Do Proton-Proton collisions at the LHC energies produce Droplets of Quark-Gluon Plasma?

The proton-proton ($pp$) collisions at the Large Hadron Collider (LHC), CERN, Switzerland has brought up new challenges and opportunities in understanding the experimental findings in contrast to the conventional lower energy $pp$ collisions. Usually $pp$ collisions are used as the baseline measurement at the GeV and TeV energies in order to understand a possible high density QCD medium formation in heavy-ion collisions. However, the TeV $pp$ collisions have created a new domain of research, where scientists have started observing heavy-ion-like features (signatures) in high-multiplicity $pp$ collisions. This warrants a relook into TeV $pp$ collisions, if at all QGP-droplets are produced in such collisions. In this presentation, I discuss some of the new findings and concepts emerging out in $pp$ collisions at the LHC energies along with some of the new emergent phenomena in particle production.Comment: 5 pages, 4-captioned figures, Presented in the plenary session of Workshop on Frontiers in High Energy Physics (FHEP-2019), Hyderabad, India (To appear in Springer Proc.

QCD thermodynamics with dynamical overlap fermions

We study QCD thermodynamics using two flavors of dynamical overlap fermions with quark masses corresponding to a pion mass of 350 MeV. We determine several observables on N_t=6 and 8 lattices. All our runs are performed with fixed global topology. Our results are compared with staggered ones and a nice agreement is found.Comment: 14 pages, 6 figures, 1 tabl

Numerical study of hot strongly interacting matter

I review recent progress in study of strongly interacting matter at high temperatures using Monte-Carlo simulations in lattice QCD.Comment: Talk presented at Conference on Computational Physics, Oct. 30 - Nov. 3, 2011, Gatlinburg TN, LaTeX uses jpconf11.clo, jpconf.cl

Hadronic vacuum polarization contribution to the anomalous magnetic moments of leptons from first principles

We compute the leading, strong-interaction contribution to the anomalous magnetic moment of the electron, muon and tau using lattice quantum chromodynamics (QCD) simulations. Calculations include the effects of $u$, $d$, $s$ and $c$ quarks and are performed directly at the physical values of the quark masses and in volumes of linear extent larger than $6\,\mathrm{fm}$. All connected and disconnected Wick contractions are calculated. Continuum limits are carried out using six lattice spacings. We obtain $a_e^\mathrm{LO-HVP}=189.3(2.6)(5.6)\times 10^{-14}$, $a_\mu^\mathrm{LO-HVP}=711.1(7.5)(17.4)\times 10^{-10}$ and $a_\tau^\mathrm{LO-HVP}=341.0(0.8)(3.2)\times 10^{-8}$, where the first error is statistical and the second is systematic.Comment: 17 pages, 8 figures (in 13 PDF files), RevTeX 4.1. Minor changes to results and to text. References updated. Matches version published in Physical Review Letter

QCD thermodynamics with continuum extrapolated dynamical overlap fermions

We study the finite temperature transition in QCD with two flavors of dynamical fermions at a pseudoscalar pion mass of about 350 MeV. We use lattices with temporal extent of $N_t$=8, 10 and 12. For the first time in the literature a continuum limit is carried out for several observables with dynamical overlap fermions. These findings are compared with results obtained within the staggered fermion formalism at the same pion masses and extrapolated to the continuum limit. The presented results correspond to fixed topology and its effect is studied in the staggered case. Nice agreement is found between the overlap and staggered results

Compact Stars - How Exotic Can They Be?

Strong interaction physics under extreme conditions of high temperature and/or density is of central interest in modern nuclear physics for experimentalists and theorists alike. In order to investigate such systems, model approaches that include hadrons and quarks in a unified approach, will be discussed. Special attention will be given to high-density matter as it occurs in neutron stars. Given the current observational limits for neutron star masses, the properties of hyperonic and hybrid stars will be determined. In this context especially the question of the extent, to which exotic particles like hyperons and quarks affect star masses, will be discussed.Comment: Contributon to conference "Nuclear Physics: Present and Future", held in Boppard (Germany), May 201

Scalar density fluctuation at critical end point in NJL model

Soft mode near the critical end point in the phase diagram of two-flavor Nambu--Jona-Lasinio (NJL) model is investigated within the leading 1/N_c approximation with N_c being the number of the colors. It is explicitly shown by studying the spectral function of the scalar channel that the relevant soft mode is the scalar density fluctuation, which is coupled with the quark number density, while the sigma meson mode stays massive.Comment: 9 pages, 4 figure

The QCD equation of state from the lattice

The equation of state of QCD at finite temperatures and baryon densities has a wide range of applications in many fields of modern particle and nuclear physics. It is the main ingredient to describe the dynamics of experimental heavy ion collisions, the expansion of the early universe in the standard model era and the interior of compact stars. On most scales of interest, QCD is strongly coupled and not amenable to perturbative investigations. Over the last decade, first principles calculations using lattice QCD have reached maturity, in the sense that for particular discretisation schemes simulations at the physical point have become possible, finite temperature results near the continuum limit are available and systematic errors begin to be controlled. This review summarises the current theoretical and numerical state of the art based on staggered and Wilson fermions.Comment: 72 pages, 36 figures, typos corrected, summary table added; version published by Prog.Part.Nucl.Phy

Entropy Creation in Relativistic Heavy Ion Collisions

We review current ideas on entropy production during the different stages of a relativistic nuclear collision. This includes recent results on decoherence entropy and the entropy produced during the hydrodynamic phase by viscous effects. We start by a discussion of decoherence caused by gluon bremsstrahlung in the very first interactions of gluons from the colliding nuclei. We then present a general framework, based on the Husimi distribution function, for the calculation of entropy growth in quantum field theories, which is applicable to the early ("glasma") phase of the collision during which most of the entropy is generated. The entropy calculated from the Husimi distribution exhibits linear growth when the quantum field contains unstable modes and the growth rateis asymptotically equal to the Kolmogorov-Sina\"i (KS) entropy. We outline how the approach can be used to investigate the problem of entropy production in a relativistic heavy-ion reaction from first principles. Finally we discuss some recent results on entropy production in the strong coupling limit, as obtained from AdS/CFT duality.Comment: 34 pages, 14 figure