Copenhagen, Czech Republic
Copenhagen, Czech Republic

The Niels Bohr Institute is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics and biophysics.The Institute was founded in 1921, as the Institute for Theoretical Physics of the University of Copenhagen, by the Danish theoretical physicist Niels Bohr, who had been on the staff of the University of Copenhagen since 1914, and who had been lobbying for its creation since his appointment as professor in 1916. On the 80th anniversary of Niels Bohr's birth - October 7, 1965 - the Institute officially became The Niels Bohr Institute. Much of its original funding came from the charitable foundation of the Carlsberg brewery, and later from the Rockefeller Foundation.During the 1920s, and 1930s, the Institute was the center of the developing disciplines of atomic physics and quantum physics. Physicists from across Europe often visited the Institute to confer with Bohr on new theories and discoveries. The Copenhagen interpretation of quantum mechanics is named after work done at the Institute during this time.On January 1, 1993 the institute was fused with the Astronomic Observatory, the Ørsted Laboratory and the Geophysical Institute. The new resulting institute retained the name Niels Bohr Institute. Wikipedia.

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Sneppen K.,Niels Bohr Institute
Reports on Progress in Physics | Year: 2017

This review emphasizes aspects of biology that can be understood through repeated applications of simple causal rules. The selected topics include perspectives on gene regulation, phage lambda development, epigenetics, microbial ecology, as well as model approaches to diversity and to punctuated equilibrium in evolution. Two outstanding features are repeatedly described. One is the minimal number of rules to sustain specific states of complex systems for a long time. The other is the collapse of such states and the subsequent dynamical cycle of situations that restitute the system to a potentially new metastable state. © 2017 IOP Publishing Ltd.

Agency: GTR | Branch: NERC | Program: | Phase: Research Grant | Award Amount: 510.21K | Year: 2014

The Atlantic Oceans conveyor belt circulation is a fundamental component of the global climate system, transporting heat from low to high latitudes, and thus warming Northern Europe. The strength of this circulation is thought to have varied abruptly in the past, giving rise to rapid climate changes of more than 10 degrees C in a decade during the last glacial period. Changes of this nature today would have a severe impact on society, so we want to know more about the sensitivity of this circulation. In order to do this, we will study intervals of rapid climate and circulation change in the past. To better understand these past circulation changes we will reconstruct the concentration of radiocarbon in surface and deep waters in the North Atlantic Ocean. This is known as a radiocarbon reservoir age, and it is highly sensitive to the rate of ocean circulation. Therefore, by reconstructing reservoir ages, we can tell how quickly the ocean was circulating during intervals of rapid climate change. We also need to know what the reservoir age was in the past if we want to use radiocarbon as a dating tool, to tell the age of geological and archeological objects and events. Radiocarbon can be thought of as a stopwatch for a geological sample. For a marine sample, however, there is already some time on the clock when we press go. This extra time before starting the clock is the reservoir age, and we must know what it is in order to accurately tell geological time. By reconstructing reservoir ages, we will therefore improve understanding of rapid circulation and climate change, and also improve the most important dating tool used in earth and archeological sciences. To reconstruct radiocarbon reservoir ages we need to measure the radiocarbon content of a sample, and also to know its age independently, so we can work out what was already on the clock when the sample formed. To do this we will make radiocarbon measurements on shells taken from sediment cores from the North Atlantic, and pair them with a range of exciting new techniques that can tell their age. Firstly we will look for layers of volcanic ash in the sediment cores, which we can date using their argon content, and match to precisely dated ash layers in ice cores and on Iceland. Secondly we can look at changes in sea surface temperature records, and match these to the same events that are precisely dated in ice cores. Thirdly we will use the concentration of thorium in sediments to tell how much sediment accumulated between these ash and temperature tie points. Fourthly, we will combine all this information using statistical modelling, which will also provide a good measure of the uncertainty in our results. This work will create maps of reservoir ages and how they changed in the North Atlantic over the last 10 to 50 thousand years, with a special focus on times of rapid climate change. To help us link the reservoir ages to different circulation regimes, we will use a climate model that can simulate radiocarbon. We will make this models ocean circulation operate in different ways, and see which circulations best match our data. This will allow us to better understand how ocean circulation changed in the past to cause rapid climate change, and improve confidence in how ocean circulation may operate in the future. Finally, we will package our reservoir age maps into a tool that can be used by earth scientists and archeologists to improve their radiocarbon dating.

Agency: GTR | Branch: STFC | Program: | Phase: Research Grant | Award Amount: 20.00K | Year: 2015

Entropy is an art-science collaboration that aims to frame public talks about astronomy with a live audio-visual performance. The best way to describe it is as an astronomy-documentary-meets-electronic-music-concert and it will be performed at science, music, and art festivals across the UK and internationally. Alongside the main event, several workshops will be organised, centred around the science and aimed at schoolchildren, where the children will be able to speak with the scientists to learn about astronomy. For the audio-visual performance, bespoke music tracks have been produced, inspired and guided by the contents of the talks. To supplement them, visualisations will now be created that will be projected on special screens during the performance and will enhance the immersive, and interactive aspects of the event. These visualisations will be created from real astronomical data from experiments like the Sloan Digital Sky Survey and the Dark Energy Survey, as well as from computer simulations of supernova explosion, growth of the cosmic web etc. Furthermore, some of the concepts described in talks, for example the cosmic inflation at the birth of our universe, or the creation of ordinary matter when inflation ends are very difficult to visualise for the public and not many scientifically correct videos of them exist in the public domain. Such videos will be created as a part of this project and after the initial year of performances, they will be released under the Creative Commons Licence into the public domain. The Entropy team started working together in 2011, when they first formed under a working title of Neutrino. They consisted of: Zazralt Magic now at the Niels Bohr Institute in Copenhagen, whose expertise lie in the field of stellar astrophysics, Katarina Markovic now at the Institute for Cosmology and Gravitation in Portsmouth, who is a cosmologist, and Dopplereffekt, from Munich, Germany, who are a renown electronic music duo, whose compositions have always been inspired by science and technology. Later, the team was joined by Antivj from Brussels, Belgium, who are a cutting-edge visual arts studio and will create the visuals as well as the stage set-up. This project presents science to the public in an entirely new format that will appeal to science, music and art fans alike. We expect to reach several thousand people in the first year just with the live performance. Online we count on tens of thousands of views of the material we release and expect that it will be used by many scientists and outreach officers in their public engagement activities in the future.

Boels R.,Niels Bohr Institute
Journal of High Energy Physics | Year: 2010

There has been substantial calculational progress in the last few years for gauge theory amplitudes which involve massless four dimensional particles. One of the central ingredients in this has been the ability to keep precise track of the Poincaré algebra quantum numbers of the particles involved. Technically, this is most easily done using the well-known four dimensional spinor helicity method. In this article a natural generalization to all dimensions higher than four is obtained based on a covariant version of the representation theory of the Poincaré algebra. Covariant expressions for all possible polarization states, both bosonic and fermionic, are constructed. For the fermionic states the analysis leads directly to pure spinors. The natural extension to the representation theory of the on-shell supersymmetry algebra results in an elementary derivation of the supersymmetry Ward identities for scattering amplitudes with massless or massive legs in any integer dimension from four onwards. As a proof-of-concept application a higher dimensional analog of the vanishing helicity-equal amplitudes in four dimensions is presented in (super) Yang-Mills theory, Einstein (super-)gravity and superstring theory in a flat background. © SISSA 2010.

Denney K.D.,Niels Bohr Institute
Astrophysical Journal | Year: 2012

We use a combination of reverberation mapping data and single-epoch (SE) spectra of the C IV emission line in a sample of both low- and high-redshift active galactic nuclei to investigate sources of the discrepancies between C IV- and Hβ-based SE black hole (BH) mass estimates. We find that for all reverberation mapped sources, there is a component of the line profile that does not reverberate, and the velocity characteristics of this component vary from object to object. The differing strength and properties of this non-variable component are responsible for much of the scatter in C IV-based BH masses compared to Hβ masses. The C IV mass bias introduced by this non-variable component is correlated with the shape of the C IV line, allowing us to make an empirical correction to the BH mass estimates. Using this correction and accounting for other sources of scatter, such as poor data quality and data inhomogeneity, reduces the scatter between the C IV and Hβ masses in our sample by a factor of ∼2, to only ∼0.2dex. We discuss the possibility that this non-variable C IV component originates in an orientation-dependent outflow from either the proposed broad-line region disk wind or the intermediate-line region, a high-velocity inner extension of the narrow-line region. © 2012. The American Astronomical Society. All rights reserved.

We report on the measurement of various flow harmonics, vn, with multi-particle cumulants, and present the results from a study of the inter-correlation among different order symmetry planes Ψn via multi-particle mixed harmonic correlations. This provides comprehensive experimental information on the fluctuating event-by-event shape of the initial conditions, which is currently among the main sources of large theoretical uncertainties in describing the evolution of the system created in heavy-ion collisions. © 2013 CERN.

Zoubos K.,Niels Bohr Institute
Letters in Mathematical Physics | Year: 2012

We review the role of integrability in the planar spectral problem of four-dimensional superconformal gauge theories besides N = 4 SYM. The cases considered include the Leigh-Strassler marginal deformations of N = 4 SYM, quiver theories which arise as orbifolds of AdS 5 × S 5 on the dual gravity side, as well as various theories involving open spin chains. © 2011 Springer.

Sieg C.,Niels Bohr Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

We derive the three-loop dilatation operator of the flavor SU(2) subsector of N=4 supersymmetric Yang-Mills theory in the planar limit by a direct Feynman diagram calculation in N=1 superspace. The transcendentality three contributions which appear in intermediate steps cancel among each other, leaving a rational result which confirms the predictions from integrability. We derive finiteness conditions that allow us to avoid the explicit evaluation of entire classes of Feynman graphs and also yield constraints on the D-algebra manipulations. Based on these results, we discover universal cancellation mechanisms. As a check for the consistency of our result, we verify the cancellation of all higher-order poles. © 2011 American Physical Society.

Jensen J.,Niels Bohr Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The inelastic scattering of neutrons from magnetic excitations in the antiferromagnetic phase of the langasite compound Ba 3NbFe 3Si 2O 14 is analyzed theoretically. In the calculations presented, the strongly coupled spin-52 Fe triangles are accounted for as trimerized units. The weaker interactions between the trimers are included within the mean field and random phase approximations. The theory is compared with linear spin-wave theory, and a model is developed that leads to good agreement with the published results from unpolarized and polarized neutron-scattering experiments. © 2011 American Physical Society.

Mazumdar A.,Lancaster University | Mazumdar A.,Niels Bohr Institute | Rocher J.,Free University of Colombia
Physics Reports | Year: 2011

We review the particle theory origin of inflation and curvaton mechanisms for generating large scale structures and the observed temperature anisotropy in the cosmic microwave background (CMB) radiation. Since inflaton or curvaton energy density creates all matter, it is important to understand the process of reheating and preheating into the relevant degrees of freedom required for the success of Big Bang Nucleosynthesis. We discuss two distinct classes of models, one where inflaton and curvaton belong to the hidden sector, which are coupled to the Standard Model gauge sector very weakly. There is another class of models of inflaton and curvaton, which are embedded within Minimal Supersymmetric Standard Model (MSSM) gauge group and beyond, and whose origins lie within . gauge invariant combinations of supersymmetric quarks and leptons. Their masses and couplings are all well motivated from low energy physics, therefore such models provide us with a unique opportunity that they can be verified/falsified by the CMB data and also by the future collider and non-collider based experiments. We then briefly discuss the stringy origin of inflation, alternative cosmological scenarios, and bouncing universes. © 2010 Elsevier B.V.

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