Nuclear Theory nucl-th

In the silent heart of creation, where particles converge and part, an act of pure harmony is born. Two Higgs bosons meet and for a fleeting moment form a single whole — and if one demands that their quantum entanglement always reaches its limit, like a tuning fork setting a perfect pitch, then the equations suddenly light up with a new symmetry.

In 1976, Gerard 't Hooft noticed that the vacuum of a gauge theory is not as simple as it seems: it possesses a topological structure that manifests itself in a nonzero topological susceptibility.

A quantum system, once born, does not forget it. Even after dozens of lifetimes, a trace of the initial state remains in its decay: a slowly decreasing power-law tail. For two fluorescent dyes, erythrosine B and eosin Y, this tail has been observed for the first time in two spectral channels simultaneously.

The collision of two neutron stars is a strike heard across the universe. Gravitational wave detectors pick up the ripples in spacetime, but the most interesting sound begins after the impact: the merger remnant, a rapidly spinning hypermassive neutron star, continues to vibrate, emitting waves for a few more…

For centuries, three branches of physics (cosmology, particle physics, and nuclear physics) worked like isolated shores.

Measured dipole moment of tantalum-181: 3.39 × 10⁻³² e·cm — like spotting a one-atom shift across the entire Solar System. An ordinary atomic nucleus is perfectly balanced, like a spinning top. In tantalum, that balance is broken: the positive and negative charges are slightly offset from each other.

Conventional atomic clocks are essentially optical counters: they rely on spectroscopy — a method for measuring the frequency of radiation with high precision as electrons jump between energy levels.

Ultracold atoms can act as one. When a neutrino is born inside such a cloud, it usually slips away unnoticed.

Our Sun emits streams of neutrinos — particles that barely interact with matter. Passing through the dense solar material, they change their type — scientists call this 'flavor.' It's like a voice that changes as it moves through a crowd: the thicker the crowd, the more it gets distorted.

A proton slams into a deuteron — a tiny bundle of a proton and a neutron. In the past, such collisions were described by equations where time flows the same for everyone, as in everyday life. But when particles are accelerated to near-light speeds, time slows down for them and lengths contract. It's like two runners on a track measuring the distance with different rulers.

Neutron stars — the super-dense remnants of supernovae — create gravitational waves when they collide. These ripples in space can be thought of as a silent melody: the more precisely we catch its notes, the better we understand the interiors of these objects.

Just as in a crowded room each new person sharply increases the pressure on the walls, in a neutron star increasing density leads to a rise in internal resistance. But even this resistance has an absolute ceiling.

Inside a neutron star, matter is compressed to unimaginable densities. Previously, scientists speculated about its exact makeup, cycling through possible equations linking pressure and density. The new method tosses out guesswork: it directly ties the measurable mass and radius to the internal structure.

Two particles cling to each other like climbers on the same rope and fly toward a wall. When they hit, will they bounce off together, or will the rope snap? What does it depend on? Physicists considered the simplest case: everything happens on a single line, the particles attract only when they occupy the same point, and the wall is perfectly rigid.

Water freezes at zero and boils at one hundred degrees. Matter made of quarks and gluons also has boundaries between states, but instead of a thermometer, the temperature here is measured in millions of electron-volts.

The calcium-48 nucleus is like a locked room with 48 nucleons inside. Rearrangements are happening within: a neutron turns into a proton, and the room slowly rebuilds itself into another — titanium-48. The process takes an unimaginably long time: on average, a trillion trillion years, but it does happen. To describe such a rearrangement, physicists assembled the nuclear wavefunction from pieces.

Tiny black holes, the size of an atom but heavier than an asteroid, were born right after the Big Bang. Now, they are probably the dark matter — the invisible mass that keeps galaxies from flying apart. You can't catch them directly: they emit almost nothing.

Inside a neutron star, matter is squeezed so tightly that a teaspoon of its material would weigh as much as a mountain. We can't directly see what happens to particles under such conditions, but stars tell us about themselves through gravitational waves and light when two such stars merge.

The antiproton is a mirror twin of the proton: same mass, but negative charge. When it approaches an atomic nucleus, the particles can annihilate, turning into radiation.

The atomic nucleus is not just a bag of protons and neutrons. It is a quantum system where particles are bound by invisible threads of entanglement. When two protons or neutrons interact, their states become intertwined so that describing one without the other is impossible.

An electron beam strikes a proton like a billiard ball hitting another ball. But between them is no empty space: the particles exchange virtual photons and Z bosons, like players passing a ball behind their backs. This exchange slightly alters the scattering trajectory, and hidden within it is a hint of new physics.

In the first minutes after the Big Bang, the Universe was like a blazing hot stove. On it, according to the 'recipe' of the standard theory, hydrogen, helium, and a bit of lithium were supposed to cook. But telescopes see only a third of the lithium that this recipe calls for.

The phi meson is a particle that lives only for an instant, but it can briefly stick to protons and neutrons in an atomic nucleus. Physicists have studied what happens if such a meson finds itself inside light nuclei of helium and hydrogen.

An unstable atomic nucleus is like a drop of water on a sizzling skillet: it exists for only a moment, and its shape is constantly changing. Physicists have learned to describe such drops — nuclei that live for less than a billionth of a second and decay almost as soon as they are born.

A neutron star is the ultra-dense remnant of a supernova explosion, whose existence was predicted by Fritz Zwicky back in the 1930s. Later, Jocelyn Bell Burnell detected them as pulsars — rotating sources of strictly periodic radio signals.

A bell doesn't ring with a single note — after being struck, it sounds with several harmonics at once. An atomic nucleus vibrates in much the same way: after a collision, it can oscillate, and these oscillations show up in the emitted gamma rays.

The diffusion equation, a mathematical tool describing how particles spread out in space, has long painted a paradoxical picture: a disturbance, like ripples on Water, instantly engulfs the entire universe. This challenged the theory of relativity, which holds that nothing can move faster than light.

An atomic nucleus usually lives in a single energy state, like a ball resting on the floor. But thorium-229 has a rare exception: the nucleus can get stuck on a tiny step above the floor — the so-called isomeric state. This step is so low that it can be nudged by ordinary light, not just hard radiation.

Inside a neutron star, matter is squeezed so tightly that a single teaspoon weighs as much as a mountain. Under such pressure, ordinary particles, protons and neutrons, can transform into exotic particles known as hyperons. These particles resemble neutrons but contain strange quarks.

The neutron is the particle that makes up most of a neutron star. On its own, it is unstable: a free neutron lives for about fifteen minutes, then decays into a proton, an electron, and an antineutrino.

Light and matter in the tiny world obey laws that are hard to compute even on a supercomputer. Physicists build special "quantum simulators"—setups where cold atoms play the roles of particles and fields. But until now, such simulators could only depict the field in its simplest form: as if it were either present or absent.

An atomic nucleus usually has a well-defined shape — elongated like a melon or flattened like a pumpkin. But silicon-30 behaves differently: it seems unable to make up its mind.

At the heart of a neutron star, matter is squeezed so tightly that protons and neutrons transform into heavier particles — hyperons. These particles resemble neutrons but contain a strange quark. For a long time, physicists couldn't understand how a star with hyperons inside could be as heavy as observations show.

The atomic nucleus is not a solid ball but a drop of liquid that can be squeezed. To understand how elastic it is, physicists accelerate gold nuclei and smash them into each other. On impact, the matter compresses to densities like those in a neutron star, then flies apart. The shape of this debris tells us about the properties of the matter inside.

Inside a proton, quarks are held together by gluons, like springs. Let go of one quark — the spring stretches and snaps, creating a new quark. That's the strong force at work, and simulating it in real time on a regular computer is nearly impossible: there are too many possibilities, all tangled together. Enter the quantum computer.

The antiproton is the proton's twin, only with a negative charge. When such a twin approaches a nucleus, it doesn't just bounce off: a whole dance of attraction and repulsion unfolds between them.

In April 2023, Japanese satellites detected a super-intense X-ray burst on the neutron star MAXI J1752–457. The star cooled down in 4 days — five times faster than usual. Like someone cracked open a cosmic window.

Long before that, Fritz Zwicky predicted that a supernova explosion gives birth to a tiny neutron star. Years later, Jocelyn Bell Burnell caught its pulses, discovering pulsars.

Deep inside a massive star, two carbon nuclei collide and merge into a single magnesium nucleus. This process determines how quickly the star burns its fuel and which chemical elements it manages to create. But calculating such a fusion on paper has proven incredibly difficult: nuclei are not billiard balls but quantum systems that can rearrange themselves in many ways.

When matter accumulates on the surface of a neutron star, the ultra-dense remnant of a dead star, an explosion occurs, akin to a giant thermonuclear bomb. In this inferno, nuclei of elements not found on Earth are born within seconds. To understand which ones, their masses must be known with great precision.