We study the transverse momentum ( $p_T$ ) differential anisotropic flow and flow fluctuation in Pb+Pb collisions at $\sqrt{s_{_{NN}}}$ =5.02 TeV at the LHC. A (3+1)-dimensional CLVisc hydrodynamics framework with fluctuating TRENTO (or AMPT) initial conditions is utilized to simulate the space-time evolution of the quark-gluon plasma (QGP) medium. The effects of shear viscosity and the sub-nucleon structure on anisotropic flow and flow fluctuation are analyzed. Our result shows that shear viscosity tends to suppress both flow coefficients ( ${v_2\{2}\}$ , ${v_2\{4\}}$ , and ${\langle v_2\rangle}$ ) and flow fluctuation ( ${\sigma_{v_2}}$ ) owing to its smearing effect on local density fluctuation. The flow coefficients appear to be insensitive to the sub-nucleon structure, whereas the flow fluctuation ${\sigma_{v_2}}$ tends to be suppressed by the sub-nucleon structure in central collisions but enhanced in peripheral collisions. After taking into account the sub-nucleon structure effect, our numerical result can qualitatively describe the relative flow fluctuations ( ${v_2\{4\}/v_2\{2\}}$ , $F({v_2})$ ) measured by the ALICE Collaboration at the LHC. We further investigate the effects of shear viscosity, sub-nucleon structure, and initial condition model on the flow angle and flow magnitude decorrelations ( ${A_2^f}$ , ${M_2^f}$ ) using the four-particle correlation method. We find that the flow decorrelation effect is typically stronger in central collisions than in peripheral collisions. The flow angle decorrelation is found to be insensitive to the shear viscosity and sub-nucleon structure, whereas the flow magnitude decorrelation shows quite different behaviors when using the TRENTO and AMPT initial condition models. Our study sheds light on the anisotropic flow, transport properties, and initial structure of the QGP created in high-energy nuclear collisions.

China

Germany

Jie Zhu

Canada

Xiang-Yu Wu

Guang-You Qin

Anisotropic flow, flow fluctuation, and flow decorrelation in relativistic heavy-ion collisions: the roles of sub-nucleon structure and shear viscosity * Supported in part by the Natural Science Foundation of China (12225503, 11890710, 11890711, 11935007). Zhu Jie is supported in part by the China Scholarship Council (202306770009). Wu Xiang-Yu is supported in part by the National Science Foundation within the framework of the JETSCAPE collaboration (OAC-2004571) and in part by the Natural Sciences and Engineering Research Council of Canada. Some of the calculations were performed in the Nuclear Science Computing Center at Central China Normal University (NSC$^{3}$), Wuhan, Hubei, China.

We present a systematic investigation of lepton pair production through photon-photon fusion processes in heavy-ion collisions. It is demonstrated that the dilepton production at a given impact parameter ( <math altimg='si1.svg'><msub><mrow><mi>b</mi></mrow><mrow><mo>&#8869;</mo></mrow></msub></math>) with a fixed transverse momentum imbalance ( <math altimg='si2.svg'><msub><mrow><mi>q</mi></mrow><mrow><mo>&#8869;</mo></mrow></msub></math>) can be factorized into a unified formula in terms of the Wigner photon distribution of heavy nuclei. We show that this framework provides a comprehensive description of all the relevant data from RHIC to the LHC, with a strong evidence that the quasi-real photon can be radiated not only from the nucleus as a whole, standing for the coherent contribution, but also from the sub-structures inside the nucleus, representing the incoherent contribution. Further predictions are made for the anisotropies in the correlations between <math altimg='si2.svg'><msub><mrow><mi>q</mi></mrow><mrow><mo>&#8869;</mo></mrow></msub></math>, <math altimg='si1.svg'><msub><mrow><mi>b</mi></mrow><mrow><mo>&#8869;</mo></mrow></msub></math>, and the dilepton transverse momentum ( <math altimg='si3.svg'><msub><mrow><mi>P</mi></mrow><mrow><mo>&#8869;</mo></mrow></msub></math>). This will help us to constrain the photon Wigner distribution which plays a crucial role to study the gluonic matter of nucleus at small- <italic>x</italic> through the diffractive photoproduction processes in heavy ion collision.

France

Yu Shi

Hong Kong

Spain

Lin Chen

Shu-Yi Wei

Bo-Wen Xiao

Lighting up the photon Wigner distribution via dilepton productions

We explore the impact of initial state soft gluon radiations on the azimuthal angle asymmetries in photo-production of hard di-jet via coherent diffraction in ultraperipheral heavy ion collisions, as well as in electron-proton (ep) and electron-nucleus (eA) collisions. The primary production mechanism is identified as the diffractive production of two hard jets, accompanied by a collinear gluon emission along the beam direction. In contrast, the diffractive exclusive di-jet production, where the initial state radiation is absent, is suppressed due to color transparency. Our analysis shows that azimuthal asymmetries, traditionally attributed to final state gluon emissions, are reduced by the presence of initial state radiations. The sensitivity of azimuthal asymmetries to both initial and final state radiations suggests that they could provide novel insights into the mechanisms of di-jet production in diffractive processes.

Ding Shao

Cheng Zhang

Jian Zhou

Ya-jin Zhou

Revisiting azimuthal angular asymmetries in diffractive di-jet production

Conditions for anti-Unruh effect in (1+1)-dimensional spacetime are obtained. For detectors with Gaussian switching functions, the analytical results are similar to previous ones, indicating that anti-Unruh effect occurs when the energy gap matches the characteristic time scale. However, this conclusion does not hold for detectors with square wave switching functions, in which case the condition turns out to depend on both the energy gap and the characteristic time scale in some nontrivial way. We also show analytically that there is no anti-Unruh effect for detectors with Gaussian switching functions in (3+1)-dimensional spacetime.

Dawei Wu

Ji-chong Yang

Conditions for anti-Unruh effect

We study two accelerating Unruh-DeWitt detectors coupled linearly or quadratically with a scalar field, by using an approach different from previous ones. We use Rindler frame, and integrate over the spacetime coordinates before over the momenta. In this way, the divergent problem previously encountered is avoided. We show that entanglement between the detectors can be created by coupling with the field, and is divergent only in the limit that the two detectors coincide in spacetime. For linear coupling, entanglement increases monotonically with the decrease of acceleration, as previously found, while for quadratic coupling, entanglement behaves non-monotonically, as noted for the first time.

Shan-Chang Tang

Birth and death of entanglement between two accelerating Unruh-DeWitt detectors coupled with a scalar field

We extend the previously developed small-<math><mrow><mi>x</mi></mrow></math> parton shower algorithm to include the kinematic constraint effect and <math><msub><mi>k</mi><mi>t</mi></msub></math> resummation effect. This work enables the Monte Carlo generator to simultaneously resum large-<math><msub><mi>k</mi><mi>t</mi></msub></math> and small-<math><mi>x</mi></math> logarithms in the saturation regime for the first time. It is an important step towards simulating processes involving multiple well separated hard scales, such as dijet production in eA collisions at the EIC.

Parton shower algorithm with the saturation effect

We obtain an exact rotating BTZ-like black hole solution by solving the corresponding gravitational field equations and the bumblebee motion equations in Einstein-bumblebee gravity theory. Result is presented for the purely radial Lorentz symmetry violating and can only exist with a linear functional potential of the bumblebee field. This black hole has two horizons and an ergosphere which are dependent on the bumblebee coupling constant  $$\ell $$  <math> <mi>ℓ</mi> </math>  . The concepts of the area and volume of the horizon should be renewed in this LV spacetime due to the nontrivial contribution of coupling between the bumblebee field and the Ricci tensor. Only in this way, the entropy-area relation, first law of thermodynamics and the Smarr formula can still be constructed. We also study the AdS/CFT correspondence of this black hole, find that the entropy product of its inner and outer horizons is universal. So the central charges of the dual CFT on the boundary can be obtained via the thermodynamic method, and they can reappear black hole mass and angular momentum in the bulk.

Chikun Ding

Jun Chen

Yuebing Zhou

Changqing Liu

Yuehua Xiao

Rotating BTZ-like black hole and central charges in Einstein-bumblebee gravity

The behavior of accelerating Unruh-DeWitt detectors coupled with a spinor field in (3+1)-dimensional spacetime is investigated. For a single point-like detector with Gaussian switching function, the transition probability increases with the acceleration and thus the antiUnruh effect effect cannot occur. Due to the spinor structure of the Dirac field, UV divergences are encountered in the calculation of the entanglement between the detectors. After introducing some UV cutoff Λ, the negativity of detectors is shown to behave nonmonotonically with respect to the acceleration. Besides, the negativity increases with the cutoff Λ and decreases with the distance between the detectors. The mutual information between the two detectors is also discussed.

Accelerating Unruh-DeWitt detectors coupled with a spinor field

Using the RT formula and the subregion CV conjecture, we numerically investigate the holographic entanglement entropy (HEE) and holographic subregion complexity (HSC) for two holographic d-wave superconducting models with backreactions. We find that the HEE and HSC can probe these two d-wave superconducting phase transitions. The HEE of the superconducting phase is always lower than that of the normal phase. For the HSC, however, it behaves differently and interestingly, which depends on both the strip-width  $$L_{x}$$  <math> <msub> <mi>L</mi> <mi>x</mi> </msub> </math>   and backreaction  $$\kappa $$  <math> <mi>κ</mi> </math>  . More specifically, when the backreaction is larger than a particular critical value, or the strip-width of the boundary subsystem is smaller than a particular critical value, the HSC in the superconducting phase is larger than that in the normal phase, and vice versa.

Yuanceng Xu

Dong Wang

Qiyuan Pan

Holographic entanglement entropy and complexity for D-wave superconductors

We develop a novel Monte Carlo parton branching algorithm based on the Gribov-Levin-Ryskin (GLR) equation. The formulations of both forward evolution and backward evolution for the GLR equation are presented. The results from the Monte Carlo implementation of the GLR equation are in full agreement with its numerical solutions. Our work thus paves the way for developing an event generator that embodies the saturation effect.