We compute amplitudes for the \(g^* g^* \to q \bar q V^*\) process (two virtual gluons into a quark, an antiquark, and a boson) at the tree level using the spinor-helicity formalism. The resulting analytic expressions are much shorter than squared amplitudes obtained using trace methods. Our results can be used to expedite numerical calculations in phenomenological studies of the Drell–Yan process in high-energy factorization framework.

Poland

Denmark

Spinor-helicity Calculation of the \(g^* g^* \to q \bar q V^*\) Amplitude at the Tree Level

The spin polarization of \({\mit \Lambda }\) hyperons produced in inclusive reactions with unpolarized protons on unpolarized targets has been studied for almost 40 years. The NA61/SHINE experiment at the CERN SPS has a great potential to study transverse polarization in \(p\)–\(p\) and \(p\)–\(A\) collisions. In this work, we discuss the impact of magnetic field and limited detector acceptance on the possible polarization measurement by this experiment. Our analysis shows that the magnetic field impact on the \({\mit \Lambda }\) polarization due to precession is one order of magnitude smaller than the detector acceptance-based polarization bias, and the identification of an experimental signal similar to that observed before by other experiments is possible.

Lambda Transverse Polarization in NA61/SHINE at the CERN SPS: Feasibility Studies

The fractal and phase transitional properties of each type of pions (i.e. \(\pi ^{\pm ,0}\)) through one-dimensional \(\eta \)-space, at an energy of \(\sqrt {s}=13\) TeV, have been studied with the help of the Scaled Factorial Moment (SFM) framework. To generate simulated data sets for \(pp\) collisions under the minimum bias (MB) condition at \(\sqrt {s}=13\) TeV, we have employed the Monte Carlo-based event simulator PYTHIA. Various parameters such as the Levy index \((\mu )\), degree of multifractality \((r)\), anomalous fractal dimension \((d_q)\), multifractal specific heat \((c)\), and critical exponent \((\nu )\) have been calculated. To study the Bose–Einstein (BE) effect due to identical particles (here pions), we have also derived these parameters for mixed-pion pairs (i.e. \(\{\pi ^{+},\pi ^{-}\}\), \(\{\pi ^{+},\pi ^{0}\}\), and \(\{\pi ^{-},\pi ^{0}\}\)) and we find that the effects of identical particles weakened for the mixture with respect to the individual distributions. The quest for the quark–hadron phase transition has also been conducted within the framework of the Ginzburg–Landau (GL) theory of second-order phase transition. Analysis revealed that for PYTHIA-generated MB events, there is a clear indication of the quark–hadron phase transition according to the GL theory. Furthermore, the values of the multifractal specific heat (\(c\)) for each \(\pi ^{+}, \pi ^{-}, \pi ^{0}\), and the mixture-pair data sets of pions generated by the PYTHIA model at MB condition indicate a transition from multifractality to monofractality in \(pp\) collisions at \(\sqrt {s}=13\) TeV.

India

Egypt

The Study of Strongly-intensive Observables for \(\pi ^{\pm ,0}\) in \(pp\) Collisions at LHC Energy in the Framework of PYTHIA Model

Weakly nonlocal (WNL) Quantum Field Theories (QFTs) may define a new class of UV-completions in particle physics and gravity, without introducing any new elementary particle. One problematic issue is how to realize spontaneous symmetry breaking without introducing an infinite tower of ghosts in the perturbative spectrum. In this article, a WNL extension of the Standard Model (SM) is proposed: the Fuzzy Standard Model (FSM). It is a smooth deformation of the SM based on covariant star-products of fields. This new formalism realizes electroweak symmetry breaking without ghosts at tree-level. We give evidence that the FSM exhibits Vainshtein screening, aka classicalization, in the deep-UV. This could solve the electroweak hierarchy problem if it occurs at the TeV-scale.

France

Ghost-free Electroweak Symmetry Breaking with Weakly Nonlocal Interactions

We show that the rank decomposition of a real matrix \(r\), which is a Spin(3,1) tensor, leads to \(2k\) Majorana bispinors, where \(k= \mathrm {rank}\: r\). The Majorana bispinors are determined up to local GL\((k, \mathbb {R})\) transformations. The bispinors are combined in pairs to form \(k\) complex Dirac fields. We analyze in detail the case \(k=1\), in which there is just one Dirac field with the well-known standard Lagrangian. The GL\((1, \mathbb {R})\) symmetry gives rise to a new conserved current, different from the well-known U(1) current. The U(1) symmetry is present too. All global continuous internal symmetries in the \(k=1\) case form the SO(2,1) group. As a side result, we clarify the discussed in literature issue whether there exist algebraic constraints for the matrix \(r\) which would be equivalent to the condition \(\mathrm {rank}\: r=1\).

Note on Spin(3,1) Tensors, the Dirac Field and GL\((k, \mathbb {R})\) Symmetry

In this work, the possible dynamics of the massive leptonic photon \(Z_{l}\) are reconsidered via the \(e^{+}e^{-}\rightarrow \mu ^{+}\mu ^{-}\) process at the Compact Linear Collider (CLIC) with the updated center-of-mass energies (380, 1500, and 3000 GeV). We show that new generation colliders as CLIC can observe the massive leptophilic vector boson \(Z_{l}\) with mass up to the center-of-mass energy, provided that the leptonic coupling constant is \(g_{l}\geq 10^{-3}\). In this study, we also estimated the cross sections by artificial neural networks using the theoretical results we obtained for CLIC. According to the results obtained, it was seen that these predictions could be made through machine learning.

Türkiye

A Search for Leptonic Photon, \(Z_{l}\), at All Three CLIC Energy Stages by Using Artificial Neural Networks (ANN)

In these lectures, we present the behavior of conventional \(\bar {q}q\) mesons, glueballs, and hybrids in the large-\(N_{c}\) limit of QCD. To this end, we use an approach based on rather simple “NJL-like” bound-state equations. The obtained large-\(N_{c}\) scaling laws are general and coincide with the known results. A series of consequences, such as the narrowness of certain mesons and the smallness of some interaction types, the behavior of chiral and dilaton models at large \(N_{c},\) and the relation to the compositeness condition and the standard derivation of large-\(N_{c}\) results, are explained. The bound-state formalism shows also that mesonic molecular and dynamically generated states do not form in the large-\(N_{c}\) limit. The same fate seems to apply also to tetraquark states, but here further studies are needed. Next, following the same approach, baryons are studied as bound states of a generalized diquark (\(N_{c}-1\) antisymmetric object) and a quark. Similarities and differences with regular mesons are discussed. All the standard scaling laws for baryons and their interaction with mesons are correctly reproduced. The behavior of chiral models involving baryons and describing chirally invariant mass generation is investigated. Finally, properties of QCD in the medium at large\(N_{c}\) are studied: the deconfinement phase transition is investigated along the temperature and the chemical potential directions, respectively. While the critical temperature for deconfinement \(T_{\mathrm {dec}}\) is \(N_{c}\)-independent\(,\) the critical chemical potential is not and increases for growing \(N_{c},\) thus for very large \(N_{c}\), one has confined matter below \(T_{\mathrm {dec}}\) and deconfined above. Yet, in the confined phase but for large densities, one has a ‘stiff-matter’ phase whose pressure is proportional to \(N_{c}\) (just as a gas of quarks would do) in agreement with a quarkyonic phase. Within the QCD phase diagrams, the features of different models at large\(N_{c}\) are reviewed and the location of the critical endpoint is discussed. In the end, the very existence of nuclei and the implications of large-\(N_{c}\) arguments for neutron stars are outlined.

Introductory Visual Lecture on QCD at Large \(N_{c}\): Bound States, Chiral Models, and Phase Diagram

Understanding the properties and physical phase of the dense strongly interacting matter present in the cores of neutron stars or created in their binary mergers remains one of the most prominent open problems in nuclear astrophysics. While most microscopic analyses have historically relied on solvable phenomenological models of nuclear and quark matter, in recent years a model-independent approach utilizing only controlled ab-initio calculations and astrophysical observations has emerged as a viable alternative.In these lecture notes, I review recent progress in first-principles weak-coupling calculations within high-density quark matter, shedding light on its thermodynamic and transport properties. I cover the most important technical tools used in such calculations, introduce selected highlight results, and explain how this information can be used in phenomenological studies of neutron-star physics. The notes do not offer a self-consistent treatment of the topics covered, but rather aim at filling gaps in existing textbooks on thermal field theory and at connecting the dots in a story developed in several recent research articles, to which the interested reader is directed for further technical details.

Finland

Particle-theory Input for Neutron-star Physics

In these lecture notes, I review how to use large-\(N\) techniques to solve quantum field theories in various dimensions. In particular, the case of \(N\)‑dimensional quantum mechanics, non-relativistic cold and dense neutron matter, and scalar field theory in four dimensions are covered. A recurring theme is that large-\(N\) solutions are fully non-perturbative, and can be used to reliably access quantum field theory for parameter regions where weak-coupling expansions simply fail.

United States

Quantum Field Theory in Large-\(N\) Wonderland: Three Lectures

The QCD effective charge extracted from the experimental data is used to construct the vector interaction of a Dirac relativistic model for the charmonium spectrum. The process required to fit the spectrum is discussed and the relationship with a previous study of the vector interaction is analyzed.