4,760 research outputs found
Phase Space Matching and Finite Lifetime Effects for Top-Pair Production Close to Threshold
The top-pair production cross section close to threshold in
collisions is strongly affected by the small lifetime of the top
quark. Since the cross section is defined through final states containing the
top decay products, a consistent definition of the cross section depends on
prescriptions how these final states are accounted for the cross section.
Experimentally, these prescriptions are implemented for example through cuts on
kinematic quantities such as the reconstructed top quark invariant masses. As
long as these cuts do not reject final states that can arise from the decay of
a top and an anti-top quark with a small off-shellness compatible with the
nonrelativistic power-counting, they can be implemented through imaginary phase
space matching conditions in NRQCD. The prescription-dependent cross section
can then be determined from the optical theorem using the forward
scattering amplitude. We compute the phase space matching conditions associated
to cuts on the top and anti-top invariant masses at next-to-next-to-leading
logarithmic (NNLL) order and partially at next-to-next-to-next-to-leading
logarithmic (NLL) order in the nonrelativistic expansion and, together
with finite lifetime and electroweak effects known from previous work, analyze
their numerical impact on the cross section. We show that the phase
space matching contributions are essential to make reliable NRQCD predictions,
particularly for energies below the peak region, where the cross section is
small. We find that irreducible background contributions associated to final
states that do not come from top decays are strongly suppressed and can be
neglected for the theoretical predictions.Comment: 62 pages, 21 figure
Electroweak Absorptive Parts in NRQCD Matching Conditions
Electroweak corrections associated with the instability of the top quark to
the next-to-next-to-leading logarithmic (NNLL) total top pair threshold cross
section in e+e- annihilation are determined. Our method is based on absorptive
parts in electroweak matching conditions of the NRQCD operators and the optical
theorem. The corrections lead to ultraviolet phase space divergences that have
to be renormalized and lead to NLL mixing effects. Numerically, the corrections
can amount to several percent and are comparable to the known NNLL QCD
corrections.Comment: 17 pages, revtex4, 4 postscript figures included; minor changes in
text and references, title modified in printed versio
Three-Loop Anomalous Dimension of the Heavy Quark Pair Production Current in Non-Relativistic QCD
The three-loop non-mixing contributions to the anomalous dimension of the
leading order quark pair production current in non-relativistic QCD are
computed. It is demonstrated that the renormalization procedure can only be
carried out consistently if the dynamics of both soft and the ultrasoft degrees
of freedom is present for all scales below the heavy quark mass, and if the
soft and ultrasoft renormalization scales are always correlated.Comment: 19 pages, revtex, 5 postscript figures include
Charm Quark Mass from Inclusive Semileptonic B Decays
The MSbar charm quark mass is determined to be m_c(m_c)=1224+-17+-54 MeV from
a global fit to inclusive B meson decay data, where the first error is
experimental, and includes the uncertainty in alpha_s, and the second is an
estimate of theoretical uncertainties in the computation. We discuss the
implications of the pole mass renormalon in the determination of m_c.Comment: 7 pages, 2 tables; revtex4. References added, minor changes; version
to appear in PL
An isogeometric analysis for elliptic homogenization problems
A novel and efficient approach which is based on the framework of
isogeometric analysis for elliptic homogenization problems is proposed. These
problems possess highly oscillating coefficients leading to extremely high
computational expenses while using traditional finite element methods. The
isogeometric analysis heterogeneous multiscale method (IGA-HMM) investigated in
this paper is regarded as an alternative approach to the standard Finite
Element Heterogeneous Multiscale Method (FE-HMM) which is currently an
effective framework to solve these problems. The method utilizes non-uniform
rational B-splines (NURBS) in both macro and micro levels instead of standard
Lagrange basis. Beside the ability to describe exactly the geometry, it
tremendously facilitates high-order macroscopic/microscopic discretizations
thanks to the flexibility of refinement and degree elevation with an arbitrary
continuity level provided by NURBS basis functions. A priori error estimates of
the discretization error coming from macro and micro meshes and optimal micro
refinement strategies for macro/micro NURBS basis functions of arbitrary orders
are derived. Numerical results show the excellent performance of the proposed
method
B decays in the upsilon expansion
Theoretical predictions for B decay rates are rewritten in terms of the
Upsilon(1S) meson mass instead of the b quark mass, using a modified
perturbation expansion. The theoretical consistency of this expansion is shown
both at low and high orders. Our method improves the behavior of the
perturbation series for semileptonic and nonleptonic inclusive decay modes, as
well as for exclusive decay form factors. The results are applied to the
determination of the semileptonic B branching ratio, charm counting, the ratio
of B -> X tau nu and B -> X e nu decay rates, and form factor ratios in B -> D*
e nu decay. We also comment on why it is not possible to separate perturbative
and nonperturbative effects in QCD.Comment: 21 page
On Electroweak Matching Conditions for Top Pair Production at Threshold
We determine the real parts of electroweak matching conditions relevant for
top quark pair production close to threshold in e+e- annihilation at
next-to-next-to-leading logarithmic (NNLL) order. Numerically the corrections
are comparable to the NNLL QCD corrections.Comment: 12 pages, revtex4, 1 postscript figure included; minor changes in
text and references, version published in Phys. Rev.
The Globalization Strategy of Vietnamese IT Enterprises in the Context of ASEAN Economic Community Via the Case Study of Fpt Corporation Hoang Van Cuong, (Director of International Mobility Department, Fpt University Vietnam)
Vietnam IT Industry has been growing rapidly duringthe past 15 years. It has been considered as the mainshort cut to develop the Vietnamese economy from a lowincome to a middle income country (MIC). From 2002to 2013, the revenue of software industry increased 52times to reach nearly 3 US billion. Hanoi and Ho Chi Minh City – the twobiggest cities in Vietnam have been ranked in the Top100 outsourcing destinations by Tholons (an advisoryfirm for global outsourcing and investment).ASEAN is one of the key markets for Vietnam'sIT industry. The region also provides a high potentiallabor force market to solve the human resourceproblems of the IT enterprises. In this context, ASEANEconomic Community will have a significant influenceto the development of Vietnam's IT enterprises.This paper will discuss the globalizationstrategy of Vietnamese IT enterprises in the context ofASEAN Economic community via the case of FPTCorporation – the leading IT Company in Vietnamwhich currently has its office in Singapore, Malaysia,Thailand, Laos, Cambodia, Myanmar, Indonesia andthe Philippines
A Renormalization Group Improved Calculation of Top Quark Production near Threshold
The top quark cross section close to threshold in annihilation is
computed including the summation of logarithms of the velocity at
next-to-next-to-leading-logarithmic order in QCD. The remaining theoretical
uncertainty in the normalization of the total cross section is at the few
percent level, an order of magnitude smaller than in previous
next-to-next-to-leading order calculations. This uncertainty is smaller than
the effects of a light standard model Higgs boson.Comment: changed figures, added reference
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