In theoretical physics, massive gravity is a theory of gravity that modifies general relativity by endowing the graviton with a nonzero mass. In the classical theory, this means that gravitational waves obey a massive wave equation and hence travel at speeds below the speed of light.
Massive gravity has a long and winding history, dating back to the 1930s when Wolfgang Pauli and Markus Fierz first developed a theory of a massive spin-2 field propagating on a flat spacetimebackground. It was later realized in the 1970s that theories of a massive graviton suffered from dangerous pathologies, including a ghost mode and a discontinuity with general relativity in the limit where the graviton mass goes to zero. While solutions to these problems had existed for some time in three spacetime dimensions,[1][2] they were not solved in four dimensions and higher until the work of Claudia de Rham, Gregory Gabadadze, and Andrew Tolley (dRGT model) in 2010.
One of the very early massive gravity theories was constructed in 1965 by Ogievetsky and Polubarinov (OP).[3] Despite the fact that the OP model coincides with the ghost-free massive gravity models rediscovered in dRGT, the OP model has been almost unknown among contemporary physicists who work on massive gravity, perhaps because the strategy followed in that model was quite different from what is generally adopted at present.[4] Massive dual gravity to the OP model[5] can be obtained by coupling the dual graviton field to the curl of its own energy-momentum tensor.[6][7] Since the mixed symmetric field strength of dual gravity is comparable to the totally symmetric extrinsic curvature tensor of the Galileons theory, the effective Lagrangian of the dual model in 4-D can be obtained from the Faddeev–LeVerrier recursion, which is similar to that of Galileon theory up to the terms containing polynomials of the trace of the field strength.[8][9] This is also manifested in the dual formulation of Galileon theory.[10][11]
The fact that general relativity is modified at large distances in massive gravity provides a possible explanation for the accelerated expansion of the Universe that does not require any dark energy. Massive gravity and its extensions, such as bimetric gravity,[12] can yield cosmological solutions which do in fact display late-time acceleration in agreement with observations.[13][14][15]
Observations of gravitational waves have constrained the Compton wavelength of the graviton to be λg > 1.6×1016 m, which can be interpreted as a bound on the graviton mass mg < 7.7×10−23 eV/c2.[16] Competitive bounds on the mass of the graviton have also been obtained from solar system measurements by space missions such as Cassini and MESSENGER, which instead give the constraint λg > 1.83×1016 m or mg < 6.76×10−23 eV/c2.[17]
https://en.wikipedia.org/wiki/Massive_gravity#The_Boulware-Deser_ghost
https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_universe
https://en.wikipedia.org/wiki/Dark_energy
https://en.wikipedia.org/wiki/Dark_matter
https://en.wikipedia.org/wiki/Dark_flow
https://en.wikipedia.org/wiki/Dark_fluid
https://en.wikipedia.org/wiki/Topology
https://en.wikipedia.org/wiki/Negative_mass
https://en.wikipedia.org/wiki/Pressure#Negative_pressures
https://en.wikipedia.org/wiki/Cavitation
https://en.wikipedia.org/wiki/Observable_universe#Large-scale_structure
https://en.wikipedia.org/wiki/Cold_dark_matter
https://en.wikipedia.org/wiki/Weakly_interacting_massive_particles
Obtaining the correct abundance of dark matter today via thermal production requires a self-annihilation cross section of , which is roughly what is expected for a new particle in the 100 GeV mass range that interacts via the electroweak force.
WIMP-like particles are predicted by R-parity-conserving supersymmetry, a popular type of extension to the Standard Model of particle physics, although none of the large number of new particles in supersymmetry have been observed.[6] WIMP-like particles are also predicted by universal extra dimension and little Higgs theories.
| Model | parity | candidate |
|---|---|---|
| SUSY | R-parity | lightest supersymmetric particle (LSP) |
| UED | KK-parity | lightest Kaluza-Klein particle (LKP) |
| little Higgs | T-parity | lightest T-odd particle (LTP) |
The main theoretical characteristics of a WIMP are:
- Interactions only through the weak nuclear force and gravity, or possibly other interactions with cross-sections no higher than the weak scale;[7]
- Large mass compared to standard particles (WIMPs with sub-GeV masses may be considered to be light dark matter).
Because of their lack of electromagnetic interaction with normal matter, WIMPs would be invisible through normal electromagnetic observations. Because of their large mass, they would be relatively slow moving and therefore "cold".[8] Their relatively low velocities would be insufficient to overcome the mutual gravitational attraction, and as a result, WIMPs would tend to clump together.[9] WIMPs are considered one of the main candidates for cold dark matter, the others being massive compact halo objects (MACHOs) and axions. (These names were deliberately chosen for contrast, with MACHOs named later than WIMPs.[10]) Also, in contrast to MACHOs, there are no known stable particles within the Standard Model of particle physics that have all the properties of WIMPs. The particles that have little interaction with normal matter, such as neutrinos, are all very light, and hence would be fast moving, or "hot".
https://en.wikipedia.org/wiki/Weakly_interacting_massive_particles
https://en.wikipedia.org/wiki/Carbon_disulfide
Observations of the large-scale structure of the universe show that matter is aggregated into very large structures that have not had time to form under the force of their own self-gravitation. It is generally believed that some form of missing mass is responsible for increasing the gravitational force at these scales, although this mass has not been directly observed. This is a problem; normal matter in space will heat up until it gives off light, so if this missing mass exists, it is generally assumed to be in a form that is not commonly observed on earth.
https://en.wikipedia.org/wiki/Cryogenic_Dark_Matter_Search
https://en.wikipedia.org/wiki/Scintillator
The axion (/ˈæksiÉ’n/) is a hypothetical elementary particle postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interest as a possible component of cold dark matter.
https://en.wikipedia.org/wiki/Axion
Because dark matter has not yet been observed directly, if it exists, it must barely interact with ordinary baryonic matter and radiation, except through gravity. Most dark matter is thought to be non-baryonic in nature; it may be composed of some as-yet undiscovered subatomic particles.[b] The primary candidate for dark matter is some new kind of elementary particle that has not yet been discovered, in particular, weakly interacting massive particles(WIMPs).[14] Many experiments to directly detect and study dark matter particles are being actively undertaken, but none have yet succeeded.[15] Dark matter is classified as "cold", "warm", or "hot" according to its velocity (more precisely, its free streaming length). Current models favor a cold dark matterscenario, in which structures emerge by gradual accumulation of particles.
https://en.wikipedia.org/wiki/Dark_matter
Forward used the properties of negative-mass matter to create the concept of diametric drive, a design for spacecraft propulsion using negative mass that requires no energy input and no reaction mass to achieve arbitrarily high acceleration.
Forward also coined a term, "nullification", to describe what happens when ordinary matter and negative matter meet: they are expected to be able to cancel out or nullify each other's existence. An interaction between equal quantities of positive mass matter (hence of positive energy E = mc2) and negative mass matter (of negative energy −E = −mc2) would release no energy, but because the only configuration of such particles that has zero momentum (both particles moving with the same velocity in the same direction) does not produce a collision, such interactions would leave a surplus of momentum.
https://en.wikipedia.org/wiki/Negative_mass
https://en.wikipedia.org/wiki/Antimatter
https://en.wikipedia.org/wiki/Mirror_matter
https://en.wikipedia.org/wiki/Effective_mass_(spring–mass_system)
https://en.wikipedia.org/wiki/Lambda-CDM_model
https://en.wikipedia.org/wiki/Negative_mass
https://en.wikipedia.org/wiki/Linear_induction_accelerator
https://en.wikipedia.org/wiki/Angular_acceleration
https://en.wikipedia.org/wiki/0
https://en.wikipedia.org/wiki/Magnetic_scalar_potential
https://en.wikipedia.org/wiki/Accelerator_physics
https://en.wikipedia.org/wiki/Pyrolytic_carbon
https://en.wikipedia.org/wiki/Bismuth
https://en.wikipedia.org/wiki/Hyperloop
https://en.wikipedia.org/wiki/Electrodynamic_suspension#Levitation_melting
https://en.wikipedia.org/wiki/Aerodynamic_levitation
https://en.wikipedia.org/wiki/Electrostatic_levitation
Magnetic levitation
https://en.wikipedia.org/wiki/Launch_loop
https://en.wikipedia.org/wiki/Synchronous_motor
https://en.wikipedia.org/wiki/Linear_stage
https://en.wikipedia.org/wiki/Skew-symmetric_matrix
- Supramolecular chemistry
- 09-18-2021-0806 - Spiro compounds
- https://en.wikipedia.org/wiki/Compressible_flow
- https://en.wikipedia.org/wiki/Shear_rate
https://en.wikipedia.org/wiki/Hyperfine_structure
- https://en.wikipedia.org/wiki/Void_(astronomy)
https://en.wikipedia.org/wiki/Quintessence_(physics)
https://en.wikipedia.org/wiki/Scalar_field
https://en.wikipedia.org/wiki/Symmetric_matrix
https://en.wikipedia.org/wiki/Quadrupole
https://en.wikipedia.org/wiki/Vector_field
https://en.wikipedia.org/wiki/Preon
https://en.wikipedia.org/wiki/Pressuron
https://en.wikipedia.org/wiki/Spinor
Hyperfine Structure
Qubit in ion-trap quantum computing[edit]
The hyperfine states of a trapped ion are commonly used for storing qubits in ion-trap quantum computing. They have the advantage of having very long lifetimes, experimentally exceeding ~10 minutes (compared to ~1 s for metastable electronic levels).
The frequency associated with the states' energy separation is in the microwave region, making it possible to drive hyperfine transitions using microwave radiation. However, at present no emitter is available that can be focused to address a particular ion from a sequence. Instead, a pair of laser pulses can be used to drive the transition, by having their frequency difference (detuning) equal to the required transition's frequency. This is essentially a stimulated Raman transition. In addition, near-field gradients have been exploited to individually address two ions separated by approximately 4.3 micrometers directly with microwave radiation.[16]
See also[edit]
https://en.wikipedia.org/wiki/Hyperfine_structure
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