HEP Lattice hep-lat

Two actors on the same stage. One is a fermion, finicky and demanding, hard to make follow the rules of a quantum simulator. The other is a boson, easygoing and undemanding, ready to take any role. The director hopes the audience won't notice the substitution.

A stretched string between two quarks doesn't pop instantly like a rubber band. It first vibrates, develops knots, and only then breaks, if it breaks at all. This isn't just a metaphor; it's an accurate description of what physicists call confinement: quarks are permanently locked inside hadrons, and the only way to separate them is to snap the flux tube that binds them.

Physicists used a quantum simulator — a device that mimics the behavior of charged particles, to study their collisions at enormous energies.

Matter is like a house. In some rooms, there is the strict order of a crystal, where every atom is in its place. In others, the chaos of superfluid helium, where atoms forget about their neighbors.

The expansion of the universe is like a dance floor stretching wider. For decades, physicists assumed that more stretching would spawn more particles, like the floor spontaneously generating new dancers. But those models ignored an obvious fact: dancers sometimes link arms. When particles interact, new simulations reveal, they actually suppress creation.

Neutrinos are the most elusive of all known particles. Every second, trillions of neutrinos from the Sun fly through your body, but you never notice: they barely interact with matter. To catch even one, physicists build giant detectors — pools of water or liquid argon deep underground.

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.

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.

A quantum computer made of trapped ions played the role of a tiny universe. In it, particles didn't just move; they wove into knots that change their properties when swapped. Such knots are called Fibonacci anyons: they aren't ordinary particles but rather vortices in the fabric of space.

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.

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 ordinary proton consists of three quarks, like a three-legged stool. But nature does not forbid assembling a 'chair' from four quarks, if two of them are heavy beauty quarks and two are light. Such particles are called tetraquarks, and until now they have been studied mainly at large accelerators, by colliding particles and sifting through the debris.

The proton is not a solid ball. Inside, it's a seething mix of quarks and gluons. Gluons are the particles that glue quarks together, much like wood glue binds pieces of wood. The question is: how much of the proton's "weight" comes from this glue? Physicists have calculated this on a computer by discretizing space and time into a fine grid.

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 proton is not a smooth ball but a tangle of quarks and gluons in constant motion, exchanging energy. Finding out exactly how energy, pressure, and spin are distributed inside it is impossible to do directly: measurements yield only sparse, noisy points. It's like trying to guess a face from a few blurry photos taken from different angles.

A heavy stone falls into a pond, and ripples spread across the water with a distinctive pattern — from that pattern, you can infer what lies beneath the surface. Physicists study particle decays in much the same way: rare transformations in which a heavy particle suddenly becomes a lighter one, emitting light or a pair of charged particles.

Inside every proton and neutron, invisible work is underway: gluons, the particles that carry the strong force, glue quarks together into a single whole. You can think of this field as rubber bands that keep quarks from flying apart.

Water boils at 100 degrees Celsius, but if you squeeze it hard enough, it behaves differently. Similarly, quarks and gluons, the building blocks of protons and neutrons, change their properties in a strong magnetic field.

The muon resembles the electron but is 200 times heavier and lives for two millionths of a second. Its magnetic moment, how the particle responds to a magnetic field, has been measured with fantastic precision. Yet the measured value is slightly larger than theory predicts.

Heavy particles, which physicists call baryons, are like tiny families of three quarks. The common baryons are protons and neutrons, which make up everything around us. But there are also exotic relatives: instead of light quarks, they harbor charm or bottom quarks — heavy and short-lived.

If you place a kaon in an electric field, it stretches slightly, like a balloon rubbed on wool. This response, the electric polarizability, shows how rigidly the particle is built inside. For the charged kaon, it has been measured for the first time, and the number is about one ten-thousandth of the volume occupied by a proton.

To understand how the universe emerged from the Big Bang, physicists look to Georges Lemaître's idea of expansion, which rests on the laws of Hendrik Lorentz. One daring approach replaces elementary particles with giant tables of numbers — as if instead of the usual roulette balls, you use numbered cards.

If you try to break a proton apart and pull out a quark, you're in for a surprise. Ordinary forces, like the electric force, weaken as particles fly apart. Here, it's the opposite. The farther a quark gets from its neighbors, the harder it's pulled back.

When water boils in a pot, the bubbles of steam don't appear just anywhere: they prefer to cling to scratches or dust particles on the bottom.

A quantum calculation sometimes resembles an interpreter who gets distracted by every rustle in the hall, and a one-hour meeting turns into two. In physics, such a "rustle" is called the sign problem: it arises when probabilities in formulas become negative or complex, and ordinary computer simulations start to fail.

In the scorching core of a star, two helium nuclei approach each other like two dancers on a crowded stage. Their dance is alpha scattering, the basis of stellar helium burning. How smoothly they twirl determines how quickly the star burns its fuel. Previously, this dance was described in simplified terms.

Electric charge is not like a number chiseled in stone. In the vacuum around any charged particle, pairs of particles and antiparticles are constantly born and annihilated, like the foam in a glass of champagne. The bubbles screen the true charge, making it appear smaller or larger depending on how close we get.

The neutron is one of the most neutral particles in nature. But if you add a special parameter to the laws of physics, called the theta term Standard Model, a tiny charge imbalance appears inside the neutron. One edge becomes slightly positive, the other slightly negative.

The proton is not a solid ball but a tiny prison. Inside it, three quarks are locked up, and the gluon field keeps them from escaping — something like invisible threads that only grow stronger if the quarks try to move apart.

A scale capable of weighing the invisible: that's exactly how the ratio of decays of light mesons (pion and kaon) into electrons and muons works. If nature follows the same rules for all generations of particles, the pans of this scale show a strictly defined number. But if an unknown force lurks somewhere, the needle will waver.

A quantum computer is usually like an assembly line: operations proceed one after another, and each error accumulates. In the new work, physicists tried a different path — an architecture where the computation grows out of the measurement process itself. They took 56 ions in a trap and wove them into a three-dimensional cloud of entangled particles.

Ordinary ice turns into water at zero degrees. And matter at nuclear density, quark-gluon plasma, undergoes something similar at about 155 MeV (roughly two trillion degrees).

Quarks, the building blocks of protons and neutrons, usually pair up or form trios. But sometimes they assemble into larger, unstable combinations that live for mere fractions of a second. Two such particles, Bs0* and Bs1, have long been a puzzle: calculations hinted they should be bound, but the precision wasn't enough to say so with confidence.

A translator who used to catch only fragments of sentences now hears the entire conversation. Similarly, physicists studying strong interactions have long been unable to calculate how two particles respond to a flash of light when they do not form a stable nucleus.