Our research interests

Quarks and gluons are the fundamental building blocks of matter, yet under normal conditions, they are confined within hadrons such as protons and neutrons due to the strong nuclear force. The phase diagram of nuclear matter, illustrated here on the side, depicts how nuclear matter behaves at high temperatures and/or densities.

Consider water: when heated to a critical temperature, it transitions from liquid to vapor. Similarly, fossils of dinosaurs or plants, when heated to around 1,800 K and subjected to pressures of approximately 50,000 kg/cm², transform into diamonds. Both these transitions exemplify how substances change their state under extreme temperature and pressure.

This prompts the question: what happens when we heat or compress protons and neutrons? Lattice QCD calculations predict that at temperatures above approximately 160 MeV (around 2×10¹² K, which is 100,000 times hotter than the Sun’s core), quarks and gluons are no longer confined within hadrons. Instead, they form a new phase called the quark-gluon plasma (QGP). At the Large Hadron Collider (LHC), experiments aim to produce and study this state to deepen our understanding of the strong force.

To explore high-density regimes, astronomers turn their gaze skyward. Neutron stars are the universe’s most compact objects, with masses up to twice that of the Sun compressed into a radius of just 5–15 km. The densities within their cores can surpass four or five times that of normal nuclear matter, though what exactly constitutes their internal composition remains uncertain. The equation of state (EoS) -the relationship between internal pressure and density- serves as a key link between the star’s internal properties and its observable characteristics, such as mass and radius, especially when analyzed through general relativity.

Recent observations of neutron star mergers via gravitational wave signals provide additional means to test hypotheses about their internal makeup. The simplest assumption is that neutron stars are composed mainly of neutrons, some protons, electrons, and neutrinos. However, at densities exceeding twice nuclear density, it becomes energetically favorable for neutrons to be replaced by hyperons—hadrons containing at least one strange quark, such as the Λ hyperon (uds). The equation of state involving nucleons and hyperons depends on hyperon-nucleon and hyperon-nucleon-nucleon interactions, which change as density increases. Neutron stars could also include other hadrons like kaons (K⁺ = u-anti-s) or antikaons (K⁻ = s-anti-d). Their production is favored because, as bosons, they can occupy the same energy ground state, affecting the star’s internal dynamics.