We present a novel approach for investigating the spin structure of hadrons based on the two-point function in quantum field theory. In a rotating frame, we derive two independent expressions of the two-point function and identify their equivalence, which allows for a complete decomposition of the total spin of a composite system into the angular momenta of its constituent particles. Applying this approach to the proton, we analyze its spin structure in the massless quark limit. Our results indicate that the quark spin contribution accounts for approximately 27% of the total proton spin at a low-energy scale, significantly deviating from the prediction of the non-relativistic quark model.

Japan

HyungJoo Kim

Philipp Gubler

Poland

Chihiro Sasaki

Proton spin decomposition via QCD sum rules

<p>The degeneracy of chiral partners is an ideal signal for measuring the restoration of the spontaneously broken chiral symmetry in QCD. In this work we investigate the observability of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ϕ</mi></math> - <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>f</mi><mn>1</mn></msub><mrow><mo>(</mo><mn>1420</mn><mo>)</mo></mrow></mrow></math> degeneracy in the J-PARC E16 experiment, which measures dielectrons emitted from 30-GeV pA collisions. We for this purpose make use of an effective Lagrangian approach, which naturally incorporates the broken charge-conjugation symmetry in nuclear matter and the ensuing anomaly-induced mixing between vector and axial-vector mesons, to compute the spectral function relevant for the experimental measurement. The real-time dynamics of the pA collision is obtained from a transport simulation. Including experimental background and resolution effects on top of that, we find that a signal of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ϕ</mi></math> - <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>f</mi><mn>1</mn></msub><mrow><mo>(</mo><mn>1420</mn><mo>)</mo></mrow></mrow></math> mixing can be observed at around 2.5 <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>σ</mi></math>, with the Run2 statistics planned for the J-PARC E16 experiment with an ideal mixing strength.</p>

Ren Ejima

Kenta Shigaki

Toward a direct measurement of partial restoration of chiral symmetry at J-PARC E16 via density-induced chiral mixing

We discuss the modeling of the hadronic phase of QCD at finite magnetic field in the framework of hadron resonance gas (HRG). We focus on the statistical description of particle yields that include contribution from resonance decays. We demonstrate that the swift increase in the number of protons with magnetic field predicted in the HRG is due to the assumption of structureless resonances. We discuss fluctuations of conserved charges and show that at present the qualitative comparison of the model predictions with the lattice QCD data should be treated with care. We also discuss the principle of detailed balance which allows us to study the magnetic field dependence of neutral resonances.

Michał Marczenko

Michał Szymański

Pok Man Lo

Bithika Karmakar

Pasi Huovinen

Krzysztof Redlich

Magnetic effects in the hadron resonance gas

We investigate the effect of screening of the four-quarks contact interactions by the ring diagram at finite temperature and density in an effective chiral model inspired by QCD in the Coulomb gauge. As a consequence, a medium-dependent coupling naturally emerges which, in a class of chiral models, brings the chiral crossover temperature down to the value calculated in lattice QCD at low net-baryon density. Furthermore, it implies a stronger divergence of the chiral susceptibility at the critical point compared to the mean-field dynamics. At high densities, the screening induces a substantial instability region and its size depends on the regularization schemes. We discuss the properties of an effective potential for a class of models described by momentum-independent gap equations. In particular, we introduce the method to construct an approximate effective potential from the gap equations to determine the location of the first-order phase transition.

Influence of dynamical screening of four-quarks interaction on the chiral phase diagram

We present for the first time a Friedmann-like construction in the framework of an osculating Finsler–Randers–Sasaki (F–R–S) geometry. In particular, we consider a vector field in the metric on a Lorentz tangent bundle, and thus the curvatures of horizontal and vertical spaces, as well as the extra contributions of torsion and non-linear connection, provide an intrinsic richer geometrical structure, with additional degrees of freedom, that lead to extra terms in the field equations. Applying these modified field equations at a cosmological setup we extract the generalized Friedmann equations for the horizontal and vertical space, showing that we obtain an effective dark energy sector arising from the richer underlying structure of the tangent bundle. Additionally, as it is common in Finsler-like constructions, we obtain an effective interaction between matter and geometry. Finally, we consider a specific model and we show that it can describe the sequence of matter and dark-energy epochs, and that the dark-energy equation of state can lie in the quintessence or phantom regimes, or cross the phantom divide.

Greece

E. Kapsabelis

Chile

China

Emmanuel Saridakis

P. Stavrinos

Finsler–Randers–Sasaki gravity and cosmology

The exploration of critical phenomena in phase transitions of strongly interacting matter governed by quantum chromodynamics (QCD) is one of the goals of present ultrarelativistic heavy-ion collision experiments at BNL and CERN. The key research direction is to locate the putative critical point on the phase diagram of QCD linked to the chiral symmetry restoration at finite temperature and/or density. One of the main theoretical tools used for this purpose is the fluctuations of conserved charges, such as the net-baryon number. However, due to experimental limitations, analyses of heavy-ion collision data suffer from a very doubtful basing of the net-proton number being a proxy for the total net-baryon number fluctuations. In this work, we use the parity doublet model to investigate the fluctuations of the net-baryon number density in hot and dense hadronic matter. The model accounts for chiral criticality within the mean-field approximation. We focus on the qualitative properties and systematics of the first- and second-order susceptibility of the net-baryon number density, and their ratios for nucleons of positive and negative parity, as well as their correlator. We show that the fluctuations of the positive-parity nucleon do not necessarily reflect the fluctuations of the total net-baryon number density at the phase boundary of the chiral phase transition. We also investigate the nontrivial structure of the correlator. Furthermore, we discuss and quantify the differences between the fluctuations of the net-baryon number density in the vicinity of the chiral and liquid-gas phase transition in nuclear matter. We indicate a possible relevance of our results with the interpretation of the experimental data on net-proton number fluctuations in heavy-ion collisions.

United States

Germany

Volker Koch

Fluctuations and correlations of baryonic chiral partners

We show that there are certain perturbatively stable non-supersymmetric AdS vacua which are also brane-jet stable. Also we extend the analysis of brane-jets to the AdS vacua from curved domain walls like Janus solutions. First, we apply the brane-jet analysis to the non-supersymmetric Janus solutions of type IIB supergravity found by Bak, Gutperle and Hirano. Second, we study the brane-jet of AdS 4 vacua from eleven-dimensional supergravity on Sasaki-Einstein manifolds: the supersymmetric and the skew-whiffed Freund-Rubin, the Pope-Warner, and the Englert solutions. Third, we examine the non-supersymmetric AdS 4 vacua from Q 1,1,1 and M 1,1,1 manifolds discovered by Cassani, Koerber and Varela. It turns out that all the AdS vacua we consider in this work are brane-jet stable. Especially, the Janus, the skew-whipped Freund-Rubin, and the AdS 4 vacua from Q 1,1,1 and M 1,1,1 are perturbatively stable within known subsectors of truncations and also brane-jet stable.

South Korea

Minwoo Suh

Brane-jet stabilities from Janus and Sasaki-Einstein

The 2d (0, 2) supersymmetric gauge theories corresponding to the classes of Y  p,k (ℂℙ1 × ℂℙ1) and Y  p,k (ℂℙ2) manifolds are identified. The complex cones over these Sasaki-Einstein 7-manifolds are non-compact toric Calabi-Yau 4-folds. These infinite families of geometries are the largest ones for Sasaki-Einstein 7-manifolds whose metrics, toric diagrams, and volume functions are known explicitly. This work therefore presents the largest list of 2d (0, 2) supersymmetric gauge theories corresponding to Calabi-Yau 4-folds with known metrics.

Sebastián Franco

Dongwook Ghim

Rak-Kyeong Seong

Brane brick models for the Sasaki-Einstein 7-manifolds Y  p,k (ℂℙ1 × ℂℙ1) and Y  p,k (ℂℙ2)

We construct the spectral functions for light vector mesons at finite density and temperature in the presence of a novel mixing between parity partners, induced by baryon density via the Wess-Zumino-Witten action. As the main origin of in-medium broadening, a set of baryon resonances that strongly couple to the vector mesons and the modifications of kaons and antikaons due to the Kaplan-Nelson term are included. It is shown that the vector spectra, even with the broadening effects, exhibit sizable signatures of chiral symmetry restoration thanks to the chiral mixing depending on three-momenta carried by the vector mesons. Those spectral functions are used to calculate the integrated production rates of lepton pairs, and a proper binning in momenta and potential decrease in the vector-meson masses due to chiral symmetry restoration are discussed in quantifying the signatures.

Anomaly-induced chiral mixing in cold and dense matter

We discuss in detail the different analogues of Dolbeault cohomology groups on Sasaki-Einstein manifolds and prove a new vanishing result for the transverse Dolbeault cohomology groups   <math> <msubsup> <mi>H</mi> <mover> <mi>∂</mi> <mo>¯</mo> </mover> <mfenced> <mi>p</mi> <mn>0</mn> </mfenced> </msubsup> <mfenced> <mi>k</mi> </mfenced> </math>  $$ {H}_{\overline{\partial}}^{\left(p,0\right)}(k) $$  graded by their charge under the Reeb vector. We then introduce a new cohomology, η-cohomology, which is defined by a CR structure and a holomorphic function f with non-vanishing η ≡ df. It is the natural cohomology associated to a class of supersymmetric type IIB flux backgrounds that generalise the notion of a Sasaki-Einstein manifold. These geometries are dual to finite deformations of the 4d   <math> <mi>N</mi> </math>  $$ \mathcal{N} $$  = 1 SCFTs described by conventional Sasaki-Einstein manifolds. As such, they are associated to Calabi-Yau algebras with a deformed superpotential. We show how to compute the η-cohomology in terms of the transverse Dolbeault cohomology of the undeformed Sasaki-Einstein space. The gauge-gravity correspondence implies a direct relation between the cyclic homologies of the Calabi-Yau algebra, or equivalently the counting of short multiplets in the deformed SCFT, and the η-cohomology groups. We verify that this relation is satisfied in the case of S5, and use it to predict the reduced cyclic homology groups in the case of deformations of regular Sasaki-Einstein spaces. The corresponding Calabi-Yau algebras describe non-commutative deformations of ℙ2, ℙ1 × ℙ1 and the del Pezzo surfaces.