![]() ![]() This dramatically improves the odds of an interaction. But just as a long, slow wave would pick up the whole patch of debris at once, a low-energy neutrino sees the entire atomic nucleus as one “coherent” whole. Similarly, a high-energy neutrino typically picks out individual protons and neutrons with which to interact. When such narrow waves pass under floating debris, they can pick out one leaf or twig at a time to toss around. The high-energy neutrinos sought by most experiments are like short, choppy ocean waves. CEvNS relies on the quantum mechanical equivalence between particles and waves, comparable to ocean waves. The new experimental collaboration, known as COHERENT, instead looks for a phenomenon called CEvNS (pronounced “sevens”), or coherent elastic neutrino-nucleus scattering. Physicists must compensate by offering thousands of tons of atoms for passing neutrinos to strike. Because the weak force operates only at subatomic distances, the odds of a tiny neutrino bouncing off of an individual neutron or proton are minuscule. But neutrinos deign to communicate with other particles only via the “weak” force-the fundamental force that causes radioactive materials to decay. Under previous approaches, a neutrino reveals itself by stumbling across a proton or neutron amidst the vast emptiness surrounding atomic nuclei, producing a flash of light or a single-atom chemical change. Their feat paves the way for new supernova research, dark matter searches and even nuclear nonproliferation monitoring. But in a study published today in Science, researchers working at Oak Ridge National Laboratory (ORNL) detected never-before-seen neutrino interactions using a detector the size of a fire extinguisher. ![]() That rarity has made life miserable for physicists, who resort to building huge underground detector tanks for a chance at catching the odd neutrino. Among the hundred trillion neutrinos that pass through you every second, only about one per week actually grazes a particle in your body. Of all the characters in the particle physics cast, they are the most reluctant to interact with other particles. ![]() To survive, the most plausible modification for MOND may be an additional degree of dynamical freedom in a covariant incarnation.Neutrinos are famously antisocial. The phase-space densities derived from lensing observations are inconsistent with neutrino masses ranging from 2-7eV, and hence do not support the 2eV-range particles required by MOND. Here, we show for the first time that a combination of strong and weak gravitational lensing effects can set interesting limits on the phase-space density of dark matter in the centres of clusters. Gravitational lensing allows us to estimate the enclosed mass in clusters on small (~20-50kpc) and large (~several 100kpc) scales independent of the assumptions of equilibrium. Both Modified Newtonian Dynamics (MOND) and General Relativity (GR) would require similar amounts of non-baryonic matter in clusters as MOND boosts the gravity only mildly on cluster scales. ![]() Clusters of galaxies offer a robust test bed for probing the nature of dark matter that is insensitive to the assumption of the gravity theories. ![]()
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