News Article | October 27, 2016
UPTON, NY - Sally Dawson, a theoretical physicist at the U.S. Department of Energy's Brookhaven National Laboratory, has been named a recipient of the 2017 J.J. Sakurai Prize for Theoretical Particle Physics. The award, given by the American Physical Society (APS), recognizes Dawson and her three co-authors of The Higgs Hunter's Guide, a seminal book first published in 1989 on the physics of Higgs bosons-fundamental particles predicted by the accepted theory of particle physics as essential to generating the mass of fundamental particles, and discovered in experiments at the Large Hadron Collider (LHC) in 2012. Dawson and her co-recipients-Gordon L. Kane of the University of Michigan, Howard E. Haber of the University of California, Santa Cruz, and John F. Gunion of the University of California, Davis-are long-term and ongoing colleagues. They were cited for their "instrumental contributions to the theory of the properties, reactions, and signatures of the Higgs boson." They will receive the award, which consists of $10,000 to be shared and certificates citing their achievements, at a ceremony during an APS meeting themed "Quarks 2 Cosmos" on Sunday, January 29, 2017, in Washington, D.C. "It's a great honor to receive this award with such distinguished scientists," said Dawson. She noted that she was just a postdoc when she first met Haber, recounted early discussions with Kane about the need to catalog what was then known about the Higgs as a way to guide future experiments, and pointed out Gunion's role as the first to calculate one of the signals by which the Higgs was eventually discovered. "This was all happening around the time the Superconducting Super Collider (SSC), and subsequently the LHC, were first proposed. We've known one another a long time." Dawson is best known for developing mathematical models to explain and predict the processes by which Higgs particles are produced. These precise theoretical calculations helped to guide searches for evidence of the Higgs at the LHC, located at the European Centre for Nuclear Research (CERN), which spans the Swiss/French border. The LHC's 2012 discovery of the Higgs contributed to the 2013 Nobel Prize in Physics, which was awarded to the theoretical physicists who predicted the particle's existence nearly fifty years earlier. "You never would have found the Higgs if you didn't know what you were looking for," Dawson explained to further highlight the importance of the theory work. "The searches were based on years of calculations and the detectors were designed to find this thing based on that theoretical work, which is still ongoing," Dawson said. Today, Dawson and her colleagues are collaborating to more accurately predict the production and decay processes for Higgs particles at the LHC. "You can calculate things now that you could never imagine calculating 20 years ago," she said. "People have developed new ways of calculating. It's not just brute force. We are smarter and have more tools now," she added. Comparing experimental measurements with predictions calculated using different theoretical assumptions gives scientists a way to check the accuracy of their theories-including the long-standing Standard Model, which has, so far, been successful in describing all known particles and their interactions. Dawson is particularly interested in exploring the interactions of Higgs particles produced in pairs. "If the Standard Model is correct, we can predict these interactions, but we need to be able to test them," she said. "If the predictions don't come out as expected, the mechanism that gives other particles their mass is not the whole story. And that would be very, very interesting," she said. To accumulate enough events to be able to do these analyses, the LHC will run through 2035. But Dawson noted that to finish the story, and really be able to measure all the properties of the Higgs, "we are going to need an even higher energy machine." Dawson joined Brookhaven Lab's Physics Department in 1986 after earning a B.S. in physics and mathematics from Duke University in 1977 and a Ph.D. in physics from Harvard University in 1981. She was a research associate at Fermilab from 1981 to 1983 and Lawrence Berkeley National Laboratory from 1983 to 1986. After arriving at Brookhaven Lab, Dawson rose through the ranks, leading the High Energy Theory Group from 1998 to 2004 and the Physics Department as chair from 2005 to 2007 before returning to research in 2008. She has also been an adjunct professor at Stony Brook University's Yang Institute for Theoretical Physics since 2001. Additional honors include being named a fellow of the American Physical Society in 1995 and the American Association for the Advancement of Science in 2006, and a recipient of the prestigious Humboldt Research Award in 2015. The J.J. Sakurai Prize was endowed by the family and friends of physicist Jun Sakurai, a well-known contributor in the field of quantum mechanics and particle physics, to encourage outstanding work in the field of particle theory. The award is given annually. Dawson's research at Brookhaven is supported by the DOE Office of Science. Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov. One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.
News Article | March 4, 2016
As political turmoil and conflict rock Ukraine, the country’s main scientific organization is in a bind. In January, Parliament passed a law to modernize the ailing National Academy of Sciences of Ukraine (NASU). Yet an austerity budget imposed around the same time makes this impossible to achieve — at least this year. The resulting cuts to science funding threaten the jobs of young researchers in particular, who are best poised to revitalize the country’s failing economy. “We have an extraordinarily high number of potential young scientists who are ready to work for the welfare of the country,” says Liliya Hrynevych, who chairs the Ukrainian Parliament’s Committee on Science and Education and voted in favour of the modernizing law. “But without setting priorities for science and research, it will be impossible for Ukraine to become a strong and wealthy European nation.” The academy employs some 20,000 scientists across 120 research institutes. On 26 November, Parliament began to debate a “law of Ukraine on scientific and technical activity”, in an attempt to streamline and strengthen the organization, which was founded in the Soviet era. Long deemed outdated and resistant to modernization, the academy uses an opaque system to award funding, and many of its members are elderly, not least the 97-year-old metallurgist Boris Paton, who has run the NASU for decades. The law stipulates the creation of a science advisory council that includes foreign specialists, and an independent grant-giving agency. All NASU institutes will undergo an external evaluation to examine their productivity and efficiency, and overall, government science spending must increase from a current 0.3% of gross domestic product to at least 1.7% by fiscal year 2017 — near the European Union average. But before the law took effect, Ukraine passed its 2016 austerity budget, in the wake of widespread closure of mines and factories, inflation, debt and currency devaluation. The budget allocates a meagre 2.05 billion hryvnia (US$76 million) to the NASU — about 12% less than in 2015, continuing a trend of decline (see ‘Ailing academy’). The cutbacks are irreconcilable with the science law, says Hrynevych, who is campaigning in Parliament for a budget revision after the first quarter of 2016. The budget will leave the academy with scarcely enough to cover the scant salaries (about US$200 per month on average) paid to its administrative staff and scientists. “We won’t be able to buy any new equipment this year, and purchase of consumables will need to be reduced to a minimum,” says Anatoly Zagorodny, director of the Bogolyubov Institute for Theoretical Physics in Kiev and a vice-president of the academy. The fresh cuts, he says, will also force institutes to reduce staff — in some circumstances, by more than one-third — and to discontinue many areas of research, even though science is crucial to economic recovery, he adds. Young scientists are the least protected by existing labour laws and so will feel the brunt of the job cuts, says Irina Yehorchenko, a research fellow at the NASU’s Institute of Mathematics in Kiev. She and some of her colleagues launched a petition in December calling on the country’s president, Petro Poroshenko, to save Ukrainian science. “I, for one, might be able to find a postdoc position abroad,” says Oleksandr Skorokhod, a cell biologist at the NASU Institute of Molecular Biology and Genetics in Kiev who is chair of the academy’s Council of Young Scientists. “But I’d much rather stay and try to change the bad state of affairs in my country.” Ukrainian science has struggled to recover from Russia’s annexation of the Crimea peninsula in 2014. General consensus in the international community is that Crimea is still part of the Ukraine — the United Nations General Assembly declared invalid a March 2014 referendum in which voters in Crimea approved the peninsula’s secession from Ukraine. But all 22 Crimean institutes formerly run by the NASU are now under Russian control, and only a few of their 1,320 staff members have relocated to Ukraine-controlled territory. The academy lost access to its only research ship, the RV Professor Vodianytsky, three astronomical observatories in Nauchny, Katsiveli and Yevpatoria and the 204-year-old Nikitsky Botanical Garden near Yalta, on the Black Sea shore. The Ukrainian government, moreover, expects scientists in Ukraine to cut all ties with colleagues who stayed on the peninsula, says Hrynevych, because any collaboration would be viewed as legitimizing the Russian occupation. The armed conflict with pro-Russian militants in eastern Ukraine is also causing problems for scientists, especially in the country’s Donbas region. Some 12,000 scientists and university lecturers there — about 60% of the former staff of 26 research institutes and universities in the province — have moved to safe institutions in Kiev and elsewhere. But many evacuating scientists left behind equipment or lost irreplaceable research material. Marine, environmental and climate studies in the Black Sea region, mining-related geology and a variety of archaeological and historical research have all been hit hard, says Zagorodny.
News Article | February 24, 2017
When researchers associated with the Laser Interferometer Gravitational-Wave Observatory (LIGO) — which consists of two detectors, one each in Hanford, Washington, and Livingston, Louisiana — announced the first ever detection of gravitational waves in February 2016, scientists hailed it as a new era in experimental physics. The ability to detect these ripples in the fabric of space-time, they argued, could one day allow us to create “gravitational maps” of the universe, giving us glimpses of objects and phenomena that would otherwise remain forever hidden. According to a study published in the latest edition of the journal Physical Review D, the LIGO project — in its advanced LIGO (aLIGO) iteration — could, in theory, achieve much more. The authors of the study state that LIGO’s gravitational wave detectors may be able to detect axions — a class of hypothetical particles that some physicists believe makes up dark matter — created by spinning black holes. Dark matter is the name given to the mysterious stuff that makes up 85 percent of the universe’s mass. The problem is, we don’t know what it’s made of. It may be Weakly Interacting Massive Particles (WIMPs), which are heavy particles that interact with normal matter only through gravity and the weak nuclear force, or axions — a class of extremely light particles whose existence is predicted by an extension of quantum chromodynamics, which is a theory that lies within the ambit of the Standard Model of particle physics. A recent calculation, made by researchers at the Forschungszentrum Jülich research center in Germany, suggests that if axions do constitute the bulk of dark matter, they would have a mass of between 50 and 1,500 microelectronvolts, making them up to 10 billion times lighter than electrons. This means that every cubic centimeter of the universe should contain an average of 10 million axions, and regions having larger concentration of dark matter, such as our local region of the Milky Way, should contain roughly 1 trillion axions per cubic centimeter. In the latest study, a team of researchers from the Perimeter Institute for Theoretical Physics, the Stanford Institute for Theoretical Physics, and the Center for Cosmology and Particle Physics at New York University argue that if these hypothetical particles have the predicted mass, spinning and colliding black holes should produce a cloud of axions — much like the cloud of electrons around an atom’s nucleus — due to a phenomenon known as superradiance. This should, in turn, produce gravitational waves, that can, in theory, be detected by LIGO. In addition, LIGO’s detectors may also be able to observe changes in a black hole’s angular momentum as it is slowed down by the cloud of axions — although this approach is less promising as measuring a black hole’s spin is an extremely daunting task. “It's an awesome idea,” Tracy Slatyer, a particle astrophysicist at the Massachusetts Institute of Technology (MIT) in Cambridge, who was not involved in the work, told Science magazine. “The [LIGO] data is going to be there, and it would be amazing if we saw something. ... This is probably the most promising paper I’ve seen so far on the new physics we might probe with gravitational waves.”
News Article | October 6, 2016
A child swings on a swing, gaining momentum with its legs. For physicists, this is a reasonably easy movement. They call it parametric oscillation. Things are getting more complicated if - in addition to the child's efforts - the mother (or the father) is around to push the swing. The interaction between the pushing force and the parametric oscillation can become very intricate, making it hard to calculate how much force the parent expends from the resulting irregular swinging motion. An interdisciplinary team of theoretical and experimental physicists at ETH Zurich has now succeeded in this very calculation. The researchers have been able to describe for the first time how parametric oscillation (the child's own drive) can be used to measure an external force (the parent's push). Their discovery has applications for sensors, and the scientists have submitted a patent application for the underlying principle. "Many of today's sensors are already based on oscillations," says Oded Zilberberg, a professor at the Institute for Theoretical Physics. "With small resonators you can measure, for example, force, pressure, mass, sound or temperature. Atomic force microscopes are also built on this principle." But these applications - often found in the field of microtechnology - currently use less intricate oscillations known as harmonic oscillations. For these measurements to use intricate oscillations, as Zilberberg and his colleagues propose, a paradigm shift is necessary: sensors would have to be designed differently. The new principle brings particular advantages for very small sensors, says the physicist. It would make it possible to build extremely small yet precise sensors, as the measuring signal in the new principle stands out better against background noise than with current methods. The scientists discovered the new principle while analysing parametric oscillations in a quantum physics experiment with laser-trapped rubidium atoms. Having understood the fundamental interaction between parametric and pushed oscillations, the researchers then directly demonstrated the effect using a parametrically oscillating guitar string. The scientists exerted a pulsating force on the string while continuously varying the frequency of the pulse. The researchers observed that the strength of the vibration of the string (amplitude) did not change fully continuous, but there was rather a sharp jump in amplitude at a particular frequency. As they discovered, this 'jump frequency' depends directly on the strength of the applied force and can therefore be used as a force meter. Zilberberg and his colleagues are now looking for industrial partners to help develop high-resolution sensors. The new principle could even be applied in computer technology. Zilberberg: "In the very early stages of the computer age there were computer memories that were based on oscillators, known as parametrons. The computer industry later lost interest in them, but our discovery could breathe new life into this field of research." More information: Luca Papariello et al, Ultrasensitive hysteretic force sensing with parametric nonlinear oscillators, Physical Review E (2016). DOI: 10.1103/PhysRevE.94.022201 R. Chitra et al. Dynamical many-body phases of the parametrically driven, dissipative Dicke model, Physical Review A (2015). DOI: 10.1103/PhysRevA.92.023815
Rezzolla L.,Institute for Theoretical Physics |
Kumar P.,University of Texas at Austin
Astrophysical Journal | Year: 2015
The merger of a binary of neutron stars provides natural explanations for many of the features of short gamma-ray bursts (SGRBs), such as the generation of a hot torus orbiting a rapidly rotating black hole, which can then build a magnetic jet and provide the energy reservoir to launch a relativistic outflow. However, this scenario has problems explaining the recently discovered long-term and sustained X-ray emission associated with the afterglows of a subclass of SGRBs. We propose a new model that explains how an X-ray afterglow can be sustained by the product of the merger and how the X-ray emission is produced before the corresponding emission in the gamma-band, though it is observed to follow it. Overall, our paradigm combines in a novel manner a number of well-established features of the emission in SGRBs and results from simulations. Because it involves the propagation of an ultra-relativistic outflow and its interaction with a confining medium, the paradigm also highlights a unifying phenomenology between short and long GRBs. © 2015. The American Astronomical Society. All rights reserved.
Nieuwenhuizen T.M.,Institute for Theoretical Physics
Foundations of Physics | Year: 2011
It is explained on a physical basis how absence of contextuality allows Bell inequalities to be violated, without bringing an implication on locality or realism. Hereto we connect first to the local realistic theory Stochastic Electrodynamics, and then put the argument more broadly. Thus even if Bell Inequality Violation is demonstrated beyond reasonable doubt, it will have no say on local realism, because absence of contextuality prevents the Bell inequalities to be derived from local realistic models. © 2010 The Author(s).
Koivisto T.,Institute for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011
A variational principle was recently suggested by Goenner, where an independent metric generates the spacetime connection. It is pointed out here that the resulting theory is equivalent to the usual Palatini theory. However, a bimetric reformulation of the variational principle leads to theories which are physically distinct from both the metric and the metric-affine ones, even for the Einstein-Hilbert action. They are obtained at a decoupling limit of C-theories, which contain also other viable generalizations of the Palatini theories. © 2011 American Physical Society.
Koivisto T.S.,Institute for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011
C-theory provides a unified framework to study metric, metric-affine and more general theories of gravity. In the vacuum weak-field limit of these theories, the parameterized post-Newtonian parameters β and γ can differ from their general relativistic values. However, there are several classes of models featuring long-distance modifications of gravity but nevertheless passing the Solar System tests. Here it is shown how compute the parameterized post-Newtonian parameters in C-theories and also in nonminimally coupled curvature theories, correcting previous results in the literature for the latter. © 2011 American Physical Society.
McFadden P.,Institute for Theoretical Physics |
Skenderis K.,Institute for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010
We propose a holographic description of four-dimensional single-scalar inflationary universes, and show how cosmological observables, such as the primordial power spectrum, are encoded in the correlation functions of a three-dimensional quantum field theory (QFT). The holographic description correctly reproduces standard inflationary predictions in the regime where a perturbative quantization of fluctuations is justified. In the opposite regime, wherein gravity is strongly coupled at early times, we propose a holographic description in terms of perturbative large N QFT. Initiating a holographic phenomenological approach, we show that models containing only two parameters, N and a dimensionful coupling constant, are capable of satisfying the current observational constraints. © 2010 The American Physical Society.
Koivisto T.S.,Institute for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010
Nonsingular cosmologies are investigated in the framework of f(R) gravity within the first order formalism. General conditions for bounces in isotropic and homogeneous cosmology are presented. It is shown that only a quadratic curvature correction is needed to predict a bounce in a flat or to describe cyclic evolution in a curved dust-filled universe. Formalism for perturbations in these models is set up. In the simplest cases, the perturbations diverge at the turnover. Conditions to obtain smooth evolution are derived. © 2010 The American Physical Society.