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Category: particle physics – Page 10

The gravitino: A new candidate for dark matter

Dark matter remains one of the biggest mysteries in fundamental physics. Many theoretical proposals (axions, WIMPs) and 40 years of extensive experimental searches have failed to provide any explanation of the nature of dark matter.

Several years ago, in a theory unifying and gravity, new, radically different candidates were proposed: superheavy charged gravitinos.

Now, a paper published in Physical Review Research by scientists from the University of Warsaw and Max Planck Institute for Gravitational Physics shows how new underground detectors, in particular the JUNO detector starting soon to take data, even though designed for neutrino physics, are also extremely well suited to eventually detect charged dark matter gravitinos.

Life’s building blocks may not be stable—just really, really long-lived

Although the building blocks of life such as hydrogen and oxygen appear stable to us, many theories of physics predict that they are actually just tremendously long-lived, with the particles found in their nuclei slowly, but ultimately decaying.

To investigate this idea, researchers have been hunting for evidence of this by looking for faint signals of decaying in Japan’s Super-Kamiokande observatory.

So far, no definitive signals of decay have emerged, implying that if the proton does decay, it probably has a lifetime exceeding 1033 years—that’s 10 with 32 zeros behind it.

Time crystals arise from quantum interactions once thought to prevent their formation

Nature has many rhythms: the seasons result from Earth’s movement around the sun, the ticking of a pendulum clock results from the oscillation of its pendulum. These phenomena can be understood with very simple equations. However, regular rhythms can also arise in a completely different way—by themselves, without an external clock, through the complex interaction of many particles. Instead of uniform disorder, a fixed rhythm emerges—this is referred to as a “time crystal.”

Calculations by TU Wien (Vienna) now show that such time crystals can also be generated in a completely different way than previously thought. The quantum physical correlations between the particles, which were previously thought to be harmful for the emergence of such phenomena, can actually stabilize time crystals. This is a surprising new insight into the quantum physics of many-particle systems.

The findings are published in the journal Physical Review Letters.

First-Ever Simulations Reveal Ghost Particles Shapeshifting in Violent Neutron Star Mergers

New simulations show that neutrino flavor transformations change both the composition and the signals left behind after neutron star collisions. When two neutron stars collide and merge, the result is one of the most energetic events in the universe. These cataclysms generate multiple kinds of si

The Hunt for Dark Matter Has a New, Surprising Target

Dark Matter remains one of the biggest mysteries in fundamental physics. Many theoretical proposals (axions, WIMPs) and 40 years of extensive experimental search have not explained what Dark Matter is. Several years ago, a theory that seeks to unify particle physics and gravity introduced a radically different possibility: superheavy, electrically charged gravitinos as Dark Matter candidates.

A recent paper in Physical Review Research by scientists from the University of Warsaw and the Max Planck Institute for Gravitational Physics shows that new underground detectors, in particular the JUNO detector that will soon begin taking data, are well-suited to detect charged Dark Matter gravitinos even though they were designed for neutrino physics. Simulations that bridge elementary particle physics with advanced quantum chemistry indicate that a gravitino would leave a signal in the detector that is unique and unambiguous.

In 1981, Nobel Prize laureate Murray Gell-Mann, who introduced quarks as fundamental constituents of matter, observed that the particles of the Standard Model—quarks and leptons—appear within a purely mathematical theory formulated two years earlier: N=8 supergravity, noted for its maximal symmetry. N=8 supergravity includes, in addition to the Standard Model matter particles of spin 1/2, a gravitational sector with the graviton (of spin 2) and 8 gravitinos of spin 3/2. If the Standard Model is indeed connected to N=8 supergravity, this relationship could point toward a solution to one of the hardest problems in theoretical physics — unifying gravity with particle physics. In its spin ½ sector, N=8 supergravity contains exactly 6 quarks (u, d, c, s, t, b) and 6 leptons (electron, muon, taon and neutrinos), and it forbids any additional matter particles.

Proposed framework describes physics from perspective of quantum reference frames

In an article published in Communications Physics, researchers from the Université libre de Bruxelles and the Institute for Quantum Optics and Quantum Information in Vienna present a new framework for describing physics relative to quantum reference frames, unveiling the importance of previously unrecognized “extra particles.”

In any experiment, specifying a physical quantity of interest always relies on a . For example, identifying the time at which an event happens only makes sense relative to a clock. Similarly, the position of a particle is usually defined relative to other particles. Reference frames are typically treated as classical systems, that is, they are assumed to have definite values when measured relative to other reference frames.

However, as far as we know, every system is ultimately quantum. As such, it can, in principle, exist in indefinite states called quantum superpositions. What does the physical world look like when described from the perspective of a reference frame that can be in a quantum superposition? Can we define consistent rules for changing between different perspectives?

Mixing neutrinos of colliding neutron stars changes how merger unfolds, simulations reveal

The collision and merger of two neutron stars—the incredibly dense remnants of collapsed stars—are some of the most energetic events in the universe, producing a variety of signals that can be observed on Earth.

New simulations of neutron star mergers by a team from Penn State and the University of Tennessee Knoxville reveal that the mixing and changing of tiny particles called that can travel astronomical distances undisturbed impacts how the merger unfolds, as well as the resulting emissions. The findings have implications for longstanding questions about the origins of metals and as well as understanding physics in , the researchers said.

The paper, published in the journal Physical Review Letters, is the first to simulate the transformation of neutrino “flavors” in neutron star mergers. Neutrinos are fundamental particles that interact weakly with other matter, and come in three flavors, named for the other particles they associate with: electron, muon and tau. Under specific conditions, including the inside of a neutron star, neutrinos can theoretically change flavors, which can change the types of particles with which they interact.

Lasers just made atoms dance, unlocking the future of electronics

Scientists at Michigan State University have discovered how to use ultrafast lasers to wiggle atoms in exotic materials, temporarily altering their electronic behavior. By combining cutting-edge microscopes with quantum simulations, they created a nanoscale switch that could revolutionize smartphones, laptops, and even future quantum computers.

New approach improves accuracy of quantum chemistry simulations using machine learning

A new trick for modeling molecules with quantum accuracy takes a step toward revealing the equation at the center of a popular simulation approach, which is used in fundamental chemistry and materials science studies.

The effort to understand materials and eats up roughly a third of national lab supercomputer time in the U.S. The gold standard for accuracy is the quantum many-body problem, which can tell you what’s happening at the level of individual electrons. This is the key to chemical and material behaviors as electrons are responsible for chemical reactivity and bonds, electrical properties and more. However, quantum many-body calculations are so difficult that scientists can only use them to calculate atoms and molecules with a handful of electrons at a time.

Density functional theory, or DFT, is easier—the computing resources needed for its calculations scale with the number of electrons cubed, rather than rising exponentially with each new electron. Instead of following each individual electron, this theory calculates electron densities—where the electrons are most likely to be located in space. In this way, it can be used to simulate the behavior of many hundreds of atoms.

Plasmon effects in neutron star magnetospheres could pose new limits on the detection of axions

Dark matter is an elusive type of matter that does not emit, reflect or absorb light, yet is predicted to account for most of the universe’s mass. As it cannot be detected and studied using conventional experimental techniques, the nature and composition of dark matter have not yet been uncovered.

One of the most promising candidates (i.e., hypothetical particles that dark matter could be made of) are axions. Theory suggests that axions could convert into light particles (i.e., photons) under specific conditions, which could in turn generate signals that can be picked up by sophisticated equipment.

In , such as those surrounding neutron stars with large magnetic fields (i.e., magnetars), the conversion of axions into photons has been predicted to generate weak radio signals that could be detected using powerful Earth-based or space-based radio telescopes.

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