scholarly journals Two-loop splitting in double parton distributions

2019 ◽  
Vol 7 (2) ◽  
Author(s):  
Markus Diehl ◽  
Jonathan Gaunt ◽  
Peter Plössl ◽  
Andreas Schafer
Keyword(s):  
Perturbation Theory ◽  
Momentum Space ◽  
Short Distance ◽  
Sum Rules ◽  
Leading Order ◽  
Parton Distributions ◽  
Double Parton Scattering ◽  
Colour Singlet ◽  
Parton Scattering

Double parton distributions (DPDs) receive a short-distance contribution from a single parton splitting to yield the two observed partons. We investigate this mechanism at next-to-leading order (NLO) in perturbation theory. Technically, we compute the two-loop matching of both the position and momentum space DPDs onto ordinary PDFs. This also yields the 1 \to 21→2 splitting functions appearing in the evolution of momentum-space DPDs at NLO. We give results for the unpolarised, colour-singlet DPDs in all partonic channels. These quantities are required for calculations of double parton scattering at full NLO. We discuss various kinematic limits of our results, and we verify that the 1 \to 21→2 splitting functions are consistent with the number and momentum sum rules for DPDs.

scholarly journals Transverse Momentum Dependence in Double Parton Scattering

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Jonathan R. Gaunt ◽  
Tomas Kasemets
Keyword(s):  
Transverse Momentum ◽  
Cross Section ◽  
Momentum Dependence ◽  
Transverse Momentum Dependence ◽  
Double Parton Scattering ◽  
Colour Singlet ◽  
The Status ◽  
The Cross ◽  
Parton Scattering ◽  
Near Future

In this review, we describe the status of transverse momentum dependence (TMD) in double parton scattering (DPS). The different regions of TMD DPS are discussed, and expressions are given for the DPS cross section contributions that make use of as much perturbative information as possible. The regions are then combined with each other as well as single parton scattering to obtain a complete expression for the cross section. Particular emphasis is put on the differences and similarities to transverse momentum dependence in single parton scattering. We further discuss the status of the factorisation proof for double colour singlet production in DPS, which is now on a similar footing to the proofs for TMD factorisation in single Drell-Yan, discuss parton correlations, and give an outlook on possible research on DPS in the near future.

scholarly journals PION TRANSITION FORM FACTOR AT THE TWO-LOOP LEVEL VIS-À-VIS EXPERIMENTAL DATA

2009 ◽  
Vol 24 (35n37) ◽  
pp. 2858-2867 ◽  
Author(s):  
S. V. MIKHAILOV ◽  
N. G. STEFANIS
Keyword(s):  
Experimental Data ◽  
Perturbation Theory ◽  
Form Factor ◽  
Light Cone ◽  
Transition Form Factor ◽  
Sum Rules ◽  
Leading Order ◽  
Transition Form ◽  
Qcd Sum Rules ◽  
Theoretical Results

We use light-cone QCD sum rules to calculate the pion-photon transition form factor, taking into account radiative corrections up to the next-to-next-to-leading order of perturbation theory. We compare the obtained predictions with all available experimental data from the CELLO, CLEO, and the BaBar Collaborations. We point out that the BaBar data are incompatible with the convolution scheme of QCD, on which our predictions are based, and can possibly be explained only with a violation of the factorization theorem. We pull together recent theoretical results and comment on their significance.

Soft QCD

2018 ◽  
Author(s):  
John Campbell ◽  
Joey Huston ◽  
Frank Krauss
Keyword(s):  
Experimental Data ◽  
Perturbation Theory ◽  
Phenomenological Models ◽  
Cross Sections ◽  
Strong Interaction ◽  
Scattering Amplitude ◽  
Double Parton Scattering ◽  
Fragmentation Functions ◽  
Effective Models ◽  
Parton Scattering

In Chapter 7, we discuss various aspects of the strong interaction containing a strong non-perturbative or low-scale component. We first briefly summarise the treatment of the total and inelastic cross sections through the analyticity of the scattering amplitude, which leads to the language of Regge poles. We introduce multiple parton interactions, with the underlying theoretical ideas for their description mainly driven by experimental data, before remarking on double parton scattering. Hadronisation, i.e. the transition from the parton of perturbation theory to the observable hadrons, is introduced by first using the idea of fragmentation functions and then discussing two popular phenomenological models describing this transition. We conclude this chapter by remarking on some ideas concerning the description of hadron decays through effective models.

scholarly journals Two-loop splitting in double parton distributions: the colour non-singlet case

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
M. Diehl ◽  
J. R. Gaunt ◽  
P. Plößl
Keyword(s):  
Perturbation Theory ◽  
Leading Order ◽  
Dominant Contribution ◽  
Parton Distributions

Abstract At small inter-parton distances, double parton distributions receive their dominant contribution from the splitting of a single parton. We compute this mechanism at next-to-leading order in perturbation theory for all colour configurations of the observed parton pair. Rapidity divergences are handled either by using spacelike Wilson lines or by applying the δ regulator. We investigate the behaviour of the two-loop contributions in different kinematic limits, and we illustrate their impact in different channels.

scholarly journals NEW PREDICTIONS OF GENERALIZED SPIN POLARIZABILITIES IN HEAVY BARYON CHIRAL PERTURBATION THEORY

2006 ◽  
Vol 21 (10) ◽  
pp. 2027-2148 ◽  
Author(s):  
CHUNG-WEN KAO
Keyword(s):  
Perturbation Theory ◽  
Chiral Perturbation Theory ◽  
Spin Structure ◽  
Sum Rules ◽  
Heavy Baryon ◽  
Virtual Compton Scattering ◽  
Leading Order ◽  
Chiral Perturbation ◽  
Theoretical Understanding ◽  
Existing Data

We review the recent progress of the theoretical understanding of the spin structure of the nucleon based on Heavy Baryon Chiral Perturbation Theory (HBChPT). At low Q2 the spin structure of the nucleon is encoded into the generalized spin polarizabilities (spin GP's) extracted from the virtual Compton scattering (VCS) amplitudes. The spin GP's of the nucleon have been calculated up to next-to-leading order in HBChPT. Furthermore, the forward spin generalized polarizabilities, which are related to the nucleon polarized structure functions g1 and g2 through the sum rules based on dispersion relations, also have been calculated in HBChPT up to next-to-leading order. As a summary, the physics content of the existing data is discussed and some perspectives for future theoretical and experimental activities in this field are also presented.

scholarly journals Z plus jets production via double parton scattering in pA collisions at the LHC

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
Boris Blok ◽  
Federico Alberto Ceccopieri
Keyword(s):  
Cross Section ◽  
Leading Order ◽  
Order Accuracy ◽  
Centrality Dependence ◽  
Double Parton Scattering ◽  
The Cross ◽  
Parton Scattering

Abstract We present results on Zjj production via double parton scattering in pA collisions at the LHC. We perform the analysis at leading and next-leading order accuracy with different sets of cuts on jet transverse momenta and accounting for the single parton scattering background. By exploiting the experimental capability to measure the centrality dependence of the cross section, we discuss the feasibility of DPS observation in already collected data at the LHC and in future runs.

A Perturbation Theory for the Population of Atomic Energy Levels in Non-Lte Plasmas

1988 ◽  
Vol 102 ◽  
pp. 343-347
Author(s):  
M. Klapisch
Keyword(s):  
Perturbation Theory ◽  
Small Parameter ◽  
Classification Scheme ◽  
Sum Rules ◽  
Energy Levels ◽  
Natural Classification ◽  
Quantum Numbers ◽  
Formal Expansion ◽  
Atomic Energy Levels ◽  
As Effects

AbstractA formal expansion of the CRM in powers of a small parameter is presented. The terms of the expansion are products of matrices. Inverses are interpreted as effects of cascades.It will be shown that this allows for the separation of the different contributions to the populations, thus providing a natural classification scheme for processes involving atoms in plasmas. Sum rules can be formulated, allowing the population of the levels, in some simple cases, to be related in a transparent way to the quantum numbers.

scholarly journals Determination of α(Mz) from an hyperasymptotic approximation to the energy of a static quark-antiquark pair

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Cesar Ayala ◽  
Xabier Lobregat ◽  
Antonio Pineda
Keyword(s):  
Perturbation Theory ◽  
Energy Range ◽  
Short Distance ◽  
Weak Coupling ◽  
Strong Consistency ◽  
Lattice Data ◽  
Static Potential ◽  
Static Energy ◽  
Static Quark

Abstract We give the hyperasymptotic expansion of the energy of a static quark-antiquark pair with a precision that includes the effects of the subleading renormalon. The terminants associated to the first and second renormalon are incorporated in the analysis when necessary. In particular, we determine the normalization of the leading renormalon of the force and, consequently, of the subleading renormalon of the static potential. We obtain $$ {Z}_3^F $$ Z 3 F (nf = 3) = $$ 2{Z}_3^V $$ 2 Z 3 V (nf = 3) = 0.37(17). The precision we reach in strict perturbation theory is next-to-next-to-next-to-leading logarithmic resummed order both for the static potential and for the force. We find that the resummation of large logarithms and the inclusion of the leading terminants associated to the renormalons are compulsory to get accurate determinations of $$ {\Lambda}_{\overline{\mathrm{MS}}} $$ Λ MS ¯ when fitting to short-distance lattice data of the static energy. We obtain $$ {\Lambda}_{\overline{\mathrm{MS}}}^{\left({n}_f=3\right)} $$ Λ MS ¯ n f = 3 = 338(12) MeV and α(Mz) = 0.1181(9). We have also MS found strong consistency checks that the ultrasoft correction to the static energy can be computed at weak coupling in the energy range we have studied.

scholarly journals Strong CP violation in spin-1/2 singly charmed baryons

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Y. Ünal ◽  
Ulf-G. Meißner
Keyword(s):  
Perturbation Theory ◽  
Dipole Moment ◽  
Form Factor ◽  
Cp Violation ◽  
Mass Shell ◽  
Chiral Expansion ◽  
Renormalization Scheme ◽  
Leading Order ◽  
Chiral Perturbation ◽  
Charmed Baryons

Abstract We report on the calculation of the CP-violating form factor F3 and the corresponding electric dipole moment for charmed baryons in the spin-1/2 sector generated by the QCD θ-term. We work in the framework of covariant baryon chiral perturbation theory within the extended-on-mass-shell renormalization scheme up to next-to-leading order in the chiral expansion.

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