Nobel prizes and CFTP

Physics at CFTP and the Nobel Prize of 2013.
The Nobel Prize in Physics 2013 was awarded jointly to François Englert and Peter W. Higgs "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles". In 2012, experiments at CERN, involving various scientists from IST's Department of Physics and LIP, found the scalar particle predicted by the theoretical model. In the next few years the fundamental question is whether there is only one scalar particle, as predicted in the simplest models, or whether there are several scalars. CFTP members have been studied multi-scalar models for the past decades, making it a world leader in this area. Thus, CFTP will be at the heart of the exciting decade ahead, where theory and experiment cooperate to understand the new results from CERN's LHC accelerator.

Particles and interactions:
All matter we observe is made up of three families of four particles each, subject to three types of interactions (plus gravity). There is a well determined theoretical framework describing this picture, involving special relativity and quantum mechanics. In it, both matter and interactions are described by fields and particles. Particles like the electron also have wave properties; interactions like electromagnetism are mediated by particles (the photon). The fundamental difference is that matter particles have spin (internal angular momentum) 1/2, while interaction particles have spin 1. This picture works so well that it is known as the "Standard Model". The need for scalar particles:
Over many decades, physicists found that assuming certain symmetries (certain regularities) allowed them to guess what the interactions should look like. And these results were consistent with experiment, except for a nagging problem: all particles should have zero mass, in blatant contradiction to what we all know to be true. In 1964, Englert and Brout, and, independently, Higgs found a solution to this problem. Particles could have mass and interactions could have the needed symmetries if there were a scalar field whose job was to give all particles their mass. The outcome of this mechanism is a new particle of spin 0 (a so-called scalar, also known as the Higgs boson). The discovery: After almost half a century, a scalar particle was finally found at CERN's LHC in 2012, thus vindicating the theoretical work of 1964. This is what prompted the Swedish Academy of Sciences to award the Nobel Prize to the theoretical work.

>Open questions:
In the Standard Model, the number of particles mediating each interaction is determined by the mathematical properties of the symmetries involved in that interaction. In contrast, the number of matter particles is not known a priori; it was determined experimentally at a previous CERN experiment that there must be three families of matter particles (up to a certain energy). Now that at least one scalar particle has been found, we must determine experimentally how many there are.

Work at CFTP:
The idea that there could be more than one Higgs boson has occupied the mind of CFTP's members for many decades. One early example is "Weinberg-Salam Model with Two Higgs Doublets and the Delta I=1/2 Rule" published by G. C. Branco in 1977. CFTP members have given leading contributions to all aspects of multi-Higgs models, including its relation to CP violation, the flavour problem, their detectability, its implications in a supersymmetric setting, etc... The 2012 review "Theory and phenomenology of two-Higgs-doublet models" co-authored by 4 CFTP members, has collected over 200 citation in less than two years. This positions CFTP at the forefront of the upcoming world effort to understand the scalar sector. More importantly, CFTP has a tradition of including early in their careers both Master and PhD students in this research. If you are looking for an exciting career in Theoretical Physics, come in a visit with us.



Physics at CFTP and the Nobel Prize 2008
It is with great excitement that, at CFTP, we received the news that the Nobel Prize for Physics for 2008 has been awarded to Yoichiro Nambu, Makoto Kobayashi and Toshihide Maskawa.
Yoichiro Nambu got the prize "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics". Today, this idea is incorporated in all the modern theories of Particle Physics, namely in the so-called Higgs mechanism, that is responsible for giving masses to the Standard Model Particles, and predicts one particle, the Higgs boson that soon will searched for in the LHC at CERN. Also Nambu's ideas had a strong impact on hadronic Physics - chiral symmetry, and its spontaneous breaking, is one essential feature of QCD, and is responsible for essential features of the structure of hadrons, and their interaction or couplings. This is currently one of the research interests at CFTP (Teresa Pea, Joo Seixas, Pedro Bicudo ) focusing on predictions for the meson and baryon spectra, and the nuclear interaction.

Makoto Kobayashi e Toshihide Maskawa were awarded the prize "the proposal of a successful mechanism for CP violation in the Standard Model", which is one of the hot topics of research at CFTP. Their work, and our research, are also intimately related to the Creation of Matter in the Universe, as well as to the understanding of fermion masses and mixing, the so-called Mass Problem, one of the most profound questions in Fundamental Physics.
The recent measurement of gamma by BaBar and Belle provided irrefutable evidence that the CKM (Cabibbo Kobayashi and Maskawa) matrix is indeed complex thus confirming the pioneering proposal of Kobayashi and Maskawa in 1973. This important conclusion was also stated in works involving collaborations of CFTP members, e.g. in New physics and evidence for a complex CKM, Nucl. Phys. B 725 (2005) 155 by F.J. Botella, G.C. Branco, M. Nebot and M.N. Rebelo or in Yukawa Textures, New Physics and Nondecoupling published in Phys. Rev. D 76 (2007) 033008, by G.C. Branco, M.N. Rebelo and J.I. Silva-Marcos.

Another important aspect of the origin of CP violation is the question of whether CP is a good symmetry of the Lagrangian, only broken by the vacuum. In the context of Supersymmetric Theories it is a great challenge to construct models where CP is spontaneously broken and yet the CKM matrix is complex. One of the rare examples of such a model was constructed by CFTP members: Spontaneous CP Violation in a SUSY Model with a complex CKM by G.C. Branco, D.Emmanuel-Costa, J.C.Romo, published in Phys. Lett. B 639 (2006) 661. It is also known that the strength of CP violation in the Standard Model is not sufficient to generate the Baryon Asymmetry of the Universe (BAU). Almost all extensions of the Standard Model including Supersymmetry have new sources of CP violation. The members of CFTP have been actively investigating models with possible additional sources for CP violation and also the generation of (BAU) through leptogenesis. These are some of the present hottest topics in Particle Physics. Click here for an extensive list of papers of CFTP written on CP violation.
One of the best general references on CP violation is the book written by three CFTP members, published in the Oxford International Series of Monographs on Physics, the same series where appeared the famous Dirac Book on Quantum Mechanics: CP Violation, Gustavo C. Branco, Luis Lavoura, Joao P. Silva, International Series of Monographs on Physics, No. 103 Oxford University Press. Oxford, UK: Clarendon (1999) 511 p. (The three CFTP members who authored this Book received The Gulbenkian Science Prize for this work).
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