Many physicists believe that dark matter is made up of some particle yet to be discovered. But despite years of effort, WIMPs have so far not shown up in experiments designed to detect them. An alternative to the WIMP model of dark matter calls for a form of "dark electromagnetism" including "dark photons" and other particles. Dark photons would have some weak coupling with "regular" photons.
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In their new paper, Terning and postdoctoral researcher Christopher Verhaaren add a twist to this idea: a dark magnetic "monopole" that would interact with the dark photon. In the macroscopic world, magnets always have two poles, north and south. A monopole is a particle that acts like one end of a magnet. Monopoles are predicted by quantum theory, but have never been observed in an experiment.
The scientists suggest that dark monopoles would interact with dark photons and dark electrons in the same way that theory predicts electrons and photons interact with monopoles. And that implies a way to detect these dark particles.
The physicist Paul Dirac predicted that an electron moving in a circle near a monopole would pick up a change of phase in its wave function. Because electrons exist as both particles and waves in quantum theory, the same electron could pass on either side of the monopole and as a result be slightly out of phase on the other side. This interference pattern, called the Aharonov-Bohm effect, means that an electron passing around a magnetic field is influenced by it, even if it does not pass through the field itself.
Terning and Verhaaren argue that you could detect a dark monopole because of the way it shifts the phase of electrons as they pass by. Electron beams are relatively easy to come by: electron microscopes were used to demonstrate the Aharonov-Bohm effect in the s, and electron beam technology has improved with time, Terning noted. Theoretically, dark matter particles are streaming through us all the time. To be detectable in Terning and Verhaaren's model, the monopoles would have to be excited by the Sun. Then they would take about a month to reach Earth, traveling at about a thousandth of the speed of light.
On the other hand, the predicted phase shift is extremely small -- smaller than that needed to detect gravity waves, for example. However, Terning noted that when the LIGO gravity wave experiment was first proposed, the technology to make it work did not exist -- instead, technology caught up over time. Scientists believe that it is made up of exotic particles unlike the normal baryonic matter, which we, the Earth, Sun and stars are made of, and it is invisible so it has only been inferred from its gravitational effects.
The XENON detector ran from January to June for its first run, and in their paper on arxiv, the team revealed they found three candidate events that might be due to Dark Matter. But two of these were expected to appear anyway because of background noise, the team said, so their results are effectively negative. Not necessarily — the team will keep working on their search. Plus, results from a preliminary analysis from Sources: EurekAlert, physicsworld. Trying to understand the warping of space and time is something like visualizing a scene from Alice in Wonderland where rooms can change sizes and locations.
The most-used description of the warping of space-time is how a heavy object deforms a stretched elastic sheet. But new conceptual tools that combines theory and computer simulations are providing a better way to for scientists to visualize what takes place when gravity from an object or event changes the fabric of space.
Researchers at Caltech, Cornell University, and the National Institute for Theoretical Physics in South Africa developed conceptual tools that they call tendex lines and vortex lines which represent gravitation waves. The researchers say that tendex and vortex lines describe the gravitational forces caused by warped space-time and are analogous to the electric and magnetic field lines that describe electric and magnetic forces.
Vortex lines, on the other hand, describe the twisting of space. They tried out the tools specifically on computer simulated black hole collisions, and saw that such impacts would produce doughnut-shaped vortex lines that fly away from the merged black hole like smoke rings. The researchers also found that a bundle of vortex lines spiral out of the black hole like water from a rotating sprinkler.
Depending on the angles and speeds of the collisions, the vortex and tendex lines — or gravitational waves — would behave differently. Geoffrey Lovelace, a member of the team from Cornell. The researchers say the tendex and vortex lines provide a powerful new way to understand the nature of the universe. Their paper has been published in the April 11 in the Physical Review Letters.
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If verified, this could re-write particle physics as we know it. Physicists try to identify the particles they see by studying the combinations of more-familiar particles into which they decay, while trying to find new particles, such as the theoretical Higgs Boson which is predicted by the Standard Model of particle physics. The Standard Model contains a description of the elementary particles and forces inside atoms which make up everything around us. The model has been successful at making predictions that have been subsequently verified. There are sixteen named particles in the Standard Model, and the last particles discovered were the W and Z bosons in , the top quark in , and the tauon neutrino in But most physicists agree the Standard Model is probably not the final word in particle physics.
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Instead, they saw about events which indicate a new particle weighing about times as much as a proton, the team said at the webcast from Fermilab and in their paper on arXiv. The researchers estimate the statistical chances of random jets or jet pairs from other sources producing a fake signal that strong at 1 in The Standard Model does not predict anything like what was seen in the CDF experiment, and since this particle has not been seen before and appears to have some strange properties, the physicists want to verify and retest before claiming a discovery.
The Tevatron accelerator at Fermilab is scheduled to be shut down later this year, due to lack of funding and because of sentiments that it would be redundant to the Large Hadron Collider. Cosmic Variance. Science News. Quantum gravity theories may have more to say. By extending general relativity into a quantized structure for space-time, maybe we can bridge the gap between small and large scale physics.
With conventional special relativity, two different inertial frames of reference may measure the speed of the same object differently. So, if you are on a train and throw a tennis ball forward, you might measure it moving at 10 kilometers an hour. Give or take a few nanometers per second, you are both correct. It works out that for the person on the platform, the components of speed distance and time are changed on the train so that distances are contracted and time dilated i.
And by the math of Lorenz transformations , these effects become more obvious the faster than train goes. Now, doubly special relativity, proposes that not only is the speed of light always the same regardless of your frame of reference, but Planck units of mass and energy are also always the same.
This means that relativistic effects like mass appearing to increase on the train do not occur at the Planck i. Doubly special relativity might also be generalized towards a theory of quantum gravity — which, when extended up from the Planck scale, should deliver results indistinguishable from general relativity. And at the Planck scale, a Planck mass is 2. To put it another way, at the Planck scale, gravity becomes a significant force in quantum physics. Although really, all we are saying that is that there is one Planck unit of gravitational force between two Planck masses when separated by a Planck length — and by the way, a Planck length is the distance that light moves within one unit of Planck time!
And since one Planck unit of energy 1. It all sounds terribly exciting, but this line of thinking has been criticized as being just a trick to make the math work better, by removing important information about the physical systems under consideration. Nonetheless, since even the Large Hadron Collider is not expected to deliver direct evidence about what may or may not happen at the Planck scale — for now, making the math work better does seem to be the best way forward.
Further reading: Zhang et al.
The effective Planck mass and the scale of inflation
Gravitational waves are apparently devilishly difficult things to model with Einstein field equations, since they are highly dynamic and non-symmetric. Traditionally, the only way to get close to predicting the likely effects of gravity waves was to estimate the required Einstein equation parameters by assuming the objects causing the gravity waves did not generate strong gravity fields themselves — and nor did they move at velocities anywhere close to the speed of light.
Trouble is, the mostly likely candidate objects that might generate detectable gravity waves — close binary neutron stars and merging black holes — have exactly those properties. They are highly compact, very massive bodies that often move at relativistic i. Hence a recent paper titled: On the unreasonable effectiveness of post-Newtonian approximation in gravitational physics. So, firstly no-one has yet detected gravity waves.
But even in , Einstein considered their existence likely and demonstrated mathematically that gravitational radiation should arise when you replace a spherical mass with a rotating dumbbell of the same mass which, due to its geometry, will generate dynamic ebb and flow effects on space-time as it rotates. However, as well as sensitive detection equipment like LISA, you also need to calculate what sort of phenomena and what sort of data would represent definitive evidence of a gravity wave — which is where all the theory and math required to determine these expected values is vital. Initially, theoreticians worked out a post-Newtonian i.
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Einstein era approximation i. Then came the era of numerical relativity where the advent of supercomputers made it possible to actually model all the dynamics of close massive binaries moving at relativistic speeds, much as how supercomputers can model very dynamic weather systems on Earth.
Surprisingly, or if you like unreasonably , the calculated values from numerical relativity were almost identical to those calculated by the supposedly bodgy post-Newtonian approximation.
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