CECs Researchers from the Theoretical Physics Laboratory Develop Research Lines Highly Specialized in the Field of the Particle Physics.

Particle physics studies the most elementary components of the matter, and to better understand them, resorts to the large-scale experiments. Currently this experimental data source comes from colliders, such as Large Hadron Collider (LHC) which has for its main task to "make hadrons collide" and to examine what happens after that phenomenon.

The analytical complexity of the data from these collisions is huge. It´s like to smash head-on two trucks charged of crystal ware and analyze pieces of glass to try to understand how a glass of champagne is made – at night, when it rains and without flashlight. This is precisely the research field in which CECs theoretical physicists work.

Hadrons are particles made of quarks held together by the strong nuclear force which is one of the fundamental forces in the universe. At the moment, when the collision occurs, hadrons fall apart releasing their components which are quarks and gluons. These emissions are called parton shower producing the phenomena called hadronization which means that the free energy create others partons (quarks and gluons) to form new hadrons. They are output in specific directions called jets represented by coloured lines which can be appreciated on the photos which were given to us by the colliders such as the LHC.

Particle collisions provide an excellent opportunity of the empirical testing for Supersymmetry (SUSY). In simple terms, supersymmetry implies that there is a partner of big mass for each type of particles. This is a replica in the form of boson if the "normal" particle is a fermion, and vice versa. It means that a boson is always accompanied by a fermion as its superpartner. And a fermion is always accompanied by a superpartner boson.

Since it hasn´t been possible to observe them in nature, in order to see supersymmetric particles, very high energy collisions have been developed. This energy can create high mass particles so if these superparticles appear it means that the supersymmetry exists.

Supersymmetry presents a curious paradox: on the one hand, there is a wide consensus among theoretical physicists that should exist, but on the other hand, in spite more than four decades of extensive search in accelerators, no evidence of SUSY has been found, at least in its simplest form, making even some of the original proponents recant their support of the idea.

Jorge Zanelli and Pablo Pais, the physics from CECs Theoretical Physics Laboratory, in a recent paper published under the title "Local supersymmetry without SUSY partners", propose an analysis that retains the essence of the paradigm of supersymmetry, but differs in three important aspects of its standard construction. The distinctive features of this theory that mark the difference with supersymmetry are: the number of bosonic and fermionic states is not necessarily the same; there are no superpartners with the equal mass; although this supersymmetry originates in a local gauge theory including gravity, there is no gravitino (the supersymmetric partner of the graviton); that fermions acquire mass from their coupling to the background or from higher order self-couplings, while bosons remain massless.

On the other side, it hasn´t been possible to calculate the particles post collision processes occurring with different issues arising in specific directions called jets; so here is the essence of quantum chromodynamics theory (or QCD). Its functions which can´t be calculated have been performed experimentally. One of them is called fragmentation functions which allows understanding how the jets, which represent probabilities that a parton emitted out with some energy or momentum, occur.

Its study example is the paper entitled "Gribov gap equation at finite temperature" by Fabrizio Cánfora, Pablo Pais and Patricio Salgado-Rebolledo, all of them are from Theoretical Physics Laboratory of CECs. In this paper one of the most characteristic features of QCD is analyzed: asymptotic freedom, anomalous behaviour called by the mediators of the interaction (gluons) capacity to interact with each other which weakens progressively in short distances and allows at the same time to perform the standard perturbative analysis in the ultraviolet regime.

The phenomenon of confinement with the property of asymptotic freedom are two properties of the quantum chromodynamics theory formulated to give an account of the strong interactions acting on the particles which have a colour charge, and constitute one of the main problems opened in theoretical physics, so that their study represents a valid and current challenge.

The study of supersymmetry and quantum chromodynamics represents the main research challenge, in which researchers from Theoretical Physics Laboratory of CECs contribute significantly.

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References:

• 1. Local supersymmetry without SUSY partners. PHYSICS-LETTERS-B735-(2014), PAGES-314-321 DOI: 10.1016/j.physletb.2014.06.031
• 2. Gribov gap equation at finite temperatura. The European Physical Journal C May 2014, 74:2855, DOI: 10.1140/epjc/s10052-014-2855-x