XQCD 2018

Quarkonia are produced in the heavy ion collisions and their production is modified compared with elementary collisions. This modification in the production of Quarkonia happens due to the presence of hot and dense QCD matter, named as quark-gluon plasma (QGP) formed in ultra relativistic heavy ion collisions. Existence of such kind of medium is observed in assymetric (p-Pb) collisions at 5.02...

The Hadron-Resonance Gas (HRG) approach - used to model hadronic matter at small baryon potentials $\mu_B$ and finite temperature $T$ - is extended to finite and large chemical potentials by introducing interactions between baryons in line with relativistic mean-field theory defining an interacting HRG (IHRG). Using lattice data for $\mu_B=0$ as well as information on the nuclear equation of...

We develop a kinetic framework to describe the matter in which the fermions are chiral. We extend the previous works about the chiral kinetic theory in external electromagnetic field to the case of curved spacetime. The berry curvature and chiral anomaly are encoded automatically. We use our framework to analyze the chiral vortical effect (CVE) and show connections between CVE in rotating...

Recent lattice QCD studies at vanishing density exhibit the parity-doubling structure for the low-lying baryons around the chiral crossover temperature. This finding is likely an imprint of the chiral symmetry restoration in the baryonic sector of QCD, and is expected to occur also in cold dense matter, which makes it of major relevance for compact stars. By contrast, the latter is typically...

The sign problem emerges in lattice QCD as soon as non-vanishing Baryon chemical potential is studied. This prevents direct simulations of the phase structure of strongly interacting matter. Complex Langevin simulations have been successfully used for various models or approximations of QCD. However, in some scenarios it converges to incorrect results. Here I will discuss a new method that...

We study the Stephanov model, which is a Random Matrix Theory model for QCD at finite baryon density, using the Complex Langevin algorithm. Naive implementation of the algorithm shows convergence towards the phase quenched or quenched theory rather than to the intended theory with dynamical quarks. A detailed analysis of this issue various potential resolutions of the failure of this algorithm...

A novel equation of state with the surface tension induced by particles’ interactions was generalized to describe the properties of the neutron stars. In this equation the interaction between particles occurs via the hard core repulsion by taking into account the proper volumes of particles. Recently, this model was successfully applied to the description of the properties of nuclear and...

Utilizing the dual QCD model in terms of the magnetic symmetry structure of non-Abelian gauge theories, the modified version of the dual QCD hadronic bag has been constructed in term of fuzzy bag which mainly satisfy the main qualitative feature observed for a strongly interacting QGP. Such picture identifies the new degrees of freedom as thermal monopoles such that the QCD matter behaves as a...

We develop a macroscopic description of the space-time evolution of the energy-momentum tensor during the pre-equilibrium stage of a high-energy heavy-ion collision. Based on a weak coupling effective kinetic description of the microscopic equilibration process (\`a la ``bottom-up"), we calculate the non-equilibrium evolution of the local background energy-momentum tensor as well as the...

The color-singlet representation of lattice QCD with staggered fermions offers a framework to soften the sign problem at finite density. This allows for the computation of the complete QCD phase diagram at strong coupling as well as at $\mathcal{O}(\beta)$. Furthermore, the chiral limit is cheap and thermodynamic quantities such as the energy density and the pressure can be computed easily....

Hybrid Monte Carlo is traditionally employed in lattice QCD calculations. In principle, however, its applicability extends to a wide range of other interacting Fermion systems. One such system which can be simulated without a fermion-sign problem is the extended Hubbard model at half-filling, which describes electrons that can hop between the sites of a crystal lattice and includes on-site...

A deep convolutional neural network (CNN) is constructed and trained in supervision to identify the QCD transition from the averaged final-state pion spectra ρ(pT,φ) in simulations of heavy-ion collisions with a hybrid model (iEBE-VISHNU), which couples (2+1)-D relativistic viscous hydrodynamics to a hadronic cascade “afterburner” (UrQMD). Hidden correlations in ρ(pT,φ) are captured by the...

The lack of an order parameter in Yang-Mills theory with dynamical fundamental quarks is a long-standing problem in QCD. We exploit a web of dualities and information-theoretic techniques to study the phase structure of QCD from a new perspective. In particular, we examine the deconfinement transition in a deformed model of QCD: this is QCD compactified over a circle and considered at...

Strongly coupled systems are ubiquitous especially in the field of high energy and condensed matter physics. Investigation of these systems is complicated as conventional and perturbative methods fail to describe them. But with the introduction of AdS/CFT duality (or holography), it is now possible to capture the essential features of strongly coupled systems. In this work, we study the...

Isospin asymmetry is the well-known property of dense quark matter, which exists in the compact stars and is produced in heavy ion collisions. On the other hand, the formation of dense quark matter in both of these cases is usually accompanied by a magnetic field strong enough to promote chiral magnetic effect (CME). To investigate quark matter under these conditions, we take into account...

I discuss the computation of phase diagrams of theories, which have similar symmetries as QCD, like the Gross-Neveu model or the NJL model in the limit of an infinite number of fermion flavors using lattice field theory and related numerical approaches. Particular focus is put on phases, where condensates are spatially inhomogeneous. First results are presented.

The SU(3) flavor parity-doublet quark-hadron model is used to investigate the phase diagram of QCD matter. The quark sector of the model is tuned to the $\mu_B=0$ lattice QCD data on trace anomaly. The structure of the baryon number susceptibilities in the temperature/chemical potential plane is studied in some detail. The model predicts three phase transitions - nuclear first-order...

The QCD phase diagram at finite temperature and density has a very rich physical structure which can be explored with first principle lattice QCD calculations. Simulations of lattice QCD with non-vanishing real chemical potential ($\mu$) suffer from the infamous "sign problem". However, one can perform simulations using purely imaginary chemical potentials where the "sign problem" is...

The QCD phase diagram is studied in the presence of an isospin asymmetry using continuum extrapolated staggered quarks with physical masses. In particular, we investigate the phase boundary between the normal and the pion condensation phases and the chiral/deconfinement transition. The simulations are performed with a small explicit breaking parameter in order to avoid the accumulation of zero...

The formation of quark matter in core-collapse supernovae and neutron star mergers could leave interesting observable imprints on the resulting electromagnetic, gravitational and neutrino emissions. In fact, simulations have shown that the early formation of quark matter could have a significant impact upon the dynamics of core-collapse supernovae, including a characteristic second...

Fluctuations have been playing an important role in understanding observables in high-energy nuclear collisions. Higher harmonics of azimuthal angle distributions, for example, can be attributed to initial fluctuations of transverse profile from event to event. In this presentation, we focus on thermal fluctuations during hydrodynamic evolution (i.e. hydrodynamic fluctuations) of the...

Elucidating the production process of heavy quark bound states is a central goal in heavy-ion collisions [1]. Two central questions exist: Do bound states of heavy quarks form in the early time evolution of the glasma? If so, in which time regime can that happen? An Answer requires the development of a non-perturbative treatment of the real-time-dynamics of heavy quarkonia. Here we present...

Elucidating the production process of heavy quark bound states is a central goal in heavy-ion collisions [1]. Two central questions exist: Do bound states of heavy quarks form in the early time evolution of the glasma? If so, in which time regime can that happen? An Answer requires the development of a non-perturbative treatment of the real-time-dynamics of heavy quarkonia. Here we present...

A new framework for relativistic hydrodynamics with spin is proposed. It is based on the conservation laws for charge, energy, momentum, and angular momentum. The conservation laws lead to hydrodynamic equations for the charge density, local temperature, and fluid velocity, as well as for the polarization tensor. The resulting set of differential equations extend the standard picture of...

One of the main challenges in simulations on Lefschetz thimbles is the computation of the relative weights of contributing thimbles. In this work we propose a solution to that problem by means of computing those weights using a reweighting procedure. Besides we present recipes for finding parametrizations of thimbles and anti-thimbles for a given theory. Moreover, we study some approaches to...

The dominant cost of most lattice QCD simulations is the inversion of the Dirac operator required to calculate the force term in the RHMC update. One way to improve this situation is to use multiple psuedofermions, which reduces the force and hence allows a larger integration step size to be used, at the cost of having to invert the Dirac operator for each pseudofermion field. Recently...

I will illustrate how our recently developed renormalization group optimized perturbation theory (RGOPT) resums perturbative expansions in thermal field theories. The convergence and scale dependence of RGOPT thermodynamical quantities are drastically improved as compared to standard perturbative expansions, and it cures the odd drastic scale dependence observed in other related methods such...

We will discuss some results about the behaviour of the screening properties of high-T QCD at finite density. More precisely we will report on the dependence on the baryon chemical potential of the QCD screening masses and of the heavy-quark free energy, as extracted from 2+1 flavours Lattice QCD simulations at the physical point. While for the screening masses a particularly interesting...

During last few years our group developed the most advanced model of the hadron resonance gas [1] which not only allowed us to achieve the best description of all hadronic multiplicities measured from the lowest AGS to the highest RHIC energies, but also to reveal the remarkable irregularities at chemical freeze-out [2-5]. It is intriguing that in central nuclear collisions we found two sets...

We first motivate the need for an improved equation of state, accounting for the finite size of hot, quantum and relativistic quark-gluon plasmas, such as created in modern Heavy Ion Collisions (HIC). We then focus on finite size corrections by means of relevant spatial compactifications, while considering a single non-interacting massless scalar field as a toy model. Consequently, we present...

Attempts to extract the order of the chiral transition of QCD at zero chemical potential, with two dynamical flavours of massless quarks, from simulations with progressively decreasing pion mass have remained inconclusive because of their increasing numerical cost. In an alternative approach to this problem, we consider the path integral as a function of continuous number $N_f$ of degenerate...

The phase diagram of QCD is one of the most interesting problems in modern physics which so far has not been sufficiently investigated from first principle calculations at mu/T > 1, mainly due to the sign problem of lattice QCD. One of the most promising methods to tackle the sign problem in lattice simulations is the complex Langevin method, which recently has been successfully applied to...

We study the effect of an external static magnetic field of strength comparable with the QCD scale $\Lambda_{QCD}\sim200$ MeV on the deconfinement/chiral restoration transition. Lattice simulations have been carried out with $2+1$ flavours, Symanzik three-level improved gauge action and stout improved rooted staggered fermions. In particular, the dependence of the pseudocritical temperature...

For the understanding of the fluctuation measurements in heavy-ion collisions it is crucial to develop quantitatively reliable dynamical descriptions. In order to study the phase transition, both in crossover regime as well as near the conjectured QCD critical point, the non-perturbative nature needs to be fully included. In this talk, we outline a novel QCD-assisted transport approach...

Nonzero chiral density leads to a plenty of interesting unusual phenomena, including chiral catalysis, chiral magnetic effect and others. We study how nonzero chiral density affects topological and confinement properties of the system. We present the dependence of the string tension and topological susceptibility on chiral chemical potential. We see that both observables grow with chiral...

We study, by Monte-Carlo simulations, an SU(3) Yang Mills theory at finite temperature with a deformation proportional to the square of the trace of Polyakov loop. Due to this deformation, we can force the system to recover center symmetry even after the usual deconfinement transition. We analyse the properties of this new phase, in which center symmetry is not spontaneously broken,...

We explore the feasibility of new algorithms, devised for an efficient sampling of the topological charge distribution in the high temperature phase of QCD, and present some preliminary results regarding the temperature dependence of the topological susceptibility

In semi-central AA collisions, both deconfined matter (QGP) and strong strong electromagnetic fields from fast moving charge nucleus can be produced when nuclei collide with each other. QGP with extremely large energy density result in strong color screening on the heavy quarkonium potential and quarkonium yield suppression. At the same time, abundant number of heavy(or strange) quarks inside...

For quark matter studies in astrophysics the thermodynamic bag model (tdBag) has been widely used. It approximates the effect of quark confinement, but does not explicitly account for the breaking of chiral symmetry, an important property of Quantum Chromodynamics (QCD). It also doesn't account for repulsive vector interaction necessairy for astrophysical studies. vBag extends the tdBag...