6,580 research outputs found
Transverse Momentum Distribution Through Soft-Gluon Resummation in Effective Field Theory
We study resummation of transverse-momentum-related large logarithms
generated from soft-gluon radiations in soft-collinear effective field theory.
The anomalous dimensions of the effective quark and gluon currents, an
important ingredient for the resummation, are calculated to two-loop order. the
result at next-to-leading-log reproduces that obtained using the standard
method for deep-inelastic scattering, Drell-Yan process, and Higgs production
through gluon-gluon fusion. We comment on the extension of the calculation to
next-to-next-to-leading logarithms.Comment: 13 pages, one figur
Transverse Momentum Dependent Light-Cone Wave Function of B-Meson and Relation to the Momentum Integrated One
A direct generalization of the transverse momentum integrated(TMI) light-cone
wave function to define a transverse momentum dependent(TMD) light-cone wave
function will cause light-cone singularities and they spoil TMD factorization.
We motivate a definition in which the light-cone singularities are regularized
with non-light like Wilson lines. The defined TMD light-cone wave function has
some interesting relations to the corresponding TMI one. When the transverse
momentum is very large, the TMD light-cone wave function is determined
perturbatively in term of the TMI one. In the impact -space with a small
, the TMD light-cone wave function can be factorized in terms of the TMI
one. In this letter we study these relations. By-products of our study are the
renormalization evolution of the TMI light-cone wave function and the
Collins-Soper equation of the TMD light-cone wave function, the later will be
useful for resumming Sudakov logarithms.Comment: Minor change in text, 7 pages, two figure
Hard Scattering Factorization from Effective Field Theory
In this paper we show how gauge symmetries in an effective theory can be used
to simplify proofs of factorization formulae in highly energetic hadronic
processes. We use the soft-collinear effective theory, generalized to deal with
back-to-back jets of collinear particles. Our proofs do not depend on the
choice of a particular gauge, and the formalism is applicable to both exclusive
and inclusive factorization. As examples we treat the pi-gamma form factor
(gamma gamma* -> pi^0), light meson form factors (gamma* M -> M), as well as
deep inelastic scattering (e- p -> e- X), Drell-Yan (p pbar -> X l+ l-), and
deeply virtual Compton scattering (gamma* p -> gamma(*) p).Comment: 35 pages, 4 figures, typos corrected, journal versio
Medium-induced parton splitting kernels from Soft Collinear Effective Theory with Glauber gluons
We derive the splitting kernels for partons produced in large
scattering processes that subsequently traverse a region of
strongly-interacting matter using a recently-developed effective theory \SCETG.
We include all corrections beyond the small- approximation, consistent with
the power counting of \SCETG. We demonstrate how medium recoil, geometry and
expansion scenarios, and phase space cuts can be implemented numerically for
phenomenological applications. For the simplified case of infinite transverse
momentum kinematics and a uniform medium, we provide closed-form analytic
results that can be used to validate the numerical simulations.Comment: 9 pages, 3 figure
Soft Pion Emission in DVCS
We examine soft-pion emission in deeply virtual Compton scattering. Contrary
to previous claims, we find that the amplitude for soft-pion emission is not
directly related to the generalized parton distributions in the nucleon.Comment: 9 pages, 2 figure
Spectroscopic evidence of charge exchange X-ray emission from galaxies
What are the origins of the soft X-ray line emission from non-AGN galaxies?
XMM-Newton RGS spectra of nearby non-AGN galaxies (including starforming ones:
M82, NGC 253, M51, M83, M61, NGC 4631, M94, NGC 2903, and the Antennae
galaxies, as well as the inner bulge of M31) have been analyzed. In particular,
the K{\alpha} triplet of O VII shows that the resonance line is typically
weaker than the forbidden and/or inter-combination lines. This suggests that a
substantial fraction of the emission may not arise directly from optically thin
thermal plasma, as commonly assumed, and may instead originate at its interface
with neutral gas via charge exchange. This latter origin naturally explains the
observed spatial correlation of the emission with various tracers of cool gas
in some of the galaxies. However, alternative scenarios, such as the resonance
scattering by the plasma and the relic photo-ionization by AGNs in the recent
past, cannot be ruled out, at least in some cases, and are being examined. Such
X-ray spectroscopic studies are important to the understanding of the
relationship of the emission to various high-energy feedback processes in
galaxies.Comment: 5 pages, published in Astronomical Notes, for "Charge exchange in the
Universe" workshop, Paris 201
Two-Loop Renormalization of Heavy--Light Currents at Order 1/m_Q in the Heavy-Quark Expansion
We present exact results, at next-to-leading order in renormalization-group
improved perturbation theory, for the Wilson coefficients appearing at order
1/m_Q in the heavy-quark expansion of heavy-light current operators. To this
end, we complete the calculation of the corresponding two-loop anomalous
dimension matrix. Our results are important for determinations of |V_{ub}|
using exclusive and inclusive semileptonic B decays. They are also relevant to
computations of the decay constant f_B based on a heavy-quark expansion.Comment: 16 pages, 2 figures; third author added and one reference updated,
results unchange
Resummation of Threshold Logarithms in Effective Field Theory For DIS, Drell-Yan and Higgs Production
We apply the effective field theoretic (EFT) approach to resum the large
perturbative logarithms arising when partonic hard scattering cross-sections
are taken to the threshold limit. We consider deep inelastic scattering,
Drell-Yan lepton pair production and the standard model Higgs production
through gluon-gluon fusion via heavy-top loop. We demonstrate the equivalence
of the EFT approach with the more conventional, factorization-based methods to
all logarithmic accuracies and to all orders in perturbation theory. Specific
EFT results are shown for the resummation up to next-to-next-to-next leading
logarithmic accuracy for the above mentioned processes. We emphasize the
relative simplicity by which we derive most of the results and more importantly
their clear physical origin. We find a new relation between the functions
in the quark and gluon form factors and the matching coefficients
in Drell-Yan and Higgs production, which may explain their universality
believed to hold to all orders in perturbation theory.Comment: 28 pages. Some typos corrected. Two references adde
Improved Determination of |V_{ub}| from Inclusive Semileptonic B-Meson Decays
We reduce the perturbative uncertainty in the determination of |V_{ub}| from
inclusive semileptonic B decays by calculating the rate of B -> X_u l nu events
with dilepton invariant mass q^2>(M_B-M_D)^2 at subleading order in the hybrid
expansion, and to next-to-leading order in renormalization-group improved
perturbation theory. We also resum logarithmic corrections to the leading
power-suppressed contributions. Studying the effect of different b-quark mass
definitions we find that the branching ratio after the cut is Br(B -> X_u l
nu)=(20.9+-4.0)|V_{ub}|^2, where the dominant error is due to the uncertainty
in the b-quark mass. This implies that |V_{ub}| can be determined with a
precision of about 10%.Comment: 15 pages, 2 figure
Heavy-to-light B meson form factors at large recoil energy -- spectator-scattering corrections
We complete the investigation of loop corrections to hard
spectator-scattering in exclusive B meson to light meson transitions by
computing the short-distance coefficient (jet-function) from the hard-collinear
scale. Adding together the two coefficients from matching QCD to SCET_I to
SCET_II, we investigate the size of loop effects on the ratios of
heavy-to-light meson form factors at large recoil. We find the corrections from
the hard and hard-collinear scales to be of approximately the same size, and
significant, but the perturbative expansions appear to be well-behaved. Our
calculation provides a non-trivial verification of the factorization arguments.
We observe considerable differences between the predictions based on
factorization in the heavy-quark limit and current QCD sum rule calculations of
the form factors. We also include the hard-collinear correction in the B -> pi
pi tree amplitudes, and find an enhancement of the colour-suppressed amplitude
relative to the colour-allowed amplitude.Comment: 55 pages, LaTeX, uses axodraw.st
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