972 research outputs found
Threshold resummation of quark-gluon partonic channels at next-to-leading power
We discuss recent progress concerning the resummation of large logarithms at
next-to-leading power (NLP) in scattering processes near threshold. We begin by
briefly reviewing the diagrammatic and SCET approach, which are used to derive
factorization theorems for physical observables in this kinematic limit. Then,
we focus on the quark-gluon channel in deep inelastic scattering and Drell-Yan.
We show that the use of consistency conditions for the cancellation of leading
poles in the hadronic cross section can be used to achieve the resummation of
large leading logarithms (LLs) at NLP, both within diagrammatic and SCET
methods. In this context it is also possible to investigate the problem of
endpoint divergences appearing at NLP in SCET, and relate its solution to the
concept of re-factorization.Comment: Contribution to the Proceedings of "Loops and Legs in Quantum Field
Theory - LL2022", 25-30 April, 2022, Ettal, German
Factorization and resummation at next-to-leading-power
We discuss recent progress concerning the resummation of large logarithms at
next-to-leading power (NLP) in scattering processes such as Drell-Yan and deep
inelastic scattering near threshold, and thrust in the two-jet limit. We start
by reviewing the approach based on soft-collinear effective field theory and
show that the standard factorization into short distance coefficients,
collinear and soft functions at NLP leads in general to the appearance of
endpoint divergences, which prevent the naive application of resummation
techniques based on the renormalization group. Taking thrust as a case study,
we then show that these singularities are indeed an artifact of the effective
theory, and discuss how they can be removed to recover a finite factorization
theorem and achieve resummation at NLP, at LL accuracy. Last, we discuss recent
work concerning the calculation of all collinear and soft functions necessary
to reproduce Drell-Yan near threshold up to NNLO in perturbation theory. This
calculation provides useful data to extend resummation at NLP beyond LL
accuracy.Comment: Contribution to the proceedings of RADCOR2023, Crieff, Scotland, UK.
V2: references adde
NNLL Momentum-Space Resummation for Stop-Pair Production at the LHC
If supersymmetry near the TeV scale is realized in Nature, the pair
production of scalar top squarks is expected to be observable at the Large
Hadron Collider. Recently, effective field-theory methods were employed to
obtain approximate predictions for the cross section for this process, which
include soft-gluon emission effects up to next-to-next-to-leading order (NNLO)
in perturbation theory. In this work we employ the same techniques to resum
soft-gluon emission effects to all orders in perturbation theory and with
next-to-next-to-logarithmic (NNLL) accuracy. We analyze the effects of NNLL
resummation on the stop-pair production cross section by obtaining NLO+NNLL
predictions in pair invariant mass and one-particle inclusive kinematics. We
compare the results of these calculations to the approximate NNLO predictions
for the cross sections.Comment: 25 pages, 6 figure
Approximate NNLO Predictions for the Stop-Pair Production Cross Section at the LHC
If the minimal supersymmetric standard model at scales of around 1 TeV is
realized in nature, the total top-squark pair production cross section should
be measurable at the CERN Large Hadron Collider. In this work we present
precise predictions for this observable, which are based upon approximate NNLO
formulas obtained using soft-collinear effective theory methods.Comment: 36 pages, 7 figures and 11 tables. Version published in JHEP 1307
(2013) 04
Probing new physics in electroweak penguins through B_d and B_s decays
An enhanced electroweak penguin amplitude due to the presence of unknown new
physics can explain the discrepancies found between theory and experiment in
the B -> pi K decays, in particular in A_CP(B^- -> pi^0 K^-) - A_CP(\bar{B}^0
-> pi^+ K^-), but the current precision of the theoretical and experimental
results does not allow to draw a firm conclusion. We argue that the \bar{B}_s
-> phi rho^0 and \bar{B}_s -> phi pi^0 decays offer an additional tool to
investigate this possibility. These purely isospin-violating decays are
dominated by electroweak penguins and we show that in presence of a new physics
contribution their branching ratio can be enhanced by about an order of
magnitude, without violating any constraints from other hadronic B decays. This
makes them very interesting modes for LHCb and future B factories. In
arXiv:1011.6319 we have performed both a model-independent analysis and a study
within realistic New Physics models such as a modified-Z^0-penguin scenario, a
model with an additional Z' boson and the MSSM. In this article we summarise
the most important results of our study.Comment: 8 pages, 5 figures, LaTeX. Talk given at Discrete2010, Rome, 6-11
December 2010; References adde
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