49,428 research outputs found
Field dependent quasiparticles in the infinite dimensional Hubbard model
We present dynamical mean field theory (DMFT) results for the local spectral
densities of the one- and two-particle response functions for the infinite
dimensional Hubbard model in a magnetic field. We look at the different regimes
corresponding to half-filling, near half-filling and well away from
half-filling, for intermediate and strong values of the local interaction .
The low energy results are analyzed in terms of quasiparticles with field
dependent parameters. The renormalized parameters are determined by two
different methods, both based on numerical renormalization group (NRG)
calculations, and we find good agreement. Away from half-filling the
quasiparticle weights, , differ according to the spin type
or . Using the renormalized parameters, we
show that DMFT-NRG results for the local longitudinal and transverse dynamic
spin susceptibilities in an arbitrary field can be understood in terms of
repeated scattering of these quasiparticles. We also check Luttinger's theorem
for the Hubbard model and find it to be satisfied in all parameter regimes and
for all values of the magnetic field.Comment: 14 pages, 21 figure
Runtime Verification of Temporal Properties over Out-of-order Data Streams
We present a monitoring approach for verifying systems at runtime. Our
approach targets systems whose components communicate with the monitors over
unreliable channels, where messages can be delayed or lost. In contrast to
prior works, whose property specification languages are limited to
propositional temporal logics, our approach handles an extension of the
real-time logic MTL with freeze quantifiers for reasoning about data values. We
present its underlying theory based on a new three-valued semantics that is
well suited to soundly and completely reason online about event streams in the
presence of message delay or loss. We also evaluate our approach
experimentally. Our prototype implementation processes hundreds of events per
second in settings where messages are received out of order.Comment: long version of the CAV 2017 pape
Graph Abstraction and Abstract Graph Transformation
Many important systems like concurrent heap-manipulating programs, communication networks, or distributed algorithms are hard to verify due to their inherent dynamics and unboundedness. Graphs are an intuitive representation of states of these systems, where transitions can be conveniently described by graph transformation rules.
We present a framework for the abstraction of graphs supporting abstract graph transformation. The abstraction method naturally generalises previous approaches to abstract graph transformation. The set of possible abstract graphs is finite. This has the pleasant consequence of generating a finite transition system for any start graph and any finite set of transformation rules. Moreover, abstraction preserves a simple logic for expressing properties on graph nodes. The precision of the abstraction can be adjusted according to properties expressed in this logic to be verified
Project management techniques for highly integrated programs
The management and control of a representative, highly integrated high-technology project, in the X-29A aircraft flight test project is addressed. The X-29A research aircraft required the development and integration of eight distinct technologies in one aircraft. The project management system developed for the X-29A flight test program focuses on the dynamic interactions and the the intercommunication among components of the system. The insights gained from the new conceptual framework permitted subordination of departments to more functional units of decisionmaking, information processing, and communication networks. These processes were used to develop a project management system for the X-29A around the information flows that minimized the effects inherent in sampled-data systems and exploited the closed-loop multivariable nature of highly integrated projects
Factorization and Endpoint Singularities in Heavy-to-Light decays
We prove a factorization theorem for heavy-to-light form factors. Our result
differs in several important ways from previous proposals. A proper separation
of scales gives hard kernels that are free of endpoint singularities. A general
procedure is described for including soft effects usually associated with the
tail of wavefunctions in hard exclusive processes. We give an operator
formulation of these soft effects using the soft-collinear effective theory,
and show that they appear at the same order in the power counting as the hard
spectator contribution.Comment: 5 pages, Added details on comparison with the literatur
Characterization of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid
In this work we characterize the recently discovered active main belt object
P/2012 F5 (Gibbs), which was discovered with a dust trail > 7' in length in the
outer main belt, 7 months prior to aphelion. We use optical imaging obtained on
UT 2012 March 27 to analyze the central condensation and the long trail. We
find nuclear B-band and R-band apparent magnitudes of 20.96 and 19.93 mag,
respectively, which give an upper limit on the radius of the nucleus of 2.1 km.
The geometric cross-section of material in the trail was ~ 4 x 10^8 m^2,
corresponding to a dust mass of ~ 5 x 10^7 kg. Analysis of infrared images
taken by the Wide-Field Infrared Survey Explorer in September 2010 reveals that
the object was below the detection limit, suggesting that it was less active
than it was during 2012, or possibly inactive, just 6 months after it passed
through perihelion. We set a 1-sigma upper limit on its radius during this time
of 2.9 km. P/2012 F5 (Gibbs) is dynamically stable in the outer main belt on
timescales of ~ 1 Gyr, pointing towards an asteroidal origin. We find that the
morphology of the ejected dust is consistent with it being produced by a single
event that occurred on UT 2011 July 7 20 days, possibly as the result of
a collision with a small impactor.Comment: 29 pages, 5 figures. Accepted for publication in Ap
Soft-Collinear Messengers: A New Mode in Soft-Collinear Effective Theory
It is argued that soft-collinear effective theory for processes involving
both soft and collinear partons, such as exclusive B-meson decays, should
include a new mode in addition to soft and collinear fields. These
"soft-collinear messengers" can interact with both soft and collinear particles
without taking them far off-shell. They thus can communicate between the soft
and collinear sectors of the theory. The relevance of the new mode is
demonstrated with an explicit example, and the formalism incorporating the
corresponding quark and gluon fields into the effective Lagrangian is
developed.Comment: 22 pages, 5 figures. Extended Section 6, clarifying the relevance of
different types of soft-collinear interaction
A proof of factorization for B -> D pi
We prove that the matrix elements of four fermion operators mediating the
decay B^0 -> D^+ \pi^- and B^- -> D^0 \pi^- factor into the product of a form
factor describing the B -> D transition and a convolution of a short distance
coefficient with the nonperturbative pion light-cone wave function. This is
shown to all orders in alpha_s, up to corrections suppressed by factors of
1/mb, 1/mc, and 1/E_pi. It is not necessary to assume that the pion state is
dominated by the q-qbar Fock state.Comment: 4 pages, 3 figs, PRL versio
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