Dark photons, the hypothetical gauge bosons associated with an additional <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>U</mi><msup><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mo>′</mo></msup></mrow></math> symmetry, can couple to standard model particles through a small kinetic mixing parameter <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ɛ</mi></math> with the ordinary photon. This mechanism provides a portal between the dark sector and visible matter. In this study, we present a procedure to derive theoretical upper bounds on the kinetic mixing parameter <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>ɛ</mi><mn>2</mn></msup><mrow><mo>(</mo><msub><mi>M</mi><mi>U</mi></msub><mo>)</mo></mrow></mrow></math> by analyzing dilepton spectra from heavy-ion collisions across a broad energy range, from SIS to LHC energies. Our analysis is based on the microscopic parton-hadron-string dynamics (PHSD) transport approach, which successfully reproduces the measured dilepton spectra in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mo>+</mo><mi>p</mi></mrow><mo>,</mo><mo> </mo><mrow><mi>p</mi><mo>+</mo><mi>A</mi></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>A</mi><mo>+</mo><mi>A</mi></mrow></math> collisions across the same energy range. Besides the dilepton channels resulting from interactions and decays of standard model particles (such as mesons and baryons), the PHSD has been extended to include the decay of hypothetical dark photons into dileptons, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>U</mi><mo>→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></mrow></math>. The production of these dark photons occurs via Dalitz decays of <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>π</mi><mn>0</mn></msup><mo>,</mo><mo> </mo><mi>η</mi><mo>,</mo><mo> </mo><mi>ω</mi><mo>,</mo><mo> </mo><msup><mi>η</mi><mo>′</mo></msup></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Δ</mi></math> resonances; direct decays of <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ρ</mi><mo>,</mo><mo> </mo><mi>ω</mi></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ϕ</mi></math>; the kaon mode <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>K</mi><mo>+</mo></msup><mo>→</mo><msup><mi>π</mi><mo>+</mo></msup><mi>U</mi></mrow></math>; and thermal <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>q</mi><mover accent="true"><mi>q</mi><mo>¯</mo></mover></mrow></math> annihilation in the quark-gluon plasma. Our results show that high-precision measurements of dilepton spectra in heavy-ion collisions provide a sensitive and competitive probe of dark photons in the MeV to multi-GeV mass range. Furthermore, we quantify the experimental accuracy required to constrain the remaining viable parameter space of kinetic mixing in dark photon scenarios.

Germany

A.W. Romero Jorge

E. Bratkovskaya

T. Song

L. Sagunski

Constraints on kinetic mixing of dark photons from dilepton spectra

We present an updated deep neural network model for inclusive electron–carbon scattering. Using the bootstrap model [B. E. Kowal et al., <a href="http://dx.doi.org/10.1103/PhysRevC.110.025501">Phys. Rev. C 110, 025501 (2024)</a>], we incorporate recent experimental data, as well as older measurements in the deep inelastic scattering region, to derive a reoptimized posterior model. We examine the impact of these new inputs on model predictions and associated uncertainties. Finally, we evaluate the resulting cross-section predictions in the kinematic range relevant to the Hyper-Kamiokande and DUNE experiments.

Poland

Beata E. Kowal

Krzysztof M. Graczyk

Artur M. Ankowski

Rwik Dharmapal Banerjee

Jose L. Bonilla

Hemant Prasad

Jan T. Sobczyk

Re-optimization of a deep neural network model for electron-carbon scattering using new experimental data

The mean transverse momentum <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>〈</mo><msub><mi>p</mi><mi>T</mi></msub><mo>〉</mo></mrow></math> of hadrons has been observed experimentally and in numerical simulations to have a power-law dependence on the hadronic multiplicity <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi></math> in ultracentral relativistic heavy-ion collisions: <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mo>〈</mo><msub><mi>p</mi><mi>T</mi></msub><mo>〉</mo></mrow><mo>∝</mo><msup><mi>N</mi><msub><mi>b</mi><mi>UC</mi></msub></msup></mrow></math>. It has been put forward that this exponent <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>b</mi><mi>UC</mi></msub></math> is the speed of sound of quark-gluon plasma measured at a temperature determined from <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>〈</mo><msub><mi>p</mi><mi>T</mi></msub><mo>〉</mo></mrow></math>. We study step by step the connection between (i) the energy and entropy of hydrodynamic simulations and (ii) experimentally measurable observables. We show that an argument based on energy and entropy should yield an exponent equal to the pressure over energy density <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>P</mi><mo>/</mo><mi>ɛ</mi></mrow></math>, rather than the speed of sound <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi>c</mi><mi>s</mi><mn>2</mn></msubsup></math>; however, we also observe that <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>〈</mo><msub><mi>p</mi><mi>T</mi></msub><mo>〉</mo></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi></math> are not sufficiently accurate proxies for the energy and entropy to make this possible in practice. From simulations, we find that the exponent <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>b</mi><mi>UC</mi></msub></math> is significantly different whether the “effective volume” is strictly constant or not, a condition that cannot be enforced experimentally. Additional tests using a modified equation of state find that the exponent <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>b</mi><mi>UC</mi></msub></math> exhibits a variable degree of correlations with the speed of sound and with <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>P</mi><mo>/</mo><mi>ɛ</mi></mrow></math>, but is not an accurate measurement of either quantity in general.

United States

Lorenzo Gavassino

Henry Hirvonen

Jean-Francois Paquet

Mayank Singh

Brazil

Gabriel Soares Rocha

Feasibility of measuring the speed of sound of the quark-gluon plasma from the multiplicity and mean <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi>T</mi></msub></math> of ultracentral heavy-ion collisions

The nucleon exhibits a rich internal structure governed by quantum chromodynamics (QCD), where its electric charge arises from valence quarks, while its spin and mass emerge from complex interactions among valence quarks, sea (anti)quarks, and gluons. At the advent of QCD, an alternative hypothesis emerged suggesting, at high energies, the transport of a nucleon's baryon number could be traced by a nonperturbative configuration of gluon fields connecting its three valence quarks, forming a <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>Y</mi></math>-shaped topology known as the gluon junction. Recent measurements by the STAR experiment are compatible with this scenario. In light of these measurements, this study aims to explore the mechanisms of baryon transport in high-energy nuclear collisions using the pythia-8 framework, which incorporates a state-of-the-art hadronization model with advanced color flow (CF) and color reconnection (CR) mechanisms that mimic signatures of a baryon junction. Within this model setup, we investigate (i) the rapidity slope of the net-baryon distributions in photon-included processes <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>(</mo><mi>γ</mi><mo>+</mo><mi>p</mi><mo>)</mo></mrow></math> and (ii) baryon over charge transport in the isobaric <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>(</mo><mi>Ru</mi><mo>+</mo><mi>Ru</mi></mrow><mo> </mo><mtext>and</mtext><mo> </mo><mrow><mi>Zr</mi><mo>+</mo><mi>Zr</mi><mo>)</mo></mrow></math> collisions. Our study highlights the importance of the CF and CR mechanisms in pythia-8, which play a crucial role in baryon transport. The results show that the CF and CR schemes significantly affect the isobaric baryon-to-charge ratio, leading to different predictions for baryon stopping and underscoring the need to account for CF and CR effects in comparisons with experimental measurements.

Niseem Magdy

Prithwish Tribedy

Chun Yuen Tsang

Zhangbu Xu

Understanding baryon stopping at the BNL Relativistic Heavy Ion Collider top energies

In our previous work [<a href="http://dx.doi.org/10.1103/PhysRevC.101.014003">Phys. Rev. C 101, 014003 (2020)</a>], we analyzed all available data on differential cross sections and spin density matrix elements for the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><mi mathvariant="normal">Λ</mi></mrow></math> reaction using an effective Lagrangian approach. There, the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>t</mi></math>-channel <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>K</mi><mo>,</mo><mo> </mo><msup><mi>K</mi><mo>*</mo></msup></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>κ</mi></math> exchanges, the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>u</mi></math>-channel <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Λ</mi><mo>,</mo><mo> </mo><mi mathvariant="normal">Σ</mi></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi mathvariant="normal">Σ</mi><mo>*</mo></msup></math> exchanges, the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>s</mi></math>-channel <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi><mo>,</mo><mo> </mo><mrow><mi>N</mi><mrow><mo>(</mo><mn>2060</mn><mo>)</mo></mrow><mn>5</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mrow><mo>(</mo><mn>2000</mn><mo>)</mo></mrow><mn>5</mn><mo>/</mo><msup><mn>2</mn><mo>+</mo></msup></mrow></math> exchanges, and the interaction current were taken into account in constructing the reaction amplitudes. It was found that, overall, the agreement of the theoretical results with the corresponding data is fairly good. However, noticeable discrepancies between the model results and the data on spin density matrix elements <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>ρ</mi><mn>00</mn></msub></math> are still observed in the center-of-mass energy region around <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>W</mi><mo>≈</mo><mn>2.08</mn></mrow></math> GeV, indicating the need for additional reaction mechanisms. On the other hand, the hidden-strange pentaquark-like state <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mrow><mo>(</mo><mn>2080</mn><mo>)</mo></mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math>, which is proposed to be a <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>K</mi><mo>*</mo></msup><mi mathvariant="normal">Σ</mi></mrow></math> molecular state as the strange partner of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>P</mi><mi>c</mi></msub><mrow><mo>(</mo><mn>4457</mn><mo>)</mo></mrow></mrow></math> hadronic molecule, has been found to play quite active roles in reproducing the data for <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>K</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><msup><mi mathvariant="normal">Σ</mi><mn>0</mn></msup></mrow><mo>,</mo><mo> </mo><mrow><msup><mi>K</mi><mrow><mo>*</mo><mn>0</mn></mrow></msup><msup><mi mathvariant="normal">Σ</mi><mo>+</mo></msup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>ϕ</mi><mi>p</mi></mrow></math> photoproduction reactions. Based on these observations, in the present work, we reanalyze the data for the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><mi mathvariant="normal">Λ</mi></mrow></math> reaction by incorporating the pentaquark-like state <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mrow><mo>(</mo><mn>2080</mn><mo>)</mo></mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> in our previously proposed model. The results show that, with the inclusion of the contributions of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mrow><mo>(</mo><mn>2080</mn><mo>)</mo></mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math>, the quality of the theoretical description of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><mi mathvariant="normal">Λ</mi></mrow></math> data can be considerably improved. In particular, the data on spin density matrix elements <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>ρ</mi><mn>00</mn></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Re</mi><mspace width="0.16em"></mspace><msub><mi>ρ</mi><mn>10</mn></msub></mrow></math> in the near-threshold energy region are significantly better reproduced. This achievement indicates that the hypothesis of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mrow><mo>(</mo><mn>2080</mn><mo>)</mo></mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> molecular state is compatible with the available data for the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><mi mathvariant="normal">Λ</mi></mrow></math> reaction. The reaction mechanism of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><mi mathvariant="normal">Λ</mi></mrow></math> is analyzed and the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mrow><mo>(</mo><mn>2080</mn><mo>)</mo></mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow><mo>,</mo><mo> </mo><mrow><mi>N</mi><mrow><mo>(</mo><mn>2060</mn><mo>)</mo></mrow><mn>5</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow><mo>,</mo><mo> </mo><mrow><mi>N</mi><mrow><mo>(</mo><mn>2000</mn><mo>)</mo></mrow><mn>5</mn><mo>/</mo><msup><mn>2</mn><mo>+</mo></msup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>K</mi></math> exchanges are found to provide dominant contributions.

China

Wen-Ya Tian

Neng-Chang Wei

Yu-Fei Wang

Fei Huang

Bing-Song Zou

Effects of the hadronic molecule <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mrow><mo>(</mo><mn>2080</mn><mo>)</mo></mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> on <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>K</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><mi mathvariant="normal">Λ</mi></mrow></math> photoproduction

We present a framework for spin dynamics in the quark-gluon plasma created in relativistic heavy-ion collisions. Under the approximation of small polarization, macroscopic spin degrees of freedom decouple from the background, and their evolution equations and transport coefficients have been computed using quantum kinetic theory of massive particles with nonlocal collisions. Employing this theory, we numerically solve dissipative relativistic spin hydrodynamics. We explore three interaction scenarios between constituent particles and apply this framework to compute both global and local spin polarization of <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Λ</mi></math> hyperons in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV. Our results show that the initially vanishing spin potential relaxes toward thermal vorticity, driving global polarization. Furthermore, we demonstrate that the sign of longitudinal polarization is sensitive to the interaction type, emphasizing the need for a consistent treatment of dissipative effects in spin hydrodynamics to describe experimental data.

India

 Sapna

Italy

Sushant K. Singh

David Wagner

Spin polarization of <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Λ</mi></math> hyperons from dissipative spin hydrodynamics

We investigate hidden-charm molecular states in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Ξ</mi><mi>c</mi><mrow><mo>(</mo><mo>′</mo><mo>,</mo><mo>*</mo><mo>)</mo></mrow></msubsup><msup><mover accent="true"><mi>D</mi><mo>¯</mo></mover><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup></mrow></math> systems using the one-boson exchange model. By regulating the short-range interactions with parameter <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi></math> and cutoff <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Λ</mi></math>, we found ten bound states in isoscalar systems. Our analysis reveals that if the LHCb Collaboration's <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>P</mi><mrow><mi>c</mi><mi>s</mi></mrow></msub><mrow><mo>(</mo><mn>4459</mn><mo>)</mo></mrow></mrow></math> and Belle Collaboration's <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>P</mi><mrow><mi>c</mi><mi>s</mi></mrow></msub><mrow><mo>(</mo><mn>4472</mn><mo>)</mo></mrow></mrow></math> pentaqurks are indeed distinct states, their mass splitting can be resolved through <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Ξ</mi><mi>c</mi><mo>′</mo></msubsup><mover accent="true"><mi>D</mi><mo>¯</mo></mover><mtext>−</mtext><msub><mi mathvariant="normal">Ξ</mi><mi>c</mi></msub><msup><mover accent="true"><mi>D</mi><mo>¯</mo></mover><mo>*</mo></msup></mrow></math> coupled-channel dynamics using consistent model parameters. This framework assigns <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>1</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> spin-parity quantum numbers to <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>P</mi><mrow><mi>c</mi><mi>s</mi></mrow></msub><mrow><mo>(</mo><mn>4459</mn><mo>)</mo></mrow></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>P</mi><mrow><mi>c</mi><mi>s</mi></mrow></msub><mrow><mo>(</mo><mn>4472</mn><mo>)</mo></mrow></mrow></math>, respectively. With this consistent model parameter, we predict several new molecular candidates in the 4.3–4.7 GeV mass region, demonstrating the crucial interplay between coupled-channel effects and short-range dynamics in understanding hidden-charm pentaquarks as hadronic molecules. Additionally, we investigate the effects of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Λ</mi><msub><mi>η</mi><mi>c</mi></msub></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Λ</mi><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> decay channels on the predicted molecular states, showing how these channels influence pole positions and provide insights into the detectability of these states through different production mechanisms.

Ziye Wang

Nijiati Yalikun

Yakefu Reyimuaji

Role of the short-range dynamics in a simultaneous interpretation of <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>P</mi><mrow><mi>c</mi><mi>s</mi></mrow></msub></math> pentaquarks as <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Ξ</mi><mi>c</mi><mrow><mo>(</mo><mo>′</mo><mo>,</mo><mo>*</mo><mo>)</mo></mrow></msubsup><msup><mover accent="true"><mi>D</mi><mo>¯</mo></mover><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup></mrow></math> molecules

The quantum-mechanical definition of probability, the uncertainty principle, and Poincaré invariance provide strong basic restrictions on the ability to define spatial densities associated with form factors describing the properties of confined systems of relativistically moving constituents. Despite this, many papers ignore one or more of these restrictions. Here I show how to obtain time-independent, two-dimensional densities that are consistent with the stated restrictions. This is done using the light-front, infinite momentum frame formalism. Two-dimensional density interpretations of the axial-vector form factor and all three gravitational form factors is obtained. The resulting mass radius is smaller than the charge radius. Additionally, an expression of a two-dimensional mass density related to the trace of the energy momentum tensor is obtained. I also show that all known methods for finding three-dimensional densities—using the Breit frame, Abel transformations, Wigner distributions, and spherically symmetric wave packets with vanishing spatial extent—violate the basic restrictions in different ways. Furthermore, the use of the latter leads to densities that vanish almost everywhere in space as time increases from an initial value.

Gerald A. Miller

Impossibility of obtaining time-independent, three-dimensional, spherically symmetric densities of confined systems of relativistically moving constituents

We study magnetic properties of the hadron resonance gas in the presence of a strong (<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>0</mn><mo>≤</mo><mi>B</mi><mo>≤</mo><mn>0.15</mn><mspace width="4pt"></mspace><msup><mrow><mi>GeV</mi></mrow><mn>2</mn></msup></mrow></math>) magnetic field, using physical values of the magnetic moments of hadrons, i.e., including their anomalous parts. The values of these moments are taken from experiment, or when unavailable, from theoretical estimates. We evaluate the conserved charge susceptibilities, finding the expected sizable effects of the anomalous magnetic moments, in particular for the octet baryons, such as the proton and neutron, where they are exceptionally large. We also study in detail the large effects of the magnetic moments of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Δ</mi><mo>(</mo><mn>1232</mn><mo>)</mo></mrow></math> states, for which various theoretical estimates and experimental values differ significantly. We compare our model results with the lattice quantum chromodynamics data and find reasonable agreement within the model uncertainty.

Rupam Samanta

Wojciech Broniowski

Magnetic properties of the hadron resonance gas with physical magnetic moments

The photon production process <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>f</mi><mo>→</mo><mi>f</mi><mo>+</mo><mi>γ</mi></mrow></math> in the presence of a time-dependent chiral chemical potential <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>μ</mi><mn>5</mn></msub></math> is studied. The validity of the adiabatic approximation is demonstrated in the ultrarelativistic limit. Analytical expressions for the photon spectrum are derived for two models of the chiral magnetic conductivity <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>b</mi><mn>0</mn></msub><mo>∝</mo><msub><mi>μ</mi><mn>5</mn></msub></mrow></math>: (i) <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>b</mi><mn>0</mn></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>=</mo><msub><mi>A</mi><mn>1</mn></msub><mo>+</mo><msub><mi>B</mi><mn>1</mn></msub><mo form="prefix">tanh</mo><mrow><mo>(</mo><mi>t</mi><mo>/</mo><mi>τ</mi><mo>)</mo></mrow></mrow></math> and (ii) <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>b</mi><mn>0</mn></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>=</mo><msub><mi>A</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>t</mi><mo>/</mo><mi>τ</mi><mo>)</mo></mrow><mo>/</mo><mrow><mo>(</mo><mn>1</mn><mo>+</mo><msup><mi>t</mi><mn>2</mn></msup><mo>/</mo><msup><mi>τ</mi><mn>2</mn></msup><mo>)</mo></mrow></mrow></math>. It is known that, for constant <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>b</mi><mn>0</mn></msub></math>, photon emission may exhibit a resonance for one-photon polarization depending on the sign of <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>b</mi><mn>0</mn></msub></math>. It is shown that, in model (i), up to two resonances may occur, depending on the sign of the asymptotic values <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>b</mi><mn>0</mn></msub><mrow><mo>(</mo><mi>∞</mi><mo>)</mo></mrow></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>b</mi><mn>0</mn></msub><mrow><mo>(</mo><mo>−</mo><mi>∞</mi><mo>)</mo></mrow></mrow></math>. No resonances are observed in model (ii). Numerical calculations are performed using parameters relevant to quark-gluon plasma, and the universality of the results is discussed.

Kirill Tuchin

Chiral Cherenkov radiation in the presence of a time-dependent chiral chemical potential