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A non-extensive (3+1)-dimensional hydrodynamic model for multi-particle production processes, NEX-CLVisc, is developed in the framework of CLVisc where the viscous corrections are turned off. It assumes that the non-extensive effects consistently exist in the initial conditions set by the optical Glauber model, the equation of state and the hadron kinetic freeze-out procedure. The model is then applied to simulate the pseudo-rapidity ($\eta$) distribution, the transverse momentum ($p_{\rm T}$) spectra and the $p_{\rm T}$-differential elliptic flow ($v_2$) of charged particles in Pb-Pb collisions at $\sqrt{s_{NN}}=$ 2.76 TeV and 5.02 TeV, respectively. It is found that the model can reasonably well reproduce the experimental data of the $\eta$ distribution and the charged-particle spectra in a $p_{\rm T}$ range up to 6-8 GeV/c. When compared with the ideal hydrodynamic model, the $p_{\rm T}$-differential $v_2$ of charged particles is suppressed in the NEX-CLVisc model, which is similar to that observed in the viscous hydrodynamic model. Moreover, due to the lack of the viscous corrections and the event-by-event fluctuation, the model can only describe the $p_{\rm T}$-differential $v_2$ up to 4 GeV/c, which is smaller than the applicable range for the particle $p_{\rm T}$ spectra., Comment: 8 pages, 4 figures, 4 tables

Collective flow coefficients and spin polarization are valuable probes of the geometry and flow velocity field of the quark-gluon plasma (QGP) produced in relativistic heavy-ion collisions. Using a modified TRENTo initial condition coupled to a (3+1)-dimensional (D) viscous hydrodynamic model CLVisc, we study the directed flow and elliptic flow coefficients of hadrons, together with the global polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons in asymmetric Cu+Au collisions. We extend the 2D TRENTo model to the 3D space, and find that the initial tilted geometry of the QGP fireball with respect to the longitudinal direction leads to a decrease of directed flow from positive to negative values with increasing pseudorapidity, an enhancement of elliptic flow at forward and backward pseudorapidities, and a non-monotonic dependence of global polarization on the transverse momentum of hyperons. The initial longitudinal flow velocity gradient further enhances the values of directed flow and global polarization. Our model calculation provides a satisfactory description of the rapidity, transverse momentum, and centrality dependences of the directed flow of charged hadrons in Cu+Au collisions for the first time, and proposes that such asymmetric heavy-ion collisions create a better environment for studying the initial tilted geometry and longitudinal flow field of the QGP than symmetric Au+Au collisions do., Comment: 15 pages, 12 figures

In non-central heavy-ion collisions, the quark-gluon plasma (QGP) encounters the most intense magnetic field ever produced in nature, with a strength of approximately 10$^{19 - 20}$ Gauss. Recent lattice-QCD calculations reveal that the QGP exhibits paramagnetic properties at high temperatures. When an external strong magnetic field is applied, it generates an anisotropic squeezing force density that competes with pressure gradients resulting from the purely QGP geometric expansion. In this study, we employ (3+1)-dimensional ideal hydrodynamics simulations to estimate the paramagnetic squeezing effect of this force density on the anisotropic expansion of QGP in non-central Pb+Pb collisions at the Large Hadron Collider (LHC). We consider both up-to-date magnetic susceptibility and various magnetic field profiles in this work. We find that the impact of rapidly decaying magnetic fields is insignificant, while enduring magnetic fields produce a strong force density that diminishes the momentum anisotropy of the QGP by up to 10% at the intial stage, leaving a visible imprint on the elliptic flow $v_{2}$ of final charged particles. Our results provide insights into the interplay between magnetic fields and the dynamics of QGP expansion in non-central heavy-ion collisions., Comment: 11 pages, 8 figures, published in Phys. Rev. C 110, 014902 (2024)

Superconductivity is a macroscopic quantum phenomenon and it is commonly believed that the in-plane superconducting transition temperature (Tc) should be isotropic for superconductors with crystal structures of stacking layers (quasi two-dimensional). Here, we report the observation of piezostrain-induced in-plane anisotropy of Tc in FeSe0.5Te0.5 (FST) thin films grown on ferroelectrics. The as-prepared FST shows tetragonal phase with equal in-plane lattice parameters and absence of in-plane anisotropy of Tc. Upon applying electric fields, piezostrain induces difference of the in-plane lattice parameters (a-b) and in-plane anisotropy of Tc. The in-plane anisotropy of Tc correlates with a-b and becomes more remarkable for larger values of a-b. Some possible extrinsic effects were ruled out by experiments and analysis. It is suggested that electronic nematicity with one direction induced by piezostrain and inhomogeneous superconductivity in FST are involved in this unusual phenomenon. This work reveals the exotic behavior of FST and will stimulate exploration of similar behavior in other unconventional superconductors., Comment: 22 pages, 4 figures

We investigate the hyperon polarization and its relation with the directed flow of the quark-gluon plasma (QGP) in non-central Au+Au collisions at $\sqrt{s_{\textrm{NN}}} = 27$ GeV. A modified 3-dimensional (3D) Glauber model is developed and coupled to a (3+1)-D viscous hydrodynamic evolution of the QGP. Within this framework, we obtain a satisfactory simultaneous description of the directed flow of identified particles and $\Lambda$ polarization, and show sensitivity of polarization to both the tilted geometry and the longitudinal flow profile of the QGP. A non-monotonic transverse momentum dependence of the $\Lambda$ polarization is found in our calculation, which is absent from hydrodynamic simulation using other initialization methods and can be tested by future experimental data with higher precision. The relation between the global polarization and directed flow of $\Lambda$ is explored as the longitudinal flow field or the medium deformation varies. Due to the common origin of these two observables, their combination may provide a more stringent constraint on the initial condition of the QGP., Comment: 15 pages, 12 figures, published in Phy. Rev. C

We study the directed flow of identified particles in Au+Au collisions at $\sqrt{s_\text{NN}}=7.7$ to 62.4 GeV. The Glauber model is extended to include both a tilted deformation of the QGP fireball with respect to the longitudinal direction and a non-zero longitudinal flow velocity gradient in the initial state. By combining this improved initial condition with a (3+1)-dimensional viscous hydrodynamic model calculation, we obtain a satisfactory description of the transverse momentum spectra and the rapidity dependent directed flow coefficient of different hadron species. Our calculation indicates the sensitivity of the hadron directed flow, especially its splitting between protons and antiprotons, to both the initial geometry and the initial longitudinal flow velocity. Therefore, the combination of directed flow of different hadrons can provide a tight constraint on the initial condition of nuclear matter created in heavy-ion collisions. The initial condition extracted from the directed flow is further tested with the global polarization of $\Lambda$ and $\bar{\Lambda}$ within the same theoretical framework, where we obtain a reasonable description of these hyperon polarization observed at different collision energies at RHIC., Comment: 13 pages, 7 figures

Heavy quark observables are applied to probe the initial energy density distribution with violation of longitudinal boost invariance produced in relativistic heavy-ion collisions. Using an improved Langevin model coupled to a (3+1)-dimensional viscous hydrodynamic model, we study the nuclear modification factor ($R_\text{AA}$), directed flow ($v_1$) and elliptic flow ($v_2$) coefficients of heavy mesons and their decayed electrons at the RHIC energy. We find that the counter-clockwise tilt of the nuclear matter in the reaction plane results in a positive (negative) heavy flavor $v_1$ in the backward (forward) rapidity region, whose magnitude increases with the heavy quark transverse momentum. The difference in the heavy flavor $R_\text{AA}$ between different angular regions is also proposed as a complementary tool to characterize the asymmetry of the medium profile. Our model results are consistent with currently available data at RHIC and provide predictions that can be tested by future measurements., Comment: 10 pages, 6 figures, comments are welcome

Using a (3+1)-D hydrodynamic model CLVisc, we study the directed flow ($v_{1}$) of light hadrons produced in Au+Au, Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\textrm{NN}}}=$ 200 GeV. The evolution of tilted energy density, pressure gradient and radial flow along the $x$-direction are systematically investigated. Counter-clockwise tilt of initial fireball is shown to be a vital source of the directed flow for final light hadrons. A good description of directed flow is provided for light hadrons in central and mid-central Au+Au and isobar collisions at RHIC. Our numerical results show a clear system size dependence for light hadron $v_{1}$ across different collision systems. We further study the effect of nuclear structure on the directed flow and find that the $v_{1}$ for light hadrons is insensitive to the nuclei with quadrupole deformation., Comment: 11 pages, 9 figures, 3 tables, published in Chin. Phys. C

Extremely large angular orbital momentum can be produced in non-central heavy-ion collisions, leading to a strong transverse polarization of partons that scatter through the quark-gluon plasma (QGP) due to spin-orbital coupling. We develop a perturbative approach to describe the formation and spacetime evolution of quark polarization inside the QGP. Polarization from both the initial hard scatterings and interactions with the QGP have been consistently described using the quark-potential scattering approach, which has been coupled to realistic initial condition calculation and the subsequent (3+1)-dimensional viscous hydrodynamic simulation of the QGP for the first time. Within this improved approach, we have found that different spacetime-rapidity-dependent initial energy density distributions generate different time evolution profiles of the longitudinal flow velocity gradient of the QGP, which further lead to an approximately 15% difference in the final polarization of quarks collected on the hadronization hypersurface of the QGP. Therefore, in addition to the collective flow coefficients, the hyperon polarization may serve as a novel tool to help constrain the initial condition of the hot nuclear matter created in high-energy nuclear collisions., Comment: 13 pages, 11 figures

Heavy quarks are valuable probes of the electromagnetic field and the initial condition of the quark-gluon plasma (QGP) matter produced in high-energy nuclear collisions. Within an improved Langevin model that is coupled to a (3+1)-dimensional viscous hydrodynamic model, we explore the origin of the directed flow coefficient ($v_1$) of heavy mesons and their decay leptons, and its splitting ($\Delta v_{1}$) between opposite charges. We find that while the rapidity dependence of the heavy flavor $v_1$ is mainly driven by the titled energy density profile of the QGP with respect to the longitudinal direction at the RHIC energy, it is dominated by the electromagnetic field at the LHC energy. The $\Delta v_{1}$ serves as a novel probe of the spacetime evolution profile of the electromagnetic field. Our results of $D$ mesons and their decay electrons are consistent with the available data at RHIC and LHC, and our predictions on the heavy flavor decay muons can be further tested by future measurements., Comment: 12 pages, 10 figures, 1 table. Published: Phys. Rev. C 105, 054907 (2022)

We study the origin of the directed flow of charged particles produced in relativistic heavy-ion collisions. Three different initial conditions, Boz$\dot{\textrm{e}}$k-Wyskiel, CCNU and Shen-Alzhrani, of energy density distributions are coupled to the (3+1)-dimensional viscous hydrodynamic model CLVisc, and their effects on the development of the anisotropic medium geometry, pressure gradient and radial flow are systematically compared. By comparing to experimental data at both RHIC and LHC, we find that the directed flow provides a unique constraint on the tilt of the initial medium profile in the plane spanned by the impact parameter and space-time rapidity. Within mid-rapidity, the counter-clockwise tilt is shown to be a crucial source of the positive/negative force by the pressure gradient along the impact parameter ($x$) direction at backward/forward rapidity, which drives a negative slope of the $x$ component of the medium flow velocity with respect to rapidity, and in the end the same feature of the charged particle directed flow., Comment: 12 pages, 10 figures, any comments or suggestions are welcome

Following the Boz$\dot{\textrm{e}}$k-Wyskiel parametrization tilted initial condition, an alternative way to construct a longitudinal tilted fireball based on the Glauber collision geometry is presented. This longitudinal tilted initial condition combined with the Ideal-CLVisc (3 + 1)D hydrodynamic model, a nonvanishing directed flow coefficient $v_{1}$ in a wide rapidity range is observed. After comparing the model's results with experimentally observed data of directed flow coefficient $v_{1}(\eta)$ from $\sqrt{s_{NN}}$ = 200 GeV Cu + Cu, Au + Au collisions at RHIC energy to $\sqrt{s_{NN}}$ = 2.76 TeV and $\sqrt{s_{NN}}$ = 5.02 TeV Pb + Pb collisions at the LHC energy. We find that the directed flow measurements in heavy-ion collisions can set strong constraints on the imbalance of forward and backward incoming nuclei and on the magnitude asymmetry of pressure gradients along the $x$ direction., Comment: 11 pages, 9 figures and 3 tables; any comments and feedback are welcome. To appear as a Regular Article in Physical Review C

Squeezed light is a critical resource in quantum sensing and information processing. Due to the inherently weak optical nonlinearity and limited interaction volume, considerable pump power is typically needed to obtain efficient interactions to generate squeezed light in bulk crystals. Integrated photonics offers an elegant way to increase the nonlinearity by confining light strictly inside the waveguide. For the construction of large-scale quantum systems performing many-photon operations, it is essential to integrate various functional modules on a chip. However, fabrication imperfections and transmission crosstalk may add unwanted diffraction and coupling to other photonic elements, reducing the quality of squeezing. Here, by introducing the topological phase, we experimentally demonstrate the topologically protected nonlinear process of spontaneous four-wave mixing enabling the generation of squeezed light on a silica chip. We measure the cross-correlations at different evolution distances for various topological sites and verify the non-classical features with high fidelity. The squeezing parameters are measured to certify the protection of cavity-free, strongly squeezed states. The demonstration of topological protection for squeezed light on a chip brings new opportunities for quantum integrated photonics, opening novel approaches for the design of advanced multi-photon circuits., Comment: 6 pages, 4 figures, comments welcome!

The unknown $\gamma$-ray excess in the northwest region of Arp 220 was revisited by analyzing $\sim$11.8 years of the \textit{Fermi} Large Area Telescope (\textit{Fermi}-LAT) data in this study. We found that its photon flux was approximately three times higher than that of the previous study in the 0.2-100 GeV band, and the corresponding significance level$\sim8.15\sigma$ was approximately four times higher than before. The light curves of 15 and 45 time bins from the whole time all showed two active periods, and the variability of the second period was more significant than that of the first period. The spectral indices from the two active periods were not statistically different and were close to the range of $\gamma$-ray flat-spectrum radio quasars observed by \textit{Fermi}-LAT. Because the position of CRATES J153246+234400 was consistent with the best-fit position of our analysis, we suggest that CRATES J153246+234400 is more likely a $\gamma$-ray counterpart for the variational region. For Arp 220, there was no significant variability in the $\gamma$-ray emission.

In this work, we reanalyzed 11 years of spectral data from the \textit{Fermi} Large Area Telescope (\textit{Fermi}-LAT) of currently observed starburst galaxies (SBGs) and star-forming galaxies (SFGs). We used a one-zone model provided by \textbf{NAIMA} and the hadronic origin to explain the GeV observation data of the SBGs and SFGs. We found that a protonic distribution of a power-law form with an exponential cutoff can explain the spectra of most SBGs and SFGs. However, it cannot explain the spectral hardening components of NGC 1068 and NGC 4945 in the GeV energy band. Therefore, we considered the two-zone model to well explain these phenomena. We summarized the features of various model parameters, including the spectral index, cutoff energy, and protonic total energy. Similar to the evolution of supernova remnants (SNRs) in the Milky Way, we estimated the protonic acceleration limitation inside the SBGs to be likely in the order of 10$^{2}$ TeV using the one-zone model; this is close to those of SNRs in the Milky Way.

A new $\gamma$-ray source with a significance level of approximately 5$\sigma$ was reported in the region of SNR G272.2-3.2, analysing the approximately 12.4 years of observation data from the Fermi Large Area Telescope (Fermi-LAT). Its $\gamma$-ray spatial distribution did not show extended feature, and it had a soft spectrum with the spectral index of 2.56$\pm$0.01 of a power-law model. No significant variability of its light curve (LC) with 10 time bins was identified, and its spatial positions in the X-ray and GeV bands overlapped. We suggest that the new $\gamma$-ray source is a likely counterpart of SNR G272.2-3.2. Analysing its spectrum, we discussed the likely origins of the $\gamma$-ray emission.

The solutions of relativistic viscous hydrodynamics for longitudinal expanding fireballs is investigated with the Navier-Stokes theory and Israel-Stewart theory. The energy and Euler conservation equations for the viscous fluid are derived in Rindler coordinates with the longitudinal expansion effect is small. Under the perturbation assumption, an analytical perturbation solution for the Navier-Stokes approximation and numerical solutions for the Israel-Stewart approximation are presented. The temperature evolution with both shear viscous effect and longitudinal acceleration effect in the longitudinal expanding framework are presented and specifically temperature profile shows symmetry Gaussian shape in the Rindler coordinates. In addition, in the presence of the longitudinal acceleration expanding effect, the results of the Israel-Stewart approximation are compared to the results from Bjorken and Navier-Stokes approximation, and it gives a good description than the Navier-Stokes theories results at the early stages of evolution., Comment: 8 pages, 6 figures, ansatz of the viscous hydrodynamics, welcome comments

Relativistic hydrodynamics represents a powerful tool to investigate the time evolution of the strongly interacting quark gluon plasma created in ultrarelativistic heavy ion collisions. The equations are solved often numerically, and numerous analytic solutions also exist. However, the inclusion of viscous effects in exact, analytic solutions has received less attention. Here we utilize Hubble flow to investigate the role of bulk viscosity, and present different classes of exact, analytic solutions valid also in the presence of dissipative effects., Comment: 6 pages, 1 figure. Presented at the XIV Workshop on Particle Correlations and Femtoscopy, June 3-7, 2019, Dubna, Russia