Issue 1, 2014
Issue 1, 2014
Massive gravity, a modification of general relativity in which gravitons have mass, has an interesting history. Massive gravity was long believed to be internally inconsistent, but physicists at Stockholm University now claim to have constructed a consistent theory for massive gravity. This theory is a viable alternative to general relativity and can address some of its problems. In Einstein's theory of general relativity gravitational waves...... [Read more]
Professor Katherine Freese of the University of Michigan has begun a three year term as Director of Nordita starting September...
For the first time in its history, the Norwegian Research Council has accepted applications from scientists working at...
The Nordita Youtube Channel has been extended with two new five-minute videos highlighting research and researchers at...
Six years have passed since the ERC AstroDyn Project at Nordita was born. On 24 July 2008, a sunny day, an email said that...
The first GATIS network meeting of the year took place in Kings College London (KCL), UK, on 10th to 14th of February, 2014....
Massive gravity, a modification of general relativity in which gravitons have mass, has an interesting history. Massive gravity was long believed to be internally inconsistent, but physicists at Stockholm University now claim to have constructed a consistent theory for massive gravity. This theory is a viable alternative to general relativity and can address some of its problems.
Illustration: Angnis Schmidt-May
In Einstein's theory of general relativity gravitational waves spread with the speed of light, and the quanta of the gravitational field, the gravitons, are expected to do the same (*). To be more precise, gravitons move with the speed of massless particles because they are assumed to be massless. But whether or not a particle is indeed massless is in the end a question of experiment.
Neutrinos were long believed to be massless, but we know today that at least two of them have tiny non-zero masses (whose absolute value has not yet been determined). The mass of the photon is known to be zero to extremely high precision on experimental grounds. But what about gravity? This is a timely question because a small mass would lead to a long-distance modification of general relativity, and present observational evidence left physicists with some puzzles at these long distances, notably dark energy and dark matter.
However, to be able to even properly ask whether gravitons have masses, we need a consistent theory for massive gravity. But making gravitons massive is a challenge for the theoretical physicist. In fact, it was long believed to be impossible.
The problems start when you want to introduce a mass-term into general relativity. For vector fields, you can take a contraction of fields of the form A?A? to stand in front of the mass term. In general relativity the field is the metric tensor, and the only full contractions that you can create without using derivatives are constant: they create a cosmological constant, not a graviton mass. If you want a mass-term in general relativity you need a second two-tensor, that is a field which looks like a metric but isn't the metric. Theories of this type are also known as 'bi-metric'. Massive gravity is thus intimately related to bi-metric gravity.
But that's only the beginning of the problems, a beginning that dates back more than 70 years.
In 1939, Fierz and Pauli wrote down a theory of massive gravity in the perturbative limit. They found that for the theory to be consistent meaning free of 'ghosts' that lead to unphysical instabilities the parameters in the mass-terms must have specific values. With these values, the theory is viable.
In 1970 however, van Dam and Veltman and, independently, Zakharov, showed that in the Fierz-Pauli approach, the limit in which the mass of the graviton is taken to zero is not continuous and does, contrary to naïve expectations, not reproduce general relativity. Any graviton mass, regardless how small, leads to deviations that can contribute factors of order one to observables, which is in conflict with observation. The Fierz-Pauli theory now seemed theoretically fine, but experimentally ruled out.
Two years later, in 1972, Vainshtein argued that this discontinuity is due to the treatment of the gravitational degrees of freedom in the linearization procedure and can be cured in a full, non-linear, version of massive gravity. Unfortunately, in the same year, Deser and Boulware claimed that any non-linear completion of the Fierz-Pauli approach reintroduces the ghost. So now massive gravity was experimentally fine but theoretically sick.
Nothing much happened in this area for more than 30 years. Then, in the early 2000s, the wormy can was opened again by Arkani-Hamed et al and Creminelli et al, but they essentially confirmed the Deser-Boulware problem.
The situation began to look brighter in 2010, when de Rahm, Gabadadze and Tolley proposed a theory of massive gravity that did not suffer from the ghost-problem in a certain limit. Needless to say, after massive gravity had been thought dead and buried for 40 years, nobody really believed this would work. The de Rahm-Gabadadze approach did not make many friends because the second metric was treated as a fixed background field, and the theory was shown to allow for superluminal propagation (and, more recently, acausality).
However, starting in 2011, Fawad Hassan and Rachel Rosen from Stockholm University (i.e. next door from Nordita), succeeded in formulating a theory of massive gravity that does not suffer from the ghost instability. The key to success was a generalization of the de Rahm-Gabadadze approach in which the second metric is also fully dynamic, and the interaction terms between the two metrics take on a specific form. The specific form of the interaction terms is chosen such that it generates a constraint which removes the ghost field. The resulting theory is to best present knowledge fully consistent and symmetric between the two metrics.
(Which, incidentally, explains my involvement with the subject, as I published a paper with a fully dynamic, symmetric, bi-metric theory in 2008, though I wasn't interested in the massive case and don't have interaction terms. The main result of my paper is that I ended up in defense committees of Fawad's students.)
In the last years, the Stockholm group has produced a series of very interesting papers that not only formalizes their approach and shows its consistency, but they also derived specific solutions. This is not a small feat as it is already difficult to find solutions in general relativity if you have only one metric and having two doesn't make the situation easier. Indeed, not many solutions are presently known, and the known ones have quite strong symmetry assumptions. (More students in the pipe...)
Meanwhile, others have studied how well this modification of general relativity fares as an alternative to ΛCDM. It has been found that massive gravity can fit all cosmological data without the need to introduce an additional cosmological constant. But before you get too excited about this, note that massive gravity has more free parameters than ΛCDM, that being the coupling constants in the interaction terms.
What is missing right now though is a smoking-gun signal, some observation that would allow to distinguish massive gravity from standard general relativity and could be used to distinguish between both. This is presently a very active area of research and one that I'm sure we'll hear more about.
(*) To be precise, in the classical theory we should be speaking of gravitational waves instead. The frequent confusion between gravitational waves and gravitons, the latter of which only exist in quantized gravity, is a bad habit but forgivable. Far worse are people who say 'gravity wave' when they refer to a gravitational wave. A gravity wave is a type of cloud formation and has nothing to do with linearized gravity.
The first GATIS network meeting of the year took place in Kings College London (KCL), UK, on 10th to 14th of February, 2014. The Nordita GATIS fellows, James Gordon and Xinyi Chen, attended the meeting. Xinyi reports:
The GATIS (Gauge Theories as an Integrable System) network is an EU-funded Marie Curie Initial Training Program, of which Nordita is one of 17 partners. The event held at KCL was a gathering of mostly young researchers from different partner institutions. It consisted of two separate parts. The first part was a scientific workshop, called "Strongly Coupled Gauge Theories", while the second part was devoted to a soft-skill training program on scientific communication, with subsequent proposals about outreach projects of the network.
The scientific workshop lasted two days, where a total of 22 researchers gave short presentations about their current research. I had the opportunity to give my first talk as PhD student, about my ongoing project with my supervisor, Nordita Professor Konstantin Zarembo, and fellow PhD student James Gordon. I presented the model we are currently working on, the so-called N=2* Super Yang-Mills theory, in the holographic setting. Some of our preliminary results were showed as well.
During the following two days, one of the private partners of the GATIS network, SISSA Medialab, gave us an introductory course on scientific communication. Group activities were organized, such as practicing talks aimed at various audiences, and writing scientific news titles and abstracts for the general public.
On the last day, participants, including some senior researchers from the network, formed three groups to discuss GATIS outreaching projects. This was mediated by professionals from two other privates sectors, Milde Marketing and Mann beisst Hund. We discussed a website project, which might involve a blog addressed to a non-specialist audience; a visual project, which will consist of a short film about the network; and, last but not least, a social media project, both for internal communication and public outreach. Future meetings of GATIS fellows and the private companies will further develop these projects.
The experience, overall, was enriching, with a friendly atmosphere. More information about GATIS can be found on its official website: gatis.desy.eu
Outreach
The University of Iceland website Vísindavefurinn (Web of Science) has been named as the best Icelandic "medium" and the best non-profit website. Vísindavefurinn was launched in 2000. Initially it was conceived as a temporary contribution to the project of the University of Iceland, Reykjavik - European City of Culture in 2000. Soon, however, due to the large public interest in Science, it was decided to keep the project going. Vísindavefurinn deals with all sciences, from astronomy to molecular biology. Visitors can read the answers to the most popular scientific questions, but also, they can submit new questions and the employees of the University and supporters of the website can directly answer or find the answer. As described by the Selection Committee: "The web is filled with exciting and interesting content about everything between heaven and earth, it is at once one of the most reliable, user-friendly" and extremely popular scientific website.
Grants, Research Policies, International Cooperation
The international project GARCIA has been awarded a grant by the EU 7th Framework Programme.
The project GARCIA, Gendering the Academy and Research: Combating Career instability and asymmetries, is a collaboration between Belgium, Switzerland, Slovenia, the Netherlands, Austria, Iceland, and Italy, which is responsible for the project management. The total amount of the grant is just below 2.3 million EUR for a three-year period. The grant is an important recognition for gender studies at the University of Iceland.
Research Policies
In a public speech, the rector of the University of Iceland, Kristin Ingólfsdóttir, comes back to the cutting of public financial funding of the university. As she explained, in order to reach the level of public investments in other Nordic universities the income must grow by five billion ISK (over 30 million EUR). Currently the University of Iceland has about 14 thousand students and 2000 staff. It plays a crucial role in Icelandic education and development of new knowledge and wealth based on research and science.
She mentioned how basic research has contributed to capital growth, and how the University of Iceland has been a leading center for innovation and new industries in Iceland. She recalled recent three start-up companies based on research in ophthalmic in cooperation with scientists working on computer science, statistics, pharmacology, and electrical engineering.
Alumni, Awards
Yasser Roudi of the Kavli Institute for Systems Neuroscience in Trondheim, Norway, has been awarded the 2014 Fridtjof Nansen Prize for Young Scientists by the Norwegian Academy of Science and Letters. Yasser held a Nordita Fellowship from 2008 to 2010 and is currently a Corresponding Fellow.
Alumni, Awards
Professor Risto Nieminen (Aalto University, former Director of Nordita) and Professor Irma Thesleff (University of Helsinki) have been awarded the honorary title of Academician of Science. President of the Republic Sauli Niinistö granted the titles at a presidential session in February 2014.
Grants
The Swedish research council has selected grant recipients to receive a total of 50 MSEK over 10 years in a recently established program for distinguished professors. Two out of nine professors are physicists: Anne L'Huillier at Lund University got funded for the project proposal "Lund's attosecond science center and Olle Eriksson at Uppsala University received funding for "Dynamics in Materials".
In the Media, Nordita
Financial Times Magazine has listed Nordita Assistant Professor Sabine Hossenfelder as one of the next big names in physics, as "a rising leader in quantum gravity research, a young field that explores the interplay between the theory of general relativity and quantum mechanics."
Many greetings from us at Nordita (and some of our friends at the Astronomy Department)! <br>Here we are celebrating Nowruz, the Iranian new year.
Professor Katherine Freese of the University of Michigan has begun a three year term as Director of Nordita starting September 1, 2014. Professor Freese is an internationally recognized researcher working on a wide range of topics in theoretical astro-particle physics and cosmology. She received her PhD in Physics 1984 from the University of Chicago and held postdoctoral appointments at Harvard University, the Institute for Theoretical Physics at UC Santa Barbara, and UC Berkeley. From 1987 to 1991 she was an Assistant Professor at MIT and then moved to the University of Michigan, where she is currently the George Eugene Uhlenbeck Professor of Physics. In 2012 she was awarded an honorary doctorate at Stockholm University and it was recently announced that she will receive a Grant for the International Recruitment of a Leading Researcher from Vetenskapsrådet (Swedish Research Council) for a total of 101 500 000 SEK over a period of 10 years. We congratulate her on this well-deserved recognition and wish her every success during her time at Nordita.
Meet the Norditians.
Outgoing Nordita Director Larus Thorlacius has now returned to his position as Professor of Physics at the University of Iceland, but will continue to spend part of his time in Stockholm as a Guest Professor of Theoretical Physics at Stockholm University.
Lárus Thorlacius (left) receiving a gift that will kickstart his new career from Nordita board chairman Kalle-Antti Suominen.
(Photo: Per Osland)
John Wettlaufer of Yale University (USA) is a familiar figure at Nordita. During the fall of 2008, he spent his sabbatical at Nordita; see Nordita Newsletter 2008/3, funded in part by the Wenner Gren Foundation, the Stochholm Astrobiology Graduate School, and Nordita. He came back to Nordita in 2011, again supported by the Wenner Gren Foundation; see Nordita Newsletter 2011/2. He was then awared the distinguished Tage Erlander Guest Professorship of 2012; see Nordita Newsletter 2011/3.
The Swedish Research Council (VR) has now awared him a 106 MSEK grant for a 10 year stay under the scheme "Grants for international recruitment of leading researchers". We wish John a prosperous time at Nordita!
John Wettlaufer (left) at the inaugural lecture of the Tage Erlander Guest Professorship for 2012, together with Prof. Sven Stafström, head of the Swedish Research Council. (Photo: Fabio Del Sordo)
At its general meeting on April 9, 2014, the Royal Swedish Academy of Sciences elected Nordita Professor Axel Brandenburg as Foreign Member of the Academy's class for astronomy and space science. This honor recognizes the numerous significant contributions and leadership of Axel Brandenburg within the fields of magnetohydrodynamics and turbulence in astrophysical plasmas. For more information see the news release of the Academy.
Grants, International Cooperation
For the first time in its history, the Norwegian Research Council has accepted applications from scientists working at research institutes funded by the Nordic Council of Ministers, including Nordita, and in Fall 2013 Nordita won its first Norwegian grant when it was decided to fund a concentrated 4-year effort at Nordita in Stockholm and NTNU in Trondheim to improve our understanding of particle transport and clustering in stratified turbulent flows. This work couples large-scale numerical simulations with numerically guided analytical approaches. An ultimate goal is to have a physically consistent model of particle transport in raindrop formation.
Particle motion and particle accumulation in turbulent flows with temperature gradients are also of great importance for many critical applications in the modern world. Examples include the Diesel engine, industrial boilers, and prediction of rain initiation in the atmosphere. There are also astrophysical applications, in particular the conglomeration of dust in the context of protoplanetary accretion discs.
For further details, see the home page on the project Particle transport and clustering in stratified turbulent flows.
The Knut and Alice Wallenberg Foundation has granted 28.5 MSEK for the "Discovering Dark Matter Particles in the Laboratory", an experimental project with Jan Conrad of Stockholm University leading the Swedish effort and with Nordita's Katherine Freese as Co-PI.
The nature of the dark matter in the Universe that comprises 95% of the mass in galaxies including our own Milky Way is as yet unknown. The XENON 1T experiment consists of a tonne of Xenon liquid that produces two pulses of scintillation light when struck by a dark matter particle coming in from the Galaxy. The discovery of dark matter would solve one of the longest outstanding problems in all of modern physics.
The Knut and Alice Wallenberg Foundation has granted 33 MSEK to Bernhard Mehlig of Gothenburg University, Sweden, to understand "Bottlenecks for Particle Growth in Turbulent Aerosols". Axel Brandenburg and Dhrubaditya Mitra of Nordita are involved in this work as Co-PIs. A kickoff meeting will be held at Nordita on 7 November.
Bernhard Mehlig protecting himself from intermittent showers of turbulent aerosols in Gothenburg.
(Photo: Johan Wingborg)
Nordita is happy to be the administrative host for two VR (Swedish Research Council) International PostDocs for the next three years. One of them is former Nordita fellow Mikhail Modestov, who chose Princeton University as his host university and the other one is Fabio Del Sordo, former PhD student at Nordita, who chose Yale University as his host university. Both are expected to spend a fraction of their time at Nordita.
Six years have passed since the ERC AstroDyn Project at Nordita was born. On 24 July 2008, a sunny day, an email said that "the panel has recommended your proposal for funding at a sufficiently high position on the priority list, which is expected to allow actual funding." In the original proposal of 2008, fourteen milestones were set. All of them have been addressed and have led to publications; see this project progress report for details. Particularly productive outcomes include Task 2 on the test-field method (10 publications), Task 7 on dynamos in spherical shell segments (13 publications), Task 8 on magnetic flux concentrations near the surface (18 publications), Task 9 on coronal mass ejections from a dynamo (6 publications), and Task 10 on convective dynamos in spherical shell (7 publications). The outcomes of these five tasks make up more than half of the 105 publications that acknowledge the ERC Advanced Grant. Some of these achievements have been reported in earlier issues of this Newsletter (two articles in issue 2/2013 and one in issue 2/2011). The Pencil-Code pencil-code.googlecode.com is an open source community effort and used heavily in this project. Over the period of the grant, the code has grown significantly: from revision 10328 of 1 February 2009 to 21669 on 9 April 2014. And that's not all: the solar activity has recovered from its deepest low since 1908 to peak sunspot numbers of around 100, as pointed out by the PI in the picture.
Center: What should a solar physics group do if not take a whiteboard under the arm and move the group meeting out onto the sun-basked lawn in front of the Nordita building.
Right: At the cake and coffee reception in January 2014 marking the conclusion of the AstroDyn project, project leader Axel Brandenburg used the most recent ISES Solar Cycle Sunspot Number Progression chart to illustrate the close correlation between the growth of the project and the number of sunspots; from the time the project ends the sunspot number is predicted to decrease again.
The fifth annual Nordita Winter School on Theoretical Physics took place at Nordita in Stockholm January 6-17, 2014. This year the focus was on theoretical condensed matter physics, and the school was organized by David Abergel (Nordita), Eddy Ardonne (Stockholm University), Alexander Balatsky (Nordita) and Stephen Powell (University of Nottingham).
The winter school attracted students from all five Nordic countries, along with Latvia and Poland. They were given an overview of the most important ideas underlying modern condensed matter theory and an introduction to current trends of particular interest with the aim of providing them with useful tools for entering into rapidly developing areas of research. Topics included strongly correlated electrons, topological states of matter, unconventional superconductivity, and the physics of low-dimensional structures.
Lecturers included David Abergel (Nordita), Alexander Balatsky (Nordita), Annica Black-Schaffer (Uppsala University), Piers Coleman (Rutgers University), Vladimir Fal'ko (Lancaster University), Hans Hansson (Stockholm University), Dirk van der Marel, University of Geneva), Felix von Oppen (Freie Universität Berlin), Nicola Spaldin (ETH Zurich) and Mikael Fogelström (Chalmers University).
The Nordita Winterschool 2015 will be held at Nordita 716 January 2015. The focus will be on high-energy physics. Deadline for applications is 30 November, 2014.
Sarah Jabbari, PhD student at Nordita and Stockholm University, successfully defended her licentiate thesis "Origin of Solar Surface Activity and Sunspots" on 19 May 2014, with Vasilis Archontis of the University of St Andrews as opponent. Her thesis is based on three papers in which she combines for the first time the so-called negative effective magnetic pressure instability with the dynamo instability. Her model may provide an alternative to the current paradigm of sunspot formation. Sarah is supported through the VR project grant 621-2011-5076, Turbulent dynamo simulation in a spherical shell segment , awared to Axel Brandenburg in January 2012.
Left to right: Axel Brandenburg (supervisor, Nordita), Vasilis Archontis (opponent, U. of St. Andrews), and Sarah Jabbari (licentiate); absent are committee members Jesper Sollerman and Jorrit Leenaarts (Dept. of Astronomy, Stockholm U.)
On 21 May 2014, Apostolos Vasileiadis, master student at Stockholm University, successfully defended his masters thesis "Particle Diffusion in Periodic Obstacle Arrays".
Left to right: Ralf Eichhorn (supervisor, Nordita) and Apsotolos Vasileiadis (master); absent are Astrid de Wijn (co-supervisor) and Hannes Hübel and Cristophe Clément (committee members; all three from Stockholm U.).
Research Training
Rays - Research Academy for Young Scientists, is a non-profit organization that organizes summer research schools
for second-year high-school students that want to pursue a career in science. The 2014 school, where the young scientists spent four weeks of their summer vacations, was held in beautiful Strängnäs, south-west of Stockholm.
The programme consisted of training sessions in scientific methodology, inspirational talks by invited researchers, visits to research insititutes and corporate R&D departments, and work on the student's own research project under the supervision of researchers from Stockholm University, KTH Royal Institute of Technology and Karolinska Institute. One of this year's supervisors was Nordita assistant professor Dhrubaditya Mitra, with support from postdoc Bidya Binay Karak. Students spent the final week writing their reports, which then were presented at a public seminar at the Stockholm Technical Museum on 12 July 2014.
The three Rays at Nordita, left to right: Ottilia Andersson (Södra Latins gymnasium, Stockholm), Toomas Liiv (Danderyds gymnasium, Stockholm), and Jakob Broman (ProCivitas, Malmö).
Four new Nordita Fellowships have been awarded to
In addition, Marcelo Dias, formerly of Brown University, has taken up a joint postdoctoral position in soft condensed matter physics at the Aalto Science Institute (AScI) and Nordita, with residence at AScI for two years followed by a third year as a Nordita Fellow.
There were 399 fellowship applications this year. They were evaluated and ranked by the three Nordic Research Committees and by the Nordita faculty. We would like to take this opportunity to thank committee members for their time and commitment to Nordita.
The "Nordita Fellowships" are postdoctoral positions supported by Nordita. In addition, we have several PhD and postdoctoral positions financed by various grants won by Nordita senior staff. These are new postdocs arriving in fall 2014:
For the first time ever, Nordita and Uppsala University have advertised jointly a tenured position as assistant professor in high energy physics. Due to fortunate circumstances, two people have now been hired:
They are expected to share their time between both places to conduct research in high-energy physics and to teach.
Welcome lunch for some of the new Norditians in September.
Nordita postdoctoral fellow Juha Jäykkä left Nordita in December 2013 to take up a position at Cambridge University.
Juha receives his farewell present, a souvenir from Sweden, from condensed matter physics group leader Sasha Balatsky.
In January 2014, visiting professor Matthias Rheinhardt ended his second longer visit at Nordita, to return to the University of Helsinki.
Astrophysics group leader Axel Brandenburg thanks Matthias at the occasion of the completion of the ERC AsdroDyn project, an event attended by both Norditians and Stockholm University astronomers.
Then in July and August, four more Nordita postdoctoral fellows left Nordita: Sreejith Ganesh Jaya (to the Max Planck Institute for the Physics of Complex Systems in Dresden), Blaise Goutéraux (to Stanford University), Mikhail Modestov (to Princeton University), Anthony van Eysden (to Montana State University).
Around the same time, James Gordon ended his one-year stay at Nordita as a visiting PhD student. He now continues his studies at the University of British Columbia.
We would like to take this opportunity to thank Juha, Matthias, Sreejith, Blaise, Mikhail, Anthony and Jamie for their time at Nordita and for their contribution to the vitality of the institute. They have our best wishes for their future career.
Various travel grants were awared to Nordita's PhD students. Among them are two Dahlmark Grants from the Astronomy Department at Stockholm University. One went to Sarah Jabbari and one to Illa R. Losada for conferences in Germany, the US, and India. Sarah Jabbari also won a travel grant from the Jubilee donation of the Knut and Alice Wallenberg Foundation for a conference in the US.
For many decades, polarized radio emission from external galaxies has been used to infer the strength and structure of their magnetic field. This emission is caused by relativistic electrons gyrating around magnetic field lines and producing the polarized synchrotron emission. The plane of polarization gives an indication about the electric (and thus magnetic) field vectors at the source of emission. The line-of-sight component of the field can be inferred through the Faraday effect that leads to a wavelength-dependent rotation of the plane of polarization.
In practice, an observer will always see a superposition of different polarization planes from different depths, which can lead to a reduction in the degree of polarization. Firstly, the orientation of the magnetic field changes, causing different polarization planes at different positions. Secondly, Faraday rotation causes the plane of polarization to rotate. The decrease in polarized emission resulting from this superposition is referred to as Faraday depolarization. This was regarded as a problem that can be alleviated partially by restricting oneself to observations at shorter wavelengths. This situation has changed with the advent of new generations of radio telescopes that can measure polarized emission over a broad and continuous range of wavelengths. This allows one to apply the method of Burn (1966, Mon. Not. Roy. Astron. Soc. 133, 67) that utilizes the wavelength-dependent depolarization to determine the distribution of radio sources with respect to Faraday depth.
This was also the topic of a one-week workshop organized by form Nordita fellow Oliver Gressel in September 2013. As a direct outcome of this workshop, two papers have now appeared that examine the possibility of detecting helical magnetic fields in the radio sky; one is by the Nordita astrophysics research committee member Cathy Horellou (Onsala) together with Andrew Fletcher (Newcastle) and the other one is by Axel Brandenburg (Nordita) and Rodion Stepanov (Perm). Both papers appeared on 16 January on the arXiv (arXiv:1401.4152 and arXiv:1401.4102) and have now been published.
The Nordita Youtube Channel has been extended with two new five-minute videos highlighting research and researchers at Nordita.
For other video presentations of research at Nordita, see www.nordita.org/video
Also check out our comments on what's on in the world of physics on the Nordita Facebook Page, and for deeper analysis read Sabine Hossenfelder's Blog 'Backreaction'.
One of the best things with working at Nordita is the international atmosphere at the institute. Our students and researchers come to us from all over the world, and thanks to our scientific programs we have hundreds of international visitors, enriching the institute both scientifically and culturally.
The theme of this year's Nordita Winter School was condensed matter physics. One of the lecturers at the school, Nicola Spaldin from ETH Zurich, is an inspiring virtuoso not only in questions concerning the Berry phase, ferroelectrics, and topological insulators, but also on the clarinet. Whenever she travels to Stockholm she takes the opportunity to play together with the Fjord Quintet. And we at Nordita are treated with an exclusive concert.
The Fjord Quintet at the Winter School concert, 14 January 2014: Sigrid Neumann (violin 1), Lars-Arne Axelsson (violin 2), Krister Persson (violoncello), Erik Hagersten (viola), and Nicola Spaldin (clarinet). On the program: Brahms' Clarinet Quintet and Debyssy's "Petit Pièce".
As mentioned on the top of this page, we celebrated Nowruz earlier this year. This is what Nordita PhD student Sara Jabbari taught us about the Persian new year: Nowruz marks the first day of spring and the beginning of the year in the Persian calendar. It is celebrated on the day of the astronomical Northward equinox, which usually occurs on March 21 or the previous/following day depending on where it is
observed. The moment the sun crosses the celestial equator and equalizes night and day is calculated exactly every year and families gather together to observe the rituals. Last time it happened was on 20 March 2014 at 6 pm, and Norditians were ready, standing around our version of Haft S?n (or the seven "S"s), a traditional table setting at Nowruz, with seven items that start with the letter "S" or S?n in the Persian alphabet, each item symbolizing qualities like love, patience, health and affluence. Can you spot our Haft S?n items? s?b (apples), sabzeh (wheat, barley or lentil sprouts), samanu (a sweet pudding made from germinated wheat), senjed (the dried fruit of the Oleaster tree), s?r (garlic), somaq (sumac berries) and serkeh (vinegar).
If the Persian spring celebration Nowruz made us all healthy and affluent for the remainder of the year, it unfortunately didn't bring out the Swedish spring. This was our second attempt to use culture to quash the Nordic winter, after our 1 March Maslenitsa party, the Russian version of the celebration of the end of the winter or the start of the lent, like Swedidh Fettisdagen, French Mardi Gras, or British Shrove Tuesday.
Nordita postdoc Alexander Krikun (leftmost in the first photo) promised to make the pancakes traditionally eaten at Maslenitsa (in frying pans on the Nordita BBQ, no less), and the rest of us brought caviar and other salty and sweet fillings. The sunny-golden pancakes inspired Sarah to a major break-through in her work on determining the origin of sunspots (rightmost photo).
After that we gave up on spring magic, even neglecting the Swedish arrival-of-spring bonfire rituals at Valborg, 30 April. Braving the cold, we had our first BBQ, this most Norditian of rituals, on 7 March, continuing grilling outdoors on and off to Midsummer Eve, 20 June, when the weather still was about the same. Can you guess which photos were taken on which of these dates?
The next Nordita Board Meeting will be in Stockholm on 6 February 2015.
Participants of the Nordita Board meeting in September 2014. Back row, left to right: Jes Madsen (Aarhus U.), Ivan Shelykh (U. of Iceland), Leif Kari (KTH), David Abergel (Nordita), Helle Kiilerich (Nordita/NBI), Asle Sudbø (NTNU).
Middle row, left to right: Jonathan Edge (Nordita), Ulf Wahlgren (Nordita), Katri Huitu (U. of Helsinki), Susanne Viefers (U. of Oslo), Måns Henningsson (Chalmers).
Bottom row, left to right: Marianne Persson-Söderlind (Nordita), Kalle-Antti Suominen (U. of Turku), Katherine Freese (Nordita), Mikko Alava (Aalto U.), Axel Brandenburg (Nordita), Gunnlaugur Björnsson (U. of Iceland).
→ See List of all Nordita Events: www.nordita.org/events
School
7—16 January 2015
The purpose of this winter school is to provide PhD students and young postdocs in the Nordic countries with introductory courses in a range of the most important topics in the field of theoretical particle physics. The school will provide a way to bring together students and young postdocs across different fields, research institutions and countries.
Coordinators: Paolo Di Vecchia, Konstantin Zarembo
Workshop
25—27 February 2015
This workshop series provides a forum where scientists in the Nordic countries working in the area of Statistical Physics can meet regularly. Topics covered include diffusion problems, physics of DNA and bio-molecules, population dynamics, pattern formation, non-equilibrium transport, bacterial motility, single-molecule kinetics, dynamics and structure of networks, statistical inference, Monte-Carlo simulation techniques, self-assembly, soft condensed matter (colloids, liquid crystals etc.), work relations and fluctuation theorems, and many more.
Coordinators: Alberto Imparato, Ralf Eichhorn
Program
2—20 March 2015
The cosmological constant and the physics behind dark energy that accelerates the expansion of the universe remain among the biggest mysteries in theoretical physics. An intriguing possibility is that these problems stem from extrapolating Einstein's General relativity from the Solar system to the far infrared cosmological scales. In the other extreme, at the ultraviolet regime Einstein's theory encounters notorious infinities resulting in spacetime singularities and obstacles to quantisation, which suggest new gravitational physics with possible repercussions to early universe physics. The program aims at establishing new links between fundamental physics and cosmological and astrophysical experiments from the fruitful interface of extended theories of gravity.
Coordinators: Fawad Hassan, Lavinia Heisenberg, David Fonseca Mota, Tomi Koivisto, Kari Enqvist
Workshop
9—13 March 2015
Scientific recording of sunspots started with Galileo in 1609. Since Hale (1908) we know that sunspots are strong concentrations of magnetic field of up to 4000 gauss. They could be formed by subsurface magnetic flux tubes piercing the surface. Meanwhile, numerical simulations by many different groups suggest that strong magnetic fields could be generated in the bulk of the convection zone. This would mean that sufficiently strong magnetic fields may be generated not far from the surface. However, at the surface the magnetic field appears to be strongly concentrated into only a few isolated spots - in stark contrast to the more diffuse magnetic field beneath the surface. This is still a mystery.
Coordinators: Axel Brandenburg, Nishant Singh, Göran Scharmer, Illa R. Losada
Workshop
23—27 March 2015
Renormalization group methods are a key element of theoretical particle physics and may also be central for constructing a fundamental theory of gravity, e.g., based on Weinberg’s asymptotic safety conjecture. The aim of this program is to bring together theorists and phenomenologists in order to discuss ideas related to the application of the renormalization group in quantum gravity and the consequences of asymptotic safety for cosmology, black holes and a possible ultraviolet completion of the standard model of particle physics including gravity.
Coordinators: Frank Saueressig, Dario Benedetti, Astrid Eichhorn
Program
18 May — 12 June 2015
The aim is to study quantum control and dynamics of few-particle systems in an active collaborative effort between experimentalists and theorists, as well as between recognized senior researchers and young investigators. The activity is motivated by recent advances in the physics of ultrafast phenomena in the femto- and attosecond time scale - a regime within reach of novel light sources. New insights into fundamental many-body physics are expected when ultrafast atomic and solid-state processes can be monitored in real time.
Coordinators: Jan Petter Hansen, Eva Lindroth, Esa Räsänen
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