ProfessorArchil Kobakhidze

Project Opportunities

Title: Exploring fundamental physics with gravitational waves

Summary of opportunity:

The discovery of gravitational waves has opened an entirely new avenue for probing some of the most fundamental aspects of the universe. In particular, several well-motivated extensions of Einstein’s General Relativity and standard cosmology can now be tested in the strong-gravity regime through gravitational-wave measurements at current and future observatories worldwide. While the properties of gravitational-wave signals and their sources are relatively well understood within the framework of Einstein’s theory, alternative theories remain far less explored. This project aims to address this gap by providing a robust theoretical framework for interpreting observations and by creating a unique opportunity to investigate novel physical phenomena and theoretical ideas, including alternative theories of gravity, exotic compact objects composed of dark matter, and cosmological phase transitions in the early universe.

The Project aims to develop new theoretical techniques and utilise them to model and analyse various gravitational wave signals within the alternative theories of space, time and matter.

Selected publications:

• C. Boehm, A. Kobakhidze, C.A.J. O'Hare, Z.S.C. Picker and M. Sakellariadou, ``Eliminating the LIGO bounds on primordial black hole dark matter,'' JCAP 03, 078 (2021).
• Y. Kim, A. Kobakhidze and Z.S.C. Picker, ``Probing Quadratic Gravity with Binary Inspirals,'' Eur. Phys. J. C 81, no.4, 362 (2021).
• A. Kobakhidze, C. Lagger, A. Manning and J. Yue, ``Gravitational waves from a supercooled electroweak phase transition and their detection with pulsar timing arrays,'' Eur. Phys. J. C 77, no.8, 570 (2017)
• A. Kobakhidze, C. Lagger and A. Manning, ``Constraining noncommutative spacetime from GW150914,'' Phys. Rev. D 94, no.6, 064033 (2016).

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Project Opportunities

Title: Exploring the implications of quantum gravity on particle physics via topology

Summary of opportunity:

The development of the quantum description of relativistic systems culminated in the Standard Model, the theory that most accurately explains natural phenomena in terms of elementary particles and the fundamental strong, weak, and electromagnetic interactions. The critical missing element in this framework is a complete and empirically verified quantum description of gravitation, described classically by Einstein’s General Relativity. From an observational standpoint, the main obstacle is that detectable gravitational effects arise through local interactions of macroscopic objects, for which quantum signatures are notoriously difficult to measure. Conversely, in microscopic systems—where quantum effects are pronounced—gravitational interactions are exceedingly weak and remain beyond the reach of current and foreseeable experimental technologies. This absence of a quantum theory of gravity is often referred to as the “unfinished revolution” in physics.

In a series of works over the past few years, we have identified a novel and robust way to infer quantum-gravity effects in particle-physics systems. The key insight is that the properties of relativistic systems are not determined solely by local interactions; they also depend on the global (topological) features of the lowest-energy configuration—the vacuum state. This vacuum structure can be modified by topological solutions in gravity known as gravitational instantons. The presence of such instantons, and the rich vacuum structure they induce, requires the introduction of new interactions in the Standard Model that violate charge (C) and parity (P) combined symmetry (CP). This leads to a range of intriguing implications for early-universe cosmology, particularly for mechanisms that dynamically generate visible matter. Moreover, CP violation induced by gravitational instantons has been shown to undermine the conventional axion solution to the longstanding strong CP problem.

The proposed project aims to explore and significantly advance research in this direction, both at the theoretical and phenomenological levels.

Selected publications:

• S.Arunasalam and A.Kobakhidze,``Charged gravitational instantons: extraCPviolation and charge quantisation in the Standard Model,'' Eur. Phys. J. C79, no.1, 49 (2019), [arXiv:1808.01796 [hep-th]].
• Z.Chen and A.Kobakhidze,``Coloured gravitational instantons, the strong-CP problem and the companion axion solution,'' Eur. Phys. J. C82, no.7, 596 (2022), [arXiv:2108.05549 [hep-ph]].
• Z. Chen, A. Kobakhidze, C. A. J. O'Hare, Z. S. C. Picker and G. Pierobon,``Phenomenology of the companion-axion model: photon couplings,'' Eur. Phys. J. C82, no.10, 940 (2022), [arXiv:2109.12920 [hep-ph]].
• Z. Chen, A. Kobakhidze, C. A. J. O'Hare, Z. S. C. Picker and G. Pierobon, ``Cosmology of the companion-axion model: dark matter, gravitational waves, and primordial black holes,'' [arXiv:2110.11014 [hep-ph]].

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Project Opportunities

Title: New emergent particle states in the Standard Model and beyond

Summary of opportunity:

Over the past several decades, breakthrough theoretical and experimental discoveries have led to the establishment of the Standard Model of particle physics. This theory provides the most accurate fundamental description of physical phenomena; however, it remains incomplete. This incompleteness is clearly indicated by various experimental findings, such as neutrino oscillations and dark matter, as well as theoretical considerations of naturalness and consistency criteria. The search for new physics beyond the standard model has primarily relied on specifically designed theoretical models that describe local interactions of known matter with hypothetical particles. Despite extensive global efforts, no evidence of new physics has emerged so far.

This project proposes a paradigm shift by recognising that global (topological) features of the vacuum state - the lowest energy quantum state - carry crucial information about the particle spectrum and new interactions. Notably, the existence of fermionic vacuum condensates and the emergence of new particle states in theories with topologically non-trivial θ-vacuum structures can be inferred generically, independent of any specific model. By applying these considerations to Einstein's theory of General Relativity, we provide theoretical evidence for a theory of spontaneously broken supersymmetry with a distinct particle content, along with the emergence of a new particle state, the electroweak ηw, within the Standard Model.

With such powerful insights, it is essential to quantitatively explore the implications of these phenomena within current particle physics frameworks. Such studies will fill critical knowledge gaps and advance our understanding toward the potential empirical discovery of new particle states.

Selected publications:

• G. Dvali, A. Kobakhidze and O. Sakhelashvili, ``η<sub>w</sub>-meson from topological properties of the electroweak vacuum,''  Phys. Rev. D112, no.9, 093006 (2025).
• G. Dvali, A. Kobakhidze and O. Sakhelashvili, ``Electroweak η_w meson,'' Phys. Rev. D111, no.11, 11 (2025).
• G. Dvali, A. Kobakhidze and O. Sakhelashvili, ``Hint to supersymmetry from the GR vacuum,'' Phys. Rev. D110, no.8, 8 (2024).