Tagged: Axions Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 1:16 pm on July 12, 2017 Permalink | Reply
    Tags: Axions, , HAYSTAC - Haloscope at Yale Sensitive To Axion Cold Dark Matter, , ,   

    From Yale: “Needle in a HAYSTAC” 

    Yale University bloc

    Yale University

    July 5, 2017
    Elizabeth Ruddy

    1
    No image caption or credit.

    Imagine searching for a needle in a haystack. The needle weighs about 100 billion times less than an electron and has no charge. It acts like a wave rather than a particle, and the haystack is the size of our universe. Needles like this may exist in the tens of trillions in every cubic centimeter of space—the trick is proving that they’re there.

    That is the mission of the HAYSTAC Project at Yale, which stands for the Haloscope at Yale Sensitive To Axion Cold Dark Matter. HAYSTAC is a collaboration between Yale University, University of California, Berkeley and University of Colorado, Boulder. The project is based here in the Wright Laboratory, lead by Professor Steve Lamoreaux and a team of Yale scientists and graduate students. The scientists began their project about five years ago and released their first results this past February in The Physics Review Letters. The first author was Yale graduate student Ben Brubaker.

    “The goals of the experiment are to detect dark matter, or failing that, to at least rule out some possible models for what dark matter is,” explained Brubaker. “In simplest terms, dark matter started out as an astrophysics question: that is, there is more mass in the universe than can be accounted for by the mass we can see [through] all the wavelengths we can detect: visible light, radio waves, ultraviolet.” Dark matter is the “invisible” matter.

    The HAYSTAC project is dedicated specifically to the detection of the axion, a subatomic particle that was proposed in 1983 as a likely candidate for dark matter. Like the aforementioned needle, axions are theorized to have almost miniscule mass, no charge, and no spin. Based on the gravitational movement of stars and galaxies, we know that 80 percent of the matter in our universe is dark matter, but axions interact with other matter so weakly they become almost impossible to detect. Because they are so light, they have very little energy and behave more like waves than particles. As a result, the scientists must employ an unusual identification strategy to find them.

    2
    The HAYSTAC axion detector probes the universe for axions, a potential candidate for dark matter. No image credit.

    The HAYSTAC detection device essentially produces a magnetic field that converts the axions to photons. The frequency of oscillation of the photons is determined by the mass of the axion. Therefore, when the detector is tuned in to one specific frequency at a time, it can amplify these oscillations to make them detectable.

    “Our detector is in essence a tunable radio receiver, and we painstakingly tune the receiving frequency looking for an increase in noise. It is like driving through a desert looking for a station on the car radio: you tune slowly in hopes of finding something,” said Professor Lamoreaux, the head of the project.

    In the February report, the team demonstrated its recent breakthroughs in design: they had achieved sufficient sensitivity to test out much higher frequencies in the potential mass range than ever before. By incorporating technology from other fields such as quantum electronics, Lamoreaux and his colleagues have made the detector colder and quieter than any of its contemporaries, eliminating as much of the background noise as possible. According to Brubaker, the device is kept at about 0.1 degree Celsius above absolute zero, the unattainable temperature at which atoms physically stop moving. Freezing temperatures are critical for sensitivity because a major source of noise is thermal radiation: photons being shed by matter and interfering with the detection of axions.

    According to Professor Lamoreaux, their detector is currently the most sensitive radio receiver ever built. “Imagine a match lit on the surface of the Moon…the rate of energy entering the pupil of your eye, when the match is viewed from the Earth, is about the level of sensitivity we achieve.”

    The size of the detector scales inversely with the mass range being tested, so the Wright Lab instrument will only be able to search a small portion of the wide range of possible dark matter masses. However, the team has proven they have a design with the sensitivity capability necessary to perform these sweeps. Their design is a pioneering model for the future.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Yale University Campus

    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

    Advertisements
     
  • richardmitnick 5:00 pm on June 13, 2017 Permalink | Reply
    Tags: A different kind of dark matter could help to resolve an old celestial conundrum, Axions, , , , , , Dark matter superfluid, Dark matter vortices, , Kent Ford, , ,   

    From Quanta: “Dark Matter Recipe Calls for One Part Superfluid” 

    Quanta Magazine
    Quanta Magazine

    June 13, 2017
    Jennifer Ouellette

    A different kind of dark matter could help to resolve an old celestial conundrum.

    1
    Markos Kay for Quanta Magazine

    For years, dark matter has been behaving badly. The term was first invoked nearly 80 years ago by the astronomer Fritz Zwicky, who realized that some unseen gravitational force was needed to stop individual galaxies from escaping giant galaxy clusters. Later, Vera Rubin and Kent Ford used unseen dark matter to explain why galaxies themselves don’t fly apart.

    Yet even though we use the term “dark matter” to describe these two situations, it’s not clear that the same kind of stuff is at work. The simplest and most popular model holds that dark matter is made of weakly interacting particles that move about slowly under the force of gravity. This so-called “cold” dark matter accurately describes large-scale structures like galaxy clusters. However, it doesn’t do a great job at predicting the rotation curves of individual galaxies. Dark matter seems to act differently at this scale.

    In the latest effort to resolve this conundrum, two physicists have proposed that dark matter is capable of changing phases at different size scales. Justin Khoury, a physicist at the University of Pennsylvania, and his former postdoc Lasha Berezhiani, who is now at Princeton University, say that in the cold, dense environment of the galactic halo, dark matter condenses into a superfluid — an exotic quantum state of matter that has zero viscosity. If dark matter forms a superfluid at the galactic scale, it could give rise to a new force that would account for the observations that don’t fit the cold dark matter model. Yet at the scale of galaxy clusters, the special conditions required for a superfluid state to form don’t exist; here, dark matter behaves like conventional cold dark matter.

    “It’s a neat idea,” said Tim Tait, a particle physicist at the University of California, Irvine. “You get to have two different kinds of dark matter described by one thing.” And that neat idea may soon be testable. Although other physicists have toyed with similar ideas, Khoury and Berezhiani are nearing the point where they can extract testable predictions that would allow astronomers to explore whether our galaxy is swimming in a superfluid sea.

    Impossible Superfluids

    Here on Earth, superfluids aren’t exactly commonplace. But physicists have been cooking them up in their labs since 1938. Cool down particles to sufficiently low temperatures and their quantum nature will start to emerge. Their matter waves will spread out and overlap with one other, eventually coordinating themselves to behave as if they were one big “superatom.” They will become coherent, much like the light particles in a laser all have the same energy and vibrate as one. These days even undergraduates create so-called Bose-Einstein condensates (BECs) in the lab, many of which can be classified as superfluids.

    Superfluids don’t exist in the everyday world — it’s too warm for the necessary quantum effects to hold sway. Because of that, “probably ten years ago, people would have balked at this idea and just said ‘this is impossible,’” said Tait. But recently, more physicists have warmed to the possibility of superfluid phases forming naturally in the extreme conditions of space. Superfluids may exist inside neutron stars, and some researchers have speculated that space-time itself may be a superfluid. So why shouldn’t dark matter have a superfluid phase, too?

    To make a superfluid out of a collection of particles, you need to do two things: Pack the particles together at very high densities and cool them down to extremely low temperatures. In the lab, physicists (or undergraduates) confine the particles in an electromagnetic trap, then zap them with lasers to remove the kinetic energy and lower the temperature to just above absolute zero.

    2
    Lucy Reading-Ikkanda/Quanta Magazine

    The dark matter particles that would make Khoury and Berezhiani’s idea work are emphatically not WIMP-like. WIMPs should be pretty massive as fundamental particles go — about as massive as 100 protons, give or take. For Khoury’s scenario to work, the dark matter particle would have to be a billion times less massive. Consequently, there should be billions of times as many of them zipping through the universe — enough to account for the observed effects of dark matter and to achieve the dense packing required for a superfluid to form. In addition, ordinary WIMPs don’t interact with one another. Dark matter superfluid particles would require strongly interacting particles.

    The closest candidate is the axion, a hypothetical ultralight particle with a mass that could be 10,000 trillion trillion times as small as the mass of the electron. According to Chanda Prescod-Weinstein, a theoretical physicist at the University of Washington, axions could theoretically condense into something like a Bose-Einstein condensate.

    But the standard axion doesn’t quite fit Khoury and Berezhiani’s needs. In their model, particles would need to experience a strong, repulsive interaction with one another. Typical axion models have interactions that are both weak and attractive. That said, “I think everyone thinks that dark matter probably does interact with itself at some level,” said Tait. It’s just a matter of determining whether that interaction is weak or strong.

    Cosmic Superfluid Searches

    The next step for Khoury and Berezhiani is to figure out how to test their model — to find a telltale signature that could distinguish this superfluid concept from ordinary cold dark matter. One possibility: dark matter vortices. In the lab, rotating superfluids give rise to swirling vortices that keep going without ever losing energy. Superfluid dark matter halos in a galaxy should rotate sufficiently fast to also produce arrays of vortices. If the vortices were massive enough, it would be possible to detect them directly.

    Inside galaxies, the role of the electromagnetic trap would be played by the galaxy’s gravitational pull, which could squeeze dark matter together enough to satisfy the density requirement. The temperature requirement is easier: Space, after all, is naturally cold.

    Outside of the “halos” found in the immediate vicinity of galaxies, the pull of gravity is weaker, and dark matter wouldn’t be packed together tightly enough to go into its superfluid state. It would act as dark matter ordinarily does, explaining what astronomers see at larger scales.

    But what’s so special about having dark matter be a superfluid? How can this special state change the way that dark matter appears to behave? A number of researchers over the years have played with similar ideas. But Khoury’s approach is unique because it shows how the superfluid could give rise to an extra force.

    In physics, if you disturb a field, you’ll often create a wave. Shake some electrons — for instance, in an antenna — and you’ll disturb an electric field and get radio waves. Wiggle the gravitational field with two colliding black holes and you’ll create gravitational waves. Likewise, if you poke a superfluid, you’ll produce phonons — sound waves in the superfluid itself. These phonons give rise to an extra force in addition to gravity, one that’s analogous to the electrostatic force between charged particles. “It’s nice because you have an additional force on top of gravity, but it really is intrinsically linked to dark matter,” said Khoury. “It’s a property of the dark matter medium that gives rise to this force.” The extra force would be enough to explain the puzzling behavior of dark matter inside galactic halos.

    A Different Dark Matter Particle

    Dark matter hunters have been at work for a long time. Their efforts have focused on so-called weakly interacting massive particles, or WIMPs. WIMPs have been popular because not only would the particles account for the majority of astrophysical observations, they pop out naturally from hypothesized extensions of the Standard Model of particle physics.

    Yet no one has ever seen a WIMP, and those hypothesized extensions of the Standard Model haven’t shown up in experiments either, much to physicists’ disappointment.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    With each new null result, the prospects dim even more, and physicists are increasingly considering other dark matter candidates. “At what point do we decide that we’ve been barking up the wrong tree?” said Stacy McGaugh, an astronomer at Case Western Reserve University.

    Unfortunately, this is unlikely to be the case: Khoury’s most recent computer simulations suggest that vortices in the dark matter superfluid would be “pretty flimsy,” he said, and unlikely to offer researchers clear-cut evidence that they exist. He speculates it might be possible to exploit the phenomenon of gravitational lensing to see if there are any scattering effects, similar to how a crystal will scatter X-ray light that passes through it.

    Gravitational Lensing NASA/ESA

    Astronomers could also search for indirect evidence that dark matter behaves like a superfluid. Here, they’d look to galactic mergers.

    The rate that galaxies collide with one another is influenced by something called dynamical friction. Imagine a massive body passing through a sea of particles. Many of the small particles will get pulled along by the massive body. And since the total momentum of the system can’t change, the massive body must slow down a bit to compensate.

    That’s what happens when two galaxies start to merge. If they get sufficiently close, their dark matter halos will start to pass through each other, and the rearrangement of the independently moving particles will give rise to dynamical friction, pulling the halos even closer. The effect helps galaxies to merge, and works to increase the rate of galactic mergers across the universe.

    But if the dark matter halo is in a superfluid phase, the particles move in sync. There would be no friction pulling the galaxies together, so it would be more difficult for them to merge. This should leave behind a telltale pattern: rippling interference patterns in how matter is distributed in the galaxies.

    Perfectly Reasonable Miracles

    While McGaugh is mostly positive about the notion of superfluid dark matter, he confesses to a niggling worry that in trying so hard to combine the best of both worlds, physicists might be creating what he terms a “Tycho Brahe solution.” The 16th-century Danish astronomer invented a hybrid cosmology in which the Earth was at the center of the universe but all the other planets orbited the sun. It attempted to split the difference between the ancient Ptolemaic system and the Copernican cosmology that would eventually replace it. “I worry a little that these kinds of efforts are in that vein, that maybe we’re missing something more fundamental,” said McGaugh. “But I still think we have to explore these ideas.”

    Tait admires this new superfluid model intellectually, but he would like to see the theory fleshed out more at the microscopic level, to a point where “we can really calculate everything and show why it all works out the way it’s supposed to. At some level, what we’re doing now is invoking a few miracles” in order to get everything to fit into place, he said. “Maybe they’re perfectly reasonable miracles, but I’m not fully convinced yet.”

    One potential sticking point is that Khoury and Berezhiani’s concept requires a very specific kind of particle that acts like a superfluid in just the right regime, because the kind of extra force produced in their model depends upon the specific properties of the superfluid. They are on the hunt for an existing superfluid — one created in the lab — with those desired properties. “If you could find such a system in nature, it would be amazing,” said Khoury, since this would essentially provide a useful analog for further exploration. “You could in principle simulate the properties of galaxies using cold atoms in the lab to mimic how superfluid dark matter behaves.”

    While researchers have been playing with superfluids for many decades, particle physicists are only just beginning to appreciate the usefulness of some of the ideas coming from subjects like condensed matter physics. Combining tools from those disciplines and applying it to gravitational physics might just resolve the longstanding dispute on dark matter — and who knows what other breakthroughs might await?

    “Do I need superfluid models? Physics isn’t really about what I need,” said Prescod-Weinstein. “It’s about what the universe may be doing. It may be naturally forming Bose-Einstein condensates, just like masers naturally form in the Orion nebula. Do I need lasers in space? No, but they’re pretty cool.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 4:44 pm on May 19, 2017 Permalink | Reply
    Tags: , Axions, , , ,   

    From CERN Courier: “CAST experiment constrains solar axions” 

    CERN Courier
    May 19, 2017

    CERN CAST Axion Solar Telescope

    2
    Two-photon coupling constraints

    In a paper published in Nature Physics, the CERN Axion Solar Telescope (CAST) has reported important new exclusion limits on coupling of axions to photons. Axions are hypothetical particles that interact very weakly with ordinary matter and therefore are candidates to explain dark matter. They were postulated decades ago to solve the “strong CP” problem in the Standard Model (SM), which concerns an unexpected time-reversal symmetry of the nuclear forces. Axion-like particles, unrelated to the strong-CP problem but still viable dark-matter candidates, are also predicted by several theories of physics beyond the SM, notably string theory.

    A variety of Earth- and space-based observatories are searching possible locations where axions could be produced, ranging from the inner Earth to the galactic centre and right back to the Big Bang. CAST looks for solar axions using a “helioscope” constructed from a test magnet originally built for the Large Hadron Collider. The 10 m-long superconducting magnet acts like a viewing tube and is pointed directly at the Sun: solar axions entering the tube would be converted by its strong magnetic field into X-ray photons, which would be detected at either end of the magnet. Starting in 2003, the CAST helioscope, mounted on a movable platform and aligned with the Sun with a precision of about 1/100th of a degree, has tracked the movement of the Sun for an hour and a half at dawn and an hour and a half at dusk, over several months each year.

    In the latest work, based on data recorded between 2012 and 2015, CAST finds no evidence for solar axions. This has allowed the collaboration to set the best limits to date on the strength of the coupling between axions and photons for all possible axion masses to which CAST is sensitive. The limits concern a part of the axion parameter space that is still favoured by current theoretical predictions and is very difficult to explore experimentally, allowing CAST to encroach on more restrictive constraints set by astrophysical observations. “Even though we have not been able to observe the ubiquitous axion yet, CAST has surpassed even the sensitivity originally expected, thanks to CERN’s support and unrelenting work by CASTers,” says CAST spokesperson Konstantin Zioutas. “CAST’s results are still a point of reference in our field.”

    The experience gained by CAST over the past 15 years will help physicists to define the detection technologies suitable for a proposed, much larger, next-generation axion helioscope called IAXO. Since 2015, CAST has also broadened its research at the low-energy frontier to include searches for dark-matter axions and candidates for dark energy, such as solar chameleons.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

     
  • richardmitnick 8:13 am on May 2, 2017 Permalink | Reply
    Tags: , Axions, , CAST-CERN Axion Solar Telescope, , Helioscope, , ,   

    From CERN: “CERN CASTs new limits on dark matter” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    1 May 2017
    Stefania Pandolfi

    1
    CAST, CERN’s axion solar telescope, moves on its rail to follow the Sun (Image: Max Brice/CERN)

    In a paper published today in Nature Physics, the CAST experiment at CERN presented new results on the properties of axions – hypothetical particles that would interact very weakly with ordinary matter and therefore could explain the mysterious dark matter that appears to make up most of the matter in the universe.

    Axions were postulated by theorists decades ago, initially to solve an important issue in the Standard Model of particle physics related to the differences between matter and antimatter. The particle was named after a brand of washing detergent, since its existence would allow the theory to be “cleaned up”.

    A variety of Earth- and space-based observatories are searching possible locations where axions could be produced, ranging from the inner Earth to the galactic centre and right back to the Big Bang.

    The CERN Axion Solar Telescope (CAST) experiment is looking for axions from the sun using a special telescope called a helioscope constructed from a test magnet originally built for the Large Hadron Collider. The 10-metre-long superconducting magnet acts like a viewing tube and is pointed directly at the sun: any solar axions entering the tube would be converted by its strong magnetic field into X-ray photons, which would be detected at either end of the magnet by specialised detectors. Since 2003, the CAST helioscope, mounted on a movable platform, has tracked the movement of the sun for an hour and a half at dawn and an hour and a half at dusk, over several months each year. The detector is aligned with the sun with a precision of about one hundredth of a degree.

    In the paper published today, based on data recorded between 2012 and 2015, CAST finds no evidence for solar axions. This has allowed the collaboration to set the best limits to date on the strength of the coupling between axions and photons for all possible axion masses to which CAST is sensitive. “The limits concern a part of the axion parameter space that is still favoured by current theoretical predictions and is very difficult to explore experimentally,” explains the deputy spokesperson for CAST, Igor Garcia Irastorza. “For the first time, we have been able to set limits that are similar to the more restrictive constraints set by astrophysical observations,” he says.

    Since 2015, CAST has broadened its research at the low-energy frontier to include searches for other weakly-interacting particles from the dark energy sector, such as “solar chameleons”. The experience gained by CAST over the past 15 years will also help physicists define the detection technologies suitable for a proposed, much larger, next-generation axion helioscope called IAXO.

    “Even though we have not been able to observe the ubiquitous axion yet, CAST has surpassed even the sensitivity originally expected, thanks to CERN’s support and unrelenting work by CASTers,” says CAST spokesperson Konstantin Zioutas. “CAST’s results are still a point of reference in our field.”

    See the full article here.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    CernCourier
    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 1:31 pm on March 28, 2017 Permalink | Reply
    Tags: Axions, , , , , , SUPERRADIANCE   

    From PI via GIZMODO: “Mind-Blowing New Theory Connects Black Holes, Dark Matter, and Gravitational Waves” 

    Perimeter Institute
    Perimeter Institute

    GIZMODO

    3.28.17
    Ryan F. Mandelbaum

    The past few years have been incredible for physics discoveries. Scientists spotted the Higgs boson, a particle they’d been hunting for almost 50 years, in 2012, and gravitational waves, which were theorized 100 years ago, in 2016. This year, they’re slated to take a picture of a black hole. So, thought some theorists, why not combine all of the craziest physics ideas into one, a physics turducken? What if we, say, try to spot the dark matter radiating off of black holes through their gravitational waves?

    It’s really not that strange of an idea. Now that scientists have detected gravitational waves, ripples in spacetime spawned by the most violent physical events, they want to use their discovery to make real physics observations. They think they have a way to spot all-new particles that might make up dark matter, an unknown substance that accounts for over 80 percent of all of the gravity in the universe.

    The basic idea is that we’re trying to use black holes… the densest, most compact objects in the universe, to search for new kinds of particles,” Masha Baryakhtar, postdoctoral researcher at the Perimeter Institute for Theoretical Physics in Canada, told Gizmodo. Especially one particle: “The axion. People have been looking for it for 40 years.”

    Black holes are the universe’s sinkholes, so strong that light can’t escape their pull once it’s entered. They’ve got such powerful gravitational fields that they produce gravitational waves when they collide with each other. Dark matter might not be made from particles (specks of mass and energy), but if it was, we might observe it as axions, particles around one quintillion (a billion billion) times lighter than an electron, hanging around black holes. Now that you understand all the terms, here’s how the theory works.

    Baryakhtar and her teammates think that black holes are more than just bear traps for light, but nuclei at the center of a sort of gravitational atom. The axions would be the electrons, so to speak. If you already know about black holes, you know they have incredibly hot, high-energy discs of gas orbiting them, produced by the friction between particles accelerated by the black hole’s gravity. This theory ignores that stuff, since axions wouldn’t interact via friction.

    Keeping with the atom analogy, the axions can jump around the black hole, gaining and losing energy the same way that electrons do. But electrons interact via electromagnetism, so they let out electromagnetic waves, or light waves. Axions interact via gravity, so they let out gravitational waves. But like I said earlier, axions are tiny. Unlike a tiny atom, the black hole in these “gravity atoms” rotates, supercharging the space around it and coaxing it into producing more axions. Despite the axion’s tiny mass, this so-called superradiance process could generate 10^80 axions, the same number of atoms in the entire universe, around a single black hole. Are you still with me? Crazy spinning blob makes lots of crazy stuff.

    Craziest of all, we should be able to hear a gravitational wave hum from these axions moving around and releasing gravitational waves in our detectors, similar to the way you see spectral lines coming off of electrons in atoms in chemistry class. “You’d see this at a particular frequency which would be roughly twice the axion mass,” said Baryakhtar.

    There are giant gravitational wave detectors scattered around the world; presently there’s one called LIGO (Laser Interferometer Gravitational Wave Observatory) in Washington State, another LIGO in Louisiana, and one called Virgo in Italy that are sensitive enough to detect gravitational waves, and with upgrades, to detect axions and prove their theory right.



    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA



    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Scientists would essentially need to record data, play it back, and tune their analysis like a radio to pick up the signal at just the right frequency.

    There are other ways the team thinks it could spot this superradiance effect, by measuring the spins in sets of colliding black holes. If black holes really do produce axions, scientists would see very few quickly-spinning black holes in collisions, since the superradiance effects would slow down some of the colliding black holes and create a visible effect in the data, according to the research published this month in the journal Physical Review D. The black hole spins would have a specific pattern which we should be able to spot in the gravitational wave detector data.

    Other scientists were immediately excited about this paper. “I’m always super excited about new ways to detect my favorite pet particle, the axion! Also, SUPERRADIANCE!” Dr. Chanda Prescod-Weinstein, the University of Washington axion wrangler, told Gizmodo in an email. “It’s so cool, and I haven’t read a paper that talked about [superradiance] in years. So it was really fun to see superradiance and axions in one paper.”

    There are a few drawbacks, as there are with any theory. These theorized black hole atoms would have to produce axions of a certain mass, but that mass isn’t an ideal one for the axion to be a dark matter particle, said Prescod-Weinstein. Plus, the second detection idea, the one that looks at the spin rate of colliding black holes, might not work. “They say [in the paper] that they don’t take into account the potential influence of another black hole” in the colliding pair, Dr. Lionel London, a research associate at Cardiff University School of Physics and Astronomy specializing in gravitational wave modeling, told Gizmodo. “If this does turn out to be a significant effect and they’re not including it, this could cast doubt on their results.” But there’s hope. “There’s good reason to believe the effect of a companion [black hole] won’t be large.”

    When would we spot these kinds of events? As of now, the LIGO and Virgo gravitational wave detectors probably aren’t ready. “With the current sensitivity we’re on the edge” of detecting axions, said Baryakhtar. “But LIGO will continue improving their instruments and at design sensitivity we might be able to see as many as 1000s of these axion signals coming in,” she said. Thousands of hums from these black hole-atoms.

    So, if you’ve gotten all the way to this point of the story and still don’t understand what’s going on, a recap: We’ve got these gravitational wave detectors that cost hundreds of millions of dollars each, that are good at spotting really crazy things going on in the universe. Theorists have come up with an interesting way to use them to solve one of the most important interstellar mysteries: What the heck is dark matter? As with most new ideas in theoretical physics, this is something cool to think about and isn’t ready for the big time… yet.

    “I think that timescale is always a concern, but we’re just getting started with LIGO discoveries,” said Prescod-Weinstein. “So who knows what’s around the corner over the next 10 years.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Perimeter

    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

     
  • richardmitnick 7:18 pm on February 24, 2017 Permalink | Reply
    Tags: Axions, ,   

    From Science: “Spinning black holes could fling off clouds of dark matter particles” 

    ScienceMag
    Science Magazine

    Feb. 22, 2017
    Adrian Cho

    1

    A spinning black hole (white) should produce huge clouds of particles called axions (blue), which would then produce detectable gravitational waves, a new calculation predicts. Masha Baryakhtar

    Few things are more mind bending than black holes, gravitational waves, and the nearly massless hypothetical particles called axions, which could be the mysterious dark matter whose gravity holds galaxies together. Now, a team of theoretical physicists has tied all three together in a surprising way. If the axion exists and has the right mass, they argue, then a spinning black hole should produce a vast cloud of the particles, which should, in turn, produce gravitational waves akin to those discovered a year ago by the Laser Interferometer Gravitational-Wave Observatory (LIGO). If the idea is correct, LIGO might be able to detect axions, albeit indirectly.

    “It’s an awesome idea,” says Tracy Slatyer, a particle astrophysicist at the Massachusetts Institute of Technology (MIT) in Cambridge, who was not involved in the work. “The [LIGO] data is going to be there, and it would be amazing if we saw something.” Benjamin Safdi, a theoretical particle physicist at MIT, is also enthusiastic. “This is really the best idea we have to look for particles in this mass range,” he says.

    A black hole is the intense gravitational field left behind when a massive star burns out and collapses to a point. Within a certain distance of that point—which defines the black hole’s “event horizon”—gravity grows so strong that not even light can escape. In September 2015, LIGO detected a burst of ripples in space called gravitational waves that emanated from the merging of two black holes.

    The axion—if it exists—is an uncharged particle perhaps a billionth as massive as the electron or lighter. Dreamed up in the 1970s, it helps explain a curious mathematical symmetry in the theory of particles called quarks and gluons that make up protons and neutrons. Axions floating around might also be the dark matter that’s thought to make up 85% of all matter in the universe. Particle physicists are searching for axions in experiments that try to convert them into photons using magnetic fields.

    But it may be possible to detect axions by studying black holes with LIGO and its twin detectors in Louisiana and Washington states, argue Asimina Arvanitaki and Masha Baryakhtar, theorists at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, and their colleagues.

    If its mass is in the right range, then an axion stuck in orbit around a black hole should be subject to a process called superradiance that occurs in many situations and causes photons to multiply in a certain type of laser. If an axion strays near, but doesn’t cross, a black hole’s event horizon, then the black hole’s spin will give the axion a boost in energy. And because the axion is a quantum particle with some properties like those of the photon, that boost will create more axions, which will, in turn, interact with the black hole in the same way. The runaway process should thus generate vast numbers of the particles.

    But for this to take place, a key condition has to be met. A quantum particle like the axion can also act like a wave, with lighter particles having longer wavelengths. For superradiance to kick in, the axion’s wavelength must be as long as the black hole is wide. So the axion’s mass must be extremely light: between 1/10,000,000 and 1/10,000 the range probed in current laboratory experiments. The axions wouldn’t just emerge willy-nilly, either, but would crowd into huge quantum waves like the orbitals of the electrons in an atom. As fantastical as that sounds, the basic physics of superradiance is well established, Safdi says.

    The axion cloud might reveal itself in multiple ways, Baryakhtar says. Most promising, axions colliding in the cloud should annihilate one another to produce gravitons, the particles thought to make up gravitational waves just as photons make up light. Emerging from orderly quantum clouds, the gravitons would form continuous waves with a frequency set by the axion’s mass. LIGO would be able to spot thousands of such sources per year [Physical Review D], Baryakhtar and colleagues estimate in a paper published 8 February in Physical Review D—although tracking those continuous signals may be harder than detecting bursts from colliding black holes. Spotting multiple same-frequency sources would be a “smoking gun” for axions, Slatyer says.

    The axion clouds could produce indirect signals, too. In principle, a black hole can spin at near light speed. However, generating axions would sap a black hole’s angular momentum and slow it. As a result, LIGO should observe that the spins of colliding black holes never reach that ultimate speed, but top out well below it, Baryakhtar says. Detecting that limit on spin would be challenging, as LIGO can measure a colliding black hole’s spin with only 25% precision.

    Safdi cautions that the analysis assumes that LIGO will see lots of black-hole mergers and will perform as expected. And if LIGO doesn’t see the signals, it won’t rule out the axion, he says. Still, he says, “This is probably the most promising paper I’ve seen so far on the new physics we might probe with gravitational waves.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 1:47 pm on November 2, 2016 Permalink | Reply
    Tags: Axions, , , , , , that if axions do make up the bulk of dark matter   

    From phys.org- “Supercomputer comes up with a profile of dark matter: Standard Model extension predicts properties of candidate particle” 

    physdotorg
    phys.org

    November 2, 2016

    2
    Simulated distribution of dark matter approximately three billion years after the Big Bang (illustration not from this work). Credit: The Virgo Consortium/Alexandre Amblard/ESA

    In the search for the mysterious dark matter, physicists have used elaborate computer calculations to come up with an outline of the particles of this unknown form of matter. To do this, the scientists extended the successful Standard Model of particle physics which allowed them, among other things, to predict the mass of so-called axions, promising candidates for dark matter. The German-Hungarian team of researchers led by Professor Zoltán Fodor of the University of Wuppertal, Eötvös University in Budapest and Forschungszentrum Jülich carried out its calculations on

    “Dark matter is an invisible form of matter which until now has only revealed itself through its gravitational effects. What it consists of remains a complete mystery,” explains co-author Dr Andreas Ringwald, who is based at DESY and who proposed the current research. Evidence for the existence of this form of matter comes, among other things, from the astrophysical observation of galaxies, which rotate far too rapidly to be held together only by the gravitational pull of the visible matter. High-precision measurements using the European satellite “Planck” show that almost 85 percent of the entire mass of the universe consists of dark matter. All the stars, planets, nebulae and other objects in space that are made of conventional matter account for no more than 15 percent of the mass of the universe.

    “The adjective ‘dark’ does not simply mean that it does not emit visible light,” says Ringwald. “It does not appear to give off any other wavelengths either – its interaction with photons must be very weak indeed.” For decades, physicists have been searching for particles of this new type of matter. What is clear is that these particles must lie beyond the Standard Model of particle physics, and while that model is extremely successful, it currently only describes the conventional 15 percent of all matter in the cosmos. From theoretically possible extensions to the Standard Model physicists not only expect a deeper understanding of the universe, but also concrete clues in what energy range it is particularly worthwhile looking for dark-matter candidates.

    The unknown form of matter can either consist of comparatively few, but very heavy particles, or of a large number of light ones. The direct searches for heavy dark-matter candidates using large detectors in underground laboratories and the indirect search for them using large particle accelerators are still going on, but have not turned up any dark matter particles so far. A range of physical considerations make extremely light particles, dubbed axions, very promising candidates. Using clever experimental setups, it might even be possible to detect direct evidence of them. “However, to find this kind of evidence it would be extremely helpful to know what kind of mass we are looking for,” emphasises theoretical physicist Ringwald. “Otherwise the search could take decades, because one would have to scan far too large a range.”

    The existence of axions is predicted by an extension to quantum chromodynamics (QCD), the quantum theory that governs the strong interaction, responsible for the nuclear force. The strong interaction is one of the four fundamental forces of nature alongside gravitation, electromagnetism and the weak nuclear force, which is responsible for radioactivity. “Theoretical considerations indicate that there are so-called topological quantum fluctuations in quantum chromodynamics, which ought to result in an observable violation of time reversal symmetry,” explains Ringwald. This means that certain processes should differ depending on whether they are running forwards or backwards. However, no experiment has so far managed to demonstrate this effect.

    The extension to quantum chromodynamics (QCD) restores the invariance of time reversals, but at the same time it predicts the existence of a very weakly interacting particle, the axion, whose properties, in particular its mass, depend on the strength of the topological quantum fluctuations. However, it takes modern supercomputers like Jülich’s JUQUEEN to calculate the latter in the temperature range that is relevant in predicting the relative contribution of axions to the matter making up the universe. “On top of this, we had to develop new methods of analysis in order to achieve the required temperature range,” notes Fodor who led the research.

    The results show, among other things, that if axions do make up the bulk of dark matter, they should have a mass of 50 to 1500 micro-electronvolts, expressed in the customary units of particle physics, and thus be up to ten billion times lighter than electrons. This would require every cubic centimetre of the universe to contain on average ten million such ultra-lightweight particles. Dark matter is not spread out evenly in the universe, however, but forms clumps and branches of a weblike network. Because of this, our local region of the Milky Way should contain about one trillion axions per cubic centimetre.

    Thanks to the Jülich supercomputer, the calculations now provide physicists with a concrete range in which their search for axions is likely to be most promising. “The results we are presenting will probably lead to a race to discover these particles,” says Fodor. Their discovery would not only solve the problem of dark matter in the universe, but at the same time answer the question why the strong interaction is so surprisingly symmetrical with respect to time reversal. The scientists expect that it will be possible within the next few years to either confirm or rule out the existence of axions experimentally.

    The Institute for Nuclear Research of the Hungarian Academy of Sciences in Debrecen, the Lendület Lattice Gauge Theory Research Group at the Eötvös University, the University of Zaragoza in Spain, and the Max Planck Institute for Physics in Munich were also involved in the research.

    S. Borsanyi et al, Calculation of the axion mass based on high-temperature lattice quantum chromodynamics, Nature (2016). DOI: 10.1038/nature20115

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page. set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 7:45 am on July 23, 2016 Permalink | Reply
    Tags: Asimina Arvanitaki, Axions, , , , ,   

    From Quanta: Women in Science – “Mining Black Hole Collisions for New Physics” Asimina Arvanitaki 

    Quanta Magazine
    Quanta Magazine

    July 21, 2016
    Joshua Sokol

    1
    Asimina Arvanitaki during a July visit to the CERN particle physics laboratory in Geneva, Switzerland. Samuel Rubio for Quanta Magazine

    When physicists announced in February that they had detected gravitational waves firsthand, the foundations of physics scarcely rattled. The signal exactly matched the expectations physicists had arrived at after a century of tinkering with Einstein’s theory of general relativity. “There is a question: Can you do fundamental physics with it? Can you do things beyond the standard model with it?” said Savas Dimopoulos, a theoretical physicist at Stanford University. “And most people think the answer to that is no.”

    Asimina Arvanitaki is not one of those people. A theoretical physicist at Ontario’s Perimeter Institute of Theoretical Physics, Arvanitaki has been dreaming up ways to use black holes to explore nature’s fundamental particles and forces since 2010, when she published a paper with Dimopoulos, her mentor from graduate school, and others. Together, they sketched out a “string axiverse,” a pantheon of as yet undiscovered, weakly interacting particles. Axions such as these have long been a favored candidate to explain dark matter and other mysteries.

    In the intervening years, Arvanitaki and her colleagues have developed the idea through successive papers. But February’s announcement marked a turning point, where it all started to seem possible to test these ideas. Studying gravitational waves from the newfound population of merging black holes would allow physicists to search for those axions, since the axions would bind to black holes in what Arvanitaki describes as a “black hole atom.”

    “When it came up, we were like, ‘Oh my god, we’re going to do it now, we’re going to look for this,’” she said. “It’s a whole different ball game if you actually have data.”

    That’s Arvanitaki’s knack: matching what she calls “well-motivated,” field-hopping theoretical ideas with the precise experiment that could probe them. “By thinking away from what people are used to thinking about, you see that there is low-hanging fruit that lie in the interfaces,” she said. At the end of April, she was named the Stavros Niarchos Foundation’s Aristarchus Chair at the Perimeter Institute, the first woman to hold a research chair there.

    It’s a long way to come for someone raised in the small Grecian village of Koklas, where the graduating class at her high school — at which both of her parents taught — consisted of nine students. Quanta Magazine spoke with Arvanitaki about her plan to use black holes as particle detectors. An edited and condensed version of those discussions follows.

    QUANTA MAGZINE: When did you start to think that black holes might be good places to look for axions?

    ASIMINA ARVANITAKI: When we were writing the axiverse paper, Nemanja Kaloper, a physicist who is very good in general relativity, came and told us, “Hey, did you know there is this effect in general relativity called superradiance?” And we’re like, “No, this cannot be, I don’t think this happens. This cannot happen for a realistic system. You must be wrong.” And then he eventually convinced us that this could be possible, and then we spent like a year figuring out the dynamics.

    What is superradiance, and how does it work?

    An astrophysical black hole can rotate. There is a region around it called the “ergo region” where even light has to rotate. Imagine I take a piece of matter and throw it in a trajectory that goes through the ergo region. Now imagine you have some explosives in the matter, and it breaks apart into pieces. Part of it falls into the black hole and part escapes into infinity. The piece that is coming out has more total energy than the piece that went in the black hole.

    You can perform the same experiment by scattering radiation from a black hole. Take an electromagnetic wave pulse, scatter it from the black hole, and you see that the pulse you got back has a higher amplitude.

    So you can send a pulse of light near a black hole in such a way that it would take some energy and angular momentum from the black hole’s spin?

    This is old news, by the way, this is very old news. In ’72 Press and Teukolsky wrote a Nature paper that suggested the following cute thing. Let’s imagine you performed the same experiment as the light, but now imagine that you have the black hole surrounded by a giant mirror. What will happen in that case is the light will bounce on the mirror many times, the amplitude [of the light] grows exponentially, and the mirror eventually explodes due to radiation pressure. They called it the black hole bomb.

    The property that allows light to do this is that light is made of photons, and photons are bosons — particles that can sit in the same space at the same time with the same wave function. Now imagine that you have another boson that has a mass. It can [orbit] the black hole. The particle’s mass acts like a mirror, because it confines the particle in the vicinity of the black hole.

    In this way, axions might get stuck around a black hole?

    This process requires that the size of the particle is comparable to the black hole size. Turns out that [axion] mass can be anywhere from Hubble scale — with a quantum wavelength as big as the universe — or you could have a particle that’s tiny in size.

    So if they exist, axions can bind to black holes with a similar size and mass. What’s next?

    What happens is the number of particles in this bound orbit starts growing exponentially. At the same time the black hole spins down. If you solve for the wave functions of the bound orbits, what you find is that they look like hydrogen wave functions. Instead of electromagnetism binding your atom, what’s binding it is gravity. There are three quantum numbers you can describe, just the same. You can use the exact terminology that you can use in the hydrogen atom.

    How could we check to see if any of the black holes LIGO finds have axion clouds orbiting around black hole nuclei?

    This is a process that extracts energy and angular momentum from the black hole. If you were to measure spin versus mass of black holes, you should see that in a certain mass range for black holes you see no quickly rotating black holes.

    This is where Advanced LIGO comes in.

    LSC LIGO Scientific Collaboration
    VIRGO Collaboration bloc

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    You saw the event they saw. [Their measurements] allowed them to measure the masses of the merging objects, the mass of the final object, the spin of the final object, and to have some information about the spins of the initial objects.

    If I were to take the spins of the black holes before they merged, they could have been affected by superradiance. Now imagine a graph of black hole spin versus mass. Advanced LIGO could maybe get, if the things that we hear are correct, a thousand events per year. Now you have a thousand data points on this plot. So you may trace out the region that is affected by this particle just by those measurements.

    That would be supercool.

    That’s of course indirect. So the other cool thing is that it turns out there are signatures that have to do with the cloud of particles themselves. And essentially what they do is turn the black hole into a gravitational wave laser.

    Awesome. OK, what does that mean?

    Yeah, what that means is important. Just like you have transitions of electrons in an excited atom, you can have transitions of particles in the gravitational wave atom. The rate of emission of gravitational waves from these transitions is enhanced by the 1080 particles that you have. It would look like a very monochromatic line. It wouldn’t look like a transient. Imagine something now that emits a signal at a very fixed frequency.

    Where could LIGO expect to see signals like this?

    In Advanced LIGO, you actually see the birth of a black hole. You know when and where a black hole was born with a certain mass and a certain spin. So if you know the particle masses that you’re looking for, you can predict when the black hole will start growing the [axion] cloud around it. It could be that you see a merger in that day, and one or 10 years down the line, they go back to the same position and they see this laser turning on, they see this monochromatic line coming out from the cloud.

    You can also do a blind search. Because you have black holes that are roaming the universe by themselves, and they could still have some leftover cloud around them, you can do a blind search for monochromatic gravitational waves.

    Were you surprised to find out that axions and black holes could combine to produce such a dramatic effect?

    Oh my god yes. What are you talking about? We had panic attacks. You know how many panic attacks we had saying that this effect, no, this cannot be true, this is too good to be true? So yes, it was a surprise.

    The experiments you suggest draw from a lot of different theoretical ideas — like how we could look for high-frequency gravitational waves with tabletop sensors, or test whether dark matter oscillates using atomic clocks. When you’re thinking about making risky bets on physics beyond the standard model, what sorts of theories seem worth the effort?

    What is well motivated? Things that are not: “What if you had this?” People imagine: “What if dark matter was this thing? What if dark matter was the other thing?” For example, supersymmetry makes predictions about what types of dark matter should be there. String theory makes predictions about what types of particles you should have. There is always an underlying reason why these particles are there; it’s not just the endless theoretical possibilities that we have.

    And axions fit that definition?

    This is a particle that was proposed 30 years ago to explain the smallness of the observed electric dipole moment of the neutron. There are several experiments around the world looking for it already, at different wavelengths. So this particle, we’ve been looking for it for 30 years. This can be the dark matter. That particle solves an outstanding problem of the standard model, so that makes it a good particle to look for.

    Now, whether or not the particle is there I cannot answer for nature. Nature will have to answer.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 10:42 am on March 25, 2015 Permalink | Reply
    Tags: Axions, , ,   

    From FNAL: “From the Center for Particle Astrophysics – Building a dark matter radio” 

    FNAL Home

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    1
    Craig Hogan, head of the Center for Particle Astrophysics, wrote this column.

    You may have heard lately that the famous cosmic dark matter — the mysterious new kind of stuff that makes up most of the gravitational mass of the universe — may not, in fact, be completely dark, but may actually emit small amounts of light. That would be very exciting, because we might detect the light and use it to help figure out what the stuff is made of.

    For example, the Fermi Gamma-Ray Space Telescope detects light, in the form of photons from the center of our galaxy, that may be caused by massive dark matter particles annihilating each other.

    NASA Fermi Telescope
    NASA/Fermi

    Such high-energy photons can be created if the individual dark matter particles themselves are massive— much more massive than any known stable particle.

    But it’s also possible that the dark matter particles have extraordinarily low mass — even smaller than the tiny masses associated with neutrinos. In that case, the light emitted by dark matter, if any, would not show up as high-energy gamma rays; instead, it would show up as radio waves. Indeed, even the dark matter itself acts more like a coherent oscillating wave field than a collection of individual particles. In this situation, the best way to search for them may not be a traditional particle detector but a receiver more like a radio.

    A leading candidate for this kind of dark matter is called an axion. The existence of such a field was predicted long ago, not from a need for dark matter, but as a way to explain why strong interactions (the quantum chromodynamics of the Standard Model that control the structure of atomic nuclei) do not appear to distinguish the past from the future as the other interactions do.

    2
    Standard Model of Particle Physics. The diagram shows the elementary particles of the Standard Model (the Higgs boson, the three generations of quarks and leptons, and the gauge bosons), including their names, masses, spins, charges, chiralities, and interactions with the strong, weak and electromagnetic forces. It also depicts the crucial role of the Higgs boson in electroweak symmetry breaking, and shows how the properties of the various particles differ in the (high-energy) symmetric phase (top) and the (low-energy) broken-symmetry phase (bottom).

    In standard cosmology, if such a particle has a low mass, roughly in the microwave range of radio frequencies, it could be produced in sufficient abundance to be some, or even all, of the cosmic dark matter.

    If so, we might find them in the laboratory. It turns out that if cosmic axions from our galaxy pass through a strong magnet, they give off a small amount of radio light at exactly the frequency corresponding to their tiny mass. To detect them, we want to build a radio tuned to that mass. The radio in this case uses a highly resonant cavity, similar to those that Fermilab uses all the time to accelerate particles. We don’t know the mass of the axion exactly, so to search for the axion, we have to tune the radio — the cavity — until we get a signal.

    The Axion Dark Matter Experiment has started a search like this at the University of Washington.

    ADMX Axion Dark Matter Experiment
    AXION DME
    Axion Dark Matter Experiment, U Washington

    (Because the experiment is not sensitive to cosmic rays, the actual apparatus does not have to be deep underground, but is on campus.) The tuning starts at low frequencies, searching for axions of relatively low mass, where it can use relatively large cavities. But there is a long way to go: Theory provides only a rough guess about the mass of the axion, and nobody yet knows exactly how to build smaller cavities that can efficiently search for higher-mass axions.

    Fermilab scientists and engineers are planning to make unique contributions to state-of-the-art higher-frequency cavity designs for the higher-mass search, drawing on their years of experience with radio-frequency cavities in accelerators. This unique fusion of accelerator science and dark matter science is an exciting example of the synergy that happens at Fermilab.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 7:04 pm on January 31, 2015 Permalink | Reply
    Tags: Axions, ,   

    From ars technica: “If dark matter is really axions, we could find out soon” 

    Ars Technica
    ars technica

    Jan 23 2015
    Xaq Rzetelny

    1
    Lawrence Livermore National Lab

    From observations of the Milky Way galaxy, we’ve learned that in any given cubic meter of space, even the particular cubic meter that snugly fits your seated form as you read this article, there’s a small amount of matter—only about 50 proton masses worth—passing through in any given moment. But unlike the particles that make up your seated form, this matter doesn’t interact. It doesn’t reflect light, it isn’t repelled by solid objects, it passes right through walls. This mysterious substance is known as dark matter.

    Since there’s so little of it in each cubic meter, you would never notice its presence. But over the vast distances of space, there’s a lot of cubic meters, and all that dark matter adds up. It’s only when you zoom out and look at the big picture that dark matter’s gravitational influence becomes apparent. It’s the main source of gravity holding every galaxy together; it binds galaxies to one another in clusters; and it warps space around galaxy clusters, creating a lensing effect.

    But despite its importance to the large-scale structure of the Universe, we still don’t know what dark matter really is. Currently, the best candidate is WIMPs, or Weakly Interacting Massive Particles (Which makes sense, now that we know it’s not MAssive Compact Halo Objects, or MACHOs). But WIMPs are not the only option—there are quite a few other possibilities being investigated. Some of them are other kinds of massive particles, which would constitute cold dark matter, while others aren’t particles at all.

    Axions, theoretical particles that were originally predicted to solve a tricky problem involving the strong nuclear force, happen to have just the right properties to be a good candidate for dark matter. Leslie Rosenberg, a physicist at the University of Washington, Seattle, recently wrote an overview of the experiments being done to investigate the possibility of axions being dark matter for the journal PNAS.

    Hot or Cold?

    Among the various models of dark matter, there are two overarching categories: Hot (HDM) and Cold Dark Matter (CDM). The hot variety gets its name because its particles would be whipping around at incredibly high speeds, up to significant fractions of the speed of light. But hot dark matter seems to be a dead end as a possibility. If particles were traveling that fast, most of them would be able to escape the gravitational pull of their host galaxy. Instead, dark matter forms into nice, spherical halos around every galaxy—which means that it’s probably cold.

    The physical difference between HDM and CDM is mass. If dark matter is composed of low-mass particles, then it would be easy for the particles to accelerate, and since the particles interact so little with other particles, it would be very hard to slow them down; hence the relativistic speeds of HDM. CDM, then, would have to be a higher-mass particle, because those aren’t as easy to accelerate. WIMPs would fall into this category.

    Axions, meanwhile, occupy a unique sort of middle ground between HDM and CDM. They are low-mass particles, low enough that they might have been HDM, except that they would have been slowed down gravitationally in the very early Universe. In effect, they now behave like CDM, moving slowly and thus potentially forming the dark matter halos we observe, even though they have the mass of HDM. Crucially, axions interact weakly enough with light and other matter that they fulfill the ‘dark’ part of dark matter.

    One advantage to axions as dark matter is that there’s only a very specific mass range of axions that would be consistent with the dark matter we observe. If the axions were much lighter or much heavier, they would produce observable differences—sufficiently observable that we would have already seen them. For example, the supernova explosion sn1987a would have lost energy as axions transported it out of the exploding star, which would have resulted in a noticeably different neutrino flash than the one recorded on Earth.

    1
    This image shows the remnant of Supernova 1987A seen in light of very different wavelengths. ALMA data (in red) shows newly formed dust in the centre of the remnant. Hubble (in green) and Chandra (in blue) data show the expanding shock wave

    ALMA Array
    ALMA

    NASA Hubble Telescope
    Hubble

    NASA Chandra Telescope
    Chandra

    That narrow range of possibilities makes the axion hypothesis very easy to conclusively test. Since it’s such a narrow range, a test that turns up negative could rule out axions as a possibility altogether. (They might still exist, but they would be ruled out as a dark matter candidate). And in science, testability makes a hypothesis very attractive (at least until the test rules out your favorite model).

    So how do we find it?

    Another advantage of axions is that they can spontaneously decay into things that might be observed. An axion can turn into two photons, and that light could hypothetically be detected. The reverse process, light turning into an axion, is also possible—and it may even play a role in the propagation of light. The light would briefly become an axion, which would then decay back into two photons, with the briefly-existing axion being considered a virtual axion.

    Another effect axions could have would be on the Sun—its seismic activity and energy output could be affected by the interactions of axions. And those Solar axions could scatter off a germanium crystal, producing X-rays that could be observed. Additionally, the dark matter axions in the halos around astronomical objects, like other galaxies, could spontaneously decay and produce photons that we might see in telescopes.

    Unfortunately, none of these tests are sensitive enough to detect the expected mass range of axions that would be dark matter. To find axions in the right range, there are a few methods that might work—and some of them are being tried in experiments right now.

    Astronomical axions

    Astronomical objects can provide an opportunity to observe axions. Supernovae should produce them (as noted above), as should other astronomical objects such as the Sun.

    In the core of the Sun, light scatters off of the particles it encounters there, bouncing around from particle to particle until its random path allows it to escape the Sun (some 170,000 years after the light was produced). As the light scatters in this process, it can be converted into an axion. That axion might then turn back into two photons while still inside the Sun. Since the axion was produced in the Sun’s hot core, the photons ultimately observed here on Earth would be in the form of X-rays. Alternatively, we could potentially detect the axions themselves, should they escape the Sun.

    But it would be difficult to distinguish whether the axions detected this way are dark matter or simply part of a normal physics process. More energetic events, like supernovae, would also fall short of producing unambiguously detectable dark matter axions.

    The best experiment using this method right now is the CERN Axion Solar Telescope. Using a dipole magnet from the Large Hadron Collider on a steerable mount, this device could achieve good sensitivity to axions escaping the Sun—but it’s just barely more sensitive to dark matter axions than observations of the supernova sn1987a were. So, while this experiment could not rule out axions by itself, it might further constrain the properties of axion dark matter.

    A more sensitive version is being conceived, however, which might provide better insight.

    Shining light through walls!

    Another technique with a chance of detecting dark matter axions is the “Shining light through walls” technique, which is just what it sounds like. (A name we didn’t make up, in case you were wondering). As we’ve seen, light can convert into axions and axions can be converted into light. So if researchers wanted to create axions in the lab, they might start with some light.

    By sending some polarized light through a dipole magnet, some of the light can be converted into axions.

    2
    Magnetic Field of a simple dipole bar magnet

    The axions would then be able to pass right through a wall, as though it weren’t there, and appear on the other side. If they encounter a second dipole magnet, it will convert the axions back into photons, which are then detected. To be fair, this isn’t a measurement of pre-existing axions, so it doesn’t demonstrate that the dark matter we’re observing is composed of axions—only that axions in the right mass range exist. But that by itself would provide a strong argument that dark matter is axions.

    The problem with this technique is that the process happens very infrequently—so infrequently that it would be very hard to tell such a light burst from the surrounding noise. As a result, the technique wouldn’t be sensitive enough to detect axions in the dark matter mass range.

    But there are some experiments being constructed that have addressed that problem by adding devices called Fabry-Perot optical resonators to both sides of the wall. This has the effect of increasing the number of photons that decay into axions and vice versa, which should make it a vastly stronger signal—strong enough to stand out from the noise. But despite the improvements, these experiments probably still won’t be sensitive enough to detect axion dark matter, though they might be able to find other forms of axions.

    Catching axions

    Another approach is known as the Radio Frequency (RF) technique. This relies on an axion’s ability to decay into light, and could allow researchers to catch one. Axions that are part of the Milky Way’s dark matter halo should be passing through the Earth at all times, putting them within reach. The only thing that’s needed is the right catcher’s mitt. Like other dark matter candidates, axions pass right through solid matter, so it’s tricky to devise a device to catch one. But unlike other dark matter candidates, axions might interact with a magnetic field. If so, the axion could be stimulated to decay into microwave photons. Those photons could then be detected.

    The catcher’s mitt, in this case, is a device called an RF cavity, a metal cylinder which serves as a resonator, keeping the electromagnetic waves it catches inside.

    This approach has been taken by the Axion Dark Matter eXperiment (ADMX).

    ADMX Axion Dark Matter Experiment
    ADMX

    That RF cavity device is four meters tall, but the actual cavity itself, the part where the axion’s photons will be caught, is only about half a meter tall, and surrounded by a powerful, wrap-around magnet. The main difficulty with this experiment, as with so many experiments in astronomy, is reducing noise. Axions that are part of the Milky Way’s halo should produce some extremely weak photons, which are very difficult to distinguish from the background noise.

    To deal with this issue, the ADMX device has recently been refitted, replacing its transistor amplifiers with Superconducting QUantum Interference Devices (SQUIDs). The SQUIDs are more effective at amplifying the signal of the microwave photons the device catches, helping them to stand out from the noise. The ADMX, enhanced with the SQUIDs, is sensitive enough that it should be able to detect axions from the Milky Way’s dark matter halo with a high degree of certainty. Over the next few years, this experiment could conclusively rule out axions as the identity of dark matter—or it could confirm this hypothesis.

    Conclusions

    The possibilities raised by these experiments—especially by ADMX—are exciting, as they represent clear progress toward solving the puzzle that is dark matter. And that’s no trivial puzzle, as an understanding of dark matter is important to our understandings of the Universe as a whole.

    But in science, things are often more complicated than they seem at first, as the author cautions in the paper. “it may be that the relation between axion mass and couplings is loosened. In such a case, there could well be surprises,” he writes. Nonetheless, he doesn’t downplay the potential significance of ADMX: “sensitivity to dark matter QCD axions has at last been achieved with the RF cavity technique, and we may know soon whether the dark matter is made of axions.”

    If dark matter does turn out to be axions, it will be good news in one sense at least: physicists will be able to directly detect and experiment with dark matter, a boon for cosmology. Considering that it’s not yet certain that dark matter interacts at all—and it would be essentially impossible to directly observe if it doesn’t—that would be good news indeed.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon
    Stem Education Coalition
    Ars Technica was founded in 1998 when Founder & Editor-in-Chief Ken Fisher announced his plans for starting a publication devoted to technology that would cater to what he called “alpha geeks”: technologists and IT professionals. Ken’s vision was to build a publication with a simple editorial mission: be “technically savvy, up-to-date, and more fun” than what was currently popular in the space. In the ensuing years, with formidable contributions by a unique editorial staff, Ars Technica became a trusted source for technology news, tech policy analysis, breakdowns of the latest scientific advancements, gadget reviews, software, hardware, and nearly everything else found in between layers of silicon.

    Ars Technica innovates by listening to its core readership. Readers have come to demand devotedness to accuracy and integrity, flanked by a willingness to leave each day’s meaningless, click-bait fodder by the wayside. The result is something unique: the unparalleled marriage of breadth and depth in technology journalism. By 2001, Ars Technica was regularly producing news reports, op-eds, and the like, but the company stood out from the competition by regularly providing long thought-pieces and in-depth explainers.

    And thanks to its readership, Ars Technica also accomplished a number of industry leading moves. In 2001, Ars launched a digital subscription service when such things were non-existent for digital media. Ars was also the first IT publication to begin covering the resurgence of Apple, and the first to draw analytical and cultural ties between the world of high technology and gaming. Ars was also first to begin selling its long form content in digitally distributable forms, such as PDFs and eventually eBooks (again, starting in 2001).

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: