The project in High Energy Physics Phenomenology and Computational Physics aims to develop innovative methods and algorithms to establish an efficient framework for higher order corrections for multi-particle processes, including a) amplitude reduction at the integrand level beyond one-loop, b) the evaluation of multi-loop Master Integrals and c) the application of the above-mentioned techniques to scattering processes at the LHC and beyond.
The project in Particle Physics and Cosmology aims to study problems at the interface of particle physics and cosmology, such as inflation, baryogenesis, dark energy and matter, the microwave background anisotropies. The discovery of the scalar Higgs Particle creates expectations for a supersymmetric-BSM particle spectrum structure which may include cosmic vortices or Q-balls with novel astrophysical effects. Modelling aspects of the Standard Cosmological Model with Scalar, and Gauge Fields (gluon condensation) is a recurring theme of research in Cosmology in our Group.
The project in Gauge and String theories aims to study the interaction of matter, which carries not only internal charges, but also arbitrary high spins. This extension leads to a theory in which fundamental forces are mediated by integer-spin gauge quanta and the photon, W-bosons and gluons become members of a bigger family of tensor gauge bosons. A new topological mechanism of mass generation is possible in this extension. These predictions can be tested at LHC.
The project on Non-linear Chaotic Dynamics and Complex Systems involves both research and teaching. It pertains to the interplay between chaotic dynamics and fundamental interactions. Noteworthy results have been the observation of chaos in Yang Mills theories such as QCD as well as more recently in matrix and membrane dynamics of M-theory. Moreover, the principles of chaos have been successfully shown to give rise to novel random number generator algorithms (MIX-MAX) which can be used in Monte-Carlo Simulations in high energy elementary particle experiments, like the LHC ones.
Finally puzzling aspects of the Physics of Quantum Black Holes have resulted in a consensus among physicists about the properties that the microscopic degrees of freedom of Black Hole Horizons must satisfy consistently with the founding Principles of Quantum Mechanics. Following the flow of development our group has succeeded in building new types of many body models of matter systems satisfying novel Principles of Holographic chaos, nonlocality, and fast scrambling behaviour of their constituent parts.
Major outcomes and achievements
- Two-loop Feynman Integrals and scattering amplitudes.
On the frontier of multi-loop calculations, the group achieved a major milestone, by completing the analytic representation of all massless planar five-point amplitudes with one off-shell leg [JHEP 01 (2021), 199]. This is a unique result world-wide. The methodology used is based upon the Simplified Differential Equations Approach (SDE) [JHEP 07 (2014), 088]. Recently, the calculation of the hexabox families has also been completed [arXiv:2201.07509 [hep-ph]]. We have also studied one-loop pentagon integrals to arbitrary order in the dimensional regulator [JHEP 06 (2021), 037]. The SDE method has been also successfully applied to the canonical basis for the three-loop ladder-box with one external mass off-shell, obtaining subsequently a canonical basis for the massless three-loop ladder-box as well as its solution [JHEP 02 (2021), 080]. On the frontier of two-loop scattering amplitudes, we have studied the reduction of two-loop amplitudes at the integrand level, as part of the newly developed software package HELAC-2LOOP [J.Phys.Conf.Ser. 2105 (2021) 5, 012010]. All the above-mentioned work is essential to obtain high-precision predictions for scattering processes at the LHC, especially for the forthcoming high-luminosity Run as well as for future colliders [CERN Yellow Reports: Monographs, 3/2019].
- Modeling of Quantum Black Hole (BH) Near Horizon Geometries.
Arnold’s Cat Map Discretization Proposal
One approach that our work has followed is based on our proposal for a finite discretization of the Black Hole Horizon Geometry and Dynamics [JHEP 02 (2014) 109]. Our hypothesis resolves the finite Entropy puzzle of Bekenstein-Hawking attributing to its microscopic dof the desired properties of chaoticity, nonlocality and fast scrambling. We have realized our proposal in the case of extremal Black Holes for which the radial and temporal near horizon geometry is known to be AdS2(R) = SL(2, R)/ SO(1,1) . Our discretization is implemented by replacing the set of real numbers with the set of integers modulo N with AdS2 going over to AdS2[N]. We have modeled the dynamics of the BH dof by generalized Arnol’d Cat Maps SL(2,N) which are isometries of the geometry at both the classical and quantum levels [Eur.Phys.J. C78 (2018) 412]. In a subsequent paper [Sigma 17 (2021) 004] we have demonstrated the existence of a smooth continuum limit to this discrete and random horizon geometry AdS2[N] recovering the standard non-compact AdS2 (R) continuum space-time.
Bernstein-Maldacena-Nastase (BMN) Matrix Model as a Dynamical System
A second direction is our effort to improve on the old BH-Membrane Paradigm of BH Horizons (Thorne-Price) in an attempt to incorporate in it the desirable properties of non-locality chaoticity and fast scrambling of Infalling Information. We do it in the context of the Bernstein-Maldacena-Nastaze(BMN) Bosonic Matrix model in 11d maximally supersymmetric plane-wave backgrounds. In the classical (large-N membrane) limit of the model [Phys.Lett.B 773 (2017) 265-270] we demonstrate the existence of ellipsoidal configurations-solutions with SO(6)(spinning) x SO(3)( static) symmetry on which we investigate their (in)stability profile both under radial and spherical perturbations to both 1st order [Phys.Rev.D 97 (2018) 12, 126019] and 2nd order [Phys.Rev.D 104 (2021) 10, 106002]. We establish the presence of a cascade of instabilities which originate to 1st order from only the dipole (j=0) and quadrupole (j=1) sectors which propagate and destabilize all higher j multipoles to 2nd order.
- MIXMAX
Modern powerful computers open a new era for the application of the Monte Carlo Method (MC) for modelling and simulation of high complexity systems. The MC method is an important computational technique and has a significant application in physical sciences, engineering, risk analysis, finance and business, climate change, medical applications, spread of viral infections, dosimetry, computational biology and genetics, molecular chemistry, pharmacology, artificial intelligence, quantum and statistical physics, material science, among many other multidisciplinary applications. At the heart of the MC method are the Pseudo Random Number Generators (PRNG). The MIXMAX Consortium led by G.Savvidy systematically developed a new generation of state-of-the-art PRNG’s based on Kolmogorov-Anosov C-K systems. The MIXMAX generators demonstrated excellent statistical properties, high performance and superior high-quality output and became a multidisciplinary usable product. This innovative class of PRNG’s was proposed earlier by the members of the Consortium and relies on the fundamental results of Ergodic theory. The NCSR “Demokritos” group of the Consortium developed an efficient C/C++ code of the C-K system generators with tuneable parameters embedded into a user-friendly environment and with an online manual. In collaboration with the CERN EP-SFT group the MIXMAX generators were integrated into the concurrent and distributed MC toolkit Geant4, the foundation library CLHEP and data analysis framework ROOT. These software tools have wide Applications in High Energy Physics at CERN, in CMS experiment, at SLAC, FNAL and KEK National Laboratories and are part of the CERN’s active Technology Transfer policy. Their Space Applications for ESA missions include space environment, instrument shielding, dose estimates and radiation risks. The Medical Applications include radiotherapy by photon, proton, and ion beams. The generator is available in the PYTHIA event generator. The Consortium disseminated the product worldwide, it can be downloaded from the GSL-GNU Scientific Library, Wikipedia and is freely available to the public.
- Entanglement Entropy and Holography (HAPPEN)
The goal of program HAPPEN was the study of the relation between quantum entanglement and gravity in the context of the holographic duality. In the bulk theory the entanglement entropy is given in terms of the area of minimal surfaces. The study of minimal surfaces via the Pohlmeyer reduction and the dressing method provided new solutions and tools for the study of holographic entanglement entropy [JHEP 11 (2020) 128]. The developed methods found direct generalizations in the field of classical string solutions in symmetric spaces [EPJ C 78 (2018) 11, 977, EPJ C 78 (2018) 8, 668, EPJ C 79 (2019) 10, 869, JHEP 09 (2019) 106], and shed light to more theoretical issues of non-linear sigma models [JHEP 03 (2021) 024]. In a different approach the RG flow of the holographic entanglement entropy was studied through the description of minimal surfaces in asymptotically AdS spaces as a geometric flow [PRD 101 (2020) 8, 086015]. Finally, the entanglement entropy in free field theory at finite temperature was systematically studied and calculated analytically in a perturbative approach to show an area law for the mutual information [arXiv:1907.04817, JHEP 02 (2020) 091].
Prizes and Distinctions
2019 Academy of Athens: “Lykourgeion” Prize in theoretical physics to Dr G.Linardopoulos (2019, Th-Hep Research Associate) for his work “Scalar one-point functions and matrix product states of AdS/dCFT”. Published in: Phys.Lett.B 781 (2018) 238-243.