I am a professor at the University of Valencia and a researcher at the Institute for Corpuscular Physics (IFIC). My work tackles fundamental open questions in particle physics: the nature of dark matter, the origin of neutrino masses, and the Universe’s baryon asymmetry.

I did my undergraduate studies in Physics at the University of Athens, where I graduated in 1985. I then commenced my doctorate studies at the University of California, Los Angeles (UCLA), from where I obtained my Ph.D. degree in 1990. 

My thesis advisor was John M. Cornwall, and my thesis research centered on the construction of gauge-independent off-shell Green’s functions with the method known as “pinch technique”. My doctorate work offered new insights on the structure of the three-gluon vertex, a central ingredient of Quantum Chromodynamics. In addition, the application of the pinch technique led to the first gauge-independent definition of the neutrino charge radius, a quantity currently measured atEnuES and CEnuES experiments. 

Subsequently, I had a two-year post-doctoral appointment (1990-1992) at Brookhaven National Laboratory (BNL), a three-year post-doctoral appointment (1992-1995) at New York University (NYU), a one-year appointment at the CPT of Marseille, and a one-year post-doc at University of Manchester (1997), after which I obtained a Marie Curie Fellowship at the Theory Division of CERN for two years (1997-1999). Since 1999 I have been employed by the University of Valencia, Department of Theoretical Physics, first as visiting professor, then as Ramon y Cajal fellow, and finally as “Profesor Titular”, which is my current position.

A considerable part of my early scientific activity was dedicated in the development of the aforementioned “pinch technique “. In its original form, this technique is a systematic rearrangement of the standard perturbative expansion (Feynman diagrams) contributing to a physical amplitude in such a way as to define gauge-independent sub-amplitudes, which may be interpreted as effective Green’s functions (e.g., propagators and vertices). The activity related to this technique gave rise to a plethora of phenomenological and formal applications, such as the definitions of the QCD equivalent of the strong effective charge, in complete analogy to the text-book construction of the “Gell-Mann -- Low “effective charge known from Quantum Electrodynamics. In addition, a particularly relevant success for phenomenology has been the self-consistent description of resonant amplitudes, in collaboration with Professor A. Pilfatsis (University of Manchester).

During the years 2000-2005 I focused my efforts on the formal foundations of the pinch technique in collaboration with Daniele Binosi (currently a permanent researcher at ECT*, Trento, Italy), who, at the time, was carrying out his doctorate work at the University of Valencia. Our collaboration gave rise to an elegant formulation of the pinch technique in the language of the so-called “background field method” and the “Batalin-Vilkovisky” quantization scheme. The resulting doctorate thesis won the “outstanding thesis prize” for the year 2002, awarded by the University of Valencia, signifying it as the best thesis of the entire university. 

At the level of publications, it is important to emphasize two special items, namely (i) the review article “Pinch Technique: Theory and Applications”, Physics Reports 479 (2009), co-authored with D. Binosi, which to date has collected 450 citations (source HEP Inspires) and (ii) a Cambridge University Monograph (2011), titled “The Pinch Technique and its Applications to Non-Abelian Gauge Theories”, co-authored with J. M. Cornwall and D. Binosi in 2010.

Since 2007 my research activity has centered on some of the most important non-perturbative aspects of Quantum Chromodynamics (QCD), such as the generation of a mass gap in the gauge sector, the phenomenon of dynamical chiral symmetry breaking, the study of the structure of the fundamental vertices of the theory, and the formation of the observed bound states (hadrons) out of the fundamental degrees of freedom known as gluons and quarks.

 In particular, I am one of the major proponents of the key notion that the famous “Schwinger mechanism” operates in the gauge sector of QCD, leading to the subsequent emergence of an effective gluon mass scale. This result has far-reaching consequences for the physics of strong interactions, because it cures the infrared divergences known from perturbation theory, and allows for completely finite predictions for the key QCD observables measured in a variety of experimental installations.

In addition, the emergence of the aforementioned mass allows the meaningful extension of the QCD effective charge, originally defined perturbatively through the pinch technique, to the low-energy regime of the theory. This constitutes a theoretical milestone, because, historically, such a connection has been thwarted by the presence of the destabilizing “Landau pole”.  In this sense,  one accomplishes the smooth transition between the two most celebrated phenomena of QCD, namely asymptotic freedom in the ultraviolet and confinement in the infrared. This work has attracted considerable attention, giving rise to several publications, four invited review articles, and numerous presentations at international workshops.

In addition, and with equal vigor, I have been involved in the study of the non-perturbative structure of the fundamental Green’s functions (also known as “correlation function”) of QCD.  This ongoing activity is based on the fruitful synergy between continuous approaches (Schwinger-Dyson equations) and gauge-fixed lattice simulations.  These functions represent the building blocks of the physical observables studied in hadronic physics, and are of the utmost importance for the meaningful comparison between theory and experimental reality. Especially important in this context is the three-gluon vertex, which is instrumental for the manifestation of asymptotic freedom, one pf the most celebrated properties of Yang-Mills theories, in general, and of QCD in particular. This particular vertex has received particular attention in the last 5 years, and has been scrutinized in detail, in collaboration with the lattice groups of the University of Huelva and the University of Pablo de Olavide (Sevilla).  This research gave rise to terms such as the “zero crossing” and the “planar degeneracy”, which have become household names among the practitioners of this field.

My research activity includes also Physics beyond the Standard Model. In particular, I have various works on the physics related with extra dimensions, mainly in collaboration with Professor Arcadi Santamaria. In addition, I have a long-standing collaboration with Professor Nick Mavromatos (King’s College, London and University of Athens); our more distinguished work is a collection of articles on CPT violation and entanglement, and certain theoretical aspects pertaining to the Moedal collaboration.  

I have an extensive network of collaborators, particularly in Germany, Brazil, Italy, and China.  Specifically, I have been coordinating for over a decade the activities of the QCD group of the University of Campinas, (Sao Paolo). This intense collaboration gave rise to a large number of publications and doctorate titles.  In addition, I hold a one-year EMMI visiting position, (https://www.gsi.de/emmi_visiting_professors) of  GSI, to be carried out at the Institute for Theoretical Physics, University of Heidelberg, for the purpose of strengthening my ongoing collaboration with the research group of Prof. Jan Pawlowski. Moreover, I am a member of the international collaboration led by Professor Craig D. Roberts of the Institute of Nonperturbative Physics (INP) in Nanjing, China, with whom I have co-authored several highly cited articles (94 citations/article). In addition, I have strong ties and fruitful collaboration with the Sevilla and Huelva groups, and in particular with Professors J. Rodríguez-Quintero and F. De Soto.

I am a member of the International MoEDAL Collaboration (Monopole and Exotics Detector at the LHC), https://home.cern/tags/moedal , and I have been voting member of the “International Light Cone Advisory Committee (ILCAC, http://www.ilcacinc.org/ ), for the period 2010-2020. Furthermore I was awarded the American Physical Society (APS) Outstanding Referee Award for the year 2017.  

I have a total of 188 publications, 142 of them in high impact peered review journals, and 40 Conference Proceedings. All these publications have accumulated a total of 9447 citations. My “h factor” is h=59.   https://inspirehep.net/literature?sort=mostrecent&size=25&page=1&q=a%20papavassiliou%2Cj&ui-citation-summary=true

[Biography, english version]