Pearson correlations of both the net-Ξ±–net-kaon numbers and the antideuteron–antiproton numbers, in pp, p–Pb, and Pb–Pb collisions. The measured fluctuations are compared with different hadronization models to explore the compatibility with a charge-equilibration scenario. In all cases, the experimental data agree with Thermal-FIST canonical-statistical calculations, allowing for the extraction of the correlation length for strange and baryon quantum number conservation.

Primitive to conventional geometry projection for efficient phonon transport calculations

The primitive Wigner-Seitz cell and corresponding first Brillouin zone (FBZ) are typically used in calculations of lattice vibrational and transport properties as they contain the smallest number of degrees of freedom and thus have the cheapest computational cost. However, in complex materials, the FBZ can take on irregular shapes where lattice symmetries are not apparent. Thus, conventional cells (with more atoms and regular shapes) are often used to describe materials, though dynamical and transport calculations are more expensive. Here we discuss an efficient anharmonic lattice dynamic method that maps conventional cell dynamics to primitive cell dynamics based on translational symmetries. Such symmetries have not been utilized in typical lattice dynamical calculations. This leads to phase interference conditions that act like conserved quantum numbers and a conservation rule for phonon scattering that is hidden in conventional dynamics which significantly reduces the computational cost. We demonstrate this method for phonon transport in a variety of materials with inputs from first-principles calculations and attribute its efficiency to reduced scattering phase space and fewer summations in scattering matrix element calculations.

Fission hindrances in transfermium nuclei

Very heavy nuclei owe their stability against spontaneous fission to quantum shell effects, which depend on the local density of single-particle states. The height but also the width and the structure of the barrier in multi-dimensional deformation space determine the fission half-lives. Other effects come into play, such as the conservation of quantum numbers and superfluidity or stiffness of the system in the fission process. This is why odd nuclei have longer fission partial half-lives with respect to their even neighbours and also why multi-quasi-particle states, such as high-K states, are thought to be more stable against fission than the ground state. We will report here on two different fission studies carried out with the GABRIELA detector array at the focal plane of the recoil separator SHELS. The first study concerns the fission properties of 253Rf, the most neutron deficient Rf isotope known to date. The second study focusses on a new measurement of the fission hindrance of the known 8- isomer in 254No.

Diffusion matrix associated with the diffusion processes of multiple conserved charges in a hot and dense hadronic matter

Bulk matter produced in heavy ion collisions has multiple conserved quantum numbers like baryon number, strangeness and electric charge. The diffusion process of these charges can be described by a diffusion matrix describing the interdependence of diffusion of different charges. The diffusion coefficient matrix is estimated here from the Boltzmann kinetic theory for the hadronic phase within relaxation time approximation. In the derivation for the same, we impose the Landau-Lifshitz conditions of fit. This leads to e.g. the diagonal diffusion coefficients to be manifestly positive definite. The explicit calculations are performed within the ambit of hadron resonance gas model with and without excluded volume corrections. It is seen that the off-diagonal components can be significant to affect the charge diffusion in a fluid with multiple conserved charges. The excluded volume correction effects is seen to be not significant in the estimation of the elements of the diffusion matrix.

Momentum: QFT, Quantum Black Holes, and Some Cosmological Implications

The paper studies the general Pauli-like equation for a Dirac fermions doublet on the background of an external non-Abelian monopole field. The variables separation has been fulfilled, the non-relativistic approximation for the radial systems has been derived. For the case of a minimal value of the conserved quantum number j = 0, the Pauli equation has been obtained in the form of one second-order differential equation. In the case j > 0, the problem has been reduced to the system of two coupled second order equations. In Bogomol'nyi-Prasad-Sommerfeld approximation, this system of equations has been solved in terms of hypergeometric functions.

Operators for generic effective field theory at any dimension: on-shell amplitude basis construction

We describe a general procedure to construct the independent and complete operator bases for generic Lorentz invariant effective field theories, given any kind of gauge symmetry and field content, up to any mass dimension. By considering the operator as contact on-shell amplitude, the so-called amplitude operator correspondence, we provide a unified construction of the Lorentz and gauge and flavor structures by Young Tableau tensor. Several bases are constructed to emphasize different aspects: independence (y-basis and m-basis), repeated fields with flavors (p-basis and f-basis), and conserved quantum numbers (j-basis). We also provide new algorithms for finding the m-basis by defining inner products for group factors and the p-basis by constructing the matrix representations of the Young symmetrizers from group generators. The on-shell amplitude basis gives us a systematic way to convert any operator into such basis, so that the conversions between any other operator bases can be easily done by linear algebra. All of these are implemented in a Mathematica package: ABC4EFT (Amplitude Basis Construction for Effective Field Theories).

Studying strangeness and baryon production in small systems through Ξ—hadron correlations using the ALICE detector

These proceedings summarise recent measurements of angular correlations between the Ξ baryon and identified hadrons in pp collisions at √S = 13 TeV using the ALICE detector. The results are compared with both string-based (PYTHIA8 with extensions) and core-corona (EPOS-LHC) models, to improve our understanding of strangeness and baryon production in small systems. The results favour baryon production through string junctions over diquark breaking, but the PYTHIA models fail at describing the relatively wide Ξ—strangeness jet peak, indicating stronger diffusion of strange quarks in data. On the other hand, EPOS-LHC is missing local conservation of quantum numbers, making it difficult to draw any conclusion about the core-corona model.

Differential two-particle number and momentum correlations with the AMPT, UrQMD, and EPOS models in Pb-Pb collisions at sNN=2.76 TeV

We report studies of charge-independent (CI) and charge-dependent (CD) two-particle differential number correlation functions, $R_{2} \left( \Delta \eta, \Delta \varphi \right)$, and transverse momentum correlation functions, $P_2 \left( \Delta \eta, \Delta \varphi \right)$ of charged particles produced in \PbPb\ collisions at the LHC centre-of-mass energy $\sqrt{s_{\rm NN}} =$ 2.76 TeV with the UrQMD, AMPT and EPOS models. Model predictions for $R_2$ and $P_2$ correlation functions are presented for inclusive charged hadrons ($h^\pm$) in selected transverse momentum ranges and with full azimuthal coverage in the pseudorapidity range $|\eta|< 1.0$. We compare these predictions for the strength, shape, and particularly the width of the correlation functions with recent measurements of these observables by the ALICE collaboration. Our analysis indicate that comparative studies of $R_2$ and $P_2$ correlation functions provide valuable insight towards the understanding of particle production in Pb--Pb collisions. We find, in particular, that these models have quantitatively different predictions for these three observables but none reproduce the measured correlation functions reported by the ALICE collaboration. Accounting for quantum number conservation in models, particularly charge conservation, is mandatory to reproduce the detailed measurements of number and transverse momentum correlation functions.

Parity symmetry as the origin of ‘spin’ in the quantum spin Hall effect

The quantum spin Hall effect arises due to band inversion in topological insulators, and has the defining characteristic that it hosts helical edge channels at zero magnetic field, leading to a finite spin Hall conductivity. The spin Hall conductivity is understood as the difference of the contributions of two spin states. In the effective four-band BHZ model, these two spin states appear as two uncoupled blocks in the Hamiltonian matrix. However, this idea breaks down if additional degrees of freedom are considered. The two blocks cannot be identified by proper spin $S_z$ or total angular momentum $J_z$, both not conserved quantum numbers. In this work, we discuss a notion of block structure for the more general k.p model, defined by a conserved quantum number that we call isoparity, a combination of parity $z\to-z$ and spin. Isoparity remains a conserved quantity under a wide range of conditions, in particular in presence of a perpendicular external magnetic field. From point-group considerations, isoparity is fundamentally defined as the action of $z\to-z$ on the spatial and spinorial degrees of freedom. Since time reversal anticommutes with isoparity, the two blocks act as Kramers partners. The combination of conductivity and isoparity defines spin conductivity. This generalized notion of spin Hall conductivity uncovers the meaning of 'spin': It is not the proper spin $S_z$, but a crystal symmetry that is realized by a spinorial representation.

Quantizing the Eisenhart lift

The classical Eisenhart lift is a method by which the dynamics of a classical system subject to a potential can be recreated by means of a free system evolving in a higher-dimensional curved manifold, known as the lifted manifold. We extend the formulation of the Eisenhart lift to quantum systems, and show that the lifted manifold recreates not only the classical effects of the potential, but also its quantum mechanical effects. In particular, we find that the solutions of the Schrodinger equations of the lifted system reduce to those of the original system after projecting out the new degrees of freedom. In this context, we identify a conserved quantum number, which corresponds to the lifted momentum of the classical system. We further apply the Eisenhart lift to Quantum Field Theory (QFT). We show that a lifted field space manifold is able to recreate both the classical and quantum effects of a scalar field potential. We find that, in the case of QFT, the analogue of the lifted momentum is a quantum charge that is conserved not only in time, but also in space. The different possible values for this charge label an ensemble of Fock spaces that are all disjoint from one another. The relevance of these extended Fock spaces to the cosmological constant and gauge hierarchy problems is considered.

From Feynman rules to conserved quantum numbers, III

The present article complements the earlier ones in this series. The first part contains various results on the constituent system Cκ(M) of a graph model M, and on its feasibility system Iη(M) (which comprises a number of identities that define the number conservation rules). Those results include the general form of the (particle) number conservation rules in models without explicit propagator mixing.A few types of graph models (including self-conjugate and quasi-normal models) are defined. Oversimplifying, a model M is self-conjugate if it has a certain (weak) combinatorial type of C-symmetry, and M is quasi-normal if Iη(M) fully determines for which multisets of coloured, unlinked half-edges there is a graph in M with that exact multiset. It is shown not only that every self-conjugate model is quasi-normal, but also that some extensions of self-conjugate models are still quasi-normal. Most conveniently, self-conjugate models (and even some extended models) may be recognized in polynomial time.These results seem to lead to the following conclusion: for many (possibly ‘most’ of the) consistent, relevant QFT models, a complete correlation function 〈F〉 is graphical — i.e. there exist Feynman diagram(s) for 〈F〉 — if and only if 〈F〉 is allowed by the number conservation rules (i.e. by a complete system of such rules). Since these rules can be computed in polynomial time then, for many QFT models, deciding whether 〈F〉 is graphical also takes polynomial time.

Reproductive freeze-in of self-interacting dark matter

We present a mechanism for dark matter (DM) production involving a self-interacting sector that at early times is ultra-relativistic but far-underpopulated relative to thermal equilibrium (such initial conditions often arise, e.g., from inflaton decay). Although elastic scatterings can establish kinetic equilibrium we show that for a broad variety of self-interactions full equilibrium is never established despite the DM yield significantly evolving due to $2\to k$ ($k>2$) processes (the DM carries no conserved quantum number nor asymmetry). During the active phase of the process, the DM to Standard Model temperature ratio falls rapidly, with DM kinetic energy being converted to DM mass, the inverse of the recently-discussed `cannibal DM mechanism'. Potential observables and applications include self-interacting DM signatures in galaxies and clusters, dark acoustic oscillations, the alteration of free-streaming constraints, and possible easing of $\sigma_8$ and Hubble tensions.

Beam energy dependence of net- Λ fluctuations measured by the STAR experiment at the BNL Relativistic Heavy Ion Collider

The measurements of particle multiplicity distributions have generated considerable interest in understanding the fluctuations of conserved quantum numbers in the Quantum Chromodynamics (QCD) hadronization regime, in particular near a possible critical point and near the chemical freeze-out. We report the measurement of efficiency and centrality bin width corrected cumulant ratios ($C_{2}/C_{1}$, $C_{3}/C_{2}$) of net-$\Lambda$ distributions, in the context of both strangeness and baryon number conservation, as a function of collision energy, centrality and rapidity. The results are for Au + Au collisions at five beam energies ($\sqrt{s_{NN}}$ = 19.6, 27, 39, 62.4 and 200 GeV) recorded with the Solenoidal Tracker at RHIC (STAR). We compare our results to the Poisson and negative binomial (NBD) expectations, as well as to Ultra-relativistic Quantum Molecular Dynamics (UrQMD) and Hadron Resonance Gas (HRG) model predictions. Both NBD and Poisson baselines agree with data within the statistical and systematic uncertainties. The ratios of the measured cumulants show no features of critical fluctuations. The chemical freeze-out temperatures extracted from a recent HRG calculation, which was successfully used to describe the net-proton, net-kaon and net-charge data, indicate $\Lambda$ freeze-out conditions similar to those of kaons. However, large deviations are found when comparing to temperatures obtained from net-proton fluctuations. The net-$\Lambda$ cumulants show a weak, but finite, dependence on the rapidity coverage in the acceptance of the detector, which can be attributed to quantum number conservation.

Cross-conductivity: Novel transport coefficients to constrain the hadronic degrees of freedom of nuclear matter

In general, the constituents of the bulk matter produced in heavy-ion collisions carry, besides electric charge, multiple other conserved quantum numbers like baryon number and strangeness. Therefore, an electric field will not only generate an electric current but, at the same time, also currents in baryon number and strangeness. We propose that the impact of the electric field on these conserved currents should be characterized by additional transport coefficients, which we call cross-conductivities. In this paper, we introduce and present a calculation of these cross-conductivities from the Green-Kubo formalism within the transport code SMASH for different chemical compositions of hadron resonance gases. We find that the coefficients underlie an ordering in the active degrees of freedom and that thus the chemical composition of the system plays a crucial role. Further, we argue that in future comparisons of lattice QCD calculations with these findings, one could constrain which degrees of freedom and their corresponding charge properties are relevant for the QCD dynamics of the system.

Hybrid purification and sampling approach for thermal quantum systems

We propose an algorithm which combines the beneficial aspects of two different methods for studying finite-temperature quantum systems with tensor networks. One approach is the ancilla method, which gives high-precision results but scales poorly at low temperatures. The other method is the minimally entangled typical thermal state (METTS) sampling algorithm which scales better than the ancilla method at low temperatures and can be parallelized, but requires many samples to converge to a precise result. Our proposed hybrid of these two methods purifies physical sites in a small central spatial region with partner ancilla sites, sampling the remaining sites using the METTS algorithm. Observables measured within the purified cluster have much lower sample variance than in the METTS approach, while sampling the sites outside the cluster reduces their entanglement and the computational cost of the algorithm. The sampling steps of the algorithm remain straightforwardly parallelizable. The hybrid approach also solves an important technical issue with METTS that makes it difficult to benefit from quantum number conservation. By studying S=1 Heisenberg ladder systems, we find the hybrid method converges more quickly than both the ancilla and METTS algorithms at intermediate temperatures and for systems with higher entanglement.

Diffusion processes involving multiple conserved charges: A study from kinetic theory and implications to the fluid-dynamical modeling of heavy ion collisions

The bulk nuclear matter produced in heavy ion collisions carries a multitude of conserved quantum numbers: electric charge, baryon number, and strangeness. Therefore, the diffusion processes associated to these conserved charges cannot occur independently and must be described in terms of a set of coupled diffusion equations. This physics is implemented by replacing the traditional diffusion coefficients for each conserved charge by a diffusion coefficient matrix, which quantifies the coupling between the conserved quantum numbers. The diagonal coefficients of this matrix are the usual charge diffusion coefficients, while the off-diagonal entries describe the diffusive coupling of the charge currents. In this paper, we show how to calculate this diffusion coefficient matrix from kinetic theory and provide results for a hadron resonance gas and a gas of partons. We further find that the off-diagonal entries can reach similar magnitudes compared to the diagonal entries. In order to provide some insight on the influence that the coupling between the net charge diffusion currents can have on heavy ion observables, we present first results for the diffusive evolution of a hadronic system in a simple (1+1)D-fluid dynamics approach, and study different configurations of the diffusion matrix.

A portalino to the dark sector

“Portal” models that connect the Standard Model to a Dark Sector allow for a wide variety of scenarios beyond the simplest WIMP models. Kinetic mixing of gauge fields in particular has allowed a broad range of new ideas. However, the models that evade CMB constraints are often non-generic, with new mass scales and operators to split states and suppress indirect detection signals. Models with a “portalino”, a neutral fermion that marries a linear combination of a standard model neutrino and dark sector fermion and carries a conserved quantum number, can be simpler. This is especially interesting for interacting dark sectors; then the unmarried linear combination which we identify as the standard model neutrino inherits these interactions too, and provides a new, effective interaction between the dark sector and the standard model. These interactions can be simple Z′ type interactions or lepton-flavor changing. Dark matter freezes out into neutrinos, thereby evading CMB constraints, and conventional direct detection signals are largely absent. The model offers different signals, however. The “portalino” mechanism itself predicts small corrections to the standard model neutrino couplings as well as the possibility of discovering the portalino particle in collider experiments. Possible cosmological and astroparticle signatures include monochromatic neutrino signals from annihilation, spectral features in high energy CR neutrinos as well as conventional signals of additional light species and dark matter interactions.

Strangeness production in low energy heavy ion collisions via Hagedorn resonances

A novel, unorthodox picture of the dynamics of heavy ion collisions is developed using the concept of Hagedorn states. A prescription of the bootstrap of Hagedorn states respecting the conserved quantum numbers baryon number B, strangeness S, isospin I is implememted into the GiBUU transport model. Using a strangeness saturation suppression factor suitable for nucleon-nucleon-collisions, recent experimental data for the strangeness production by the HADES collaboration in Au+Au and Ar+KCl is reasonable well described. The experimental observed exponential slopes of the energy distributions are nicely reproduced. Thus, a dynamical model using Hagedorn resonance states, supplemented by a strangeness saturation suppression factor, is able to explain essential features (multiplicities, exponential slope) of experimental data for strangeness production in nucleus-nucleus collisions close to threshold.