APFEL++ Early Harvest

This release contains many developments and improvements, and a few bug fixes. Some of the most important developments are:

• Extension of the python interface to include also the DIS structure functions and other functionalities.
• Implementation of the O(α_s³) TMD matching functions for both PDFs and FFs. A benchmark against RadISH for the TMD PDFs has also been performed (thanks to Luca Rottoli and Pier Monni).
• Implementation of resummation-scale variations for the evolution of α_s, PDFs, and TMDs. In the case of α_s and TMDs an analytic solution in terms of g-functions has also been implemented.
• Implementation and benchmark against HOPPET of the inclusive DIS structure functions to O(α_s³) (thanks to Alexander Karlberg).
• Implementation of the approximate N³LO evolution for PDFs as in the MSHT PDF set (https://github.com/MSHTPDF/N3LO_additions).
• Implementation of an interface to LHAPDF: APFEL++ fills in a LHAPDF grid without dumping it to file allowing for the use of all functionalities of LHAPDF on a set evolved with APFEL++.

In memory of a beacon who went off too early.

APFEL++ Ariane

The main feature of this version of APFEL++ is the implementation of the evolution of generalised parton distributions (GPDs). So far only leading-order unpolarised evolution is implemented but the structure allows for an easy extension to higher orders and polarised GPDs planned for the next future.

Additional functionalities newly implemented include:

• the possibility to handle evolution with explicitly scale dependent splitting functions,
• the implementation of polarised DIS structure functions up to next-to-leading order,
• new integration strategies. Specifically a 2D integrator and the Gauss-Kronrod algorithm (now set as a default).

This release also includes minor bug fixing and performance enhancements.

APFEL++ King of the Pippins

The main feature of this version of APFEL++ is a more solid treatment of the intrinsic heavy-flavour distributions. Specifically, any intrinsic contribution is left untouched below the respective threshold and matched consistently in correspondence of the threshold itself. Both forward and backward evolutions are supported. This update is particularly relevant for fits of fragmentation functions in which heavy-flavour distributions are sizeable and thus need to be fitted to data.

Other relevant changes are:

• reorganisation of the configuration procedure through CMake,
• more accurate Doxygen documentation,
• extension of the technical documentation including matching conditions,
• extension of the DoubleObject class to handle objects of different kinds.

(The name of this release, "King of the Pippins", is a french apple sort. This is indeed the first release of APFEL++ since my move to CEA Paris-Saclay. Somewhere in the back of my mind, though, this name also reminds me of a tiny little, ridiculous character with a delirium of omnipotence... pretty much like somebody that I came across some time ago.)

APFEL++ Lodi

This version of APFEL++ implements several bug fixes, improvements, and functionality extensions. While the TMD sector keeps growing, a new GPD branch has started. Here is a list of the main changes related to physics implemented in this release:

• a first implementation of the leading-order GPD evolution,
• implementation of the (exact) NNNLO and (exact) NNLO corrections to the quark TMD matching functions,
• correction factor due to the exact integration over the fiducial region of the two-body phase space (moved from NangaParbat),
• implementation of single-inclusive-annihilation e+e- cross-sections up to NNLO,
• thorough check and debugging of TMD scale variations.

On a more technical side, other relevant changes are:

• generalisation of the Hankel transform methods to objects other than double,
• numerical integration and differentiation on the interpolation grids based on the analytic integral and derivative of the Lagrange interpolating functions,
• implementation (and debugging) of the harmonic polylogarithms of weight 5,
• restructuring of the kernel.

(The name of this release, "Lodi", (on top of being an apple sort) recalls the Italian province where the spread of Coronavirus in Italy has started.)

APFEL++ Liberty

Stable version of the code used for the fits of TMD PDFs from Drell-Yan data to be released soon. The main features of this release are the following:

• N3LL corrections to the Sudakov form factor,
• adopting new logarithmic ordering (primed and non-primed),
• automatic formatting of the code using astyle,
• tidying up the code that computes pT-integrated SIDIS cross sections to NLO accuracy,
• including function that computes electro-weak charges for Drell-Yan in the narrow-width approximation,
• work towards the computation of the Higgs pT spectrum in gluon fusion,
• including double-exponential quadrature for the computation of the Hankel transform.

APFEL++ Breeze

First stable release of APFEL++.

Main news:

• Semi inclusive DIS
• full set of ingredients for TMD phenomenology
• longitudinally and transversely polarised DGLAP evolution
• interface to LHAPDF for the interpolation