6,012 research outputs found
Soft-collinear effective theory and heavy-to-light currents beyond leading power
An important unresolved question in strong interaction physics concerns the
parameterization of power-suppressed long-distance effects to hard processes
that do not admit an operator product expansion (OPE). Recently Bauer et al.\
have developed an effective field theory framework that allows one to formulate
the problem of soft-collinear factorization in terms of fields and operators.
We extend the formulation of soft-collinear effective theory, previously worked
out to leading order, to second order in a power series in the inverse of the
hard scale. We give the effective Lagrangian and the expansion of ``currents''
that produce collinear particles in heavy quark decay. This is the first step
towards a theory of power corrections to hard processes where the OPE cannot be
used. We apply this framework to heavy-to-light meson transition form factors
at large recoil energy.Comment: 46 pages, LaTeX; v2: two references added, eq. (52) correcte
An Analysis of the Inclusive Decay and Constraints on the -Meson Distribution Amplitudes
We calculate the -meson energy spectrum in the decay in the leading-order perturbative
QCD in the static quark limit for the Orthoquarkonium. Our principal result is
the extraction of parameters of the effective vertex
function (EVF) involving a virtual and a real gluon from the available data on
the hard part of the -meson energy spectrum. The perturbative QCD
based framework provides a good description of the available CLEO data,
allowing to constrain the lowest Gegenbauer coefficients and
of the quark-antiquark and gluonic distribution amplitudes of the
-meson. The resulting constraints are combined with the existing
ones on these coefficients from an analysis of the and
transition form factors and the requirement of positivity
of the EVF, yielding and
for GeV. This reduces
significantly the current uncertainty on these coefficients. The resulting EFV
, including the
-meson mass effects, is presented.Comment: 23 pages, 8 figures; use epsfig.sty; Typos corrected, numerical
analysis further refined; added an equation; to appear in the European
Physical Journal
Consistent SDNs through Network State Fuzzing
The conventional wisdom is that a software-defined network (SDN) operates under the premise that the logically centralized control plane has an accurate representation of the actual data plane state. Nevertheless, bugs, misconfigurations, faults or attacks can introduce inconsistencies that undermine correct operation. Previous work in this area, however, lacks a holistic methodology to tackle this problem and thus, addresses only certain parts of the problem. Yet, the consistency of the overall system is only as good as its least consistent part. Motivated by an analogy of network consistency checking with program testing, we propose to add active probe-based network state fuzzing to our consistency check repertoire. Hereby, our system, PAZZ, combines production traffic with active probes to continuously test if the actual forwarding path and decision elements (on the data plane) correspond to the expected ones (on the control plane). Our insight is that active traffic covers the inconsistency cases beyond the ones identified by passive traffic. PAZZ prototype was built and evaluated on topologies of varying scale and complexity. Our results show that PAZZ requires minimal network resources to detect persistent data plane faults through fuzzing and localize them quickly
Evolution of Directed Triangle Motifs in the Google+ OSN
Motifs are a fundamental building block and distinguishing feature of networks. While characteristic motif distribution have been found in many networks, very little is known today about the evolution of network motifs. This paper studies the most important motifs in social networks, triangles, and how directed triangle motifs change over time. Our chosen subject is one of the largest Online Social Networks, Google+. Google+ has two distinguishing features that make it particularly interesting: (1) it is a directed network, which yields a rich set of triangle motifs, and (2) it is a young and fast evolving network, whose role in the OSN space is still not fully understood. For the purpose of this study, we crawled the network over a time period of six weeks, collecting several snapshots. We find that some triangle types display significant dynamics, e.g., for some specific initial types, up to 20% of the instances evolve to other types. Due to the fast growth of the OSN in the observed time period, many new triangles emerge. We also observe that many triangles evolve into less-connected motifs (with less edges), suggesting that growth also comes with pruning. We complement the topological study by also considering publicly available user profile data (mostly geographic locations). The corresponding results shed some light on the semantics of the triangle motifs. Indeed, we find that users in more symmetric triangle motifs live closer together, indicating more personal relationships. In contrast, asymmetric links in motifs often point to faraway users with a high in-degree (celebrities)
Pseudoscalar Meson Mixing in Effective Field Theory
We show that for any effective field theory of colorless meson fields, the
mixing schemes of particle states and decay constants are not only related but
also determined exclusively by the kinetic and mass Lagrangian densities. In
the general case, these are bilinear in terms of the intrinsic fields and
involve non-diagonal kinetic and mass matrices. By applying three consecutive
steps this Lagrangian can be reduced into the standard quadratic form in terms
of the physical fields. These steps are : (i) the diagonalization of the
kinetic matrix, (ii) rescaling of the fields, and (iii) the diagonalization of
the mass matrix. In case, where the dimensions of the non-diagonal kinetic and
mass sub-matrices are respectively, and , this procedure
leads to mixing schemes which involve angles and
field rescaling parameters. This observation holds true irrespective with the
type of particle interactions presumed. The commonly used mixing schemes,
correspond to a proper choice of the kinetic and mass matrices, and are derived
as special cases. In particular, - mixing, requires one angle, if
and only if, the kinetic term with the intrinsic fields has a quadratic form.Comment: REVTeX, 6 page
Vector meson - mixing and their form factors in light-cone quark model
The vector meson - mixing is studied in two alternative
scenarios with different numbers of mixing angles, i.e., the one-mixing-angle
scenario and the two-mixing-angle scenario, in both the octect-singlet mixing
scheme and the quark flavor mixing scheme. Concerning the reproduction of
experimental data and the behavior of transition form factors,
one-mixing-angle scenario in the quark flavor scheme performs better than that
in the octet-singlet scheme, while the two-mixing-angle scenario works well for
both mixing schemes. The difference between the two mixing angles in the
octet-singlet scheme is bigger than that in the quark flavor scheme.Comment: 16 pages, 7 figures, final version to appear in PR
Factorization in exclusive semileptonic radiative B decays
We derive a new factorization relation for the semileptonic radiative decay B
-> \pi \ell \nu \gamma in the kinematical region of a slow pion p_\pi ~ \Lambda
and an energetic photon E_\gamma >> \Lambda, working at leading order in
\Lambda/m_b. In the limit of a soft pion, the nonperturbative matrix element
appearing in this relation can be computed using chiral perturbation theory. We
present a phenomenological study of this decay, which may be important for a
precise determination of the exclusive nonradiative decay.Comment: 10 pages, 3 figures; minor corrections, one reference adde
Aligning technology and language arts standards
The standards of language arts and technology blend fluidly to provide for an optimal learning environment. Language Arts teachers and students of all levels can gain significantly from the incorporation of multimedia software into the curriculum. Educators demonstrate responsible teaching when the initiative is taken to incorporate these otherwise separate areas together. Multimedia provides for an additional method for students to obtain, demonstrate, and share information. The use of technology into all curricular areas helps to develop life skills that are considered necessities in many jobs today
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