188,060 research outputs found
v4 for identified particles at RHIC from viscous hydrodynamics
Using ideal and viscous hydrodynamics, the ratio of azimuthal moments
v4/(v2)^2 is calculated for pions, protons, and kaons in sqrt{s}=200 A*GeV
Au+Au collisions. For any value of viscosity here is little dependence on
particle species. Ideal hydrodynamics and data show a flat curve as a function
of pt. Adding viscosity in the standard way destroys this flatness. However, it
can be restored by replacing the standard quadratic ansatz for delta f (the
viscous correction to the distribution function at freeze-out) with a weaker
momentum dependence.Comment: Proceedings of Hot Quarks 2010, 21-26 June 2010 La Londe Les Maures,
4 pages, 2 figure
Nonlinear stability of flock solutions in second-order swarming models
In this paper we consider interacting particle systems which are frequently
used to model collective behavior in animal swarms and other applications. We
study the stability of orientationally aligned formations called flock
solutions, one of the typical patterns emerging from such dynamics. We provide
an analysis showing that the nonlinear stability of flocks in second-order
models entirely depends on the linear stability of the first-order aggregation
equation. Flocks are shown to be nonlinearly stable as a family of states under
reasonable assumptions on the interaction potential. Furthermore, we
numerically verify that commonly used potentials satisfy these hypotheses and
investigate the nonlinear stability of flocks by an extensive case-study of
uniform perturbations.Comment: 22 pages, 1 figure, 1 tabl
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Scaling laws of resistive magnetohydrodynamic reconnection in the high-Lundquist-number, plasmoid-unstable regime
The Sweet-Parker layer in a system that exceeds a critical value of the
Lundquist number () is unstable to the plasmoid instability. In this paper,
a numerical scaling study has been done with an island coalescing system driven
by a low level of random noise. In the early stage, a primary Sweet-Parker
layer forms between the two coalescing islands. The primary Sweet-Parker layer
breaks into multiple plasmoids and even thinner current sheets through multiple
levels of cascading if the Lundquist number is greater than a critical value
. As a result of the plasmoid instability, the system
realizes a fast nonlinear reconnection rate that is nearly independent of ,
and is only weakly dependent on the level of noise. The number of plasmoids in
the linear regime is found to scales as , as predicted by an earlier
asymptotic analysis (Loureiro \emph{et al.}, Phys. Plasmas \textbf{14}, 100703
(2007)). In the nonlinear regime, the number of plasmoids follows a steeper
scaling, and is proportional to . The thickness and length of current sheets
are found to scale as , and the local current densities of current
sheets scale as . Heuristic arguments are given in support of theses
scaling relations.Comment: Submitted to Phys. Plasma
Valuation and hedging of the ruin-contingent life annuity (RCLA)
This paper analyzes a novel type of mortality contingent-claim called a
ruin-contingent life annuity (RCLA). This product fuses together a
path-dependent equity put option with a "personal longevity" call option. The
annuitant's (i.e. long position) payoff from a generic RCLA is \$1 of income
per year for life, akin to a defined benefit pension, but deferred until a
pre-specified financial diffusion process hits zero. We derive the PDE and
relevant boundary conditions satisfied by the RCLA value (i.e. the hedging
cost) assuming a complete market where No Arbitrage is possible. We then
describe some efficient numerical techniques and provide estimates of a typical
RCLA under a variety of realistic parameters.
The motivation for studying the RCLA on a stand-alone basis is two-fold.
First, it is implicitly embedded in approximately \$1 trillion worth of U.S.
variable annuity (VA) policies; which have recently attracted scrutiny from
financial analysts and regulators. Second, the U.S. administration - both
Treasury and Department of Labor - have been encouraging Defined Contribution
(401k) plans to offer stand-alone longevity insurance to participants, and we
believe the RCLA would be an ideal and cost effective candidate for that job
Decay Modes of the Hoyle State in
Recent experimental results give an upper limit less than 0.043\% (95\% C.L.)
to the direct decay of the Hoyle state into 3 respect to the sequential
decay into {Be}+. We performed one and two-dimensional tunneling
calculations to estimate such a ratio and found it to be more than one order of
magnitude smaller than experiment depending on the range of the nuclear force.
This is within high statistics experimental capabilities. Our results can also
be tested by measuring the decay modes of high excitation energy states of
C where the ratio of direct to sequential decay might reach 10\% at
(C)=10.3 MeV. The link between a Bose Einstein Condensate (BEC) and
the direct decay of the Hoyle state is also addressed. We discuss a
hypothetical `Efimov state' at (C)=7.458 MeV, which would mainly
{\it sequentially} decay with 3 of {\it equal energies}: a
counterintuitive result of tunneling. Such a state, if it would exist, is at
least 8 orders of magnitude less probable than the Hoyle's, thus below the
sensitivity of recent and past experiments.Comment: 6 pages, 2 figures, accepted by Phys. Lett.
Symbol error rate analysis for M-QAM modulated physical-layer network coding with phase errors
Recent theoretical studies of physical-layer network coding (PNC) show much interest on high-level modulation, such as M-ary quadrature amplitude modulation (M-QAM), and most related works are based on the assumption of phase synchrony. The possible presence of synchronization error and channel estimation error highlight the demand of analyzing the symbol error rate (SER) performance of PNC under different phase errors. Assuming synchronization and a general constellation mapping method, which maps the superposed signal into a set of M coded symbols, in this paper, we analytically derive the SER for M-QAM modulated PNC under different phase errors. We obtain an approximation of SER for general M-QAM modulations, as well as exact SER for quadrature phase-shift keying (QPSK), i.e. 4-QAM. Afterwards, theoretical results are verified by Monte Carlo simulations. The results in this paper can be used as benchmarks for designing practical systems supporting PNC. © 2012 IEEE
CP violation in in the model III 2HDM
We have calculated the Wilson coefficients (i=1,2) in the
renormalization scheme in the model III 2HDM. Using the obtained
Wilson coefficients, we have analyzed the CP violation in decays (q=d,s) in the model. The CP asymmetry, , depends on the
parameters of models and in can be as large as 40% and
35% for and respectively. It can reach 4% for decays.
Because in SM CP violation is smaller than or equal to O() which is
unobservably small, an observation of CP asymmetry in the decays would unambiguously signal the existence of new physics.Comment: revtex4, 16 pages, 7 figure
- …