QUP Scientists Show Black Holes Can Hold Keys to Mysteries of Fundamental Strong Force:

The fundamental strong force described by quantum chromodynamics (QCD) that holds nuclei of atoms together remains explored only in limited regimes. Primordial black holes (PBHs) formed in the early Universe may hold the keys to unlocking and probing unexplored strong force dynamics at high temperatures, reports a new study published in Physical Review Letters.

Figure 1. Schematic of black hole formation during strong force QCD phase transition at high temperatures in the early Universe, which results in nucleation of bubbles with hadron phase where quarks form composite particles like proton and neutron. (Credit: Volodymyr Takhistov)

In their work, Assistant Professor Volodymyr Takhistov, a Senior Scientist of International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (QUP) and Theory Center at the High Energy Accelerator Research Organization (KEK), together with collaborating researchers from the United States and South Korea, have uncovered an intriguing connection between enigmatic PBHs and possible new phase transitions of QCD at high temperatures.
In the Standard Model of particle physics QCD phase transition occurs at energies below GeV (corresponding to femtometer scales), confining quarks to hadrons such as protons and neutrons.

However, novel QCD phase transitions are predicted in a variety of theories of new physics and quantum fields. While it may be challenging to recreate relevant extreme conditions to study their dynamics in laboratories, they can be tested and probed in the vast realms of early cosmology, where the Universe itself provides the perfect laboratory.

Change in the equation of state due to a high temperature QCD transition in the early Universe can dramatically enhance collapse of cosmological perturbations, leading to efficient formation of PBHs. Intriguingly, the resulting PBHs can constitute the whole abundance of the mysterious dark matter that comprises ~85% of all matter in the Universe.

First hints of unusual QCD transition may have already been seen by the Subaru Hyper-Suprime Cam microlensing survey, designed to detect the gravitational lensing effects caused by PBHs passing in front of distant stars. A discovered candidate asteroid-mass PBH event is consistent with a novel QCD phase transition at a temperature of around ~10 TeV. Other possible signatures of such novel strong force dynamics are coincidence gravitational waves, which could be responsible for the claimed signals of NANOGrav pulsar timing array consortium and could be further tested with upcoming experiments such as space-based LISA and DECIGO.

The study connects a number of conventionally unrelated fields of research to explore the mysteries of fundamental strong force, including astronomical surveys, cosmological black holes and quantum chromodynamics as well as particle physics.

Details of their study were published in Physical Review Letters on May 31.

Paper details
Journal: Physical Review Letters
Title: Signatures of a High Temperature QCD Transition in the Early Universe
Authors: Philip Lu (1), Volodymyr Takhistov (2,3,4), George M. Fuller (5)
DOI: 10.1103/PhysRevLett.130.221002
Author affiliations:
1 Center for Theoretical Physics, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea
2 International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (QUP, WPI), High Energy Accelerator Research Organization (KEK), Oho 1-1, Tsukuba, Ibaraki 305-0801, Japan
3 Theory Center, Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
4 Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
5 Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA

Paper abstract (PRL):
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