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Silviu S. Pufu

Publications and source records attributed to Silviu S. Pufu.

99 records · Page 6Linked to original sources
arXiv2008

Bulk viscosity of strongly coupled plasmas with holographic duals

We explain a method for computing the bulk viscosity of strongly coupled thermal plasmas dual to supergravity backgrounds supported by one scalar field. Whereas earlier investigations required the computation of the leading dissipative term in the dispersion relation for sound waves, our method requires only the leading frequency dependence of an appropriate Green's function in the low-frequency limit. With a scalar potential chosen to mimic the equation of state of QCD, we observe a slight violation of the lower bound on the ratio of the bulk and shear viscosities conjectured in arXiv:0708.3459.

hep-th↗
arXiv2008

Entropy production in collisions of gravitational shock waves and of heavy ions

We calculate the area of a marginally trapped surface formed by a head-on collision of gravitational shock waves in AdS_D. We use this to obtain a lower bound on the entropy produced after the collision. A comparison to entropy production in heavy ion collisions is included. We also discuss an O(D-2) remnant of conformal symmetry which is present in a class of gravitational shock wave collisions in AdS_D and which might be approximately realized (with D=5) in central heavy-ion collisions.

hep-th↗
arXiv2008

Thermodynamics and bulk viscosity of approximate black hole duals to finite temperature quantum chromodynamics

We consider classes of translationally invariant black hole solutions whose equations of state closely resemble that of QCD at zero chemical potential. We use these backgrounds to compute the ratio zeta/s of bulk viscosity to entropy density. For a class of black holes that exhibits a first order transition, we observe a sharp rise in zeta/s near T_c. For constructions that exhibit a smooth cross-over, like QCD does, the rise in zeta/s is more modest. We conjecture that divergences in zeta/s for black hole horizons are related to extrema of the entropy density as a function of temperature.

hep-th↗
arXiv2007

Shock waves from heavy-quark mesons in AdS/CFT

We calculate the far-field stress-energy tensor of a quark gluon plasma due to a heavy-quark meson moving through it, using a semi-classical description in string theory of the meson as a string hanging into anti-de Sitter space. We find that these mesons create a shock wave but no diffusion wake, in contrast to single heavy quarks described via a trailing string, where the diffusion wake is strong. If thermal QCD responds similarly to heavy quarks and heavy quarkonia, the presence or suppression of the diffusion wake constitutes a prediction which can in principle be checked in heavy-ion collisions.

hep-th↗
arXiv2007

Energy disturbances due to a moving quark from gauge-string duality

Using AdS/CFT, we calculate the energy density of a quark moving through a thermal state of N=4 super-Yang-Mills theory. Relying on previous work for momentum-space representations as well as asymptotic behaviors, we Fourier transform to position space and exhibit a sonic boom at a speed larger than the speed of sound. Nontrivial structure is found at small length scales, confirming earlier analytical work by the authors.

hep-th↗
arXiv2006

Stability of strings binding heavy-quark mesons

We investigate the stability against small deformations of strings dangling into AdS_5-Schwarzschild from a moving heavy quark-anti-quark pair. We speculate that emission of massive string states may be an important part of the evolution of certain unstable configurations.

hep-th↗
arXiv2006

The stress tensor of a quark moving through N=4 thermal plasma

We develop the linear equations that describe graviton perturbations of AdS_5-Schwarzschild generated by a string trailing behind an external quark moving with constant velocity. Solving these equations allows us to evaluate the stress tensor in the boundary gauge theory. Components of the stress tensor exhibit directional structures in Fourier space at both large and small momentum. We comment on the possible relevance of our results to relativistic heavy ion collisions.

hep-th↗