446 research outputs found
Holographic bulk viscosity: GPR vs EO
Recently Eling and Oz (EO) proposed a formula for the holographic bulk
viscosity, in arXiv:1103.1657, derived from the null horizon focusing equation.
This formula seems different from that obtained earlier by Gubser, Pufu and
Rocha (GPR) in arXiv:0806.0407 calculated from the IR limit of the two-point
function of the trace of the stress tensor. The two were shown to agree only
for some simple scaling cases. We point out that the two formulae agree in two
non-trivial holographic theories describing RG flows. The first is the strongly
coupled N=2* gauge theory plasma. The second is the semi-phenomenological model
of Improved Holographic QCD.Comment: 21 pages, 2 figure
On jet quenching parameters in strongly coupled non-conformal gauge theories
Recently Liu, Rajagopal and Wiedemann (LRW) [hep-ph/0605178] proposed a first
principle, nonperturbative quantum field theoretic definition of ``jet
quenching parameter'' \hat{q} used in models of medium-induced radiative parton
energy loss in nucleus-nucleus collisions at RHIC. Relating \hat{q} to a
short-distance behavior of a certain light-like Wilson loop, they used gauge
theory-string theory correspondence to evaluate \hat{q} for the strongly
coupled N=4 SU(N_c) gauge theory plasma. We generalize analysis of LRW to
strongly coupled non-conformal gauge theory plasma. We find that a jet
quenching parameter is gauge theory specific (not universal). Furthermore, it
appears it's value increases as the number of effective adjoint degrees of
freedom of a gauge theory plasma increases.Comment: 14 pages, latex; v2: PRD versio
Unequal but fair?:About the perceived legitimacy of the standing economic order
Public Summary Acknowledged as the defining challenge of our time, economic inequality has far reaching individual and societal consequences. It negatively affects productivity, decision-making, and health outcomes on the one hand, and political stability and economic growth on the other. Increased competition for resources not allocated at the top skews available reference frames and leads to adoption of unachievable standards, generating stressful social comparisons and anxiety that may intensify inter-group conflicts. Yet, as this dissertation shows on data from surveys from across the world, many of the worse off tend to believe that the social world in general is fair and that large differences in incomes are justified and even necessary. To understand why and how are the widespread and entrenched differences in incomes and wealth not being contested at a larger scale, this dissertations links perceptions and judgments of economic inequalities to their perceived, and often misjudged, normativity. It is argued that there is a need for a greater attention and understanding of people’s beliefs about what are the popular opinions and shared values regarding political issues. It is not only that people not know of inequalities, underestimate them, or attempt to rationalize their existence as fair and deserved. It is that people also need to know that their sentiments are shared by others. Based on results of multiple experimental studies, this thesis explored and supported a possibility that people who believe that the unequal status quo is unsatisfactory and that the standing system should be challenged and changed also tend to believe that their views are not shared by the general population. Even more, such thinking tends to get reinforced when someone else is critical of the system in place. Thus, instead of rising in spirit and assuming that others will finally see at least some of the negative outcomes of the way things are, those hoping for change may get demoralized, feel isolated in their views, and may feel drawn to compromises they shouldn't need to consider
Viscosity Bound and Causality in Superfluid Plasma
It was argued by Brigante et.al that the lower bound on the ratio of the
shear viscosity to the entropy density in strongly coupled plasma is translated
into microcausality violation in the dual gravitational description. Since
transport properties of the system characterize its infrared dynamics, while
the causality of the theory is determined by its ultraviolet behavior, the
viscosity bound/microcausality link should not be applicable to theories that
undergo low temperature phase transitions. We present an explicit model of
AdS/CFT correspondence that confirms this fact.Comment: 27 pages, 5 figures. References added, typos fixe
Gauge/gravity correspondence in accelerating universe
We discuss time-dependent backgrounds of type IIB supergravity realizing
gravitation duals of gauge theories formulated in de Sitter space-time as a
tool of embedding de Sitter in a supergravity. We show that only the
gravitational duals to non-conformal gauge theories are sensitive to a specific
value of a Hubble parameter. We consider two nontrivial solutions of this type:
a gravity dual to six-dimensional (1,1) little string theory, and to a
four-dimensional cascading SU(N+M)xSU(N) supersymmetric gauge theory (related
to fractional D3-branes on a singular conifold according to Klebanov et al), in
accelerating universe. In both cases we argue that the IR singularity of the
geometry is regulated by the expansion of the gauge theory background
space-time.Comment: 13 pages, harvmac, v2: reference added, v3: D3,NS5 discussion
improved, PRD versio
On effective action of string theory flux compactifications
We discuss four dimensional effective actions of string theory flux
compactifications. These effective actions describe four dimensional gravity
coupled to overall Kahler modulus of the compactification manifold. We
demonstrate the agreement between ten dimensional equations of motion of
supergravity with localized branes, and equations of motion derived from the
effective action. The agreement is lost however if one evaluates the full
effective action on the equations of motion for a subset of the supergravity
modes, provided these modes depend on-shell on the Kahler modulus.Comment: 25 pages; v2: refs adde
Transport coefficients, membrane couplings and universality at extremality
We present an efficient method for computing the zero frequency limit of
transport coefficients in strongly coupled field theories described
holographically by higher derivative gravity theories. Hydrodynamic parameters
such as shear viscosity and conductivity can be obtained by computing residues
of poles of the off-shell lagrangian density. We clarify in which sense these
coefficients can be thought of as effective couplings at the horizon, and
present analytic, Wald-like formulae for the shear viscosity and conductivity
in a large class of general higher derivative lagrangians. We show how to apply
our methods to systems at zero temperature but finite chemical potential. Our
results imply that such theories satisfy universally in the
Einstein-Maxwell sector. Likewise, the zero frequency limit of the real part of
the conductivity for such systems is shown to be universally zero, and we
conjecture that higher derivative corrections in this sector do not modify this
result to all orders in perturbation theory.Comment: 29 pages, v2: Small text changes for clarity, typos correcte
Gauge/string correspondence in curved space
We discuss Gubser-Klebanov-Polyakov proposal for the gauge/string theory
correspondence for gauge theories in curved space. Specifically, we consider
Klebanov-Tseytlin cascading gauge theory compactified on S^3. We explain regime
when this gauge theory is a small deformation of the superconformal N=1 gauge
theory on the world volume of regular D3-branes at the tip of the conifold. We
study closed string states on the leading Regge trajectory in this background,
and attempt to identify the dual gauge theory twist two operators.Comment: 26 pages, v2: refs adde
Cavitation effects on the confinement/deconfinement transition
Cavitation is a process where the viscous terms in a relativistic fluid
result in reducing the effective pressure, thus facilitating the nucleation of
bubbles of a stable phase. The effect is particularly pronounced in the
vicinity of a (weak) first-order phase transition. We use the holographic
correspondence to study cavitation in a strongly coupled planar cascading gauge
theory plasma close to the confinement/deconfinement phase transition. While in
this particular model the shift of the deconfinement temperature due to
cavitation does not exceed 5%, we speculate that cavitation might be important
near the QCD critical point.Comment: 4 pages, 1 figure; v2: minor amendments, journal versio
Comments on supergravity dual of pure N=1 Super Yang Mills theory with unbroken chiral symmetry
Maldacena and Nunez [hep-th/0008001] identified a gravity solution describing
pure N=1 Yang-Mills (YM) in the IR. Their (smooth) supergravity solution
exhibits confinement and the U(1)_R chiral symmetry breaking of the dual YM
theory, while the singular solution corresponds to the gauge theory phase with
unbroken U(1)_R chiral symmetry. In this paper we discuss supersymmetric type
IIB compactifications on resolved conifolds with torsion. We rederive singular
background of [hep-th/0008001] directly from the supersymmetry conditions. This
solution is the relevant starting point to study non-BPS backgrounds dual to
the high temperature phase of pure YM. We construct the simplest black hole
solution in this background. We argue that it has a regular Schwarzschild
horizon and provides a resolution of the IR singularity of the chirally
symmetric extremal solution as suggested in [hep-th/0011146].Comment: 34 pages, LaTeX, v2: references added, v3: section 2 reduced, minor
clarifications, to be published in PR
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