The HotQCD Collaboration

“…One model of the region above but near T c is the semi-QGP [3][4][5][6]. This incorporates the results of numerical simulations on the lattice [7], which show that colored excitations are strongly suppressed when T → T + c , as the expectation value of the Polyakov loop decreases markedly.A notable property of heavy ion collisions is elliptic flow, how the initial spatial anisotropy of peripheral collisions is transformed into a momentum anisotropy. The large elliptic flow of hadrons can be well modeled by hydrodynamic models in which the QCD medium is close to an ideal fluid [8][9][10].…”

mentioning

confidence: 99%

“…At high temperature ∼ 1 [26], while = 0 in the confined phase of a pure gauge theory. With dynamical quarks, > 0 at any nonzero temperature, but lattice simulations show that the value of the (renormalized) loop is small at T c , (T c ) ≈ 0.1 [7].The simplest way to represent a phase where < 1 is to work in mean field theory, taking A 0 to be a constant, diagonal matrix, (A cl 0 ) ab = δ ab Q a /g [3-6]. The Polyakov loop is then = 1/N c a e iQ a /T , where the color index a = 1 .…”

mentioning

confidence: 99%

mentioning

confidence: 99%

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Production and Elliptic Flow of Dileptons and Photons in a Matrix Model of the Quark-Gluon Plasma

et al. 2015

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We consider the thermal production of dileptons and photons at temperatures above the critical temperature in QCD. We use a model where color excitations are suppressed by a small value of the Polyakov loop, the semi Quark-Gluon Plasma (QGP). Comparing the semi-QGP to the perturbative QGP, we find a mild enhancement of thermal dileptons. In contrast, to leading logarithmic order in weak coupling there are far fewer hard photons from the semi-QGP than the usual QGP. To illustrate the possible effects on photon and dileptons production in heavy ion collisions, we integrate the rate with a realistic hydrodynamic simulation. Dileptons uniformly exhibit a small flow, but the strong suppression of photons in the semi-QGP tends to bias the elliptical flow of photons to that generated in the hadronic phase.PACS numbers: 11.10. Wx, 12.38.Mh, 25.75.Cj, 25.75.Nq The collisions of heavy nuclei at ultra-relativistic energies can be used to investigate the properties of the Quark-Gluon Plasma (QGP). At both the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), much of the collision takes place at temperatures which are not that far above that for the transition, T c . This is a difficult region to study: perturbative methods can be used at high temperature, but not nearSimilarly, hadronic models are valid at low temperature, but break down near T c [2]. One model of the region above but near T c is the semi-QGP [3][4][5][6]. This incorporates the results of numerical simulations on the lattice [7], which show that colored excitations are strongly suppressed when T → T + c , as the expectation value of the Polyakov loop decreases markedly.A notable property of heavy ion collisions is elliptic flow, how the initial spatial anisotropy of peripheral collisions is transformed into a momentum anisotropy. The large elliptic flow of hadrons can be well modeled by hydrodynamic models in which the QCD medium is close to an ideal fluid [8][9][10].Electromagnetic signals, such as dilepton or photon production, are another valuable probe, since they reflect properties of the quark and gluon distributions of the QGP, and once produced, escape without significant interaction [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. For example, if most photons are emitted at high temperature in the QGP, since the flow at early times is small, one would expect a small net elliptic flow for photons. However, recently both the PHENIX experiment at RHIC [22] and the ALICE experiment at the LHC [23] have found a large elliptic flow for photons, comparable to that of hadrons. This is most puzzling [17,18,24].In this paper we present the results for the thermal production of hard dileptons and photons in the semi-QGP, and compare them with those of the perturbative QGP. Surprisingly, we find a sharp qualitative difference between the two. In the semi-QGP, the production of dileptons is similar between the deconfined and confined phases, while photon production is strongly suppressed near T c . We compute to leading ord...

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Compact Stars—How Exotic Can They Be?

Schramm

Dexheimer

Negreiros

et al. 2014

Nuclear Physics: Present and Future

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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.

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The HotQCD Collaboration

Cited by 219 publications

References 0 publications

From chiral quark dynamics with Polyakov loop to the hadron resonance gas model

From chiral quark dynamics with Polyakov loop to the hadron resonance gas model

Production and Elliptic Flow of Dileptons and Photons in a Matrix Model of the Quark-Gluon Plasma

Compact Stars—How Exotic Can They Be?

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