Distinguished EPJ Referees

EPJ C Highlight: Exploring the duality of gravity and gauge theory

Gauge/gravity duality aims to unify leading physical theories. https://commons.wikimedia.org/ wiki/File:Calabi_yau.jpg

This EPJ C Topical Collection presents a series of reviews showcasing the latest developments and applications of gauge/gravity duality, and aims at dissemination to a wider physics community in a way that enables building upon these concepts.

The gauge/gravity duality states that gravity and quantum spacetime emerges, i.e. can be reconstructed from a quantum gauge theory living at the boundary. Over the past 25 years, this duality, with concrete instances uncovered by string theory, has revolutionised our understanding of systems ranging from black holes, to matter made up of strongly interacting quantum particles featuring intricate webs of entanglement. In this Topical Collection, the journal EPJ C presents a collection of articles reviewing the latest advances in the fundamental understanding of this duality and its groundbreaking applications.


EPJ C Topical Issue on New frontiers in holographic duality: From quantum complexity and black holes to hydrodynamics and neutron stars

Guest Editor: Ayan Mukhopadhyay

Over the last 25 years, holographic duality has revolutionised our understanding of gauge theories, quantum many-body systems and also quantum black holes. This topical issue is a collection of review articles on recent advances in fundamentals of holographic duality and its applications with special focus on a few areas where it is inter-disciplinary to a large measure. The aim is to provide a sufficient background on relevant phenomenology and other theoretical areas such as quantum information theory to researchers whose primary expertise is in quantum fields, strings and gravity, and also the necessary concepts and methods of holography to researchers in other fields, so that these recent developments could be grasped and hopefully further developed by a wider community.


EPJ C: Giulia Zanderighi new Editor-in-Chief for Theoretical Physics I: Phenomenology of the Standard Model and Beyond

The publishers of The European Physical Journal C – Particles and Fields are pleased to announce the appointment of Professor Giulia Zanderighi as new Editor-in-Chief for Theoretical Physics I: Phenomenology of the Standard Model and Beyond, replacing Professor Dieter Zeppenfeld as of 1 May 2022.

Giulia Zanderighi is Director at the Max Planck Institute for Physics and heads the department “Novel Computational Methods in Particle Physics”. She also holds a Liesel Beckmann Professorship at the Technische University in Munich. Her research focusses on collider particle physics.

EPJ C: Prof. Laura Baudis awarded with the 2022 Charpak-Ritz Prize

Congratulations to Laura Baudis, Associate Editor of EPJC and former Editor-in-Chief of the section Experimental Astroparticle Physics from 2016 to 2021, for this special distinction. This prize recognizes her “leadership in international astro-particle physics collaborations, outreach activities and seminal contributions to dark matter research”. A full account can be found here.

EPJ C Highlight - A cautionary tale of machine learning uncertainty

Underestimating machine learning uncertainty

By decorrelating the performance of machine learning algorithms with imperfections in the simulations used to train them, researchers could be estimating uncertainties that are lower than their true values.

The Standard Model of particle physics offers a robust theoretical picture of the fundamental particles, and most fundamental forces which compose the universe. All the same, there are several aspects of the universe: from the existence of dark matter, to the oscillating nature of neutrinos, which the model can’t explain – suggesting that the mathematical descriptions it provides are incomplete. While experiments so far have been unable to identify significant deviations from the Standard Model, physicists hope that these gaps could start to appear as experimental techniques become increasingly sensitive.

A key element of these improvements is the use of machine learning algorithms, which can automatically improve upon classical techniques by using higher-dimensional inputs, and extracting patterns from many training examples. Yet in new analysis published in EPJ C, Aishik Ghosh at the University of California, Irvine, and Benjamin Nachman at the Lawrence Berkeley National Laboratory, USA, show that researchers using machine learning methods could risk underestimating uncertainties in their final results.


EPJ C – New structure for the theory sections as of 2022


The publishers of The European Physical Journal C - Particles and Fields (EPJ C) are pleased to announce a new structure for the theory sections of the journal. As of January 2022 the current section ‘Theoretical Physics II: Gravitation, Astroparticle Physics, Cosmology, Quantum Field Theories’ (Editor-in-Chief: Prof. Kostas Skenderis, Deputy Editor-in-Chief Prof. Dominik Schwarz) will be split – into ‘Theoretical Physics II: Astroparticle Physics and Cosmology - Models and Phenomenology’, to be headed by Dominik Schwarz; and ‘Theoretical Physics III: Quantum Field Theory and Gravity - Fundamental and Formal Aspects’, to be headed by Kostas Skenderis. This change reflects the rapid development of the current Theoretical Physics II section under Kostas Skenderis over the past few years. We would like to thank Professor Skenderis for his excellent management of the section and to welcome Professor Schwarz as a new Editor-in-Chief of EPJ C. As head of the Astroparticle Physics and Cosmology Working Group at Bielefeld University, Schwarz is an expert on the interfaces between particle physics and cosmology and between modelling and observational cosmology. His research interests include cosmological inflation and the thermal history of the Universe, the cosmic microwave background and large-scale structures, dark matter and dark energy.

EPJ C Highlight - Hubble tension: Showing the cracks in Gaussian Processes

Tensions emerge through measurements of H0. Figure source: https://upload.wikimedia.org/ wikipedia/commons/0/0b/ Planck_satellite_cmb.jpg

Today, Gaussian Processes data reconstruction is viewed as a vital tool in cosmology. Yet through new analysis of tensions in the value of Hubble’s constant, two researchers suggest that the approach may not be as valid as currently thought.

The technique of Gaussian Processes (GP) is widely used to reconstruct cosmological parameters, most notably the expansion rate of the universe, using observational data. For many cosmologists, the crowning achievement of this approach is its ‘model independence’ – meaning it can be applied universally across all models. Through new analysis published in EPJ C, Eoin Ó Colgáin at Sogang University, Seoul, and Mohammad Mehdi Sheikh-Jabbari at IPM, Tehran, use the Hubble constant (H0) to show that this may not be the case – and that it may be time to question the validity of model independence itself.


EPJ C Highlight - The first black hole image: A gravitomagnetic monopole as an alternative explanation

The first image taken of the compact object at the heart of M87. Researchers consider this to be a supermassive black hole, but a new research paper asks if the image have an alternative cause. Credit: Event Horizon Telescope Collaboration

The Event Horizon Telescope made science history when it captured the first image of the supermassive black hole in the galaxy M87. New research suggests alternative explanations for the massive compact object at the centre of this galaxy questioning if this could contain gravitomagnetic monopole.

The Event Horizon Telescope (EHT) has recently mapped the central compact object of the galaxy M87 with an unprecedented angular resolution. Though the remarkable breakthrough has been interpreted based on theory that M87 contains a rotating or “Kerr” black hole. New research published in EPJ C by Chandrachur Chakraborty and Qingjuan Yu at the Kavli Institute for Astronomy and Astrophysics, Peking University (KIAA-PKU), Masoumeh Ghasemi-Nodehi and Youjun Lu, at the National Astronomical Observatories of China, looks at possible alternative explanations for the image.


EPJ C Highlight - Factoring in gravitomagnetism could do away with dark matter

The rotational curve of the galaxy Messier 33 shows the difference between observations and what should be expected from models of gravity. Until now, this disparity has been explained by ‘dark matter’ but a new paper suggests an alternative explanation. Credit: Mario De Leo, CC BY-SA 4.0, via Wikimedia Commons

Models of galactic rotation curves built of a general relativistic framework could use gravitomagnetism to explain the effects of dark matter.

Observations of galactic rotation curves give one of the strongest lines of evidence pointing towards the existence of dark matter, a non-baryonic form of matter that makes up an estimated 85% of the matter in the observable Universe. Current assessments of galactic rotation curves are based upon a framework of Newtonian accounts of gravity, a new paper published in EPJ C, by Gerson Otto Ludwig, National Institute for Space Research, Brazil, suggests that if this is substituted with a general relativity-based model, the need to recourse to dark matter is relieved, replaced by the effects of gravitomagnetism.


EPJ C Highlight - Placing cosmological constraints on quantum gravity phenomenology

Hawking radiation is still poorly understood. Source https://en.wikipedia.org/wiki/ Black_hole#/media/File: IonringBlackhole.jpeg

Researchers have used cosmological data to place stringent new limits on a model which emerges in attempts to reconcile gravity with the principles of quantum mechanics.

A description of gravity compatible with the principles of quantum mechanics has long been a widely pursued goal in physics. Existing theories of this ‘quantum gravity’ often involve mathematical corrections to Heisenberg’s Uncertainty Principle (HUP), which quantifies the inherent limits in the accuracy of any quantum measurement. These corrections arise when gravitational interactions are considered, leading to a ‘Generalized Uncertainty Principle’ (GUP). Two specific GUP models are often used: the first modifies the HUP with a linear correction, while the second introduces a quadratic one. Through new research published in EPJ C, Serena Giardino and Vincenzo Salzano at the University of Szczecin in Poland have used well-established cosmological observations to place tighter constraints on the quadratic model, while discrediting the linear model.


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