HEP Theory hep-th

The universe is expanding faster and faster, and the standard explanation is a positive cosmological constant, that is, a de Sitter vacuum. String theory, which aspires to be the theory of quantum gravity, should be able to describe such a vacuum, but after decades of effort, no reliable construction has emerged.

Two vessels of water at different temperatures are separated by a thin partition. As long as the partition is intact, each vessel lives its own life: in one, the water is hot; in the other, it's icy. But once the partition is removed, the temperatures begin to equalize, and eventually both vessels reach the same state.

Imagine a city drawn on a sheet of paper. The streets are the same, the intersections are in place, but the distances between blocks have suddenly changed.

In the first moments after the Big Bang, space expanded at an incredible rate. A tiny quantum ripple, embedded in the uncertainty principle itself, pushed matter apart more strongly than any known force. This ripple is the generalized uncertainty principle, or GUP.

A postal money order doesn't arrive instantly but after a set delay, and the amount credited to the recipient's account ends up larger than what the sender deposited in cash. That's roughly how the new protocol, dubbed temporal quantum energy teleportation (TQET), works. In ordinary quantum energy teleportation, two parties, Alice and Bob, share a common quantum state.

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 2008, a group of physicists spent months of supercomputer time to compute a single quantity in quantum gravity theory. This is the vertex amplitude of spinfoam, a number that sets the probability of a local quantum transition of spacetime.

The shadow of a black hole is not just a dark silhouette. It is an imprint of the entire spacetime geometry, including the subtlest quantum effects.

In a chain of cold spins stretched along a single line, order and disorder can intertwine into a pattern that defies the usual rules. Two states of matter, two kinds of "order," are separated by a crossroads where the roads do not converge but diverge.

In an accelerator, two Higgs particles collide. For a fleeting moment, their fates intertwine, then separate, carrying away information about the encounter.

In the concert hall of quantum theory, strict discipline long reigned: it was believed that operators, those performers of complexity, could only grow at a certain speed. The universal operator growth hypothesis stated that Lanczos coefficients, the numbers measuring an operator's growth rate, could not grow faster than linearly.

At the edge of spacetime, where all light rays end, live symmetries that physicists have debated for half a century. They are called superrotations, transformations of the celestial sphere that diverge at isolated points, like vortices in superfluid helium.

A black hole in anti-de Sitter space is not a void but rather a pot of boiling liquid. This liquid has two phases: small and large black holes, like steam and water. At a certain pressure, they merge at a critical point, just as water at 374 °C and 218 atmospheres loses the distinction between liquid and gas.

Two telescopes look at the same Universe and see different expansion rates. Local measurements from supernovae give 73.04 ± 1.04 km/s/Mpc, while cosmic microwave background data within the standard model predict 67.36 ± 0.54.

The universe is expanding, and the pace of that expansion is set by dark energy, the mysterious force accelerating the recession of galaxies. In the standard cosmological model, its density is constant: a cosmological constant, an unwavering metronome since the birth of the cosmos.

A heat engine is like a sailboat: to move forward, it needs a difference. Usually that means a temperature difference between hot and cold reservoirs. But what if the reservoir itself starts moving? The wind that fills the sails is created not only by a pressure difference but also by the motion of air masses.

In general relativity, a black hole has long been regarded as a perfect mirror: no matter what fields fall onto it, it does not deform. The tidal Love numbers, which measure how a body deforms under an external tidal field, turned out to be zero for scalar, electromagnetic, and gravitational perturbations.

Gravitational waves from a neutron star merging with a black hole carry the imprint of the intricate dynamics of spacetime. To decode that imprint, physicists compute scattering amplitudes, the quantum probabilities that two bodies fly apart at a given angle.

An electron flies out of a tritium nucleus with an energy of 18.57 keV, leaving behind an invisible partner: a neutrino. If that neutrino has access to a fifth dimension, its mass splits into a whole tower of states, and each one takes its own bite out of the spectrum.

The road to equilibrium for a quantum detector resembles a mountain route: the climb is always faster than the descent. An atom accelerated through the vacuum, sensing quantum field fluctuations, heats up to the Unruh temperature.

A century ago, Einstein's equations predicted black holes, but inside them physics broke down: particle trajectories ended at the singularity, a point of infinite curvature. It was a dead end, the end of spacetime. Now physicist Itzhak Bars proposes a radical twist: the singularity is not a wall but a door.

A gravitational-wave detector catches not only the roar of mergers but also the quiet splash when a star or gas cloud dives into a supermassive black hole. Such a dive, like a stone falling into a well, generates waves at all frequencies at once—and in that spectrum lies encoded the nature of the well itself.

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.

The universe is putting on a show, and the lead role goes to dark energy. For a long time, the actor seemed unchanging: the cosmological constant (the vacuum energy that accelerates cosmic expansion) set the same tone throughout.

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.

A black hole is not just the universe's trash can; it is more like a safe with a secret code. For decades, it was thought that any signal sent toward the event horizon would be partially reflected back: curved spacetime acts like a funhouse mirror, and some energy always escapes.

Every evening, in the city archive, the attendant places new folders on the shelves. If too many arrive during the day, the shelves sag, and the next morning the archive responds to requests more slowly. A black hole's memory works in much the same way: it doesn't just store information, it physically feels its weight.

Cosmic rays are elementary particles carrying colossal energy that pierce the intergalactic void. When two such particles smash head-on, the energy density at the point of impact could be enough to collapse into a black hole the size of an atomic nucleus.

The early universe was far from perfect: some regions stretched faster than others, creating folds and warps. But a quantum bounce — the transition from contraction to expansion, driven by the laws of the microworld — fixes everything.

The Universe is a grand highway where galaxies, like cars, are moving apart faster and faster. The gas pedal is controlled by mysterious dark energy.

The 'double copy' method in physics is a culinary trick: a chef takes a cold soup recipe, doubles the ingredients, and gets a recipe for a hot roast. Likewise, particle interactions via electric forces (the basis of the Standard Model) morph into gravity, which describes spacetime curvature.

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 Universe is filled with invisible mass, dark matter, which reveals itself only through gravity. One hypothesis suggests that dark matter consists of primordial black holes — objects formed in the extreme conditions just after the Big Bang.

Black holes are rarely alone in the cosmos. They are often shrouded in invisible clouds of hypothetical dark matter particles — so light that they feel only gravity, barely interacting with each other or ordinary matter.

Usually, we think of the number of dimensions as fixed: length, width, height. But in the quantum world, even that can be changeable. A new theory describes systems where dimension isn't a constant but a quantum property, capable of being different simultaneously. A balloon is flat when cold, round when warm.

A black hole is not a bottomless funnel but a cosmic cooking pot. Inside it, matter obeys laws familiar to us from the behavior of water: under some conditions it resembles boiling steam, under others — a cooling liquid.

According to one physical hypothesis, our voluminous world might be a projection from a flat surface. From such a Universe, tiny closed bubbles — baby universes — sometimes pinch off. For a long time, they were thought to be empty, devoid of internal diversity. It turned out that the information inside them is scattered, like shards of a broken mirror.

According to the laws of the microworld, an electron obeying the Dirac equation trembles even at complete rest. This is Zitterbewegung — an oscillation with an amplitude of trillionths of a millimeter, like a spinning top on an invisible axis.

A wormhole is a tunnel that pierces through curved space and connects distant regions of the Universe. Recently, Juan Maldacena and his colleagues proposed a working model of such a hole based on a special combination of spatial curvature and quantum particles.

In the familiar world, we have three spatial dimensions. However, theoretical physics allows for additional, hidden directions — compactified, that is, curled up to microscopic sizes.