An artist’s conception of how BOSS uses quasars to measure the distant universe. Light from distant quasars is partly absorbed by intervening gas, which is imprinted with a subtle ring-like pattern of known physical scale. Astronomers have now measured this scale with an accuracy of two percent, precisely measuring how fast the universe was expanding when it was just 3 billion years old. (Illustration by Zosia Rostomian, Lawrence Berkeley National Laboratory, and Andreu Font-Ribera, BOSS Lyman-alpha team, Berkeley Lab.)
La survey del cielo denominata Baryon Oscillation Spectroscopic Survey (BOSS), che rappresenta la parte più grande della terza survey Sloan Digital Sky Survey (SDSS-III), ha osservato i quasar distanti per realizzare una mappatura delle variazioni di densità del gas intergalattico a redshift elevati permettendo così di tracciare la struttura dell’Universo primordiale. BOSS ci fornisce da un lato una carta temporale della storia evolutiva dell’Universo al fine di avere maggiori indizi sulla natura dell’energia scura e dall’altro ci permette di realizzare nuove misure della struttura su larga scala, le più precise mai ottenute sull’espansione cosmica sin dall’epoca in cui si sono formate le prime galassie.
Schema dello spettrometro di risonanza per lo studio degli effetti della gravità su scale molto piccole. Credit: TU
Non sempre occorre un acceleratore di particelle per fare esperimenti di fisica fondamentale. I primi risultati di un esperimento a bassa energia sulla gravità newtoniana, spinto fino ad un limite più piccolo di cinque ordini di grandezza, stringono il cerchio sulle proprietà potenziali che forze e particelle potrebbero assumere al di là di questo limite di sensibilità pari ad almeno qualche centinaia di migliaia di volte. Infatti, un nuovo metodo sviluppato da alcuni fisici della Vienna University of Technlogy, denominato spettroscopia di risonanza gravitazionale, si è rivelato così sensibile che ora potrà essere applicato per studiare le due componenti più enigmatiche dell’Universo, la materia scura e l’energia scura.
All the particles we know to exist make up only about five per cent of the mass and energy of the Universe. The rest, dark matter and dark Energy, remains mysterious. A European collaboration led by researchers from the Vienna University of Technology has now carried out extremely sensitive measurements of gravitational effects at very small distances at the Institut Laue-Langevin (ILL) in Grenoble. These experiments provide limits for possible new particles or fundamental forces, which are a hundred thousand times more restrictive than previous estimations.
Undiscovered Particles? Dark matter is invisible, but it acts on matter by its gravitational pull, influencing the rotation of galaxies. Dark energy, on the other hand, is responsible for the accelerated expansion of the Universe. It can be described by introducing a new physical quantity, Albert Einstein’s cosmological constant. Alternatively, so-called quintessence theories have been put forward: “Perhaps empty space is not completely empty after all, but permeated by an unknown field, similar to the Higgs-field”, says Professor Hartmut Abele (TU Vienna), director of the Atominstitut and group leader of the research group. These theories are named after Aristotle’s “quintessence”, a hypothetical fifth element, in addition to the four classical elements of ancient Greek philosophy.
If new kinds of particles or additional forces of nature exist, it should be possible to observe them here on Earth.
Tobias Jenke and Hartmut Abele from the Vienna University of Technology developed an extremely sensitive instrument, which they used together with their colleagues to study gravitational forces. Neutronsare perfectly suited for this kind of research. They do not carry electric charge and they are hardly polarizable. They are only influenced by gravity, and possibly by additional, yet unknown forces.
Forces at Small Distances The technique they developed takes very slow neutrons from the strongest continuous ultracold neutron source in the world, at the ILL in Grenoble and funnels them between two parallel plates. According to quantum theory, the neutrons can only occupy discrete quantum states with energies which depend on the force that gravity exerts on the particle. By mechanically oscillating the two plates, the quantum state of the neutron can be switched. That way, the difference between the energy levels can be measured. “This work is an important step towards modelling gravitational interactions at very short distances. The ultracold neutrons produced at ILL together with the measurement devices from Vienna are the best tool in the world for studying the predicted tiny deviations from pure Newtonian gravity”, says Peter Geltenbort (ILL Grenoble). Different parameters determine the level of precision required to find such tiny deviations, for instance the coupling strength between hypothetical new fields and the matter we know. Certain parameter ranges for the coupling strength of quintessence particles or forces have already been excluded following other high-precision measurements. But all previous experiments still left a large parameter space in which new physical non-Newtonian phenomena could be hidden.
A Hundred Thousand Times Better than Other Methods The new neutron method can test theories in this parameter range: “We have not yet detected any deviations from the well-established Newtonian law of gravity”, says Hartmut Abele. “Therefore, we can exclude a broad range of parameters”. The measurements determine a new limit for the coupling strength, which is lower than the limits established by other methods by a factor of a hundred thousand. Even if the existence of certain hypothetical quintessence particles is disproved by these measurements, the search will continue as it is possible that new physics can still be found below this improved level of accuracy. Therefore, Gravity Resonance Spectroscopy will need to be improved further, and increasing the accuracy by another few orders of magnitude seems feasible to the Abele’s team.
However, if even that does not yield any evidence of deviations from known forces, Albert Einstein would win yet another victory: his cosmological constant would then appear more and more plausible.
Uno studio recente condotto da Richard Schnee, un professore di fisica della Syracuse University, pubblicato sulla rivista online Symmetry, tenta di far luce sulla natura e origine della materia scura, quella componente elusiva che costituisce quasi il 27% del contenuto materia-energia dell’Universo, considerando la possibilità di eseguire una serie di esperimenti che permettano di trovare degli indizi su quelle eventuali particelle che non sono molto pesanti.
“Scientists looking for dark matter face a serious challenge, in that no one knows its properties”, says Schnee, also principal investigator of the Cryogenic Dark Matter Search (CDMS) Physics Lab at SU. “Experiments have seen no signs of dark matter particles that have high masses, but a few experiments have claimed hints of possible interactions from dark matter particles with low masses”. An expert in particle physics, Schnee hopes to find traces of dark matter with an experiment that is more sensitive to such low-mass dark matter particles. His group is part of a multinational team of scientists working on SuperCDMS, an experiment in the University of Minnesota’s Soudan Underground Laboratory that is designed to detect dark matter. Although dark matter has never been seen directly, it is thought to be six times more prevalent in the universe than normal matter. “Everywhere we look, objects are accelerating due to gravity, but the acceleration is too large to be caused by only the matter we see”, Schnee says. “Even more remarkably, we can infer that this extra dark matter is composed not of normal atoms, but other kinds of particles”. Scientists believe the mystery particles are WIMPs (Weakly Interacting Massive Particles), which travel at hundreds of thousands of miles per hour through space and shower the Earth on a continuous basis. Unlike normal matter, WIMPs do not absorb or emit light, so they cannot be viewed with a telescope. “Spotting the occasional WIMP that interacts with something is extremely challenging because particle interactions from natural radioactivity occur at a much higher rate. Detecting a WIMP is like spotting a needle in a haystack”, Schnee continues. Enter CDMS, whose hypersensitive detectors can differentiate between rare WIMP interactions and common ones involving radioactivity. The size of a hockey puck, a CDMS detector is made up of a semiconductor crystal of germanium that, when cooled to almost absolute zero, can detect individual particular interactions. The presence of layers of Earth, like those at the Soudan lab, provide additional shielding from cosmic rays that otherwise would clutter the detector, as it waits for passing dark matter particles. “We cool our detectors to very low temperatures, so we can detect small energies that are deposited by the collisions of dark matter particles with the germanium”, says Schnee. “Other materials, including argon, xenon and silicon, are also used to detect low-mass dark matter particles. We need to consider as many materials as possible, along with germanium”. SU is one of 14 universities working collaboratively in the search for WIMPs. In the Physics Building, Schnee and his team have constructed an ultra-low radon“clean room,” in hopes of reducing the number of interactions from radioactivity that look like WIMPs. (Alpha and beta emissions from radon, a type of radioactive gas, can mimic WIMP interactions in a detector.) “Unfortunately, radon is all around us, so, even with this ‘clean room,’ some radon-induced interactions will still mimic WIMPs“, Schnee says. “All of us are building different types of detectors and are constantly improving our methods, in hopes of spotting WIMP interactions”.
The inaugural cosmology conference in April 2014 will celebrate 40th anniversary of KASI. The workshop will cover recent progresses in observational and theoretical cosmology including the galaxies and large-scale structures, peculiar velocities, cosmic microwave background radiation, type Ia supernovae and gravitational lensing on the observational side, and the early universe, inflation, dark energy, dark matter, non-Gaussianity and numerical simulation in the theoretical side. Through close assessment of the present data and our current understanding we will be able to make plans for opening future windows in studying and describing our universe.
At left is a map of gamma rays with energies between 1 and 3.16 GeV detected in the galactic center by Fermi’s LAT; red indicates the greatest number. Prominent pulsars are labeled. Removing all known gamma-ray sources (right) reveals excess emission that may arise from dark matter annihilations. Image Credit: T. Linden, Univ. of Chicago
“The new maps allow us to analyze the excess and test whether more conventional explanations, such as the presence of undiscovered pulsars or cosmic-ray collisions on gas clouds, can account for it“, said Dan Hooper, an astrophysicist at Fermilab in Batavia, Ill., and a lead author of the study. “The signal we find cannot be explained by currently proposed alternatives and is in close agreement with the predictions of very simple dark matter models“.
The following animation zooms into an image of the Milky Way, shown in visible light, and superimposes a gamma-ray map of the galactic center from NASA’s Fermi. Raw data transitions to a view with all known sources removed, revealing a gamma-ray excess hinting at the presence of dark matter.
Dark matter, the mysterious substance estimated to make up approximately more than one-quarter of the mass of the Universe, is crucial to the formation of galaxies, stars and even life but has so far eluded direct observation. At a recent UCLA symposium attended by 190 scientists from around the world, physicists presented several analyses that participants interpreted to imply the existence of a dark matter particle.
“The likely mass would be approximately 30 billion electron-volts“, said the symposium’s organizer, David Cline, a professor of physics in the UCLA College of Letters and Science and one of the world’s experts on dark matter. The physicists at the Feb. 26–28 event were in agreement that “there seems to be an excess in the available data that could be due to dark matter“, Cline said. “At this symposium, it was obvious that excitement is building in the fields of dark matter theory and, especially, detection“, said Cline, who noted that there are several ways dark matter can be observed and that all were discussed at the UCLA meeting. “Because dark matter makes up the bulk of the mass of galaxies and is fundamental in the formation of galaxies and stars, it is essential to the origin of life in the Universe and on Earth“, Cline said. The first evidence for dark matter was discovered in 1933 using the Mt. Wilson telescope outside of Los Angeles. More recently, various theoretical models and detector improvements have made it possible to search for dark matter particles at extremely sensitive levels, some of the most sensitive measurements made by any scientists in the world. One search technique involves using the vast amount of dark matter in our galaxy. The NASA Fermi Satellite Telescope, an international collaboration involving NASA, the Goddard Space Flight Center and the SLAC National Accelerator Laboratory, searches for gamma rays, very high-energy light particles, from this dark matter. There are models of dark matter that would allow a signal in the galactic dark matter consistent with the claims at the meeting and provide a small interaction consistent with the “null results” in the direct dark matter searches all over the world. Much larger direct dark matter detectors are being planned in the U.S., Italy, Canada and China (including Xenon 3 Ton, LUX-ZEPLIN 7 Ton and DarkSide, which will weigh five tons). “These larger detectors potentially could see a dark matter signal in the next few years“, Cline said.
Dark matter is widely thought to be a kind of massive elementary particle that interacts weakly with ordinary matter. Physicists refer to these particles as WIMPS, for weakly interacting massive particles, and think they originated from the Big Bang. WIMPs are thought to be streaming constantly through the solar system and the Earth.
Another search method is to look for an interaction of a WIMP with xenon or argon nuclei and others (like germanium) in very low-background laboratories deep underground in Italy, the U.S., Canada, China and other countries. While these experiments have seen no signal of a WIMP above 30 billion electron volts, “there is no incompatibility with the interesting excess in the FERMI data“, Cline said. “The discovery of the Higgs boson, which won the 2013 Nobel Prize in physics, plays a role in the search for dark matter“, Cline said, adding that this topic was discussed in detail at the meeting. “Dark matter“, he said, “could consist of axions, WIMPs or sterile neutrinos, all of which were discussed at the symposium” (post). The UCLA dark matter symposium is convened every two years; this was the 11th such meeting. Cline said he and his colleagues hope to clarify the dark matter puzzle at the 2016 symposium.
It was at this same dark matter symposium in 1998 that two groups of scientists reported that the Universe is accelerating, as well as expanding, a finding Cline described as “one of the greatest discoveries in the history of science”.
Un gruppo di astrofisici dell’Università di Leiden, guidati da Alexey Boyarsky, potrebbero aver identificato alcune tracce della presenza di materia scura attraverso la rivelazione di una nuova particella, il neutrino sterile, un ipotetico tipo di neutrino che non interagisce con nessuna delle interazioni fondamentali. Intanto, qualche giorno fa, un altro gruppo di ricercatori di Harvard hanno riportato risultati simili.
The two groups this week reported that they have found an indirect signal from dark matter in the spectra of galaxies and clusters of galaxies. They made this discovery independent of one another, but came to the same conclusion: a tiny spike is hidden in the X-ray spectra of the Perseus galaxy cluster, at a frequency that cannot be explained by any known atomic transition. The Harvard group see the same spike in many other galaxy clusters, while Boyarsky also finds it in the nearby Andromeda galaxy. The researchers put it down to the decay of a new kind of neutrino, called ‘sterile’ because it has no interaction with other known neutrinos.
A sterile neutrino does have mass, and so could be responsible for the missing dark matter.
The first indications for the existence of dark matter in space were found more than eighty years ago, but there are still many questions surrounding this invisible matter. Sterile neutrinos are a highly attractive candidate for the dark matter particle, because they only call for a minor extension of the already known and extensively tested standard model for elementary particles. Boyarsky and his colleagues have already had this extension of the standard model ready for some time, but were waiting for the first observation of the mysterious particle. Measurements at higher resolution will shed light on the matter, and there is reason to hope that the spectral line just discovered will finally eliminate the problem of the missing mass.
Large galaxy redshift surveys have revealed that the Universe has a striking weblike structure. On these scales, galaxies and matter in the universe are arranged in a complex network of dense compact clusters, elongated filaments, two-dimensional sheets, and huge near-empty voids. The Cosmic Web is one of the most intriguing and striking patterns found in nature, rendering its analysis and characterization far from trivial. The absence of an objective and quantitative procedure for identifying and isolating clusters, filaments and voids in the cosmic matter distribution has been a major obstacle in investigating the structure and dynamics of the Cosmic Web. The overwhelming complexity of the individual structures and their connectivity, the huge range of densities and the intrinsic multiscale nature prevent the use of simple tools that may be sufficient in less demanding problems. One aspect that the workshop will focus on strongly is the analysis and identification of the Cosmic Web and its various components. Progress on the study of the weblike geometry of the Megaparsec and sub-Megaparsec matter distribution and of the relation between the large scale weblike environment and the galaxies populating its constituents has been hampered by the absence of a well-defined, commonly accepted language for quantifying its structure and topology. Quantities as basic and general as the mass and volume content of clusters, filaments, walls and voids are still not firmly established or defined. Since there is not yet a common framework to objectively define filaments and walls, the comparison of results of different studies concerning properties of the filamentary network — such as their internal structure and dynamics, evolution in time, and connectivity properties — is usually rendered cumbersome and/or difficult. Over the years, a variety of heuristic measures were forwarded to analyze specific aspects of the spatial patterns in the large scale Universe. In recent years we have seen the development of more solid and well-defined machineries for the description, characterization and quantitative analysis of the intricate and complex spatial patterns of the Cosmic Web. They address the full range of weblike features simultaneously, instead of focusing just on voids, or filaments in their own right. For a successful identification and characterization of the Cosmic Web we also need sophisticated reconstructions of the cosmic density field on the basis of the observed galaxy distribution.
During the course of the workshop, we will discuss and assess the different identification and reconstruction techniques, and contrast them with an aim towards developing a consensus among experts in the field. Amongst the specific issues that will be addressed are the following ones:
to increase our understanding of dynamics and evolution of the Cosmic Web, and the relation between the dark matter, gaseous
and galaxy distribution.
to obtain a handle on the way in which the web environment affects the formation and evolution of galaxies.
to obtain a representative census of the various methods to dissect the Cosmic Web and to identify its various components.
to assess and explore the fundamental differences between the different web analysis techniques.
to adapt techniques used for idealized theoretical and numerical circumstances to a range of observational data and surveys. Compare
the performance of the instruments for analysis of computer simulations with those used for the analysis of observational data and surveys.
to provide participants (before the meeting) with a z = 0 simulation snapshot and to compile comparative analyses of the simulation during the workshop. This comparison is intended to be published in a peer-reviewed journal.
Al CERN di Ginevra sono pronti per lanciare una nuova sfida, ancora più grande. E’ quanto hanno affermato in questi giorni i fisici delle particelle che oggi come non mai ritengono necessaria la costruzione di un nuovo, gigantesco acceleratore, almeno sette volte più potente dell’attuale Large Hadron Collider (LHC) grazie al quale è stato possibile rivelare una particella che tanto assomiglia al bosone di Higgs (post).
Particle physics takes the long-term view. Originally conceived in the 1980s, the LHC took another 25 years to come into being. This accelerator, which is unlike any other, is just at the start of a programme which is expected to run for another 20 years. Even now, as consolidation work aimed at a restart in 2015 continues, detailed plans are being hatched for a large-scale upgrade to increase luminosity and thereby exploit the LHC to its full potential.
The HL (High Luminosity) LHC is CERN1’s number-one priority and will increase the number of collisions accumulated in the experiments by a factor of ten from 2024 onwards.
Even though the LHC programme is already well defined for the next two decades, the time has come to look even further ahead, so CERN is now initiating an exploratory study for a future long-term project centred on a new-generation circular collider with a circumference of 80 to 100 kilometres. A worthy successor to the LHC, whose collision energies will reach 14 TeV, such an accelerator would allow particle physicists to push back the boundaries of knowledge even further. The Future Circular Colliders (FCC) programme will focus especially on studies for a hadron collider, similar to the LHC, capable of reaching unprecedented energies in the region of 100 TeV. The FCC study will be a global venture for particle physics and stems from the recommendation in the European Strategy for Particle Physics, published in May 2013, that a feasibility study be conducted on future fundamental research projects at CERN. It will be conducted over the coming five years and starts with an international kick-off meeting at the University of Geneva from 12 to 15 February. The FCC will thus run in parallel with another study that has already been under way for a number of years, the Compact Linear Collider, or “CLIC”, another option for a future accelerator at CERN. The aim of the CLIC study is to investigate the potential of a linear collider based on a novel accelerating technology. “We still know very little about the Higgs boson, and our search for dark matter and supersymmetry continues. The forthcoming results from the LHC will be crucial in showing us which research paths to follow in the future and what will be the most suitable type of accelerator to answer the new questions that will soon be asked,” says Sergio Bertolucci, Director for Research and Computing at CERN. “We need to sow the seeds of tomorrow’s technologies today, so that we are ready to take decisions in a few years’ time,” adds CERN’s Director for Accelerators and Technology, Frédérick Bordry. The goal of the two studies is to examine the feasibility of the various possible machines, to evaluate their costs and to produce a conceptual design report for the FCC and elaborate on the one already produced for CLIC in time for the next European Strategy update around 2018/2019.
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