Jayanta Dey, Sabyasachi Ghosh, Chowdhury Aminul Islam
Here we studied the possible diffusion speed for relativistic fluid in different effective quantum chromodynamics models: Nambu-Jona-Lasinio (NJL), Polyakov loop extended NJL, entangled PNJL (EPNJL) model.
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Role of different extensions of Nambu\textendash Jona-Lasinio (NJL) model like addition of vector interaction, Polyakov loop extended version (PNJL) and the entangled PNJL (EPNJL) models on transport coefficients like shear viscosity, bulk viscosity, electrical conductivity and thermal conductivity are critically analyzed. We have considered the standard expressions of transport coefficients, obtained in relaxation time approximation of kinetic theory. Influence of temperature dependent order parameters on temperature profile of transport coefficients are analyzed. Causal aspect of massless ca…
This lecture presents an overview of the status of the investigation of the properties of the quark-gluon plasma using relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). It focuses on the insights that have been obtained by the comparison between experimental data from both facilities and theoretical calculations.
We study two aspects of the CFL phase of QCD in the NJL approximation. The first one is the issue of the dependence on μof the ultraviolet cutoff in the gap equation, which is solved allowing a running coupling constant. The second one is the dependence of the gap on the strange quark mass; using the high density effective theory we perform an expansion in the parameter (m_s/μ)^2 after checking that its numerical validity is very good already at first order.
Some magnetic aspects of QCD are discussed at finite density and temperature. Possibility of spontaneous magnetization is studied within Landau Fermi-liquid theory, and the important roles of the screening effects for gluon propagation are elucidated. Static screening for the longitudinal gluons improves the infrared singularities, while the transverse gluons receive only dynamic screening. The latter property gives rise to a novel non-Fermi-liquid behaviour for the magnetic susceptibility. Appearance of a density-wave state is also discussed in relation to chiral transition, where pseudoscala…
Solving the QCD renormalization group equation at the 2-loop and 3-loop orders we obtain explicit expressions for the coupling as a function of the scale in terms of the Lambert W function. We study the nature of the ``Landau singularities'' in the complex Q^2 plane and show that perturbative freezing can lead, in certain cases, to an analyticity structure that is consistent with causality. We analyze the Analytic Perturbation Theory (APT) approach which is intended to remove the ``Landau singularities'', and show that at 2-loops it is uniquely defined in terms of the Lambert W function, and t…
I review recent progress on understanding QCD dynamics involved in exclusive $B$ meson decays. Different frameworks, including light-cone sum rules, QCD factorization, perturbative QCD, soft-collinear effective theory, light-front QCD, are discussed. Results from lattice QCD are quoted for comparison. I point out the important issues in the above QCD methods, which require further investigation.
We discuss the model $\barα_{an}(Q^2)$ recently proposed for the QCD running coupling $\barα_s(Q^2)$ in the Euclidean domain on the basis of the "asymptotic-freedom" expression and on causality condition in the form of the $Q^2$-analyticity. The model contains no adjustable parameters and obeys the important features: (i) Finite ghost-free behavior in the "low $Q^2$" region and correspondence with the standard RG-summed UV expressions;%\item~ % (ii) The universal limiting value $\barα_{an}(0)$ expressed only via group symmetry factors. This value as well as the $\barα_{an}$ behavior in the who…
The shear viscosity coefficient and the corresponding relaxation time for causal dissipative hydrodynamics are calculated based on the microscopic formula proposed in [T. Koide and T. Kodama, Phys. Rev. \textbf{E 78}, 051107 (2008)]. Here, the exact formula is transformed into a more compact form and applied it to evaluate these transport coefficients in the chiral perturbation theory and perturbative QCD. It is shown that in the leading order calculation, the causal shear viscosity coefficient $η$ reduces to that of the ordinary Green-Kubo-Nakano formula, and the relaxation time $τ_π$ is rela…
We summarize the current status of our understanding of the structure of the perturbative QCD expressions for the QCD generalization of the Crewther relation.
The weak mixing angle measured in neutrino scattering differs from the world average of other measurements by about 3 sigma. I discuss QCD corrections of perturbative and nonperturbative (parton structure) origin to the underlying neutrino observables.
After some general remarks on non-perturbative QCD I present shortly models which lead to a color-electric flux tube formation. The implications of such a flux tube formation especially on high energy scattering are discussed.
I give an overview of what our present knowledge of QCD predicts and does not predict for polarized hard scattering. For experimental programs, a big issue is how much further we can expect our theoretical understanding of QCD to improve.
Consequences of QCD current algebra formulated on a light-like hyperplane are derived for the forward scattering of vector and axial-vector currents on an arbitrary hadronic target. It is shown that current algebra gives rise to a special class of sum rules that are direct consequences of the independent chiral symmetry that exists at every point on the two-dimensional transverse plane orthogonal to the lightlike direction. These sum rules are obtained by exploiting the closed, infinite-dimensional algebra satisfied by the transverse moments of null-plane axial-vector and vector charge distrib…
We discuss various aspects of parity, CP, and time reversal invariances in QCD. In particular, we focus attention on the previously proposed possibility that these experimentally established symmetries of strong interactions may be broken at finite temperature and/or density. This would have dramatic signatures in relativistic heavy ion collisions; we describe some of the most promising signals.
Hard processes in high-energy proton-nucleus collisions are a powerful tool in order to investigate several importants aspects of QCD in a nuclear medium, such as nuclear shadowing, parton multiple scattering or medium-induced gluon radiation. I review in these proceedings recent progress in that field.
If a leptoquark is produced at HERA as a narrow resonance, various effects tend to broaden the measurable mass distribution considerably. These effects are discussed here, with special emphasis on initial- and final-state QCD radiation. A proper understanding is important to assess the significance of data and to devise strategies for better mass reconstruction.
This contribution presents a selection of the topics (parton densities, fixed-order calculations, parton showers, soft-gluon resummation) discussed in my introductory lectures at the Workshop and includes a pedagogical overview of the corresponding theoretical tools.
A brief review of jet physics is presented with an emphasis upon open theoretical problems (non-perturbative domain; hadronization and confinement) and new phenomena (hadroproduction in heavy ion collisions).
The different phases of QCD at finite temperature and density lead to interesting effects in cosmology and astrophysics. In this work I review some aspects of the cosmological QCD transition and of astrophysics at high baryon density.
In order to study such effects like parton saturation in final states at the LHC one of the approaches is to combine physics of the BK and the CCFM evolution equations. We report on recently obtained resummed form of the BK equation and nonlinear extension of the CCFM equation - the KGBJS equation.
Possibility of experimental identification of QCD-instantons in high energy collisions is studied by means of correlations analysis in final states. Instanton-induced processes amplitudes are performed in the framework of QCD in Gauss approximation. Hadronization is taken into account by Monte-Carlo method. Obtained results can be used as additional criterions of QCD-instanton identification at HERA (DESY). Unlike previous results in this report we consider also nonzero quarks modes contribution into parton distributions of instanton processes.
We present the results of a recent investigation of the short-distance structure of non-perturbative interaction between light quarks. We analyze the connection between topology and the dynamics responsible for the spontaneous breaking of chiral symmetry. By measuring some appropriate correlation functions on the lattice, we provide compelling evidence for instanton-induced dynamics.
Initial- and final-state interactions from gluon-exchange, normally neglected in the parton model have a profound effect in QCD hard-scattering reactions, leading to leading-twist single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, and nuclear shadowing and antishadowing--leading-twist physics not incorporated in the light-front wavefunctions of the target computed in isolation. I also discuss the use of diffraction to materialize the Fock states of a hadronic projectile and test QCD color transparency.
Recently, deeper understanding of QCD emerges from the study of the AdS/CFT correspondence. New results include the properties of quark-gluon plasma and the confinement/deconfinement phase transition, which are both very important for the scenario of the QCD phase transition in the early universe. In this paper, we study some aspects of how the new results may affect the old calculations of the cosmological QCD phase transition, which are mainly based on the studies of perturbative QCD, lattice QCD and the MIT bag model.
Magnetic properties of quark matter are discussed. The possibility of ferromagnetic transition is studied by using the one-gluon-exchange interaction. Magnetic susceptibility is evaluated within Landau Fermi liquid theory, and the important roles of the screening for the gluon propagation are elucidated. Static screening for the longitudinal gluons improves the infrared singularities, while the transverse gluons receive only dynamic screening. The latter property gives rise to a novel non-Fermi-liquid behaviour in the magnetic susceptibility. The critical density is estimated to be around the …
We conclude that nucleon is a many body complex system whose low-energy behaviour is determined mainly by strong interaction. Non-perturbative approach to QCD, such as QCD sum rule and the QCD based effective theory, and the models such as a statistical model, have a complementary role in exposing different aspects of nucleonic properties.
We present results on the chiral transition temperature Tc in 2+1 flavor QCD extrapolated to the continuum limit and the physical light quark mass. The extrapolations are based on the data from simulations on lattices with temporal extent Ntau=6, 8 and 12 with the HISQ/tree and Ntau=8 and 12 with the asqtad action. The chiral transition is analyzed in terms of universal O(N) scaling functions. After performing simultaneous asqtad and HISQ/tree continuum extrapolation the chiral transition temperature is Tc=154 +/- 9 MeV. We also discuss the deconfinement aspects of the transition in terms of t…
Several topics in hadron physics at different scales of resolution are discussed. First, deep-inelastic scattering from nucleons and nuclei is viewed in a light-cone coordinate space picture. Then the smooth transition from parton to hadron degrees of freedom is demonstrated by using a generalized Q^2-dependent polarizabilities of the nucleon. Turning to low energy QCD we summarize recent developments related to the role of strange quarks in Chiral SU(3) Dynamics, a non-perturbative coupled channel approach to hadronic processes. Finally we elaborate on a unification of QCD Sum Rules with aspe…
We discuss some aspects of a recently proposed semi-classical transport theory for QCD plasmas based on coloured point particles. This includes the derivation of effective transport equations for mean fields and fluctuations which relies on the Gibbs ensemble average. Correlators of fluctuations are interpreted as collision integrals for the effective Boltzmann equation. The approach yields a recipe to integrate-out fluctuations. Systematic approximations (first moment, second moment, polarisation approximation) based on a small plasma parameter are discussed as well. Finally, the application …
In these lectures I review some basic examples of how the concepts of universality and scaling can be used to study aspects of the chiral and the deconfinement transition, if not in QCD directly but in QCD-like theories. As an example for flavor dynamics I discuss a quark-hadron model to describe the phase diagram of two-color QCD with the functional renormalization group. Universal aspects of deconfinement are illustrated mainly in the 2+1 dimensional SU(N) gauge theories with second order transition where many exact results from spin models can be exploited.
The QCD factorization approach provides the theoretical basis for a systematic analysis of nonleptonic decay amplitudes of B mesons in the heavy-quark limit. After recalling the basic ideas underlying this formalism, several tests of QCD factorization in the decays B -> D^(*) L, B -> K^* gamma, and B -> pi K,pi pi are discussed. It is then illustrated how factorization can be used to obtain new constraints on the parameters of the unitarity triangle.
We study dynamical aspects of large N QCD_4 via supergravity on Anti de Sitter black hole geometry. We compute the mass spectrum, the topological susceptibility and the gluon condensate and make a comparison to lattice simulations. We present analogous results for QCD_3.
We investigate the phenomenology of freely expanding fluids, with different material properties, evolving through the Israel-Stewart (IS) causal viscous hydrodynamics, and compare our results with those obtained in the relativistic Eckart-Landau-Navier-Stokes (ELNS) acausal viscous hydrodynamics. Through the analysis of scaling invariants we give a definition of thermalization time which can be self-consistently determined in viscous hydrodynamics. Next we construct the solutions for one-dimensional boost-invariant flows. Expansion of viscous fluids is slower than that of one-dimensional ideal…
Phenomenological consequences of the infrared singular, instantaneous part of the gluon propagator in Coulomb gauge are investigated. The corresponding quark Dyson-Schwinger equation is solved, neglecting retardation and transverse gluons and regulating the resulting infrared singularities. While the quark propagator vanishes as the infrared regulator goes to zero, the frequency integral over the quark propagator stays finite and well-defined. Solutions of the homogeneous Bethe-Salpeter equation for the pseudoscalar and vector mesons as well as for scalar and axial-vector diquarks are obtained…
Dissipative relativistic fluid dynamics is not always causal and can favor superluminal signal propagation under certain circumstances. On the other hand, high-energy nuclear collisions have a microscopic description in terms of QCD and are expected to follow the causality principle of special relativity. We discuss under which conditions the fluid evolutions for a radial expansion are hyperbolic and how the properties of the solutions are encoded in the associated characteristic curves. The expansion dynamics is causal in relativistic sense if the characteristic velocities are smaller than th…
I discuss some non-perturbative aspects of hot gauge theories as related to the unscreened static magnetic interactions. I first review some of the infrared divergences which cause the breakdown of the perturbation theory. Then I show that kinetic theory, as derived from quantum field theory, is a powerful tool to construct effective theories for the soft modes, which then can be treated non-perturbatively. The effective theory at the scale $gT$ follows from a collisionless kinetic equation, of the Vlasov type. The effective theory at the scale $g^2T$ is generated by a Boltzmann equation which…
I review the meaning of ``QCD factorization'' in hadronic two-body B decays and then discuss recent results of theoretical (rather than phenomenological) nature: the proof of factorization at two loops; the identification of ``chirally enhanced'' power corrections; and the role of annihilation contributions.
This thesis is devoted to the study of some aspects of perturbative QCD, and in particular to the development of high-precision techniques for the extraction of physical parameters such as structure functions, parton distributions, and the strong coupling from the analysis of deep inelastic scattering data. First, we will discuss scaling violations of singlet and nonsinglet truncated moments, and the use of truncated momets to solve the Altarelli-Parisi equation. Then we will suggest an approach based on neural networks to the parametrization and interpolation of experimental data, which retai…
I review several topics in electroproduction which test fundamental aspects of QCD. These include the role of final-state interactions in producing diffractive leptoproduction processes, the shadowing of nuclear structure functions, and target-spin asymmetries. The antishadowing of nuclear structure functions is shown to be quark-flavor specific, suggesting that some part of the anomalous NuTeV result for $\sin^2θ_W$ could be due to the non-universality of nuclear antishadowing for charged and neutral currents. I also discuss the physics of the heavy-quark sea, hidden color in nuclear wavefunc…
We study non-linear quantum corrections to transverse momentum broadening (TMB) of a fast parton propagating in dense QCD matter in the leading logarithmic approximation. These non-local corrections yield an anomalous super-diffusive behavior characterized by a heavy tailed distribution which is associated with Lévy random walks. Using a formal analogy with the physics of traveling waves, we show that at late times the transverse momentum distribution tends to a universal scaling regime. We derive analytic solutions in terms of an asymptotic expansion around the scaling limit for both fixed an…
Exclusive B decays can be factorized as convolutions of hard scattering amplitudes involving the weak interaction with universal hadron distribution amplitudes, thus providing a new QCD-based phenomenology. In addition, semi-leptonic decay amplitudes can be computed exactly in terms of the diagonal and off-diagonal overlap of hadronic light-cone wavefunctions. I review these formalisms and the essential QCD ingredients. canonical form of the light-cone wavefunctions, valid at low values of the transverse momenta, is presented. The existence of intrinsic charm Fock states in the B meson wavefun…
Nonextensive aspects of gluon distribution and the implications to QCD phenomenology
该研究利用非广延统计力学分析胶子横动量分布，解释高能碰撞中的饱和与标度现象，并统一描述多种碰撞系统强子产生的高低$p_T$区域。
We review some aspects of spin physics where QCD instantons play an important role. In particular, their large contributions in semi-inclusive deep-inelastic scattering and polarized proton on proton scattering. We also review their possible contribution in the $\mathcal{P}$-odd pion azimuthal charge correlations in peripheral $AA$ scattering at collider energies.
We study an effective theory of QCD at high density in detail, including the finite temperature effects and the leading order correction in $1/μ$ expansion. We investigate the Cooper pair gap equation and find that the color-flavor locking phase is energetically preferred at high density. We also find the color-superconducting phase transition occurs in dense quark matter when the chemical potential is larger than $250\pm 100~{\rm MeV}$ and the temperature is lower than 0.57 times the Cooper pair gap in the leading order in the hard-dense-loop approximation. The quark-neutrino four-Fermi coupl…
We discuss the theoretical underpinnings for the extraordinary success of perturbative QCD in the description of HERA data. In particular, we examine recent progress in the understanding of perturbative QCD at small x. We explain the relation between evolution equations in Q^2 and x, and how they can be used for simultaneous resummation of the relevant large logs at HERA. We show that while the HERA data can be understood within our current knowledge of the perturbative expansion of QCD, they pose stringent constraints on the perturbatively inaccessible behaviour of QCD in the Regge limit.
Causal-Horizon Scaling of Quarkonium Suppression in Strong QCD Fields
研究强连续抑制与小 azimuthal 非对称性对底onium态的观测，提出早期时间几何生存机制，通过夸克onium半径与因果视界比值模型解释抑制模式，并预测RHIC/LHC能量依赖性。
I analyze the IR fixed point structure of Landau gauge QCD. Precisely the fixed point with a strong kinematic singularity of the quark-gluon vertex that proved crucial for the recently proposed confinement mechanism in the quenched approximation is absent in dynamical QCD. Therefore, the IR singularities do not induce asymptotic quark confinement but the long-range interaction is screened by unquenching loops at scales of the order of the quark mass. This provides the prerequisite for a microscopic description of deconfinement and string breaking. The fixed points determine the qualitative for…
We study the stability of Kaluza-Klein (KK) modes in five-dimensional N=1 supersymmetric QCD compactified on S^1 using the D3-brane probe realization. We find a phenomenon in which the quark KK mode with the KK number n=1 decays while other KK modes are stable. This is contrary to the ordinary assumption that the state with n=1 is the most stable in quark KK modes. In addition, we show that a massive gauge singlet state carrying the KK number exists stably. This provides a proper candidate for dark matter.
Baryon production is studied within the framework of quantized fragmentation of QCD string. Baryons appear in the model in a fairly intuitive way, with help of causally connected string breakups. A simple helical approximation of QCD flux tube with parameters constrained by mass spectrum of light mesons is sufficient to reproduce masses of light baryons.
The flavor dependence of the QCD phase diagram presents universal properties in the heavy quark limit. For the wide class of models where the quarks are treated at the one-loop level, we show, for arbitrary chemical potential, that the flavor dependence of the critical quark masses-for which the confinement-deconfinement transition is second order-is insensitive to the details of the (confining) gluon dynamics and that the critical temperature is constant along the corresponding critical line. We illustrate this with explicit results in various such one-loop models studied in the literature: e…
We present results on the chiral and deconfinement properties of the QCD transition at finite temperature. Calculations are performed with 2+1 flavors of quarks using the p4, asqtad and HISQ/tree actions. Lattices with temporal extent N_tau=6, 8 and 12 are used to understand and control discretization errors and to reliably extrapolate estimates obtained at finite lattice spacings to the continuum limit. The chiral transition temperature is defined in terms of the phase transition in a theory with two massless flavors and analyzed using O(N) scaling fits to the chiral condensate and susceptibi…
The effects of the QCD critical point on the spectra and flow coefficients of hadrons
本研究利用相对论粘性因果流体动力学模拟，探讨QCD临界点对重离子碰撞中强子谱和流系数的影响，发现火球时空积分会显著掩盖临界点效应。
QCD under extreme conditions has been studied for a long time, and the chiral limit has been a grey area mostly. In this write-up of my talk, I review some of the recent developments made by the community to unveil various features of QCD towards the chiral limit, which includes calculation of the chiral critical temperature and determination of the order of chiral phase transition for various numbers of flavors. Acknowledging the importance of the studies regarding the effective restoration of $U_A(1)$, I try to give a comprehensive overview about the various studies done in the last few year…
Some Physics (obtaining lattice-compatible deconfinement temperature, some transport coefficients and Einstein's relation) and Mathematics (torsion classes and supersymmetry) issues pertaining to the delocalized SYZ type IIA mirror of [1] and its M theory uplift in the MQGP limit of [2], are discussed.
In this paper we derive holographic wave equations for hadrons with arbitrary spin starting from an effective action in a higher-dimensional space asymptotic to anti-de Sitter (AdS) space. Our procedure takes advantage of the local tangent frame, and it applies to all spins, including half-integer spins. An essential element is the mapping of the higher-dimensional equations of motion to the light-front Hamiltonian, thus allowing a clear distinction between the kinematical and dynamical aspects of the holographic approach to hadron physics. Accordingly, the non-trivial geometry of pure AdS spa…
We discuss the properties of ghost and gluon propagators in Landau gauge Yang-Mills theory and their relation to the confinement problem. In general two types of infrared behavior of these functions are allowed from their functional equations: scaling and decoupling. Both solutions show positivity violations in the gluon propagator and lead to a confining Polyakov loop potential. However, only the scaling solution agrees with the Kugo-Ojima confinement scenario and the related formulation of a physical Hilbert space of Yang-Mills theory. Our numerical results for the gluon dressing function ag…
We study a possible symmetrical behavior of the effective charges defined in the Euclidean and Minkowskian regions and prove that such symmetry is inconsistent with the causality principle.
We modified the current soft wall model by considering the Non-conformal aspect low energy QCD.
Infrared divergences from the exchange of dynamically screened magnetic gluons (photons) lead to the breakdown of the Fermi liquid description of the {\em normal} state of cold and dense QCD and QED. We implement a resummation of these divergences via the renormalization group to obtain the spectral density, dispersion relation, widths and wave function renormalization of single quasiparticles near the Fermi surface. We find that all feature scaling with anomalous dimensions: $ω_p({k}) \propto |k-k_F|^{\frac{1}{1-2λ}} ~ ; ~ Γ(k) \propto |k-k_F|^{\frac{1}{1-2λ}} ~;~ Z_p({k}) \propto |k-k_F|^{\f…
We review recent advances in the understanding of the Quantum Chromodynamics (QCD) transition and its nature, paying special attention to the analysis of chiral symmetry restoration within different approaches based on effective theories. After presenting some of the main aspects of the current knowledge of the phase diagram from the theoretical, experimental and lattice sides, we discuss some recent problems where approaches relying on effective theories have been particularly useful. In particular, the combination of ideas such as Chiral Perturbation Theory, unitarity and Ward Identities all…
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