170,602 research outputs found
Hamiltonian Reduction of -theories at the Level of Correlators
Since the work of Bershadsky and Ooguri and Feigin and Frenkel it is well
known that correlators of current algebra for admissible
representations should reduce to correlators for conformal minimal models. A
precise proposal for this relation has been given at the level of correlators:
When primary fields are expressed as with being
a variable to keep track of the representation multiplet (possibly
infinitely dimensional for admissible representations), then the minimal model
correlator is supposed to be obtained simply by putting all . Although
strong support for this has been presented, to the best of our understanding a
direct, simple proof seems to be missing so in this paper we present one based
on the free field Wakimoto construction and our previous study of that in the
present context. We further verify that the explicit correlators we
have published in a recent preprint reduce in the above way, up to a constant
which we also calculate. We further discuss the relation to more standard
formulations of hamiltonian reduction.Comment: 13 pages, LaTe
Electron Bloch Oscillations and Electromagnetic Transparency of Semiconductor Superlattices in Multi-Frequency Electric Fields
We examine phenomenon of electromagnetic transparency in semiconductor
superlattices (having various miniband dispersion laws) in the presence of
multi-frequency periodic and non-periodic electric fields. Effects of induced
transparency and spontaneous generation of static fields are discussed. We paid
a special attention on a self-induced electromagnetic transparency and its
correlation to dynamic electron localization. Processes and mechanisms of the
transparency formation, collapse, and stabilization in the presence of external
fields are studied. In particular, we present the numerical results of the time
evolution of the superlattice current in an external biharmonic field showing
main channels of transparency collapse and its partial stabilization in the
case of low electron density superlattices
Can hadronic rescattering explain the "jet quenching" at RHIC?
Recent RHIC data have shown novel nuclear modifications of moderate to high
pt particle production in central Au+Au collisions, including a suppression of
hadron production and a disappearance of back-to-back hadron pairs. In this
paper, we investigate whether final-state hadronic interactions of the jet
fragments can reproduce the RHIC data. We find that hadronic rescattering can
account for the disappearance of back-to-back hadron pairs, but cannot
reproduce other features of the RHIC data.Comment: 6 pages, 6 figures, submitted to Phys. Rev.
Stochastic Tools for Network Intrusion Detection
With the rapid development of Internet and the sharp increase of network
crime, network security has become very important and received a lot of
attention. We model security issues as stochastic systems. This allows us to
find weaknesses in existing security systems and propose new solutions.
Exploring the vulnerabilities of existing security tools can prevent
cyber-attacks from taking advantages of the system weaknesses. We propose a
hybrid network security scheme including intrusion detection systems (IDSs) and
honeypots scattered throughout the network. This combines the advantages of two
security technologies. A honeypot is an activity-based network security system,
which could be the logical supplement of the passive detection policies used by
IDSs. This integration forces us to balance security performance versus cost by
scheduling device activities for the proposed system. By formulating the
scheduling problem as a decentralized partially observable Markov decision
process (DEC-POMDP), decisions are made in a distributed manner at each device
without requiring centralized control. The partially observable Markov decision
process (POMDP) is a useful choice for controlling stochastic systems. As a
combination of two Markov models, POMDPs combine the strength of hidden Markov
Model (HMM) (capturing dynamics that depend on unobserved states) and that of
Markov decision process (MDP) (taking the decision aspect into account).
Decision making under uncertainty is used in many parts of business and
science.We use here for security tools.We adopt a high-quality approximation
solution for finite-space POMDPs with the average cost criterion, and their
extension to DEC-POMDPs. We show how this tool could be used to design a
network security framework.Comment: Accepted by International Symposium on Sensor Networks, Systems and
Security (2017
A physically motivated toy model for the BH-spheroid coevolution
We present a summary of the results obtained with a time-dependent, one-zone
toy model aimed at exploring the importance of radiative feedback on the
co-evolution of massive black holes (MBHs) at the center of stellar spheroids
and their stellar and gaseous components. We consider cosmological infall of
gas as well as the mass and energy return for the evolving stellar population.
The AGN radiative heating and cooling are described by assuming photoionization
equilibrium of a plasma interacting with the average quasar SED. Our results
nicely support a new scenario in which the AGN accretion phase characterized by
a very short duty-cycle (and now common in the Universe) is due to radiative
feedback. The establishment of this phase is recorded as a fossil in the
Magorrian and Mbh-sigma relations.Comment: 2 pages. Proceedings of the MPA/MPE/ESO/USM Conference "Growing Black
Holes: accretion in a cosmological context", ESO Astrophysics Symposia, A.
Merloni, S. Nayakshin and R. Sunyaev ed
General two-order-parameter Ginzburg-Landau model with quadratic and quartic interactions
Ginzburg-Landau model with two order parameters appears in many
condensed-matter problems. However, even for scalar order parameters, the most
general U(1)-symmetric Landau potential with all quadratic and quartic terms
contains 13 independent coefficients and cannot be minimized with
straightforward algebra. Here, we develop a geometric approach that circumvents
this computational difficulty and allows one to study properties of the model
without knowing the exact position of the minimum. In particular, we find the
number of minima of the potential, classify explicit symmetries possible in
this model, establish conditions when and how these symmetries are
spontaneously broken, and explicitly describe the phase diagram.Comment: 36 pages, 7 figures; v2: added additional clarifications and a
discussion on how this method differs from the MIB-approac
QCD and Hadron Dynamics
Perturbative QCD predicts and describes various features of multihadron
production. An amazing similarity between observable hadron systems and
calculable underlying parton ensembles justifies the attempts to use the
language of quarks and gluons down to small momentum scales, to approach the
profound problems that are commonly viewed as being entirely non-perturbative.Comment: Talk at the Royal Society meeting "Structure of Matter", London, May
200
Spin-dependent properties of a two-dimensional electron gas with ferromagnetic gates
A theoretical prediction of the spin-dependent electron self-energy and
in-plane transport of a two-dimensional electron gas in proximity with a
ferromagnetic gate is presented. The application of the predicted
spin-dependent properties is illustrated by the proposal of a device
configuration with two neighboring ferromagnetic gates which produces a
magnetoresistance effect on the channel current generated by nonmagnetic source
and drain contacts. Specific results are shown for a silicon inversion layer
with iron gates. The gate leakage current is found to be beneficial to the spin
effects.Comment: 3 pages, 2 figures, Replaced with revised versio
Matrix Model Calculations beyond the Spherical Limit
We propose an improved iterative scheme for calculating higher genus
contributions to the multi-loop (or multi-point) correlators and the partition
function of the hermitian one matrix model. We present explicit results up to
genus two. We develop a version which gives directly the result in the double
scaling limit and present explicit results up to genus four. Using the latter
version we prove that the hermitian and the complex matrix model are equivalent
in the double scaling limit and that in this limit they are both equivalent to
the Kontsevich model. We discuss how our results away from the double scaling
limit are related to the structure of moduli space.Comment: 44 page
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