scholarly journals Precision calculations of the double radiative bottom-meson decays in soft-collinear effective theory

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Yue-Long Shen ◽  
Yu-Ming Wang ◽  
Yan-Bing Wei
Keyword(s):  
Equations Of Motion ◽  
Form Factors ◽  
Bottom Meson ◽  
Photon Radiation ◽  
Effective Theory ◽  
Tree Level ◽  
Meson Decay ◽  
Neutral Meson ◽  
Power Correction ◽  
Soft Collinear Effective Theory

Abstract Employing the systematic framework of soft-collinear effective theory (SCET) we perform an improved calculation of the leading-power contributions to the double radiative Bd,s-meson decay amplitudes in the heavy quark expansion by including the perturbative resummation of enhanced logarithms of mb/ΛQCD at the next-to-leading-logarithmic accuracy. We then construct the QCD factorization formulae for the subleading power contributions arising from the energetic photon radiation off the constituent light-flavour quark of the bottom meson at tree level. Furthermore, we explore the factorization properties of the subleading power correction from the effective SCET current "Image missing" at $$ \mathcal{O}\left({\alpha}_s^0\right) $$ O α s 0 by virtue of the operator identities due to the classical equations of motion. The higher-twist contributions to the Bd,s→ γγ helicity form factors from the two-particle and three-particle bottom-meson distribution amplitudes are evaluated with the perturbative factorization technique, up to the twist-six accuracy. In addition, the subleading power weak-annihilation contributions from both the current-current and QCD penguin operators are taken into account at the one-loop accuracy. We proceed to apply the operator-production-expansion-controlled dispersion relation for estimating the power-suppressed soft contributions to the double radiative Bd,s-meson decay form factors, which cannot be factorized into the light-cone distribution amplitudes of the heavy-meson and the resolved photon as well as the hard-scattering kernel calculable in perturbation theory canonically. Phenomenological explorations of the radiative Bd,s→ γγ decay observables in the presence of the neutral-meson mixing, including the CP-averaged branching fractions, the polarization fractions and the time-dependent CP asymmetries, are carried out subsequently with an emphasis on the numerical impacts of the newly computed ingredients together with the theory uncertainties from the shape parameters of the HQET bottom-meson distribution amplitudes.

scholarly journals Consistent treatment of rapidity divergence in soft-collinear effective theory

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Junegone Chay ◽  
Chul Kim
Keyword(s):  
Heavy Quark ◽  
Soft Mode ◽  
Form Factors ◽  
Effective Theory ◽  
Large Rapidity ◽  
Soft Modes ◽  
Heavy Quark Mass ◽  
Soft Collinear Effective Theory ◽  
Matching Procedure ◽  
Consistent Treatment

Abstract In soft-collinear effective theory, we analyze the structure of rapidity divergence due to the collinear and soft modes residing in disparate phase spaces. The idea of an effective theory is applied to a system of collinear modes with large rapidity and soft modes with small rapidity. The large-rapidity (collinear) modes are integrated out to obtain the effective theory for the small-rapidity (soft) modes. The full SCET with the collinear and soft modes should be matched onto the soft theory at the rapidity boundary, and the matching procedure becomes exactly the zero-bin subtraction. The large-rapidity region is out of reach for the soft mode, which results in the rapidity divergence. The rapidity divergence in the collinear sector comes from the zero-bin subtraction, which ensures the cancellation of the rapidity divergences from the soft and collinear sectors. In order to treat the rapidity divergence, we construct the rapidity regulators consistently for all the modes. They are generalized by assigning independent rapidity scales for different collinear directions. The soft regulator incorporates the correct directional dependence when the innate collinear directions are not back-to-back, which is discussed in the N-jet operator. As an application, we consider the Sudakov form factor for the back-to-back collinear current and the soft-collinear current, where the soft rapidity regulator for a soft quark is developed. We extend the analysis to the boosted heavy quark sector and exploit the delicacy with the presence of the heavy quark mass. We present the resummed results of large logarithms in the form factors for various currents with the light and the heavy quarks, employing the renormalization group evolution on the renormalization and the rapidity scales.

Symmetry-breaking corrections to the form factors for heavy-to-heavy B-meson at large recoil

2019 ◽  
Vol 34 (08) ◽  
pp. 1950046
Author(s):  
Saba Shafaq ◽  
Ishtiaq Ahmed ◽  
M. Jamil Aslam
Keyword(s):  
Perturbation Theory ◽  
Symmetry Breaking ◽  
Heavy Quark ◽  
B Meson ◽  
Form Factors ◽  
Heavy Meson ◽  
Effective Theory ◽  
Vertex Corrections ◽  
Soft Collinear Effective Theory ◽  
Heavy Quark Limit

The present study investigates the decay of B to heavy meson using the soft collinear effective theory. By assigning different loop momenta, the factorization has been tested and it is found to be valid to all orders in the perturbation theory. It is noted that theory contains one hard collinear and two soft modes depending upon virtuality of different momenta. In the next step, symmetry-conserving relations (in heavy quark limits) to the form factors have been studied. These relations are then used to parametrize the form factors to get symmetry-breaking corrections. These symmetry-breaking corrections can be calculated using perturbative (vertex corrections) as well as nonperturbative (hard spectator interactions) QCD. It is found that in the heavy quark limit, these symmetry contributions do not contribute to the form factors that appear in physical observables for the case of [Formula: see text] decays which are contrary to the heavy-to-light meson decays.

THE HEART OF FACTORIZATION

2014 ◽  
Vol 25 ◽  
pp. 1460014
Author(s):  
MATTHEW D. SCHWARTZ
Keyword(s):  
Effective Field Theory ◽  
Recent Progress ◽  
Gauge Theories ◽  
Effective Field ◽  
Effective Theory ◽  
Tree Level ◽  
Soft Collinear Effective Theory ◽  
Factorization Formula ◽  
The Many ◽  
Traditional Approaches

Factorization is at the heart of nearly any calculation in pertubative QCD. It follows from the universal behavior of gauge theories in soft and collinear limits. This talk gives a summary of recent progress on producing a more transparent understanding of factorization and connecting traditional approaches to those of Soft-Collinear Effective Theory. The main result is the formulation and proof, at tree-level, of a factorization formula in QCD. The proof exploits the many advantages of spinor helicity methods, but does not use any effective field theory tricks. Once the factorization formula is proven, the transition to an effective theory description is effortless.

scholarly journals Precision calculations of B→V form factors from soft-collinear effective theory sum rules on the light-cone

2020 ◽  
Vol 101 (7) ◽  
Author(s):  
Jing Gao ◽  
Cai-Dian Lü ◽  
Yue-Long Shen ◽  
Yu-Ming Wang ◽  
Yan-Bing Wei
Keyword(s):  
Light Cone ◽  
Sum Rules ◽  
Form Factors ◽  
Effective Theory ◽  
Soft Collinear Effective Theory

scholarly journals Charming ALPs

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Adrian Carmona ◽  
Christiane Scherb ◽  
Pedro Schwaller
Keyword(s):  
Ultra Violet ◽  
New Physics ◽  
Low Energy ◽  
Effective Theory ◽  
Tree Level ◽  
Meson Decay ◽  
Fixed Target ◽  
The Standard Model ◽  
Model Independent ◽  
Key Features

Abstract Axion-like particles (ALPs) are ubiquitous in models of new physics explaining some of the most pressing puzzles of the Standard Model. However, until relatively recently, little attention has been paid to its interplay with flavour. In this work, we study in detail the phenomenology of ALPs that exclusively interact with up-type quarks at the tree-level, which arise in some well-motivated ultra-violet completions such as QCD-like dark sectors or Froggatt-Nielsen type models of flavour. Our study is performed in the low-energy effective theory to highlight the key features of these scenarios in a model independent way. We derive all the existing constraints on these models and demonstrate how upcoming experiments at fixed-target facilities and the LHC can probe regions of the parameter space which are currently not excluded by cosmological and astrophysical bounds. We also emphasize how a future measurement of the currently unavailable meson decay D → π + invisible could complement these upcoming searches.

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