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Dark matter might cause fundamental constants to change over time

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dark matter_1The fundamental constants of nature—such as the speed of light, Planck’s constant, and Newton’s gravitational constant—are thought to be constant in time, as their name suggests. But scientists have questioned this assumption as far back as 1937, when Paul Dirac hypothesized that Newton’s gravitational constant might decrease over time.

Now in a new paper published in Physical Review Letters, Yevgeny V. Stadnik and Victor V. Flambaum at the University of New South Wales in Sydney, Australia, have theoretically shown that dark matter can cause the fundamental constants of nature to slowly evolve as well as oscillate due to oscillations in the dark matter field. This idea requires that the weakly interacting dark matter particles be able to interact a small amount with standard model particles, which the scientists show is possible.
In their paper, the scientists considered a model in which dark matter is made of weakly interacting, low-mass particles. In the early Universe, according to the model, large numbers of such dark matter particles formed an oscillating field. Because these particles interact so weakly with standard model particles, they could have survived for billions of years and still exist today, forming what we know as dark matter.
Although these low-mass dark matter particles are weakly interacting, they are thought to still interact with standard model particles to some extent, but it’s unclear exactly how much. By using data from experiments that have measured the amount of helium produced during big bang nucleosynthesis, as well as measurements of the rare element dysprosium and the cosmic microwave background, Stadnik and Flambaum have derived the most stringent limits to date on how strongly such dark matter particles interact with photons, electrons, and light quarks, improving on existing constraints by up to 15 orders of magnitude.
The new limits on the dark matter interaction strength allow for the possibility that an oscillating, low-mass dark matter field coupled to standard model particles causes variations in the fundamental constants. As the scientists explain, this could have important implications for understanding life’s origins.
“The fundamental constants are ‘fine-tuned’ to be consistent with the existence of life in the Universe,” Stadnik told Phys.org. “If the physical constants were even slightly different, life could not have appeared. The discovery of varying fundamental ‘constants’ may help shed important light on how the physical constants came to have their life-sustaining values today. We simply appeared in an area of the Universe where they are consistent with our existence.”
Whether or not the fundamental constants actually do vary due to dark matter is still an open question, but the scientists hope that future experiments with atomic clocks, laser interferometers, and other devices may help test out the new idea.
“We have shown that linking dark matter and variation of the fundamental constants of Nature leads to a major breakthrough in the sensitivity of dark matter searches,” Flambaum said. “We plan to continue searching for other novel signatures of dark matter that may lead to the direct detection of dark matter for the first time.”

Read more at: phys.org – arxiv.org

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November 19, 2015 at 8:56 pm

Posted in COSMOLOGY, DARK MATTER

Dark matter may power supernovae

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Stellar explosions known as type Ia supernovae could be triggered by dark matter. So says a physicist in the US, who has worked out how certain burnt-out stars can explode even though they lack the mass to generate fusion reactions. According to the new research, the stars ignite because they accumulate so-called asymmetric dark matter, which, if real, could be detectable in a new generation of earthbound experiments.
Asymmetric dark matter, like familiar visible matter, would come in both matter and antimatter varieties. It was proposed on the basis that the density of dark matter in the universe today, as revealed by its gravitational interactions, is only about five times that of normal matter. In cosmological terms, the two matter densities are almost identical, and this suggests a common link between visible and dark matter. That being a very slight imbalance between matter and antimatter, which, following mutual annihilation in the early universe, resulted in the densities observed today.
This similarity does not apply to the current favourite dark-matter particles – weakly interacting massive particles (WIMPs) – which are their own antiparticles and could not have undergone a lopsided annihilation.

In the latest work [Dark matter ignition of type Ia supernovae], Joseph Bramante of the University of Notre Dame in Indiana looked for evidence of asymmetric dark matter in observations of type Ia supernovae, the “standard candles” that showed the universe’s expansion to be accelerating. Such supernovae are thought to be generated by white dwarfs, the very dense burnt-out remnants of Sun-like stars. Normally, white dwarfs are not massive enough to compress to the point where their internal temperature allows fusion reactions to take place. But astrophysicists believe they can accumulate additional mass by sucking material from nearby stars. They would eventually reach the “Chandrasekhar limit” of about 1.4 solar masses, at which point they would collapse and then blow apart as a result of an explosive burst of fusion energy.
…. Read more at physicsworld.com

 

 

Written by physicsgg

October 7, 2015 at 7:05 pm

LHC results for dark matter from ATLAS and CMS

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The ATLAS and CMS DM searches covered a huge range of final states during the first data-taking run of the LHC looking for signs of WIMP production. Although observation is consistent with SM background expectation, stringent limits have been set on different benchmark models, emphasising the complementarity of collider searches and direct detection searches. Collider searches can powerfully constraint the low DM-mass region where the direct detection experiments suffer a lack of sensitivity.
However the current benchmark models employed to describe the DM-SM interaction suffer of validity limitations in the high-energy regime. Thus a different choice will be performed for Run-II making use of simplified models which explicitly define the mediator particle, providing a more fair description of the interaction itself, and overcoming Effective Field Theory approach limitations.
Read more at http://arxiv.org/pdf/1510.01516v1.pdf

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October 7, 2015 at 1:13 pm

Posted in DARK MATTER, High Energy Physics

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XENON1T will join the hunt for dark matter this autumn

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The XENON1T detector being assembled within the large tank that holds it deep underground. (Courtesy: Elena Aprile/XENON1T)

The XENON1T detector being assembled within the large tank that holds it deep underground. (Courtesy: Elena Aprile/XENON1T)

The hunt for dark matter will gain a more-than-an-order-of-magnitude boost in detection sensitivity when the next-generation XENON1T detector achieves first light this autumn. The challenges of constructing the world’s largest direct-detection dark-matter experiment and the scientific prospects for the future were presented by project spokesperson Elena Aprile of Columbia University, US, at the April Meeting of the American Physical Society in Maryland last weekend.
The XENON experiment began 10 years ago with XENON10, a 25 kg tank of liquid xenon deep under a mountain at the Gran Sasso National Laboratory in Italy. XENON100 followed in 2008 with 161 kg of liquid xenon and more than a hundred times the sensitivity of its predecessor. As the latest iteration, XENON1T is far more than a “second generation” detector – it contains 3300 kg of xenon and another hundred times the sensitivity of XENON100. Read the rest of this entry »

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May 1, 2015 at 5:24 pm

The dark side of cosmology: Dark matter and dark energy

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The multiple components that compose our universe. Dark energy comprises 69% of the mass energy density of the universe, dark matter comprises 25%, and “ordinary” atomic matter makes up 5%. There are other observable subdominant components: Three different types of neutrinos comprise at least 0.1%, the cosmic background radiation makes up 0.01%, and black holes comprise at least 0.005%.

The multiple components that compose our universe.
Dark energy comprises 69% of the mass energy density of the universe, dark matter comprises 25%, and “ordinary” atomic matter makes up 5%. There are other observable subdominant components: Three different types of neutrinos comprise at least 0.1%, the cosmic background radiation makes up 0.01%, and black holes comprise at least 0.005%.

A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of “dark matter,” a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of “dark energy,” energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales…
…Read more at http://www.sciencemag.org/content/347/6226/1100.full

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March 6, 2015 at 5:58 pm

Revealing the Nature of Dark Matter

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Dr. Dan Hooper, a Theoretical Astrophysicist at Fermilab, explores the current status of the dark matter search and some new thoughts on the nature of this mystery.
A signal of gamma rays has been observed from the center of the Milky Way, and it may be the breakthrough that we have long been waiting for. If these gamma-rays are in fact being produced by the interactions of dark matter particles, they promise to reveal much about this elusive substance, and may be a major step toward identifying of the underlying nature of our universe’s dark matter.

Written by physicsgg

February 12, 2015 at 5:56 pm

Posted in DARK MATTER

New calculations support dark-matter discovery by DAMA

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A controversial claim by the DAMA group that it has detected dark matter in an underground lab in Italy might turn out to be true after all, according to physicists in Europe and the US. The new research reconciles the claimed detection with apparently null results from other experiments, as well as indirect astrophysical evidence. It proposes that dark matter interacts with ordinary matter not via one of the four known fundamental forces but instead through a fifth force mediated by an axion-like particle.

Dark matter is an as-yet-unknown substance that does not emit electromagnetic radiation but which numerous observations suggest makes up at least 80% of the matter in the universe. DAMA, a collaboration of physicists from Italy and China, says it has directly observed dark matter in a sodium-iodide detector located beneath Gran Sasso mountain east of Rome. The basis for its claim is a seasonal variation in the number of tiny flashes of light that should occur when dark matter collides with nuclei in the detector. The group argues that this variation – which peaks in June and has a minimum in December – is just what would be expected as the Earth moves through a “halo” of dark matter surrounding the Milky Way. Read the rest of this entry »

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January 12, 2015 at 9:34 pm

Posted in DARK MATTER

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Physicists suggest new way to detect dark matter

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Associate professor Chris Kouvaris from the University of Southern Denmark. Credit: University of Southern Denmark

Associate professor Chris Kouvaris from the University of Southern Denmark. Credit: University of Southern Denmark

For years physicists have been looking for the universe’s elusive dark matter, but so far no one has seen any trace of it. Maybe we are looking in the wrong place? Now physicists from University of Southern Denmark propose a new technique to detect dark matter.
The universe consists of atoms and particles – and a whole lot more that still needs to be detected. We can only speculate about the existence of this unknown matter and energy. Read the rest of this entry »

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November 19, 2014 at 10:21 pm