Kavli Institute for Theoretical Physics

Santa Barbara, CA, United States

Kavli Institute for Theoretical Physics

Santa Barbara, CA, United States
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Caron-Huot S.,Institute for Advanced Study | Caron-Huot S.,Kavli Institute for Theoretical Physics
Journal of High Energy Physics | Year: 2011

Scattering amplitudes in superconformal field theories do not enjoy this symmetry, because the definition of asymptotic states involve a notion of infinity. Concentrating on planar N = 4 Yang-Mills, we consider a generalization of scattering amplitudes which depends on twice as many Grassmann variables. We conjecture that it restores at least half of the superconformal symmetries, and all of the dual superconformal symmetries. The object arises naturally as the dual of a null polygonal Wilson loop in an (x; θ; θ̄) superspace. We support the conjecture by using it to obtain the total differential of all n-point two-loop MHV amplitudes, and showing that the result passes consistency checks. Potential all-loop constraints are also discussed. © SISSA 2011.


Le Breakthrough Prize in Life Sciences 2017 est décerné à Stephen J. Elledge, Harry F. Noller, Roeland Nusse, Yoshinori Ohsumi et Huda Yahya Zoghbi Le Breakthrough Prize in Fundamental Physics 2017 est décerné à Joseph Polchinski, Andrew Strominger et Cumrun Vafa Le Breakthrough Prize in Mathematics 2017 est décerné à Jean Bourgain Le prix New Horizons in Physics est décerné à Asimina Arvanitaki, Peter W. Graham et Surjeet Rajendran ; Simone Giombi et Xi Yin ; et Frans Pretorius Le prix New Horizons in Mathematics est décerné à Mohammad Abouzaid, Hugo Duminil-Copin, et Benjamin Elias et Geordie Williamson Le deuxième Breakthrough Junior Challenge annuel est remporté par les étudiantes Antonella Masini, 18 ans (Pérou) et Deanna See, 17 ans (Singapour) Le Special Breakthrough Prize in Fundamental Physics 2016 a été décerné en mai aux fondateurs et aux membres de l'équipe de LIGO, et attribué à Kip Thorne, Rainer Weiss et à la famille de Ronald Drever Les lauréats seront récompensés lors d'un brillant gala de remise des prix présenté par Morgan Freeman, qui verra un spectacle en direct d'Alicia Keys et des interventions de Daniel Ek (PDG de Spotify), Jeremy Irons, Mark et Scott Kelly, Hiroshi Mikitani (PDG de Rakuten), Sienna Miller, Bryce Dallas Howard, Vin Diesel, Kevin Durant, Dev Patel, Sundar Pichai (PDG de Google), Alex Rodriguez, Will.i.am, Susan Wojcicki (PDG deYouTube) et des fondateurs des Breakthrough Prize SAN FRANCISCO, 5 décembre 2016 /PRNewswire/ -- Le Breakthrough Prize et ses fondateurs Sergey Brin et Anne Wojcicki, Yuri et Julia Milner, Mark Zuckerberg et Priscilla Chan, ont annoncé ce soir les lauréats des Breakthrough Prizes 2017, qui marquent le cinquième anniversaire de cette organisation reconnaissant les meilleures réussites en sciences de la vie, physique fondamentale et mathématiques. Ce sont au total 25 millions de dollars qui ont été décernés lors de la cérémonie de gala qui a eu lieu dans la Silicon Valley et a été présentée par Morgan Freeman. Chaque Breakthrough Prize représente un montant de 3 millions de dollars, ce qui en fait la récompense monétaire individuelle la plus élevée dans le domaine de la science. Cette année, un total de sept prix a été décerné à neuf personnes, alors que le Special Breakthrough Prize in Fundamental Physics, d'une valeur de 3 millions de dollars, a été divisé entre les trois fondateurs et les quelque mille membres de l'équipe de LIGO. Par ailleurs, trois prix New Horizons in Physics d'un montant de 100 000 USD ont été décernés à six physiciens en début de carrière, et trois autres prix New Horizons in Mathematics de 100 000 dollars ont été attribués à quatre jeunes mathématiciens. Et cette année il y a eu deux gagnantes du Breakthrough Junior Challenge, et chaque lauréate a reçu jusqu'à 400 000 dollars en prix destiné à la formation, pour elles-mêmes, pour leur professeur respectif et leur école. Depuis sa création en 2012, le Breakthrough Prize a attribué près de 200 millions de dollars pour récompenser des recherches qui bousculent les paradigmes de la physique fondamentale, des sciences de la vie et des mathématiques. « Il n'y a jamais eu d'époque plus importante pour soutenir les sciences », a déclaré le fondateur de Facebook, Mark Zuckerberg. « Les lauréats du Breakthrough Prize 2017 représentent les leaders de la recherche scientifique en physique, mathématiques et sciences de la vie. Leurs avancées vont ouvrir de nouvelles possibilités et contribuer à faire du monde un endroit meilleur pour tout le monde. » Le Breakthrough Prize in Life Sciences 2017 a été décerné à Stephen J. Elledge (École de médecine de Harvard) ; Harry F. Noller (Université de Californie, Santa Cruz) ; Roeland Nusse (Université Stanford) ; Yoshinori Ohsumi (Institut de Technologie de Tokyo) ; Huda Yahya Zoghbi (Baylor College of Medicine). Le Breakthrough Prize in Fundamental Physics 2017 a été décerné à Joseph Polchinski (Université de Californie, Santa Barbara) ; Andrew Strominger (Université de Harvard) et Cumrun Vafa (Université de Harvard). Les trois lauréats ont rejoint ceux du Special Prize in Fundamental Physics précédemment annoncé et attribué en mai 2016. Ronald Drever (Institut de Technologie de Californie, Pasadena), Kip Thorne (Institut de Technologie de Californie, Pasadena) et Rainer Weiss (Institut de technologie du Massachusetts) ont été reconnus en mai pour leur détection des vagues gravitationnelles, ce qui ouvre de nouveaux horizons en astronomie et en physique. Les trois gagnants du Prix spécial se partageront un montant d'un million de dollars, et les 1 012 membres de l'équipe de LIGO se partageront 2 millions de dollars. Le Breakthrough Prize in Mathematics 2017 a été décerné à Jean Bourgain (Institute for Advanced Study). La cérémonie de cette année marquera le cinquième anniversaire de l'organisation, et les lauréats seront sur le devant de la scène ce soir lors d'un gala exclusif organisé conjointement par les fondateurs Sergey Brin et Anne Wojcicki, Yuri et Julia Milner, Mark Zuckerberg et Priscilla Chan, et par le rédacteur en chef de Vanity Fair, Graydon Carter. L'acteur qui a remporté un Award® de l'Académie, Morgan Freeman, présentera le gala, qui verra un spectacle de l'actrice quinze fois primée par les Grammy Award®, Alicia Keys, et les interventions de personnalités comme Jeremy Irons, Mark et Scott Kelly, Hiroshi Mikitani (PDG de Rakuten), Sienna Miller, Bryce Dallas Howard, Vin Diesel, Kevin Durant, Dev Patel, Sundar Pichai (PDG de Google), Alex Rodriguez, Will.i.am, Susan Wojcicki (PDG de YouTube), ainsi que des fondateurs du Breakthrough Prize. La soirée sera placée sous le thème de « la portée universelle des idées ». « La science est universelle », a déclaré Yuri Milner. « Ce soir elle a rassemblé certains des plus grands acteurs, sportifs, musiciens, universitaires, entrepreneurs, astronautes et, bien entendu, scientifiques du monde entier, pour célébrer ce que l'esprit humain est capable de faire. Et cela a attiré un public venu des quatre points de la planète. » L'un des moments forts sera les discours prononcés par les deux étudiantes qui ont remporté le Breakthrough Junior Challenge, Antonella Masini, 18 ans (Pérou) et Deanna See, 17 ans (Singapour). Le Breakthrough Junior Challenge est un concours mondial de vidéos scientifiques conçu pour inspirer la pensée créative sur les concepts fondamentaux en sciences de la vie, physique ou mathématiques. En reconnaissance de leurs candidatures gagnantes, les deux étudiantes ont reçu jusqu'à 400 000 dollars en prix pour la formation, dont une bourse d'une valeur de 250 000 dollars, 50 000 dollars pour les professeurs qui les ont respectivement inspirées, ainsi qu'un laboratoire de pointe évalué à 100 000 dollars. Des candidatures venant de 146 pays ont été reçues pour l'édition 2016 du concours mondial, qui a démarré le 1er septembre 2016. Le Breakthrough Junior Challenge a été fondé par Mark Zuckerberg et Priscilla Chan, Yuri et Julia Milner, à travers la Breakthrough Prize Foundation, et se fonde sur une bourse provenant du fonds de Mark Zuckerberg à la Silicon Valley Community Foundation, et sur une bourse de Milner Global Foundation. « Le Breakthrough Junior Challenge encourage les étudiants à mieux comprendre les mondes des sciences et des mathématiques et à trouver du plaisir à les explorer », a déclaré la cofondatrice du Breakthrough Prize, la Dr Priscilla Chan. « Antonella et Deanna ont toutes les deux un brillant avenir dans les sciences et je suis ravie de récompenser leur travail. Ce sont aussi de grandes oratrices, dont les capacités à exprimer ces idées complexes d'une façon accessible et captivante est une vraie source d'inspiration. J'ai vraiment hâte de voir comment elles vont changer le monde. » Par ailleurs, six prix New Horizons – un prix annuel doté de de 100 000 dollars, qui reconnait les réussites de physiciens et de mathématiciens en début de carrière, ont été attribués. Le prix New Horizons in Physics a été décerné à : Le prix New Horizons in Mathematics a été décerné à : La cérémonie sera réalisée et produite, pour la quatrième fois, par Don Mischer, aux côtés des producteurs exécutifs Charlie Haykel et Juliane Hare de Don Mischer Productions. La cérémonie sera intégralement diffusée en direct sur NATIONAL GEOGRAPHIC à 10 h, heure de l'Est américain et 9 h, heure du centre, le dimanche 4 décembre. Un montage d'une heure de la cérémonie sera également retransmis sur FOX le dimanche 18 décembre, à 19 heures, heure de l'Est et 20 heures, heure du Pacifique, et à l'échelle mondiale sur NATIONAL GEOGRAPHIC dans 171 pays et en 45 langues. Le Breakthrough Prize in Life Sciences récompense des avancées qui transforment la compréhension des systèmes vivants et de l'extension de la vie humaine, avec un prix consacré au travail contribuant à la compréhension des maladies neurologiques. Chacun des cinq lauréats des prix de Sciences de la vie a reçu une récompense de 3 millions de dollars. Stephen J. Elledge, professeur de génétique et de médecine, titulaire de la chaire Gregor Mendel, au département de génétique à l'École de médecine de Harvard et de la division de génétique au Brigham and Women's Hospital et chercheur au Howard Hughes Medical Institute, pour expliciter la façon dont les cellules eucaryotes sentent et répondent aux dommages faits dans leur ADN et pour donner des informations sur le développement et le traitement du cancer. Harry F. Noller, directeur du Center for Molecular Biology of RNA (Centre de la biologie moléculaire de l'ARN), Robert L. Sinsheimer, professeur de biologie moléculaire et professeur émérite de biologie moléculaire, cellulaire et du développement à l'Université de Californie, Santa Cruz, pour avoir découvert le rôle central de l'ARN dans la formation des centres actifs du ribosome, la machinerie fondamentale de la synthèse des protéines dans toutes les cellules, connectant ainsi la biologie moderne à l'origine de la vie et expliquant également combien d'antibiotiques naturels perturbent la synthèse des protéines. Roeland Nusse, professeur de biologie du développement à l'université Stanford et chercheur au Howard Hughes Medical Institute, pour sa recherche pionnière sur la voie des protéines Wnt, l'un des systèmes de signalement intercellulaire fondamentaux dans le développement, le cancer et la biologie des cellules souche. Yoshinori Ohsumi, professeur honoraire, Institut de la recherche innovante de l'Institut de technologie de Tokyo pour élucider l'autophagie, le système de recyclage que les cellules utilisent pour générer des substances nutritives provenant de leurs composants non essentiels ou endommagés. Huda Yahya Zoghbi, professeur du département de pédiatrie, de génétique moléculaire et humaine, de neurologie et de neurosciences au Baylor College of Medicine, chercheur au Howard Hughes Medical Institute et directeur du Jan and Dan Duncan Neurological Research Institute (NRI) à l'Hôpital pour enfants du Texas, pour ses découvertes sur les causes génétiques et les mécanismes biochimiques de l'ataxie spinocérébelleuse et du syndrome de Rett, découvertes qui ont ouvert des fenêtres sur la pathogénèse des maladies neurodégénératives et neurologiques. Le Breakthrough Prize in Fundamental Physics reconnait les plus grandes idées sur les questions les plus profondes que nous pose l'univers. Les trois gagnants, qui se partagent un prix de 3 millions de dollars, sont : Joseph Polchinski, professeur au département de physique et membre du Kavli Institute for Theoretical Physics à l'Université de Californie, Santa Barbara ; Andrew Strominger, directeur du Center for the Fundamental Laws of Nature de l'université Harvard ; et, Cumrun Vafa, professeur de sciences, titulaire de la chaire Donner, au département de physique de l'université Harvard. Tous les trois ont reçu le prix pour les avancées transformatrices en théorie quantique des champs, théorie des cordes et gravité quantique. Le Breakthrough Prize in Mathematics récompense les meilleurs mathématiciens au monde qui ont contribué à des avancées majeures dans ce domaine. Jean Bourgain, professeur de mathématiques, titulaire de la chaire IBM von Neumann, à l'École de mathématiques de l'Institute for Advanced Study, Princeton, New Jersey, pour ses multiples contributions qui transforment l'analyse, la combinatoire, les équations différentielles partielles, la géométrie hautement dimensionnelle et la théorie des numéros. Le New Horizons in Physics Prize est décerné à de prometteurs chercheurs en début de carrière qui ont déjà produit un travail important en physique fondamentale. Le prix New Horizons in Mathematics est décerné à de prometteurs chercheurs en début de carrière qui ont déjà produit un travail important en mathématiques. Le deuxième Breakthrough Junior Challenge annuel reconnaît deux vainqueurs cette année - Antonella Masini, 18 ans, du Pérou, et Deanna See, 17 ans, de Singapour. Antonella et Deanna recevront chacune jusqu'à 400 000 dollars en prix pour la formation. La vidéo d'Antonella, présentée dans la catégorie « physique », est axée sur l'intrication quantique. La vidéo de sciences de la vie de Deanna, intitulée « Superbugs! And Our Race against Resistance » (Superbactéries ! Et notre course contre la résistance) abordait la résistance aux antibiotiques. Les images et les vidéos choisies du gala du Breakthrough Prize 2017 – tapis rouge et cérémonie – peuvent être téléchargées à des fins d'utilisation par la presse sur : Pour la cinquième année consécutive, les Breakthrough Prizes vont reconnaître les meilleurs scientifiques au monde. Chaque prix a une valeur de 3 millions de dollars et récompense dans les domaines des sciences de la vie (jusqu'à cinq prix par an), de la physique fondamentale (un prix par an) et des mathématiques (un prix par an). Par ailleurs, jusqu'à trois prix New Horizons in Physics et jusqu'à trois prix New Horizons in Mathematics sont décernés à de jeunes chercheurs chaque année. Les lauréats participent à une cérémonie de remise des prix télévisée conçue pour célébrer leurs réussites et pour inspirer la nouvelle génération de scientifiques. Dans le cadre de l'agenda de la cérémonie, ils participent aussi à un programme de conférences et de débats. Les Breakthrough Prizes ont été fondés par Sergey Brin et Anne Wojcicki, Mark Zuckerberg et Priscilla Chan, Yuri et Julia Milner. Des comités de sélection composés de précédents lauréats du Breakthrough Prize choisissent les vainqueurs. Vous trouverez des informations sur les Breakthrough Prizes en cliquant sur www.breakthroughprize.org.


Cardy J.,University of Oxford | Cardy J.,All Souls College | Cardy J.,Kavli Institute for Theoretical Physics
Physical Review Letters | Year: 2014

We consider a quantum quench in a finite system of length L described by a 1+1-dimensional conformal field theory (CFT), of central charge c, from a state with finite energy density corresponding to an inverse temperature Îâ‰L. For times t such that â.,"/2


Cardy J.,University of Oxford | Cardy J.,All Souls College | Cardy J.,Kavli Institute for Theoretical Physics
Physical Review Letters | Year: 2011

We show that block entanglement entropies in one-dimensional systems close to a quantum critical point can, in principle, be measured in terms of the population of low-lying energy levels following a certain type of local quantum quench. © 2011 American Physical Society.


Pesin D.,University of Washington | Pesin D.,Kavli Institute for Theoretical Physics | Pesin D.,University of Texas at Austin | Balents L.,Kavli Institute for Theoretical Physics
Nature Physics | Year: 2010

Recent theory and experiment have revealed that strong spin-orbit coupling can have marked qualitative effects on the band structure of weakly interacting solids, leading to a distinct phase of matter, the topological band insulator. We show that spin-orbit interaction also has quantitative and qualitative effects on the correlation-driven Mott insulator transition. Taking Ir-based pyrochlores as a specific example, we predict that for weak electron-electron interaction Ir electrons are in metallic and topological band insulator phases at weak and strong spin-orbit interaction, respectively. We show that by increasing the electron-electron interaction strength, the effects of spin-orbit coupling are enhanced. With increasing interactions, the topological band insulator is transformed into a topological Mott insulator phase having gapless surface spin-only excitations. The proposed phase diagram also includes a region of gapless Mott insulator with a spinon Fermi surface, and a magnetically ordered state at still larger electron-electron interaction.


Kallin C.,McMaster University | Berlinsky J.,Kavli Institute for Theoretical Physics
Reports on Progress in Physics | Year: 2016

Chiral superconductivity is a striking quantum phenomenon in which an unconventional superconductor spontaneously develops an angular momentum and lowers its free energy by eliminating nodes in the gap. It is a topologically non-trivial state and, as such, exhibits distinctive topological modes at surfaces and defects. In this paper we discuss the current theory and experimental results on chiral superconductors, focusing on two of the best-studied systems, Sr2RuO4, which is thought to be a chiral triplet p-wave superconductor, and UPt3, which has two low-temperature superconducting phases (in zero magnetic field), the lower of which is believed to be chiral triplet f-wave. Other systems that may exhibit chiral superconductivity are also discussed. Key signatures of chiral superconductivity are surface currents and chiral Majorana modes, Majorana states in vortex cores, and the possibility of half-flux quantum vortices in the case of triplet pairing. Experimental evidence for chiral superconductivity from μSR, NMR, strain, polar Kerr effect and Josephson tunneling experiments are discussed. © 2016 IOP Publishing Ltd.


In 2014, UC Santa Barbara soft condensed-matter physicist Greg Huber and colleagues explored the biophysics of such shapes—helices that connect stacks of evenly spaced sheets—in a cellular organelle called the endoplasmic reticulum (ER). Huber and his colleagues dubbed them Terasaki ramps after their discoverer, Mark Terasaki, a cell biologist at the University of Connecticut. Huber thought these "parking garages" were unique to soft matter (like the interior of cells) until he happened upon the work of nuclear physicist Charles Horowitz at Indiana University. Using computer simulations, Horowitz and his team had found the same shapes deep in the crust of neutron stars. "I called Chuck and asked if he was aware that we had seen these structures in cells and had come up with a model for them," said Huber, the deputy director of UCSB's Kavli Institute for Theoretical Physics (KITP). "It was news to him, so I realized then that there could be some fruitful interaction." The resulting collaboration, highlighted in Physical Review C, explored the relationship between two very different models of matter. Nuclear physicists have an apt terminology for the entire class of shapes they see in their high-performance computer simulations of neutron stars: nuclear pasta. These include tubes (spaghetti) and parallel sheets (lasagna) connected by helical shapes that resemble Terasaki ramps. "They see a variety of shapes that we see in the cell," Huber explained. "We see a tubular network; we see parallel sheets. We see sheets connected to each other through topological defects we call Terasaki ramps. So the parallels are pretty deep." However, differences can be found in the underlying physics. Typically matter is characterized by its phase, which depends on thermodynamic variables: density (or volume), temperature and pressure—factors that differ greatly at the nuclear level and in an intracellular context. "For neutron stars, the strong nuclear force and the electromagnetic force create what is fundamentally a quantum-mechanical problem," Huber explained. "In the interior of cells, the forces that hold together membranes are fundamentally entropic and have to do with the minimization of the overall free energy of the system. At first glance, these couldn't be more different." Another difference is scale. In the nuclear case, the structures are based on nucleons such as protons and neutrons and those building blocks are measured using femtometers (10-15). For intracellular membranes like the ER, the length scale is nanometers (10-9). The ratio between the two is a factor of a million (10-6), yet these two vastly different regimes make the same shapes. "This means that there is some deep thing we don't understand about how to model the nuclear system," Huber said. "When you have a dense collection of protons and neutrons like you do on the surface of a neutron star, the strong nuclear force and the electromagnetic forces conspire to give you phases of matter you wouldn't be able to predict if you had just looked at those forces operating on small collections of neutrons and protons." The similarity of the structures is riveting for theoretical and nuclear physicists alike. Nuclear physicist Martin Savage was at the KITP when he came across graphics from the new paper on arXiv, a preprint library that posts thousands of physics, mathematics and computer science articles. Immediately his interest was piqued. "That similar phases of matter emerge in biological systems was very surprising to me," said Savage, a professor at the University of Washington. "There is clearly something interesting here." Co-author Horowitz agreed. "Seeing very similar shapes in such strikingly different systems suggests that the energy of a system may depend on its shape in a simple and universal way," he said. Huber noted that these similarities are still rather mysterious. "Our paper is not the end of something," he said. "It's really the beginning of looking at these two models." More information: "Parking-garage" structures in nuclear astrophysics and cellular biophysics, Phys. Rev. C 94, 055801 – Published 1 November 2016, journals.aps.org/prc/abstract/10.1103/PhysRevC.94.055801


News Article | November 4, 2016
Site: www.newscientist.com

The conditions are vastly different, but the pasta is the same. The insides of neutron stars and the membranes inside our cells can form strikingly similar structures resembling cavatappi pasta spirals, which could forge a new link between the cosmos and life on Earth. Neutron stars are the ultra-dense cores left behind after a stellar explosion. They are thought to have a liquid core of free neutrons beneath a solid crust, in which protons, neutrons and electrons clump together under competing attractive and repulsive forces. Simulations had shown that those forces can make the crustal material arrange itself into a dense layer of “nuclear pasta” shapes, sometimes taking the form of lasagna-like sheets connected by spiral bridges. Now, Matt Caplan at Indiana University Bloomington and his colleagues have pointed out that the same patterns show up inside cells. Despite the fact that neutron stars are 14 orders of magnitude denser than the constituents of cells, the forces in both interact in a similar way, making the resulting self-assembling shapes nearly identical. This parallel came to light through a lucky coincidence. Biophysicist Greg Huber of the Kavli Institute for Theoretical Physics in Santa Barbara, California, happened to see a photograph from a conference talk given by Caplan, depicting a spiral bridge structure. Huber noticed the similarity between nuclear pasta and the endoplasmic reticulum, a network of membranes found in many cells that is responsible for folding proteins. He wrote to Caplan’s team to point out the coincidence, and they teamed up to compare new simulations of nuclear pasta with observations of cells. The team suggest that the similarities point to a deeper connection between stars and cells, and provide a way for the two fields to share insights. “Self-assembly is universal,” says Caplan. “It lets us bridge a gap between two fields, because we can take the language of biophysics and use it to understand neutron star interiors, and the biophysicists can take computational methods from astrophysics.” In the cell, the bridges may help membranes remain parallel and connected, yielding more space for ribosomes, which sit on the endoplasmic reticulum’s surface and build proteins. In a neutron star, on the other hand, the spiral bridges that link dense sheets of particles scatter electrons and slow the neutron star’s cooling. So the very structures that keep neutron stars warm could help our bodies produce vital proteins. “It was interesting to see that there is more evidence that some mechanisms in biological systems and nuclear astrophysics are similar,” says Bastian Schütrumpf at Michigan State University, who has studied structures called gyroids that show up in both neutron star crusts and butterfly wings. But for Huber, the fact that these shapes arise in such different environments points to a larger puzzle. “It’s the enduring mystery of what we found, that these two very different systems have these very deep similarities,” Huber says. “To me the important part is the questions that are raised.”


News Article | November 7, 2016
Site: www.techtimes.com

Cell cytoplasm and neutron stars feature the same parking garage-like structures within them, researchers have found. Back in 2014, Greg Huber, a soft condensed-matter physicist from the University of California Santa Barbara and colleagues discovered that the endoplasmic reticulum, a cellular organelle, formed evenly spaced sheet stacks connected by helices. They called the structure Terasaki ramps in reference to University of Connecticut cell biologist Mark Terasaki, who discovered it first. However, at the time, the researchers thought that Terasaki ramps were specific to soft matter. That was until Huber chanced upon research by Charles Horowitz, a nuclear physicist from Indiana University. With the help of computer simulations, Horowitz and his colleagues found the same evenly spaced sheet stacks connected by helices present in neutron star crusts. Huber shared how he gave Horowitz a call to ask if he was aware that the structures they observed were also present in human cells. "It was news to him, so I realized then that there could be some fruitful interaction," he said. When the two research teams got together, the result was a collaboration in exploring the relationship between the two different models of matter. The findings were published in the journal Physical Review C. For nuclear physicists, the shapes they observe when carrying out computer simulations for neutron stars are called nuclear pasta, which include parallel sheets and tubes (lasagna and spaghetti, respectively) bound by helical shapes that look a lot like Terasaki ramps. But while human cells and neutron stars have similar interior structures, they differ when it comes to underlying physics. Inside cells, forces holding together membranes are entropic fundamentally and are associated with the minimization of overall free energy within the system. Neutron stars, on the other, feature strong electromagnetic and nuclear force. According to Horowitz, observing highly similar shapes with striking differences in their systems points to the possibility that a system's energy depends on the shape it takes. It's clearly interesting, if you ask nuclear physicist Martin Savage. He was at the Kavli Institute for Theoretical Physics when he saw the graphics for the structures and his interest was piqued immediately. He was surprised that phases of matter that are similar in nature could spring from biological systems. While it has identified similarities between human cells and neutron stars, the study, added Horowitz, is not the end. Rather, it marks the beginning of further research into the two highly different models with very similar interior structures. There are still some areas the researchers don't understand, after all. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.


News Article | November 3, 2016
Site: astrobiology.com

Similar shapes - structures consisting of stacked sheets connected by helical ramps - have been found in cell cytoplasm (left) and neutron stars (right). According to research published in the journal Physical Review C, neutron stars and cell cytoplasm have something in common: structures that resemble multistory parking garages. In 2014, UC Santa Barbara soft condensed-matter physicist Greg Huber and colleagues explored the biophysics of such shapes -- helices that connect stacks of evenly spaced sheets -- in a cellular organelle called the endoplasmic reticulum (ER). Huber and his colleagues dubbed them Terasaki ramps after their discoverer, Mark Terasaki, a cell biologist at the University of Connecticut. Huber thought these "parking garages" were unique to soft matter (like the interior of cells) until he happened upon the work of nuclear physicist Charles Horowitz at Indiana University. Using computer simulations, Horowitz and his team had found the same shapes deep in the crust of neutron stars. "I called Chuck and asked if he was aware that we had seen these structures in cells and had come up with a model for them," said Huber, the deputy director of UCSB's Kavli Institute for Theoretical Physics (KITP). "It was news to him, so I realized then that there could be some fruitful interaction." The resulting collaboration, highlighted in Physical Review C, explored the relationship between two very different models of matter. Nuclear physicists have an apt terminology for the entire class of shapes they see in their high-performance computer simulations of neutron stars: nuclear pasta. These include tubes (spaghetti) and parallel sheets (lasagna) connected by helical shapes that resemble Terasaki ramps. "They see a variety of shapes that we see in the cell," Huber explained. "We see a tubular network; we see parallel sheets. We see sheets connected to each other through topological defects we call Terasaki ramps. So the parallels are pretty deep." However, differences can be found in the underlying physics. Typically matter is characterized by its phase, which depends on thermodynamic variables: density (or volume), temperature and pressure -- factors that differ greatly at the nuclear level and in an intracellular context. "For neutron stars, the strong nuclear force and the electromagnetic force create what is fundamentally a quantum-mechanical problem," Huber explained. "In the interior of cells, the forces that hold together membranes are fundamentally entropic and have to do with the minimization of the overall free energy of the system. At first glance, these couldn't be more different." Another difference is scale. In the nuclear case, the structures are based on nucleons such as protons and neutrons and those building blocks are measured using femtometers (10-15). For intracellular membranes like the ER, the length scale is nanometers (10-9). The ratio between the two is a factor of a million (10-6), yet these two vastly different regimes make the same shapes. "This means that there is some deep thing we don't understand about how to model the nuclear system," Huber said. "When you have a dense collection of protons and neutrons like you do on the surface of a neutron star, the strong nuclear force and the electromagnetic forces conspire to give you phases of matter you wouldn't be able to predict if you had just looked at those forces operating on small collections of neutrons and protons." The similarity of the structures is riveting for theoretical and nuclear physicists alike. Nuclear physicist Martin Savage was at the KITP when he came across graphics from the new paper on arXiv, a preprint library that posts thousands of physics, mathematics and computer science articles. Immediately his interest was piqued. "That similar phases of matter emerge in biological systems was very surprising to me," said Savage, a professor at the University of Washington. "There is clearly something interesting here." Co-author Horowitz agreed. "Seeing very similar shapes in such strikingly different systems suggests that the energy of a system may depend on its shape in a simple and universal way," he said. Huber noted that these similarities are still rather mysterious. "Our paper is not the end of something," he said. "It's really the beginning of looking at these two models."

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