Chiral Transition of N=4 Super Yang-Mills with Flavor on a 3-Sphere

We use the AdS/CFT correspondence to perform a numerical study of a phase transition in strongly-coupled large-Nc N = 4 Super-Yang-Mills theory on a 3-sphere coupled to a finite number Nf of massive N = 2 hypermultiplets in the fundamental representation of the gauge group. The gravity dual system is a number Nf of probe D7-branes embedded in AdS_5 x S^5. We draw the phase diagram for this theory in the plane of hypermultiplet mass versus temperature and identify for temperatures above the Hawking-Page deconfinement temperature a first-order phase transition line across which the chiral condensate jumps discontinuously.Comment: 23 pages, 15 figures, minor corrections, reference added, nine figures improved, no change in results or conclusions; expanded discussion of fixing finite counterterms in section 3.3, figures updated, no changes to conclusion

Trans-disciplinary Collaboration to Enhance Coastal Resilience: Envisioning a National Community Modeling Initiative

This section presents a synthesis of the major outcomes from the coastal resilience workshops. This paper is based on the presentations and discussions that have been guided by the Chair and numerous stakeholders such as university researchers, Non Governmental Organizations, and federal, state, and local governments. SURA’s workshop series promotes collaboration and fully-integrated processes, and it should be noted that the actual workshop is only a first step; the follow-up work is likely to continue for years. The major results from this workshop relate to the development of trans-disciplinary approaches that help a community to bounce back after hazardous events such as hurricanes, coastal storms, and flooding – rather than simply rebuilding in the aftermath. The workshops have included participants from academia, industry, and government. They provide opportunity to share coastal resilience research and projects focused on helping the community to rebound quickly from climate and extreme weather related events, including sea level rise. The purpose of the paper is to showcase how social and natural scientists can collaborate to reduce the negative human health, environmental, and economic effects of coastal hazards

Trans-disciplinary Collaboration to Enhance Coastal Resilience: Envisioning a National Community Modeling Initiative

This section presents a synthesis of the major outcomes from the coastal resilience workshops. This paper is based on the presentations and discussions that have been guided by the Chair and numerous stakeholders such as university researchers, Non Governmental Organizations, and federal, state, and local governments. SURA’s workshop series promotes collaboration and fully-integrated processes, and it should be noted that the actual workshop is only a first step; the follow-up work is likely to continue for years. The major results from this workshop relate to the development of trans-disciplinary approaches that help a community to bounce back after hazardous events such as hurricanes, coastal storms, and flooding – rather than simply rebuilding in the aftermath. The workshops have included participants from academia, industry, and government. They provide opportunity to share coastal resilience research and projects focused on helping the community to rebound quickly from climate and extreme weather related events, including sea level rise. The purpose of the paper is to showcase how social and natural scientists can collaborate to reduce the negative human health, environmental, and economic effects of coastal hazards

Thermodynamics of the PNJL model

QCD thermodynamics is investigated by means of the Polyakov-loop-extended Nambu Jona-Lasinio (PNJL) model, in which quarks couple simultaneously to the chiral condensate and to a background temporal gauge field representing Polyakov loop dynamics. The behaviour of the Polyakov loop as a function of temperature is obtained by minimizing the thermodynamic potential of the system. A Taylor series expansion of the pressure is performed. Pressure difference and quark number density are then evaluated up to sixth order in quark chemical potential, and compared to the corresponding lattice data. The validity of the Taylor expansion is discussed within our model, through a comparison between the full results and the truncated ones.Comment: 6 pages, 5 figures, Talk given at the Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions (Hot Quarks 2006), Villasimius, Italy, 15-20 May 200

Quasiparticle Model of Quark-Gluon Plasma at Imaginary Chemical Potential

A quasiparticle model of the quark-gluon plasma is compared with lattice QCD data for purely imaginary chemical potential. Net quark number density, susceptibility as well as the deconfinement border line in the phase diagram of strongly interacting matter are investigated. In addition, the impact of baryo-chemical potential dependent quasiparticle masses is discussed. This accomplishes a direct test of the model for non-zero baryon density. The found results are compared with lattice QCD data for real chemical potential by means of analytic continuation and with a different (independent) set of lattice QCD data at zero chemical potential.Comment: Nov 2007. 28 p

The Equation of State for Two Flavor QCD at Non-zero Chemical Potential

We present results of a simulation of QCD on a 4x16^3 lattice with 2 continuum flavors of p4-improved staggered fermion with mass m/T=0.4. Derivatives of the thermodynamic grand potential with respect to quark chemical potential mu_q up to fourth order are calculated, enabling estimates of the pressure, quark number density and associated susceptibilities as functions of mu_q via Taylor series expansion. Discretisation effects associated with various staggered fermion formulations are discussed in some detail. In addition it is possible to estimate the radius of convergence of the expansion as a function of temperature. We also discuss the calculation of energy and entropy densities which are defined via mixed derivatives of the thermodynamic grand potential with respect to the bare couplings and quark masses.Comment: 30 pages, LaTeX2e File, 17 Postscript figure

Quasi-Particle Description of Strongly Interacting Matter: Towards a Foundation

We confront our quasi-particle model for the equation of state of strongly interacting matter with recent first-principle QCD calculations. In particular, we test its applicability at finite baryon densities by comparing with Taylor expansion coefficients of the pressure for two quark flavours. We outline a chain of approximations starting from the Phi-functional approach to QCD which motivates the quasi-particle picture.Comment: Aug 2006. 6 pp. Invited Talk given at Hot Quarks 2006, Villasimius, Sardinia, Italy, 15-20 May 200

Shear viscosity of the Quark-Gluon Plasma from a virial expansion

We calculate the shear viscosity $\eta$ in the quark-gluon plasma (QGP) phase within a virial expansion approach with particular interest in the ratio of $\eta$ to the entropy density $s$, i.e. $\eta/s$. The virial expansion approach allows us to include the interactions between the partons in the deconfined phase and to evaluate the corrections to a single-particle partition function. In the latter approach we start with an effective interaction with parameters fixed to reproduce thermodynamical quantities of QCD such as energy and/or entropy density. We also directly extract the effective coupling \ga_{\rm V} for the determination of $\eta$. Our numerical results give a ratio $\eta/s\approx 0.097$ at the critical temperature $T_{\rm c}$, which is very close to the theoretical bound of $1/(4\pi)$. Furthermore, for temperatures $T\leq 1.8 T_{\rm c}$ the ratio $\eta/s$ is in the range of the present experimental estimates $0.1-0.3$ at RHIC. When combining our results for $\eta/s$ in the deconfined phase with those from chiral perturbation theory or the resonance gas model in the confined phase we observe a pronounced minimum of $\eta/s$ close to the critical temperature $T_{\rm c}$.Comment: Published in Eur. Phys. J. C, 7 pages, 2 figures, 3 tabl

Meson screening masses from lattice QCD with two light and the strange quark

We present results for screening masses of mesons built from light and strange quarks in the temperature range of approximately between 140 MeV to 800 MeV. The lattice computations were performed with 2+1 dynamical light and strange flavors of improved (p4) staggered fermions along a line of constant physics defined by a pion mass of about 220 MeV and a kaon mass of 500 MeV. The lattices had temporal extents Nt = 4, 6 and 8 and aspect ratios of Ns / Nt \geq 4. At least up to a temperature of 140 MeV the pseudo-scalar screening mass remains almost equal to the corresponding zero temperature pseudo-scalar (pole) mass. At temperatures around 3Tc (Tc being the transition temperature) the continuum extrapolated pseudo-scalar screening mass approaches very close to the free continuum result of 2 \pi T from below. On the other hand, at high temperatures the vector screening mass turns out to be larger than the free continuum value of 2 \pi T. The pseudo-scalar and the vector screening masses do not become degenerate even for a temperature as high as 4Tc. Using these mesonic spatial correlation functions we have also investigated the restoration of chiral symmetry and the effective restoration of the axial symmetry. We have found that the vector and the axial-vector screening correlators become degenerate, indicating chiral symmetry restoration, at a temperature which is consistent with the QCD transition temperature obtained in previous studies. On the other hand, the pseudo-scalar and the scalar screening correlators become degenerate only at temperatures larger than 1.3Tc, indicating that the effective restoration of the axial symmetry takes place at a temperature larger than the QCD transition temperature.Comment: Published versio