Time-Delay Polaritonics

Non-linearity and finite signal propagation speeds are omnipresent in nature, technologies, and real-world problems, where efficient ways of describing and predicting the effects of these elements are in high demand. Advances in engineering condensed matter systems, such as lattices of trapped condensates, have enabled studies on non-linear effects in many-body systems where exchange of particles between lattice nodes is effectively instantaneous. Here, we demonstrate a regime of macroscopic matter-wave systems, in which ballistically expanding condensates of microcavity exciton-polaritons act as picosecond, microscale non-linear oscillators subject to time-delayed interaction. The ease of optical control and readout of polariton condensates enables us to explore the phase space of two interacting condensates up to macroscopic distances highlighting its potential in extended configurations. We demonstrate deterministic tuning of the coupled-condensate system between fixed point and limit cycle regimes, which is fully reproduced by time-delayed coupled equations of motion similar to the Lang-Kobayashi equation

Shocks in asymmetric simple exclusion processes of interacting particles

In this paper, we study shocks and related transitions in asymmetric simple exclusion processes of particles with nearest neighbor interactions. We consider two kinds of inter-particle interactions. In one case, the particle-hole symmetry is broken due to the interaction. In the other case, particles have an effective repulsion due to which the particle-current-density drops down near the half filling. These interacting particles move on a one dimensional lattice which is open at both the ends with injection of particles at one end and withdrawal of particles at the other. In addition to this, there are possibilities of attachments or detachments of particles to or from the lattice with certain rates. The hydrodynamic equation that involves the exact particle current-density of the particle conserving system and additional terms taking care of the attachment-detachment kinetics is studied using the techniques of boundary layer analysis.Comment: 10 pages, 8 figure

Female impersonation as an alternative reproductive strategy in giant cuttlefish

Out of all the animals, cephalopods possess an unrivalled ability to change their shape and body patterns. Our observations of giant cuttlefish (Sepia apama) suggest this ability has allowed them to evolve alternative mating strategies in which males can switch between the appearance of a female and that of a male in order to foil the guarding attempts of larger males. At a mass breeding aggregation in South Australia, we repeatedly observed single small males accompanying mating pairs. While doing so, the small male assumed the body shape and patterns of a female. Such males were never attacked by the larger mate-guarding male. On more than 20 occasions, when the larger male was distracted by another male intruder, these small males, previously indistinguishable from a female, were observed to change body pattern and behaviour to that of a male in mating display. These small males then attempted to mate with the female, often with success. This potential for dynamic sexual mimicry may have played a part in driving the evolution of the remarkable powers of colour and shape transformation which characterize the cephalopods

Resolved gamma ray emission of the supernova remnant W51C and HESS J1857+026 obtained with the MAGIC telescopes

Diese Dissertation untersucht den Urspung der kosmischen Strahlung mit Beobachtungen der MAGIC Teleskope im Bereich der hoch energeticher Gammastrahlenastronomie. Gammastrahlung wird bei der Wechselwirkung relativistischer Teilchen erzeugt. Im Gegensatz zur geladenen kosmichen Strahlung, werden Gammastrahlen nicht von interstellaren Magnetfeldern beinflusst. Daher erlaubt die Ankunftsrichtung von Gammastrahlen die Bestimmung ihres Ursprungs. Ein Teil dieser Arbeit widmet sich der Verbesserung der Analyse von MAGIC-daten. Im besonderen wurde ein neuer Algorithmus zur Hintergrundbestimmung entwickelt, wodurch die systematischen Unsicherheiten deutlich verbessert werden konnten. Zudem wurde die Reflekivitaet und Fokusierung beider MAGIC Teleskope anhand des Vergleichs zwischen echten und simulierten Muonereignissen bestimmt. Die heutige Meinung ist, dass die Ueberreste von Supernovae, die expandierende Schockwellen der Sternimplosionen, der Ursprung der galaktischen kosmischen Strahlung sind. Obwohl hoch energetische Gammastrahlung von vielen dieser Objekte beobachtet wurde, erlaubt die schwierige Unterscheidung von leptonisch und hadronsich produzierter Gammastrahlung in den meisten Faellen keine klaren Schlussfolgerungen ueber die Anwesenheit relativistischer Hadronen und damit kosmischer Strahlung. Da Gammastrahlung aus hadronischen Wechselwirkungen, nahezu ausschliesslich in inelastischen Proton-Proton Kollisionen erzeugt wird, ist ihre Produktion umso effektiver, desto hoeher die Dichte des mediums ist. Die Region W51 beherbergt den 30000 Jahre alten Supernovaueberrest W51C, welcher teilweise mit der grossen Molekuelwolke W51B kollidiert. MAGIC hat ausgedehnte Gammastrahlung von dieser Region mit hoher statistischer Signifikanz (11 sigma) gemessen. Es konnte gezeigt werden, dass das Zentrum der Emission in dem Bereich hoher Dichte liegt, wo der Supernovaueberrest mit der Molekuelwolke kollidiert. Das Energiespektrum wurde im Bereich von 75 GeV bis 5.5 TeV gemessen und folgt einem Potenzgesetz. Die moegliche Kontamination dieser Emission durch einen nahegelegenen potentiellen Pulsarwindnebel zeigt keine Energieabhaengigkeit und wurde als ~20\% der Gesamtemission bestimmt. Die Modellierung der nicht thermischen Mutliwellenlaengenemission deutet stark auf einen hadronischen Ursprung der Gammastrahlung hin. Diese Beschreibung impliziert, dass in etwa 16% der kinetsiche Energie der Schockwelle von W51C zur Produktion kosmischer Strahlung genutzt wurden. Damit is W51C eine der wenigen bekannten Supernovaueberreste wo eine Beschleunigung von Protonen der komsischer Strahlung, zumindestens bis 50 TeV, direkt beobachtet wird. HESS J1857+026 ist eine nicht identifizierte TeV-Quelle, die moeglicherweise den Pulsarwindnebel des, von der Gammastrahlung umschlossenen, hochenergetischen Pulsares PSR J1856+0245 darstellt. Eine augedehnte Emission wurde von MAGIC mit einer statistischen Signifikanz von mehr als 12 sigma gemessen. Das berechnete Spektrum verbindet die vorherigen Daten von Fermi/LAT und HESS, wobei es mit beiden Messungen ueberlappt. Anhand der MAGIC und Fermi/LAT Daten wurde ein Abweichung von einem einfachen Potenzgesetz bei ca. 100~GeV festgestellt. Bei hoeheren Energien werden zwei Emissionsregionen aufgeloest. Ueberhalb von einem TeV koennen zwei voneinander getrennte, einzeln signifikante Regionen festgestellt werden. Diese Dissertation zeigt die ersten morphologischen Untersuchungen, die mit den MAGIC Teleskopen durchgefuehrt wurden. Es wurde gezeigt, dass die Faehigkeit Strukturen in galaktischen Quellen aufloesen zu koennen, wichtige Informationen ueber die Physik der Teilchenbeschleunigung in astrophysikalischen Objekten liefert.This work addresses the long standing question of the origin of galactic cosmic rays by the use of very high energy gamma ray emission observed with the MAGIC telescopes. Gamma rays are produced in the interaction of relativistic particles. In contrast to the charged cosmic rays, gamma rays are not deflected by interstellar magnetic fields and therefore point back to their origin. A part of this work was dedicated to the improvement of the the MAGIC data analysis. In particular a new method to determine the background has been developed resulting in a reduction of the systematic uncertainties. Moreover, the optical point spread function and the light collection efficiency of both MAGIC telescopes have been determined by the comparison of real and simulated muon events. The common believe is that supernova remnants are the sources of galactic cosmic rays. While several supernova remnants are known to emit very high energy gamma rays, the difficulty to distinguish between leptonic and hadronic production mechanisms prevents in most cases clear evidence for the presence of relativistic hadrons and therefore cosmic rays. Gamma rays originating from relativistic hadrons are almost exclusively produced in inelastic proton-proton interactions and therefore more efficiently produced in regions of high matter density. The region W51 host the middle-age supernova remnant W51C which partially collides with the large molecular cloud W51B. MAGIC detected extended gamma ray emission in the W51 region with >11 sigma. It could be shown that the centroid of the emission is spatially consistent with the high density region of the interaction zone between the remnant and the molecular cloud. The differential energy spectrum extends from 75 GeV up to 5.5 TeV and follows simple power-law. A possible contribution of a nearby pulsar wind nebula candidate is constrained to be ~20% of the overall emission and shows no dependence on energy. A modeling of the non-thermal multiwavelength emission strongly suggests a hadronic origin of the observed emission. This models implies that about 16% of kinetic energy of the supernova remnant W51C has been converted into cosmic rays. W51C is therefore one of the few known supernova remnants where most likely the acceleration of cosmic rays, at least up to energies of 50 TeV per proton, is directly observed. HESS J1857+026 is an unidentified TeV source which could be explained as a pulsar wind nebula of the energetic pulsar PSR J1856+0245 enclosed in the gamma ray emission. MAGIC detected extended gamma ray emission with >12 sigma from the object. The derived spectrum connects previous measurements of Fermi/LAT and HESS and overlaps with both of them. The MAGIC and Fermi/LAT data reveal a spectral break at around 100 GeV. At high energies, the emission resolves in two regions. Two spatially distinct and statistically significant emission regions are established above 1 TeV. This thesis shows the first morphological studies in very high energy gamma rays performed with the MAGIC telescopes. The ability to resolve structures in galactic gamma ray sources has been proven to give important insights into the underlying physics of particle acceleration in astrophysical environments

Bulk and surface transitions in asymmetric simple exclusion process: Impact on boundary layers

In this paper, we study boundary-induced phase transitions in a particle non-conserving asymmetric simple exclusion process with open boundaries. Using boundary layer analysis, we show that the key signatures of various bulk phase transitions are present in the boundary layers of the density profiles. In addition, we also find possibilities of surface transitions in the low- and high- density phases. The surface transition in the low-density phase provides a more complete description of the non-equilibrium critical point found in this system.Comment: 9 pages including figure

The Infrared Afterglow of Supermassive Black Hole Mergers

We model the spectra and light curves of circumbinary accretion disks during the time after the central black holes merge. The most immediate effect of this merger is the dissipation of energy in the outer regions of the disk due to the gravitational wave energy and linear momentum flux released at merger. This has the effect of perturbing the gas in the disk, which then radiates the dissipated energy over a cooling timescale, giving a characteristic infrared signal for tens of thousands of years when the total black hole mass is M~10^8 M_sun. On the basis of a simple cosmological merger model in which a typical supermassive black hole undergoes a few major mergers during its lifetime, we predict that ~10^4-10^5 of these IR sources should be observable today and discuss the possibility of identifying them with multi-wavelength surveys such as SWIRE/XMM-LSS/XBootes and COSMOS.Comment: v2: expanded discussion of optical depth calculations; ApJ in pres

A novel non-Fermi-liquid state in the iron-pnictide FeCrAs

We report transport and thermodynamic properties of stoichiometric single crystals of the hexagonal iron-pnictide FeCrAs. The in-plane resistivity shows an unusual "non-metallic" dependence on temperature T, rising continuously with decreasing T from ~ 800 K to below 100 mK. The c-axis resistivity is similar, except for a sharp drop upon entry into an antiferromagnetic state at T_N 125 K. Below 10 K the resistivity follows a non-Fermi-liquid power law, rho(T) = rho_0 - AT^x with x<1, while the specific heat shows Fermi liquid behaviour with a large Sommerfeld coefficient, gamma ~ 30 mJ/mol K^2. The high temperature properties are reminiscent of those of the parent compounds of the new layered iron-pnictide superconductors, however the T -> 0 properties suggest a new class of non-Fermi liquid.Comment: 6 pages, 4 figure

The Fermi surface and f-valence electron count of UPt3

Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt3. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt3 are localized by correlation effects -- agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this 'partially localized' model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed 'fully itinerant' model of the electronic structure of UPt3. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface.Comment: 23 pages, 12 figures, latex, iopart clas

Did LIGO detect dark matter?

We consider the possibility that the black-hole (BH) binary detected by LIGO may be a signature of dark matter. Interestingly enough, there remains a window for masses $20\,M_\odot \lesssim M_{\rm bh} \lesssim 100\, M_\odot$ where primordial black holes (PBHs) may constitute the dark matter. If two BHs in a galactic halo pass sufficiently close, they radiate enough energy in gravitational waves to become gravitationally bound. The bound BHs will rapidly spiral inward due to emission of gravitational radiation and ultimately merge. Uncertainties in the rate for such events arise from our imprecise knowledge of the phase-space structure of galactic halos on the smallest scales. Still, reasonable estimates span a range that overlaps the $2-53$ Gpc$^{-3}$ yr$^{-1}$ rate estimated from GW150914, thus raising the possibility that LIGO has detected PBH dark matter. PBH mergers are likely to be distributed spatially more like dark matter than luminous matter and have no optical nor neutrino counterparts. They may be distinguished from mergers of BHs from more traditional astrophysical sources through the observed mass spectrum, their high ellipticities, or their stochastic gravitational wave background. Next generation experiments will be invaluable in performing these tests.Comment: 5 pages, 2 figures, updated to match version published in PR