## Challenging the Standard Model of physics

Scientists developed novel mathematical descriptions of high-energy particle interactions. Application to experimental data promises insight into the existence, or not, of new particle physics descriptions to replace a 40-year–old model.

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The Standard Model of particle physics is likely the best description available at this time of what makes up the Universe and how it interacts. Developed in the 1970s, it explains most experimental results and has precisely predicted many novel phenomena discovered since then. According to the Model, the Universe consists of 12 matter particles and 4 force particles that act on them.

Six of the matter particles are quarks and one of the four force particles is the gluon that 'glues' them together. In addition to quarks, gluons can also interact with themselves. At short distances, a mathematical operator called the quantum chromodynamic (QCD) Lagrangian has conventionally been used to describe gluon–gluon and gluon–quark interactions.

A self-interacting gluonic system was recently observed at the Hadron–Electron Ring Accelerator (HERA) in Germany, at which time the Balitskii–Fadin–Kuraev–Lipatov (BFKL) equation became famous for its prediction of the associated gluon distribution.

Investigators initiated the EU-funded project 'Low-x gluon distribution from the discretised BFKL equation' (LOWXGLUE) to study the properties of gluon density in gluon–gluon interactions as well as in gluon–quark interactions for insight into high-energy particle reactions.

The scientists discovered that the solution to the BFKL equation connects the low and extreme high-energy behaviour in a way that contradicts the so-called decoupling theorem. The latter, as its name implies, states that these behaviours are decoupled at scales smaller than those characteristic of new physics, or the theoretical developments needed to explain the important and acknowledged discrepancies in the Standard Model.

LOWXGLUE investigators pursued this line of research to make a significant contribution to the description of the data and to elucidate where the decoupling theorem could be violated, having to do with the so-called infrared boundary.

The outcomes of LOWXGLUE promise to be important tools for investigation of the presence or not of new physics beyond the scope of the Standard Model. Fitting experimental data such as that obtained at HERA to the mathematical models developed will thus advance the fields of particle physics and quantum dynamics. Providing the missing pieces of the Standard Model puzzle so long sought after is also a possibility.

Six of the matter particles are quarks and one of the four force particles is the gluon that 'glues' them together. In addition to quarks, gluons can also interact with themselves. At short distances, a mathematical operator called the quantum chromodynamic (QCD) Lagrangian has conventionally been used to describe gluon–gluon and gluon–quark interactions.

A self-interacting gluonic system was recently observed at the Hadron–Electron Ring Accelerator (HERA) in Germany, at which time the Balitskii–Fadin–Kuraev–Lipatov (BFKL) equation became famous for its prediction of the associated gluon distribution.

Investigators initiated the EU-funded project 'Low-x gluon distribution from the discretised BFKL equation' (LOWXGLUE) to study the properties of gluon density in gluon–gluon interactions as well as in gluon–quark interactions for insight into high-energy particle reactions.

The scientists discovered that the solution to the BFKL equation connects the low and extreme high-energy behaviour in a way that contradicts the so-called decoupling theorem. The latter, as its name implies, states that these behaviours are decoupled at scales smaller than those characteristic of new physics, or the theoretical developments needed to explain the important and acknowledged discrepancies in the Standard Model.

LOWXGLUE investigators pursued this line of research to make a significant contribution to the description of the data and to elucidate where the decoupling theorem could be violated, having to do with the so-called infrared boundary.

The outcomes of LOWXGLUE promise to be important tools for investigation of the presence or not of new physics beyond the scope of the Standard Model. Fitting experimental data such as that obtained at HERA to the mathematical models developed will thus advance the fields of particle physics and quantum dynamics. Providing the missing pieces of the Standard Model puzzle so long sought after is also a possibility.