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  • richardmitnick 3:52 pm on January 11, 2017 Permalink | Reply
    Tags: , , , , Dark Matter, , ,   

    From PI via Motherboard: “Dark Matter Hunters Are Hoping 2017 is Their Year” 

    Perimeter Institute
    Perimeter Institute

    Motherboard

    January 3, 2017
    Kate Lunau

    It can be unsettling to realize that only five percent of the universe is made of the kind of matter we know and understand—everything from the planets and stars, to trees and animals and your dining room table.

    Roughly one-quarter is dark matter. This is thought to knit the galaxies together, and has been called the “scaffolding” of the universe, but we’ve never detected it directly. Scientists believe they can see dark matter’s traces in the way that galaxies rotate, but they still have no idea what it is. (Most of the universe, about 70 percent, is dark energy, a mysterious force that permeates space and time. It’s even less well-understood than dark matter.)

    Confirming dark matter’s existence would change humankind’s perspective on the universe. 2016 was a year of dark matter disappointments, as big searches came up empty. Most are looking for WIMPs—weakly interacting massive particles, the leading contender for a dark matter particle.

    2017 might just be the year we finally catch one. And if we don’t, well, it may be that our best theories about dark matter are wrong—that we’re looking in the wrong places, with the wrong instruments. Maybe dark matter, whatever it is, will turn out to be even weirder and more surprising than anyone has so far predicted. Maybe it’s not a WIMP, but some other bizarre kind of particle.

    Then there’s the outside possibility that dark matter doesn’t exist, that it’s an illusion. If that’s the case, we’ll have to consider whether we’ve been fundamentally misreading the universe’s clues.

    Buried deep in a mine near Sudbury in northern Ontario is SNOLAB, a vast underground laboratory where scientists are performing a range of experiments, including looking for dark matter. Often compared to the lair of a Bond villain, it’s an ultra-clean, high-tech facility. Two kilometers of solid rock overhead shield its detectors from cosmic radiation, allowing them to sift for bits of matter from dying stars and the Sun: science done here won the Nobel Prize in Physics, in 2015.

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    A scientist works on the deck of DEAP-3600, a dark matter search at SNOLAB. Image: SNOLAB

    I recently travelled to SNOLAB. To get there, I had to don full mining gear (including a hardhat and headlamp), drop down underground in a rattling dark cage, and hike a kilometre or so to reach the gleaming white facility, which is cleaner inside than an operating room—a startling contrast to the dirty nickel mine that surrounds it.

    After the long hike through the mine, anyone who wants to enter SNOLAB has to undress, shower (with soap and shampoo), and put on lint-free clothing and a hairnet. Any bit of dust from the mine, which is naturally radioactive, can mess up the experiments.

    There, I met research scientist Ken Clark, a congenial physicist with a sandy-coloured beard. Like me, he was wearing safety goggles and a hardhat. Clark has worked on high-profile dark matter searches like CDMS and LUX, and collaborates on the IceCube detector at the South Pole in Antarctica.

    LBL SuperCDMS
    LBL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)
    LBL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    LUX Xenon experiment at SURF
    LUX Xenon experiment at SURF, Lead, SD, USA

    U Wisconsin ICECUBE neutrino detector at the South Pole
    IceCube neutrino detector interior
    U Wisconsin ICECUBE neutrino detector at the South Pole

    Now he’s with PICO, a dark matter search that targets the WIMP particle.

    5

    It was launched in 2013 when two other collaborations, called PICASSO and COUPP, merged.

    6
    A multi-bubble image of a neutron scattering in the PICO detector. Image: PICO Collaboration

    PICO is a bubble detector: a tank of superheated fluid kept higher than its natural boiling point. If dark matter bumps into the nucleus of another particle in the detector, it should cause a tiny bubble to form. Dark matter courses through the Earth and right through our bodies, so it will reach the detector underground, even through all that rock overhead. But that’s also part of the challenge—dark matter is thought to only rarely interact with normal matter, if at all, so it’s really tricky to catch.

    Clark believes we might just find dark matter in the next year or two. “It’s exciting times,” he said.

    Other searches are due to turn on soon, he explained, and those that are already up-and-working are getting increasingly sensitive. In 2017, Clark said it’s possible we’ll see new results from PICO, DEAP (a different detector, also at SNOLAB), as well as China’s ambitious PandaX project, and another in Italy called XENON1T. Even more searches will turn on in 2018.

    “Provided the models are correct, we should see something soon,” Clark told me.

    7
    A scientist works on the steel vessel of DEAP-3600. Image: DEAP Collaboration

    Still, there’s no guarantee, and WIMP searches keep turning up empty-handed. For example, in the summer, the highly sensitive LUX—which uses liquid xenon in a South Dakota mine as its detector—announced it had seen zero WIMPs, after looking for more than a year.

    I phoned Lisa Randall, a prominent theoretical physicist and professor at Harvard University, to ask whether she thinks there’s a chance we’ll find dark matter in the next year or two.

    “I would say kind of the opposite,” said Randall, author of Dark Matter and the Dinosaurs. While she agrees that if dark matter is indeed a WIMP, these searches could find it soon, “that’s just one possibility,” she said.

    The WIMP is “lowest-hanging fruit,” Randall continued: this theoretical particle fits snugly within what’s already known about the Standard Model of physics, which explains how the building blocks of the universe interact. And scientists can imagine ways to actually look for WIMPs, unlike some of the more far-out theories, which are much harder to test in experiments.

    “What if it’s not a WIMP?” Randall said. “Could we still learn something about what dark matter is?”

    Other scientists have different strategies for solving the dark matter puzzle.

    Leslie Rosenberg, a professor of physics at the University of Washington in Seattle, is project scientist on the Axion Dark Matter Experiment, or ADMX, which is looking for a theoretical particle called the axion, which is thought to be much lighter than a WIMP.

    ADMX Axion Dark Matter Experiment
    U Washington ADMX
    U Washington ADMX

    It’s being targeted by other searches under development around the world, Rosenberg told me. ADMX, though, is “the only high-sensitivity axion search now,” he said.

    Maybe we’re being fooled into thinking that dark matter is there.

    ADMX, which uses a resonant microwave cavity nested inside a huge superconducting magnet, started out of a collaboration that began in the mid-nineties. It’s been at full sensitivity for about a year now, Rosenberg told me, and will only get better as the team continues to tweak it. He’s hoping they turn up something soon: their next update should come in the summer of 2017.

    “Axions are bound up in our galaxy,” Rosenberg said. “There [should be] an awful lot of them, and we depend on that as the source of our signal.”

    Axions are a mainstream dark matter candidate. Other ideas get weirder.

    “Personally, I’m interested in the idea that dark matter might have nothing to do with the Standard Model,” Randall told me. “One of the possibilities is that it could be some other type of particle. Maybe it interacts [with itself] via its own light, a dark photon.”

    7
    ESA/Gaia’s first sky map of the Milky Way, based on data collected from July 2014 to Sept. 2015. Image: ESA/Gaia/DPAC

    Randall thinks that one of the best ways to learn about dark matter may be to study the structure of galaxies, and watching the universe at work, to understand how it interacts with itself. The European Space Agency’s Gaia mission, which is making a three-dimensional map of over a thousand million stars, could give insight into some of this, Randall said.

    Asimina Arvanitaki, a theoretical physicist at the Perimeter Institute for Theoretical Physics, suggested to me in a Skype call that dark matter might be detectable through resonant-mass detectors, which are used to hunt for gravitational waves. These ripples in spacetime were detected for the first time in 2016, a hundred years after Albert Einstein predicted their existence.

    Dark matter could also be behaving like a wave, “trapped by gravity and oscillat[ing] at a frequency set by the mass,” she said.

    “The funny thing is you could perhaps even hear dark matter,” Arvanitaki said, “depending on the frequency.”

    Over millions of years, humans have come up with ingenious ways to probe the world around us, from Copernicus and Kepler, through the thousands of scientists involved in the search for the Higgs boson particle at the Large Hadron Collider, and those who are now shaking out the endless diversity of exoplanets that populate our galaxy.

    Because of them, our perspective has changed. When we look up at the night sky today, we understand that just about every star we see hosts at least one planet. The first confirmed exoplanet was announced just over two decades ago.

    Nature can still surprise us.

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    The Bullet cluster, formed by the collision of two large galaxy clusters, provides some of the best evidence yet for dark matter. Image: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

    “There’s a chance that dark matter isn’t necessarily a particle at all,” Clark told me. “Some [theorists] say there’s no dark matter. It’s just that we don’t understand how gravity works at large scales,” he continued. “If that’s the case, we’re being fooled into thinking that dark matter is there.”

    Clark and the other dark matter hunters continue their search. If it’s real, “we’re not even made of what most of the universe is made of,” Rosenberg told me. In the grand scheme of things, then, it isn’t dark matter that’s really so exotic and strange—it’s us.

    See the full article here .

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    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 8:37 am on December 21, 2016 Permalink | Reply
    Tags: , Cryogenic Dark Matter Search (CDMS), Dark Matter, ,   

    From FNAL: “SuperCDMS: An end and a beginning” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    December 15, 2016
    1
    Dan Bauer

    One year ago, the Cryogenic Dark Matter Search (CDMS) collaboration warmed up its apparatus at the Soudan Underground Laboratory in northern Minnesota, after 12 years of successful operation.

    SUPER CDMS
    SUPER CDMS

    soudan-underground-lab-at-the-site-of-the-soudan-underground-mine-on-the-south-shore-of-lake-vermilion-in-the-vermilion-range-minnesota
    Soudan Underground Lab at the site of te Soudan Underground Mine on the South Shore of Lake Vermillion in the Vermillian Range, Minnesota, USA

    The CDMS II and SuperCDMS Soudan experiments produced many world-leading limits on dark matter particle detection during that time, covering masses from a few GeV to a few TeV. However, the sensitivity was limited by backgrounds and by environmental noise from the design of the facility.

    Meanwhile, based on the success of the CDMS experiments at Soudan, DOE and NSF selected the SuperCDMS collaboration to develop a next-generation experiment to be based at SNOLAB, a deeper and cleaner environment located near Sudbury in Ontario, Canada.

    SNOLAB, Sudbury, Ontario, Canada.
    SNOLAB, Sudbury, Ontario, Canada

    The focus of the new experiment will be a search for dark matter particles with masses less than 10 GeV/c2, based on the demonstrated SuperCDMS Soudan detector technologies. Such light dark matter is a feature of theoretical models that postulate a “dark sector” of particles that interact only very weakly with normal matter. The ultimate goal for SuperCDMS SNOLAB is to search for such light dark matter to sensitivities where the experiment will begin to see elastic scattering of solar neutrinos with its germanium and silicon targets.

    Thus, to focus its attention on developing the new experiment, the collaboration took the painful step of turning off a running experiment at Soudan, saying goodbye to the incredibly helpful staff from the University of Minnesota and recovering its equipment, much of which will be reused for SuperCDMS SNOLAB. To facilitate the recovery of equipment from Soudan, and provide a space for SuperCDMS SNOLAB to be built, PPD renovated an existing hall at Fermilab with the rather pedestrian designation Lab G. Lighting, HVAC and other utilities have been modernized, and a large cleanroom has been installed. The photographs shows this new clean space, which will be the temporary home for SuperCDMS SNOLAB over the next couple of years.

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    This panoramic view shows the new SuperCDMS SNOLAB cleanroom at Lab G, with SuperCDMS spokesperson Dan Bauer and senior technical specialist Mark Ruschman. Photo: Reidar Hahn

    4
    The cleanroom in Lab G will be used in the development of SuperCDMS detectors. Photo: Reidar Hahn

    Starting in 2017, with the arrival of a large new dilution refrigerator, the SuperCDMS group at Fermilab will build and commission the cryogenic apparatus that will allow SuperCDMS SNOLAB to cool its detectors to less than 30 milliKelvin. In 2019, the experiment will be installed at SNOLAB and will begin operations starting in 2020. If light dark matter particles exist, SuperCDMS SNOLAB should detect them sometime in the next decade.

    Dan Bauer is the spokesperson for SuperCDMS and the deputy head of the Fermilab Center for Particle Astrophysics.

    See the full article here .

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    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 9:46 am on December 14, 2016 Permalink | Reply
    Tags: , , , Dark Matter, Einstein’s General Relativity (GR), Emergent Gravity, , , Hubble Constant, , Weak Gravitational Lensing   

    From astrobites: “Emergent Gravity faces its First Test in Galaxy Lensing” 

    Astrobites bloc

    Astrobites

    Dec 13, 2016
    Gourav Khullar

    Title: First test of Verlinde’s theory of Emergent Gravity using Weak Gravitational Lensing measurements
    Authors: M. M. Brower, M.R. Visser, A Dvornik, et al.
    First Author’s Institution: Leiden Observatory, Leiden, The Netherlands
    Status: Submitted to The Monthly Notices of the Royal Astronomical Society (MNRAS), December 2016 [open access]

    Despite being a near-perfect model and explaining everything ranging from galactic rotation curves to high-redshift supernovae observations, Lambda-CDM has its problems. A lack of clear candidates for a dark matter particle and dark energy are two that certainly keep physicists up at night. This leads us towards alleys unexplored – theories that are creative, innovative and crucial to the scientific process, theories that could lead us to the eventual model of the universe with a clear explanations of all observations. One such theory that garnered some attention in the last few years is Emergent Gravity.

    1
    Fig 1. Galaxy rotation curves observed over the last few years indicate a dominant matter halo on the outskirts of galaxies, something that’s explained concretely by dark matter.

    What is ‘Emergent’ in Emergent Gravity?

    The idea is pretty radical yet basic – gravity isn’t a manifestation of mass in spacetime as proposed by Einstein’s General Relativity (GR) or a fundamental force that fits perfectly in a four-force model of the universe. Instead, gravity is proposed to be ’emerging’ from interactions between even more fundamental particles. This is akin to seeing thermodynamical parameters like pressure and temperature arising from interactions between atoms and molecules – what’s crucial to our discussion is the macroscopic quantity. In the case here, that quantity would be gravity. This idea has been developing over the last few decades, with Theodore Jacobson, Thanu Padmanabhan and more recently, Erik Verlinde contributing heavily to its development.

    2
    Erik Verlinde

    3
    Fig 2. High speeds of particle collision against the walls of a container lead to higher temperature, since the system possesses more kinetic energy that gets converted to thermal energy.

    Diving deep into Entropy and Gravity

    One aspect of a theoretical model like emergent gravity (EG) is that we are allowed to derive macroscopic results without having to worry about the underlying fundamental particles that could lead to gravity ’emerging’ – at least for now. This ’emergence’ can be thought of as the result of the tendency of a physical system to increase its entropy. Early work in the field towards a ‘thermodynamics-like theory of gravity’ used something called ‘holographic scaling of entropy’, which essentially scales with surface area of an enclosed volume of spacetime. Verlinde’s new work insists that due to dark energy, we see deviations in GR at long distances that can be resolved if this entropy scaling scales as volume instead of area. Keeping details aside, this leads to a different ‘force-law’, that has additional dominant matter terms that could explain dark matter (called ‘apparent dark matter’ in this case). This and this piece are excellent sources for details on the model. It can be seen that in some sense, this model combines the origin of dark matter and dark energy in a novel way.

    Basics of Weak Gravitational Lensing

    Well, how do we test this theory? Perhaps, passing it through the same standards as GR would seem appropriate.

    The idea of gravitational lensing was one of the first tests of GR i.e. the idea that light’s path gets distorted when traveling through curved spacetime surrounding massive objects. This distortion can change the light ray received from background galaxies (and hence, apparent shape and size) due to a foreground massive object like a galaxy or a galaxy cluster, leading to weak gravitational lensing. This galaxy-galaxy lensing signal is a massive success story of GR, as observations of this phenomena in the Universe fit into the model very well.

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    Fig 3. Gravitational lensing leading to a drastic distortion in light coming from background galaxies. Credit: NASA-Hubble Space Telescope.

    Since EG still gives rise to ‘apparent dark matter’, it is safe to say that the gravitational lensing formalism stays the same, since we do apply this formalim to our universe’s dark matter-dominated objects like galaxy clusters (if we believe Lambda-CDM and its predictions). This allows us to use weak lensing as a test for emergent gravity, and match observations against the predictions of this theory.

    This work

    The regime studied in this work is the low-redshift universe, or the relatively local universe, where the Hubble Constant can be treated as a constant. This is almost true because of the dominance of dark energy after redshift ~0.7-0.9. Since Verlinde’s EG isn’t evolved enough as a theory to quantify cosmology before this epoch, this work assumes a background Lambda-CDM cosmology. For studying galaxy-galaxy lensing, Brower et al. select ~33,000 galaxies from the Galaxy And Mass Assembly (GAMA) survey as ‘lenses’ and KiDS survey galaxies as background galaxies that get lensed. They model these galaxies as having a static, spherically symmetric distribution of mass- something like a point mass or an extended source resembling a point mass- because that’s what EG can handle so far.

    This work calculates the lensing effect by measuring distortions in the background galaxies’ images, termed as a ‘shear’. In the framework of GR, this quantity is comprised in something called the Extended Surface Density (ESD) profile. Brower et al. calculated the ESD for these galaxies under the many assumptions of this model, compared them with Navarror-Frenk-White (NFW) profiles of galaxies from Lambda-CDM, and found that there was general agreement in the ESD progression between the two.

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    Fig 4. From the paper, a model-fit of Emergent Gravity(Point mass model), Emergent Gravity (Extended model) and Dark Matter(NFW model). The lensing signal measured in the form of an ESD is plotted for four different galactic mass bins. It can be seen that Verlinde’s Emergent Gravity model assisted by teh assumptions made by Brower et al. match NFW profile predictions very well.

    Conclusion and Summary

    So what are the assumptions? For one, EG cannot deal with evolution of the universe at the moment. Moreover, the theory isn’t developed enough to have a basic framework of what causes gravity to ’emerge’ from fundamental interactions. The paper agrees that a more ‘sophisticated implementation of both theories’ is needed to make a statement about whether apparent dark matter explains observations better than Lambda-CDM dark matter. Till then, EG shall keep on evolving and observations shall keep on being pitted against these evolving frameworks. A very exciting space to watch!

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 2:55 pm on December 9, 2016 Permalink | Reply
    Tags: , , Dark Matter   

    From New Science: “Dark matter that talks to itself could explain galaxy mystery” 

    NewScientist

    New Scientist

    7 December 2016
    Shannon Hall

    1
    Spinning puzzle. Robert Gendler/Science Photo Library

    DARK matter might talk to itself. The mysterious substance that outweighs all visible matter in the cosmos might be best explained if it’s able to interact with itself via an invisible force.

    Take a look at any image of a galaxy and you will see that the centre is the brightest. With so much light – and therefore mass – concentrated there, astronomers expected central objects to orbit faster than those on the outer rim.

    But in the early 20th century, astronomers were surprised to find that galaxies’ outer stars appear to move about as fast as their inner stars, suggesting that there is more matter that doesn’t meet the eye. The name given to the invisible stuff is dark matter, and the standard paradigm suggests it is composed of weakly interacting massive particles, or WIMPs.

    Now new research on galactic rotation curves – graphs showing the orbital speeds of stars versus their distance from the centre of the galaxy – suggests the story might not be so simple.

    Not all rotation curves look alike – before they reach that characteristic plateau, some rise gradually, and others rise rapidly. But WIMP models struggle to explain this. Also, there has been no direct evidence of WIMPs, despite decades of searching. So Ayuki Kamada at the University of California, Riverside, and his colleagues set about finding an alternative.

    The team looked at 30 galaxies with strange rotation curves, and found that they could better explain them using a different type of dark matter: the self-interacting sort. These particles do something similar to how ordinary matter particles, like protons, interact with one another via the electromagnetic force.

    “It’s a very minimal modification,” says Manoj Kaplinghat at the University of California, Irvine. “But it’s amazing how well it actually fits. You don’t have to bend over backwards.”

    When galaxies form, cold dark matter falls to the centre and hot dark matter flows toward the outer edges. But if dark matter is allowed to interact with itself, then the particles will exchange energy and end up at the same temperature, just like the air molecules in a room. In some cases, the cool dark matter particles in the centre will grow hotter and flow toward the outer edges, building a centre less dominated by dark matter – explaining the rotation curves that rise gradually (arxiv.org/abs/1611.02716).

    Stacy McGaugh at Case Western Reserve University in Ohio is a critic of the standard dark matter paradigm, so he thinks all alternatives are worth exploring. However, adding new unseen forces to unseen particles complicates the picture unnecessarily, he says.

    “It’s what the philosophers of science would call an auxiliary hypothesis on top of an auxiliary hypothesis,” he says. “It’s already ad hoc and we’re adding more.”

    McGaugh’s favourite explanation is Modified Newtonian Dynamics (MOND), a theory that doesn’t add invisible matter but tweaks our understanding of gravity.

    An answer might come with direct detection of dark matter – whether WIMPs or the self-interacting kind.

    See the full article here .

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  • richardmitnick 8:52 am on December 7, 2016 Permalink | Reply
    Tags: , , Dark Matter, , Kilo Degree Survey (KiDS)   

    From ESO: “Dark Matter May be Smoother than Expected” 

    ESO 50 Large

    European Southern Observatory

    7 December 2016
    Hendrik Hildebrandt
    Head of Emmy Noether-Research Group
    Bonn, Germany
    Tel: +49 228 73 1772
    Email: hendrik@astro.uni-bonn.de

    Massimo Viola
    Leiden Observatory
    Leiden, The Netherlands
    Tel: +31 (0)71 527 8442
    Email: viola@strw.leidenuniv.nl

    Catherine Heymans
    Institute for Astronomy, University of Edinburgh
    Edinburgh, United Kingdom
    Tel: +44 131 668 8301
    Email: heymans@roe.ac.uk

    Konrad Kuijken
    Leiden Observatory
    Leiden, The Netherlands
    Tel: +31 715275848
    Cell: +31 628956539
    Email: kuijken@strw.leidenuniv.nl

    Richard Hook
    ESO Public Information Officer
    Garching bei Munchen, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    1

    Analysis of a giant new galaxy survey, made with ESO’s VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought. An international team used data from the Kilo Degree Survey (KiDS) to study how the light from about 15 million distant galaxies was affected by the gravitational influence of matter on the largest scales in the Universe. The results appear to be in disagreement with earlier results from the Planck satellite.

    Hendrik Hildebrandt from the Argelander-Institut für Astronomie in Bonn, Germany and Massimo Viola from the Leiden Observatory in the Netherlands led a team of astronomers [1] from institutions around the world who processed images from the Kilo Degree Survey (KiDS), which was made with ESO’s VLT Survey Telescope (VST) in Chile. For their analysis, they used images from the survey that covered five patches of the sky covering a total area of around 2200 times the size of the full Moon [2], and containing around 15 million galaxies.

    By exploiting the exquisite image quality available to the VST at the Paranal site, and using innovative computer software, the team were able to carry out one of the most precise measurements ever made of an effect known as cosmic shear. This is a subtle variant of weak gravitational lensing, in which the light emitted from distant galaxies is slightly warped by the gravitational effect of large amounts of matter, such as galaxy clusters.

    In cosmic shear, it is not galaxy clusters but large-scale structures in the Universe that warp the light, which produces an even smaller effect. Very wide and deep surveys, such as KiDS, are needed to ensure that the very weak cosmic shear signal is strong enough to be measured and can be used by astronomers to map the distribution of gravitating matter. This study takes in the largest total area of the sky to ever be mapped with this technique so far.

    Intriguingly, the results of their analysis appear to be inconsistent with deductions from the results of the European Space Agency’s Planck satellite, the leading space mission probing the fundamental properties of the Universe.

    ESA/Planck
    ESA/Planck

    CMB per ESA/Planck
    CMB per ESA/Planck

    In particular, the KiDS team’s measurement of how clumpy matter is throughout the Universe — a key cosmological parameter — is significantly lower than the value derived from the Planck data [3].

    Massimo Viola explains: “This latest result indicates that dark matter in the cosmic web, which accounts for about one-quarter of the content of the Universe, is less clumpy than we previously believed.”

    Dark matter remains elusive to detection, its presence only inferred from its gravitational effects. Studies like these are the best current way to determine the shape, scale and distribution of this invisible material.

    The surprise result of this study also has implications for our wider understanding of the Universe, and how it has evolved during its almost 14-billion-year history. Such an apparent disagreement with previously established results from Planck means that astronomers may now have to reformulate their understanding of some fundamental aspects of the development of the Universe.

    Hendrik Hildebrandt comments: “Our findings will help to refine our theoretical models of how the Universe has grown from its inception up to the present day.”

    The KiDS analysis of data from the VST is an important step but future telescopes are expected to take even wider and deeper surveys of the sky.

    The co-leader of the study, Catherine Heymans of the University of Edinburgh in the UK adds: “Unravelling what has happened since the Big Bang is a complex challenge, but by continuing to study the distant skies, we can build a picture of how our modern Universe has evolved.”

    “We see an intriguing discrepancy with Planck cosmology at the moment. Future missions such as the Euclid satellite and the Large Synoptic Survey Telescope will allow us to repeat these measurements and better understand what the Universe is really telling us,” concludes Konrad Kuijken (Leiden Observatory, the Netherlands), who is principal investigator of the KiDS survey.

    ESA/Euclid spacecraft
    ESA/Euclid spacecraft

    LSST

    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC

    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST telescope, currently under construction at Cerro Pachón Chile

    Notes

    [1] The international KiDS team of researchers includes scientists from Germany, the Netherlands, the UK, Australia, Italy, Malta and Canada.

    [2] This corresponds to about 450 square degrees, or a little more than 1% of the entire sky.

    [3] The parameter measured is called S8. Its value is a combination of the size of density fluctuations in, and the average density of, a section of the Universe. Large fluctuations in lower density parts of the Universe have an effect similar to that of smaller amplitude fluctuations in denser regions and the two cannot be distinguished by observations of weak lensing. The 8 refers to a cell size of 8 megaparsecs, which is used by convention in such studies.

    More information

    This research was presented in the paper entitled “KiDS-450: Cosmological parameter constraints from tomographic weak gravitational lensing”, by H. Hildebrandt et al., to appear in Monthly Notices of the Royal Astronomical Society.

    The team is composed of H. Hildebrandt (Argelander-Institut für Astronomie, Bonn, Germany), M. Viola (Leiden Observatory, Leiden University, Leiden, the Netherlands), C. Heymans (Institute for Astronomy, University of Edinburgh, Edinburgh, UK), S. Joudaki (Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Hawthorn, Australia), K. Kuijken (Leiden Observatory, Leiden University, Leiden, the Netherlands), C. Blake (Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Hawthorn, Australia), T. Erben (Argelander-Institut für Astronomie, Bonn, Germany), B. Joachimi (University College London, London, UK), D Klaes (Argelander-Institut für Astronomie, Bonn, Germany), L. Miller (Department of Physics, University of Oxford, Oxford, UK), C.B. Morrison (Argelander-Institut für Astronomie, Bonn, Germany), R. Nakajima (Argelander-Institut für Astronomie, Bonn, Germany), G. Verdoes Kleijn (Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands), A. Amon (Institute for Astronomy, University of Edinburgh, Edinburgh, UK), A. Choi (Institute for Astronomy, University of Edinburgh, Edinburgh, UK), G. Covone (Department of Physics, University of Napoli Federico II, Napoli, Italy), J.T.A. de Jong (Leiden Observatory, Leiden University, Leiden, the Netherlands), A. Dvornik (Leiden Observatory, Leiden University, Leiden, the Netherlands), I. Fenech Conti (Institute of Space Sciences and Astronomy (ISSA), University of Malta, Msida, Malta; Department of Physics, University of Malta, Msida, Malta), A. Grado (INAF – Osservatorio Astronomico di Capodimonte, Napoli, Italy), J. Harnois-Déraps (Institute for Astronomy, University of Edinburgh, Edinburgh, UK; Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada), R. Herbonnet (Leiden Observatory, Leiden University, Leiden, the Netherlands), H. Hoekstra (Leiden Observatory, Leiden University, Leiden, the Netherlands), F. Köhlinger (Leiden Observatory, Leiden University, Leiden, the Netherlands), J. McFarland (Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands), A. Mead (Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada), J. Merten (Department of Physics, University of Oxford, Oxford, UK), N. Napolitano (INAF – Osservatorio Astronomico di Capodimonte, Napoli, Italy), J.A. Peacock (Institute for Astronomy, University of Edinburgh, Edinburgh, UK), M. Radovich (INAF – Osservatorio Astronomico di Padova, Padova, Italy), P. Schneider (Argelander-Institut für Astronomie, Bonn, Germany), P. Simon (Argelander-Institut für Astronomie, Bonn, Germany), E.A. Valentijn (Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands), J.L. van den Busch (Argelander-Institut für Astronomie, Bonn, Germany), E. van Uitert (University College London, London, UK) and L. van Waerbeke (Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada).

    See the full article here .

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  • richardmitnick 1:35 pm on December 2, 2016 Permalink | Reply
    Tags: , , , Dark Interactions Workshop, Dark Matter   

    From BNL: “Dark Interactions Workshop Hosts Physicists from Around the World” 

    Brookhaven Lab

    November 23, 2016
    Chelsea Whyte

    Dozens of experimental and theoretical physicists convened at the U.S. Department of Energy’s Brookhaven National Laboratory in October for the second biennial Dark Interactions Workshop. Attendees came from universities and laboratories worldwide to discuss current research and possible future searches for dark sector states such as dark matter.

    1

    Two great cosmic mysteries – dark energy and dark matter — make up nearly 95% of the universe’s energy budget. Dark energy is the proposed agent behind the ever-increasing expansion of the universe. Some force must propel the accelerating rate at which the fabric of space is stretching, but its origin and makeup are still unknown. Dark matter, first proposed over 80 years ago, is theorized to be the mass responsible for most of the immense gravitational pull that galaxy clusters exert. Without its presence, galaxies and galaxy clusters shouldn’t hang together as they do, according to the laws of gravity that permeate our cosmos.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Scientists know this much. It’s a bit like a map of a continent with the outlines drawn, but large holes that need a lot of filling in. “There are a lot of things we know that we don’t know,” said Brookhaven physicist Ketevi Assamagan, who organized the workshop along with Brookhaven physicists Hooman Davoudiasl and Mary Bishai, and Stony Brook University physicist Rouven Essig.

    The Dark Interactions Workshop was created to gather great minds in search of answers to these cosmic questions, and to share knowledge across the many different types of experiments searching for dark-sector particles. “The goals are to search for several well-motivated dark-sector particles with existing and upcoming experiments, but also to propose new experiments that can lead the search for dark forces in the coming decade. This requires in-depth discussions among theorists and experimentalists,” Essig said.

    The sessions ranged from discussing theories to status updates from dark-particle searches following the first workshop two years ago. Attendees included post-docs as well as tenured scientists, and Assamagan said workshops like this are crucial for allowing a diverse and somewhat disparate group of scientists in a dense field of study to get to know each other’s work and build collaborations.

    “Dark matter is one of the hot topics in particle and astrophysics today. We know that we don’t have the complete story when it comes to our universe. Understanding the nature of dark matter would be a revolution,” Assamagan said.

    While tantalizing theories have directed physicists to build new ways to search for dark sector states, conclusive evidence still eludes scientists. “Since there is currently a vast range of possibilities for what could constitute the dark sector, a variety of innovative approaches for answering this question need to be considered,” Davoudiasl said. “To that end, meetings like this are quite helpful as they facilitate the exchange of new ideas.”

    “There’s still a lot of hope. Meetings like this one show that there are a lot of clever people working in this field and a lot of collaboration between them. Hopefully at our next workshop, we’ll be sharing evidence that we’ve discovered something of the dark sector,” said Assamagan.

    See the full article here .

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  • richardmitnick 7:05 pm on November 30, 2016 Permalink | Reply
    Tags: , , , Dark Matter, , , ,   

    From Quanta: “The Case Against Dark Matter” 

    Quanta Magazine
    Quanta Magazine

    November 29, 2016
    Natalie Wolchover

    1
    Erik Verlinde
    Ilvy Njiokiktjien for Quanta Magazine

    For 80 years, scientists have puzzled over the way galaxies and other cosmic structures appear to gravitate toward something they cannot see. This hypothetical “dark matter” seems to outweigh all visible matter by a startling ratio of five to one, suggesting that we barely know our own universe. Thousands of physicists are doggedly searching for these invisible particles.

    But the dark matter hypothesis assumes scientists know how matter in the sky ought to move in the first place. This month, a series of developments has revived a long-disfavored argument that dark matter doesn’t exist after all. In this view, no missing matter is needed to explain the errant motions of the heavenly bodies; rather, on cosmic scales, gravity itself works in a different way than either Isaac Newton or Albert Einstein predicted.

    The latest attempt to explain away dark matter is a much-discussed proposal by Erik Verlinde, a theoretical physicist at the University of Amsterdam who is known for bold and prescient, if sometimes imperfect, ideas. In a dense 51-page paper posted online on Nov. 7, Verlinde casts gravity as a byproduct of quantum interactions and suggests that the extra gravity attributed to dark matter is an effect of “dark energy” — the background energy woven into the space-time fabric of the universe.

    Instead of hordes of invisible particles, “dark matter is an interplay between ordinary matter and dark energy,” Verlinde said.

    To make his case, Verlinde has adopted a radical perspective on the origin of gravity that is currently in vogue among leading theoretical physicists. Einstein defined gravity as the effect of curves in space-time created by the presence of matter. According to the new approach, gravity is an emergent phenomenon. Space-time and the matter within it are treated as a hologram that arises from an underlying network of quantum bits (called “qubits”), much as the three-dimensional environment of a computer game is encoded in classical bits on a silicon chip. Working within this framework, Verlinde traces dark energy to a property of these underlying qubits that supposedly encode the universe. On large scales in the hologram, he argues, dark energy interacts with matter in just the right way to create the illusion of dark matter.

    In his calculations, Verlinde rediscovered the equations of “modified Newtonian dynamics,” or MOND. This 30-year-old theory makes an ad hoc tweak to the famous “inverse-square” law of gravity in Newton’s and Einstein’s theories in order to explain some of the phenomena attributed to dark matter. That this ugly fix works at all has long puzzled physicists. “I have a way of understanding the MOND success from a more fundamental perspective,” Verlinde said.

    Many experts have called Verlinde’s paper compelling but hard to follow. While it remains to be seen whether his arguments will hold up to scrutiny, the timing is fortuitous. In a new analysis of galaxies published on Nov. 9 in Physical Review Letters, three astrophysicists led by Stacy McGaugh of Case Western Reserve University in Cleveland, Ohio, have strengthened MOND’s case against dark matter.

    The researchers analyzed a diverse set of 153 galaxies, and for each one they compared the rotation speed of visible matter at any given distance from the galaxy’s center with the amount of visible matter contained within that galactic radius. Remarkably, these two variables were tightly linked in all the galaxies by a universal law, dubbed the “radial acceleration relation.” This makes perfect sense in the MOND paradigm, since visible matter is the exclusive source of the gravity driving the galaxy’s rotation (even if that gravity does not take the form prescribed by Newton or Einstein). With such a tight relationship between gravity felt by visible matter and gravity given by visible matter, there would seem to be no room, or need, for dark matter.

    Even as dark matter proponents rise to its defense, a third challenge has materialized. In new research that has been presented at seminars and is under review by the Monthly Notices of the Royal Astronomical Society, a team of Dutch astronomers have conducted what they call the first test of Verlinde’s theory: In comparing his formulas to data from more than 30,000 galaxies, Margot Brouwer of Leiden University in the Netherlands and her colleagues found that Verlinde correctly predicts the gravitational distortion or “lensing” of light from the galaxies — another phenomenon that is normally attributed to dark matter. This is somewhat to be expected, as MOND’s original developer, the Israeli astrophysicist Mordehai Milgrom, showed years ago that MOND accounts for gravitational lensing data. Verlinde’s theory will need to succeed at reproducing dark matter phenomena in cases where the old MOND failed.

    Kathryn Zurek, a dark matter theorist at Lawrence Berkeley National Laboratory, said Verlinde’s proposal at least demonstrates how something like MOND might be right after all. “One of the challenges with modified gravity is that there was no sensible theory that gives rise to this behavior,” she said. “If [Verlinde’s] paper ends up giving that framework, then that by itself could be enough to breathe more life into looking at [MOND] more seriously.”

    The New MOND

    In Newton’s and Einstein’s theories, the gravitational attraction of a massive object drops in proportion to the square of the distance away from it. This means stars orbiting around a galaxy should feel less gravitational pull — and orbit more slowly — the farther they are from the galactic center. Stars’ velocities do drop as predicted by the inverse-square law in the inner galaxy, but instead of continuing to drop as they get farther away, their velocities level off beyond a certain point. The “flattening” of galaxy rotation speeds, discovered by the astronomer Vera Rubin in the 1970s, is widely considered to be Exhibit A in the case for dark matter — explained, in that paradigm, by dark matter clouds or “halos” that surround galaxies and give an extra gravitational acceleration to their outlying stars.

    Searches for dark matter particles have proliferated — with hypothetical “weakly interacting massive particles” (WIMPs) and lighter-weight “axions” serving as prime candidates — but so far, experiments have found nothing.

    2
    Lucy Reading-Ikkanda for Quanta Magazine

    Meanwhile, in the 1970s and 1980s, some researchers, including Milgrom, took a different tack. Many early attempts at tweaking gravity were easy to rule out, but Milgrom found a winning formula: When the gravitational acceleration felt by a star drops below a certain level — precisely 0.00000000012 meters per second per second, or 100 billion times weaker than we feel on the surface of the Earth — he postulated that gravity somehow switches from an inverse-square law to something close to an inverse-distance law. “There’s this magic scale,” McGaugh said. “Above this scale, everything is normal and Newtonian. Below this scale is where things get strange. But the theory does not really specify how you get from one regime to the other.”

    Physicists do not like magic; when other cosmological observations seemed far easier to explain with dark matter than with MOND, they left the approach for dead. Verlinde’s theory revitalizes MOND by attempting to reveal the method behind the magic.

    Verlinde, ruddy and fluffy-haired at 54 and lauded for highly technical string theory calculations, first jotted down a back-of-the-envelope version of his idea in 2010. It built on a famous paper he had written months earlier, in which he boldly declared that gravity does not really exist. By weaving together numerous concepts and conjectures at the vanguard of physics, he had concluded that gravity is an emergent thermodynamic effect, related to increasing entropy (or disorder). Then, as now, experts were uncertain what to make of the paper, though it inspired fruitful discussions.

    The particular brand of emergent gravity in Verlinde’s paper turned out not to be quite right, but he was tapping into the same intuition that led other theorists to develop the modern holographic description of emergent gravity and space-time — an approach that Verlinde has now absorbed into his new work.

    In this framework, bendy, curvy space-time and everything in it is a geometric representation of pure quantum information — that is, data stored in qubits. Unlike classical bits, qubits can exist simultaneously in two states (0 and 1) with varying degrees of probability, and they become “entangled” with each other, such that the state of one qubit determines the state of the other, and vice versa, no matter how far apart they are. Physicists have begun to work out the rules by which the entanglement structure of qubits mathematically translates into an associated space-time geometry. An array of qubits entangled with their nearest neighbors might encode flat space, for instance, while more complicated patterns of entanglement give rise to matter particles such as quarks and electrons, whose mass causes the space-time to be curved, producing gravity. “The best way we understand quantum gravity currently is this holographic approach,” said Mark Van Raamsdonk, a physicist at the University of British Columbia in Vancouver who has done influential work on the subject.

    The mathematical translations are rapidly being worked out for holographic universes with an Escher-esque space-time geometry known as anti-de Sitter (AdS) space, but universes like ours, which have de Sitter geometries, have proved far more difficult. In his new paper, Verlinde speculates that it’s exactly the de Sitter property of our native space-time that leads to the dark matter illusion.

    De Sitter space-times like ours stretch as you look far into the distance. For this to happen, space-time must be infused with a tiny amount of background energy — often called dark energy — which drives space-time apart from itself. Verlinde models dark energy as a thermal energy, as if our universe has been heated to an excited state. (AdS space, by contrast, is like a system in its ground state.) Verlinde associates this thermal energy with long-range entanglement between the underlying qubits, as if they have been shaken up, driving entangled pairs far apart. He argues that this long-range entanglement is disrupted by the presence of matter, which essentially removes dark energy from the region of space-time that it occupied. The dark energy then tries to move back into this space, exerting a kind of elastic response on the matter that is equivalent to a gravitational attraction.

    Because of the long-range nature of the entanglement, the elastic response becomes increasingly important in larger volumes of space-time. Verlinde calculates that it will cause galaxy rotation curves to start deviating from Newton’s inverse-square law at exactly the magic acceleration scale pinpointed by Milgrom in his original MOND theory.

    Van Raamsdonk calls Verlinde’s idea “definitely an important direction.” But he says it’s too soon to tell whether everything in the paper — which draws from quantum information theory, thermodynamics, condensed matter physics, holography and astrophysics — hangs together. Either way, Van Raamsdonk said, “I do find the premise interesting, and feel like the effort to understand whether something like that could be right could be enlightening.”

    One problem, said Brian Swingle of Harvard and Brandeis universities, who also works in holography, is that Verlinde lacks a concrete model universe like the ones researchers can construct in AdS space, giving him more wiggle room for making unproven speculations. “To be fair, we’ve gotten further by working in a more limited context, one which is less relevant for our own gravitational universe,” Swingle said, referring to work in AdS space. “We do need to address universes more like our own, so I hold out some hope that his new paper will provide some additional clues or ideas going forward.”


    Access mp4 video here .

    The Case for Dark Matter

    Verlinde could be capturing the zeitgeist the way his 2010 entropic-gravity paper did. Or he could be flat-out wrong. The question is whether his new and improved MOND can reproduce phenomena that foiled the old MOND and bolstered belief in dark matter.

    One such phenomenon is the Bullet cluster, a galaxy cluster in the process of colliding with another.

    4
    X-ray photo by Chandra X-ray Observatory of the Bullet Cluster (1E0657-56). Exposure time was 0.5 million seconds (~140 hours) and the scale is shown in megaparsecs. Redshift (z) = 0.3, meaning its light has wavelengths stretched by a factor of 1.3. Based on today’s theories this shows the cluster to be about 4 billion light years away.
    In this photograph, a rapidly moving galaxy cluster with a shock wave trailing behind it seems to have hit another cluster at high speed. The gases collide, and gravitational fields of the stars and galalxies interact. When the galaxies collided, based on black-body temperture readings, the temperature reached 160 million degrees and X-rays were emitted in great intensity, claiming title of the hottest known galactic cluster.
    Studies of the Bullet cluster, announced in August 2006, provide the best evidence to date for the existence of dark matter.
    http://cxc.harvard.edu/symposium_2005/proceedings/files/markevitch_maxim.pdf
    User:Mac_Davis

    5
    Superimposed mass density contours, caused by gravitational lensing of dark matter. Photograph taken with Hubble Space Telescope.
    Date 22 August 2006
    http://cxc.harvard.edu/symposium_2005/proceedings/files/markevitch_maxim.pdf
    User:Mac_Davis

    The visible matter in the two clusters crashes together, but gravitational lensing suggests that a large amount of dark matter, which does not interact with visible matter, has passed right through the crash site. Some physicists consider this indisputable proof of dark matter. However, Verlinde thinks his theory will be able to handle the Bullet cluster observations just fine. He says dark energy’s gravitational effect is embedded in space-time and is less deformable than matter itself, which would have allowed the two to separate during the cluster collision.

    But the crowning achievement for Verlinde’s theory would be to account for the suspected imprints of dark matter in the cosmic microwave background (CMB), ancient light that offers a snapshot of the infant universe.

    CMB per ESA/Planck
    CMB per ESA/Planck

    The snapshot reveals the way matter at the time repeatedly contracted due to its gravitational attraction and then expanded due to self-collisions, producing a series of peaks and troughs in the CMB data. Because dark matter does not interact, it would only have contracted without ever expanding, and this would modulate the amplitudes of the CMB peaks in exactly the way that scientists observe. One of the biggest strikes against the old MOND was its failure to predict this modulation and match the peaks’ amplitudes. Verlinde expects that his version will work — once again, because matter and the gravitational effect of dark energy can separate from each other and exhibit different behaviors. “Having said this,” he said, “I have not calculated this all through.”

    While Verlinde confronts these and a handful of other challenges, proponents of the dark matter hypothesis have some explaining of their own to do when it comes to McGaugh and his colleagues’ recent findings about the universal relationship between galaxy rotation speeds and their visible matter content.

    In October, responding to a preprint of the paper by McGaugh and his colleagues, two teams of astrophysicists independently argued that the dark matter hypothesis can account for the observations. They say the amount of dark matter in a galaxy’s halo would have precisely determined the amount of visible matter the galaxy ended up with when it formed. In that case, galaxies’ rotation speeds, even though they’re set by dark matter and visible matter combined, will exactly correlate with either their dark matter content or their visible matter content (since the two are not independent). However, computer simulations of galaxy formation do not currently indicate that galaxies’ dark and visible matter contents will always track each other. Experts are busy tweaking the simulations, but Arthur Kosowsky of the University of Pittsburgh, one of the researchers working on them, says it’s too early to tell if the simulations will be able to match all 153 examples of the universal law in McGaugh and his colleagues’ galaxy data set. If not, then the standard dark matter paradigm is in big trouble. “Obviously this is something that the community needs to look at more carefully,” Zurek said.

    Even if the simulations can be made to match the data, McGaugh, for one, considers it an implausible coincidence that dark matter and visible matter would conspire to exactly mimic the predictions of MOND at every location in every galaxy. “If somebody were to come to you and say, ‘The solar system doesn’t work on an inverse-square law, really it’s an inverse-cube law, but there’s dark matter that’s arranged just so that it always looks inverse-square,’ you would say that person is insane,” he said. “But that’s basically what we’re asking to be the case with dark matter here.”

    Given the considerable indirect evidence and near consensus among physicists that dark matter exists, it still probably does, Zurek said. “That said, you should always check that you’re not on a bandwagon,” she added. “Even though this paradigm explains everything, you should always check that there isn’t something else going on.”

    See the full article here .

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    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 1:28 pm on November 28, 2016 Permalink | Reply
    Tags: Bolometers, Dark Matter, EDELWEISS experiment, IPNL, , ,   

    From IPNL: “First Results of the EDELWEISS III experiment” 

    ipnl-bloc

    Institut de Physique Nucleaire de Lyon

    13 May, 2016 [I just found these guys]
    Cazes Antoine

    1
    EDELWEISS bolometers before installation. No image credit

    The EDELWEISS experiment aims to detect WIMPs, a candidate for dark matter particles. It is located in the Modane Underground Laboratory. The experiment operates bolometers cooled to tens of Millikelvin where a WIMP might collide with a germanium nucleus and produce its recoil. This recoil is then measured by the resulting temperature rise (few microkelvin) and ionisation production (Germanium is a semiconductor material). This double measurment allow to identify nuclear recoils and thus eliminating much of the background due to gamma rays from natural radioactivity.

    For the third phase of the EDELWEISS experiment, the bolometers have been greatly improved and the cryostat was redesigned to reduce background noise and to accommodate a larger mass of detector. The experiment ran from July 2014 to April 2015. The data, equivalent to 582 kg.days were blindly analyzed and the background rejection was performed using a Boosted Decision Tree. This results in a lack of detection of WIMP and an improvement, by a factor varying between 12 to 41, compared to the previous limit EDELWEISS II: for a WIMP 5 GeV / c2, the collision cross sections WIMP -nucléon above 4.3×10-40 cm2 are excluded and those above 9.4×10-44 cm2 for WIMPs 20 GeV / c2.

    The EDELWEISS experiment is now working on a major R & D with the aim of lowering bolometers detection thresholds to explore collisions with low-mass WIMP (below 5 GeV / c2). This work is carried out in particular with the IOL cryostat installed IPNL.

    Science paper:
    Constraints on low-mass WIMPs from the EDELWEISS-III dark matter search

    See the full article here .

    ipnl-campus

     
  • richardmitnick 2:40 pm on November 25, 2016 Permalink | Reply
    Tags: , Dark Matter, GridPP, , Shear brilliance: computing tackles the mystery of the dark universe,   

    From U Manchester: “Shear brilliance: computing tackles the mystery of the dark universe” 

    U Manchester bloc

    University of Manchester

    24 November 2016
    No writer credit found

    Scientists from The University of Manchester working on a revolutionary telescope project have harnessed the power of distributed computing from the UK’s GridPP collaboration to tackle one of the Universe’s biggest mysteries – the nature of dark matter and dark energy.

    Researchers at The University of Manchester have used resources provided by GridPP – who represent the UK’s contribution to the computing grid used to find the Higgs boson at CERN – to run image processing and machine learning algorithms on thousands of images of galaxies from the international Dark Energy Survey.

    Dark Energy Icon

    The Manchester team are part of the collaborative project to build the Large Synoptic Survey Telescope (LSST), a new kind of telescope currently under construction in Chile and designed to conduct a 10-year survey of the dynamic Universe. LSST will be able to map the entire visible sky.

    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC

    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST telescope, currently under construction at Cerro Pachón Chile

    In preparation to the LSST starting its revolutionary scanning, a pilot research project has helped researchers detect and map out the cosmic shear seen across the night sky, one of the tell-tale signs of the dark matter and dark energy thought to make up some 95 per cent of what we see in the Universe. This in turn will help prepare for the analysis of the expected 200 petabytes of data the LSST will collect when it starts operating in 2023.

    The pilot research team based at The Manchester of University was led by Dr Joe Zuntz, a cosmologist originally at Manchester’s Jodrell Bank Observatory and now a researcher at the Royal Observatory in Edinburgh.

    “Our overall aim is to tackle the mystery of the dark universe – and this pilot project has been hugely significant. When the LSST is fully operating researchers will face a galactic data deluge – and our work will prepare us for the analytical challenge ahead.”
    Sarah Bridle, Professor of Astrophysics

    Dr George Beckett, the LSST-UK Science Centre Project Manager based at The University of Edinburgh, added: “The pilot has been a great success. Having completed the work, Joe and his colleagues are able to carry out shear analysis on vast image sets much faster than was previously the case. Thanks are due to the members of the GridPP community for their assistance and support throughout.”

    The LSST will produce images of galaxies in a wide variety of frequency bands of the visible electromagnetic spectrum, with each image giving different information about the galaxy’s nature and history. In times gone by, the measurements needed to determine properties like cosmic shear might have been done by hand, or at least with human-supervised computer processing.

    With the billions of galaxies expected to be observed by LSST, such approaches are unfeasible. Specialised image processing and machine learning software (Zuntz 2013) has therefore been developed for use with galaxy images from telescopes like LSST and its predecessors. This can be used to produce cosmic shear maps like those shown in the figure below. The challenge then becomes one of processing and managing the data for hundreds of thousands of galaxies and extracting scientific results required by LSST researchers and the wider astrophysics community.

    As each galaxy is essentially independent of other galaxies in the catalogue, the image processing workflow itself is highly parallelisable. This makes it an ideal problem to tackle with the kind of High-Throughput Computing (HTP) resources and infrastructure offered by GridPP. In many ways, the data from CERN’s Large Hadron Collider particle collision events is like that produced by a digital camera (indeed, pixel-based detectors are used near the interaction points) – and GridPP regularly processes billions of such events as part of the Worldwide LHC Computing Grid (WLCG).

    A pilot exercise, led by Dr Joe Zuntz while at The University of Manchester and supported by one of the longest serving and most experienced GridPP experts, Senior System Administrator Alessandra Forti, saw the porting of the image analysis workflow to GridPP’s distributed computing infrastructure. Data from the Dark Energy Survey (DES) was used for the pilot.

    After transferring this data from the US to GridPP Storage Elements, and enabling the LSST Virtual Organisation on a number of GridPP Tier-2 sites, the IM3SHAPE analysis software package (Zuntz, 2013) was tested on local, grid-friendly client machines to ensure smooth running on the grid. Analysis jobs were then submitted and managed using the Ganga software suite, which is able to coordinate the thousands of individual analyses associated with each batch of galaxies. Initial runs were submitted using Ganga to local grid sites, but the pilot progressed to submission to multiple sites via the GridPP DIRAC (Distributed Infrastructure with Remote Agent Control) service. The flexibility of Ganga allows both types of submission, which made the transition from local to distributed running significantly easier.

    By the end of pilot, Dr Zuntz was able to run the image processing workflow on multiple GridPP sites, regularly submitting thousands of analysis jobs on DES images.

    See the full article here .

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    U Manchester campus

    The University of Manchester (UoM) is a public research university in the city of Manchester, England, formed in 2004 by the merger of the University of Manchester Institute of Science and Technology (renamed in 1966, est. 1956 as Manchester College of Science and Technology) which had its ultimate origins in the Mechanics’ Institute established in the city in 1824 and the Victoria University of Manchester founded by charter in 1904 after the dissolution of the federal Victoria University (which also had members in Leeds and Liverpool), but originating in Owens College, founded in Manchester in 1851. The University of Manchester is regarded as a red brick university, and was a product of the civic university movement of the late 19th century. It formed a constituent part of the federal Victoria University between 1880, when it received its royal charter, and 1903–1904, when it was dissolved.

    The University of Manchester is ranked 33rd in the world by QS World University Rankings 2015-16. In the 2015 Academic Ranking of World Universities, Manchester is ranked 41st in the world and 5th in the UK. In an employability ranking published by Emerging in 2015, where CEOs and chairmen were asked to select the top universities which they recruited from, Manchester placed 24th in the world and 5th nationally. The Global Employability University Ranking conducted by THE places Manchester at 27th world-wide and 10th in Europe, ahead of academic powerhouses such as Cornell, UPenn and LSE. It is ranked joint 56th in the world and 18th in Europe in the 2015-16 Times Higher Education World University Rankings. In the 2014 Research Excellence Framework, Manchester came fifth in terms of research power and seventeenth for grade point average quality when including specialist institutions. More students try to gain entry to the University of Manchester than to any other university in the country, with more than 55,000 applications for undergraduate courses in 2014 resulting in 6.5 applicants for every place available. According to the 2015 High Fliers Report, Manchester is the most targeted university by the largest number of leading graduate employers in the UK.

    The university owns and operates major cultural assets such as the Manchester Museum, Whitworth Art Gallery, John Rylands Library and Jodrell Bank Observatory which includes the Grade I listed Lovell Telescope.

     
  • richardmitnick 1:14 pm on November 25, 2016 Permalink | Reply
    Tags: , Dark Matter, , NA64 experiment hunts the mysterious dark photon, ,   

    From CERN: “NA64 hunts the mysterious dark photon” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    25 Nov 2016
    Stefania Pandolfi
    Posted by Corinne Pralavorio

    1
    An overview of the NA64 experimental set-up at CERN. NA64 hunts down dark photons, hypothetic dark matter particles. (Image: Maximilien Brice/CERN)

    One of the biggest puzzles in physics is that eighty-five percent of the matter in our universe is “dark”: it does not interact with the photons of the conventional electromagnetic force and is therefore invisible to our eyes and telescopes. Although the composition and origin of dark matter are a mystery, we know it exists because astronomers observe its gravitational pull on ordinary visible matter such as stars and galaxies.

    Some theories suggest that, in addition to gravity, dark matter particles could interact with visible matter through a new force, which has so far escaped detection. Just as the electromagnetic force is carried by the photon, this dark force is thought to be transmitted by a particle called “dark” photon which is predicted to act as a mediator between visible and dark matter.

    “To use a metaphor, an otherwise impossible dialogue between two people not speaking the same language (visible and dark matter) can be enabled by a mediator (the dark photon), who understands one language and speaks the other one,” explains Sergei Gninenko, spokesperson for the NA64 collaboration.

    CERN’s NA64 experiment looks for signatures of this visible-dark interaction using a simple but powerful physics concept: the conservation of energy. A beam of electrons, whose initial energy is known very precisely, is aimed at a detector. Interactions between incoming electrons and atomic nuclei in the detector produce visible photons. The energy of these photons is measured and it should be equivalent to that of the electrons. However, if the dark photons exist, they will escape the detector and carry away a large fraction of the initial electron energy.

    Therefore, the signature of the dark photon is an event registered in the detector with a large amount of “missing energy” that cannot be attributed to a process involving only ordinary particles, thus providing a strong hint of the dark photon’s existence.

    If confirmed, the existence of the dark photon would represent a breakthrough in our understanding the longstanding dark matter mystery.


    View of the NA64 experiment set-up. (Video: Christoph Madsen/Noemi Caraban/CERN)

    See the full article here.

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    Meet CERN in a variety of places:

    Cern Courier

    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
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    CERN LHC particles

    Quantum Diaries

     
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