Theory Of Strong Interactions Research Articles

Gauge Theory Bootstrap

We propose the gauge theory bootstrap, a method to compute the pion S matrix that describes the low-energy physics of the strong interaction and other similar gauge theories. The phase shifts of the S0, P1, and S2 waves obtained are in good agreement with experimental results. The only numerical inputs are the quark mass mq, the QCD scale ΛQCD, the pion mass mπ, and the pion decay constant fπ without any other experimental data. We make use of the form-factor bootstrap recently proposed by Karateev, Kuhn, and Penedones together with a finite energy version of the Shifman-Veinshtein-Zakharov sum rules. Published by the American Physical Society 2024

Meson spectroscopy from spectral densities in lattice gauge theories

Spectral densities encode nonperturbative information that enters the calculation of a plethora of physical observables in strongly coupled field theories. Phenomenological applications encompass aspects of standard-model hadronic physics, observable at current colliders, as well as correlation functions characterizing new physics proposals, testable in future experiments. By making use of numerical data produced in a Sp(4) lattice gauge theory with matter transforming in an admixture of fundamental and 2-index antisymmetric representations of the gauge group, we perform a systematic study to demonstrate the effectiveness of recent technological progress in the reconstruction of spectral densities.To this purpose, we write and test new software packages that use energy-smeared spectral densities to analyze the mass spectrum of mesons. We assess the effectiveness of different smearing kernels and optimize the smearing parameters to the characteristics of available lattice ensembles. For concreteness, we analyze the Sp(4) lattice gauge theory with matter transforming in an admixture of fundamental and 2-index antisymmetric representations of the gauge group. We generate new ensembles for the theory in consideration, with lattices that have a longer extent in the time direction with respect to the spatial ones. We run our tests on these ensembles, obtaining new results about the spectrum of light mesons and their excitations. We make available our algorithm and software for the extraction of spectral densities, that can be applied to theories with other gauge groups, including the theory of strong interactions (QCD) governing hadronic physics in the standard model. Published by the American Physical Society 2024

Machine learning-based study of open-charm hadrons in proton-proton collisions at the Large Hadron Collider

In proton-proton and heavy-ion collisions, the study of charm hadrons plays a pivotal role in understanding the QCD medium and provides an undisputed testing ground for the theory of strong interaction, as they are mostly produced in the early stages of collisions via hard partonic interactions. The lightest open charm, D0 meson (cu¯), can originate from two separate sources. The prompt D0 originates from either direct charm production or the decay of excited open charm states, while the nonprompt stems from the decay of beauty hadrons. In this paper, using different machine learning (ML) algorithms such as XGBoost, CatBoost, and Random Forest, an attempt has been made to segregate the prompt and nonprompt production modes of the D0 meson signal from its background. The ML models are trained using the invariant mass through its hadronic decay channel, i.e., D0→π+K−, pseudoproper time, pseudoproper decay length, and distance of closest approach of D0 meson, using 8 simulated pp collisions at s=13 TeV. The ML models used in this analysis are found to retain the pseudorapidity, transverse momentum, and collision energy dependence. In addition, we report the ratio of nonprompt to prompt D0 yield, the self-normalized yield of prompt and nonprompt D0, and explore the charmonium, J/ψ to open charm, D0 yield ratio as a function of transverse momenta and normalized multiplicity. The observables studied in this paper are well predicted by all the ML models compared to the simulation. Published by the American Physical Society 2024

John Charlton Polkinghorne, 1930–2021

AbstractJohn Charlton Polkinghorne was very successful in two careers: as a theoretical physicist and as a theologian. As a physicist at Cambridge, he was one of the pioneers of applying complex variable theory to the study of properties of scattering amplitudes and contributed to the theory of strong (nuclear) interactions. In addition, he was a successful teacher, with many of his students gaining senior academic positions in universities. A postmaster's son from Weston‐super‐Mare, he married Ruth Martin, also a mathematics student at Cambridge. They had three children. John surprised many, apart from those who knew him closely, by resigning from his Chair at Cambridge to study for ordination in the Anglican Church. He became an influential theologian devoting much study to the interaction of science and religion. His position might be summed up in a phrase he was fond of, “God holds the Universe in being”, which was John's solution to what is called the fine‐tuning problem in physics: that the parameters of Nature turn out to be exquisitely adjusted to allow our universe to exist in its richness. John was a formidable administrator, became President of Queens' College, Cambridge, and chaired UK government committees on research ethics.

Inclusive, prompt and nonprompt J/ψ identification in proton-proton collisions at the Large Hadron Collider using machine learning

Studies related to J/ψ meson, a bound state of charm and anticharm quarks (cc¯), in heavy-ion collisions, provide genuine testing grounds for the theory of strong interaction, quantum chromodynamics. To better understand the underlying production mechanism, cold nuclear matter effects, and influence from the quark-gluon plasma, baseline measurements are also performed in proton-proton (pp) and proton-nucleus (p-A) collisions. The inclusive J/ψ measurement has contributions from both prompt and nonprompt productions. The prompt J/ψ is produced directly from the hadronic interactions or via feed down from directly produced higher charmonium states, whereas nonprompt J/ψ comes from the decay of beauty hadrons. In experiments, J/ψ is reconstructed through its electromagnetic decays to lepton pairs, in either e++e− or μ++μ− decay channels. In this work, for the first time, machine learning techniques are implemented to separate the prompt and nonprompt dimuon pairs from the background to obtain a better identification of the J/ψ signal for different production modes. The study has been performed in pp collisions at s=7 and 13 TeV simulated using 8. Machine learning models such as XGBoost and LightGBM are explored. The models could achieve up to 99% prediction accuracy. The transverse momentum (pT) and rapidity (y) differential measurements of inclusive, prompt, and nonprompt J/ψ, its multiplicity dependence, and the pT dependence of fraction of nonprompt J/ψ (fB) are shown. These results are compared to experimental findings wherever possible. Published by the American Physical Society 2024

Revealing the Origin of Mass through Studies of Hadron Spectra and Structure

The Higgs boson is responsible for roughly 1% of the visible mass in the Universe. Obviously, therefore, Nature has another, very effective way of generating mass. In working toward identifying the mechanism, contempo rary strong interaction theory has arrived at a body of basic predictions, viz. the emergence of a nonzero gluon mass-scale, a process-independent effective charge, and dressed-quarks with constituent-like masses. These three phenom ena – the pillars of emergent hadron mass (EHM) – explain the origin of the vast bulk of visible mass in the Universe. Their expressions in hadron observables are manifold. This contribution highlights a few; namely, some of the roles of EHM in building the meson spectrum, producing the leading-twist pion distribution amplitude, and moulding hadron charge and mass distributions.

Chasing QCD Signatures in Nuclei Using Color Coherence Phenomena

Over the last few decades, several experiments have used atomic nuclei as unique laboratories to probe the internal structure of the strongly interacting particles, namely hadrons. Indeed, the nucleus could be used as a revealing medium of the time evolution of elementary configurations of the hadron wave function. One of the ordinary approaches used to probe this picture involves searching for the onset of various phenomena which are naturally predicted by Quantum Chromo-Dynamics (QCD), the theory of strong interactions. One such phenomenon is the color transparency (CT), which refers to the production and propagation of a small size hadron-like configuration that, under specific conditions, stays intact in a transparent nuclear medium. In this paper, I will briefly review the status of the experimental search for CT effects and highlight the upcoming Jefferson Laboratory (JLab) 12 GeV experiment that will study CT at higher momentum transfer using the CLAS12 spectrometer.

Nucleon spin structure functions, considering target mass correction, and higher twist effects at the NNLO accuracy and their transverse momentum dependence

Using recent and updated world data on polarized structure functions ${g}_{1}$ and ${g}_{2}$ we perform an analysis based on quantum chromodynamics (QCD) as a theory of strong interactions at next-next-to-leading-order accuracy. We include also target mass corrections and higher twist effects to get more precise results in our fitting procedure. To confirm the validity of our fitting results several sum rules are examined and we do a comparison for them with results from other models. In our analysis we employ the Jacobi polynomials approach to obtain analytical solutions of the Dokshitzer-Gribov-LipatovAltarelli-Parisi evolution equations for parton distribution functions (PDFs). Using the extracted PDFs from our data analysis as input, we also compute the $x$- and ${\mathbf{p}}_{T}$-dependence of some transverse momentum dependence PDFs in polarized case, based on covariant parton model. These functions are naively even time-reversal at twist-two approximation. The results for transverse momentum dependences indicate proper and acceptable behavior with respect to what are presented in other literatures.

Limits of thermalization in relativistic heavy ion collisions

The goal of collider programs of high energy heavy-ion collisions is to produce a form of matter that can test non-perturbative aspects of Quantum Chromodynamics (QCD), the theory of strong interactions. One of the primary predictions from a computational approach to this quantum field theory is the existence of distinct thermodynamic states of QCD, particularly a state of deconfined quarks and gluons. An important step in establishing changes of state of QCD matter is to demonstrate that femto-scale system created in the laboratory can attain thermodynamic equilibrium. We present such a demonstration by checking that event-to-event fluctuations of several different conserved quantities have a consistent treatment in a grand canonical ensemble through a common temperature and chemical potentials. A key component of this work is that we used cumulants of up to third order in the net proton number, charge, and strangeness. We found a clear indication that the femto-scale fireball is thermalized when the collision energy in the centre of mass, sNN, is high enough. Also, the use of higher order cumulants, within the framework of grand canonical ensemble, reveals for the first time that the fireballs created at lower sNN are not in thermodynamic equilibrium. This opens the door to further studies of the approach to equilibrium, and the effects that a critical point in the phase diagram of QCD could have on such phenomena.

面向下一代对撞机的量子色动力学研究

As the fundamental theory of strong interactions, quantum chromodynamics (QCD) plays a crucial role in precision tests of the standard model (SM) and in the search for new physics. In this article, we provide a brief overview of recent progress in QCD studies relevant to collider physics, focusing on fixed-order calculations and resummation techniques, parton distribution functions and their calculations, as well as their impact on the search for new physics, SM precision tests, and studying the intrinsic properties of hadrons. Based on this, we also discuss the prospects of their applications and intersections with other disciplines in the future.

Concerning pion parton distributions

Analyses of the pion valence-quark distribution function (DF), , which explicitly incorporate the behaviour of the pion wave function prescribed by quantum chromodynamics (QCD), predict , beta (zeta gtrsim m_p)>2, where m_p is the proton mass. Nevertheless, more than forty years after the first experiment to collect data suitable for extracting the xsimeq 1 behaviour of , the empirical status remains uncertain because some methods used to fit existing data return a result for that violates this constraint. Such disagreement entails one of the following conclusions: the analysis concerned is incomplete; not all data being considered are a true expression of qualities intrinsic to the pion; or QCD, as it is currently understood, is not the theory of strong interactions. New, precise data are necessary before a final conclusion is possible. In developing these positions, we exploit a single proposition, viz. there is an effective charge which defines an evolution scheme for parton DFs that is all-orders exact. This proposition has numerous corollaries, which can be used to test the character of any DF, whether fitted or calculated.

Revisiting quark-hadron duality for heavy meson non-leptonic decays in two-dimensional QCD

We study lifetimes of heavy mesons in the 't Hooft model, a large-Nc theory of strong interaction in two-dimensional spacetime. Since this model is solvable, one can evaluate the total decay widths through hadronic amplitudes that are determined unambiguously within the formalism. We investigate quark-hadron duality by numerically comparing the exclusive result and one from the heavy quark expansion, with the contribution of Pauli interference being consistently incorporated. Within certain numerical accuracy, we find that the maximal difference between inclusive and exclusive rates for τ[Ds+]/τ[D0](τ[B+]/τ[B0]) is as large as the current experimental (theoretical) error in four-dimensions unlike τ[D+]/τ[D0], where an excellent agreement between the rates is seen.

The Fundamental Scale of QCD

There are several scales in the QCD as the theory of strong interaction: the vacuum gluonic condensate (as the divergence of the dilatation current), the nucleon mass as the basic mass scale in our universe, which is connected to the string tension $\sigma$, and the perturbative QCD scale $\Lambda_{\rm QCD}$, which defines the scale of the renormalized perturbative expansions. In this paper we connect all these scales to the vacuum condensate, using the field correlator method, where the string tension is expressed in terms of nonlocal field correlators, which are connected to the local condensates, while the perturbative $\Lambda_V$ is connected to $\sigma$ in the framework of the Background Perturbation Theory (BPT). We also demonstrate how the IR singularities and IR renormalons disappear in BPT making the resulting theory internally consistent.

Next-to-Next-to-Leading Order Study of Three-Jet Production at the LHC.

Multijet rates at hadron colliders provide a unique possibility for probing quantum chromodynamics (QCD), the theory of strong interactions. By comparing theory predictions with collider data, one can directly test perturbative QCD, extract fundamental parameters like the strong coupling α_{s}, and search for physics beyond the standard model. In this work we calculate, for the first time, the next-to-next-to-leading order (NNLO) QCD corrections to typical three-jet observables and to differential three-to-two jet ratios. The calculation is complete apart from the three-jet double virtual contributions which are included in the leading-color approximation. We demonstrate that the inclusion of the NNLO corrections significantly reduces the dependence of those observables on the factorization and renormalization scales. Besides its phenomenological value, this proof-of-principle computation represents a milestone in perturbative QCD.

Mining for Gluon Saturation at Colliders

Quantum chromodynamics (QCD) is the theory of strong interactions of quarks and gluons collectively called partons, the basic constituents of all nuclear matter. Its non-abelian character manifests in nature in the form of two remarkable properties: color confinement and asymptotic freedom. At high energies, perturbation theory can result in the growth and dominance of very gluon densities at small-x. If left uncontrolled, this growth can result in gluons eternally growing violating a number of mathematical bounds. The resolution to this problem lies by balancing gluon emissions by recombinating gluons at high energies: phenomena of gluon saturation. High energy nuclear and particle physics experiments have spent the past decades quantifying the structure of protons and nuclei in terms of their fundamental constituents confirming predicted extraordinary behavior of matter at extreme density and pressure conditions. In the process they have also measured seemingly unexpected phenomena. We will give a state of the art review of the underlying theoretical and experimental tools and measurements pertinent to gluon saturation physics. We will argue for the need of high energy electron-proton/ion colliders such as the proposed EIC (USA) and LHeC (Europe) to consolidate our knowledge of QCD knowledge in the small x kinematic domains.

Properties of the five dimensions for the truncated overlap fermions

Lattice quantum chromodynamics (QCD) simulation with chiral fermions is an attractive tool for studies on the non-perturbative field theory of strong interaction. However, it requires a large number of computer assets and is computationally very expensive. We describe the propagators of the π meson and the ρ meson constructed from the truncated overlap fermions. These propagators are calculated using lattice QCD simulations with a quench approximation. We indicate the dependence of the five dimensions for the mass of the π and ρ mesons. The residual mass at the chiral limit is also investigated.

Radiative corrections of order O(αEe/mN) to Sirlin’s radiative corrections of order O(α/π) , induced by the hadronic structure of the neutron

We investigate the contributions of the hadronic structure of the neutron to radiative $O(\alpha E_e/m_N)$ corrections (or the inner $O(\alpha E_e/m_N)$ RC) to the neutron beta decay, where $\alpha$, $E_e$ and $m_N$ are the fine-structure constant, the electron energy and the nucleon mass, respectively. We perform the calculation within the effective quantum field theory of strong low-energy pion-nucleon interactions described by the linear $\sigma$-model with chiral $SU(2) \times SU(2)$ symmetry and electroweak hadron-hadron, hadron-lepton and lepton-lepton interactions for the electron-lepton family with $SU(2)_L \times U(1)_Y$ symmetry of the Standard Electroweak Theory (Ivanov et al., Phys. Rev. D99, 093006 (2019)). We show that after renormalization, carried out in accordance with Sirlin's prescription (Sirlin, Phys. Rev. 164, 1767 (1967)), the inner $O(\alpha E_e/m_N)$ RC are of the order of a few parts of $10^{-5} - 10^{-4}$. This agrees well with the results obtained in (Ivanov et al., Phys. Rev. D99, 093006 (2019)).

Высокотемпературная сверхпроводимость в гидридах

Over the past six years (2015-2021), many superconducting hydrides with critical temperatures $T_{C}$ up to 250 K, which are currently record highs, have been discovered. Now we can already say that a special field of superconductivity has developed. This is hydride superconductivity at ultrahigh pressures. For the most part, the properties of superhydrides are well described by the Migdal-Eliashberg theory of strong electron-phonon interaction, especially when anharmonicity of phonons is taken into account. The isotope effect, the effect of the magnetic field (up to 60-70 T) on the critical temperature and critical current in the hydride samples, the dependence of $T_{C}$ on the pressure and degree of doping were investigated. The divergences between the theory and experiment are of interest, especially in the field of phase stability and in the behavior of the upper critical magnetic fields at low temperatures. This article presents a retrospective analysis of data of 2015-2021 and describes promising directions for future research of hydride superconductivity.

Thermodynamic properties of the trigonometric Rosen–Morse potential and applications to a quantum gas of mesons

In this study, we work out thermodynamic functions for a quantum gas of mesons described as color-electric charge dipoles. They refer to a particular parametrization of the trigonometric Rosen–Morse potential which allows to transform it to a perturbation of free quantum motion on the three-dimensional hypersphere, [Formula: see text], a manifold that can host only charge-neutral systems, the charge dipoles being the configuration of the minimal number of constituents. To the amount charge neutrality manifests itself as an important aspect of the color confinement in the theory of strong interaction, the Quantum Chromodynamics, we expect our findings to be of interest to the evaluation of temperature phenomena in the physics of hadrons and in particular in a quantum gas of color charge dipoles as are the mesons. The results are illustrated for [Formula: see text] and [Formula: see text] mesons.

Revisiting the determining fraction of glueball component in f 0 mesons via radiative decays of J/ψ * *Supported by National Natural Science Foundation of China (11805160, 11747040, 11675082, 11605039)

QCD theory predicts the existence of glueballs, but so far all experimental endeavors have failed to identify any such states. To remedy this discrepancy between QCD, which has proven to be a successful theory for strong interactions, and the failure of experimental searches for glueballs, one is tempted to accept the promising interpretation that the glueballs mix with regular states of the same quantum numbers. The lattice estimate of the masses of pure glueballs ranges from 1 to 2 GeV, which is the region of the family. Thus many authors suggest that the mesonic series is an ideal place to study possible mixtures of glueballs and . In this paper, following the strategy proposed by Close, Farrar and Li, we try to determine the fraction of glueball components in mesons using the measured mass spectra and the branching ratios of radiative decays into mesons. Since the pioneering papers by Close et al., more than 20 years have elapsed and more accurate measurements have been done by several experimental collaborations, so it is time to revisit this interesting topic using new data. We suppose and to be pure quark states, while for , and , to fit both the experimental data of radiative decay and their mass spectra, glueball components are needed. Moreover, the mass of the pure glueball is phenomenologically determined.