366 research outputs found
The Chern-Simons diffusion rate in strongly coupled N=4 SYM plasma in an external magnetic field
We calculate the Chern-Simons diffusion rate in a strongly coupled N=4 SUSY
Yang-Mills plasma in the presence of a constant external magnetic flux
via the holographic correspondence. Due to the strong interactions between the
charged fields and non-Abelian gauge fields, the external Abelian magnetic
field affects the thermal Yang-Mills dynamics and increases the diffusion rate,
regardless of its strength. We obtain the analytic results for the Chern-Simons
diffusion rate both in the weak and strong magnetic field limits. In the latter
limit, we show that the diffusion rate scales as and this can be
understood as a result of a dynamical dimensional reduction.Comment: 10 pages, 1 figure, typos corrected, comments adde
Conformal anomaly as a source of soft photons in heavy ion collisions
We introduce a novel photon production mechanism stemming from the conformal
anomaly of QCDxQED and the existence of strong (electro)magnetic fields in
heavy ion collisions. Using the hydrodynamical description of the bulk modes of
QCD plasma, we show that this mechanism leads to the photon production yield
that is comparable to the yield from conventional sources. This mechanism also
provides a significant positive contribution to the azimuthal anisotropy of
photons, , as well as to the radial "flow". We compare our results to the
data from the PHENIX Collaboration.Comment: 5 pages, 3 figures; version accepted to Phys. Rev. Let
Attainability in Repeated Games with Vector Payoffs
We introduce the concept of attainable sets of payoffs in two-player repeated
games with vector payoffs. A set of payoff vectors is called {\em attainable}
if player 1 can ensure that there is a finite horizon such that after time
the distance between the set and the cumulative payoff is arbitrarily
small, regardless of what strategy player 2 is using. This paper focuses on the
case where the attainable set consists of one payoff vector. In this case the
vector is called an attainable vector. We study properties of the set of
attainable vectors, and characterize when a specific vector is attainable and
when every vector is attainable.Comment: 28 pages, 2 figures, conference version at NetGCoop 201
Holographic Pomeron and the Schwinger Mechanism
We revisit the problem of dipole-dipole scattering via exchanges of soft
Pomerons in the context of holographic QCD. We show that a single closed string
exchange contribution to the eikonalized dipole-dipole scattering amplitude
yields a Regge behavior of the elastic amplitude; the corresponding slope and
intercept are different from previous results obtained by a variational
analysis of semi-classical surfaces. We provide a physical interpretation of
the semi-classical worldsheets driving the Regge behavior for (-t)>0 in terms
of worldsheet instantons. The latter describe the Schwinger mechanism for
string pair creation by an electric field, where the longitudinal electric
field E_L=\sigma_T tanh(\chi/2) at the origin of this non-perturbative
mechanism is induced by the relative rapidity {\chi} of the scattering dipoles.
Our analysis naturally explains the diffusion in the impact parameter space
encoded in the Pomeron exchange; in our picture, it is due to the Unruh
temperature of accelerated strings under the electric field. We also argue for
the existence of a "micro-fireball" in the middle of the transverse space due
to the soft Pomeron exchange, which may be at the origin of the thermal
character of multiparticle production in ep/pp collisions. After summing over
uncorrelated multi-Pomeron exchanges, we find that the total dipole-dipole
cross section obeys the Froissart unitarity bound.Comment: 17 pages, 4 figures, version 2: minor typos corrected, references
adde
Detecting event-related recurrences by symbolic analysis: Applications to human language processing
Quasistationarity is ubiquitous in complex dynamical systems. In brain
dynamics there is ample evidence that event-related potentials reflect such
quasistationary states. In order to detect them from time series, several
segmentation techniques have been proposed. In this study we elaborate a recent
approach for detecting quasistationary states as recurrence domains by means of
recurrence analysis and subsequent symbolisation methods. As a result,
recurrence domains are obtained as partition cells that can be further aligned
and unified for different realisations. We address two pertinent problems of
contemporary recurrence analysis and present possible solutions for them.Comment: 24 pages, 6 figures. Draft version to appear in Proc Royal Soc
Multi-Layer Cyber-Physical Security and Resilience for Smart Grid
The smart grid is a large-scale complex system that integrates communication
technologies with the physical layer operation of the energy systems. Security
and resilience mechanisms by design are important to provide guarantee
operations for the system. This chapter provides a layered perspective of the
smart grid security and discusses game and decision theory as a tool to model
the interactions among system components and the interaction between attackers
and the system. We discuss game-theoretic applications and challenges in the
design of cross-layer robust and resilient controller, secure network routing
protocol at the data communication and networking layers, and the challenges of
the information security at the management layer of the grid. The chapter will
discuss the future directions of using game-theoretic tools in addressing
multi-layer security issues in the smart grid.Comment: 16 page
A Gauge-Gravity Relation in the One-loop Effective Action
We identify an unusual new gauge-gravity relation: the one-loop effective
action for a massive spinor in 2n dimensional AdS space is expressed in terms
of precisely the same function [a certain multiple gamma function] as the
one-loop effective action for a massive charged scalar in 4n dimensions in a
maximally symmetric background electromagnetic field [one for which the
eigenvalues of F_{\mu\nu} are maximally degenerate, corresponding in 4
dimensions to a self-dual field, equivalently to a field of definite helicity],
subject to the identification F^2 \Lambda, where \Lambda is the
gravitational curvature. Since these effective actions generate the low energy
limit of all one-loop multi-leg graviton or gauge amplitudes, this implies a
nontrivial gauge-gravity relation at the non-perturbative level and at the
amplitude level.Comment: 6 page
Simulation modelling of chief officers’ working hours on short sea shipping
Short sea shipping poses significant problems for many seafarers, particularly for officers employed in oil tankers as chief officers. This study examines chief officers’ working conditions on short sea shipping. In this study, Simio simulation software was utilised to evaluate the working hours of chief officers. The results demonstrate that the rest periods of the chief officers have been less compromised as the navigation period increases in oil tankers operated on short sea shipping. To comply with the relevant regulations, a navigation period of 24–28 h is the minimum condition for an oil tanker to have a chief officer; however, an additional officer may be required for shorter voyages. The findings of the research provide some recommendations to maritime authorities to achieve safe short sea shipping
- …